Acoustic waves excited by phonon decay govern the fracture of brittle materials

Abstract

The behavior of brittle materials under ballistic impacts is often associated with failure waves that are producing small fracture particles with a surface area requiring large energy input. Numerous attempts to explain this effect since the 1960s did not yield convincing results. Here we propose that failure waves can be interpreted as the result of the decay of the shock-excited phonon continuum into low frequency peaks in the phonon density of states. This results in a situation where pressure amplitude of the localized acoustic waves exceeds a critical fracture quantity such as the tensile strength of the material. Experimental confirmation of this model is presented by using fractured particle size analyses and comparing their results with predicted acoustic wavelengths.