The role of porosity in collisions of granular aggregates: A simulation study of fusion, sliding, and fragmentation collisions

Context. Collisions between porous dust aggregates are crucial for the evolution of protoplanetary disks.Aims. We study how the porosity, relative velocity, and impact parameter determine whether colliding dust aggregates grow or erode (fragment) in collisions.Methods. We used a granular-mechanics simulation of aggregates composed of 20 000 grains to determine the collision outcomes of colliding aggregates. Only collisions between aggregates of an equal mass and porosity are considered.Results. The collisional outcomes can be grouped into three classes: "fusion" if the mass of the largest post-collision cluster exceeds 150% of the mass of a single aggregate; "sliding" if the two largest post-collision clusters each contain more than 75% of the initial aggregate mass; and "fragmentation" as the remaining events. Fusion occurs for low velocities and impact parameters, sliding for large impact parameters, and fragmentation dominates at large velocities. The results for central collisions show no sliding and thus strongly differ from the impact-parameter-averaged results.Conclusions. With increasing aggregate porosity, the sliding probability - and to a lesser degree also the fusion probability at small velocities - decreases and the fragmentation probability increases.