Atomic-scale mode separation for mixed-mode intergranular fracture in polycrystalline metals

Abstract

In intergranular fractures, cracks tend to propagate along grain boundaries (GBs) even under mixed-mode loadings. To quantitatively characterize the mixed-mode intergranular fractures, the stress intensity factors (SIFs) of modes I and II at the crack tip need to be found individually. In this study, an atomic-scale mode separation method is developed to determine individual SIFs from the molecular dynamics (MD) simulation of the mixed-mode intergranular fracture in crystalline metals, for which the atomic-scale J-based mutual integral and asymptotic singular field (i.e., K-field) near a semi-infinite interfacial crack in an anisotropic bimaterial as an auxiliary field are used. Additionally, atomic-level J and M integrals are also performed to determine the energy release rate and the position of a crack tip under the applied mixed-mode loadings, respectively. As a model problem, the mixed-mode fracture along GBs of nickel is investigated to demonstrate that the present atomic scale mode separation method is useful to examine mixed-mode intergranular fracture behaviors of polycrystalline metals at the atomic scale.