An Extended Mohr-Coulomb Model for Fracture Strength of Intact Brittle Materials Under Ultrahigh Pressures

An extended Mohr-Coulomb model is proposed to represent the pressure-dependent strength of intact structural ceramics under quasi-static and dynamic loading rates at high pressures. A plot of normalized shear stress versus hydrostatic pressure for a range of structural ceramics revealed that despite the differences in material properties, test methods, and strain rates, the failure strength data fall in a narrow range, which can be represented by a unified model. The overall deformation behavior of structural ceramics and their strain rate dependence of strength in multiaxial loading at high pressure beyond Hugoniot elastic limit (HEL) can be explained by an exponential pressure dependence in the Mohr-Coulomb model. The analysis also suggests that the influence of strain rate on strength of a ceramic diminishes with increase in confinement pressure.