Crushing characteristics of granite during ultra-high speed penetration: experiments and simulations

Escaping ejecta enhanced momentum transfer due to recoil produced by the impact, depending on the complex interaction of the projectile remove with to target. The crushing behavior of the target in the initial stage of impact is often neglected, especially in meteorite-like brittle materials. Whereas, the relationship between crack evolution and stress wave propagation is vague under ultra-high speed impact. The experiments of Al sphere impacting into granite were carried out at velocities between 1800 and 4000 m/s by a two-stage light-gas gun (DBR30), revealing distinct fragmentation characteristics on granite. As the speed increases, transitions from intact to fractured, then fragmented, exhibiting distinct failure modes under shock wave loading. Smoothed particle hydrodynamics-finite element method (SPH-FEM) simulation was employed to describe the geometrical evolution of the projectile and the propagation crack in the target. It was found that the shape of the projectile gradually changes from a cone to spherical as speeds increase. Further crack fractal dimension analysis revealed that the penetration mode transition occurs within 1500-2000 m/s. This method provides a novel framework to evaluate the ultra-high speed penetration while quantifying the penetration mode and crushing effect.