Nonlinear Acoustic Pulse Evolution at Solid Wedges

The evolution of the shape of high-intensity acoustic pulses at the apex of an anisotropic elastic wedge is described by an evolution equation which contains an effective nonlinearity of second order, if the symmetry of the geometry is sufficiently low. The strength of this nonlinearity is governed by a kernel function. For silicon as a strongly anisotropic wedge material, this kernel function has been computed from the second-order and third-order elastic moduli for various wedge angles and orientations of the surfaces of the wedge. On the basis of the nonlinear evolution equation with kernel functions corresponding to rectangular wedges made of silicon, numerical simulations have been carried out for the propagation of acoustic pulses with intensities achievable in laser-ultrasonic experiments. Spiking and shock formation are found which are strongly geometry-dependent, reflecting strong effects of anisotropy.