Grain-Based Discrete Element Modeling of Thermo-Mechanical Response of Granite under Temperature

Numerical modeling is a promising way to understand the characteristics of the thermo-mechanical (TM) coupled behaviors in rocks under high-temperature impact. This paper documents the thermo-mechanical response of Eibenstock granite (EG) through laboratory experiments and numerical simulations using a proposed TM coupled Grain-Based Model (GBM). Uniaxial compression and Brazilian tests of EG specimens after 400 °C and 600 °C heating–cooling cycles were undertaken. Based on the laboratory results, a newly developed TM coupled contact constitutive law considers mineral composition, heterogeneous temperature-dependent properties, reversible α ↔ β quartz-transitions, crack-slipping displacements with strength reduction, and real-time crack evolution. The models can well reproduce the real-time thermal expansion–contraction, microstructural changes, nonlinear stress–strain behavior, temperature-dependent strength, and the ultimate failure modes of thermal-damaged specimens. The P-wave velocities and the simulated thermal cracking revealed that the material contraction during cooling leads to a width reduction of the earlier heating-formed cracks. Newly induced microcracks are rare during cooling due to the released stress concentrations of the local mineral grains. The residual thermal strain, which results from microcrack formation and the growth of pre-existing microcracks, was simulated and used as a quantitative index of thermally induced damages. The damage degree of the 600 °C samples was up to six times higher than that of the 400 °C, leading to a stronger strength reduction upon mechanical loading and a higher concave stress–strain nonlinearity caused by micro-crack closing at the beginning of loading. In general, the GBM is able to simulate the TM coupled behavior of polycrystalline rocks in a realistic manner.