Modeling failure waves in brittle materials

Abstract

Failure waves in glass were first observed in tests some 30 years ago, with a wave velocity of 1.5-2.5 km/s. In spite of the long time since then, some essential questions concerning failure waves remained unanswered. These are: 1) what is the formation mechanism of failure waves; 2) what is the propagation mechanism of failure waves; and 3) what are the kinetics of the failure process? In the past failure wave researchers assumed that material damage starts from the boundary. But in a recent experimental work on glass [9] the investigators observed that the glass starts to fail within the material behind the shock front, and not from the boundary. This seemingly small change in the way failure waves are started makes it possible to predict the mechanics of failure wave formation and propagation, using existing failure models for brittle materials. We’re using here a dynamic failure model for brittle materials that we’ve developed in recent years [10]. To get a failure wave that lags behind the shock front, we assume in that the rate of damage accumulation behind the shock front decreases exponentially with distance from the boundary. This is a plausible assumption because opening pores and cracks would become more difficult with distance from the boundary. And indeed, using this assumption we get a failure wave that propagates slower than the shock and at an approximately constant velocity.