Welding Mechanics and Fracture Assessment

Fumiyoshi Minami

Joining and Welding Research Institute, Ibaraki, Osaka, JAPAN minami@jwri.osaka-u.ac.jp

Abstract Recent progress in welding mechanics and fracture assessment procedures for weld structures in Japan is presented. The joining/welding mechanics and design emphasize the increasing need for a methodology to predict the structural performance and integrity from a stage of designing structures with the best use of materials. The presentation focuses on the computational methodologies for the simulation of welding/joining with emphasis on the reduction of welding residual stresses and distortion, and the fracture mechanics assessment of the structural integrity of weld components in terms of the ductile damage evaluation, fatigue design and analysis, and the standardization of the constraint-based assessment of unstable fracture. Computational Methodologies for Simulation of Welding and Joining - Simulation of Welding and Joining by Computational Approach [1], [2], [3] - High-Speed FEM for Welding Distortion and Stress Analysis [4] - Mechanics in Welding, Materials Processing and Fabrication [5] Fracture Mechanics Assessment of Structural Integrity of Weld Components - Damage Mechanics for Prediction of Ductile Fracture Performance of Welded Joints [6] - Fatigue Design and Analysis of Weld Structures [7] - International Standardization of Constraint-Based Assessment of Unstable Fracture [8], [9], [10] References [1] H. Serizawa, S. Nakamura, H. Tanigawa, H. Ogiwara and H. Murakawa: “Numerical Study of Local PWHT

Condition for EB Welded Joint between First and Side Walls in ITER-TBM”, Journal of Nuclear Materials, Vol.442 (2013), pp.S535-S540.

[2] H. Serizawa and F. Miyasaka: “New Combined Method of MPS and FEM for Simulating Friction Stir Processing,” Ceramic Engineering and Science Proceedings, Vol.36, Issue 2 (2015), pp.27-36.

[3] M. Shibahara, K. Ikushima, T. Harada, F. Kimura and T. Morimoto: “Study on Solidification Cracking Under High-Speed Narrow Gap Welding with Tandem Torches,” Proceedings of the 24th International Offshore and Polar Engineering Conference, (2015), pp.271-278.

[4] M. Mochizuki: “Numerical Simulations of Micro-, Macro-, and Mega-Scale Structurization by Welding Processes,” Mathematical Modelling of Weld Phenomena 10, TU Graz Publishing (Graz, 2013), pp. 131-139.

[5] K.Ikushima and M.Shibahara: “Large Scale Non-Linear Analysis of Residual Stresses in Multi-Pass Pipe Welds by Idealized Explicit FEM,” Welding in the World, Vol.59, No.6 (2015), pp.839-850.

[6] M. Ohata, T. Fukahori and F. Minami: “Damage Model for Predicting the Effect of Steel Properties on Ductile Crack Growth Resistance,” International Journal of Damage Mechanics, Vol.19, (2010), pp.441-459.

[7] S. Tsutsumi, H. Momii and R. Fincato: “Influence of tangential plasticity for elastoplastic behavior of a thin wall steel bridge pier under lateral bidirectional load paths,” Journal of Structural Engineering, JSCE, Vol.62A (2016), pp.72-83.

[8] F. Minami, et al: “Method of Constraint Loss Correction of CTOD Fracture Toughness for Fracture Assessment of Steel Components,” Engineering Fracture Mechanics, Vol.73 (2006), pp.1996-2020.

[9] Y. Yamashiha and F. Minami: “Constraint Loss Correction for Assessment of CTOD Fracture Toughness under Welding Residual Stress,” Engineering Fracture Mechanics, Vol.77 (2010), pp.2213-2232, Vol.77 (2010), pp.2419-2430.

[10] F. Minami, M. Ohata and Y. Takashima: “Revision of ISO 27306 for CTOD Toughness Correction for Constraint Loss,” Materials Science and Forum, Thermec 2016, (2016)

1

Welded Part

Deformation: x 40Original

After Welded

Experimental Result

Simulation Result 10mm

16mm

x

yz

[MPa]

(Current Design) (Prospective Design)

Weld Line

10mm

16mm

x

yz

x

yz

[MPa]

(Current Design) (Prospective Design)

Weld Line

Finite Element Method

Particle Method(MPS)

Joining and Welding Research InstituteOsaka University

Prediction of welding distortion by inherent strain analysis

Weld design for reducing residual stresses

Coupled method (MPS & FEM) for simulating FSW

2

600.0

480.0

360.0

240.0

120.0

0.0

-120.0

-240.0

-360.0

-480.0

-600.0

(MPa)

Development of large-scale FEM for welding mechanical analysis(IEFEM: Idealized Explicit FEM)

Nonlinear analysis of welding distortion of ship-hull block (10 million DOF)

•  IEFEM enables large-scale nonlinear analysis with 10 million degrees of freedom (DOF)

102 times larger DOF 1/102 times shorter computational time

Increase in DOF in welding mechanical analyses

~ Group number

~ Pass number

Base metal 1(SUS316)

z

y

x

Base metal 2(SFVQ1A)

Cladding (SUS308)

Weld metal (ALLOY132)

1

2

3

4

5

6

A

A’

1 6

z = 0.0

14

79

12

1915

23

2831

3540

4549

5458

63

68

7682

8893

100 108

75

1 108

z

y

x

Welding torch

• 1,125,360 nodes• 1,078,920 elements• 3,376,074 dof

Residual stress analysis of multi-pass pipe-welds (108 passes, 3 million DOF)

Welding distortion and residual stresses in structural members can be predicted by IEFEM.

104

105

106

107

108

109

1970 1980 1990 2000 2010 2030

Ana

lysi

s sca

le (D

OF)

Year

103

1022020

Base metal 1(SUS316)

z

yy

3

Materials Processing� Fabrication & Assembly�

Welding & Joining�

Evaluation of stress/strainof machined surface

High-precision prediction of distortion in assembly process of large-scale structures

Estimation of mechanical properties of welds by process mechanics

Microscopic stress and strain evaluation in grain scale

Experiment Simulation

Osaka University

Academic fusion of welding mechanics,arc physics, and materials science

444444444

Advanced damage model is developed, where the damage parameters are inferred from the notch ductility and stress triaxiality dependent ductility.

Pipe fracture performance

Φ =Σσ

⎛

⎝⎜⎜

⎞

⎠⎟⎟

2

+ a1D* exp a2

Σmσ

⎛

⎝⎜

⎞

⎠⎟−1= 0

Geometrical discontinuity Material/Mechanical heterogeneity

Bead profile Thermal cycle

Material properties, Residual stress

Round notched tension specimenNotched bend specimen

Notch ductility Stress triaxiality dependent ductility

R=1, 2, 5 (mm)

BM

WM

HAZ

Prediction of fracture performancePpppp

Simulation

Determination of ductile damage controlling parameters

Advanced damage model

Advanced damage mechanics enables prediction of pipe fracture performance with ductile crack growth.

Ductile crack initiation/growth resistance of component is controlled by two material properties; notch ductility and stress triaxiality dependent ductility.

Notch ductility Stress triaxialitydependent ductility

R=1, 2, 5 (mm)

BM

WM

HAZ

Girth weld

Crack in HAZ

Simulatedcrack growth

Ductile fracture

Osaka University

Proposal ofmechanical propertiesfor improvement of ductile performance

Weld component modelWeld component model

Bending test

Predictionof failure in FEA

Prediction of failure by FEA

Experiment

Bend test

0 5 10 15 20 25 30 35 40θe (deg.)

M (

MN

•m)

05

1015

2025

5

(since April. 1. 2016)

Joining and Welding Research InstituteOsaka University

FDWS aims at developing an advanced methodology to prevent fracture and to ensure the safe operation of structures from a stage of designing structures. The key concept is the visualization of crack performance, leading to fatigue free structures, with the standardization of fatigue assessment procedure.

Current Research Subjects

1. Critical review of current studies on fatigue design2. Link between fatigue initiation at structural discontinuity and fracture mechanics approach3. Constraint-based assessment of fatigue4. Development of fatigue tests leading to fracture performance design for weld structures5. International standardization of performance oriented design for fatigue assessment

6

Th

in W

all P

ier

Rec

tan

gu

lar

Cro

ss-S

ecti

on

Pie

r

Joining and Welding Research InstituteOsaka University

7

Constraint Loss in Tension Components

Kc, δc, Jc ( ) >> Kc, δc, Jc ( ) Tension

componentsToughnessspecimen

Pla

stic

co

nst

rain

t

Specimen geometry / Loading mode

Plastic zone confined by neutral axis ahead of crack

8

Standardization

Project leader: F. Minami

(Osaka University)

JapaneseIST

Project

ISO 27306ISO 27306

OsakaUniversity

9

Equivalent CTOD ratio β = δ / δWP

Wei

bu

ll st

ress

σW

CTOD

δ δ WP

a0 W(a0/W = 0.5)

Structuralcomponent

at the same Weibull stress level

Fracture toughness specimen

W

a0

3PBCompact

(0 < β < 1)

σW =1

V0σeff⎡⎣ ⎤⎦

mdVf∫⎡

⎣⎢

⎤

⎦⎥

1/m

Weibull stress,

Fracture toughnessspecimen

Structuralcomponent

δ cr δ WP,cr= δ cr / β

δ R

= β•δWPR δ WP

R

Proposed originally by Minami et al. at18th Int. Conf. OMAE, St. John's, Canada (1999)

ISO 27306ISO 27306Equivalent CTOD ratio, β

OsakaUniversity

10

0

0.5

1.0

1.5

2.0

0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

(2c=40mm, a=6mm)

SM490B, YR=0.7

Frac

ture

rat

io,

δδr

E No-correction (β=1)J Level I (β=0.5)B Level II & III (β=0.17)

Lrmax

= 1.11

at -100°C

ESCP

Load ratio, Lr = σσref / σY

SM490B (JIS G 3106)(RY = σY / σT = 0.7)

B = t

W a0= BH H

a0 / W = 0.5

σ∞

t = 25

σ∞

W =

195

L/2 = 370

ESCP

(Unit : mm)

c=20

a=6c=20

a=6

L/2 = 370

W=1

00

δcr = 0.022mm (0.2MOTE : 24 tests)

BS7910Level 2A-FAC

Level 2B-FAC

ISO 27306ISO 27306

FractureassessmentδWP,cr = δcr / β

OsakaUniversity

Fracture Assessment on FAD with β

11

Equivalent CTOD Ratios, β and βr

β = δ / δWP : for structural component without σr βr = δ / δWP, active : for structural component with σr at the same Weibull stress level

Wei

bu

ll st

ress

σW

Active CTOD, δ active

δ δ WP

a0 W(a0/W = 0.5)

Fracture toughness specimen

W

a0

3PBCompact

Structuralcomponentwithout σr

δ WP, active

δ WP, active : WP CTOD by applied stress (CTOD by σr is not included)

Structuralcomponent

with σr

At contained yielding: β < βr , At general yielding: β ≈ βr

OsakaUniversity

12

0

0.5

1.0

1.5

2.0

2.5

3.0

0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

BS7910: 2005Level 2A-FAC

Lr, max = 1.04

Load ratio, Lr = σσref / σY

Frac

ture

rat

io,

δr

HT780 wide plate jointsm=12

250

500

HT780

25

2a=42

250

500

HT780

25

42

BS7910 (β=1)

NoCorrection(β = 1)

βr

βCorrection by βrCorrection by β

Fracture Assessment on FAD OsakaUniversity

13

IISO 27306 Rev.ISO 27306 Rev.

Upper limit of RY (= σσY /σT) Expanded to 0.98

Annex A Main body

β = f (RY, a, m) β = f (RY, a, t, m): improved accuracy

BS7910: 2005 BS7910: 2013

New chapter: Conditions for use

Weibull parameter, m, at Level II assessment

Equivalent CTOD ratio, β, for surface cracked plates: CSCP, ESCP

Annex D: Fracture assessment on FAD

The scope and main frame are not changed. NOTE

Revised PointsOsaka

University

14

ISO 27306 Revised ISO 27306 Rev.ISO 27306 Rev.

ISO / FDIS

Closing date for voting: July 18, 2016

Approval: 13 Disapproval: 1 Abstention: 7

FDIS voting results

13/14

Votes byP-members

ISO 27306 Rev. was approved.