Fracturing Evolution of Red Sandstone: Insights from Three-Point Bending Experiment and Numerical Simulation Considering Material Inhomogeneity and Internal Discontinuities

To reveal the various propagation paths of micro-cracks under the continuous process of stress buildup, stress shadow, and stress transfer, three-point bending experiments and numerical simulations were carried out by considering material inhomogeneity and internal discontinuities. The characteristics of red sandstone fracturing evolution were analyzed from the aspects of acoustic emission (AE) energy index, infrared radiation (IR) changes, fracture surface roughness, stress fields and so on. The test results indicate that four stages are divided in the gradual process of energy release of red sandstone fracturing under three-point bending test, the rough fracture surfaces of crack were extremely small, tensile crack makes the largest proportion. IR and AE perform some significant precursor information of rock fracturing, e.g., a large amount of high-temperature debris scattered in infrared thermography, the maximum value of AE accumulative energy and the concentration effect of AE events location. Different tensile stress level has different features, macroscopic fracture morphology happens in a low level, and micro-cracks appears in the weakness of crystal surfaces in a high level. It needs to be emphasized that five different modes, pass through, crack-tip blunting, extended-back, crack-forking and passing round, were concluded in terms of the repeated process of stress buildup, stress shadow & stress transfer. These achievements contribute to the better understanding of the failure mechanisms of red sandstone.