Influence of porosity on high-velocity mass-asymmetric collisions

Abstract

Using granular mechanics, we study the influence of porosity on the collisions of spherical granular aggregates with a mass ratio of around 60. At high filling factors, the projectile produces a crater on the target, similar to impacts on a granular bed. However, at low filling factors, the small projectile passes through the large target, strongly fragmenting it. By a consideration of the lateral grain velocities during the collision, we attribute this behaviour to the 'piston effect', in which the projectile loses momentum mainly to the grains below it. Due to an increase in grain-grain interactions as porosity decreases, the piston effect loses its importance for higher filling factors, φ ≿ 0.2. These results may prove useful in modelling collisions occurring in debris discs.