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Copyright Akshata Nagabhushana 2012 ALL RIGHTS RESERVED
ABSTRACT Reliable damage detection is crucial for assessing the integrity of a structure. A structural health monitoring (SHM) system reduces the chances of fatal accidents by performing continuous monitoring of a structure. In this thesis, a well-established SHM technique, the Lamb wave-based approach, is used for damage detection in composite materials. Composite coupons are fabricated using a vacuum assisted resin transfer molding (VARTM) process. The damage to be detected is a pre-existing transverse crack in the coupon. Surface mounted piezoelectric actuators are used to generate Lamb waves in the composite coupon. Experiments were carried out on a composite coupon with a manufactured embedded crack-like defect in the middle four plies for two different orientations, [016]T and [06/904/06]T, and a composite coupon with a surface crack with [016]T orientation. The response from both undamaged and damaged (simulated crack) coupons is obtained using surface mounted piezoelectric sensors. A numerical study of the composite coupon with the simulated crack was conducted using finite element methods (FEM) and the model was verified using the experimental results. The FEM model is validated for crack modeling using static shear lag analysis applied at the crack as well as for dynamic loading. The active Lamb wave method, using the anti-symmetric mode, could detect a surface crack but was insensitive to the embedded crack. The effect of crack depth and crack location on damage detection efficiency was also studied. FEM models were also used for sensor placement optimization. ii
Page 1: EXPERIMENTAL ANALYSIS AND FEA MODEL
Page 5 and 6: ACKNOWLEDGEMENTS I’m extremely gr
Page 7 and 8: CONTENTS ABSTRACT ……………
Page 9 and 10: 6.2.4 FFT analysis of a surface cra
Page 11 and 12: LIST OF FIGURES Figure 1.1. A picto
Page 13 and 14: Figure 5.16. Abaqus models showing
Page 15 and 16: Figure 7.3. A flow chart demonstrat
Page 17 and 18: To ensure performance and to improv
Page 19 and 20: extraction, damage sensitive featur
Page 21 and 22: 2.1 Introduction to Lamb waves CHAP
Page 23 and 24: an actuator located at one end of a
Page 25 and 26: material is such that electrical pu
Page 27 and 28: 2.6 Transverse crack In this thesis
Page 29 and 30: evolutionary algorithms [54] and st
Page 31 and 32: material setup was sealed in a vacu
Page 33 and 34: CHAPTER 4 EXPERIMENTAL ANALYSIS The
Page 35 and 36: This experimental system was found
Page 37 and 38: Figure 4.5. Experimental test resul
Page 39 and 40: width. The composite coupons were f
Page 41 and 42: Table 5.1. Material properties of I
Page 43 and 44: Table 5.3. Comparison of the exact
Page 45 and 46: Figure 5.5. FE model of a composite
Page 47 and 48: interlaminar stresses are dominant.
Page 49 and 50: Figure 5.9. Comparison of exact def
Page 51 and 52: Table 5.7. Material properties of t
Page 53 and 54:
5.4 PZT modeling The PZT actuator w
Page 55 and 56:
a) b) Figure 5.16. Abaqus models sh
Page 57 and 58:
coupon with a surface crack. A pict
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5.5.3 Embedded crack at various dep
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5.08 mm 5.08 mm 5.08 mm Actuator en
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CHAPTER 6 RESULTS AND DISCUSSION 6.
Page 65 and 66:
6.2 FFT analysis A fast Fourier tra
Page 67 and 68:
Figure 6.5. FFT spectrum based on A
Page 69 and 70:
a) b) Figure 6.8. An enlarged view
Page 71 and 72:
Figure 6.10. Complete FFT spectrum
Page 73 and 74:
enlarged view of the FFT spectrum a
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Figure 6.15. A graphical representa
Page 77 and 78:
Start Abaqus .inp generation Abaqus
Page 79 and 80:
Damage classification was performed
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and dynamic simulation benchmark te
Page 83 and 84:
REFERENCES [1] J. Teresko, "Boeing
Page 85 and 86:
aluminum plates," Ultrasonics, Ferr
Page 87 and 88:
[51] I. Bartoli, "Structural health
Page 89 and 90:
APPENDIX A: Conference contribution
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