structural health monitoring – potential for smart

Austrian Research Centers GmbH - ARC 16. Dezember 2008

Structural Health Monitoring Structural Health Monitoring ––

Potential for smart composite aircraft structuresPotential for smart composite aircraft structures

M. Scheerer, ARCM. Scheerer, ARC

Zukunft der Faserverbundwerkstoffe in der österreichischen Luftfahrtindustrie und -forschungMontag, 1. Dezember 2008, TU Wien

Austrian Research Centers GmbH - ARC

2

16. Dezember 2008

Definition

� Structural Health Monitoring (SHM): Implementation of a NDE-System (Non-Destructive Examination) in a component or structure for a continuous monitoring of the structural status (health) of the component / structure in operation.

� Imitation of the nervous system of the human body (Speckmann)

Failure mechanism of materials

NDT Methods for Online Inspection

Algorithm for damage analyses

Determination of remaining life


3

16. Dezember 2008

Motivation for SHM� Certification Issues Potential for SHM by impact

& delamination detection

Hachenber D. 2002, “The role of Advanced Numerical

Methods in the Design and Certification of Future

Composite Aircraft Structures“ 5th world congress on

Computational Mechanics WCCM V, Vienna, Austria,

July 7-12, 2002

100%

90%

60%

50%

33%

Failure strain level (Mean)

Scattering (B-value)

Stress intensity

(impact & notch Sensitivity)

Environment (hot/wet)

Ultimate Design Strain

(„Ultimate Load“ j=1.5)

Required Safety Factor 1.5

Limit design Strain

Max. load spectrum

(„Limit Load“ j=1.0)

-10%

-30%

-10%

100%

90%

60%

50%

33%

Failure strain level (Mean)

Scattering (B-value)

Stress intensity

(impact & notch Sensitivity)

Environment (hot/wet)

Ultimate Design Strain

(„Ultimate Load“ j=1.5)

Required Safety Factor 1.5

Limit design Strain

Max. load spectrum

(„Limit Load“ j=1.0)

-10%

-30%

-10%

� Individual Maintenance / Repair

Strategies –

� From Time Based Maintenance to

Condition Based Maintenance

� Control of difficult / impossible to

inspect parts

� Optimized Design

To date:

uncertainties in integrity of their manufacture

susceptibility to barely visible impact damage (BVID)

↓Design load: 33% of failure load

compared to 60% in metals


4

16. Dezember 2008

Types of Monitoring System


5

16. Dezember 2008

Type of Sensors

Sensor Technologies

Smart Materialies Fibreoptics MEMS

Piezos SMA´s CNT´s FBG´́́́s EFPI BOTDR

Electr.

⇑

⇓

Mechan

Therm

⇑

⇓

Mechan

Elektr.

⇑

⇓

Mechan

Displacement / strain

⇑

⇓

Optical properties


6

16. Dezember 2008

Type of Methods

SHM - Methods

Acoustic Methods

ImpedanceEddy

current

Acoustic

Emission

Guided

Waves

Phased

Array

CVM

vibration

Electrical Methods Stat. / dyn. strain

Defects

creates

acoustic

signal

Acoustic

signal

modified

by defect

Acoustic

beam

modified

by signal

Impedance

from piezo

modified by

defect

EM – field

modified

by defect

Local

strain

modified

by defect

Global

vibration

modified by

defect

Pressure

exchange

by defect

strain


7

16. Dezember 2008

Comparison of the SHM Methods

0.01

0.1

1

10

100

0.01 0.1 1 10 100

size of sensor [mm]

siz

e o

f d

am

ag

e [

mm

]

Modal Analyses (E)

Optical Fibre (S)

Lamb Wave (E)

Acoustic Emission (H)

Eddy Current (S)

Strain

Gauge

(S)

Sensor coverage:

entire plate (E)

Half Plate (H)

Sensor Area (S)0.01

0.1

1

10

100

0.01 0.1 1 10 100

power required by sensor [W]

size o

f dam

age [m

m]

Modal Analyses (E)

Eddy Current (S)Sensor coverage:

entire plate (E)

Half Plate (H)

Sensor Area (S)

Strain

Gauge

(S)

AE

(H)

Lamb Wave (E)

Optical Fibre (S)


8

16. Dezember 2008

Research Activities at ARC

� Fatigue Damage Quantification by On-line Acoustic Emission and FBG strain analyses (Funded within the Austrian Aeronautics Research K-Net and the EU FP6-Project SMIST)

� Impact Damage Quantification by On-line Acoustic Emission Analyses (Funded within the EU FP6-project Cost Efficient Small AiRcraft)

� Project ASHMOSD - Austrian Structural Health Monitoring System Demonstrator (Funded within the Take Off Program)


9

16. Dezember 2008

Test set-up:

4-point bending tests with AE

and FBG sensors

Fatigue Damage Quantification by On-line Acoustic Emission and FBG strain analyses

Test campaign:

4-point bending tests at different load levels

and frequencies in deflection and load control


10

16. Dezember 2008


0.00

100.00

200.00

300.00

400.00

500.00

600.00

700.00

800.00

900.00

1000.00

1 10 100 1000 10000 100000 1000000

cycles

av. h

it r

ate

[s

-1] 8-bl-55: 1.36% strain control (stress: 795 MPa)

Test01-85%: 755 MPa stress control (strain: 1.3%)

8-bl-55: rel. hit rate

Test01-85%: rel hit rate

rela

tive s

tiff

ne

ss [

%]

100

40

50

60

70

80

90

0

10

20

30

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 200 400 600 800 1000 1200

average hit rate [s-1]

rela

tive s

tiff

ness

8-bl-55

Test01-85%

large scatter band

Rel. stiffness and averagehit rate vs. cycles

Rel. stiffness vs. averagehit rate


11

16. Dezember 2008


Input: Transient AE Signals (as function of time)

Weighting of filtered LE based on FEM Effect of position of local damage on the global stiffness reduction

Filtered, localized and FEM based weighted relative hit rate

Correlation between filtered, localized and FEM based weighted relative hit rate and

global stiffness change

Correlation between filtered, localized and FEM based weighted relative hit rate and

location, (type) and severity of damage

Op

tim

izat

ion

lo

op

s

Model

Time - Frequency Analyse

Max. Amplitude (for each time window), Frequency at max. Amplitude

Location Processor

Location of located Event (LE), Clustering (Number of LE in a defined region)

Filtering of LE (Noise from other sources than defects) Frequency Range, Amplitude Range, Position (position of pressure and support roles)

Signal processing

Normalization of the weighted, filtered LE by results from static tests

(FE

M)

Mo

del

of

stru

ctu

re w

ith

def

ects

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.01 0.10 1.00 10.00 100.00 1000.00

relative localized weighted hit rate

rel. s

tiff

ne

ss

Correl. Fact.: 0.960

FPF (20 x 20 mm²)

SPF (20 x 20 mm²)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0.01 0.1 1 10 100 1000

rel. local hit rate / (cycle x area) [1/s cm²]

rel. lo

cal s

tiff

ness


12

16. Dezember 2008


0

10

20

30

40

50

60

70

80

90

100

-40 -20 0 20 40

position [mm]

rel.

lo

cal

hit

ra

te /

cy

cle

are

a [

1/s

cm

²]..

rel hits/cycle

calculated rel stiffness

1

0.8

0

0.2

0.4

0.6

rel. lo

cal sti

ffn

ess

0.3

0.5

0.7

0.9

0.1

FPF

TPF

SPF

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0.01 0.1 1 10 100 1000

rel. local hit rate / (cycle x area) [1/s cm²]

rel. l

oc

al s

tiff

ne

ss


13

16. Dezember 2008

Impact Damage Quantification by On-line Acoustic Emission Analyses

Bending tests with AE Monitoring :

33% of maximum strain / 100 cycles

Impact Damage Introduction:

0 / 5 J / 10 J / 15 J / 20 J

Damage quantification by

conventional US C-san


14

16. Dezember 2008

Impact Damage Quantification of GFRP Plates by On-line Acoustic Emission Analyses

US C-scan AE-Monitoring Results

10 J

20 J


15

16. Dezember 2008

AE based Damage assessment of structures / components

Reference AE measurment on coupon

with defined load before damage

Introduce different amounts of damage

Verify amount of damage with

conventional NDT

AE Measurment of coupon with defined

load for different amounts of damage

Calculate correlation function between

relative AE feature and amont of

damage

Databasis

Reference AE measurment on

component with defined load before

damage

Usage of component

AE Measurment of structure with

defined load after usage

Evaluation of relative AE feature

Comparrison with the databasis

Damage status of the structure

Coupon Component


16

16. Dezember 2008

ASHMOSDAustrian Structural Health Monitoring System Demonstrator

Goal

� Development of an Austrian SHM system for on-line monitoring of aeronauticstructures

Projekt-Data

� Coordination: ARC

� Volumen: 3.6 M€

� Duration: 3 years / Start: Oct. 2007

Research Partners:

ARC, IMA, Joanneum, ÖAW, Profactor; SCCH

Industrial Partners

Bernard Ing, FACC, Siemens

Cooperation:

EADS-IW, EADS-M, Airbus


17

16. Dezember 2008

SHM at ARC: Overall Goal

Off- & Online

Diagnostic

Conventional NDT &

mechanical Testing

Prognostic –

Remaining Life

Adaptive Structures

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

relative max hit rate

rela

tive s

tiff

ness

-6.00E-04

-4.00E-04

-2.00E-04

0.00E+00

2.00E-04

4.00E-04

6.00E-04

8.00E-04

0.00E+00 5.00E-05 1.00E-04 1.50E-04 2.00E-04 2.50E -04

right

left

back

7B-L-55, 10 cycles 1000 cycles 100 000 cycles


18

16. Dezember 2008

Conclusion

� SHM: Reduced Maintenance Cost via Condition Based Maintainance (CBM) and Optimized Aircraft Design

� Potential for Composite Structure Design as Smart Structure by implementing a SHM system

� Still a lot of technology challenges

� Accurate Material Models incorporating damage evolution and fatigue

� Validation of diagnostic systems for damage size and location identification

� Techniques for sensor embedding & connection (including wiring)

� Power & Data Handling

� Validation of SHM under aircraft service condition including repair & replacement procedures


19

16. Dezember 2008

Future Aspects for SHM

� SHM Prognosis

Diagnosis PrognosisResidual Life &

Performance Prediction

Smart Sensing

Technologies

Material

Characterization

Structural & Damage

Modeling

M. Scott et al., Structural Health Monitoring – The

Future of Advanced Composite Structures, 5th Int.

Workshop on SHM, Stanford CA, Sept. 12-14 2005

� Through Life Monitoring including Process Monitoring

structural health monitoring – potential for smart

Documents