Impulsive fracture of fused quartz and silicon crystals by nonlinear surface acoustic waves

During nonlinear evolution of laser-generated surface acoustic wace (SAW) pulses the stress increases with distance of propagation, and causes fracturing of brittle materials. This effect was used to evaluate the strength of isotropic fused quartz and anisortropic crystalline silicon with respect to impulsice loading in the nanosecond range and spontaneous cracking without using seed cracks. Crack nucleation and propagation along the surface was studied by optical microscopy and into the depth o f the bulk by the focused ion beam technique and confocal microscopy. In fused quartz, fracturing produced characteristic regular patterns at the surface with cracks extending into the bulk at an angle of 30º-35º to the surface in the direction of SAW propagation. On Si(111) surfacescracks extended at the surface in the 110 direction and propagated along the weak 111 cleavage plane into the bulk. Other crack planes were observed in only a few cases, e.g., at a larger depth and on the Si(100) surfaces. The observed fracture behavior was rationalized by the complex displacement and stress tensor fields induced by elliptically polarized SAWs.