Evaluation of local stress state due to grain-boundary sliding during creep within a crystal plasticity finite element multi-scale framework

TL;DR

This study develops a multi-scale computational framework combining interface elements, special triple point/line elements, and crystal plasticity models to analyze how grain-boundary sliding influences creep deformation and internal stress development in polycrystalline materials, especially Type 316 stainless steel.

Contribution

It introduces a novel integrated modeling approach to quantify the effects of grain-boundary sliding on creep behavior and internal stresses in realistic polycrystalline aggregates.

Findings

Grain boundary sliding significantly affects stress distribution during creep.

Crystallographic orientation mismatch influences sliding magnitude and stress.

Boundaries transverse to load carry higher normal stresses, up to 180 MPa.

Abstract

Previous studies demonstrate that grain-boundary sliding could accelerate creep rate and give rise to large internal stresses that can lead to damage development, e.g. formation of wedge cracks. The present study provides more insight into the effects of grain-boundary sliding (GBS) on the deformation behaviour of realistic polycrystalline aggregates during creep, through the development of a computational framework which combines: i) the use of interface elements for sliding at grain boundaries, and ii) special triple point (in 2D) or triple line (in 3D) elements to prevent artificial dilation at these locations in the microstructure with iii) a physically-based crystal plasticity constitutive model for time-dependent inelastic deformation of the individual grains. Experimental data at various scales is used to calibrate the framework and compare with model predictions. We pay particular consideration to effects of grain boundary sliding during creep of Type 316 stainless steel, which is used extensively in structural components of the UK fleet of Advanced Gas Cooled Nuclear Reactors (AGRs). It is found that the anisotropic deformation of the grains and the mismatch in crystallographic orientation between neighbouring grains play a significant role in determining the extent of sliding on a given boundary. Their effect on the development of stress within the grains, particularly at triple grain junctions, and the increase in axial stress along transverse boundaries are quantified. The article demonstrates that the magnitude of the stress along the facets is highly-dependent on the crystallographic orientations of the neighbouring grains and the relative amount of sliding. Boundaries, transverse to the applied load tend to carry higher normal stresses of the order of 100-180 MPa, in cases where the neighbouring grains consist of plastically-harder crystallographic orientations.