Calculating distributions of local thermal conductivities in ablative materials: mesoscale modeling of the effects of structural randomness on materials properties

Ablative materials used for heat shields are inherently random, consisting of networks of fibers embedded in a matrix of more volatile material that undergoes pyrolysis. Models of the responses of these materials to conditions expected during spacecraft reentry are essential to the design of safe and effective heat shields. Existing materials response codes generally treat these random, network-based, porous solids as homogeneous and continuous. This neglects the critical effects of micro- and mesoscale randomness and disorder on macroscale materials behavior. Despite its importance, randomness is challenging to model, as calculations that resolve structural details internal to ablative materials are limited to relatively small volumes, or periodic approximations, of real materials. Leveraging a recently developed toolkit for the rapid generation of statistically meaningful sets of simulated representative volume elements (sRVEs), distributions of thermal conductivities at the mesoscale will be calculated for a range of structural geometries selected to approximate real ablative materials. These results will provide probability distributions of local thermal conductivities for larger scale materials response models, and will be used to examine the effects of structural variations (including fiber aspect ratio, fiber-fiber connectivity, and fiber alignment/arrangement) on thermal conductivity.