Particle Scale Dynamics of Oblique Granular Impact

When a solid projectile impacts a granular target, it experiences a drag force and abruptly comes to rest as its momentum transfers to the grains. An empirical law successfully describes the force experienced by the projectile, and the corresponding grain-scale mechanisms have been deciphered for normal impacts. However there is little work exploring non-normal impacts. Here, we extend previous studies to explore the oblique impact case, in which a significant horizontal component of the drag force is present. In our experiments, a projectile impacts a quasi-two-dimensional bed of bidisperse photoelastic grains. We use high-speed imaging to measure high-resolution position data of the projectile's trajectory and simultaneously visualize force chain propagation in the granular medium. When the impact angle becomes important, the spatial structure of the stress response reveals relatively weak force chain propagation in the horizontal direction. This is accompanied by an increasingly curved projectile trajectory. Based on these observations, we describe the change of the granular impact drag force with impact angle.