Microscale Modeling of Particle Impact on Thermal Protection System Materials During High-Speed Entry

Micron-sized particles suspended in planetary atmospheres can damage thermal protection systems (TPS) during entry of space capsules into planetary bodies. TPS materials are complex heterogeneous carbon composites, where the microstructure of the composite can play a pivotal role in the propagation of 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 particles. The simulations are initially compared against experiments that used borosilicate as the impacting particle and fused silica as the target surface. The simulations reproduce the damage profiles, diameters, and depths of the craters being formed on the target silica surface. A parametric study is then performed by varying the fracture strength of the target surface and the impacting particle. It is found that the profiles of the damaged region on the silica surface primarily depend on the fracture strength of the silica surface, and not the impacting particle. The simulations are extended to model the damage of porous carbon composites that are used as TPS materials. Microstructures of carbon composites are generated using an in-house code that has been shown to reproduce features of the real material in past studies. While the crater depth on the fused silica surface was within 38% irrespective of the fracture strength of the particle, the damaged depth changes by at least an order of magnitude when a carbon composite surface is used and the fracture strength of the impacting particle is varied. Finally, the influence of damage on the effective permeability is computed using the direct simulation Monte Carlo technique. The maximum increase in the permeability force for the damaged microstructures is found to be 22%, which is within the statistical variability of the material properties observed for the TPS material that is under investigation.