Intergranular normal stress distributions in untextured polycrystalline aggregates

Abstract

From a general point of view, InterGranular Stress-Corrosion Cracking (IGSCC) results from the interplay between mechanical loading and grain boundaries opening. The former leads to intergranular stresses in polycrystalline aggregates, the latter being either stress-accelerated or stress-induced. This work aims at obtaining intergranular normal stress distributions in uncracked polycrystalline aggregates, which is considered as a key milestone towards IGSCC initiation predictive modelling. Based on the finite element method, numerical simulations have been performed on Voronoi polycrystalline aggregates considering a wide variety of material constitutive equations: crystal elasticity (cubic and hexagonal symmetries) with different anisotropy ratios and crystal plasticity for different sets of slip systems under the assumption of uniform critical resolved shear stress: Face-Centered Cubic (FCC), Body-Centered Cubic (BCC) and Hexagonal Close Packed (HCP) with or without hardening, and for both uniaxial and equibiaxial macroscopic loading conditions. In the elastic regime, a correlation between standard deviations of intergranular normal stress distributions and a universal elastic anisotropy index proposed recently is found and explained through a simple model. For macroscopic strain larger than the yield strain, the evolution of standard deviations with strain is rationalized by accounting only for the macroscopic elastic strain and the standard deviation of Taylor factor. These numerical results associated with physically-based simple models allow to estimate easily intergranular normal stress concentrations, constituting a tool for classifying polycrystalline aggregates according to their potential susceptibility to IGSCC.