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Remote detection of stage ii to stage iii cracking in steel bridge girder material
1. Remote Detection of Stage II to Stage III
Cracking in Steel Bridge Girder Material
M. Hossain
ASNT 20th Annual Research Symposium & Spring Conference
San Francisco, California
21-25 March, 2011
This project is sponsored by the U.S. Department of Commerce, NIST-TIP
(Cooperative Agreement Number 70NANB9H9007)
2. Background
S
Safe area
N
da/dN
unstable cracking
critical cracking level
Paris Law:
stable cracking
da/dN=C(∆K)m
threshold
K
2
3. Background
Voltage, mV
Time, μS
Acoustic emission (AE) techniques:
High sensitivity and reliability
Capability of locating and quantifying active cracks
3
4. Objective
Bridge Prognostic System
• Self-Powered
• Wireless Sensor Network
• Structural Bridge Health Prognosis
Current tasks
• Understand mechanism of acoustic emission(AE) corresponding to
crack growth behavior in the steel bridge material
• Data interpretation to identify structural damage and deterioration
• Modeling to assess the remaining fatigue life
4
5. Experimental Procedure
12.0 in
3.25 in
R15I WDI
9.5 in
12.0 in
AE-monitored fatigue tests:
Compact tension (CT) specimens, made of A572G50
MTS 810 hydraulic machine
Crack growth: clip gage, microscope and fiber light
AE sensors: R15I 5, WDI 3
Sensor Highway II-Remote Asset Integrity Monitor
5
6. Data Filtering and Reducing Procedures
1. Eliminate AE collected below 80% of peak load
Yielding
2 4 Crack extension
Pmax
Y-stress Crack opening
load
Pmean Crack closure
Grating
1 3 5
Pmin Reversed yielding
time
Y-strain
Stress-strain behavior at crack tip in a load cycle
6
7. Data Filtering and Reducing Procedures
Counts
2. Friction emission tests to understand
Peak Threshold
characteristics of noise
amplitude
3. Pencil lead break tests to understand
characteristics of genuine hits
Rise time
Duration
2 3
7
8. Data Filtering and Reducing Procedures
4. Swansong Ⅱ filter to minimize mechanical noise
8
9. Data Filtering and Reducing Procedures
5. Evaluate quality of filtered AE data
9
10. Results and Discussion
1. Sparse dataset
4
3.5 Hit rate
3
2.5
Hit rate
2
10% increase of cyclic loads
1.5
1
0.5
0
0 5,000 10,000 15,000 20,000
Load cycles
10
11. Results and Discussion
2. Determination of critical cracking level
400,000 350
Cumulative absolute energy
Maximum stress intensity, MPa√m
350,000
Cumulative absolute energy, aJ
300
Maximum stress intensity
300,000
250
250,000
200
200,000
150
150,000 10% increase of cyclic loads
100
100,000
50,000 50
critical level
0 0
0 3,000 6,000 9,000 12,000 15,000 18,000
Load cycles
11
12. Results and Discussion
2. Determination of critical cracking level
16,000,000 350
Cumulative signal strength
Maximum stress intensity, Mpa√m
Cumulative signal strength, V-T
14,000,000 300
Maximum stress intensity
12,000,000
250
10,000,000
200
8,000,000
150
6,000,000 10% increase of cyclic loads
100
4,000,000
2,000,000 50
critical level
0 0
0 3,000 6,000 9,000 12,000 15,000 18,000
Load cycles
12
15. Results and Discussion
3. Prediction of fatigue life
Absolute energy of AE, U ∝ J(∆K), released energy due to crack growth
dU/dN=B(∆K)p
log(dU/dN)=plog(∆K)+log(B) Eq.(1)
Paris Law: da/dN=C(∆K)m; ∆K = ?
da/dN=D(dU/dN)q Eq.(2)
Applies to Stage Ⅱcracking
15
16. Results and Discussion
3. Prediction of fatigue life
2 crack growth rate, da/dN
absolute energy rate, dU/dN
1 Linear (crack growth rate, da/dN)
Linear (absolute energy rate, dU/dN)
Log(da/dN), log(dU/dN)
0
-1 log(dU/dN) = 5.7489log(∆K) - 10.865
-2
-3
log(da/dN) = 3.8338log(∆K) - 9.9518
-4
1.75 1.8 1.85 1.9 1.95 2 2.05
Stress intensity range, log(∆K)
16
17. Results and Discussion
3. Prediction of fatigue life
70
60
experimental crack
Crack length, mm
50
predicted crack
40
30
20
10
0
0 10,000 20,000 30,000 40,000
Load cycles
17
19. Conclusions and Perspective
Summary:
AE absolute energy can provide warning signs for critical cracking in
steel bridge material.
Absolute energy rate was found to most suitable feature.
Specific material constants in terms of both AE and crack growth
behavior should be evaluated.
Robust data filtering techniques are required.
The combination of a Swansong II filter with a waveform-based
approach was found to be appropriate.
Further work:
Mechanism of AE corresponding to crack growth in welded bridge
elements
19
20. Acknowledgements
This work is performed under the support of the U.S. Department of
Commerce, National Institute of Standards and
Technology, Technology Innovation Program, Cooperative
Agreement Number 70NANB9H9007. Special thanks to Jean-Louis
Staudenmann.
South Carolina DOT for providing access to bridges and related
information for this project.
Valery Godinez, Adrian Pollock, Miguel Gonzalez (Mistras); Brian
Metrovich (Case Western Reserve Univ.); Fabio Matta (Univ. of
South Carolina).
20
22. Annex1 Construction of a and dU/dN arrays for Fatigue Life Prediction
Array of a:
original a: ao
final a:
o generally, Kmax=F∙S∙(π∙afinal)1/2 = KIC ,
where F=f(geometry), S- applied stress, KIC – fracture toughness
o compact tension(CT) specimen-cantilever beam:
Kmax=Fp∙P/(t∙b1/2) = KIC ,
where Fp =fp (av/b), av=(afinal-1+ afinal)/2, P-applied load, t-thickness, b-width
CT SE
o single edge(SE) specimen-freely supported beam:
Kmax=F∙Sg∙(π∙afinal)1/2 = KIC,
where F=f(av/b), Sg = 6M/(b2∙t), M-applied moment
a(i+1)=r∙ai , r ≈1.10,
Array of dU/dN:
original dU/dN: (du/dN)o
final dU/dN: (dU/dN)final=B(∆KIC )p , ∆K= KIC∙(1-R), where B, p-material constants, R-load ratio
(dU/dN)(i+1) / (dU/dN)i = B(∆K(i+1) / (∆K )i ) p = B(r) p/2 , r ≈1.10
22
Editor's Notes
In-service steel bridges are reaching their fatigue lives every year. Fatigue life is usually described as S-N curve. Here, S represents applied stress. N is the number of load cycles. For a given material and set of loading conditions, if the number of load cycles exceeds the fatigue life, crack will develop in the structure. Crack growth rate curve describes crack growth behavior. da/dN is crack growth rate. Delta K is stress intensity range. Crack growth has three stages: Stage I-low speed cracking near threshold, Stage II-stable cracking and Stage III-unstable cracking. Stage Ⅱ is of practical importance. The stage Ⅲ will result in catastrophic failure, so the critical cracking level is the transition point between stage Ⅱ and stage Ⅲ.The pictures come from an in-service and cracked steel bridge in South Carolina. There is a growing need for nondestructive testing techniques to evaluate the fatigue damage and predict remaining fatigue life.
Joint venture project. Imagine:if no accurate data interpretation, the acquired signals are useless no matter how excellent the techniques, the instruments are.Importance of current task
Joint venture project. Imagine:if no accurate data interpretation, the acquired signals are useless no matter how excellent the techniques, the instruments are.Importance of current task
It has been demonstrated that AE technique is able to detect cracking location, identify structural damage and predict fatigue life for steel bridge material.Perspective: Mechanism of AE corresponding to crack growing under varied loading conditions and in welded bridge elements