Dynamic Behavior of a Porous Brittle Material: Experiments and Modeling

Abstract

The purpose of our research is to study porous polycrystalline graphite under various loading conditions. New experimental data are provided. Some of them concern impacts of a 500μm diameter steel sphere at velocities above 4000 m/s on thick carbon targets, leading to strong debris ejection and cratering. A high speed frame camera showed the debris velocity distribution to lie in the 10-200 m/s range. Post-mortem tomographies have also been performed. They reveal some subsurface cracks, but also provide some evidence that the fragmented sphere lies below the target surface. Dynamic loadings involving similar energy densities (above 2000J/cm2) can also be reached through the interaction of a nanosecond intense laser focalized on a carbon target. An experimental result obtained on a laser facility is presented. Numerical simulations have been performed in order to explain the observed results. An Eulerian hydrocode has been chosen because of the large deformation occurring under considered experiments. We have used a classical model to describe the porous behavior, including equation of state, elasticity, shear strength and densification. In this paper, we focus on the effect of the addition to this porous model of a failure criterion relying on the Weibull theory. The selection of the parameters is based on one set of data and the fit is demonstrated against another test. The overall agreement with the experimental data is good.