Cratering and collapse of an inclined granular layer by oblipue impact of a spherical projectile

The oblique impact of a solid sphere onto an inclined granular layer is experimentally studied. The inclination angle of the target granular layer is varied from 0 to 33 degrees. The incident angle is also varied from 10 to 170 degrees. The range of impact velocity is 10 - 100 m/s. As a result, we observe following behaviors. When the incident angle is 90±10 degrees (almost normal impact), simple penetration of the projectile is observed. However, rebound or ricochet of the projectile occurs when the incident angle is smaller than 70 degrees (or larger than 110 degrees). When the target granular layer is steep enough, the transient crater produced by the impact is significantly modified by the asymmetric collapse of crater wall. Due to these complex effects, the final crater shape becomes complex. In this study, the characteristic dimensions of the crater (diameter, depth, and cavity volume) are measured and scaled by the effective impact kinetic energy transferred to the target by the projectile impact. While the crater volume can be scaled with a universal exponent, the specific volume value depends on the inclination angle.