SPH calculations of asteroid disruptions: The role of pressure dependent failure models

Abstract

We present recent improvements of the modeling of the disruption of strength dominated bodies using the Smooth Particle Hydrodynamics (SPH) technique. The improvements include an updated strength model and a friction model, which are successfully tested by a comparison with laboratory experiments. In the modeling of catastrophic disruptions of asteroids, a comparison between old and new strength models shows no significant deviation in the case of targets which are initially non-porous, fully intact and have a homogeneous structure (such as the targets used in the study by Benz&Asphaug (1999). However, for many cases (e.g. initially partly or fully damaged targets, rubble-pile structures, etc.) we find that it is crucial that friction is taken into account and the material has a pressure dependent shear strength. Our investigations of the catastrophic disruption threshold $Q^*_{D}$ as a function of target properties and target sizes up to a few 100 km show that a fully damaged target modeled without friction has a $Q^*_{D}$ which is significantly (5-10 times) smaller than in the case where friction is included. When the effect of the energy dissipation due to compaction (pore crushing) is taken into account as well, the targets become even stronger ($Q^*_{D}$ is increased by a factor of 2-3). On the other hand, cohesion is found to have an negligible effect at large scales and is only important at scales $\lesssim$ 1km. Our results show the relative effects of strength, friction and porosity on the outcome of collisions among small ($\lesssim$ 1000 km) bodies. These results will be used in a future study to improve existing scaling laws for the outcome of collisions (e.g. Leinhardt&Stewart, 2012).