Effects of oxidation on the effective thermomechanical properties of porous ultra-high temperature ceramics in compression via computational micromechanics and MPM

Due to the harsh flight environment of hypersonic platforms, Ultra-High Temperature Ceramics (UHTCs) imbued with macroscale porosity have been introduced as candidates for providing thermal insulation of sensitive on-board components. This study employs an oxidized state approach for modeling the coupled effects of surface oxidation and continuum damage in the effective thermomechanical response of such materials within the framework of computational micromechanics. Using an in-house Material Point Method (MPM) computational tool, two-dimensional plane strain simulations were performed on representative hexagonal structures of TiB2 with 10%, 40% and 70% macroporosity. Oxide layers ranging from 5 to 50 μm were applied to the structures in place of a transient, diffusion-based oxidation solver. Simulations with applied compressive strains of up to 30% were then performed on hexagonal structures with and without the oxide layer present. A range of dynamic thermal gradients were also applied to investigate the damage due to thermal expansion coefficient mismatch. Finally, the oxidized state modeling approach was applied to large porous structures derived from micro computed tomography images of TiB2 foam.