Transient Pulse Propagation and Dynamic Analysis of Fracture in Composite Laminated Plates
Elastic wave propagation and scattering in composite plates have been investigated in this thesis both in frequency and time domains. The fundamental tool used in this study involves the Green's functions and they are formulated based on a propagator matrix method for a laminated composite plate in the frequency domain. Properties of each ply can be transversely isotropic. The transient responses are then obtained by using a fast Fourier transform (FFT). Characterization of the impact load due to a steel ball drop onto an edge of a glass plate has been a part of this study to test the reliability of a PVDF transducer. The test model is a combination of the numerical deconvolution technique and an acoustic emission experiment. The study shows that PVDF transducers have good sensitivity as a receiver for quantitative nondestructive (QNDE) applications. The layering effect on the propagation of elastic waves in a laminated composite plate is also investigated. Comparisons between laminated plates with different numbers of plies and an equivalent homogenized composite plate have been used to investigate the frequency range and the minimum number of plies in a laminated plate with certain thickness for which the equivalent homogenized plate model is valid. This is motivated by the desire to simplify the model calculations for scattering in these plates. Scattering of elastic waves by horizontal cracks in a unidirectional transversely isotropic plate as well as by delamination cracks in an 8-layer cross-ply composite plate has been investigated by a hybrid method combining finite element discretization in the near field and boundary integral representation of the far field. It is found that by using an array of sensors, the cracks with large length-to-depth ratio can be quantitatively characterized. An inverse prediction technique based on the round trip travel time of the trapped Rayleigh wave between crack tips and the resonance frequency using a plate model with simply supported ends is also suggested. Furthermore, the sensitivity of the Rayleigh-Lamb wave speeds on depths of the delamination cracks in a laminated composite plate are discussed. All these results are useful in nondestructive evaluation (NDE) of defects in laminated composite plates. The aforementioned hybrid finite element method has also been implemented to investigate dynamic fracture of delamination cracks in laminated composite plates. The dynamic energy release rates of different fracture modes are investigated. The numerical results are consistent with those obtained by an experiment due to a ball drop impact. This suggests the feasibility of the hybrid finite element method for the analysis of dynamic fracture mechanics.
- Pub Date:
- February 1991
- PULSE PROPAGATION;
- Engineering: Mechanical; Applied Mechanics; Physics: Acoustics