technical digest r2 - 大阪大学 3rd international conference on laser peening and related...
TRANSCRIPT
The 3rd International Conference on Laser Peening and Related Phenomena
October 11 – 14, 2011
Osaka, Japan
Program and Technical Digest
Conference Chairs
Yuji Sano Toshiba Corporation, Japan
Omar Hatamleh NASA - Johnson Space Center, USA
Welcome to the 3rd International Conference on Laser Peening and Related Phenomena
On behalf of the organizing committee, we would like to welcome you to the 3rd International Conference on Laser Peening and Related Phenomena. Following the successful conclusion of the 1st conference in Houston in December 2008 and the 2nd conference in San Francisco in April 2010, we have decided to proceed with a 3rd conference in Osaka from October 11 to 14, 2011. Laser Peening (LP) or Laser Shock Processing (LSP) is an effective surface technology to increase the resistance of metallic components to high‐cycle fatigue (HCF), stress corrosion cracking (SCC), wear, etc. through imparting compressive residual stress on the surface. Since laser peening is based on widespread science and technology ranging from plasma physics to automated robotic system, interdisciplinary cooperation and information exchange are highly effective to accelerate research and development on laser peening. The aim of this conference series is to provide a forum for the discussion of the latest innovations and studies in laser peening and their application to industrial sectors among scientists and engineers from all over the world. In the 3rd conference, we extended the scope to include the science and technology relating to laser peening such as laser‐ material interaction, alternative methods, residual stress measurement, etc. in order to increase understanding of underlying physics in laser peening and promote further applications. Finally, we would like to sincerely express our gratitude to all the invited speakers, presenters, participants and sponsors for irreplaceable support and cooperation. October 11, 2011
The Chairs of the Organizing Committee The 3rd International Conference on Laser Peening and Related Phenomena
Yuji SANO Toshiba Corporation
Omar HATAMLEH NASA ‐ Johnson Space Center
Contents
Corporate Sponsors ････････････････････････････････ 1
Committee Members ･･････････････････････････････ 2
Floor Map ･･･････････････････････････････････････ 3
Official and Social Programs ･････････････････････････ 4
Welcome Reception ････････････････････････････ 4
Technical Tour, Banquet ･････････････････････････ 4
3rd ICLP Student Awards ････････････････････････････ 5
Conference Proceedings ････････････････････････････ 5
Technical Digest ･･･････････････････････････････････ 6
Opening session on Tuesday, 11th ･････････････････ 8
Technical Session on Tuesday, 11th ････････････････ 16
Technical Session on Wednesday, 12th ･････････････ 24
Technical Session on Thursday, 13th ･･･････････････ 50
Student Session on Thursday, 13th ････････････････ 72
Technical Session on Friday, 14th ･････････････････ 86
Corporate Sponsors
Showa Optronics Co., Ltd. < http://www.soc-ltd.co.jp/en/ >
NISSEI ELECTRIC CO., LTD. < http://www.nissei-el.co.jp/ >
Rayture Systems Co., Ltd. < http://www.rayture-sys.co.jp/ >
Beamtech Optronics Co., Ltd. < http://www.beamtech-laser.com/ >
1
Committee Members Takafumi Adachi: Fuji Heavy Industries, Japan Koichi Akita: Japan Atomic Energy Agency, Japan Igor Altenberger: Wieland‐Werke AG, Germany Jeffrey Bunch: The Boeing Company, USA C. Brent Dane: Metal Improvement Company, USA Jeff Dulaney: LSP Technologies, Inc., USA Michael Fitzpatrick: The Open University, UK Domenico Furfari: Airbus, Germany Makoto Gonokami: The University of Tokyo, Japan Ramana V. Grandhi: Wright State University, USA Janez Grum: University of Ljubljana, Slovenia Omar Hatamleh: NASA ‐ Johnson Space Center, USA Koji Hatanaka: The University of Tokyo, Japan Ulrike Heckenberger: EADS, Germany Manabu Heya: Osaka Sangyo University, Japan Michael R. Hill: University of California‐Davis, USA Akio Hirose: Osaka University, Japan Goran Ivetic: University of Bologna, Italy Sungho Jeong: Gwangju Institute of Science & Technology, Korea Yoshiaki Kato: Graduate School for the Creation of New Photonics Industries, Japan Ryosuke Kodama: Osaka University, japan Kristina Langer: Wright‐Patterson AFB, USA S. R. Mannava: University of Cincinnati, USA Kiyotaka Masaki: Okinawa National College of Technology, Japan Noriaki Miyanaga: Osaka University, Japan Miguel Morales: Universidad Politecnica de Madrid, Spain Jose Luis Ocana: Universidad Politecnica de Madrid, Spain Norimasa Ozaki: Osaka University, Japan Patrice Peyre: LALP, France Yoshihiro Sakino: Osaka University, Japan Tomokazu Sano: Osaka University, Japan Yuji Sano: Toshiba Corporation, Japan James Smith: NASA ‐ Johnson Space Center, USA Akira Sugiyama: Japan Atomic Energy Agency, Japan Vijay K. Vasudevan: University of Cincinnati, USA Lothar Wagner: Technische Universitat Clausthal, Germany Tsutomu Yabuzaki: Osaka Electro‐Communication University, Japan Shigenori Yagi: Mitsubishi Electric Corporation, Japan Hitoki Yoneda: University of Electro‐Communications, Japan
2
Floor Map
3
Official and Social Programs
WELCOME RECEPTION
Welcome Reception will be held on Oct. 10 Monday evening in the restaurant "Grande Toque" which is next to the conference room 1202 located in the 12th floor of the Osaka International Convention Center.
Registration desk will be open in front of the restaurant during the reception.
TECHNICAL TOUR
of Kansai Photon Science Institute (KPSI) and
EXCURSION & BANQUET
Technical Tour of Kansai Photon Science Institute (KPSI), and Excursion & Banquet will be held on Oct. 14 Friday afternoon. Bus will depart from the convention center after the closing remark for the KPSI of Japan Atomic Energy Agency followed by the ancient capital of Nara. After touring some historic monuments which are registered as World Heritage site, banquet will be held in "Nara Hotel" which has more than 100 years' history. Bus will return to the convention center around 9pm.
TECHNICAL TOUR
of the Photon Pioneers Center (PHoPs) and
the Institute of Laser Engineering (ILE)
Technical Tour of the Photon Pioneers Center (PhoPs) and the Institute of Laser Engineering (ILE) in Osaka University will be held on Oct. 15 Saturday morning. Bus will depart from the convention center at 9am and return there around 1pm. PhoPs and ILE is a world‐class facility for the use of high‐power lasers in the research fields of Laser Fusion, High Energy Density Science, and Power Photonics.
4
3rd ICLP Student Awards Two student sessions will be open in parallel in the conference rooms 1202 and 1102
on Thursday evening, 13th. Outstanding presenters are awarded at the closing session on Friday, 14th.
Conference Proceedings The PROCEEDINGS of the conference will be published as a supplementary volume of
THE REVIEW OF LASER ENGINEERING, a journal of The Laser Society of Japan and delivered to all participants as a form of CD‐R.
After the conference, the committee recommends some presenters to submit
manuscripts, considering the quality of the presentation at the conference. All participants have a right to submit manuscripts based on their presentations. The submitted manuscripts will be peer reviewed by the committee members and invited reviewers to keep the quality of the publication.
The TEMPLATE of the manuscripts and the COPYRIGHT TRANSFER FORM will be
posted on the conference web after the conference.
5
Technical Digest
Opening session
Tuesday, 11th
6
7
R&D on high power lasers in Osaka University and its contribution to science
Ryosuke Kodama
Photon Pioneers Center in Osaka University (Osaka-PhoPs), Japan
[email protected] Photon science is vital in various fields from core research to industrial applications. Osaka University has intensively brought together activities in the individual researchers and institutes to shape up into world-leading research and innovation through collaboration and cooperative relationship. In 2008, the Ministry of Education, Culture, Sports, Science and Technology (MEXT) started a 10-year Photon Frontier Network program. The program recognizes two networks; one is the Advanced Photon Science Alliance (APSA) and the other is the Consortium for Photon Science and Technology (C-Phost). C-Phost consists of major institutions in photon science, i.e., Osaka University, the Kansai Photon Science Institute (KPSI), Kyoto University, and the Institute for Molecular Science. In January 2009, the Photon Pioneers Center (PhoPs) was launched in Osaka University with the mission of vigorously promoting the MEXT program. Laser peening is one of the imperative applications of high power lasers, and Osaka University has fully supported to organize this conference. Actually, there are a dozen of presentations from the members in the MEXT program. On the occasion of the technical tours, the participants visit KPSI, PhoPs and the Institute of Laser Engineering (ILE) of Osaka University. They are world-class facilities for the use of high-power lasers in the research fields, e.g., high energy density science, laser fusion, power photonics, etc. I hope you will enjoy your stay in Osaka and feel the cutting-edge science and technology in Kansai area.
The Early History of Laser Shock Processing
Allan H. Clauer
LSP Technologies, Inc., Dublin, OH, USA
The early history of laser shock processing began in the early 1960’s, with the realization that vaporization of a material surface irradiated by a laser beam could impart a significant pressure on the surface under the beam. This realization was followed by a series of studies which led to the discovery that by confining the vapor with an overlay transparent to the laser beam, the plasma pressure was enhanced to the point that laser irradiation of the material within a vacuum at very high laser intensities was no longer necessary to achieve useful pressures. This demonstrated that useful laser-induced shock waves could be produced with in-air processing. Through the 1970’s and 1980’s, researchers at Battelle Memorial Institute in Ohio, investigated the use of laser shock processing to modify material properties. In the 1980’s, the first prototype laser demonstrating industrial laser peening feasibility was designed and built at Battelle. Also beginning in the late 1980’s, French investigators made significant contributions to the understanding of laser-induced shock wave behavior and application of laser peening to metal fatigue and corrosion phenomena. Beginning in the mid-1990’s, Toshiba developed and implemented a laser peening system adapted to underwater processing of welds inside nuclear pressure vessels. In the mid-1990’s, LSP Technologies became the first company to offer laser peening services to industry, and General Electric performed the first industrial production of laser peened parts. Since then, laser peening of commercial parts has been steadily growing.
8
An overview of the effects of laser peening on friction stir welded aluminum alloys
Omar Hatamleh
NASA – Johnson Space Center, Houston, Texas 77058, USA
Friction stir welding (FSW) is considered a reliable and efficient metal-joining process that is now being widely used in industry. Nevertheless, the high thermal input generated during the welding process, and the rigid clamping arrangements used to restrain the plates during welding can result in residual stresses in and around the weld region. The magnitude and distribution of these residual stresses can be detrimental, and can be significant contributors to the durability of the FSW joints and surrounding material. Therefore, laser peening was investigated as a technique for improving the fatigue and mechanical properties in FSW. Laser peening is a surface modification technique that can generate a compressive residual stress that is capable of reaching deeper than conventional shot peening. In this investigation, the effects of laser peening on friction stir welding were investigated and contrasted to the results obtained using shot peening. The study includes the effect on mechanical properties, surface roughness, and fatigue properties.
Research activities during twenty years in France - from LALP to PIMM (1987-2011)
Patrice Peyre, Laurant Berthe and Remy Fabbro
PIMM – UMR 8006 CNRS – Arts et Métiers Paris-Tech, 75013 PARIS, France
In France, the first investigations concerning laser-shock wave generation and their applications to materials have been published in the late 80’s, approximately 15 years after the pioneer works in USA. Since then, intensive work has been systematically carried out on all the different aspects involved in laser-shock processing, from the early physical description of shock wave generation in confined regime, including analytical and experimental aspects (1988-1995), to the very recent applications of femtosecond pulses (2010), and the study of the dynamic behavior of materials or interfaces. This presentation aims at making a large overview on all these activities related to LSP, including the basics of the process, and with a specific focus on peening applications, on the dynamic behavior under laser-shock loading, and more globally, on the more recent works in the French community. Last, the oncoming French activities on LSP will also be addressed briefly.
9
R&D on Laser Processing in HZG and Expectation to Laser Peening
N. Kashaev, D. Schnubel, S. Riekehr, V. Ventzke, and N. Huber
1 Institute of Materials Research, Materials Mechanics, Helmholtz-Zentrum Geesthacht, 21502 Geesthacht, Germany
The research activities at Helmholtz-Zentrum Geesthacht (HZG) aim at the development of advanced light-weight components and structures, which will be based on the next generation light weight alloys. Laser beam processes are used for joining and locally modifying the microstructure and the mechanical properties of those alloys. The simulation of laser processes, the prediction of the induced residual stresses and their effect of the fatigue crack growth is used to identify the optimum process conditions. The computer simulation supported process development was demonstrated on the laboratory scale with coupon specimens that have been processed by Laser Surface Treatment (LST) as a local modification process. It has been found that the compression residual stresses, which equilibrate the tensile residual stresses in the LST treated area, have a remarkable effect on the crack propagation rate to a distance of several 10 mm. In addition to the thoroughly investigated LST-process the very promising Laser Shock Peening (LSP) process for generating the required residual stress profiles will be focus of future research. The work on LST and LSP will be conducted to establish a spectrum of suitable processes for improving the damage tolerance behaviour of metallic structures. An important expectation for LSP in particular is the establishment of this technology for repair of metallic light weight structures under field conditions.
Summary of LSP Research Activities at CLUPM (Spain)
J.L. Ocaña
Centro Láser UPM. Universidad Politécnica de Madrid Campus Sur UPM. Edificio La Arboleda. Ctra. de Valencia, km. 7,300. 28031 Madrid. SPAIN
Laser Shock Processing has been a research subject at CLUPM (Laser Centre and formerly Dept. of Applied Physics at the Polytechnical University of Madrid, Spain) since 1988. By that time, the first attempts to develop a calculational code for the predictive assessment of the laser plasma interaction at high intensities were started [1,2] and, in the next years, the cooperation with international labs in the field of high-intensity laser interaction modelling and diagnosis and the implementation of a in house experimental facility were accomplished [3]. Since 2000, the Centre has developed a research program on LSP characterized by the aim to develop a coupled theoretical-experimental analysis and performing capability focussed to the understanding, predictive assessment and material properties testing of LSP treatment of materials typically considered as strategic in aeronautical and nuclear applications (namely different stainless steels and different Aluminum and Titanium alloys). In this line, a set of coupled numerical simulation models, process experimental diagnosis and testing facilities and a practical experimental knowledge have been developed allowing a valuable knowledge-based process specification capability. In the present talk a summary will be provided on the developed analysis methodologies and main attained results in the line of the 3rd ICLP Conference. Work partly supported by MEC/MCINN (Spain; Projects DPI2005-09152-C02-01 and MAT2008-02704/MAT) UPM (Spain, Project CM CCG07-UPM/MAT-1964) and EADS-CASA (Spain). [1] Ocaña J. L. et al.: "Numerical simulation and experimental diagnosis of the laser–plasma interaction in high intensity processing Applications". Proc. SPIE, vol. 1810 566–571 (1992). [2] Ocaña, J.L. et al.: "A model for the coupled predictive assessment of plasma expansion and material compression in laser shock processing applications". Proc. SPIE, vol. 3885, 252–263 (2000). [3] Ocaña, J.L. et al.: "Predictive assessment and experimental characterization of the influence of irradiation parameters on surface deformation and residual stresses in laser-shock-processed metallic alloys". Proc. SPIE 5448, 642-653 (2004).
10
Ongoing research activities on laser peening in Europe and expectation of aerospace industry
Domenico Furfari
Airbus Operations GmbH, Kreetslag 10, 21129 Hamburg, Germany
The Laser shock Peening (LSP) technology was developed in US beginning ’70. In Europe this technology came later and the interest by Industries starts to increase in the last decade. Excluding Rolls Royce which currently use this technology to extend fatigue life of gas turbine blades of the new generation of their products, there is currently no other industries in EU using this technology. Research activities focusing on basic understanding of the phenomena started in France (former LALP laboratories now PIMM) at the early stages of the technology development [1]. In Spain a laser peening laboratory has been developed at the Polytechnic University of Madrid in the last decade [2]. During the last 5 years the R&T activities in this field had a steep increase. Academia such as Cranfield University, Open University in UK investigated the use of Laser Shock Peening to recover fatigue life degradation in mechanically damaged 2mm thick aluminium sheet. Manchester University, Oxford University and Swansea University in UK in cooperation with industrial partners (Rolls Royce, MIC-UK, MoD-UK, and Airbus) launched cooperative research program. In Italy, Bologna University plays an important role to develop knowledge in this field. On the 16th -18th of February this year the 1st European Laser Shock Peening Meeting has been organized by Bologna University at Bertinoro. Helmotz Zentrum Geesthacht is planning a dedicated research project for the next 3 years with the final goal to develop a laser peening station at their facility [3]. CSIR National Laser Centre (NLC) in South African led initiative sets out a three-year plan to establish a laser shock peening (LSP) infrastructure to ensure uptake of this technology by the aerospace and other industries. All the activities above mentioned focusing on the understanding of the laser peening phenomena but often do not take into account the expectation of aerospace industries. For instance having a compact system “easy to handle” when application on repair field is required is not considered in the current development plan of the technology suppliers in EU. Rotorcraft industries may have a various range of fatigue critical components of rotorcrafts parts that could be treated. The field of interest ranges from airframe structures to rotor and transmission parts, which are very different in terms of material, shape, thickness and production process, hence the LSP technology has to show a great flexibility in order to be applied to combinations of different materials such as steels, titanium and aluminum alloys. The potentiality of LSP has been highlighted already with the systems developed by MIC, LSPT and TOSHIBA. The industrial applications were currently found for processing engine blades (MIC/Rolls Royce and LSPT/GE), nuclear reactor components (TOSHIBA), or forming thick panels (MIC/BOEING). More recently MIC together with Boeing has carried out a study to demonstrate the enhancement of the fatigue behaviour of the wing attachment of F22 with the final goal to increase Aircraft Service Life [4]. Looking to the future of laser shock peening, the gap still to be filled is making LSP a technology mature enough to be applied in fatigue critical components. The final goal should be: lowering processing cost, increase the understanding and the confidence how to apply LSP and to design the components, taken into account the residual stresses induced by the process. Laser Shock Peening supplied by MIC or LSPT involves complex optics system to deliver the laser beam from the source to the surface to be treated. “Surface pre-treatment” (i.e. ablative layer to be applied onto the surface each peen layer) has an impact on cost for this technology (the cost can be reduced by 30% if the ablative layer is not required). Investigations on different ablative layer to be used to protect the surface prior laser peening treatment were carried out [5] and results similar to the ones obtained with Al tape as ablative layer can be obtained using coating painted or sprayed onto the surface. TOSHIBA system represents an attractive alternative of the systems developed by MIC and LSPT. The ultra-compact system combines the advantage to have a compact and lighter system to be used in structural repair field where the accessibility is matter of concern. The laser with lower power (less complex optics system using fiber optics technology) and the not required surface protection during the process (no ablative layer results in cost reduction of the process) represents the most attractive features. This provides the only available solution when the treatment should be done in structural part made of Al alloys with typical thickness below 5mm. On
11
the other hand the price we have to pay is the fact that the system is not suitable for forming issues (spot sizes 1-2mm will result in non-economical value to form large component such as a/c wing skin or fuselage panels) and will provide less “efficiency” in terms of fatigue life enhancement of thick products (e.g. 20-30mm). [1] P. Peyre, “Research activities during twenty years in France - from LALP to PIMM (1987-2011),” 3rd International Conference on Laser Peening and Related Phenomena, October 2011, Osaka, Jp. [2] J. Ocana, “Summary of LSP Research Activities at CLUPM (Spain),” 3rd International Conference on Laser Peening and Related Phenomena, October 2011, Osaka, Jp. [3] N. Kashaev, “R&D on Laser Processing in HZG and Expectation to Laser Peening,” 3rd International Conference on Laser Peening and Related Phenomena, October 2011, Osaka, Jp. [4] D. Jensen, “Adaptation of LSP Capability for Use on F-22 Raptor Primary Structure at an Aircraft Modification Depot,” 2nd International Conference on Laser Peening, April 2010, S. Francisco, CA. [5] J. Dulaney, “Production Laser Peening Using Automated Overlay Applicators,” 2nd International Conference on Laser Peening, April 2010, S. Francisco, CA.
Overview of laser peening research in Air Force Research Laboratory
Kristina Langer
Air Force Research Laboratory, Wright-Patterson Air Force Base, OH 45433-7542, USA
Commercial Applications of Laser Peening
C. Brent Dane, L. Hackel, F. Harris, J. Curtis, and D. Francis Metal Improvement Company, Livermore, CA
Metal Improvement Company (MIC), a wholly-owned subsidiary of the Curtiss-Wright Corporation, has developed a full commercial laser peening capability with four processing plants in the U.S. (Livermore, CA, Frederickson, WA, and Palmdale, CA) and one in the U.K. (Earby, Lanc). In this presentation, we will present MIC’s laser peening commercial capabilities. We will also describe the technology that has been developed to laser peen parts that range from small gears a few inches in diameter to large wing skins over one hundred feet long. The MIC laser peening systems relies on high-pulse-energy flashlamp-pumped glass laser systems that can place high-quality square or rectangular spots onto the treatment surface at a pulse-repetition-frequency of up to 5Hz. Several methods are used to scan the spots across the surface of the part in precise and repeatable patterns during processing. Smaller parts are manipulated with robotic arms through a fixed laser beam. For larger parts that are not easily moved during processing, the high power beam can be scanned across treatment surface while the part is stationary. Complex work pieces often benefit from a hybrid approach where the position of both the part and the beam are actively scanned during processing. Delivery of the water tamping layer is accomplished with a separate robotic arm, through a fixed nozzle attached to the beam scanning tool, or with computer-controlled fixed nozzles attached to the work piece. The way in which these approaches have been adapted and scaled to components such as aircraft engine blades, gas and steam turbine blades, large bladed rotors, and very large commercial aircraft wing skins will be described. The ability to applied laser peening in direct, on-aircraft applications will be covered in a separate conference presentation.
12
Future Shock: Accelerating Technology
Jeff L Dulaney
LSP Technologies, Inc. Dublin, OH, U.S.A.
It takes an enormous effort to take technology from a laboratory research environment to commercial use. Laser Shock Processing (LSP) of the 1970s evolved into the commercial success known today as laser peening. There are many variants of laser peening in use today, and many more to be discovered, developed, and integrated into commercial use. The study of the laser-generated shock waves, so critical to laser peening, will find commercial applicability beyond imparting compressive residual stress in metals. Computer models, currently being used to support commercial applications development, will continue to improve and lead the way to new applications and uses. Overlay materials will evolve to enhance the effectiveness of laser peening through the use of special materials and techniques. In situ process controls and diagnostics will be developed to provide real-time feedback and continuous quality assurance as critical parts are being processed. Advancement of laser peening systems will enable new and unexpected applications.
Ohio Center for Laser Shock Processing for Advanced Materials and Devices
S. R. Mannava, Dong Qian, Peter Nagy, Jai A. Sekhar, and Vijay K. Vasudevan
College of Engineering and Applied Science, University of Cincinnati, Cincinnati, OH 45221, USA
An “Ohio Center for Laser Shock Processing for Advanced Materials and Devices,” the first Center of its kind in a university in the USA, was established at the University of Cincinnati (UC), Cincinnati, OH in July 2009 with a $3 million award from the State of Ohio, Department of Development Third Frontier Program and in collaboration with X-spine Systems Inc., LSP Technologies Inc., UES Inc. and Cincinnati State Technical and Community College. The Center’s far-reaching mission is to advance the science, education, technology and applications of laser shock processing of materials in close collaboration with industry and government by 1) developing a balanced research and education infrastructure to serve both academia and industry; 2) advancing research in critical areas and helping develop and commercialize new products for the orthopedic/spinal implant industry in the short term; 3) fostering proliferation of this technology to many industrial products through R&D, entrepreneurial and commercialization activities; and 4) producing the best trained technical workforce of the 21st century. The LSP center is equipped with state-of-the-art equipment for LSP processing, materials characterization, testing, modeling and simulation. Current LSP-related R&D activities encompass a broad spectrum of areas including biomedical implants, aero engine and aerospace structural materials, and nuclear materials. The Center is open to industry for process and product development and prototyping activities. The University of Cincinnati acknowledges the contribution from the State of Ohio, Department of Development and Third Frontier Commission, which provided funding in support of the Ohio Center for Laser Shock Processing for Advanced Materials and Devices project.
13
Activities on laser peening development and strategies in Asia
Yuji Sano
Power and Industrial Systems Research and Development Center, Toshiba Corporation 8, Shinsugita-cho, Isogo-ku, Yokohama 235-8523, Japan
The development of laser peening in Japan was initiated in the mid 1990s, independent of the activities in the USA and France. The purpose of the development was to mitigate stress corrosion cracking (SCC) of reactor components. Since the objects are cooled underwater in nuclear power plants (NPPs) and emit gamma radiation, remote peening with a mobile system firing water-penetrable laser pulses was inevitable. Consequently, a concept without any surface preparation or coating (LPwC) was created, which simply irradiates laser pulses to bare objects underwater. To minimize the heat input, a compact Nd:YAG laser with a pulse energy of around 0.1J and a pulse duration less than 10ns was selected. In order to expand the applicability, a fiber-delivery system was also developed. Since 1999, LPwC has been applied to prevent SCC in NPPs. One important trend in laser peening in future is to utilize micro-photonics and drastically reduce the system volume. A committee on Laser Peening was launched in 2006 under the Laser Society of Japan. The purpose of the committee was to facilitate studies for understanding underlying physics in laser peening and promote further applications. The three years activities were succeeded in 2009 by the current committee for Laser Shock and its Applications. The members of the committee range from academia to industry to encourage interdisciplinary cooperation and information exchange. Meanwhile in 2008, the Ministry of Education, Culture, Sports, Science and Technology (MEXT) has created Photon Frontier Network, a ten-years landmark program to advance photon science and technology and to foster new talent. The program is supported by two core network centers, the Consortium of Photon Science Technology (C-PhoST) in the west and the Advanced Photon Science Alliance (APSA) in the east of Japan. In this conference, many Japanese participants are the members of the Committee for Laser Shock and its Applications and/or the Photon Frontier Network program. Recently, researchers in China and Korea have extensively studied laser peening technologies. A part of the activities will be presented at this conference. Based on the coming discussion in the conference, we will propose establishing a provisional society, Asian Association of Laser Shock Science and Applications, to promote cooperative research and information exchange.
14
Promise on Microchip Lasers for Peening - Giant Micro-photonics -
Takunori Taira
Institute for Molecular Science, 38 Nishigonaka, Myodaili, Okazaki 444-8585 Japan
“Micro Solid-State Photonics” based on micro-domain and boundary controlled photonic devices allow us the giant benefits in the solid-state photonics as polycrystalline laser ceramics and periodically poled devices [1, 2]. Much progress has been made in improving the optical quality of ceramics as well as in exploring new laser materials. In this presentation, we’d like to discuss the recent progress in the giant pulsed microchip lasers. The microchip laser has well known benefit of enhancing the quantization effects to improve its laser coherence as single-axial mode oscillation [3]. Furthermore, it is possible to reduce the Q-switched pulse duration τp to the sub-nanosecond by shortened microchip cavity as following rule;
τ p ≈rη(r)
r −1− ln rτ c =
rη(r)
r −1− ln r×
2Lcδ
, (1)
where δ is the loss of cavity, r is the initial inversion ratio, η is the energy extraction efficiency, L is the cavity length, and c is the speed of light. Equation (1) indicates that the Q-switched laser pulse width could be shortened until cavity round-trip time. Consequently, the drastic brightness improvement should be expected only by cavity shortening due to high-peak-power single-frequency oscillation with a single transverse mode. In general, solid-state lasers have advantages in giant-pulse generation in Q-switching, for which the typical pulse width is a few 10’s ns, and ultrashort pulse generation in mode locking, in the ps ~ fs region. Unfortunately, for a long time, it has been difficult to cover this “pulse-gap” region, even though we can expect a fruitful phenomenon for material interactions. In this situation, the promise of pulse duration from a few ns until 10 ps in the Q-switched microchip lasers is very attractive. However, it was too difficult to scale the power of microchip laser for long time. The recent breakthrough of micro solid-state photonics made change its situation dramatically. Then, up to 6 MW peak output and 500 ps with 1064 nm was obtained on passively Q-switched Nd:YAG/Cr:YAG microchip laser [1]. The brightness of the sub-ns and diffraction limit pulse microchip laser was calculated to be >0.3 PW/sr-cm2 and the brightness temperature of 0.23-0.46 ZK (1021 K) was estimated (cf. the temperature of sun surface: ~6,000 K). In addition, this ceramic microchip laser has been upgraded to 3-beam system within a spark plug compatible size as shown in Fig. 1 [1, 4]. Further innovation in micro-domain controlled microchip lasers toward “Giant Micro-photonics” should broaden the horizons of laser peening. [1] T. Taira, “Domain-controlled laser ceramics toward Giant Micro-photonics [Invited],” Opt. Mater. Express, vol. 1, pp. 1040-1050 (2011). [2] T. Taira, "RE3+-ion-doped YAG ceramic lasers," IEEE J. Sel. Top. Quantum Electron., vol. 13, pp. 798-809 (2007). Invited Paper [3] T. Taira, A. Mukai, Y. Nozawa, and T. Kobayashi, "Single-mode oscillation of laser-diode-pumped Nd:YVO4 microchip lasers", Opt. Lett., vol. 16, pp. 1955-1957 (1991). [4] N. Pavel, M. Tsunekane and T. Taira, "Composite, all-ceramics, high-peak power Nd:YAG/Cr4+:YAG monolithic micro-laser with multiple-beam output for engine ignition," Opt. Express, vol. 19, pp. 9378-9384 (2011); CLEO 2011, USA, May 1 – 6, CMP1 (2011). - OSA News Release http://www.osa.org/about_osa/newsroom/news_releases/releases/04.2011/lasersparksrevolution.aspx - EurekAlert! (AAAS Science news wire) http://www.eurekalert.org/pub_releases/2011-04/osoa-lsr042011.php - Business Wire http://www.businesswire.com/news/home/20110420005464/en/Laser-Sparks-Revolution-Internal-Combustion-Engines - BBC News http://www.bbc.co.uk/news/science-environment-13160950 - New York Times http://wheels.blogs.nytimes.com/2011/04/27/spark-plugs-joining-carburetors-on-the-automotive-scrap-heap/ - Forbes http://blogs.forbes.com/alexknapp/2011/04/23/replacing-spark-plugs-with-lasers-for-a-more-fuel-efficient-car/ - USA Today http://content.usatoday.com/communities/sciencefair/post/2011/04/laser-ignition-may-replace-spark-plugs/1 - Discovery News http://news.discovery.com/autos/laser-car-engine-power-110502.html - USA ABC News http://abcnews.go.com/Technology/save-gas-lasers-powering-cars/story?id=13546879 - IMS web page http://www.ims.ac.jp/topics/2011/110704.html, etc.
Fig. 1. Multi-mega-watt peak and 3-beam output passively Q-switched microchip ceramic laser [4].
15
Technical Digest
Technical Session
Tuesday, 11th
16
17
Surface Integrity affected by Shot Peening
K. Tosha
Meiji University, School of Science and Technology, Department of Mechanical Engineering 1-1-1 Higashimita, Tama-ku, Kaeasaki 214-8571, Japan
This paper describes influences of factors such as particle size and velocity, and thickness, hardness and crystal
phase of work material on surface integrity. Hardness, residual stress and crystal transformation of the zone
affected by shot peening are examined for a medium carbon steel (C:0.45%, 180HV) and an austenitic stainless
steel (SUS304, 210HV). The following results are shown in this paper: (1) Hardness distributions are divided
into three types, which are work hardening, non-hardening and work softening ones. (2) Residual stress
distributions are divided into two types, which are S-type and C-type. (3) As residual stress induced by the
resistance of non affected layer, residual stress on the peened surface shows size effect of the thickness of work
material. (4) The ratio of the critical thickness to the depth of workhardened layer is about 5. (5) Strain-induced
transformation happens with shot peening. (6) The optimum affected-layer ratio (ratio of the depth of work-
hardened layer to the thickness of material), which is called the “sweet zone”, is from 0.3 to 0.4.
Fig. 1. Hardness distributions
Fig. 2. Critical thickness on residual stress
Although the hardness distribution produced by shot peening for an
annealed steel is a work hardening type, the distributions for pre-
strained steel shift to other types as shown in Fig.1. The hardness
distribution produced by shot peening changes from a hardening type
to non-hardening and then to a softening one with an increase of pre-
strain (ε), and the depth of the work hardened layer decreases as pre-
strain increases. Thus it is, therefore, not sufficient to judge the depth
of affected layer using only the hardness distribution.
Fig.2 shows the effect of the thickness of specimen on the surface
residual stresses. Critical thickness (tc) means the minimum thickness
for efficient introduction of compressive residual stresses. Surface
residual stresses fall to zero wherever the thickness of work material
and those depths of work hardened layer are overlapped. Fig. 3 shows
the relation between the critical thickness and the depth of work
hardened layer, and it’s ratio is 5.
Fig. 3. Relation between tc and depth
of work hardened layer.
[1] K. Takazawa, “Surface Integrity” Journal of Japan Society for Precision Engineering, 55, 10, 1772-1777 (1989) .
[2] Y. Sano, N. Mukai, M. Obata, “Laser Peening without Coating: Process, Effects and Applications,” Proceedings of 10th International
Conference on Shot Peening, Tokyo, Japan, 423-428 (2008).
18
Comparison of fatigue strength for shot-peened and laser peened high strength aluminum alloy
Toshiya Tsuji1, Yuji Kobayashi1, Takanori Nagano2
1SINTO KOGIO, LTD., 3-1, HONOHARA, TOYOKAWA, AICHI, 442-8505, JAPAN 2 Department of Mechanical Engineering, Miyakonojo Nationak College of Technology,
473-1, YOSHIO-CHO, MIYAKONOJO, MIYAZAKI, 885-8567, JAPAN
Email address: [email protected] Peeing process is a surface enhancement method which induces compressive residual stress and hardness to
peened metallic component due to plastic deformation. As a result, the peened metallic component improves the resistance to stress corrosion cracking and the fatigue property. There are shot-peenig and shot-peening as peening process. Shot peening process using media is a surface enhancement method widely used in automobile and aerospace industries. Laser peening process using high energy pulse laser is a competitive alternative to shot peening. Many researchers have reported that laser peened material was gotten higher fatigue strength than shot peened material.［1］, ［2］ However, most above researches have been carried out by conventional shot-peening conditions. Actually, the influence factors to improve fatigue strength vary depending on peening conditions. For example, in the case of shot-peening, fine particle shot peening used by media of media size about 0.05-0.10mm resists initial crack propagation to induce high compressive residual stress beneath the surface, as a result fatigue strength improve greater than conventional shot peening. ［3］ For an above, Peening effect (surface roughness, residual stress, hardness, amount of plastic strain) is varied depending on shot-peening conditions. Consequently, Optimum peening condition must be set up to improve greater fatigue strength. In addition, independent know-how needs to set up optimum peening conditions. In this study, as shown in Fig.1, we investigated optimum shot-peening and laser-peening condition got greater
fatigue strength, and carried out rotating bending fatigue test on these peening conditions. Each peened specimen was measured for residual stress and surface roughness. For these result, peening
conditions were selected. We defined that criterion for selecting peening conditions are conditions that can change residual stress distribution. In pretest to decide shot-peening conditions, Ceramics and, glass beads, conditioned cut wires, cast steels were
used for shot media. Shot-peening method was used in air-type shot peening machine. In pretest to decide laser-peening conditions, Nanosecond pulse laser was used for laser-peening. Laser peening conditions were carried out with overlay and without overlay. Fatigue test was carried out by Ono-type rotating bending fatigue test machine. From based on these result, the fatigue strength of laser-peened and shot-peened specimen were compared to
clarify factor improving fatigue strength for laser-peening and shot-peening.
Fig. 1 Flow chart of experimental
［1］L.Wagner, M.Mhaeda, I.Altenberger, Y.Sano “Fatigue Behavior in the Al7075-T73 and Ti-6Al-4V;
Comparing Results after Laser shock peening, shot peening and Ball –Brushing’’ The 2nd International Conference of Laser Peening (2010)
［2］Ullike C. Heckenberger, Elke Hombergsmeier, Wolfgang v. Bestenbostel, Vitus Holzinger “LSP to improve the fatigue resistance of highly stressed AA7050 components’’ The 2nd International Conference of Laser Peening (2010)
［3］Akiko Inoue, Takahiro Sekigawa, Kazuyuki Oguri, Tetsuya Tagawa, Takashi Ishikawa “Mechanism of Fatigue Life Improvement due to Fine Particle Shot Peening in High Strength Aluminum Alloy’’ Journal of the Japan Institute of Metals vol.74 No.6 370-377 (2010)
①Pretest to decide peening conditions◆ Measurement items○ Residual stress○ Surface roughness (JIS’01)
②Fatigue test on optimum peening conditions◆Test condition○ Method: Rotating bending fatigue test○ Stress ratio: R=-1
Decision of peenig condition.
19
Fundamental and Applications of Cavitation Peening
H. Soyama1 1Department of Nanomechanics, Tohoku University, 6-6-01 Aoba, Aramaki, Aoba-ku Sendai, 980-8579, Japan
Cavitation normally causes severe damage in hydraulic machinery such as pumps and valves, as severe impacts are generated at cavitation bubble collapses. However, the cavitation impacts utilized for surface enhancement in the same way of shot peening SP. The peening method using cavitation impact was called as cavitation peening or cavitation shotless peening, as shots are not required. Cavitation peening can introduce compressive residual stress into metallic materials [1, 2] and improve fatigue strength [3-5] and fretting fatigue strength [6]. Cavitation peening can relief micro strain which is introduced by heat treatment and/or mechanical finishing, with introducing compressive residual stress [7]. Usually, cavitation peening is done by a high-speed submerged water jet with a water filled chamber, i.e. cavitating peening in water CPW. Soyama successfully realized cavitation peening without the water filled chamber, by injecting a high-speed water jet into a low-speed water jet which was injected into air, i.e., cavitating peening in air CPA [8]. In order to investigate mechanism of improvement of fatigue strength by cavitation peening, Fig. 1 illustrates residual stress changing with depth from surface measured by an X-ray diffraction method, and Fig. 2 shows crack length with number of cycles. The tested material was stainless steel SUS 316L. Cavitation peening condition was controlled by the nozzle throat diameter d and the injection pressure of the high-speed water jet p1. The crack growth was evaluated by using a plate bending fatigue test with a pre-crack 5 mm in length, 0.25 mm in depth and 0.5 mm in width. The maximum bending stress was 350 MPa. As shown in Fig. 1, cavitation can introduce compressive residual stress into stainless steel about 1 mm in depth. It was concluded that the compressive residual stress introduced by the cavitating jet at d = 2 mm, p1 = 30 MPa, p2 = 0.42 MPa was bigger and deeper than that of d = 0.35 mm, p1 = 300 MPa, p2 = 0.1 MPa. Note that the both jet power defined by the injection pressure and the flow rate was nearly equal. Namely, in the case of the cavitation peening, the large cavitating jet with low injection pressure should be used [9]. As shown in Fig. 2, cavitation peening can suppress crack growth. This is one of reasons why cavitation peening can improve fatigue strength.
Fig. 1. Introduction of compressive residual stress by cavitation peening Fig. 2. Suppression of crack growth by cavitation peening
[1] H.Soyama, Y.Yamauchi, T.Ikohagi, R.Oba, K.Sato, T.Shindo and R.Oshima, “Marked Peening Effects by Highspeed Submerged-Water-Jets −Residual Stress Change on SUS 304−,” Journal of Jet Flow Engineering, Vol. 13-1, 25-32 (1996).
[2] H.Soyama, D.O.Macodiyo and S.Mall, “Compressive Residual Stress into Titanium Alloy Using Cavitation Shotless Peening Method,” Tribology Letters, Vol. 17, 501-504 (2004).
[3] H.Soyama, T.Kusaka and M.Saka, “Peening by the Use of Cavitation Impacts for the Improvement of Fatigue Strength,” Journal of Materials Science Letters, Vol. 20, 1263-1265 (2001).
[4] H.Soyama, K.Saito and M.Saka, “Improvement of Fatigue Strength of Aluminum Alloy by Cavitation Shotless Peening,” Journal of Engineering Materials and Technology, Trans. ASME, Vol. 124, 135-139 (2002).
[5] H. Soyama and Y. Sekine, “Sustainable Surface Modification Using Cavitation Impact for Enhancing Fatigue Strength Demonstrated by a Power Circulating-Type Gear Tester,” International Journal of Sustainable Engineering, Vol. 3, 25-32 (2010).
[6] H. Lee, S. Mall and H. Soyama, “Fretting Fatigue Behavior of Cavitation Shotless Peened,” Tribology Letters, Vol. 36, 89-94 (2009). [7] H.Soyama and N.Yamada, “Relieving Micro-Strain by Introducing Macro-Strain in a Polycrystalline Metal Surface by Cavitation
Shotless Peening,” Materials Letters, Vol. 62, 3564-3566 (2008). [8] H.Soyama, T.Kikuchi, M.Nishikawa and O.Takakuwa “Introduction of Compressive Residual Stress into Stainless Steel by Employing
a Cavitating Jet in Air,” Surface & Coatings Technology, Vol. 205, 3167-3174 (2011). [9] H.Soyama and O.Takakuwa, “Enhancement of Aggressivity of Cavitating Jet and Its Practical Application,” Journal of Fluid Science
and Technology, Vol. 6, 510-521 (2011).
-600
-400
-200
0
200
0 0.2 0.4 0.6 0.8 1
CPW (d=0.35mm, p1=300MPa, p2=0.1MPa, tp=1s/mm)Not peened
CPW (2mm, 30MPa, 0.42MPa, 1s/mm)
CPA (1mm, 30MPa, 20s/mm)
SP, 1s/mm
CPW (2mm, 30MPa, 0.1MPa, 6s/mm) CPW (2mm, 30MPa, 0.1MPa, 6s/mm) + CPA
Depth from the sureface z mm
Res
idua
l stre
ss σ
R M
Pa
0
5
10
15
20
0 20,000 40,000 60,000Number of cycles n
Cra
ck le
ngth
a m
m
Not peened
SP, 1s/mm
CPW (2mm, 30MPa,0.1MPa, 6s/mm)
CPW (2mm, 30MPa, 0.1MPa, 6s/mm) + CPA
20
Comparison of Effects of LSP, UNSM and Cavitation Peening on Residual Stress, Microstructure and Local
Mechanical Properties of 316 Stainless Steel, Ti64, IN718 SPF Alloys
Amrinder Gill,1 Yixiang Zhao,1 James Guenes, 1 Young-Sik Pyun,2 Hitoshi Soyama,3 S. R. Mannava,1 Dong Qian1 and Vijay K. Vasudevan1
1College of Engineering and Applied Science, University of Cincinnati, Cincinnati, OH 45221-0012, USA 2Sun Moon University, Dept. of Mechanical Engineering, Cheonan, S. Korea
3Tohoku University, Dept. of Nanomechanics, Sendai, Japan
Email: [email protected]
In this study the effects of different surface treatment processes, namely, laser shock peening (LSP), ultrasonic nanostructure surface modification (UNSM) and water-jet cavitation peening (CP) on residual stress, near-surface microstructure, plasticity and local mechanical properties in 316 stainless steel, IN718 and Ti64 alloys were studied using a host of techniques. The results revealed that the magnitude and depth of residual stress, surface roughness, near-surface microstructure and properties can vary substantially depending on the process. These results will be presented and discussed, including highlights of the merits and demerits of each process.
21
Nanoscale near-surface microstructures and high temperature fatigue of laser-shock peened and deep rolled
Ti-6Al-4V
I. Altenberger1, R.O. Ritchie2, R.K. Nalla3, L. Wagner4 and Y. Sano5
1Wieland-Werke AG, Ulm, Germany 2University of California, Berkeley, CA 94720, USA
3Lens Vector Inc., Mountain View, USA 4Clausthal University of Technology,38678 Clausthal-Zellerfeld, Germany
5Toshiba Corporation, Yokohama, Japan
[email protected] Mechanical surface treatments such as laser-shock peening or deep rolling are known to induce highly strain-hardened nanoscale microstructures as well as deep compressive residual stress layers into surface regions of fan blade titanium alloys such as Ti-6Al-4V [1,2]. The benefit of such treatments is well documented for cyclic loading at room temperature. In addition, it appears that the induced microstructures are stable enough to provide significant lifetime and strength improvements even at temperatures up to 550°C which is far above the operating temperature of such components. This study seeks to provide basic understanding for the strengthening mechanisms of deep rolled/laser-shock peened and high temperature fatigued Ti-6Al-4V under stress-control. For this purpose, the stability of near-surface microstructures is investigated by SEM (scanning electron microscopy) and TEM (transmission electron microscopy) after step-wise thermal exposure by in situ heating and after isothermal stress-controlled fatigue up to 550°C. Furthermore, for structural assessment of the softening or hardening behaviour, the plastic strain amplitude is recorded as a function of temperature and number of cycles. The resulting stress-life behaviour, plotted in the form of Wöhler-curves, clearly indicates that laser-shock peening and deep rolling are both extremely efficient methods for fatigue strength enhancement of solution treated and overaged Ti-6Al-4V, even at elevated temperatures up to 550°C, despite a very pronounced relaxation of compressive residual stresses.
Fig. 1. TEM-bright-field-micrographs of the near-surface microstructure of laser-shock peened Ti-6Al-4V (bimodal globular microstructure), fatigued in air under stress control with a stress amplitude of 460 MPa, a load ratio of R = -1 and f = 5 Hz after
half the number of cycles to failure (a) dislocation tangles directly beneath the surface after fatigue at T = 250°C (b) dislocation tangles directly beneath the surface after fatigue at T = 550°C
[1] R.K. Nalla, I. Altenberger, U. Noster, G. Y. Liu, B. Scholtes, R. O. Ritchie, "On the influence of mechanical surface treatments –deep rolling and laser shock peening- on the fatigue behaviour of Ti-6Al-4V at ambient and elevated temperatures", Mater. Sci. Eng. A, 355, 216- 230 (2003). [2] I. Altenberger, E.A. Stach, G. Liu, R.K. Nalla, R.O. Ritchie, "An in situ transmission electron microscope study of the thermal stability of near-surface microstructures induced by deep rolling and laser-shock peening", Scripta Materialia, 48, 1593-1598 (2003).
(b) 250 nm250 nm (a) 250 nm250 nm
22
23
Technical Digest
Technical Session
Wednesday, 12th
24
25
Laser developments at the Japan Atomic Energy Agency
H. Kiriyama, M. Mori, M. Suzuki, H. Okada, Y. Ochi, M. Tanaka, A. Kosuge, M. Kando, K. Kondo, K. Nagashima, A. Sugiyama, S. Bulanov, A. Yokoyama, and P. R. Bolton
Kansai Photon Science Institute, Japan Atomic Energy Agency, 8-1-7 Umemidai, Kizugawa-city, Kyoto 619-0215, Japan
[email protected] Lasers have found many applications in high field science, nonlinear optics and materials processing, such as particle acceleration, terahertz wave generation and laser shock peening (LSP). LSP is a relatively new surface treatment technique and has been shown to be effective in improving the fatigue properties of a number of metals and alloys. The feasibility of LSP has been confirmed with femtosecond to nanosecond laser pulses experimentally [1-3]. The core competence of our Kansai Photon Science Institute, Japan Atomic Energy Agency is advanced lasers with high brilliance and high average power in the pulse duration range from femtoseconds to nanoseconds. The following outlines some of the progress that has been made in the laser development at the Kansai Photon Science Institute of JAEA. In the femtosecond region, an ultra-high peak power Ti:sapphire laser system named J-KAREN [4] has been constructed and under improvement. J-KAREN delivers a pulse duration of less than 40 fs and an output energy of 20 J. The amplifiers in the system are pumped by the second harmonic energy delivered by lamp pumped Nd-doped lasers, which limit their useful repetition rate. The repetition rate for 20 J and 2 J pulse energies is single-shot and 10 Hz, respectively [4,5]. In the picosecond region, we have been developing laser-diode (LD) pumped solid-state laser systems. The LD pumped laser system is one of the most promising candidates for realizing high repetition rate, high average power systems because of its high efficiency and correspondingly small system thermal load. It is extremely compact compared with lamp pumped systems. A high peak power Yb:YAG laser system has been designed to match J-KAREN’s power with a small footprint. The current performance is 100 mJ output energy and 0.5 ps pulse duration at a 10Hz repetition rate [6]. Current efforts are dedicated to increase the repetition rate up to 1kHz. We are also developing LD pumped Nd:YAG laser system with hundred ps pulse duration to pump an optical parametric chirped-pulse amplifier (OPCPA) for generating ultra-short (<10fs) pulses. In the preliminary experiment, the output energy of 100mJ is achieved with the pulse duration of 350 ps at a 10 Hz repetition rate. Our goal is to obtain 200 mJ output energy at a 1 kHz repetition rate. In the nanosecond region, we have constructed a LD pumped Nd:YAG laser system in the kilohertz range [7]. The average power of 360 W have been achieved with a repetition rate of 1 kHz with a 30 ns pulse. This phase conjugated system has produced excellent beam quality. With an external doubler this system has generated over 130 W green average output at 1 kHz. Also an ultra-short pulse OPCPA laser that provides sub-10 fs pulses is being developed. The LD pumped Nd:YAG laser system with hundred ps pulse duration is currently being applied to pump this OPCPA with the goal of producing over mJ output energy of 850 nm radiation at 1 kHz. In preliminary measurements, a sub nJ seed pulse is amplified with a gain of 105 in a two-stage OPCPA which uses BBO crystals. We are certain from this experiment that energies as high as over mJ should be achievable with this OPCPA system. From advanced compact lasers to high power installations, our facilities span the wide range of laser capability. Our institute has delivered a range of major new facilities over the recent past to ensure its research communities can continue to operate at the forefront of their field. [1] H. Nakano, S. Miyauti, N. Butani, T. Shibayanagi, M. Tsukamoto, and N. Abe, “Femtosecond Laser Peening of Stainless Steel,” Journal
of Laser Micro/Nanoengineering, 4, 35-38 (2009). [2] J. P. Chu, J. M. Rigsbee, G. Banaś, and H.E. Elsayed-Ali, ” Laser-shock processing effects on surface microstructure and mechanical
properties of low carbon steel,” Materials Science and Engineering A, 260, 260-268 (1999). [3] C. Rubio-GonzaLleza, C. Felix-Martineza, G. Gomez-Rosasb, J.L. Ocanac, M. Moralesc, and J.A. Porroc, “Effect of laser shock
processing on fatigue crack growth of duplex stainless steel,” Materials Science and Engineering A, 528, 914-919 (2011). [4] H. Kiriyama, M. Mori, Y. Nakai, T. Shimomura, H. Sasao, M. Tanoue, S. Kanazawa, D. Wakai, F. Sasao, H. Okada, I. Daito, M. Suzuki,
S. Kondo, K. Kondo, A. Sugiyama, P. R. Bolton, A. Yokoyama, H. Daido, S. Kawanishi, T. Kimura, and T. Tajima, “High temporal and spatial quality petawatt-class Ti:sapphire chirped-pulse amplification laser system,” Optics Letters, 35, 1497-1499 (2010).
[5] H. Kiriyama, M. Mori, Y. Nakai, T. Shimomura, M. Tanoue, A. Akutsu, S. Kondo, S. Kanazawa, H. Okada, T. Motomura, H. Daido, T. Kimura, and T. Tajima, “High temporal and spatial quality petawatt-class Ti:sapphire chirped-pulse amplification laser system,” Optics Letters, 35, 645-647 (2008).
[6] M. Suzuki, H. Kiriyama, I. Daito, H. Okada, Y. Ochi, M. Sato, Y. Tamaoki, T. Yoshii, J. Maeda, S. Matsuoka, H. Kan, P. R. Bolton, A. Sugiyama, K. Kondo, and S. Kawanishi, “Hundred mJ, sub-picoseconds, high contrast OPCPA/Yb:YAG thin disk hybrid laser system,” submitted to Optics Letters.
[7] H. Kiriyama, K. Yamakawa, T. Nagai, N. Kageyama, H. Miyajima, H. Kan, H. Yoshida, and M. Nakatsuka, “360-W average power operation with a single-stage diode-pumped Nd:YAG amplifier at a 1-kHz repetition rate,” Optics Letters, 28, 1671-1673 (2003).
26
Generation of Low Noise Sub-Picosecond Laser Pulses for Investigating Laser Peening
M. Suzuki1, H. Kiriyama1, I. Daito1, Y. Ochi1, H. Okada1, M. Sato2, T. Yoshii2, Y. Tamaoki2, J. Maeda2,
S. Matsuoka2, H. Kan2, A. Sugiyama1, P. R. Bolton1 and K. Kondo1 1 Quantum Beam Science, Japan Atomic Energy Agency
2 Development Bureau, Hamamatsu Photonics
[email protected] Residual stress compression on a metal surface by a laser peening is widely applied to large aircraft
components and power generation parts. To date, laser peening have been mainly demonstrated using nanosecond laser pulses. A new approach is being investigated with femtosecond laser pulses where the higher peak intensity can generate larger shock waves than for the nanosecond case. To understand the femtosecond laser peening mechanism, characterization of the shock wave from the laser plasma by the femtosecond laser pulse should be investigated. A femtosecond laser system typically consists of an oscillator, a pulse stretcher, a regenerative amplifier, a
multipass amplifier, and pulse compressor. Temporal noise such as prepulse or amplified spontaneous emission (ASE) can be significant with a regenerative amplifier. When the ASE or prepulse is focused on a target material prior to the femtosecond laser pulse, a preplasma is generated on the target surface making it more difficult to characterize the high peak intensity femtosecond laser plasma interaction. Optical parametric chirped pulse amplification (OPCPA) is one of most efficient techniques for further reducing ASE and prepulse in a preamplifier. Actually, the background level can improve at least two order magnitudes compared to the regenerative amplifier. The gain medium for a femtosecond laser pulse is typically a Ti:sapphire crystal. However this system is large
size and of low efficiency. A Yb:YAG CPA is more suitable for compact high peak power, high repetition rate laser system because of its high efficiency due to direct laser diode pumping and correspondingly small system thermal loading. It is also extremely compact. Also recent progress with larger aperture transparent polycrystalline ceramic with high doping concentration further enable high intensity laser pulse operation at high repetition-rates. We report the demonstration of an OPCPA/Yb:YAG ceramic thin disk hybrid laser system with an output energy of hundred mJ level of sub-picoseconds pulse duration and high temporal contrast. At a 40 MHz repetition-rate the oscillator delivered 20 nJ pulses of 5.5 nm bandwidth at a 1029 nm central
wavelength. The near transform-limited pulses of duration, 220 fs were stretched to about 1 ns with the pulse energy reduced to 12 nJ using an Öffner stretcher of 60 % efficiency. Stretched pulses were subsequently amplified and then compressed by a grating pair. Following the stretcher and prior to preamplification a commercial pulse selector extracted 10 Hz seed pulses that were synchronized to a Nd:YAG 532 nm pump laser. The combined gain of a three-stage (BBO) OPCPA preamplifier increased the output pulse energy to 3.5 mJ. Following preamplification the laser pulse energy was further increased in a Yb:YAG (7 at %) ceramic thin disk amplifer. The ceramic disk is of 0.6 mm thickness and is mounted on a 1.0 mm thick YAG (undoped) disk of diameter of 14 mm. The Yb :YAG disk was pumped by the Q-CW fiber coupled LD unit that provided pulse energy of 2 J in 2 ms (kW peak power). After 20 passes through the thin disk, we achieved a maximum output energy of 130 mJ with bandwidth of 3 nm at a 10 Hz repetition rate. The transform-limited pulse duration is estimated to be 450 fs. Now we are optimizing this amplifier to increase the output pulse energy. The Yb:YAG amplified pulse is subsequently recompressed with a gold grating pair. Because compressor efficiency exceeds 70 % we anticipate the current compressed pulse energy to be near 100 mJ. Figure 1 (b) illustrates the temporal (intensity) contrast of the final amplified pulse. The contrast level 150 ps before the main pulse is measured to be 10-8 using a third-order femtosecond cross-correlator. As seen in Fig. 1, several peaks were observed at -40 ps, -20 ps, 20ps, and 40 ps. These signals before and after amplified main pulse are attributed to reflection from the front and back surface of Yb:YAG disk. Details of this system will be presented in the presentation. Acknowledgements This work was supported by the “Consortium for Photon Science and Technology (C-PhoST)” program funded
by the Special Coordination Funds for Promoting Science and Technology commissioned by Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan, and partly the Special Coordination Fund (SCF) for Promoting Science and Technology commissioned by the MEXT of Japan.
27
25J Large Energy Q-Switched Nd:YAG Laser System for Laser Peening
Fang Zhang 1, Y. P. Yu 2, Wei Wang 3 and X. B. Qian 4
1 Beamtech Optronics Co. Ltd., 5320 Lackner Crescent, Richmond, BC V7E 5Z9 Canada,
Email: [email protected] 2, 3, 4 R&D Group, Beamtech Optronics (China) Co. Ltd.,A 2101 Jinglong Int’l, Chaoyang District, Beijing, China
Email: [email protected]
25J, 20ns (FWHM) at 1~5Hz repetition rates Nd :YAG Q-Switched laser is built by using Ø35x120mm Nd:YAG single crystals grown with Cz-technique. The “super multimode”, beam homogenization technique, and ASE control engineering are also discussed in this article. The oscillator provides 500~600mJ multimode 1064nm laser output with uniform intensity distribution by using a reticulated apodizing mask, which can also prevent the diffraction-induced rings by hard aperture and serious wave-front distortion induced by the defects of crystal lattice. The “super multimode” beam profile is shown in Fig.1. The long pulse and axis ASE energy of whole system has been limited under 300mJ. The system is developed for applications of laser peening [1, 2].
Fig.1. The near-field beam profiles of 2D and 3D Fig.2. Residual stress v.s. depth
The 25J laser system has been used in Tyrida Co. Ltd. to process the aero-engine blades and gas turbine blades. It is proved to be efficient for processing materials such as Aluminum alloy, Titanium alloy, Nickel-based superalloy and stainless steel etc. Fig.2 is one result of laser peening on a kind of aero-engine blade made of Inconel 718, which shows the compressive residual stress can attain 140ksi on surface and deep layer of compressive residual stress (about 0.075inch) is produced. Besides, the grain refinement and hardness have also been greatly improved. All of them make a contribution to extend the high-cycle fatigue (HCF) performance to 3.7 folds compared with that of without treatment. [1] B.P.Fairand, A.H.Clauer, “Laser generation of high-amplitude stress waves in materials,” Appl. Phys., 50(3): 1497-1502 (1979). [2] David W. Sokol, Allan H. Clauer, “Applications of laser peening to titanium alloys,” ASME/JSME 2004 Pressure Vessels and Piping Division Conference, San Diego, CA, July 25-29 (2004).
28
Laser hardening of the working edges of steam turbine blades
Prof. V.А. Serebryakov1, M.V. Volkov1, V.Yu. Machnov1, S. Zou2, Z. Cao2
1 The National Research University of Information Technologies, Mechanics and Optics (University ITMO), 197101, Saint Petersburg,
Kronverkskiy pr., 49 2 Beijing BAMTRI Technology and Development company, P.O.Box 863, 100024 Beijing
Results of model experiments on laser hardening and improving the corrosion resistance of the surface
working edges of the steam turbine blades with an intensity of (2÷4)109 W/cm2 are represented. The laser
facilities used for hardening were the two-stage Nd:glass laser with energy up to 45 J (0,3 Hz) and pulse
duration ~ 40 ns and the two-channel Nd:YAG laser with energy up to 3,3 J (5 Hz) and pulse duration ~ 5 ns.
Indirect laser peening (additional metal foil was used to preserve a smooth surface) of the specimens from
different alloys were carried out with the radiation intensity 2x109 W/cm2 on the target (beam diameter up to 8
mm for Nd:glass laser and 2,6x11mm for Nd:YAG laser). Fatigue strength and corrosion resistance were
determined by microstructural analysis.
Also we discuss the prospects of industrial hardening of powerful pulse-repetition rate lasers, in
particular, developed Nd: YAG laser with relatively low pulse energy up to 40 J, pulse duration 10 ns and a
repetition rate up to 10 Hz and high energy compact Nd:glass laser with pulse energy of up to 100 J, pulse
duration 20 ns and a repetition rate up to 1 Hz .
29
High Average Power Short Pulse Laser for Generation of Coherent 13.5 nm Light
H. Fujita1,2, R. Bhushan1, K. Iyama1,3, K. Tsubakimoto1,2, H. Yoshida1,2, N. Miyanaga1,2,
and M. Nakatsuka1 1Institute of Laser Engineering, Osaka University, 2-6 Yamada-oka, Suita, 565-0861 Japan
2 JST CREST, 2-3 Yonbancyo, Chiyoda-ku, Tokyo 102-8666, Japan. 3Hamamatsu Photonics, 325-6, Sunayama-cho, Naka-ku, Hamamatsu, 430-8587, Japan
We had developed a high repetition (5-100 kHz) and high average power (5 kW) Nd: YAG laser system for
EUV lithography using laser produced plasma. Results such as output power and pulse waveforms are shown in Fig.1. Key subjects were (1) reliable front-end, (2) uniform and high density pumping of main amplifier rods, and (3) compensation of thermal effects. Now, we are developing a high average power short pulse laser pumped by the Nd: YAG laser described above. The short Pulse laser will be used for the generation of coherent 13.5 nm light by the method of HHG (High Harmonic Generation). We are developing a new mask inspection method, coherent EUV scattering microscope, under the cooperation of RIKEN and University of Hyogo.
The short pulse laser system is shown in Fig. 2. A half of the Nd: YAG laser is used for the pumping of OPCPA. Average output power of 50 W is expected after compression at the end of 2011. A high average power pulse laser, 1.5 kW, 10 mJ, 1-3 ns, 150 kHz, for advanced laser processing will be reported briefly.
Fig. 1 Output power of the pump laser system (left figure) and input (solid curve) and output (dashed curve) pulse shape (right figure)
Fig. 2 Schematic drawing of the short pulse laser. Average output power of 50 W is expected at 2011.
0
1000
2000
3000
4000
5000
6000
0 5 10 15 20
5.24 kWPump power 30.4kW
Pump power 28.8kW
Ou
tpu
t P
ow
er (
W)
Input Power (W)
0
1000
2000
3000
4000
5000
6000
0 5 10 15 20
5.24 kWPump power 30.4kW
Pump power 28.8kW
Ou
tpu
t P
ow
er (
W)
Input Power (W)
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
-20 -10 0 10 20 30Time(ns)
0
1000
2000
3000
4000
5000
6000
0 5 10 15 20
5.24 kWPump power 30.4kW
Pump power 28.8kW
Ou
tpu
t P
ow
er (
W)
Input Power (W)
0
1000
2000
3000
4000
5000
6000
0 5 10 15 20
5.24 kWPump power 30.4kW
Pump power 28.8kW
Ou
tpu
t P
ow
er (
W)
Input Power (W)
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
-20 -10 0 10 20 30Time(ns)
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
-20 -10 0 10 20 30Time(ns)
Fiber fs Laser0.05 mJ, 50 fs
Gen. White LightSelect Spectrum
OPCPA15 mJ, 1 ns
Compression10 mJ, 10 fs, 5 kHz
1 kW at 200 mJ, 2 ns, 5 kHz
500 W at 2100 mJ Output Power
50 W
30
Intense Femtosecond Laser Interaction with Liquids: From Laser Ablation to X-ray Emission
K. Hatanaka1,2
1Center for Ultrafast Intense Laser Science, School of Science, The University of Tokyo, Bunkyo, Tokyo 113-0033, Japan 2PRESTO, Japan Science and technology Agency, Kawaguchi, Saitama 332-0012, Japan
Intense laser pulse irradiation onto condensed matters such as aqueous solution results in X-ray pulse emission [1-6] associated with laser ablation [7] when the laser power is more than ~1015 W/cm2. X-ray pulse intensity and spectra change not only with laser parameters like polarization [3,4] and chirp [5] or double-pulse irradiation [6] but with sample physical/chemical parameters such as surface structures even when such structures are transiently-induced [6]. This presentation will review our results on laser ablation of organic liquids and laser-induced X-ray emission mainly from the viewpoint of effects of structures of laser pulses (chirp) and sample solutions. [1] K. Hatanaka, T. Miura, H. Fukumura, “Ultrafast x-ray pulse generation by focusing femtosecond infrared laser pulses onto aqueous
solutions of alkali metal chloride”, Appl. Phys. Lett., 80, 3925-3927 (2002). [2] K. Hatanaka, T. Miura, H. Fukumura, “White X-ray pulse emission of alkali halide aqueous solutions irradiated by focused femtosecond
laser pulses: a spectroscopic study on electron temperatures as functions of laser intensity, solute concentration, and solute atomic number”, Chem. Phys., 299, 265-270 (2004).
[3] K. Hatanaka, H. Fukumura, Three-Dimensional Laser Microfabrication: Principles and Applications (Wiley, H. Misawa and S. Juodkazis, Eds.), Chapter 9, (2006).
[4] D. Sato, S. Matsushima, H. Ono, S. Kajimoto, H. Fukumura, K. Hatanaka, “Circularly Polarized Femtosecond Laser-Induced Pulsed X-ray Emission from Distilled Water”, The Review of Laser Engineering, 37, 901-904 (2009).
[5] K Hatanaka, T. Ida, H. Ono, S. Matsushima, H. Fukumura, S. Juodkazis, H. Misawa, “Chirp effect in hard X-ray generation from liquid target when irradiated by femtosecond pulses”, Opt. Exp., 16, 12650-12657 (2008).
[6] K. Hatanaka, H. Ono, H. Fukumura, “X-ray pulse emission from cesium chloride aqueous solutions when irradiated by double-pulsed femtosecond laser pulses”, Appl. Phys. Lett., 93, 064103 (2008).
[7] K. Hatanaka, Y. Tsuboi, H. Fukumura, H. Masuhara, “Nanosecond and femtosecond laser photochemistry and ablation dynamics of neat liquid benzenes”, J. Chem. Phys. B109, 3049-3060 (2002).
31
Coupled Theoretical-Experimental Characterization of Plasma Dynamics and Thermo-Mechanical Wave
Generation in Laser Shock Processing
C. Colón1, J.A. Porro2, A. Giakoumaki2, C. Correa2, M. Morales2 and J.L. Ocaña2 1 Dept. of Applied Physics, EUITI-UPM. Ronda de Valencia, 3. 28012 Madrid. SPAIN
2 Centro Láser UPM. Universidad Politécnica de Madrid Campus Sur UPM. Edificio La Arboleda. Ctra. de Valencia, km. 7,300. 28031 Madrid. SPAIN.
E-mail: [email protected]
The predictive assessment of the large amount of physical phenomena arising in LSP processes requires a deep understanding of the physics underlying their appearance, and is absolutely needed for the reliable development of practical experiments leading to effective material transformations. Such modelling must explicitly consider the formation of a plasma phase, its thermofluiddynamic behaviour under extreme pressure and temperature conditions (typically leading to pressure/shock waves), the propagation of these shock waves into the solid material and behaviour analysis of the material itself under the shockwave energy release (the direct cause for its desired plastic deformation). The calculational system developed by the authors [1] has been applied to the simulation of plasma dynamics of aluminium alloy targets subject to LSP conditions (= 1064 nm, F = 84 J/cm2 and FWHM = 9 ns). Within the limitation imposed by the 1D character of the used codes, the variation of several irradiation and material/geometry parameters has been evaluated in order to show clear guidelines for the experimental implementation of the processes. Concretely, different natures and thicknesses of the confining medium in a configuration without coating layer have been tested, the relevant results having been represented in terms of the time evolution of different physical variables with spatial dependence, namely, confining medium-target interface position, plasma pressure, fluid velocity, electron temperature and ion density (see i.e. figure 1 (a)). In order to validate the results obtained through numerical simulation, the experimental plasma observation has been carried out as a means of diagnosis for code validation. A laser produced aluminum plasma in air has been generated focusing a Q-switched Nd:YAG laser (FWHM = 9 ns) working in the fundamental frequency (1064 nm) and an irradiance of approximately 15 GW/cm2. The Al II line at 281.65 nm has been used in order to determinate the electron density and the Al II lines at 280.1178 nm, 280.5518 nm and 281.6185 nm for the temperature determination. In figure 1(b) typical atomic lines spectra recorded at different time delays are shown.
Fig. 1. (a) Colour map representation of the simulated evolution after laser pulse of the plasma pressure wave propagation in an Al target.
(b) Time evolution of Al II species spectrum after irradiation of Al 2024 sample by Q-switched Nd:YAG laser at 15 GW/cm2. Work partly supported by MEC/MCINN (Spain; Projects DPI2005-09152-C02-01 and MAT2008-02704/MAT) UPM (Spain, Project CM CCG07-UPM/MAT-1964) and EADS-CASA (Spain). [1] M. Morales et al.: “Numerical simulation of plasma dynamics in laser shock processing experiments”. Applied Surface Science 255
(2009) 5181–5185
32
Simulation on Laser Ablation for Laser Peening
H. Furukawa1, M. Heya
2 1- Institute for Laser Technology, 2-6 Yamada-oka, Suita, Osaka 565-0871, Japan
2- Department of Electronics, Information and Communication Engineering, Faculty of Engineering, Osaka Sangyo University,
3-1-1 Nakagaito, Daito-city, Osaka, 574-8530, Japan
An integrated Laser Ablation for laser Peening COde (LAPCO) was developed to estimate plasma
pressures produced by laser ablations, and plastic-elastic stress and strain in solid metals. In laser peening, the
control of laser plasmas is essential. It is very important to study on laser ablation phenomena by computer
simulations.
In LAPCO, phase transitions from solid to liquid and from liquid to gas are modeled by improved
Anisimov formula[1]. The formation of plastic-elastic stress and strain in solid metals is evaluated by solving
hydrodynamics equations, strain-displacement relation, and stress-strain relation[2]. Fig. 1 shows a schematic
diagram of an integrated Laser Ablation Peening Code (LAPCO).
Fig. 1 Schematic diagrams of an integrated Laser Ablation for laser Peening COde (LAPCO).
We have estimated and compared the temporal behaviors of the positions of the emission peak obtained by
experiments and simulations. Results are described in Fig. 2. As shown in Fig. 2, both are in good agreements
qualitatively.
600
500
400
300
200
100
0
Pos
ition
(
m)
80604020
Time (ns)
28.4 GW/cm2
22.2 GW/cm2
16.1 GW/cm2
12.2 GW/cm2
11.0 GW/cm2
5.54 GW/cm2
(a) (b)
Fig. 2 (a) Temporal behaviors of the positions of the emission peak obtained by experiments.
(b) Temporal behaviors of the positions of the emission peak obtained by simulations.
[1] S. I. Anisimov and V.A.Khoklov, "Instabilities in Laser- Matter Interaction", CRC Press (1995).
[2] P. Peyre, R. Fabbro, P. Merrien, and H. P. Lieurade,
"Laser shock processing of aluminium alloys. Application to high cycle fatigue behaviour" Materials Science and Engineering A210 (1996) 102-113.
33
Laser Peening Enabled Hip Implant Optimization
A. Malik1, C. Huang
2, R. Caruso
3, and K. Langer
4
1,2,3 Saint Louis University, Dept. of Aerospace and Mechanical Engineering, 3450 Lindell Blvd, St. Louis, MO, USA 4Air Force Research Laboratory/RBSM, Wright-Patterson AFB, Dayton, OH, USA
This work involves applying laser peening treatment to facilitate weight minimization of a titanium hip implant
made from Ti-6Al-4V alloy. Materials used for hip implants must be biocompatible, corrosion/degradation
resistant, and allow for minimally invasive implant sizes. Furthermore, the mechanical characteristics of the
implant must be comparable to that of the replaced joint; the implant must be durable under static and transient
loads; it must be flexible enough to deform without yield or fracture; and it must provide for smooth movement.
Adherence to these strict requirements means that implant materials such as titanium are typically used, leading
to high material costs. In this work, laser peening, a process to impart sub-surface compressive residual stresses
and strain hardening, is included as part of the rigorous mathematical modeling to optimize the weight and
performance of a titanium hip implant. The optimization procedure employs surrogate models derived from
high-fidelity finite element simulations of the laser peening process in order to efficiently determine parameters
for key dimensions of the implant. The results of the optimization procedure indicate manufacturing dimensions
and laser peening treatment parameters based on a low-cost, micro laser peening system involving a SureLite
EX 800 mJ, 5 ns pulsed Nd-YAG near infrared laser.
Fig. 1. Titanium hip implant. (a) Solid model of implant (b) Finite element model to facilitate laser peening enabled weight optimization.
(b)
(a)
34
Characterization of Near-Surface Microstructures in IN718 Alloy Laser Shock Peened With and Without an
Ablative Overlayer Amrinder S. Gill,1 Abhishek M. Telang,1 S. R. Mannava,1 Dong Qian1 and Vijay K. Vasudevan1
1College of Engineering and Applied Science, University of Cincinnati, Cincinnati, OH 45221-0012, USA
Email: [email protected]
Laser shock peening without a protective overlay has become of increasing interest because of the ability to reduce the process time. Peening without an overlay results in both mechanical and thermal loading of the material. Surface layers of the material from the experience melting and re-solidification along with deformation due to the shock wave. The recast layer formed in IN718 alloy as a result of laser shock peening without a protective overlay was characterized. Coupons of the alloy were laser peened with and without a protective coating and the surface layers were characterized using various techniques including X-ray Diffraction, Nanoindentation, Transmission Electron Microscopy, Scanning Electron Microscopy, Electron Back scattered Diffraction and Energy Dispersive X-Ray Spectroscopy. The results show the presence of a tensile residual stress in the surface and near-surface regions to a depth of about 50 microns, followed by a compressive residual stress state beyond that depth (Fig. 1). The presence of a non-uniform recast layer with increased surface roughness was observed, as well as areas with modified chemistry and the presence of nano particles (Fig. 2). Comparisons were made with samples shock peened using an ablative overlay and the results are discussed in relation with those from some previous studies.
Fig. 2. (Left) SEM micrograph of surface of IN718 alloy LSP-treated without a tape overlay showing that the re-cast layer contains voids and nanoparticles and (Right) cross-section TEM micrograph of recast layer showing nanoparticles.
Fig. 1. Residual stress vs distance from peened surface in IN718 alloy LSP-treated with a single impact with and without a tape overlay.
35
Effects of Laser Shock Peening on Residual Stress, Microstructure, Local Properties and Corrosion Behavior
of Alloy 600 Abhishek M. Telang,1 Amrinder S. Gill,1 James Guenes, S. R. Mannava,1 Dong Qian1 and Vijay K.
Vasudevan1
1College of Engineering and Applied Science, University of Cincinnati, Cincinnati, OH 45221-0012, USA
Email: [email protected]
Intergranular cracking (IGC) and intergranular stress corrosion cracking (IGSCC) continue to be the primary sources of materials degradation and maintenance concern for many nuclear components in light water nuclear reactors (LWRs), having cost the nuclear industry over 10 billion dollars in the last thirty years, and will likely be an issue in future GEN IV (e.g. SCWR, SFR) components. Failures due to these types of cracking have been observed for decades in nuclear steam generator tubing materials like 304 austenitic stainless steels and their welds in high temperature aqueous environments as well as in Ni-base alloys like alloy 600 (Ni-15Cr-9Fe) and their weldments, so that methods for mitigating SCC are desirable. The present work was undertaken to evaluate the effects of laser shock peening on improving the general corrosion and stress corrosion cracking resistance of alloy 600. As-received and heat-treated coupons of alloy 600 were LSP-treated under different conditions and the residual stress, near-surface microstructure and local properties were characterized. Single loop electrochemical potentiokinetic reactivation (SLEPR) and double loop EPR (DLEPR) tests were used to quantify the degree of sensitization (DOS), i.e. level of chromium depletion adjacent to the grain boundaries in the coupons and to characterize the effect of LSP on the corrosion resistance and hence on susceptibility of Alloy 600 to IGSCC. Modified Huey tests and 3 point bend tests were also used to investigate the effect of LSP on the SCC behaviour. The results show that LSP produces deep compressive residual stresses as well as hardening (Fig. 1) and plastic deformation manifested in the form of numerous slip lines. The DLEPR tests revealed that LSP has a beneficial effect on the corrosion resistance alloy 600, which is manifested in the form of a lower DOS and a decreased extent and width of grain boundary attack (Fig. 2).
Fig. 2. (Left) DOS of unpeened and LSP-treated alloy 600 determined from DLEPR test; SEM micrographs of surface of 621°C, 18h sensitized unpeened (center) and LSP-treated (right) alloy 600 after DLEPR test. Note the DOS is lowered in the 610°C, 18h-heat treated and then laser peened sample and the extent and width of grain boundary attack is also much lower.
Fig. 1. (Left) Residual stress vs distance from peened surface in alloy 600 and (Right) hardness across LSP-treated dimple.
36
Characterization of Residual Stress in Laser Shock Peened IN718 SPF Alloy with X-Rays of Different
Wavelengths Amrinder S. Gill,1 Mohammed Belassel,2 S. R. Mannava,1 Dong Qian1 and Vijay K. Vasudevan1
1College of Engineering and Applied Science, University of Cincinnati, Cincinnati, OH 45221-0012, USA 2Proto Mfg. Ltd., 2175 Solar Crescent, Oldcastle, Ontario, Canada N0R 1L0
Email: [email protected]
X-ray diffraction is one of the most widely used tools to determine residual stresses in a wide variety of materials and the x-ray wavelengths and diffraction peaks used in the analysis vary depending on the material. In the current study, coupons of the IN718 SPF alloy were laser shock peened and through thickness residual stresses were determined by measuring strain in different sets of lattice planes to study the crystal response. Specifically, residual stresses were determined with the Sin2ψ method from strains measured using the (331), (220) and (311) diffraction peaks and Cu-Kα, Cr-Kα and Cr-Kβ/Mn-Kα radiations, respectively. X-ray elastic constants were also measured for the same sets of lattice directions using a four-point test fixture for calculating the stresses from the strain data. The results showed large variations in the residual stress values, with the those measured in the near-surface regions using Cu-Kα x-rays being much lower than those measured using Mn-Kα and Cr-Kβ, which were similar (Fig. 1). The values tend to be more or less similar in regions far below the surface. It is believed that this difference is due to plastic anisotropy, which can result in widely different strain responses in different lattice planes and hence calculated stresses can have significant errors. Hence care should be taken in selecting the right type of x-rays and diffraction peak for residual stress measurement for proper representation of the stress state in the material.
Fig. 1. (Left) Residual stress and (Right) FWHM vs distance from the laser peened surface in IN 718 SPF alloy using different types of
x-rays.
37
Application of LPwC to High-Strength Structural Steel and Its Weld Zone
Y. Sakino1, K. Yoshikawa2, Y. Sano3, R. Sumiya3 and Y.-C. Kim1
1Joining and Welding Institute, Osaka University, 11-1 Mihogaoka, Ibaraki, Osaka 567-0046, Japan 2Graduate School of Engineering, Osaka University, 1-1 Yamadaoka, Suita, Osaka 565-0871, Japan
3Power and Industrial Systems Research and Development Center, Toshiba Corporation, 8 Shin-sugita Isogo ,Yokohama, Kanagawa 235-8523, Japan
[email protected] Compared to mild steel, high-strength structural steels facilitate the constructing of lighter structures through the reduction in plate thickness. Therefore, high-strength structural steel plays a significant role in large structures such as bridges. However, high stress concentration at the toe or other welded zones of the structure often results in fatigue cracking. This stress concentration is known to significantly depend on shape but not the strength of the base metal. This indicates that although tensile strength of high-strength structural steel is higher than that of mild steel, the fatigue strength of a welded structure employing high-strength structural steel does not differ greatly from that of a welded structure of mild steel. Thus, the fatigue strength at the welded zone substantially reduces the advantage of using high-strength structural steel. Of the various methods employed for improving the fatigue strength of a welded zone, the authors have focused on "Laser Peening without Coating (LPwC)". LPwC is an innovative surface enhancement technology for introducing compressive residual stress in metallic materials [1]. The LPwC condition of 490MPa grade structural steel (SM490) has been clarified. Further, it has been confirmed that LPwC generates compressive residual stress in the welded zones of structural steel, and thus, substantially extends the fatigue life [2, 3]. However, the effect of LPwC on the welded zones of high-strength structural steel under the same laser conditions as applied to SM490 is not clear. This study targets 780MPa grade steel (HT780) as a high-strength structural steel in order to clarify whether LPwC generates compressive residual stress on the surface of HT780, and whether such stress would account for prolonged fatigue life in the welded zones of HT780. The main results are summarized as follows: 1)Large compressive residual stress was generated on the base metal surface of HT780 under the peening conditions employed for SM490; 2) LPwC generated significant compressive residual stress at the boxing toe of the high-strength structural steel, where fatigue cracking is initiated; 3) In the laser-peened box-welded rib specimen of the high-strength structural steel, the initiate point of cracks varied depended on the stress range. For small stress ranges, cracks were initiated from the back side of the toe where no stress concentration was observed; 4) The fatigue limit of the boxing toe of the high-strength structural steel was improved by at least 1.5 times as a result of LPwC.
[1] Y. Sano, "Residual Stress Improvement on Metal Surface by Underwater Irradiation of High-Intensity Laser", Journal of Japan Laser
Processing Society, 9, 163-170, (2002). [2] Y. Sakino, Y. Sano and Y.-C. Kim: Fatigue Lives of Box-Welded Joints Pretreated by Laser Peening, 62nd Annual Assembly of Int. Inst.
Welding (IIW) , IIW Doc.XV-1316r1-09, (2009). [3] Y. Sakino, Y. Sano and Y.-C. Kim: Effects of Laser Peening on Residual Stress, Hardness and Roughness at Weld Toe, 62nd Annual
Assembly of Int. Inst. Welding (IIW) , IIW Doc.XV-1315r1-09, (2009).
Fig.2. S-N diagram obtained from fatigue test.
1 0 0
1 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0
105 106 107
500
200
300
104Number of repetition N (cycles)
100
400
600700
*
*** *
NP （Toe）
LP （Back side）
LP （Toe）
Str
ess
rang
e ∆σ
(MP
a)
Fig.1 Photograph of a box-welded rib specimen used fatigue test.
38
The Effect of Surface Treatments on Fatigue of
Carburized X2M Steel
Allan H. Clauer and Peter A. Gaydos
LSP Technologies, Inc.,
6145 Scherers Place, Dublin, OH 4016
[email protected] Carburized X2M specimens were testing in 3-point bending fatigue after having their surface treated with four different treatments both individually and in combination. The bend specimens were 102 mm x 34 x 8.5 mm, with the longitudinal edges of the tensile surface tapered. The surface treatments were Isotropic Surface Finishing (ISF), Low Stress Grinding (LSG), Shot Peening (SP) and Laser Shock Peening (LSP). The first three were also applied in combination with a follow-up LSP treatment, and also a combined ISF/SP/LSP treatment. The results in Figure 1 show that the fatigue strength increased with the type of surface treatment in the order of ISF, LSG, SP, LSP. The combination treatments produced fatigue strength equivalent to or slightly better than the LSP treatment alone.
Fig. 1. Effect of above surface treatments on fatigue of X-2M carburized steel in 3-point bending. The data points in the shaded green area are runouts. The following numbers indicates the number of data points at runout, color coded to the treatment. These results will be discussed in the context of residual stress profiles and scanning electron microscopy of the surfaces and fracture surfaces. The observed modifications of the surfaces and compressive residual stresses lead to observable changes in crack initiation behavior.
39
Fatigue Behavior of Laser Shock Peened Ti6242 and IN718 Plus Alloys
Gokul Ramakrishnan,1 Vibhor Chaswal,1 James Guenes, 1 Kristina Langer,2 S. R. Mannava,1 Dong Qian1 and Vijay K. Vasudevan1
1College of Engineering and Applied Science, University of Cincinnati, Cincinnati, OH 45221-0012, USA 2Air Force Research Laboratory/RBSM, WPAFB, Dayton, OH 45433, USA
Email: [email protected]
Laser shock peening (LSP) is known to dramatically improve fatigue life by introducing deep residual stresses through the surface. Since residual stress is prone to relaxation under thermal and/or mechanical loading, the thermal stability of fatigue life in such surface treated materials is important to know. In this study, the aerospace alloys Ti6242 and IN718 Plus were laser shock peened using different conditions and the residual stresses were characterized by high-energy synchrotron x-ray diffraction and conventional XRD. Near-surface microstructures and local properties were studied using electron microscopy and nano/micro indentation. The thermal stability of residual stress and microstructure were assessed over a range of temperatures and times appropriate for each alloy (Fig. 1). Fatigue S-N curve and fatigue crack growth (FCG) tests were conducted at room temperature on the unpeened, LSP-treated and LSP-treated + thermally aged specimens with and without a notch in both 3-Point Bend (3PB) geometry as well as axially. Constant amplitude (CA) fatigue cracks were allowed to grow inside the LSP patch. Crack length was determined using alternating current potential drop measurements and calibrated with concurrent optical and elastic unloading compliance using a crack mouth opening displacement gage. Interferometric profilometry was conducted during the tests to characterize the crack-tip plastic zone. The fracture surface was subsequently examined by scanning electron microscopy to identify the effect of LSP on crack wake near the edges between R = 0.1 and 0.7 and to factor out the crack closure contribution to LSP induced improvement in FCG resistance (Fig. 2). Hence, a true estimate of crack resistance coming from crack closure vs. internal LSP induced compressive residual stresses was made. The results indicated a marked improvement in FCG resistance due to LSP. The various results are presented and discussed.
Fig. 1. Residual stress vs distance from peened surface in LSP-
treated and LSP-treated + thermally aged Ti6242 alloy.
Fig. 2. Fatigue crack growth data/plot for LSP-treated IN718 Plus alloy.
!
40
Investigation of Fatigue Life Renewal in 6061-T6
Aluminum Alloys Due to Micro Laser Peening
A. Malik1, K. Langer
2, R. Caruso
3, and C. Huang
4
1,3,4 Saint Louis University, Dept. of Aerospace and Mechanical Engineering, 3450 Lindell Blvd, St. Louis, MO, USA 2Air Force Research Laboratory/RBSM, Wright-Patterson AFB, Dayton, OH, USA
Laser Peening is a technology that shows increasing promise for extending the fatigue life of diverse metal
components in the many industries, including aerospace, automotive, medical, manufacturing, and construction
sectors. While laser peening has been shown to extend the fatigue life of specialized metal components such as
turbine blades and other high value-added components, the technology is not yet understood well enough to
deploy it cost-effectively, without extensive experimental testing, for widespread application in these diverse
industries. Moreover, many potential applications, particularly in the aerospace and civil engineering fields,
would benefit from laser peening treatment applied to renew or extend the life of components that have already
consumed significant amounts of their (unpeened) useful fatigue life. The goal of this particular research is to
apply micro laser peening to components with varying degrees of existing service life in order to determine the
extent to which the corresponding fatigues lives can be reset or extended. The experimental testing involves 1)
micro laser peening of 6061-T6 aluminum alloy tubes using an 800 mJ, 5 ns pulsed, near-infrared Nd-YAG
laser, and 2) fatigue testing in an MTS-858 machine. To reduce deployment costs for potential laser peening
applications on existing, aged components, the experimental results will be further used to validate and improve
finite element/strain-life based fatigue prediction methods that accommodate pre-existing life data for industrial
applications involving aircraft grade aluminum alloys.
41
The Effect of Sequence of Operations on Fatigue Life of LSP Treated Open-hole Aluminium Specimens
G. Ivetic1, I. Meneghin1, E. Troiani1, G. Molinari1, A. Lanciotti2, V. Ristori2, J.L. Ocaña 3 , M. Morales3, J.A. Porro3, J. Plaisier4, A. Lausi4
1University of Bologna, Second Faculty of Engineering, DIEM, Via Fontanelle 40, 47121 Forlì, Italy2University of Pisa, Department of Aerospace Engineering, Via Girolamo Caruso 8, 56122 Pisa, Italy3Polytechnic University of Madrid, Centro Láser, C/ José Gutiérrez Abascal 2, 28006 Madrid, Spain
4Elettra Synchrotron Light Laboratory, Strada Statale 14 - km 163,5 in AREA Science Park, 34149 Basovizza, Trieste, Italy
Fastener holes in aeronautical structures are typical sources of fatigue cracks due to their induced local stress concentration. A very efficient solution to this problem is to establish compressive residual stresses around the fastener holes that retard the fatigue crack nucleation and its subsequent local propagation. Previous work done on the subject of the application of LSP treatment on thin, open-hole specimens [1] has proven that the LSP effect on fatigue life of treated specimens can be detrimental, if the process is not properly optimized. In fact, it was shown that the capability of the LSP to introduce compressive residual stresses around fastener holes in thin-walled structures representative of typical aircraft constructions was not superior to the performance of conventional techniques, such as cold-working.
This reduced performance of LSP can be attributed to different factors, including the fact that the treatment was performed on the specimens with an open-hole already present. It was shown that the effect of the presence of the hole introduced unwanted tensile residual stresses at the inner side of the hole, causing the premature fatigue failure of the specimens.
Therefore, an additional experimental campaign was defined in order to highlight the importance of the sequence of operations, which are the drilling of the hole and LSP treatment. Dog-bone specimens, Figure 1, in 3 mm thick Aluminium alloy 6082-T6 were prepared using a CNC machine and subsequently LSP treated (LPwC approach) at the Polytechnic University of Madrid, using an Nd-YAG laser with 2.8 J output energy, 1064 nm wavelength, 9 ns pulse and 10 Hz frequency.
In Figure 2, the curves showing obtained fatigue lives vs. maximum cyclic load applied are illustrated.
Fig. 1. Geometry of the specimen Fig 2. Fatigue lives vs. maximum cyclic load applied at R=0.1
The experimental results suggest that the LSP treatment on the pristine specimens and subsequent hole drilling causes fatigue life increase of about three times in respect to the hole drilling and subsequent LSP treatment sequence of operations. The practical implications of these findings lie in the fact that LSP, at least in the investigated configuration, cannot be applied “in service” on the fastener holes of aeronautical structures but rather “in production” on the pristine panels, prior to the drilling of the holes.
[1] G. Ivetic, I. Meneghin, E. Troiani, G. Molinari, A. Lanciotti, V. Ristori, J.L. Ocaña, M. Morales, J.A. Porro, C. Polese, A.M. Venter, “Characterisation of Fatigue and Crack Propagation in Laser Shock Peened Open Hole 7075-T73 Aluminium Specimens” , ICAF 2011 Structural Integrity: Influence of Efficiency and Green Imperatives: Proceedings of the 26th Symposium of the International Committee on Aeronautical Fatigue
10000 100000 1000000100
110
120
130
140
150
160
170
180Hole after LSPHole before LSP
Fatigue life
Sig
ma
max
at
R=0
.1
42
On the challenge to increase the fatigue resistance ofcomponents with sharp edges by laser shock peening
U. C. Heckenberger1, E. Hombergsmeier 1, and M. Furfari2
1EADS Innovation Works, 81663 Munich, Germany2Airbus Operations GmbH, Hamburg, Germany
Laser Shock Peening (LSP) is known as a mechanical process capable to introduce deep compressive residualstress fields into metallic components. In thick components such compressive residual stress fields result insignificant benefits in the fatigue resistance of the component compared to other treatments [1].
In case of sharp edges the capability of the component to retain residual stresses is influenced by the presence offree surfaces. The experimental results of the detailed investigations of this effect for the LSP treatment arepresented in this work. The results of the subsequent numerical investigations are given elsewhere [2]. NotchedAA 7050 specimens have been treated with different peening strategies (variation of paths, energy and numberof layers). The resulting residual stresses at the surface of the specimen are measured with an X-raydiffractometer (ref. Fig. 1a). The effect on the fatigue resistance has been investigated by fatigue tests andsubsequent fracture analysis in the SEM.
(a) (b)
Fig. 1 (a) Mapping of the residual stresses at the surface of the specimen. (b) Fracture surface of LSP treated specimen after fatigue test.
It is well known that residual stresses perpendicular to the free surface are vanishing towards the edge. Theinvestigations have shown that the residual stresses parallel to the free surface are decreasing as well whengetting closer to the sharp edge. For a radius of around 0.3 mm, residual stresses in loading direction of onlyabout -80 MPa are present close to the edge. As consequence an increased fatigue life has been obtained for LSPtreated specimens, but the sharp edge still remains the weak point of this set-up (ref. Fig. 1b).
[1] U. Heckenberger, E. Hombergsmeier, V. Holzinger and W. von Bestenbostel;, “Laser shock peening to improve fatigue resistance ofAA7050 components”, Int. J. of Structural Integrity, Vol. 2, 22-33 (2011).
[2] M. Sticchi, C. Crudo, D. Furfari, submitted as well to 3rd LP conference .
sharpedge
43
Fatigue testing and life predictions of laser shock peened
spinal implant rods
Sagar Bhamare1, Sethuraman Subramanian
1, S.R. Mannava
1, Dong Qian
1, Vijay Vasudevan
1 and Leonora
Felon2
1College of Engineering and Applied Science, University of Cincinnati, Cincinnati, Ohio, USA
2X-Spine Systems Inc., Dayton, Ohio, USA
The current industry standard 5.5 mm diameter rigid rods suffer fatigue failures due to high
levels of patient activity during the post-operative period. A novel design for the implant rod is
proposed to increase the flexibility and simultaneously enhance the fatigue strength by applying
the laser shock peening (LSP). According to FDA guidelines, spinal implant rods must be tested
under fatigue loading in the vertebrectomy construct set-up. Construct has number of moving
components ranging from pedicle screws, polyethylene blocks, implant rod and caps to connect
the rod to the pedicle screw. Due to complex dynamics of the construct system, it is difficult to
study the effect of LSP on the fatigue behavior of the implant rod itself. A simple method is
developed to convert the construct fatigue loading conditions to equivalent 4 point bending
loads. Conversion method is based on analytical calculations and validated by experimental
results. Using this method, effect of LSP on the fatigue behavior of flexible implant rod is
studied in 4 point bending loading set up. Life predictions obtained using in-house life prediction
models are compared with the experimental results. Finally, laser shock peened rods are tested in
the construct set-up to check the validity of the conversion method.
44
Effect of Laser Shock Peening on Corrosion and Wear
behaviour of Aluminum Alloy
U. Trdan 1, J.L. Ocaña
2, J.A. Porro
2, J. Grum
1,
1Faculty of Mechanical Engineering, Aškerčeva 6, 1000 Ljubljana, Slovenia 2Centro Láser U.P.M., Carretera de Valencia km. 7,300, 28031 Madrid, Spaint
Main author email address: [email protected]
Laser Shock Peening (LSP) is an innovative surface treatment which is already established in practice due to favorable improvement of fatigue strenght and resistance to stress corrosion cracking. The basic idea of laser driven shock waves was first recognized and explored by the early nineteen sixties [1]. When processing the material surface with intense laser pulse of appropriate characteristics plasma is produced, which, in turn, produces considerable densification of dislocations and generation of compressive residual stresses of high gradient [2]. Hatamleh et al. [3] confirmed higher corrosion resistance of laser peened friction stir welded 7075 aluminium joints in a 3.5 % NaCl solution. Laser peening was also confirmed to improve stress-corrosion cracking [4]. Trdan et al. [5,6] concluded lower pit density on laser shock peened 6xxx aluminium alloys at the polarisation corrosion tests. Purpose of this paper is a comprehensive study of LSP effect on wear and corrosion properties due to the effect of shock waves and strain hardening on precipitation hardened aluminium alloy AA 6082-T651. LSP was performed by the method of closed ablation to ensure higher shock-wave pressure and therefore higher degree of strain hardening. In the experiment a following parameters were chosen; i.e. pulse density of 900 pulses/cm2 and three beam diameters of 1.5, 2.0 and 2.5 mm, respectively. Energy level was uniform, i.e. 2.8 J. Wear experiments were executed in air by roll-on-flat tribometer with different loading conditions. At the wear experiments several variables were recorded, such as wear, sliding speed, friction force, friction coefficient, etc. Electrochemical corrosion charecteristics of specimens in the base condition and after LSP were evaluated in a 0.6M NaCl naturally aerated aqueous solution using a classic three electrode cell with a graphite rod as counter-electrode and an Hg/Hg2Cl2 saturated calomel electrode as reference electrode, where the working electrode was embedded in a teflon holder. After 1h OCP stabilization of the specimens surface, cyclic potentiodynamic polarization experiments were performed in order to determine the corrosion (Ecorr), breakdown/pitting (Epitt) and protection potentials (Eprot), respectively, where corrosion current (icorr) and polarization resistance (Rp) were established by the Tafel extrapolating method. In addition to evaluate precisely the activity difference between surfaces of LSP specimens, electrochemical impedance spectroscopy (EIS) will also be applied, where EIS will be conducted at different times of immersion (1 h, 12 h, 24 h), where the EIS output will be monitored at free corrosion potential (Ecorr) in the frequency range from 100 kHz to 5 mHz. Results confirmed that increased dislocation density in the specimen surface due to the shock waves micro plastic deformation, showed more noble compressive residual stresses. Results indicated that base material consists of three intermetallic particles, i.e. Alx(Mn, Fe), Alx(Zn, Mn, Fe, Cu) and Alx(Si, Mn, Mg, Fe), which leads to local dissolution of the material. Moreover, despite increased surface roughness due to laser shock peening, specimens showed high corrosion resistance to localized corrosion attack, due to the formation of a stable passive film, which served as an effective barrier of anodic dissolution. Furthermore, investigation of wear rate and friction coefficient confirmed a mayor influence of different LSP parameters. It has been shown that after LP wear rate is reduced. [1] Fairand, B.P., Clauer, A.H. (1978). In: Laser-Solid Interactions and Laser Processing, AIP Conference Proceedings, 50: 27-42. [2] Grum, J., Trdan, U., Hill, M.R. (2008). Materials Science Forum, 589: 379-384. [3] Hatamleh, O., Singh, P.M., Garmestani, H. (2009). Corrosion Science, 51: 135–143. [4] Sano, Y., Obata, M., Kubo, T., Mukai, N., Yoda, M., Masaki, K., Ochi, Y. (2006). Materials Science and Engineering A, 417: 334–340. [5] Trdan, U., Ocaña, J.L., Grum, J. (2011). Journal of Mechanical Engineering ,57: 385-393. [6] Trdan, U., Žagar, S., Grum, J. (2011). International Journal of Structural Integrity, 2 :9-21.
45
Influence of laser shock peening and laser melting on the surface properties and corrosion behaviour of an Al-Li-Cu
aluminum alloy
P.Peyre1, V.Vignal2 and H.Pelletier3 1PIMM – UMR 8006 CNRS – Arts et Métiers ParisTech, 75013 PARIS, France
2ICB - UMR 5609 CNRS – University of Burgondy, 21078 DIJON, France 3INSA de Strasbourg, 67084 STRASBOURG, France
Different kinds of laser shock peening treatment were applied to 2050 Al-Li-Cu aluminum alloy, with the objective of investigating its surface state and corrosion behaviour in saline solution at global and local scales. The starting material, under T3 or T8 thermal treatment, was shown to exhibit a partially recrystallized grain structure, with a large density of Al(CuFeMn) precipitates much harder than the matrix (9 GPa versus 2.5 GPa HV value under 5 mN loading), oriented along the rolling direction, and cathodic versus the Aluminum matrix. Several experimental techniques were used to investigate surface topography (Fig.1a) and surface reactivity, including conventional potentio-kinetic tests, micro-electrochemical cell to obtain local pit initiation potentials, local impedance spectroscopy to analyze surface films, and surface potential measurements using scanning kelvin probe force microscopy (SKPFM). Mechanical properties were analyzed in terms of residual stresses, where a -300 MPa stress amplitude was shown on 2050-T8 alloy (σy=500 MPa) and a -200 MPa level on 2050-T3 alloy (σy=290 MPa) When using protective coatings for LSP treatments, systematic improvements of pitting corrosion potentials were obtained at global and local scale, which have been attributed to a modification of the aluminum matrix surrounding Al(CuFeMn) precipitates. A possible explanation could come from residual compressive stresses around inclusion that could reduce local electron density and inhibit electrochemical phenomena. When LSP was carried out without thermo-absorptive layers, the deleterious surface finish, combined with tensile residual stresses promoted anticipated pit initiation and reduced corrosion resistance. As a comparison, a laser surface melting (LSM) treatment (φ=0.1 GW/cm²) under Ar shielding was shown to provoke a significant increase of surface roughness, a dissolution of precipitates and a reduction of current densities during electrochemical tests.
(a) (b)
Fig.1: (a) 3D height mapping on 2050-T3 FSW nugget (6 GW/cm² - 50 % overlap), (b) surface finish after LSM treatment (SEM) On the other hand, when applied to 2050-T3 friction stir welds, LSP treatments with or without coatings were shown to have negligible effects on the corrosion resistance during salt spray fog tests or a 4 months natural exposition near-by-the-sea. In all cases, a macroscopic localized corrosion was observed, including inter-granular, pitting and exfoliation corrosions. [1] B.Rouleau, P.Peyre, T.Baudin, J.Breuils and H.Pelletier, Applied Surface Science, 257 (2011), 7195-7203 [2] H.Amar, V.Vignal, H.Krawiec, C.Josse, P.Peyre, S.N.Da Silva, & L.F.Dick, Corrosion Science, (2011), accepted, in press [3] H.Amar, V.Vignal, H.Krawiec, O.Heintz, C.Josse and P. Peyre, Electrochemica Acta , (2011) accepted, to be published Acknowledgements : This work was supported by French ANR agency through the CAPSUL project
46
Laser peening of duplex stainless steel used in seawater desalination pump to improve wear and corrosion
resistances
Hyuntaeck Lim, Hoemin Jeong, Sungho Jeong* School of Mechatronics, Gwangju Institute of Science and Technology (GIST),
1 Oryong-dong Buk-gu, Gwangju, 500-712, Republic of Korea
*Corresponding author: E-mail: [email protected] To extend the life time and to improve the efficiency of the high pressure pump of a reverse-osmosis based seawater desalination plant, laser peening is applied to 2205 duplex stainless steel (22% Chromium-5% Nickel) that is the manufacturing material of the pump owing to its high chrolide-corrosion resistance and good mechanical properties. In this study, we report the results of experimental studies for wear and corrosion characteristics of laser-peened and unpeened duplex stainless steel. The laser peening experiments were carried out using a 2nd harmonic Nd:YAG laser (λ=532 nm, pulse width=8 ns, maximum pulse energy=1.5 J) in purified water using aluminum foil as the coating material to protect surface from ablation damage. For the evaluation of peening results, x-ray diffraction and pin-on-disk measurements were carried out to estimate the residual stress and wear rate. For the measurement of corrosion rates, both potentiondynamic polarization test and copper accelerated acetic acid salt spray test were conducted. It was found that the maximum compressive residual stress of laser peened duplex stainless steel increased by a factor of 3~4 from that of the unpeend material when the process parameters were selected properly (10GW/cm2, 75 pulse/mm2). Also, the pin-on-disk and potentiodynamic polarization tests showed that the wear volume and corrosion rate of laser peened duplex stainless steel reduced by 39% and 74.2%, respectively. The number and size of corrosion pits produced on wear track during the copper accelerated acetic acid salt spray test decreased approximately by half. Acknowledgement This research was supported by a grant (07seaheroB02-04-01) from the Plant Technology Advancement Program funded by the Ministry of Land, Transport and Maritime Affairs of the Korean government. Also, the laser system utilized in this study was supported by the Ministry of Knowledge and Economy of Korea through the Ultrashort Quantum Beam Facility Program.
47
Effects of laser multiple processing on properties of heat-resistant steel at differernt temperature
REN Xu-dong∗, RUAN Liang , HUANGFU Yong-zhuo , ZHANG Yong-kang (Jiangsu Key Laboratory of Laser Manufacture Science and Technology Ministry, Jiangsu University, Zhenjiang 212013, China)
∗ Corresponding author: REN Xu-dong, Tel.: +86 13511696639, E-mail address: [email protected]
Abstract: The heat-resistant steel after aluminized was treated by laser shock processing (LSP) with high power Nd:YAG laser, and
then was tensile tested at 400 . The effects of the high℃ -temperature behavior after LSP were analyzed from residual stress and
fracture organization. The results showed that the yield strength and tensile strength of heat-resistant steel after aluminized were
improved obviously during the tensile testing at high temperature, and the High-temperature fatigue life of 00Cr12 with composite
processing was enhanced vastly. Compared with the LSP, the High-temperature fatigue life of 00Cr12 heat-resistant steel by
aluminizing and LSP had a larger increase.
Fig-SEM of 00Cr12 heat-resistant steel after LSP at 400℃
The SEM of 00Cr12 heat-resistant steel after LSP displayed the fatigue fracture section at 400 .The inclusion ℃ , shrinkage and
other flaws of specimen internal (labeled for a circle) were seen clearly from (a), which were the originate of fatigue cracks. Due to
flaws producing cracks, the cracks expanded from the middle region to substrate surface and internal, as indicated by the arrow. (b)
was the high magnification image of (a) , a lot of spherical inclusions were found from specimen subsurface stratum at place labeled
for a circle, (c) was the high magnification image of the circle at (a), and (d) showed the energy spectrum of Spectrum1. The energy
spectrum analysis of Spectrum1 indicated that it was the oxide inclusions including rich Cr, this flaw could be the cracks originate.
Key words: Laser shock processing; Aluminizing;Residual stress; Fatigue property
Acknowledgements：The authors are grateful to the Project supported by the National Natural Science Foundation of China
(Grant No.50905080, 50735001) and China Postdoctoral Science Foundation funded project (Grant No. 20100471385)
48
49
Technical Digest
Technical Session
Thursday, 13th
50
51
Thermal Stability of Induced RS’s Fields and Fatigue Life Enhancement in High Performance Steels by LSP
J.A. Porro, M. Díaz, L. Ruiz de Lara, A. Gil-Santos and J.L. Ocaña
Centro Láser UPM. Universidad Politécnica de Madrid Campus Sur UPM. Edificio La Arboleda. Ctra. de Valencia, km. 7,300. 28031 Madrid. SPAIN.
E-mail: [email protected]
The capability of Laser Shock Processing for the induction of RS’s fields in sub-surface layers of metallic materials in view of the improvement of their fatigue life has been widely demonstrated. However, a critical point from the perspective of technological applications is the persistence and stability of such RS’s fields under cyclic loading and thermal affectation. Although previous work has been contributed analyzing the possible degradation of RS’s fields both through mechanical and thermal loads for different materials (see [1-2]), the special case of stainless steels and other high performance steels as those considered in nuclear (fission and or fusion) applications is considered to deserve an special deep insight in view of their demanded reliability: the latter alloys, i.e., show an important decrease of creep strength at temperatures above 550 ºC so that their application temperature is currently limited (see [3]). In the present paper, results are presented on the thermal stability of RS’s fields induced by LSP at the UPM Laser Centre (see [4]), both in AISI316L and low activation ferritic-martensitic steels. According to these results the capability of preservation of a certain level of compressive RS’s even at high temperatures and for large affectation times having been observed at characteristic LSP intensities(see figure). Additionally, the corresponding results of LSP induced fatigue life enhancement after thermal cycling are also presented along with some conclusions on the practical limits to be imposed to the thermal degradation for the preservation of a minimum enhancement factor by LSP.
0,0 0,2 0,4 0,6 0,8 1,0-1000
-800
-600
-400
-200
0
200
FerMar Steel, 1600 pulses/cm2, λ = 1064 nm2.8 J/pulse, spot diameter = 1,5 mm, water jet, no paint
Re
sid
ua
l st
res
ses
(M
Pa
)
Depth (mm)
Smax, T = 25ºC Smax, T = 300ºC, 8 hours Smax, T = 400ºC, 8 hours Smax, T = 500ºC, 8 hours Smax, T = 600ºC, 8 hours Smax, T = 600ºC, 1000 hours
Fig. 1. Residual stress permanence in ferritic-martensitic steel treated a 1600 pulses/cm2 after oven heating at different temperatures
Work partly supported by MEC/MCINN (Spain; Projects DPI2005-09152-C02-01 and MAT2008-02704/MAT). [1] Y. Sano et al.: “Stability of residual stress induced by laser peening under cyclic mechanical loading”. International Journal of
Structural Integrity, 2, 42-50 (2011). [2] D. J. Buchanan et al.: “Retained residual stress profiles in a laser shock-peened and shot-peened nickel base superalloy subject to
thermal exposure”. International Journal of Structural Integrity, 2, 34-41 (2011). [3] P. Fernández et al.: “Grain boundary microchemistry and metallurgical characterization of Eurofer 97 after simulated service
conditions”, J. Nucl. Mater. 329–333, 273–277 (2004). [4] J.L. Ocaña et al.: “Design Issues of Engineered Residual Stress Fields and Associate Surface Properties Modification by LSP in Al
and Ti Alloys”. Proceedings of the Fifth International WLT-Conference on Lasers in Manufacturing 2009. Munich, June 2009. A. Ostendorf et al. Eds.. pp. 387-392 (2009).
52
Coupled RS’s Fields and Deformation Control in the Laser Shock Processing of Thin Sheets for
Fatigue Life Improvement
C. Correa, J.A. Porro, M. Morales and J.L. Ocaña Centro Láser UPM. Universidad Politécnica de Madrid
Campus Sur UPM. Edificio La Arboleda. Ctra. de Valencia, km. 7,300. 28031 Madrid. SPAIN.
E-mail: [email protected] The capability of Laser Shock Processing for the induction of RS’s fields in sub-surface layers of relatively thick specimens (d > 6 mm) in view of the improvement of their fatigue life has been widely demonstrated. However, the LSP treatment of relatively thin specimens (normally d < 6 mm, but also thicker ones depending on the treatment intensity) brings, as an additional consequence, the possible bending of the treated specimen, a feature that can otherwise be employed for forming procedures according to the laser shock forming process. This effect poses a new class of problems regarding the attainment of specified RS’s depth profiles in the treated specimens, as their self-equilibration reaction after clamping removal can considerably alter the primary laser shock induced RS’s fields, thus possibly motivating undesired final RS’s field distributions, and, what can be more critical, an overall deformation of the treated component. With the aid of the available calculational system (see [1,2]) the analysis of the problem of LSP treatment for induction of RS’s fields for fatigue life enhancement in relatively thin sheets in a way compatible with reduced overall workpiece deformation due to spring-back self-equilibration has been envisaged. Numerical results directly tested against experimental results in the LSP configuration used at the UPM Laser Centre (see [3]) have been obtained confirming the critical influence of the laser energy and irradiation geometry parameters (see sample simulation results in the enclosed figures).
0 0.5 1 1.5 2-250
-200
-150
-100
-50
0
50
100
150
Depth (mm)
Res
idua
l str
ess
(MPa
)
Aluminium 2024-T351, Position = (57.5, 30) mm , λ = 1064 nm, 2.8 J/pulse, water jet, without coating
σx ; φ = 1.5 mm
σx ; φ = 2 mm
σx ; φ = 2.5 mm
Fig. 1. (a) Colour map representation of the RS’s calculated distribution in a LSP treated 2 mm thick Al2024 plate after clamp release.
(b) RS’s through-thickness transversal profiles numerically obtained for different irradiation intensities in the same sample. In the present paper, an account is provided on the general features of the problem of LSP treatment of relatively thin specimens and some design criteria are put forward in view of the coupled control of RS’s fields and sheet deformation for demonstration of fatigue life improvement, even in test specimens. Complementarily, the application of these criteria to crack growth mitigation by LSP treatment is reported. Work partly supported by MEC/MCINN (Spain; Projects DPI2005-09152-C02-01 and MAT2008-02704/MAT) UPM (Spain, Project CM CCG07-UPM/MAT-1964) and EADS-CASA (Spain). [1] M. Morales et al.: “Thermomechanical modelling of stress fields in metallic targets subject to laser shock processing”. International
Journal of Structural Integrity, 2, 51-61 (2011) [2] J.L. Ocaña et al.: “Predictive assessment and experimental characterization of the influence of irradiation parameters on surface
deformation and residual stresses in laser shock processed metallic alloys”. In: High-Power Laser Ablation IV, Phipps C.R., Ed.. SPIE Vol. 5548, pp. 642-653 (2004)
[3] J.L. Ocaña et al.: “Design Issues of Engineered Residual Stress Fields and Associate Surface Properties Modification by LSP in Al and Ti Alloys”. Proceedings of the Fifth International WLT-Conference on Lasers in Manufacturing 2009. Munich, June 2009. A. Ostendorf et al. Eds.. pp. 387-392 (2009)
53
Laser peening induced residual stresses in thin aluminium plates
M. Burak Toparli1, a, Michael E. Fitzpatrick1, b
1Materials Engineering, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK [email protected], [email protected]
Keywords: Laser peening, residual stresses, thin Al2024-T351 plates
Laser peening has been studied for different applications and is proven to be a promising surface treatment against fatigue failure. It can introduce deeper compressive residual stresses with better surface finish than other treatment techniques. However, laser peening is very challenging in thin plates, both in terms of inducing the desired residual stress field and also obtaining accurate residual stress measurements. The required laser power density to plastically deform the material for compressive residual stress generation can lead to distortion in thin plates due to the low cross section. In addition to being a problem in itself, this distortion can also cause problems in measuring the residual stresses accurately, especially by incremental hole drilling. For diffraction-based residual stress measurement techniques, there are other issues like texture due to rolling during production, large grain size, and surface effects such as pseudo-strains due to measuring with a partially-filled diffraction gauge volume.
We are working on laser peened 2-mm-thick Al2024-T351 plates having pure Al cladding on the surfaces. The aim is to investigate the peening parameters for uniform, deep compressive residual stress fields. The effects of laser power density and percent of peen spot overlapping have been studied. The residual stress fields were measured by laboratory X-Ray, synchrotron X-ray and neutron diffraction, as well as by incremental hole drilling and X-ray and layer removal techniques. Based on experimental data it can be concluded that the stress components longitudinal and transverse to the peen line are not identical to each other, with the transverse component being much less compressive. When the laser power density was increased, more compressive and deeper residual stresses are observed, however, tensile stresses started to appear in the vicinity of the surface. An increase in the peen coverage and overlapping introduces deeper residual stress fields, as expected.
Figure 1: Measured residual stresses, using incremental hole drilling, in Al2024 peened with an intensity of 3 GW/cm2. A single line of peen spots with only 5% overlapping was used. The stresses are not equibiaxial, and although there is compression in depth, the near-surface stresses are tensile, particularly perpendicular to the line of peened spots.
54
X-ray Diffraction Measurement of Residual Stress; Improved Correction Factors for In-depth Measurements
Jon Rankin, Murat Demircubuk, Serena Marley and Lloyd Hackel
Curtiss-Wright Corporation Metal Improvement Company, Laser Peening Division Livermore CA, 94551
Laser peening technology is well understood to generate deep levels of plasticity in metals in a very controlled and repeatable manner. When applied to components of relatively thick cross section or sufficient directional stiffness, laser peening can generate residual compressive stress to a depth of multiple millimeters. Applied to an operational component, this compressive stress can promote fatigue enhancement and resistance to stress corrosion cracking. In the engineering of laser peening into components a number of techniques are used for stress measurement. These include: X-ray diffractometry (XRD), the hole-drilling method, the slitting technique and 2D techniques such as contour via strain profile and neutron diffractions. Although each technique has advantages and limitations, XRD is widely used and is most accurate for surface stress measurements. The x-rays penetrate to a depth of typically 10 �m so to attain deeper results, a local spot typically of 5mm radius on the surface is electropolished away and an XRD measurement at this depth taken. Additional polishing and subsequent XRD measurements can be subsequently taken. However to be accurate these measurements at depth need to be corrected for the stress release resulting from the material removal. A correction based on work of Moore and Evans (SAE Transactions, Vol 66, 1958, pp 340-345) is often used and even provided as a software package in commercial XRD machines. This technique assumes a flat plate surface and total surface removal and can be especially inaccurate for complex surface shapes and in components minimal stiffness. Pedersen and Hansson (NDT International, Vol 22, No. 6, 1989) proposed a technique and provided numerical examples of measurement correction based on finite element analysis (FEA). Prevey et al. (Lambda Research, Diffraction Notes – No. 21, 1997) alluded to similar work applied to shot peening in 1997. Following along that approach we have evaluated FEA corrections for a number of XRD measurements of laser peened samples and compared the results to that of the XRD-machine-provided correction based on Moore-Evans. We have determined that in general the Moore-Evans analysis overcorrects and reports a smaller value of residual compressive stress than is present. We will present our analysis and a number of examples. [1] A. Author and B. Author, “Title of paper,” Journal Name, vol., startpage-endpage (year). [2] A. Author, B. Author, and C. Author, “Title of paper,” Journal Name, vol., startpage-endpage (year). [3] A. Author, Title of book (Publisher), Chapter, (year).
55
Internal Strain Distribution of Laser Peened Ti-alloy Rod Studied by High Energy Synchrotron Radiation X-Rays
T. Shobu1, K. Akita2, A. Shiro1, T. Fujishiro1, K. Kiriyama3, M. Kumagai4, and N. Hisamori5
1Japan Atomic Energy Agency, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo, 679-5148, JAPAN 2Japan Atomic Energy Agency, 2-4 Shirakata-Shirane, Tokai, Naka-gun, Ibaraki, 319-1195 JAPAN
3Comprehensive Research Organization Science and Society, 162-1 Shirakata, Tokai, Naka-gun, Ibaraki, 319-1106, JAPAN 4Tokyo city university, 1-8-21 Tamatsutsumi, Setagaya, Tokyo, 158-8557 JAPAN
5Sophia university, 7-1 Kioi, chiyoda, Tokyo, 102-8554 JAPAN
[email protected] α-β-titanium alloy Ti-6Al-4V has excellent corrosion resistance and specific strength, therefore it is widely used for mechanical components. In this study, laser peening was applied to the Ti-alloy rod to improve fatigue strength of the material and internal distributions of residual strain in the rod were measured non-destructively by synchrotron radiation X-ray diffraction technique. The effects of laser peening on the fatigue strength were discussed. The dimensions of fatigue specimen were 120 mm in length and 5 and 7 mm in diameter. Laser peening was applied on the circumference of specimen as shown in Fig.1. The strain measurements were carried out using the synchrotron radiation beamline BL22XU of the JAEA (Japan Atomic Energy Agency) at the SPring-8. The X-ray energy used was 70.23 keV, and the aperture size of divergent slits was 0.2×0.2 mm2. The strain scanning with Ti{211} reflection at a diffraction angle of 10.82 degrees was performed to measure internal strain distributions of the specimens. Fig. 2 shows the radial distributions of residual strains in the axial and the radial directions, εaxial and εradial, of φ5mm, φ7mm Ti rod with laser peening. On the surface, εaxial and εradial were compressive and tensile, respectively, and a rapid change in strain was observed in the vicinity of the surface. On the other hand, εaxial was tensile and εradial was low around zero in central region from x=-2.5 mm to +2.5mm for φ7mm Ti rod and from x=-1.5 mm to +1.5mm for φ5mm Ti rod, respecitivily. The depth introducing compressive strain in εaxial of two specimens was 1mm. The axial tensile strain increased with a decrease of the diameter of specimen. This indicates that the probability of the internal cracking may be increased with decreasing the diameter of the fatigue specimen and therefore the fatigue strength may be reduced even if the laser peening condition is the same.
-6000
-4000
-2000
0
2000
4000
6000
-4 -3 -2 -1 0 1 2 3 4
εaxial
@7mmε
radial@7mm
εaxial
@5mmε
radial@5mm
Stra
in , ×
10-6
Distance from center , mm
Fig. 1 Schematic of specimen and gauge volume. Fig. 2 Residual strain distributions of Ti rod with laser peening.
56
Optimising LSP conditions and modelling the geometric effects on residual stress
K. Shapiro1, M. Achintha2, P. Withers1, and D. Nowell2
1School of Materials, University of Manchester, Manchester, M13 9PL, UK 2Department of Engineering Science, University of Oxford, Parks Road, Oxford, OX1 3PJ, UK
Main author email address: [email protected]
The basic principle of laser shock peening (LSP) is to inhibit fatigue initiation or short crack growth by inducing compressive stresses close to the surface of a metal component. The method is particularly useful in the surface treatments of highly-stressed alloys used in the aerospace industry. LSP typically produces compressive zones over 1.5-2.0mm deep, in comparison to about 0.25mm produced by conventional shot peening. The laser parameters can be relatively easily controlled, allowing the process to be tailored to specific design requirements. Additionally, the flexibility of the process allows peening of complex geometries (e.g. leading edges of aero-engine blades). However, a comprehensive analytical or numerical method for predicting the residual stress (RS) distributions generated by LSP is lacking. Consequently, the method is not being exploited as effectively as it might be and in some situations (e.g. in complex geometries) the process has failed to give the expected benefits. The current study forms part of a wider programme of work involving a number of industrial and academic collaborators and the study developed a comprehensive understanding of the LSP process through interpretation of experimental and model results. The experimental work involves measuring and understanding how laser process parameters, specimen geometry and material properties affect the RS fields caused by LSP. X-ray and neutron diffraction techniques have been used to measure RS profiles in Ti-6Al-4V and aluminium alloys (Al2024 and Al7050), all of which are widely used in the aerospace industry for a range of LSP parameters. The experimental results are used to determine the optimal peening conditions and also to quantify the fatigue performance of specimens with a wide range of geometries. A more physically-based eigenstrain (i.e. misfit strain) model which considered the plastic strains introduced by the process has been developed to determine the RS field generated by LSP [1]. Due to propagation of the shock wave generated by a laser shock, the top layers of the specimen experience plastic deformation, and on relaxation the deformed material is loaded in compression by the undeformed material which surrounds this region. Thus, the plastic deformation caused by the shock wave generates the RS field, and also once the plastic deformations are fully stabilised the response of the workpiece is elastic. In the present model, the effect of the LSP pulse is first modelled as a dynamic pressure load in an explicit FE model in order to determine the stabilised plastic strain distribution, which is then incorporated into a static FE model as an eigenstrain. The elastic response of the static FE model gives the RS distribution generated by the original laser pulse. The eigenstrain analysis has a number of advantages. Firstly, once the eigenstrains have been determined, the complete RS distribution can be reconstructed through a single elastic analysis, and hence, the solution can be determined at a manageable computational cost. The formulation of the solution this way ensures strain compatibility, global stress equilibrium, and matches the boundary conditions. The results have shown that the LSP process parameters can be directly linked to the underlying eigenstrain distribution, and also, a given laser setting produces similar eigenstrain distributions in workpieces (of a given material) of different geometries. Therefore, it is possible to undertake a rapid assessment of the RS field caused in new or complex geometries, and also, the effect of multiple LSP shots simply by installing the appropriate eigenstrain distributions at the correct locations within the component. [1] M. Achintha and D. Nowell, “Eigenstrain modelling of residual stresses generated by laser shock peening,” Journal of Materials Processing Technology, vol. 211, 1091-1101 (2011).
57
Relaxation Behavior of Peening Residual Stress under
Mechanical Loading Investigated by Neutron Diffraction
K. Akita
1, K. Hayashi
2, K. Takeda
2,*, Y. Sano
3, and S. Ohya
2
1Quantum Beam Science Directorate, Japan Atomic Energy Agency, Tokaimura, Ibaraki-pref., Japan
2Department of Mechanical Systems Engineering, Tokyo City University, Setagaya, Tokyo, Japan 3Power and Industrial Systems Research and Development Center, Toshiba Corporation, Yokohama, Kanagawa-pref., Japan
*Present affiliation; NHK Spring Co., Ltd., Yokohama, Kanagawa-pref., Japan
Relaxation process of peening residual stress under mechanical loading was investigated by neutron stress
measurement method. The material used in this study was a structural steel JIS SM41 (yield stress y = 286
MPa). The thickness of the sample was 5 mm. Compressive residual stress was introduced by laser peening in
the both surfaces of the sample. The sample was subjected to tensile loading in a step by step. Through
thickness distributions of lattice strain of 211 diffraction plane in the loading direction were measured
nondestructively using an engineering neutron diffractometer, RESA-1 of the Japan Atomic Energy Agency.
Stresses were obtained by multiplying the measured lattice strain and the Young’s modulus of the measured
diffraction plane.
The changes of the stress distributions in the sample during tensile loading were shown in Fig. 1. At the initial
state (applied stress ap = 10 MPa), compressive residual stresses were observed in the both surface layers while
tensile residual stresses existed near the center region balancing with the surface compressive residual stress. As
the applied stress increased, the tensile stress of the center region reached the yield stress of the material at ap
=187 MPa. At ap = 289 MPa, also the surface layer reached the yield stress. Fig. 2 shows the changes of stresses
in the center region and the surface layer of the sample plotted against the applied stress. Relaxation of the
surface compressive residual stress was started at ap = 187 MPa although the stress of the surface layer did not
reach the yield stress, which would be caused by the re-distribution of the residual stress due to the plastic
deformation of the center region. Therefore, the understanding of the magnitude of balancing tensile residual
stress is important to evaluate the relaxation of the surface compressive residual stress against tensile applied
stress.
Fig. 1 Changes of the through thickness stress distributions in
tensile loading.
Fig. 2 Changes of measured stresses in the center and surface
regions plotted against applied stress.
58
Stress Relaxation Behavior of Laser Peened Test Specimen under Thermal Aging Treatment
R. Sumiya1, T. Tazawa2, Y. Yoshioka2, I. Chida1, K. Ishibashi2,
1Power and Industrial Systems Research and Development Center, Power Systems Company, Toshiba Corporation 8, Shinsugita-cho, Isogo-ku, Yokohama 235-8523, Japan
2Power Systems Company, Toshiba Corporation
E-mail:[email protected] Peening that generates compressive residual stress on the material surface is known to be effective for the improvement of fatigue strength [1]. Shot peening is commonly used for gas turbine discs made of Ni-base alloy. Laser peening (LP) [2] can be expected a similar effect like shot peening. The durability of the compressive residual stress generated by LP is confirmed by thermal aging treatment test at 350 °C [3]. The temperature of thermal power plant is higher than this, and it is predicted that more relaxation is observed. In this study, in order to confirm the durability of the compressive residual stress generated by LP under thermal power plant operation, the thermal aging treatment tests were performed. Residual stress measurements were performed by X-ray diffraction method before and after these tests, and the influences of the aging temperature and time on the relaxation behavior of the residual stress were evaluated. The material in this study is Inconel® alloy 706, which is used for the discs of gas turbines. Test specimen is the block type specimen, which has 50 mm x 50 mm surface and 30 mm thickness. Temperatures of the thermal aging treatment tests are from 450 °C to 630 °C. 450 °C is the highest temperature in an actual plant. The longest thermal aging treatment times are 10,000 hours for tests at 450 °C and 500 °C and 1,000 hours for those at 570 °C to 630 °C. In calculations of Larson-Miller parameter (C=20), 1,000 hours at 630 °C corresponds to 5x108 hours at 450 °C. The pulse energy and pulse number density of laser peening are 200 mJ and 50 pulses/mm2, respectively. Figure 1 and Figure 2 are the effects of the aging temperature and time on the residual stresses. Surface residual stress relaxations are not observed clearly except for the results at 630 °C. Only in the results at 630 °C, time dependency is observed. In the results of residual stress distributions beneath the surface, the highest compressive residual stress is at about 50μm and the depth of the compressive residual stress is about 1000 μm before thermal aging treatment test. While residual stress near the surface relaxed after thermal aging treatment tests, stresses deeper than 200 μm are almost the same values. In these distribution, aging temperature dependency is not observed clearly. In these test results, laser peened materials were confirmed that compressive residual stresses were maintained during long time thermal aging treatment.
-1200
-1000
-800
-600
-400
-200
0
1 10 100 1000 10000
Time (hrs.)
Res
idua
l stre
ss (M
Pa) 570℃ 600℃ 630℃
450℃ 500℃
-1200
-1000
-800
-600
-400
-200
0
0 500 1000
Distance beneath the surface (μm)
Res
idua
l stre
ss (M
Pa)
Before aging570℃x1000h600℃x1000h630℃x1000h
[1] S. Taira, and Y. Murakami, “On the Changes of Residual Stresses Produced by Shot Peening Due to Repeated Stressing”, Journal of the Japan Society for Testing Materials, Vol.8, No.70, 607-614 (1959). [2] Y. Sano, et al., “Development and Application of Laser Peening System to Prevent Stress Corrosion Cracking of Reactor Core Shroud”, Proceedings of the 8th International Conference on Nuclear Engineering, Baltimore, ICONE8-8441 (2000). [3] M. Obata, et al., “Relaxation Behavior of Compressive Residual Stress Formed by Laser Peening”, Proceeding of the 2009 Annual Meeting of the JSME/MMD, 343-344 (2009).
Fig. 1. Effect of the thermal aging temperature and the time on the surface residual stress
Fig. 2. Effect of the thermal aging temperature on the residual stress beneath the surface
59
Thermal Relaxation of Residual Stresses in Laser Shock Peened IN718 SPF and Ti-6Al-4V Alloys: Experiments
and Finite Element Modeling Zhong Zhou,1 Amrinder S. Gill,1 Gokul Ramakrishnan,1 Abhishek M. Telang,1 Kristina Langer,2 S. R.
Mannava,1 Dong Qian1 and Vijay K. Vasudevan1
1College of Engineering and Applied Science, University of Cincinnati, Cincinnati, OH 45221, USA 2Air Force Research Laboratory/RBSM, WPAFB, Dayton, OH 45433, USA
Email: [email protected]
Thermal relaxation of the compressive residual stresses induced by laser shock peened (LSP) or other surface treatments in titanium and nickel-base engine alloys can significantly affect their fatigue life and hence the component performance. In the present study, laser shock peening (LSP) induced residual stresses in IN718 SPF and Ti-6Al-4V alloys, and their thermal relaxation due to short-term exposure at elevated temperatures are investigated through a series of controlled experiments and through a coupled thermal-structural analysis using LS-DYNA finite element method (FEM). The Johnson-Cook (JC) material model was employed to represent the nonlinear constitutive behavior under LSP, and the model parameters for IN718 SPF and Ti-6Al-4V alloys were calibrated by comparing the prediction of LSP residual stress with experimental data obtained using the conventional Sin2ψ x-ray diffraction method. Good agreement between the thermal relaxation simulation and experimental results was obtained in LSP-treated single dimple shots as well as 50% overlap coupons that had been exposed to different temperatures for different exposure times. Representative results are shown in Figures 1 and 2 below. Both simulation and experiment revealed that the relaxation amplitude increases with the increase in temperature and exposure time. It was also found that stress relaxation mainly occurs during the initial exposure period and mostly in the near-surface regions, and the stress distribution becomes more uniform after thermal exposure. The Zener-Wert-Avrami analytical model was then applied to model the kinetics of relaxation, and the activation enthalpy of the thermal relaxation process for laser shock peened IN718 SPF and Ti-6Al-4V alloys was obtained and compared with diffusion data reported in the literature.
Fig. 1. Comparison of experimental and simulations of residual stress in as-laser peened (left) IN718 and (right) Ti64 alloys.
Fig. 2. Comparison of experimental and simulations of thermal relaxation of residual stress in laser peened (left) IN718 and (right) Ti64
alloys.
60
The study of relationship between peening effect and real-time measurement on LSP by AE
Yuji kobayashi1, Akinori Matsui1, Manabu Enoki2, Kazutaka Kobayashi2
1SINTOKOGIO,LTD.,3-1, HONOHARA, TOYOKAWA, AICHI, JAPAN 2Department of Materials Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
Email address: [email protected]
1. Introduction Laser peening is a method that peening effect got from shock wave occurred on Ultra short-Pulse Laser. The velocity of shock wave propagating inside the material is faster than the velocity of sound. And it is difficult to observe and evaluate the wave. Acoustic Emission (AE) is elastic wave that occurred from transformation of the material. The observation of AE has seen the transformation of the material. Peening effect as typified by residual stress is occurred from changes in mechanical properties, and we think that AE can evaluate of effect of Laser Shot Peening (LSP). In the present circumstances, method of evaluate intensity of LSP is established SAE that it is used measurement of Arc Height as well as shot peening. LSP applied often titanium and aluminium alloy. Existing method is unfitted to evaluate influence of LSP at titanium and aluminium alloy. Thus this method is just evaluated of LSP output. If estimate of peening effect from the non-destructive and real-time measurement data by AE, improve the accuracy of quality assurance at LSP process and it can be sublimated more added value process. In this study, we discuss evaluation of LSP by existing method and compared method by AE.
-800
-600
-400
-200
0
200
400
600
-5 0 5 10 15 20
time [μs]
amplit
ude [
mV
]
Laser Oscillator
Specimen
AE sensor
CWM
AE Wave
-800
-600
-400
-200
0
200
400
600
-5 0 5 10 15 20
time [μs]
amplit
ude [
mV
]
Laser Oscillator
Specimen
AE sensor
CWM
AE Wave
Fig. 1.Schematic drawing at measurement of AE Fig.2 1st peak value of AE vs. power density of laser
2. Experimental apparatus Fig.1 is schematic drawing at measurement of AE. When laser peening, AE got occurred. The AE wave is measured and memorized in real-time by dedicated measurement apparatus called CWM (Continuous Wave Memory) [1]. Laser is used Nd:YAG laser made by THALES Laser Co. LTD. The specification of laser is below, wavelength; 532nm, pulse width; 8ns, spot diameter; 400μm. 3. Experimental description Laser peening processed to Almen strip to investigate relation between measurement of Arc Height which is existing method and laser output. Parameter which is laser output used power density. And after laser peening processed to Almen strip, residual stress is measured to show relation Arc Height and residual stress. Relation between AE and power density is investigated. Material of specimen used A7075. AE is elastic wave that it is occurred at material deformation. The Parameter that captures the feature of material deformation is first peak value on AE wave. Thus, we investigate relation between first peak value on AE wave and power density to find out what shows the influence of AE wave occurred at changed laser output condition (Fig.2). And specimen of measurement AE at laser peening measured residual stress, too. From the above, we compared between existing method and the method of evaluation laser peening by AE. [1] K. Ito and M. Enoki, Mater Trans.48 1221-1226 (2007)
0
200
400
600
800
1000
1200
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8power density [GW/cm2]
1st p
eak
ampl
itude
[mV
]
specimen type-1specimen type-2specimen type-3
61
Laser Shock Processing Influence on Tensile Behaviour of AA2024-T351 Friction Stir Welded Joints
M. Iordachescu1, A. Valiente1, L. Caballero1, D. Iordachescu2, J.A. Porro2 and J.L. Ocaña2
1Materials Science Dpt., E.T.S.I. Caminos, Universidad Politécnica de Madrid – SPAIN 2UPM Laser Centre, Universidad Politécnica de Madrid – SPAIN
Main author email address: [email protected]
The paper presents experimental results showing the ability of LSP to improve the mechanical strength and cracking resistance of AA2024-T351 Friction Stir Welded (FSW) joints. Based on laser beam intensities above 109 W/cm2 with pulse energy of several Joules and duration of nanoseconds, Laser Shock Processing (LSP) is able of inducing a surface compressive residual stress field [1,2]. After introducing the FSW and LSP procedures, the results of microstructural analysis and micro-hardness are discussed [3]. Video Image Correlation VIC-2D was used to measure the displacement and strain fields produced during tensile testing of flat specimens; the local and overall tensile behaviour of native FSW joints vs. LSP treated were analysed. Fig. 1 presents the strain distribution measured with the VIC-2D technique during the tensile loading of the FSW flat specimens, native and superficially treated by LSP. These results indicate that LSP induces a planar field of compressive residual stresses, on both sides of the specimen, ranging from a maximum value at surface to zero at about 0.8-1 mm depth [1].
Fig. 1. VIC-2D analysis of strain during the tension test of the flat specimens: a) overall elongation, δ%, of the FSW joint - (a1) in the elastic regime, δ ≅ 0.25%; (a2) in the elastic-plastic transition, δ ≅ 0.2%; (a3) in the plastic regime, δ ≅ 0.5%; (a4) at maximum load, δ ≅ 11.5%; (a5) before failure, δ ≅ 14%; b) overall elongation, δ%, of the FSW specimen superficially treated on both sides by LSP - (b1) in the elastic regime, δ ≅ 0.25%; (b2) in the elastic-plastic transition, δ ≅ 0.2%; (b3) in the plastic regime, δ ≅ 0.5%; (b4) at maximum load, δ ≅ 8.3%; (b5) before failure, δ ≅ 10.5%; (25mm gauge length). The tensile failure of the joints, native FSW and LSP treated is governed by the combination of 5 zones of material with different strength, the weakest zone determining the fracture load. LSP superficial treatment applied on the whole FSW joint area produces a significant increase of the tensile loading capacity, and also a presumable important increase of fatigue and corrosion resistance. The compressive residual stress field resulting from LSP contributes to the structure service-life by delaying the nucleation and growth of eventual surface flaw generated in the presence of specific environments. [1] O. Hatamleh, P. M. Singh and H. Garmestani: `Stress Corrosion Cracking Behavior of Peened Friction Stir Welded 2195 Aluminum Alloy Joints´, J. Mater. Eng. Perform., 18(4), 406-413, 2009. [2] J.L. Ocaña, M. Morales, J.A. Porro, C. Molpeceres, and D. Iordachescu: `Laser shock processing of metallic materials. Prospects for application to release the residual stresses in FSW joints´, Metal. Int., 14(3), 113-116, 2009. [3] M. Iordachescu, D. Iordachescu, M. Blasco, and E. Scutelnicu: `Comparative analysis of the friction stir processing effects on as cast and rolled plates of aluminium alloys´, Metal. Int., 14(7), 99-104, 2009.
62
Dimple Formation and powder deposition on metal in Indirect Laser Peening
M.Kutsuna1, H.Inoue1, K. Shibata2, T. Abe2
1 Advanced Laser Technology Research Center Co., Ltd. 40-7 Hiromi, Anjo-cho, Anjo-shi, Aichi-ken, ZIP 446-0026 JAPAN 2 Sendai National Colldge of Technology, 48 Nodayama, Aijima-Shiote, Natori-shi, Miyagi-ken, JAPAN
[email protected] A new laser peening process has been developed to introduce micro-dimples and compressive residual stress with/without powder deposition on the surface of metallic or non-metallic parts using a metal sheet/foil since 2006(Japanese Patent No. 4058448)[1-3]. The process may be called as “ Indirect Laser Peening”, because of no plasma formation and heating on the surface of work piece.
In the present work, the dimple formation and power deposition have been investigated using a Q-switch YAG laser with a max. pulse energy of 650mJ as a wave length of 532nm. The dimple formation and the powder deposition on aluminum alloy sheets can be studied by changing the process parameters such as the beam spot size, pulsed laser energy and types of metal foil in the diameter range of 400μｍ ～800μｍ as shown in Fig.1. MoS2 powder was deposited on the work piece of aluminium alloy by indirect laser peenig process is shown in Fig.2.
Fig. 1. Experimental setup of indirect laser peening
Fig.2 MoS2. powder deposition on aluminium alloy by indirect laser
peenig using a stainless foil for reduction of friction energy loss
In addition, The plasma pressure during peening on aluminum alloy and stainless steel sheets has been measured under water and in air using a strain gauge. During laser peening on aluminium plate with a laser energy density of 10GW/cm2 , the plasma pressure was about 3.71 Gpa. However, during laser peening on stailess steel plate with the same peening condition, it was about 0.91Gpa. Laser peening under water showed higher plasma pressure comparing laser peening in air. [1] Japanese Patent No. 4058448, [2] M.Kutsuna; Indirect Laser Peening and its applications, Welding Technology(in Japanese), 55-8.pp63-69(2007). [3] M.Kutsuna, H.Inoue, K.Saito, H.Suzuki, K.Amano; Study on Indirect Laser Peening to Introduce Micro dimples and Compressive
Residual Stress Using a Metal Foil, Proc. of PLC 2009, March 17-18, 2009, Shanghai, pp8-9
63
Development of Pulse Laser Processing and Related Technologies in Maintenance for Atomic Power Plants
A. Nishimura1, Y. Yonemoto2, and Y. Shimada2
1Japan Atomic Energy Agency, Quantum Beam Science Directorate, 8-1-7 Umebidai Kidugawa Kyoto 619-0215 2Japan Atomic Energy Agency, Applied Laser Technology Institute, 65-20 Kizaki Tsuruga Fukui 914-8585
Laser peening phenomena are enhanced by water confinement. Especially, green nanosecond laser pulses are effective underwater processing. Both water and optical fiber are transparent enough so that most of laser pulse energy can be transferred from a laser system to the surface of solid target. In case of femtosecond laser pulses, nonlinear pulse chirping and super-white continuum generation appeared in water or a fiber core, which caused energy loss and fiber damage. In dry condition, however, ablation on a surface thin layer and shock wave generation in solid density plasma could show us the similar effects by green nanosecond laser peening. Femtosecond laser pulses ablated a thin layer on the stainless steel surface where tensile stress had been mechanically induced. Thermal damage was strongly restricted by femtosecond laser pulses. The surface condition after laser ablation turned to be compressive gradually, which indicated a tolerance for Stress Corrosion Cracking (SCC) [1]. Figure 1(a) shows the basic demonstration by femtosecond laser ablation. The laser processing application (patent No. 4528936) successfully produced two research directions for maintenance of nuclear power plants. One research direction was the fabrication of fiber Bragg grating (FBG) in optical fiber core by femtosecond laser processing [2]. The other research direction was the development of prototype new probing system for heat exchanger units of Fast Breeder Reactors by laser micro welding [3]. Figure 1(b) shows the part of the prototype probing system. Here it consists of a laser processing head, a composite-type optical fiber scope and an eddy current sensor. The inner surface of heat exchanger tubes could be inspected. Up to now, we have been working on both research directions in the new organization in Tsuruga since November 2009.
Fig. 1. Development from basic demonstration to the Prototype Probing System (a) The surface of SUS316L reactor core shroud material was processed by femtosecond laser pulses. (b) The new probing system was designed to inspect and repair the crack on heat exchanger tubes.
SCC troubles in Boiling Water Reactors (BWRs) had been serious since the early stage of atomic power plants. In the case of the BWRs Fukushima, they had SCC troubles about 10 years ago. Safety in the BWRs had been kept until March 11th 2011. The disastrous earthquake and tsunami attacked the coasts in East Japan. Then the BWRs of Fukushima fell into core meltdown. Here we present our developing pulse laser processing and related technologies in maintenance for atomic power plants. Application to the existing plants is now urgent. Laser processing for FBG fabrication and surface cleaning will be discussed. [1] A. Nishimura, E. Minehara, T. Tsukada, et. al, “Ablation of work hardening Layers against stress corrosion cracking of stainless steel by repetitive femtosecond laser pulses”, Proc. SPIE Vol. 5662, 673-677, (2004). [2] Y. Shimada, A. Nishimura, M. Yoshikawa and T. Kobayashi, “Design of Monitoring System of High Temperature Piping System by Heat Resistant Fiber Bragg Grating”, JLMN Vol.5, No.1, 99-102, (2010) [3] A. Nishimura, T. Shobu, K. Oka, T. Yamaguchi, Y. Shimada, et al., “Development of Inspection and Repair Technology for the Micro Cracks on Heat Exchanger Tubes”, Journal of Japan Laser Processing Society, Vol. 17, No. 4, 207-212, (2010).
(b) (a)
64
Improvement of fatigue properties on 12Cr stainless steel for low pressure turbine blades by laser peening
I. Chida1, K. Hirota1, Y. Sano1, H. Sasaki1, R. Sumiya1, T. Inukai1, I. Murakami1 and H. Nomura2
1 Toshiba Corporation, Power & Ind. Systems R&D Center,8, Shinsugita-cho, Isogo-ku, Yokohama 235-8523, Japan 2 Toshiba Plant Systems & Services Corporation
E-mail: [email protected]
In steam turbine components of both Toshiba and other companies, low pressure turbine blades with a fork
type installation portion are employed to enhance the joint strength to the rotor, as shown in Fig.1. Those turbine blades have pinholes at the forks and are connected to the rotor with some pins. Recently, some fatigue damages were found at the forks of other company’s low pressure turbine blades, caused by random vibration and steam-flashback vibration [1]. Therefore, some technologies to improve material properties of turbine blades were investigated, especially for the inside surface of pinholes. There are some reports describing that peening technology would control the occurrence of cracks and enhance the high-cycle fatigue properties of the material [2, 3]. In this paper, laser peening technologies for low pressure turbine blades developed in Toshiba are described, especially focused on the materials evaluation of the laser peened 12Cr stainless steel. Laser peening is a novel process to improve residual stress from tensile to compressive on material surface
layer by irradiating focused high-power laser pulses in water. In addition, laser peening is also well known as a process to improve fatigue properties by stress improvement. Toshiba has developed several types of laser peening devices and already applied to Japanese nuclear power reactors of both BWR and PWR as preventive maintenance against stress corrosion cracking. By using the above mentioned technologies, a laser peening technology for the folks of low pressure turbine blades was developed. Some small irradiation head with aspherical mirror has been developed to peen inside surface of the holes at forks in turbine blades. Residual stress on the peened surface was measured by X-ray method and the effectiveness of stress improvement was proved. Fatigue specimens which simulate the stress concentration zone of forks were fabricated and laser peening was performed to the surface of specimens by Q-switched and frequency- doubled Nd-YAG laser, with pulse energy of 70mJ, with pulse number density of 45 (LP1) and 27(LP2) pulses/mm2. As the results of fatigue test, fatigue strength of the laser peened specimens was improved about 40 percent compared to the unpeened specimens by employing the condition LP1 shown in Fig.2. Recently, a laser peening equipment was developed which could handle and peen the low-pressure turbine blades successively.
UnpeenedLP1LP2
104 105 106 107 108
500
400
300
200
100
0
Number of cycles to failure Nf (cycles)
Stre
ss a
mpl
itude
σa
(MPa
)
Mean Stress = 200MPaUnpeenedLP1LP2
104 105 106 107 108
500
400
300
200
100
0
Number of cycles to failure Nf (cycles)
Stre
ss a
mpl
itude
σa
(MPa
)
Mean Stress = 200MPa
Fig.2 S-N curves for unpeened and peened specimens of 12Cr stainless steel
Pin
Turbine rotor
Turbine blade
Pinhole
Fork
(Diameters 10-18mm)
Fork type installation portion
Fig.1 Schematic diagram of low pressure turbine blades
[1] Kawahara, et al., “Permanent countermeasures for the low-pressure turbine rotor damage of Hamaoka nuclear unit 5”, Proc. 5th Symp. JMS, pp.441-442(2008) [2] Y. Ochi, et al., ”Effects of degassing process on high cycle fatigue property in casting aluminum alloy”, Proceedings of the 11th International Conference on Fracture, Turin, Italy (2005) [3] K. Masaki, et al., ”Influence of Laser Peening Treatment on High-Cycle Fatigue Properties of Degassing Processed AC4CH Aluminum Alloy”, Journal of the Society of Materials Science of Japan, Vol. 55, No.7, pp.706-711 (2006)
65
Fatigue improvement of manufacturing toolby laser peening
T. Adachi1, Y. Sano2
1Fuji Heavy Industries Ltd.2Toshiba Corporation
Friction stir welding (FSW) is focused as an innovative solid-state joining technology in various industries and is also able to use for the fabrication of stiffened wing panels. In this welding process, the cylindrical pin tool composed of the shoulder and the probe is used as shown in Fig. 1 and especially the probe has more complex configuration for accomplish the superior weld properties. However the FSW tool is subjected to severe cyclic stress and high temperatures by rotating and plunging into the metal materials such as high strength aluminum alloy. In addition, the welding distance is longer in the case of the fabrication of stiffened wing panels and sometimes the pin tool is fractured in the stress concentrated area of the probe. In order to achieve more stable production with low costs, it is necessary to improve the life of the FSW tool further.Laser peening is a new surface improvement technique, which can provide a higher compressive residual stress and a deeper compressive layer than conventional technology such as shot peening and moreover has some interesting characters such as surface roughness and peening accuracy in comparison with other surface methods.In this study, we optimized the laser peening parameter for FSW tool and evaluated the properties of test coupon welded using improved FSW tool by laser peening, and moreover confirmed the improvement of the life of pin tool by the FSW trial under the same condition with the fabrication of stiffened wing skin.
Fig. 1. Schematic Drawing of Friction Stir Welding
Direction of rotationJoint
Direction of weld
Rotary tool
Tool
ProbeShoulder
66
On-Aircraft Laser Peening with a Mobile System
C. Brent Dane, Fritz Harris, Jon Rankin, Randy Hurd, and Scott Fochs Metal Improvement Company, Livermore, CA
The laser peening of a large stationary work piece such as an airplane at a customer site creates a number of significant technology challenges. These include the need for a mobile laser system, a portable beam transport system between the laser and the work piece, and a method of accurately scanning the beam in precise patterns across the component, often following complex surface shapes. At the Second International Conference on Laser Peening in 2010, we reported MIC advances in beam delivery equipment specifically designed to address these challenges. Since that presentation, this system has been placed into full commercial laser peening production on F-22 aircraft at the Lockheed Skunkworks in Palmdale, CA. The system is now in continuous service and the first aircraft was completed in April of 2011. A new mobile beam delivery system allows a laser spot pattern, consisting of hundreds up to thousands of spots, to be applied from a single robot position. High speed adjustable optical components are used to direct the beam to each treatment spot, rather than robotic motion. The beam is pre-formatted for each spot, adjusting its aspect ratio, rotation, polarization, and focusing angle to apply a very precise pattern of square spots across a 3-dimensional surface. The laser delivery tool uses optical metrology combined with a known surface model of the work piece to register the laser pattern quickly and accurately. This eliminates the need for placing each component in a known location and orientation with respect to the laser tool and is particularly valuable when laser peening large items such as aircraft. High speed gimbals under closed-loop control are used to maintain accurate alignment between the mobile laser system and the beam delivery tool. A system of optical targets placed onto key locations on the fuselage is used to monitor mechanical drift between the beam delivery robot and the aircraft. These are checked before each laser peening operation and automatic corrections are applied to the location of each peening spot to correct for any misalignment. This allows the laser peening pattern to be consistently placed with sub-millimeter accuracy onto complex shapes, eliminating the need to re-measure the location of the component being processed. The laser delivery robot can be quickly and easily positioned on either side of each F-22 using an air bearing support system. Specialized tooling allows the correct placement of the laser patterns to be verified by the MIC quality inspectors on each of 26 locations on the aircraft before and after each peening operation. This new technology is fully operational and is now being adapted to other commercial applications that also require the laser peening of large stationary components. We will also describe extensions of the mobile system under development which will enable on-aircraft laser peening of large commercial airliners.
67
Development and application of portable laser peening system to nuclear power plants
T. Uehara1, Y. Sano1, I. Chida1, K. Hirota1 , T. Hoshi1, and M. Yoda2 1 Power and Industrial Systems Research and Development Center, Toshiba Corporation,
8, Shinsugita-cho, Isogo-ku, Yokohama 235-8523, Japan 2Mechanical Technology and Design Department, Toshiba Corporation,
The authors have developed laser peening without sacrificial overlay (protective coating) [1-4] and applied it to reactor components in nuclear power plants to reduce stress corrosion cracking (SCC) susceptibility since 1999 [5-7]. Our technology employs low-energy laser pulses with a duration less than 10ns and an energy of around 100mJ from commercially-available compact Nd:YAG lasers. Flexible remote operation was realized underwater with a water-penetrable wavelength (532nm) by frequency-doubling and fiber-delivering technology of intense laser pulses [8]. Most recently, we have completed an ultra-compact laser peening system, which integrates laser oscillator and positioning robotics into a unit. Figure 1 describes the newly-developed ultra-compact laser peening system [9]. The major characteristics of the ultra-compact system are as follows: (1) The system is much tolerant of temperature fluctuation, vibration and water pressure due to the smaller volume, lesser optics and shorter optical path, compared to the earlier systems [6,7]. (2) A compact laser unit with lower output power can be used because of the negligible transmitting loss of laser pulse energy, which results from the simple optical path instead of a fiber coupling in the earlier systems. (3) The system is well suited to both mirror- and fiber- delivery technologies. In case of mirror-delivery, the system can significantly extend the focal length compared to the fiber-delivery. (4) The system can be easily installed into reactors owing to the much smaller volume and the simpler constitution than those of the earlier systems. Time required for preparation, dispatch and installation of the system could be drastically reduced. (5) The system is highly reliable due to smaller number of parts employed and the simplicity, which requires fewer personnel for the operation and maintenance. The development of compact and low-cost laser oscillators with high-repetition rate is greatly expected to boost the system capabilities and promote the further applications of laser peening.
Figure 1 Specification of the newly-developed ultra-compact laser peening system. [1] Y. Sano, N. Mukai, K. Okazaki and M. Obata, Nucl. Instr. & Meth. Phys. Res. B, 121, pp.432-436, (1997). [2] Y. Sano, M. Yoda, N. Mukai, M. Obata, M. Kanno and S. Shima, J. At. Energy Soc. Japan, 42, pp.567-573, (2000) (in Japanese). [3] Y. Sano, M. Obata, T. Kubo, N. Mukai, M. Yoda, K. Masaki and Y. Ochi, Mater. Sci. Eng. A, 417, pp.334-340, (2006). [4] Y. Sano, K. Akita, K. Masaki, Y. Ochi, I. Altenberger and B. Scholtes, J. Laser Micro/Nanoengineering, 1, pp.161-166, (2006). [5] Y. Sano et al., Proc. 8th Int. Conf. on Nuclear Engineering (ICONE-8), April 2000, Baltimore, Maryland. [6] N. Mukai, Y. Sano, M. Yoda, I Chida, T. Uehara and T. Yamamoto, Rev. Laser Eng., 33, pp.444-451, (2005) (in Japanese). [7] M. Yoda et al., Proc. 14th Int. Conf. on Nuclear Engineering (ICONE-14), July 2006, Miami, Florida. [8] T. Schmidt-Uhlig, P. Karlitschek, G. Marowsky and Y. Sano, Appl. Phys. B, 72, pp.183-186, (2001). [9] T. Uehara et al., Proc. 16th Int. Conf. on Nuclear Engineering (ICONE-16), May 2008, Orland, Florida.
68
Automatic Motion Planning Method for Laser Peening Robot System
N. Suganuma1, K. Matsuzaki2, Y.Sano3, and H. Adachi4
123Power and Industrial Systems Research and Development Center, Toshiba Corp. 8, Shinsugita-cho, Isogo-ku, Yokohama, Japan 4Isogo Nuclear Engineering Center, Toshiba Corp. 8, Shinsugita-cho, Isogo-ku, Yokohama, Japan
Laser peening is a surface enhancement process that introduces compressive residual stress on materials by
irradiating laser pulses under aqueous environment. We have applied laser peening to the nuclear power plants as a preventive maintenance against stress corrosion cracking (SCC). And we have developed laser peening robots and applied it to the maintenance of reactor internals in operating nuclear power plants. Motion planning of a maintenance robot used in narrow space such as inside of a reactor takes much time; since the interference margin is small and a suitable motion is planned by trial-and-error in each work case. To reduce this time-consuming work, we have developed an algorithm to automatically generate a motion of the robot to avoid collision with other structures in its surroundings. This algorithm generates a collision-free path and motion using virtual repulsive forces whose length is defined based on the distance between the robot and obstacles. The shape of motion path is modeled with multiple virtual springs and mass points. Its shape is changed using the repulsive force from obstacles to generate collision-free path. Then, a posture of robot is also automatically generated with repulsive forces and attractive force that pulls the end effecter to the generated path. Using this algorithm, an experiment of generating approach and trace motion was carried out for such works as peening with the 7 degrees of freedom (DOF) manipulator. As a result, it was confirmed that the proposed method was able to realize obstacle avoidance during task motion. We are planning to apply this system to laser peening robots for nuclear power plants. This system is able to
realize shortening of preparation and operation periods for maintenance work at the plant.
69
Application of Femtosecond laser-induced Impulsive Force for Biotechinology
Y. Hosokawa
Graduate School of Materials Science, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara, Japan
[email protected] When an infrared femtosecond laser pulse is focused into water through a microscope objective lens, shockwave and cavitation bubble are generated at the laser focal point. A stress wave induced by these phenomena localizes in micron scale at the threshold of the generation, it is possible to load it to biological cells with single cell level as an impulsive force. Recently we have developed several application techniques of the stress wave for biotechnology. In this presentation, these techniques are introduced. Single cell manipulation Previously, laser trapping is utilized to manipulate single biological cells. However, it is difficult to realize flexible manipulation in cell culture medium because of weakness of photon pressure, which is driving force for the laser trapping. For example, it is impossible to remove cells which adheres on a cell culture substrate or other cells. We succeeded in, for the first time, manipulating such adhering cells by the stress wave. The manipulation technique was demonstrated to break leukocyte-endothelial and inter-epithelial adhesions [1]. Gene injection Targeted delivery of biomolecules into cells in living animals is one of the most important techniques in molecular and developmental biology research, and it has potentially broad biomedical implications. We found that biomolecules can be introduced into single targeted cells in living vertebrate embryos by photoporation using the stress wave. The efficiency of the photoporation was confirmed by introducing dextran, morpholino oligonucleotides, or DNA plasmids into targeted single cells of zebrafish, chick, shark, and mouse embryos [2]. Arrangement of single cells Cell arrangement technique has been attracting much attention as an important process to reconstruct minimum structure of biological tissue or organ on a chip. We developed a new arrangement technique for biological cells utilizing the stress wave. Availability of the cell arrangement was investigated in both view of physics and biology. In view of physics, the damage of the cell in the detachment process was evaluated by visualizing the collagen matrix on the cell adhesion substrate [3]. In view of biology, the ability of cell differentiation after the arrangement was investigated [4]. Quantification of the stress wave using atomic force microscopy A bottleneck for such application in view of metrology is that method to quantify the impulsive force localizing in such small region has not been established. We developed a new local force measurement system for the impulsive force utilizing atomic force microscope (AFM) [5] and demonstrated an estimation of intercellular adhesion strength based on the quantification. From the bending movement of the AFM cantilever, magnitude of the impulse was quantified to be 10-13~10-11 [Ns], corresponding to the average force of about N in s timescale. On the basis of this result, leukocyte-endothelial and inter-epithelial adhesions were estimated as being on the order of at least 10-13 and 10-12 Ns, respectively [1]. [1] Y. Hosokawa, M. Hagiyama, T. Iino, Y. Murakami, A. Ito, Non-contact estimation of intercellular breaking force using a femtosecond laser impulse quantified by atomic force microscopy, Proc. Natl. Acad. Sci. USA, vol. 108, pp. 1777-1782, (2011). [2] Y. Hosokawa, H. Ochi, T. Iino, A. Hiraoka, M. Tanaka, Photoporation of biomolecules into single cells in living vertebrate embryos induced by a femtosecond laser amplifier, in submission (2011). [3] Y. Maezawa, Y. Hosokawa, K. Okano, M. Matsubara, H. Masuhara, In situ observation of cell detachment process initiated by femtosecond laser-induced stress wave, Appl. Phys. A, Vol. 101, pp. 127-131, (2010). [4] Y. Maezawa, K. Okano, M. Matsubara, H. Masuhara, Y. Hosokawa, Morphological evaluation of cell differentiation after the isolation of single cells by a femtosecond laser-induced impulsive force, Biomed. Microdevices, Vol. 13, pp. 117-122, (2010). [5] T. Iino and Y. Hosokawa, Direct measurement of femtosecond laser impulse in water by atomic force microscopy, Appl. Phys. Express, vol. 3, p. 107002, (2010).
70
71
Technical Digest
Student Session
Thursday, 13th
72
73
300350400450500550600650700
Stre
ssam
plitu
de(M
Pa)
104 105 106 107
Number of cycles to failure
EPSPBBUSPLPwC
02468
1012141618
EP BB USP SP LPwC
Rou
ghne
ss R
z ( µ
m)
Residual Stress State and Fatigue Behavior of Laser Shock Peened Titanium Alloys
E. Maawad1, L. Wagner1, H.-G. Brokmeier1,2, Y. Sano3 and Ch. Genzel4
1Institute of Materials Science and Engineering, Clausthal University of Technology, Agricolastr. 6, D-38678 Clausthal- Zellerfeld, Germany
2Helmholtz-Zentrum Geesthacht Centre for Materials and Coastal Research, Max-Planck-Str. 1, D-21502 Geesthacht, Germany 3Toshiba Corporation, 8 Shinsugita-cho Isogo-ku Yokohama 235-8523, Japan
4Helmholtz-Zentrum Berlin (BESSY), Albert-Einstein-Str. 15, D- 12489 Berlin, Germany
[email protected] Laser shock peening can potentially enhance fatigue life of titanium components by inducing residual compressive stresses in near-surface layers much deeper than caused by traditional shot peening (SP). In the present study, laser shock peening without coating (LPwC) [1] was applied on the alpha Ti-alloy Ti-2.5Cu and the metastable beta Ti-alloy TIMETAL LCB. The depth profiles of residual stresses and full widths at half maximum were obtained by means of energy dispersive X-ray diffraction using synchrotron radiation [2]. Residual stresses at the surface were determined by laboratory X-ray diffraction. Thermal stability of these stresses was evaluated after annealing LPwC-treated material at various elevated temperatures and exposure times and by applying a Zener-Wert-Avrami-approach [3]. Results revealed that LPwC-induced residual stresses are thermally more stable than SP-induced ones. These results are explained by the work hardening during LPwC being much lower than during SP. Furthermore, the high cycle fatigue (HCF) performance of the electropolished (EP) reference was markedly improved by LPwC. For example, results on Ti-2.5Cu are illustrated in Fig. 1 where results after LPwC are compared with those after ball-burnishing (BB), SP and ultrasonic shot peening (USP). Compared to the other mechanical surface treatments, LPwC results in the highest surface roughness (Fig. 2) due to ablative interaction between laser and the surface. The fatigue results after the various mechanical surface treatments will be discussed and contrasted.
Fig. 1. S-N curves of Ti-2.5Cu in rotating beam loading (R = -1) comparing reference EP with LPwC, BB, SP, and USP conditions
Fig. 2. Surface roughness of Ti-2.5Cu surface comparing reference EP with LPwC, BB, SP, and USP conditions
[1] Y. Sano, M. Obata, T. Kubo, N. Mukai, M. Yoda, K. Masaki and Y. Ochi, “Retardation of crack initiation and growth in austenitic stainless steels by laser peening without protective coating”, J. Materials Science and Engineering A 417, 334–340 (2006). [2] Ch. Genzel, C. Stock and W. Reimers, “Application of energy-dispersive diffraction to the analysis of multiaxial residual stress fields in the intermediate zone between surface and volume”, J. Materials Science and Engineering A, 372, 28–43(2004). [3] A. Medvedeva, J. Bergström, S. Gunnarsson, P. Krakhmalev, “Thermally activated relaxation behaviour of shot-peened tool steels for cutting tool body applications”, J. Materials Science and Engineering A, 528–3, 1773-1779 (2011).
74
Use of Laser Shock Peening to Recover Fatigue LifeDegradation in Mechanically Damaged 2 mm 2024-T351
Aluminium Sheet
N. Smyth1, M.B. Toparli2, M.E. Fitzpatrick2, and P.E. Irving1
1Cranfield University, Cranfield, Bedfordshire, MK43 0AL, United Kingdom2The Open University, Walton Hall, Milton Keynes, MK7 6AA, United Kingdom
Mechanical damage in the form of scratches can degrade the fatigue life of engineering structures andcomponents. Under cyclic loading conditions cracks can initiate at the root of scratches and propagate in thethrough thickness direction. Cini [1] found a reduction in the fatigue life of 2 mm aluminium sheet of up to 97%in the presence of scratches when compared to pristine samples. Failure crack lengths of up to 1 mm wereobserved implying that crack growth was entirely in the short crack regime.
Laser shock peening is a possible technique to recover fatigue performance of damaged sheet. Laser peeningcreates residual compressive stresses in the region of the scratch damage and these could reduce the fatiguecrack growth rates of the crack propagating from the scratch root. Many previous studies [2-4] have shown thatfatigue properties of pristine components can be significantly improved through the use of laser shock peening;however its use on thin components containing small defects of high stress concentration has not beenpreviously reported. The aim of this research is to establish the extent of improvement in fatigue life which canbe obtained and to develop a laser peening procedure and residual stress profile that will give optimumimprovement in life.
In the present work dogbone samples of 2 mm 2024-T351 clad aluminium sheet were scribed perpendicular tothe sample longitudinal axis using a diamond tool, producing scratch depths of 50 µm and 150 µm with notchroot radii of 5 µm. Two laser peening systems were used and their performance compared. These were firstly aNd:YLF laser, with an irradiance of 1.5 GW/cm2 and 7.5 mm spot size, and secondly a Nd:YAG laser with anirradiance of 31.44 GW/cm2 and 0.75 mm spot size. The full length of the scratch was treated using the lasershowever the treatment zone width was 28mm for peening with the Nd:YLF laser and 7mm for peening with theNd:YAG laser. It was observed that laser shock peening on one side only of a thin sheet caused significantdistortion of the flat sheet. Fatigue testing was performed using a servo hydraulic machine with maximumnominal stress of 200 MPa and an R ratio of 0.1. It was found that the Nd:YLF peening resulted in animprovement in fatigue life of 80% and 53% for samples containing 50 µm and 150 µm deep scratchesrespectively and the Nd:YAG peening an improvement of 216% and 243%. Residual stresses in the peened areawere measured using hole drilling and x-ray diffraction techniques. The Nd:YLF peening resulted in minimalcompressive stresses whereas the Nd:YAG peening had maximum compression of 110 MPa with significantcompressive stresses extending 0.5 mm in depth (one quarter sample thickness) before becoming tensile.
A finite element model representing a two dimensional cross section of the test sample was created using theprogram ABAQUS. The model was used to predict the improvement in fatigue lives from the application oflaser peening, assuming that fatigue life is entirely occupied by crack growth from the defect. The model wasutilized to determine a residual stress profile with optimum fatigue life. The laser shock peening was representedby incorporating the measured residual stress field in the model, followed by calculation of the stress intensityassociated with the residual stress field, and the effects of this on the effective R ratio during the crack growthstage of fatigue life. Initial predictions show that different residual stress profiles will have significantlydifferent fatigue lives, and that an optimum profile with significantly improved lives can be defined. Theexperimentally observed fatigue lives are compared with predicted ones, and are considered in the light of themeasured residual stresses and the underlying assumptions of the fatigue life model.
[1] A. Cini and P.E. Irving, “Transformation of defects into fatigue cracks; the role of Kt and defect scale on fatigue life of non-pristinecomponent, Fatigue 2010, 6-11 June 2010, Prague, Procedia Engineering, 667-677.[2] Clauer, A.H., Walters, T.W., Ford, S.C. (1983) The effects of laser shock processing on the fatigue properties of 2024-T3 Aluminum, in:Lasers in materials processing, American Society for Metals, p. 7-22.[3] Everett, R.A., Matthews, W.T., Prabhakaran, R., Newman, J.C., Dubberly, M.J. (2001), The effects of shot and laser peening on fatiguelife and crack growth in 2024 aluminum alloy and 4340 steel, NASA/TM-2001-210843, NASA, Virginia.[4] Warren, A.W., Guo, Y.B., Chen, S.C. (2008), Massive parallel laser shock peening: simulation, analysis and validation, InternationalJournal of Fatigue, 30(1), p.188-197.
75
Effects of Laser Peening on Plane Bending
Fatigue Properties of Friction Stir Welded
A6061-T6 Aluminum Alloy
Kenji Yamashiro1, Kiyotaka Masaki
2, Takashi Gushi
2 and Yuji Sano
3
1Mechanical System Engineering Course, Creative System Engineering Advanced Course,
Okinawa National College of Technology, 905 Henoko Nago-shi, Okinawa, Japan 2Okinawa National College of Technology
3Toshiba Corporation, 8 Shinsugita-cho, Isogo-ku, Yokohama, Kanagawa, Japan
In recent years, the friction stir welding (FSW) joint is used to structural components of cars, ships,
aircrafts et al. It is important to investigate the fatigue properties of the FSW joint because mechanical structure
produced by FSW is subjected repeated stress. In this study, laser peening without coating (LPwC) treatment
was applied to improve the fatigue properties of FSW joints of A6061-T6 aluminum alloy. In order to
investigate the influence of the LPwC treatment on the fatigue properties of the FSW joints, plane bending
fatigue tests were carried out for fatigue specimens with a minimum width of 20mm and a thickness of 3mm.
The weld zone is in the center of the fatigue specimen. After wire cutting of the specimens from a FSW joint
plate, the specimen surface was milled by an end mill so as to remove the notch at the edge of the tool shoulder.
These specimens were named surface reworked-FSW or SR-FSW. LPwC treated SR-FSW specimens ware
named LP-SR-FSW. The plane bending fatigue tests were conducted at 1300cpm with a stress ratio of R=-1 in
air at room temperature. Fig.1 shows the S-N diagrams of the fatigue test results. The fatigue strength at 107
cycles of the A6061 and the SR-FSW was 110MPa. Meanwhile the fatigue strength of LP-A6061 and LP-SR-
FSW were 160MPa and 120MPa, respectively. There is a big difference in the improvement of the fatigue
strength between A6061 and SR-FSW. Then, the hardness, residual stress and surface roughness profiles were
measured and the fracture surface was observed to investigate the effects of the LPwC treatment. Fig.2 shows
the hardness distribution of LP-SR-FSW. The hardness distribution of SR-FSW is also shown by the band in the
figure. The hardness in the stir zone of SR-FSW obviously decreased. By the LPwC treatment, the hardness of
the stir zone increased compared to the outside of the stir zone. However, a huge deference still remains
between A6061 and LP-SR-FSW. The residual stress measurement revealed that the compressive residual stress
was introduced on the fatigue specimens by the LPwC treatment. Although the magnitude of the compressive
residual stress in the stir zone of LP-SR-FSW was about two times greater than LP-A6061, the surface
roughness was increased by the LPwC treatment. The fatigue properties would be determined by these peening
effects.
Fig. 1 S-N diagram. Fig. 2 Hardness distributions of FSW.
103
104
105
106
107
108
50
100
150
200
250
Number of cycles to failure Nf, cycle
Str
ess a
mp
litu
de σ
a, M
Pa
●LP−A6061○A6061
△SR−FSW ▲LP−SR−FSW
76
Laser peening of Al7050 aluminium alloys to enhance
fatigue life
M. Burak Toparli1, Michael E. Fitzpatrick
1 and Domenico Furfari
2
1The Open University, Materials Engineering, Walton Hall, Milton Keynes, MK7 6AA, UK 2Airbus Operations GmbH, Hamburg, Germany
Laser peening has become an important surface treatment methods for the prevention of fatigue failures. The
superior post-peening surface finish and deeper compressive residual stress fields compared to shot peening
make this technique very attractive for application to a range of component in the aerospace industry.
In this work, laser peened Al7050 aluminium alloy samples were investigated by EADS IW and The Open
University. Residual stress measurements by hole drilling and surface X-ray diffraction were conducted by
EADS IW to identify optimum peening parameters in terms of laser power density and number of overlapping
peen layers. Different peen patterns were developed to achieve spot overlapping. After selecting peening
parameters of 4 GW/cm2, 18 ns pulse and 300% coverage, extra residual stress measurements by hole drilling,
surface X-Ray diffraction and the contour method were conducted by The Open University. X-ray and layer
removal was also applied. Residual stress measurements conclude that compressive residual stress fields up to 3
mm from the surface can be obtained by laser peening. The magnitudes of the surface stresses are very similar
to shot peening; compressive around –300 MPa. The residual stress results from different techniques show good
agreement. Fatigue tests under different loading and surface conditions were carried out by EADS IW. Laser
peened samples show better fatigue performance compared to shot peening. Laser peening delays crack
initiation and retards crack growth in compressive residual stress field. Therefore, deeper compressive residual
stresses with better surface finish can account for improved fatigue lives.
Fig. 1. Contour method result showing the residual stresses due to laser peening of 7050 sample.
77
Laser shock processing to improve surface properties of precipitation hardened aluminum alloy 6061
S. Sathyajith 1 , S. Kalainathan 2 and S.Swaroop3
Physics ,SASVIT University ,Vellore,Tamil Nadu,India--632014
Laser shock processing(LSP) is an innovative surface modification technique which enhance the metallurgical properties of metals and alloys by make use of laser generated shock wave. The target’s ablation caused by short laser pulse (in ns) with power density in GW/cm2 generate high pressure plasma, If the target is previously covered with a transparent layer such as water ,it prevents the fast expansion of plasma and induce a high intense shock wave between the transparent layer and the target.
The present study investigate the effect of shock wave and strain hardening of laser peened precipitation hardened aluminum alloy 6061 with 300 mj, 1064 nm ,10 ns Nd:YAG laser with different pulse densities with and with out protective coating. The surface roughness of peened and unpeened region was investigated using AFM .The X-ray based stress measurement showing significant increase in surface residual stress compared to unpeend surface. The hardened layer was evaluated with optical microscopy and microhardness .Corrosion studies was carried out with 3.5% NaCl solution. The shock loaded region showed significant improvement in microhardness.
78
Effects of laser-peening parameters
on plastic deformation in metals.
Miho Tsuyama1, Satoshi Yamatani1, Ryosuke Ito1, Kohei Mizuta1, Toshiya Shibayanagi2 and Hitoshi Nakano1
1 Program in Electronic Engineering, Interdisciplinary Graduate School of Science and Engineering, Kinki University,
3-4-1 Kowakae, Higashi-osaka, Osaka 577-8502 Japan 2 Joining and Welding Research Institute, Osaka University, 11-1 Mihoga-oka, Ibaraki, Osaka 567-0047 Japan
Email address: [email protected]
Laser peening is a surface treatment technique that improves the mechanical performance of metals. For instance, it can be used for resistance to crack initiation, extended fatigue life, and enhanced fatigue strength [1, 2]. These effects are based on the production of layer of compressive residual stress due to plastic deformation caused by shock waves resulting from the expansion of a plasma by an intense laser irradiation. Performance of laser peening is defined analytically by the products of two factors depending on the shock loading time and the pressure of laser-produced plasma [3]. This indicates that the laser peening effect is determined by the mechanical impulse on the target materials. Here we examine controllable parameters for efficient laser peening. At first, laser parameters which is the peak power, power density, wavelength, pulse duration number of laser shots irradiated per unit of area and geometrical arrangement of laser irradiation are important factor for laser peening. Secondly, interaction of laser with plasma should be treated for efficient shock generation. Actually, transparent layer for plasma confinement layer which is transparent to the laser wavelength has to be installed on the target materials to increase the shock amplitude without exception. Furthermore, initial properties of target materials, such as the grain size, residual stress, hardness and surface morphology should be controlled to assess the desirable condition for laser peening. We have investigated effects of laser-peening parameters on plastic deformation in several metals. For example, relation between the plastic deformation and initial state of target material has been investigated. Test sample are prepared from SUS316L annealed at the temperature ranging from 200 to 1100 degree. Second harmonic of Nd: YAG laser having the pulse duration of 4 ns has been used for the experiments. Vickers microhardness was used to probe the work hardening due to the plastic deformation by laser shock loading. Figure 1 shows the relation between hardness difference and annealing temperature for various laser intensities. The repetition rate and coverage corresponding to the number of laser shots irradiated per unit of area were fixed to be 10 Hz and 1000%, respectively. The hardness is increased as the increase on the annealing temperature, suggesting that grain distribution should be controlled for the efficient plastic deformation. Dependencies of the plastic deformation on the pulse duration, laser intensity, and coverage on the plastic deformation have been evaluated. Details will be presented at the meeting.
Fig. 1. Relation between hardness difference and the annealing temperature for various laser intensities on SUS316L.
[1]K. Ding and L. Ye, Laser shock peening, (CRC press WP), (2006). [2]Y. Sano, N. Mukai, K. Okazaki, M. Obata, "Residual Stress Improvement in Metal Surface by Underwater Laser Irradiation", Nucl. Instrum. Methods Phys. Res. B, 121, 432-437 (1997). [3] R. Fabbro, P. Peyre, L. Berthe and X. Scherpereel, " Physics and applications of laser-shock processing", J. Laser Appl., 10, 265 (1998).
79
Time-resolved Investigation of Laser Induced Shock
Process using Photoelasticity Imaging Technique: Effects
of Sacrificial Coating and Liquid Overlay
T. T. P. Nguyen1, R. Tanabe
1, and Y. Ito
1
1Department of Mechanical Engineering, Nagaoka University of Technology
1603-1, Kamitomioka, Nagaoka, Niigata, 940-2188 Japan
The use of sacrificial coatings and liquid overlays in laser induced shock process (LSP) has been reported
widely for they can significantly enhance laser induced stress wave (LSW). Although the effects have been
widely investigated, influencing mechanism of coating and liquid phase upon LSP has not been understood fully
yet, especially in their dynamic aspects.
It is rather difficult to look into the LSP dynamically since conventional imaging technique limited only to
observation in the free space side of ablation and a method for visualizing transient stress distribution inside the
substrate is not available. We have successfully developed an imaging method implying photoelasticity
technique into a pump and probe system which alows us to observe the propogation of LSW into bulk solid and
the formation of plasma and ablation plume in ambient environment simultaniously, with time resolution of
nanoseconds [1-3].
We have found that photoelasticity images of epoxy resin in under liquid irradiation provide an adequate
number of photoelasticity fringes which can be used for semi-quantitative estimation of the magnitude of LSW
(Fig.1).
Fig. 1. a) Example of photoelasticity image. Image is taken at 1200 ns delay time. Pulse energy: 60 mJ. b) Increase of the number of fringes as pulse energy increases. Images are taken at 1500 ns delay time. Water is used as liquid phase. Black bars indicate 1 mm.
Here we present a time-resolved investigation of laser induced under liquid shock processing by our custom-
designed photoelasticity imaging system with special attention on the effects of the sacrificial coating and the
liquid overlay on the LSW. Black paint has been used as sacrifical coating along with water, sillicon oil and
liquid paraffin used as liquid overlays. Investigations into the dynamics of plasma expansion, shock wave and
stress wave propagation have been made in order to clarify the contribution of sacrificial coating and liquid
phase toward laser induced shock process. The black paint coating has been proved to enhance the intensity of
the LSW considerably from visual comparison of the photoelasticity images. The thickness of liquid layer has
been demonstrated to affect the LSW: thinner layer results in smaller stress. There is the smallest thickness of
the layer above which the enhancement effect of the LSW intensity is the same as the bulk liquid. This
minimum layer thickness has been found to be dependent on the laser pulse energy. Effect of different types of
the liquid overlay on the strength of LSW has also been investigated.
Our photoelasticity method can provide a unique visualization of laser induced stress wave. Furthermore, our
investigations on dynamics of laser induced shock process would be useful to understand the processes utilizing
the ablation under liquid such like the laser peening or the laser induced wet etching.
[1] M. Matsukura, and Y. Ito, “Time-resolved photoelasticity imaging of transient stress fields in solids induced by intense laser pulses”,
Journal of Physics: Conference Series 59, pp. 749-752 (2007).
[2] Y. Ito , “Laser induced transient stress field studied by time-resolved photoelasticity technique”, Proc. of SPIE Vol. 6106, pp. 61060T-1 (2006).
[3] J. Tadano, H. Kumakura, and Y. Ito, “Coupling of focused laser pulse to surfaces of transparent materials studied by time-resolved
imaging technique”, Applied Physics A 79, pp 1031-1033 (2004).
80 mJ 10 mJ
b) a)
35 mJ Shock wave
Photoelasticity fringes
Target surface
Laser
Liquid
80
Quantitive evaluation of impact pressure of LSP process by AE inverse analysis
K. Kobayashi1, M. Enoki1, A. Matsui2, Y. Kobayashi2, M. Heya3
1Department of Materials Engineering, The University of Tokyo 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan
2Shintokogio, LTD 3-1 Honohara, Toyokawa, Aichi, 442-8505, Japan
3The Graduate School for The Creation of New Photonics Industries 1955-1 Kurematsu-Chou, Nishi-ku, Hamamatsu-City, Shizuoka, 431-1202, Japan
Email address: [email protected]
Laser peening is now recognized as an efficient surface treatment to improve the fatigue life of metal components. To evaluate the process, Almen strip is used as well as shot peening. However, this must be specific material and size so we cannot evaluate a wide variety of substrates. Acoustic emission (AE) is a phenomenon which is released elastic energy by cracking or transformation of solid material. AE method is an in-situ non-destructive evaluation (NDE) method, which detects this elastic wave by piezoelectric sensor. AE method is also useful for measuring laser peening phenomenon because an elastic wave generates when laser is radiated on a target. In this study, laser radiations were detected during the LSP process by AE method. Experimental setup is shown in Fig. 1. Nd:YAG laser is used to process. Laser pulse energy was varied by polarizer. Aluminum alloy A7075 and carbon steel S50C were used as substrate. The base dimension is 35×35mm, and the thickness is of four types: 2mm, 5mm, 10mm, and 20mm. A sensor is attached to substrate, and the elastic wave which generated from laser radiation as an AE event is detected. AE waveforms were memorized by our original apparatus, CWM (Continuous Wave Memory) [1]. Detected AE waveforms contain influence of wave propagation so we use inverse analysis method to remove it. A waveform detected by sensor, V, is the convolution of input force function; F, propagation function in the specimen; G, and response function of sensor; S as expressed in following equation.
V(t)=S(t)*G(t)*F(t) Therefore, input force function can be derived from detected AE signal by deconvolving the propagation function and the response function [2]. The propagation function was derived by calculating with FEM model, and the response function of the sensor was derived by deconvolution of lead broken experiment and simulation. For each experimental condition, input force function was derived. Moreover, impact pressure is derived from input force and laser spot area (Fig. 2).
Fig. 1. Experimental setup Fig. 2. Impact pressure by LSP in A7075 Detected signals depended on substrate and laser pulse energy. The impact pressure became bigger with increasing the laser pulse energy. However, it saturated when the laser pulse energy is above a certain level. It also depended on substrate material, and thickness. According to VISAR method, the impact pressure obtained by LSP process is about 2GPa [3]. However, from this study, it can be said that impact pressure varied according to experimental condition. [1] K. Ito and M. Enoki, Mater Trans. 48, 1221-1226 (2007) [2] D.J. Buttle, C.B. Scruby, “Characterization of Particle Impact by Quantitative Acoustic Emission”, Wear, 137, 63-90 (1990) [3] L.Berthe et al, J.Appl.Phys. 82 (6), 15, 2826-2832 (1997)
Laser oscillator
Collecting lens Substrate AE sensor
CWM
Plasma Polarizer Water
0
1
2
3
4
5
0 0.2 0.4 0.6 0.8 1
2mm5mm10mm20mm
Pre
ssur
e (G
Pa)
Power density (GW /cm2)
81
Sequencing of Laser Peening Application for Fatigue Life Extension
T. Spradlin1, R. Grandhi1, and K. Langer2
1Wright State University, 3640 Colonel Glenn Highway, Dayton, OH 45435 2AFRL, 2790 D Street, Wright-Patterson Air Force Base, OH 45433
Currently, the effect that LP shot sequencing has upon structural fatigue life has not been explored in the available literature. Investigation concerning this gap in the understanding of LP effects and applications will be the focus of this work. In previous work, the effects that adjacent shots have upon one another have been demonstrated; identifying that sequential LP shots affect adjacent residual stress fields. These works, however, have adapted a simple raster-type pattern and varied the percentage overlap, not the sequence in which the shots are applied. Various shot patterns ranging from non-sequential raster type patterns to application of LP shot rows on alternate sides of a known stress concentration will be outlined and applied. The effectiveness of these shot patterns will be assessed analytically based upon the fatigue life estimations of a simple beam in three-point bending. For the purposes of this work, and to allow comparability between results, the peak pressure, material, mid-span duration, spot radii, and percentage overlap will all remain fixed values. Using constant amplitude fatigue life estimations as a response function, parameters that can be used to optimize a LP shot patterns sequencing will be identified.
82
Linear Eigenstrain Theory: Application on a
complex geometry FE model
S. Coratella1, D. Furfari
2
1 University of Bologna - II Faculty of Engineering, venue in Forlì – Italy
1 Materials Engineering, The Open University, Walton Hall. Milton Keynes - UK 2Structure Analysis Stress Methods & Technologies - Research & Technology Group – Airbus Operations GmbH – Hamburg - Germany
The knowledge of Residual Stress distribution is important in predicting the fatigue life of a metallic component. To measure the residual stresses, different methods have been developed, many of which are destructive. Mura developed the theory of eigenstrains [1], defined as the total strains introduced in a specimen after treatments like shot peening and laser peening. Unlike elastic deformations, it has been shown by several studies that the distribution of eigenstrain does not depend on the geometry of the component but only on material, Laser Peening parameters and thickness. Hence the same residual stress profile should be found in any other complex geometry, keeping constant the material and thickness. This aspect is very important because it is then possible to optimise LSP parameters for a given material and thickness. The theory of eigenstrain is quite complex and in 2008 Hill and DeWald introduced a new simple linear theory [2] to predict the distribution of residual stress inside complex geometries. The aim of this research was to calibrate an FE model to confirm the linear theory and to study the effects on more complex geometry specimen.
Fig. 1 (a) Measured Residual stresses vs. Residual Stress from FE model, plain section; (b) Measured Residual stresses vs. Residual Stress
from FE model, curved section. Measured residual stresses have been compared with those derived from an Eigenstrain model, for AA7075 T7451 material and peening parameters of: 4 GW/cm2, 18 ns pulse length and 300% coverage. The model was reproduced in an existing FEM environment, with the mesh chosen to have an element size smaller than the distance between residual stress measurements. For the entire specimen a Young’s Modulus of 70 GPa was used. For each layer of mesh different anisotropy expansion coefficients were introduced. Finally, a delta temperature was introduced to the entire model to produce the desired eigenstrain distribution. As figure 1 (a) shows, in the central part of the specimen there is a perfect fitting between measured and simulated residual stresses. Figure 1 (b) shows the fitting between measured and simulated residual stresses in the curved region. The fitting is not as good as the first case, but this is probably due to the different element mesh and the different distribution of eigenstrains. Further studies of this problem are ongoing. [1] T. Mura, Micromechanics of defects in solids, Martinus Nijhoff Publishers, Chapter 1, 1982 [2] A. T. DeWald, M. Hill, Eigenstrain-based model for prediction of laser peening residual stresses in arbitrary three-dimensional bodies.
Part 1: model description and Part 2: model verification, J. Strain Analysis, vol. 44, pag. 1-27, 2008
LSP measured data vs. ABAQUS simulation
-300
-275
-250
-225
-200
-175
-150
-125
-100
-75
-50
-25
0
25
50
75
100
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
depth (mm)
Re
sid
ua
l S
tre
ss
(M
Pa
)
S22 obtained with ABAQUS
measured RS
LSP measured data vs. ABAQUS simulation
-350
-325
-300
-275
-250
-225
-200
-175
-150
-125
-100
-75
-50
-25
0
25
50
75
100
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
depth (mm)
Re
sid
ua
l S
tre
ss
(M
Pa
)
measured RS
S22 obtained with ABAQUS
83
FE Simulation of Laser Shock Peening. Investigation on Influence of Physical parameters and
Computational Settings.
D. Furfari1, M. Sticchi2, and C. Crudo3 1Airbus operations, GmbH Kreetslag, 10 – 21129 Hamburg, Germany
2University “Federico II” of Naples, Piazzale Vincenzo tecchio, 80 – 80130 Naples, Italy 3Alma Mater Studiorum, University of Bologna,Viale Risorgimento,2 – 40135 Bologna, Italy
Aim of this work has been the prediction of residual stress field after Laser Peening process by means of Finite Element Modeling. The work includes investigation on the influence of geometrical constraints on compressive residual stresses induced by Laser Shock Peening, study on mesh sensitivity and the validation of the model by comparing it with experimental results.
(a) (b)
Fig. 1. FE Simulation. (a) Distribution of residual Stress in Y direction in a peened model. (b) Residual Stress Trend measured on side
surface: Comparison between Sharp Edge, Round Edge of 2mm and 4 mm and Experimental results. The FE models follow closely all the treatment features like spot size, peening sequence, load condition and boundary constraints. The good agreement of the two distributions of residual stress induced by laser peening, obtained by FE simulation and experimental measurements, labels the finite element model as a reliable model to simulate the laser peening process. Investigation on geometrical constraints shows that approaching at sharp edge the residual compression decreases, reducing the beneficial effects of treatment. This unwanted behaviour could be mitigated introducing round edges of 2mm or 4 mm of radius. By creating different models for different edge shape, it was possible to highlight the mesh size element importance. FE analyses are “Mesh Sensitive”: by increasing the number of elements and by decreasing their size, the software is able to probe even the details of the real phenomenon. However, these details, could be only an amplification of real phenomenon. For this reason it was necessary to tune the simulation settings as element number, size, type and bulk viscosity coefficient in order to be closer to the physics of the phenomenon. The correct suggestion for filtering all data derived from FE simulation is provided by comparison with experimental results. Considering all these features, tuning the simulation in the appropriate way, filtering data by comparison with experimental results, makes FE model a good instrument to predict residual stress field after laser peening reducing significantly the amount of expenses of experimental tests.
84
Femtosecond Laser Shock Hardening of Pure Aluminum Yutaro Isshiki
1, Tomokazu Sano
1,2, Tomo Ogura
1, Kazuto Arakawa
2,3, Masayuki Okoshi
4, Narumi Inoue
4,
Kojiro F. Kobayashi5, Akio Hirose
1
1- Division of Materials and Manufacturing Science, Osaka University, 2-1 Yamada-Oka, Suita, Osaka 565-0871, Japan
2- JST, CREST, 2-1 Yamada-Oka, Suita, Osaka 565-0871, Japan
3- Research Center for Ultra-High Voltage Electron Microscopy, Osaka University, 7-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan
4- National Defense Academy of Japan, 1-10-20 Hashirimizu, Yokosuka, Kanagawa 239-8686, Japan
5- The Wakasa Wan Energy Research Center, 64-52-1 Nagatani, Tsuruga, Fukui 914-0192, Japan
Email: [email protected], [email protected]
The purpose of this study is to investigate the effect of the femtosecond laser driven shock wave on the
hardness of the material without using plasma confinement media. The goal is to attain the femtosecond laser
peening technique.
Samples used in the present study are pure aluminum with the purity of 99.999 %. Before laser
irradiation, samples were annealed at temperature of 350 ˚C in an hour for removal of distortion, and surfaces
were physically and chemically polished. Laser irradiation was performed in air with the intensities of 1.30×1014
,
2.64×1014
, 5.39×1014
, and 9.79×1014
W/cm2. Two kinds of grooves are formed by scanning the laser pulses with
the pulse-to-pulse distance of 10 m and 1.75 m. The hardness near the laser irradiation area was measured
using nanoindentation technique.
Figure 1 shows the hardness of the laser irradiated aluminum samples as a function of the distance from
the surface after the laser irradiation. The experimental results of the samples irradiated at 10 m intervals show
that the hardened depth becomes deeper as the laser intensity increases, and the maximum hardness is around
1.5 GPa with the laser intensity of over 2.64×1014
W/cm2. The results of the samples irradiated with 10 m or
1.75 m intervals with 0.6 mJ show that both the hardened depth and the maximum hardness of the sample at
1.75 m intervals are larger than the sample at 10 m intervals. The sample irradiated at 1.75 m intervals with
0.6 mJ has the highest hardness. The hardened depth of the sample is around 17 m, and the maximum hardness
is 2.9 Gpa, which is equivallent to the hardness of pure iron. The reason why the maximum hardness of the
samples irradiated with the intensity of 2.64 ~ 9.79×1014
W/cm2 are below 1.5 GPa is considered that the region
behind the shock front is melted by increasing temperature due to the shock copression We suggest that the
maximum pressure of the intensity of 1.30×1014
W/cm2 is below than the melting pressure, therefore the
aluminum nearer the surface becomes harder.We conclude that integration of femtosecond laser pulses which
loads the shock pressure above yield stress of the material and below the melting pressure make the hardened
depth deeper and the maximum hardness harder.
Figure 1. Hardness of the laser irradiated aluminum samples as a function of the distance from the surface after the laser irradiation.
0 2 4 6 8 10 12 14 16 18 200.0
0.5
1.0
1.5
2.0
2.5
3.0
Har
dness
(G
Pa)
Depth (m)
● 1.30×1014 W/cm2, 1.75 m/pulse
○ 1.30×1014 W/cm2, 10 m/pulse
× 2.64×1014 W/cm2, 10 m/pulse
△ 5.39×1014 W/cm2, 10 m/pulse
□ 9.79×1014 W/cm2, 10 m/pulse
85
Technical Digest
Technical Session
Friday, 14th
86
87
Investigation on Pressure Model and Technique of Absorbing Wave Layers of Laser Peening
Che Zhigang, Cao Ziwen and Zou Shikun
Laboratory of Science and Technology on Power Beam Processes, Beijing Aeronautical Manufacturing Technology Research Institute (BAMTRI), Beijing 100024, China
Investigation of pressure model Laser peening (LP) is one technique which imports high pressure shock wave into target materials to improve their performance, including fatigue life, hardness, strength and corrosion resistance. The high pressure is one of the advantages of LSP. The pressure calculation of LP is the foundation of determining the technological parameters. The pressure model has being used since it was established by Fabbro et al in 1990 [1]:
)/()/(32
01.0)( 20
2 cmGWIscmgZGPaP ××+
=αα (1)
Where Z is the combined shock wave impedance relating with target materials (Z1) and the confined medium (Z2) with 2/Z=1/Z1+1/Z2. I0 is the average value of laser intensity. There is certain limitation in this model, which was found in the base of absorbing layer completely vaporized and transformed plasma. The shock wave, produced by plasma exploding, applied entirely on the surface of target material. However the absorbing layer could not be vaporized entirely in order to protect target material from shock damage and ensure the shock effect. Then left absorbing layer plays the role for protecting target. Obviously, the deviation existed using the Fabbro et al’s model to calculate the shock pressure. Basing on the above analysis, the new pressure model is deduced in this paper, which is accordant with the practical situation and has more accurate calculation results than previous model:
)/()/()32(3
201.0)( 20
2 cmGWIscmgZGPaP ××+
=αα (2)
Where the combined shock wave impedance Z changes to 3/Z=1/Z1+1/Z2+1/Z3. Z3 is the shock wave impedance of left absorbing layer. I0 is the real value of laser intensity for square spot and uniform energy distribution. And the details of the deduction process can be seen in full paper. The pressure value obtained by this improved model is accurater than previous model on pressure prediction and simulation calculation of FEM. Technology of absorbing wave layer (AWL) Experiment investigation showed somewhat shock wave reflection existed when shocking aeroengine blade of single side. The technique of AWL was introduced using LSP on blade treatment. The results show there is almost no shock wave reflection during the shocking and the shock effect was improved.. [1] R. Fabbro, J. Fournier and P. Ballard, “Physics study of laser-produced plasma in confined geometry”, J.appl. Phys, 68(2), 775-784
(1990)
88
TheTheTheThe SSSSurfaceurfaceurfaceurface PPPProfilerofilerofilerofile andandandandMMMMicrostructureicrostructureicrostructureicrostructure ofofofof LLLLaseraseraseraser PPPPeeneeneeneenededededTi-6Al-4VTi-6Al-4VTi-6Al-4VTi-6Al-4V
ShikunShikunShikunShikun ZouZouZouZou1111,2,2,2,2,,,, ShuiliShuiliShuiliShuili GongGongGongGong1111,,,, andandandand ZiwenZiwenZiwenZiwen CaoCaoCaoCao1111,,,, ZhigangZhigangZhigangZhigang CheCheCheChe1111
1Beijing Aeronautical Manufacturing Technology Research Institute, Beijing, 100022Huazhong University of Science and Technology, Wuhan , 430074
The surface profile of laser peening with square spots was compared with that of circle spots, then themicrostructure of laser peened titanium alloy Ti-6Al-4V in the center of square spot and at the edge of squarespot was researched in this paper. The results showed that smaller size crystal was produced at the edge ofsquare spots because of the shearing strain produced nanometers crystals in laser peening titanium alloy Ti-6Al-4V.
89
ANALYSIS OF LASER SHOCK PROCESSING RESIDUALS ON THE TREATMENT OF 6061-T6 ALUMINUM ALLOY
S. Rosales de los Santosa, C. Rubio-Gonzálezb , A. Pérez-Centenoa, M.A. Santana-Arandaa,
A.Chávez-Cháveza, G. Gómez-Rosasa.
aDepartamento de Fisica, Centro Universitario de Ciencias Exactas e Ingenierias, Universidad de Guadalajara, Guadalajara Jalisco, 44000, México
bCentro de Ingeniería y Desarrollo Industrial, Pie de la cuesta No. 702, Desarrollo San
Pablo, Querétaro, Qro., 76130, México
Abstract Laser shock processing (LSP) is a technique for strengthening metals. This process induces a compressive residual stress field, which increases fatigue crack initiation life and increases wear resistance of metals. We present a configuration in the LSP concept for metal surfaces treatments in underwater layer using laser irradiation at 532 nm. A convergent lens is used to deliver 0.6 J/pulse in a 6 ns laser FWHM pulse produced by a Q-switch Nd: YAG Laser. We use pulses density of 2500/cm2 and spot of 1 mm in diameter on 6061-T6 aluminum surfaces. We found that the material ejected into the water during the LSP treatment of the 6061-T6 aluminum is transformed in four different nanostructures of aluminum oxide with diameters between 20 nm and 250 nm.
90
Influence of the Laser Pulse Width on the Effect of Laser Peening -Advantage on Laser Peening
Using a Sub-nanosecond Laser-
M. Heya1, K. Matsumoto2,3, T. Tsuji4, Y. Kobayashi4, and S. Okihara2 13-1-1 Nakagaito, Daito-city, Osaka, 574-8530, JAPAN, Department of Electronics, Information and Communication Engineering, Faculty
of Engineering, Osaka Sangyo University 21955-1 Kurematsu-chou, Nishi-ku, Hamamatsu-city, Shizuoka, 431-1202, JAPAN, The Graduate School for The Creation of New Photonics
Industries 34888 Takatsuka-cho, Minami-ku, Hamamatsu-city, Shizuoka, 432-8522, JAPAN, ENSHU Ltd.
43-1 Honohara, Toyokawa-city, Aichi, 442-8505, JAPAN, Sintokogio, Ltd.
Laser peening (LP) using Q-switch nanosecond (ns) lasers with a laser pulse width of a few to a few tens of nanoseconds has recently been used in heavy industries as a characteristic surface treatment technology. The purpose of this study was to investigate the dependence of the laser peening on the laser pulse width, with emphasis on the laser peening using sub-ns laser pulses. We compared the different types of peening techniques; ns laser peening (nsLP), sub-ns laser peening (sub-nsLP), typical shot peening (SP), and fine shot peening (FSP). The pulse widths of nsLP and sub-nsLP were 7.5 ns and 0.18 ns, respectively.
Figures 1 and 2 show the experimental results of residual stress distributions by nsLP and sub-nsLP processing. From these results, we have found that sub-nsLP in the parameters we examined can introduce the compressive residual stress effectively. Additionally, the surface roughness by sub-nsLP processing was more smoother than that by nsLP processing (See Figs. 3 and 4). Generation of compressive residual stress while supressing the surface roughness leads to the improvement of fatigue properties of metallic components. Thus, we showed the advantages of a new LP with sub-ns lasers in comparison with a conventioal LP with ns lasers.
-350
-300
-250
-200
-150
-100
-50
0
50
100
0 200 400 600 800 1000
Depth (μｍ)
Res
idua
l str
ess
(MP
a)
nsLP(200mJ) nsLP(100mJ)
nsLP(50mJ) nsLP(30mJ)
nsLP(10mJ) As-received
-350
-300
-250
-200
-150
-100
-50
0
50
100
0 200 400 600 800 1000
Depth (μｍ)
Res
idua
l str
ess
(MP
a)
sub-nsLP(50mJ) sub-nsLP(30mJ)
sub-nsLP(10mJ) sub-nsLP(5mJ)
sub-nsLP(3mJ) As-received
Fig. 1. Results of residual stress distribution by nsLP processing. Fig. 2 Results of residual stress distribution by sub-nsLP processing
0
1
2
3
4
5
6
nsLP (200mJ)
nsLP (100mJ)
nsLP (50mJ)
nsLP (30mJ)
nsLP (10mJ)
As-received
Ｒａ（μｍ）
0
1
2
3
4
5
6
sub-nsLP (50mJ)
sub-nsLP (30mJ)
sub-nsLP (10mJ)
sub-nsLP (5mJ)
sub-nsLP (3mJ)
As-received
Ｒａ（μｍ）
Fig. 3 Results of surface roughness by nsLP processing Fig. 4 Results of surface roughness by sub-nsLP processing
91
Femtosecond Laser Shock Processing of Solids
Tomokazu Sano1,2
and Akio Hirose1
1- Division of Materials and Manufacturing Science, Osaka University, 2-1 Yamada-Oka, Suita, Osaka 565-0871, Japan
2- Japan Science and Technology Agency - CREST
We easily obtain a strong shock wave using a femtosecond laser pulse without using any plasma
confinement media. Shock wave is generated by the recoil force during the plasma expansion induced by the
femtosecond laser ablation of solids, followed by the propagation into the solids. Measurements of pressure [1]
and profile [2,3], and simulation of the propagation [4] of the femtosecond laser-driven shock wave were
reported. The femtosecond laser-driven shock wave rises up to 100 - 300 GPa in a few picoseconds, retains its
peak pressure with a few picoseconds, and falls down to the ambient pressure in a few hundreds of picoseconds
for the laser intensity of 1014
- 1015
W/cm2. One of the most distinctive phenomena in the femtosecond laser-
driven shocked materials is the quenching of high-pressure phases [5-7]. Though the clear mechanism is still
open, we suggest the ultrafast compression of the femtosecond laser-driven shock wave would cause the unique
phenomena. Increase of the density of lattice defects such as dislocation and stacking faults and grain refinement
are induced by the ultrafast deformation, followed by structure transitions. Nonequilibrium state of these
structures would play an important role to retain these unique structures to the ambient pressure.
We will introduce the quenching of high-pressure phases of Fe and Si and hardening of Fe and Al using
femtosecond laser-driven shock wave. Two projects of development of in-situ measurement system with
femtosecond temporal resolution; Dynamic-TEM and X-ray Free Electron Laser-Diffraction will also be
addressed in this talk.
[1] Evans et al., Phys. Rev. Lett. 77, 3359 (1996).
[2] Gahagan et al., Phys. Rev. Lett. 85, 3205 (2000).
[3] Funk et al., Phys. Rev. B 64, 115114 (2001).
[4] Cuq-Lelandais et al., J. Phys. D: Appl. Phys. 42, 065402 (2009).
[5] Sano et al., Appl. Phys. Lett. 83, 3498 (2003).
[6] Sano et al., Appl. Surf. Sci. 247, 571 (2005).
[7] Sano et al., nature physics (under review).
92
Ultrafast and microscopic observation of laser-shock
induced material’s behaviours
N. Ozaki1, Y. Asaumi
1, A. Benuzzi-Mounaix
2, E. Brambrink
2, T. De Resseguire
3, G. Gregori
4, Y.
Inubushi5, T. Jitsui
1, D. Kimura
1, T. Kimura
1, M. Koenig
2, K. Miyanishi
1, K. Nakatsuka
1, D. Riley
6, Y.
Sakawa7, T. Sano
7, T. Sano
1, H. Uranishi
1, T. Vinci
2, N. Yokoyama
1, and R. Kodama
1
1Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan 2 Laboratoire pour l'Utilisation de Lasers Intenses (LULI), UMR7605,
CNRS - CEA - Universite Paris VI - Ecole Polytechnique, 91128 Palaiseau Cedex, France 3CNRS, Institut PPRIME, ENSMA, 86961 Futuroscope Cedex, France
4Clarendon Laboratory, University of Oxford, Oxford, OX1 3PU, United Kingdom 5RIKEN, XFEL Project Head Office, Sayo, Hyogo 679-5148, Japan
6School of Mathematics and Physics, Queens University of Belfast, Belfast BT7 INN, United Kingdom 7Institute of Laser Engineering, Osaka University, Suita, Osaka 565-0871, Japan
Laser-driven shock wave is now used for basic physics and industrial applications. Extreme condition of
material in pressure, temperature, density, strain rate, etc. is generated by strong shock wave. Presented here are
material’s behaviours under such dynamic compression observed with ultrafast and microscopic diagnostics.
93
Various Effects of Laser Shock Waves
Toshimori Sekine
Graduate School of Science, Hiroshima University, Kagamiyama 1-3-1, Higashi-Hiroshima 739-8526, Hiroshima, JAPAN [email protected]
Pulsed laser can generate various degrees of shock waves in materials. Shock wave has many effects to modify materials, not only to destroy them but also to create materials with high-performance and novel properties. One of the well-known effects is to synthesize high-pressure phases such as diamond. This effect is due to the high pressure and high temperature generated by shock compression during shock wave passage in material. A second effect of shock wave is to produce sever deformations at high strain rate (104-108 s-1). For ductile materials, there are lots of experimental and theoretical studies to evaluate the high strain rate effects in materials. Laser peening is one of such prospectives and those previous studies may help to understand the mechanism of laser peening. Plastic deformations at high strain rate produce temperature rise as an adiabatic process and soften materials. During such a process, there is an energy distribution between heating and defect generation. Experimental studies indicate that more than the half is deposited as heat. On the other hand ceramics are brittle, being different from metals. In case of ceramic powders they become more ductile and can behave like metals. Ceramics have lower thermal diffusion coefficients than metals, and sever plastic deformation at a high strain rate may deposit much localized heat where the locale temperature rise is higher than that in metal. Another effects are high quenching rate, theoretically no pressure limit, simultaneous generation of high pressure and high temperature, etc. Recently laser shock techniques have been developed to measure is-situ states of materials so that we can understand material behaviors under extreme conditions that we cannot achieve by the conventional shock wave. I will review these effects of shock waves in materials, especially using pulsed lasers.
94