A multiscale discrete element thermomechanical modeling approach of microcracking generated at high temperature by anisotropic thermal expansion in an elastic brittle polycrystalline ceramic material

Abstract

Aluminum titanate is widely used in various industries due to its superior intrinsic properties for thermal shock applications. At the microstructural scale, this material is characterized by its original grain crystallinity, leading to anisotropic thermal expansion behavior at the crystallographic grain level. Consequently, aluminum titanate undergoes spontaneous microcracking at high temperatures during operational conditions due to mismatches in the Coefficient of Thermal Expansion (CTE) between grains. These microcracks within the refractory microstructure result in quasi-brittle, non-linear mechanical behavior under tensile loading. Experimental findings suggest that the non-linear macroscopic response signifies material toughening, enhancing fracture toughness and, consequently, improving its thermal shock resistance. To better understand these phenomena, this study presents a simplified polycrystalline microstructure model using the Discrete Element Method (DEM), with aluminum titanate as the reference material. The research focuses on predicting the role of grain-level thermal anisotropy in microcrack nucleation and propagation, critical for thermal shock sustainability. A novel DEM approach, based on the bonded particle element method, is proposed. This approach quantitatively accounts for anisotropic CTE, thermomechanical coupling, crack nucleation, propagation and closure under Periodic Boundary Conditions (PBC), enabling multiscale analysis. The results obtained align quantitatively with experimental macroscopic observations, including the evolution of CTE and Young’s modulus with temperature.