Modeling the damage process of dust particle impacts at microscale during high-speed entry

Micron-sized particles suspended in planetary atmospheres can damage thermal protection systems (TPS) materials during entry of space capsules into planetary bodies. TPS materials are complex heterogeneous composites and the microstructures of the composites play a pivotal role in the propagation of the damage caused by the impact. Here, we present the application of a novel computational technique called the lattice particle method to understand the initiation and growth of craters formed on TPS materials upon impact by dust particles. A parametric study is initially performed on a flat fused silica (quartz) surface and it is found that the relative fracture strength of the impacting particle and the target surface primarily dictates the damage patterns found on the surface. The fracture strength affected not just the diameter and depth of the crater, but also the damage profiles formed on the surface. The simulations are then extended to model the damage of porous carbon composites that are used as TPS materials. Microstructures of carbon composites are digitally generated using an in-house code that has been shown to reproduce features of the real material in past studies. Simulations of representative conditions indicate that particles can penetrate over 200 μm into the microstructure, which is significantly higher than current models, which estimate penetration into the material in the O (1-10μm). Finally, the influence of the damage on the effective permeability of the material is computed using the direct simulation Monte Carlo technique. The maximum increase in the permeability force for the damaged microstructures is 20% suggesting that the crater created in the damaged microstructure does not significantly influence the path traversed by gases percolating through the porous TPS material. This study provides preliminary evidence that an erosion model developed using the data of fused silica or a cork-based composite likely cannot be used for other carbon composites, and new relations have to be developed accounting for the microstructure of a given composite.