Fracture Induced by Giant Nonlinear Acoustic Pulses

Using a technique recently developed in our research group to build up propagative strain waves from the linear to the nonlinear regime, we investigate transient fracture dynamics in strontium titanate, in which surface acoustic waves with longitudinal strain amplitudes reaching up to 3 % can be generated — well within the regime of mechanical failure. We identify dislocation lines and cleavage planes in the material from the damage induced by the propagation of high-amplitude acoustic waves. Furthermore, since our technique, based on the superposition of numerous individual laser-generated acoustic waves, can generate giant strain waves without damage to the excitation region, we analyze how fracture evolves as a function of the number of acoustic waves launched into the sample. Finally, we study the anisotropy of fracture dynamics from orientation-dependent measurements and show that counter-propagating strain waves lead to qualitatively different behaviors due to the nonlinearity of the fracture process.