Microwave-induced thermo-mechanical response of heterogeneous rock considering size effect and confining pressure

Effective fragmentation of rock is essential for underground space development. Microwave heating technology has shown great potential in rock breaking. In this study, a high-fidelity rock modeling method based on image-mesh-parameter mapping is established to characterize the texture of rock. Subsequently, a thermo-mechanical FEM approach incorporating damage degradation theory is developed to analyze the evolution of thermal stress and failure patterns under different specimen sizes and confining pressures. Open-ended microwave irradiation experiments are conducted to validate the reliability of the numerical simulations. The results indicate that the thermal stress distribution and the fracture morphology are influenced by rock heterogeneity. With larger specimen sizes, the failure mode transitions from a single-directional fracture to a radial pattern, and the damage scale shows a trend of first increasing and then decreasing. Considering thermo-mechanical evaluation indicators, the representative elementary volume (REV) size for heterogeneous granite is 25 cm. Moreover, confining pressure alters the stress distribution, exponentially reducing tensile stress area and failure scale. Owing to the loading rate effect of microwaves, a quasi-linear increase in output power and time is sufficient to increase the failure scale. This study elucidates the physical response of rocks under the coupled influences of size and confining pressure.