An analysis of the influence of grain boundary strength on microstructure dependent fracture in polycrystalline tungsten

Abstract

This work examines the influence of changes in grain boundary (GB) strength on microstructure dependent crack propagation in polycrystalline tungsten (W). The property of focus is brittleness index (BI) originally introduced by Evans and Marshall in 1976 and 1979, respectively, used in order to quantify the extent of brittleness of a material. In an earlier work, GBs of Ni-doped polycrystalline W have been characterized for embrittlement using ab-initio quantum mechanical simulations as a function of Ni atomic volume fraction and GB thickness. This work focuses on quantifying the influence of GB strength on microstructure dependent crack propagation. Continuum mechanical GB strength properties and effective W grain properties are derived from ab-initio simulation based stress–strain curves. The crack propagation simulations when GBs are considered of finite width are based on an extended finite element (XFEM) framework. Simulations that consider GBs of infinitesimal width due to mesh resolution issues are based on a combined XFEM-cohesive finite element model that employs cohesive elements at GBs. Analyses of crack propagation through finite width GBs focus on understanding the role of square root of length scale dimension in the original BI formulation. Based on analyses of crack propagation through finite width GBs oriented at angles varying from $$0^{\circ }\,\hbox {to}\,90^{\circ }$$ with respect to advancing crack, a quantitative criterion based on a failure index which predicts crack propagation path in polycrystalline W is proposed and examined.