Negative Poisson's Ratio Effect on Extensile Mechanical Behaviors of Thermal-Damaged Crystalline Rocks Under Brazilian Split Loading

A rock normally has a positive Poisson’s ratio which can significantly affect its compression-induced extensile behaviors. However, it can abnormally have a negative Poisson’s ratio (NPR) after being thermally damaged. Thus far, the NPR effect on compression-induced extensile behaviors of the thermal-damaged rock has not been clarified comprehensively. In this study, the digital image correlation was used to acquire extensile displacement fields of discal granite samples under Brazilian split loading, considering different thermal-damaged degrees. Meanwhile, a nonlinear grain-based model (GBM) implemented by the universal distinct element code (UDEC) was established to quantitively clarify related micromechanical behaviors and mechanisms. Experimental results showed that the non-thermal-damaged discal sample mainly produced lateral extension deformation from the vertical line to both sides. Nevertheless, there were anomalous contraction deformation zones bilaterally distributed near two loading points of the samples with slight and moderate thermal damages. Such a phenomenon was attributed to the NPR effect and gradually faded away with increasing the Brazilian split load. For the highly-thermal-damaged sample, it could not produce lateral contraction deformation. The nonlinear UDEC-GBM well reproduced the experimental results and micromechanically revealed the mechanisms of the NPR effect on abnormal contraction deformation of the thermal-damaged crystalline rock, which resulted from a more significant reduction of compressive stiffness than the shear stiffness at grain contacts. The NPR effect constrained lateral extension deformation and microcracking near the compressive stress zones. Hence, the Brazilian split test should have overdetermined the tensile strength of the thermal-damaged rock more significantly than the non-thermal-damaged rock.