Hypervelocity impacts of polymer spheres on graphite: experiments and simulation

Space debris is a major concern for aerospace industry, which has to design structures able to withstand hypervelocity impacts of small projectiles at several km/s. To study this phenomenon, a series of nine shots has been performed on a two-stage gas gun at velocities ranging from 2100 m/s to 6300 m/s. Projectiles were 2 mm diameter spheres made of Delrin, a polymer of density 1425 kg/m³. Targets were 15 mm thick and made of EDM3, a porous and homogeneous graphite of density 1754 kg/m³. Ultrarapide camera was used with a laser shadowgraph system to provide movies of impacts. After each shot, the generated crater has been measured using an optical profilometer. Experimental setup and results are detailed in this paper. Especially, the evolution of crater dimensions as a function of projectile velocity is shown and a scaling is proposed to compare these data to others obtained with aluminum projectiles on the same facility. Furthermore, some 2D-axisymetrical Eulerian simulations have been performed with the Hesione hydrocode developed at CEA. Our modeling of EDM3 and Delrin, which is fully described in this paper, allows to reproduce the nine shots with a good agreement.