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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
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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
Austrian Research Centers GmbH - ARC
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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
Austrian Research Centers GmbH - ARC
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Types of Monitoring System
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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
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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
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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)
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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)
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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
Austrian Research Centers GmbH - ARC
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Fatigue Damage Quantification by On-line Acoustic Emission and FBG strain analyses
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
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Fatigue Damage Quantification by On-line Acoustic Emission and FBG strain analyses
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
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Fatigue Damage Quantification by On-line Acoustic Emission and FBG strain analyses
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
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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
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Impact Damage Quantification of GFRP Plates by On-line Acoustic Emission Analyses
US C-scan AE-Monitoring Results
10 J
20 J
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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
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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
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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
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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
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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
Recommended