A study of laser generated Rayleigh and Lamb waves in graphite/epoxy composites Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/fj236598m

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  • The application of laser generated ultrasonics was first demonstrated in the mid-seventies and has shown good potential when applied to isotropic materials. However, its use with composite materials is still in the early stages of development. This study explores the potential for application of laser generated Rayleigh and Lamb waves in graphite/epoxy composites. Numerical results are obtained by the solution of the wave equations using assumed solutions, and enforcing the boundary conditions. Experimentally, Rayleigh and Lamb waves were generated by a Q-switched ruby laser in the ablation regime and detected by piezoelectric pinducers which permitted accurate phase velocity measurements. The Rayleigh wave velocity was measured at various directions relative to the fiber direction and results were found to agree closely with numerical predictions. The increase of surface wave velocity using thin plates could be useful for the application of delamination detection in thick composites and an increase of Rayleigh wave attenuation could indicate damages caused by impact. Also, surface waves can reflect from small surface cracks. Therefore, laser generated surface waves, particularly along the fiber direction, have high potential for application in non-destructive testing. Lamb wave experiments were conducted in aluminum plates and gave distinctive signals, but there were some difficulties in detecting the precise arrival of each Lamb wave mode for the graphite/epoxy composite plates.
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