Numerical and experimental investigation of the influence of temperature and grain size on the fracture behavior of rock

Abstract

Understanding the fracture behavior of rocks subjected to temperature and accounting for the rock's texture is vital for safe and efficient design. Prior studies have often focused on isolated aspects of rock fracture behavior, neglecting the combined influence of grain size and temperature on fracture behavior. This study employs specimens based on the particle flow code-grain based model to scrutinize the influence of temperature and grain size discrepancies on the fracture characteristics of sandstone. In pursuit of this goal, we manufactured ninety-six semi-circular bend specimens with grain sizes spanning from 0.5 mm to 1.5 mm, predicated on the mineral composition of sandstone. Recognizing the significance of intra-granular and inter-granular fractures, the grains were considered deformable and susceptible to breakage. The numerical model was calibrated using the results of uniaxial compressive strength (UCS) and Brazilian tests. We implemented thermo-mechanical coupled analysis to simulate mode I, mode II, and mixed mode (I-II) fracture toughness tests and subsequently studied alterations in the fracture behavior of sandstone at temperatures from 25 °C to 700 °C. Our findings revealed increased fracture toughness as the temperature escalated from 25 °C to 200 °C. However, beyond the threshold of 200 °C, we noted a decline in fracture toughness. More specifically, the drop in mode I fracture toughness was more pronounced in specimens with finer grains than those with coarser grains. Contrarily, the trend was reversed for mode II fracture toughness. In contrast, the reduction of mixed mode (I-II) fracture toughness seemed almost linear across all grain sizes. Furthermore, we identified a correlation between temperature and grain size and their collective impact on crack propagation patterns. Comparing our results with established theoretical benchmarks, we confirmed that both temperature and grain size variations influence the fracture envelopes of sandstone.