Numerical prediction of mode I microcracking and failure by the heterogeneous peridynamic plastic model with the Omori law

Motivated by the strong heterogeneity dependence of the fracture process zone (FPZ) in quasi-brittle rocks, a heterogeneous peridynamic plastic model (HPDPM) is developed to characterize the evolution of the Mode I fracture process zone (FPZ) in polycrystalline rock. The model is calibrated against three-point-bending (3-p-b) tests on Adelaide black granite by iteratively adjusting the microparameters until the numerical predictions of the crack-mouth opening displacement (CMOD) and the applied load ( F y ) reproduce the experimental measurements. The HPDPM correctly captures the asymmetric morphology of the Mode I FPZ and its evolution under load. A parametric study reveals that finer-grained rocks develop a smaller FPZ and a longer yield plateau than their coarse-grained counterparts. What is noteworthy, a higher grain-boundary strength coefficient produces a larger FPZ together with a longer yield plateau challenging the simplistic expection that the higher the boundary coefficient, the fewer bonds should be broken resulting in a smaller FPZ. Therefore, these two regimes are governed by distinct microcrack-density mechanisms. Finally, the HPDPM-derived acceleration curve is incorporated into the time-reversed Omori law to provide a quantitative instability forecast, and the predicted failure times agree well with the simulated catastrophic events.