Determination of linear and nonlinear elastic parameters from laser experiments with surface acoustic wave pulses

Time resolved laser techniques enabled the study of the nonlinear evolution of surface acoustic wave (SAW) pulses of very high-amplitudes with acoustic Mach numbers of approximately 0.01. In such waves even shock fronts can be formed during their propagation. Changes of the shape of intense SAW pulses provide information on the nonlinear acoustic parameters and the nonlinear elastic constants of the material. Measurements in polycrystalline stainless steel have shown that a compression of the nonlinear SAW pulse takes place in this metal material yielding a positive parameter of the local nonlinearity. The changes of the SAW pulse shape were calculated using a nonlinear evolution equation and the nonlinear acoustic parameters were determined by fitting the evolution equation to the experimental data. The attenuation of SAWs was determined by measuring low amplitude pulses. In addition, the velocities of longitudinal and shear waves were obtained by registering the precursors of bulk waves at the surface.