Improvements to the ɛ-α porous compaction model for simulating impacts into high-porosity solar system objects

We describe improvements to the ɛ-α porous compaction model for simulating solar system impacts. To improve the treatment of highly porous materials, we modified the ɛ-α model to account for thermal expansion of the matrix during compaction. We validated the improved model by demonstrating good agreement between numerically computed Hugoniot curves for porous iron (up to initial porosities of ∼80%) using the improved ɛ-α model and experimentally-derived Hugoniot data. Moreover, we verified that the model improvements are easily implemented into a hydrocode and preserve the efficiency advantage of a strain-based compaction function. We used the improved ɛ-α porous compaction model in the iSALE hydrocode to reproduce 2-km/s porous-target laboratory impact experiments. The simulation results were in qualitative agreement with the experiments but produced craters that were consistently deeper and larger in volume than the experiments. The results of the hydrocode simulations and laboratory experiments show a reduction in crater efficiency with increasing porosity. This reduction is more dramatic if the impactor density and velocity are higher.