Research on the development law of thermal-induced microcracks in tight sandstone under displacement constraint and temperature coupling

Differences in meso local expandable displacements within the specimen after heating of the plunger rock samples lead to significant microcracking non-homogeneity, so local expandable displacement constraints are also one of the necessary considerations when investigating the mechanical behavior of rocks after heating. Using sandstone as an example, the crack features by multi-point measurements of heated rock slices were determined first. Furthermore, digital cores are reconstructed using the polycrystalline discrete element method, and thermal damage simulations are carried out to investigate the mechanism of microcrack formation in sandstone as well as the variation characteristics of mechanical parameters under the combined influence of displacement constraints and temperature. The research findings are as follows. (1) Heating temperature and expandable displacement influence the development of intragranular cracks, resulting in preferential orientations along cleavage planes, conjugate shear cracks in a crossed pattern, and increased crack density within small particles. (2) After <italic>ϕ</italic> 25 mm×50 mm rock samples were heated at 200 ℃–1 000 ℃, the maximum expandable displacement increased linearly with temperature, but the effect of temperature on the dispersion of expandable displacement values was not significant. The number of cracks increased linearly with the expandable displacement at the beginning, and then slowed down to a stable level. 800 ℃ heating, the number of intra-grain tensile cracks exceeded the inter-grain tensile cracks in the highest proportion, while the intra-grain shear damage almost did not occur below 1 000 ℃. (3) Higher temperatures inhibit the promotion of microcrack development by expandable displacements. For example, after heating at 400 ℃, the microcrack growth rate is 668.3%, but it drops to 12.8% after heating at 1 000 ℃. As the expandable displacement increases, the non-uniform development of microcracks makes the rock macroscopically non-homogeneous, and the structure is more deteriorated leading to a decrease in mechanical parameters.