Micromechanical damage modeling of quasi-brittle materials incorporating temperature and strain rate effects

This study proposes an advanced micromechanical constitutive model to capture the complex mechanical behavior of quasi-brittle materials subjected to combined thermal and dynamic loading. The heterogeneous solid matrix is idealized as an elastic continuum containing randomly distributed penny-shaped microcracks, and their collective interactions are incorporated through the Mori–Tanaka homogenization scheme. By integrating rate-and-state friction theory with microscale interface evolution mechanisms, the model establishes thermo–rate-dependent laws for frictional sliding and damage progression, thereby capturing the complete evolution of microcrack interface slip, degradation, and coalescence. These micromechanical processes are upscaled through a coupled plasticity–damage formulation, yielding a macroscopic strength criterion that intrinsically links frictional dissipation and crack evolution with the thermal and rate sensitivity of strength. To ensure numerical robustness and computational efficiency, a semi-implicit decoupled return-mapping algorithm is adopted. The model is evaluated against experimental data for three types of rocks tested over broad ranges of temperature, confining pressure, and loading rate. The predicted responses agree closely with the measurements, successfully reproducing strength evolution, thermo-rate effects, and failure patterns, thereby demonstrating the model reliability and applicability. • A thermo-rate micromechanical model is developed for dynamic failure of quasi-brittle materials. • Rate-and-state friction is coupled with microcrack damage thermodynamically. • Temperature and strain rate effects unify into interpretable friction and damage laws. • An analytical strength criterion and stress–strain relations are derived via upscaling. • Predictions match dynamic rock experiments across wide temperature and strain-rate ranges.