Collisions between micro-sized aggregates: role of porosity, mass ratio, and impact velocity

Abstract

Dust aggregate collisions usually occur between mass-asymmetric collision partners. Granular-mechanics simulations are used to study the influence of filling factor, ϕ, and impact velocity in collisions of spherical granular aggregates with different values of their mass ratio, but the same filling factor. Three possible outcomes are observed: (i) sticking, which might include penetration of the smaller aggregate into the larger aggregate; (ii) fragmentation of the largest aggregate into two large fragments, particularly due to the so-called piston effect for low filling factors; and (iii) total destruction of the aggregates. Most of the impact energy is spent by friction, with some fraction leading to compaction of the porous material. The erosion efficiency varies significantly with impact velocity, mass ratio, and porosity, but the accretion efficiency does not show such strong variations. For highly asymmetric collisions with high impact velocities (100 m s−1), grain accretion (growth) can occur for a ‘window’ in the filling factor (0.20 <ϕ< 0.35). This window becomes wider as the impact velocity decreases. As the mass ratio of the aggregates decreases, the impact velocities that enable growth can also decrease. The mass distribution of the fragments follows a power-law distribution that is almost independent of the mass ratio, filling factor, and velocity.