Impacts into porous graphite: An investigation on crater formation and ejecta distribution

Abstract

Impact cratering experiments and simulations on a porous graphite were carried out to investigate the effects of projectile and targets properties on debris ejection and cratering process. In this study, we first describe a model for porous graphite enabling to replicate an uncommon hysteresis behaviour observed during cycled confined compressions. Then, we present hypervelocity impacts of aluminum sphere conducted at impact velocities ranging from 1000 to 5500 m.s−1 and compare it to impact data with steel spheres. Post-mortem analyses were performed with profilometer and X-ray tomographies to visualize crater morphologies, subsurface cracks and measure crater dimensions. Hydrodynamic simulations were carried out to replicate impact conditions of steel and aluminum projectile and test the capabilities of our modelling approach. The graphite model was found to reproduce with good agreement crater dimensions and morphologies. It was also observed that crater volume generated by aluminum sphere is proportional to the impactor kinetic energy Ek, which differ from the dependence of crater volume engendered by steel sphere on Ek2. Following the good replication of impact craters, we investigated the properties of ejected debris. We deduced from simulations and ejecta scaling relationships, velocity scaling exponents μ consistent with the strength-dominated regime and calculated various values of momentum enhancement factor β comprised between 1 and 2. Finally, we found that around 85 % of the total ejecta momentum was carried away by 35 % of the total excavated mass from the crater outer rim at angles comprised between 15∘ and 35∘.