Effects of loading types on micro-fracturing and the inherent acoustic emissions in isotropic rocks: a numerical study

This study investigates the micro-fracturing of a Statistical Element Volume (SEV), and the emergent acoustic emissions under three loading conditions: simple tension, direct shear, and uniaxial compression. Employing the Discrete Element Method (DEM), the spring-beam bond model, and an elliptic fracture criterion, the SEV created simulates quasi-brittle materials, akin to rocks, featuring key properties like Young’s modulus, shear modulus, Poisson’s ratio, and ratios between maximum compression /tensile strengths around 10. Our analysis reveals a fracture behavior in bond energy (and AE) following a power law behavior analogous to Gutenberg-Richter law. In tension and shear, the power laws are similar. It is under uniaxial compression that a difference is observed. The statistics of bond energy displays two regimes corresponding to two exponents b in the Gutenberg Richter law. These two regimes can be distinguished by considering the state of stress upon failure. In the post peak regime, which is also a dilatant regime of deformation, high energy events are related to compression-shear loads. Such events are very seldom in tension, shear or in the pre-peak regime under uniaxial compression.