Atomistic/mesoscopic approach to the grains boundaries fracture: The case of UO2

Abstract

In irradiated polycrystalline uranium dioxide (UO${}_2$), the pressure generated at high temperature by the noble gases in the intergranular bubbles as well as the thermomechanical stresses due to temperature gradients cause the fracture of the grain boundaries. In this study, starting from an atomistic identification of the fracture energy, one analyzes through mesocopic calculations the behavior of grain boundaries under uniaxial tensile loading up to fracture. In these mesocopical simulations, a cohesive-volumetric approach using concepts of Frictional Cohesive Zone Models (FCZM) and numerical modeling methods based on Non-Smooth Contact Dynamics (NSCD) is employed to simulate grain boundary rupture with the presence of a void under uniaxial tensile loading. The associated computational code, called XPER (eXtended Finite Element method and PERiodic homogenization), allows the analysis of fracture at grain boundaries. A parametric study on the void size and shape is conducted. Voids with sharp edges promote stress concentration, facilitating rupture initiation. The observed trends regarding the variation in void size are similar to the Griffith model, and the results align with experimental findings.