DEM Modeling of Microcracking and Acoustic Emission in Rock under Cyclic Compression with Microstructural Hardening and Memory Effects

ABSTRACT Rocks exhibit nonlinear and hysteretic deformation during loading–unloading cycles, with elastic modulus and plastic strain evolving with increasing cycle numbers and thereby affecting microcracking patterns and acoustic emission (AE). These processes are governed by micromechanical responses of heterogeneous microstructures, yet existing models often fail to represent them accurately. To address this gap, we developed a nonlinear bonded particle model (NBPM) within the discrete element method, incorporating microstructural hardening and memory effects. Compared with conventional linear bonded particle model (LBPM), the NBPM more reliably reproduces the hysteresis response of sandstone under variable‐amplitude cyclic compression, particularly elastic modulus strengthening and cumulative plastic deformation. Model analyses show that compression hardening and memory effects at mineral grain contacts amplify microstructural heterogeneity, producing incompatible deformation and tensile stress concentration zones. During unloading, the abrupt increase in contact stiffness raises the number of tensile stress concentration zones, which expand with increasing cycle numbers. Cyclic compression primarily induces tensile microcracks parallel to the loading direction, whereas unloading significantly enhances the formation of perpendicular tensile cracks. The growth rate of microcracks accelerates as the cycle numbers increase. AE results reveal a stepwise increase in events and energy release, starting with gradual growth and followed by rapid acceleration. Initial unloading is dominated by low‐energy tensile fractures, while amplified cyclic loading produces more high‐energy fracture events. The b ‐value shows a consistent decline with increasing cycle number. This study provides a mechanistic framework linking microstructural hardening, memory effects, and AE evolution, offering new insights into the multi‐scale mechanical response of rocks under cyclic disturbances.