Microscale modeling of particle impact on TPS materials during high-speed entry

Abstract

Micron-sized particles suspending in planetary atmospheres can damage thermal protectionsystems (TPS) during entry of space capsules into planetary bodies. TPS materials arecomplex heterogeneous carbon composites, where the microstructure of the composite can playa pivotal role in the propagation of the damage caused by the impact. Here, we present anapplication of a novel computational technique called the lattice particle method to understandthe initiation and growth of craters formed on TPS materials upon impact by particles. Thesimulations are initially compared against experiments that used borosilicate as the impactingparticle 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 parametricstudy is then performed by varying the fracture strength of the target surface and the impactingparticle. It is found that the profiles of the damaged region on the silica surface primarilydepends on the fracture strength of the silica surface, and not the impacting particle. Thesimulations are extended to model the damage of porous carbon composites that are used asTPS materials. Microstructures of carbon composites are generated using an in-house codethat has been shown to reproduce features of the real material in past studies. While thecrater depth on the fused silica surface was within 38% irrespective of the fracture strengthof the particle, the damaged depth changes by at least an order of magnitude when a carboncomposite 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 simulationMonte Carlo technique. The maximum increase in the permeability force for the damagedmicrostructures is found to be 20%, which suggests that the crater created in the damagedmicrostructure does not significantly influence the path traversed by gases percolating throughthe porous TPS material.