Abstract
Initiation of impulsive fracture near the source of a nonlinear surface acoustic wave (SAW) pulse, launched by laser-based transient pressure shocks, is investigated. A numerical method is developed that solves the problem of nonlinear SAW generation, the propagation of SAW pulses in nonlinear media, and the initiation and growth of cracks by such pulses. The characteristic features of SAW profiles in linear media, nonlinear media with quadratic nonlinearity, and nonlinear media with crack induction provide a tool to determine the critical stress of dynamic fracture. Former discrepancies between theoretical and experimental pulse shapes were eliminated by taking into account the effects of fracture. Good agreement was obtained with experiments in isotropic fused quartz. By calculating the stress field of the nonlinear SAW pulse modified by the interaction with a crack and by applying the condition of vanishing shear stress at the crack tip, the angle of crack penetration into the solid was estimated. At a depth of 7.1μm, for example, this angle was approximately 50° to the surface normal, in reasonable agreement with previous measurements in isotropic fused quartz.
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