A 2D continuous-discontinuous heat transport model considering thermal cracking for the combined finite-discrete element method (FDEM) using node binding scheme

Abstract

Within the framework of the combined finite-discrete element method (FDEM) employing cohesive elements, we propose a novel thermo-mechanical coupling model to simulate heat transport in fractured rock masses (i.e., heat conduction, heat transfer and heat exchange) and capture the initiation and propagation of thermal cracking. Instead of using a fictitious heat exchange coefficient for cohesive elements as those in previous work, in this model, we adopt a node binding scheme to ensure the continuity of heat conduction in the intact/continuous rock matrix domain prior to fracturing. The computational efficiency of heat conduction using the proposed approach is significantly improved ∼ 110 times (about 2560 triangle elements contained in a model), and the extra numerical parameter (i.e., the heat exchange coefficient of cohesive element) commonly used in the conventional FDEM is not required. To accommodate the finite strain theory implemented in FDEM for large deformations and rotations, we also employ the multiplicative decomposition of deformation gradient to calculate the thermal stress. We conduct a suite of numerical benchmarks to verify the effectiveness and robustness of the thermo-mechanical coupling model in terms of heat conduction, thermal cracking and heat transfer. As an application, a typical example is performed to uncover the underlying mechanism of thermal cracking induced by different temperatures and investigate the micro-fracturing of brittle crystalline rocks. The coupled thermo-mechanical coupling model may help enhance the applicability and accuracy of FDEM for deep energy exploitation.