Rate and negative Poisson's ratio effects on Compressive Mechanical behaviors of Thermal-Damaged Crystalline Rocks using a grain-based model

Rocks often have a rate effect on mechanical behaviors and exhibit a negative Poisson's ratio (NPR) effect after being thermally damaged. However, to date, their combined role in mechanical behaviors has not been clarified. This study micromechanically explores the rate and NPR effects on the compressive behaviors of thermal-damaged rocks using the compression-hardening grain-based model (CHGBM) implemented by the Universal Discrete Element Code (UDEC). The original, moderately, and highly thermal-damaged Suizhou granite samples were subjected to unconfined compression tests for calibrating UDEC-CHGBM. With developing thermal damage from the original state, the rock sample decreases in the peak stress and modulus, exhibiting a transition of pre-peak stress-stain relation from the approximately linear to nonlinear, and a transition of Poisson's ratio from the positive (lateral extension) to negative (lateral contraction). Our UDEC-CHGBM reproduced these experimental phenomena with reasonable accuracy. With increasing strain rates, the peak stress and modulus increase in a power law manner. The dynamic increase factors of the peak stress and modulus also increase with enhancing thermal-damaged degrees. Due to the thermal damage, the grain contact increased in the maximum allowable closure, thus enhancing compression-hardening capacity and nonlinear characteristics, resulting in a promotion of the rate effect. Lateral contraction deformation can reduce the proportion and magnitude of the tensile stress within the sample, and inhibit intergranular microcracking. The NPR effect depends on both the degree of thermal damage and strain rate. We shed light on the synergistic effects of the rate and NPR on macro- to micromechanical behaviors of thermal-damaged rocks.