Comparison of two models for the simulation of hypervelocity impacts on porous graphite

Hypervelocity impacts (HVI) on porous brittle materials is an important mechanism for various applications such as planetary defense, human-made spacecraft protection, and high power laser facility safety. In either case, the target fragmentation upon impact can lead to significant cratering and debris ejection. This paper presents a numerical investigation of HVI experiments on porous graphite. Two porosity models are compared. In the first one, pore collapse is assumed to be an irreversible process during compaction, whereas the second one considers that pore collapse is mainly due to elastic, i.e. reversible, deformation. Various experimental data are analyzed and compared to the simulations with both models. Three experimental data are in favor of the second model: i) volume recovering upon release after quasistatic oedometric tests; ii) crater shapes resulting from HVI experiments; iii) ejecta velocity distribution observed under HVI experiments. The detailed analysis of these results suggests that they are related to the modelling of release waves velocity, which is significantly different between both models.