Initiation and Propagation of Plastic Yielding in Duplex Stainless Steel

TL;DR

This study combines neutron diffraction experiments and finite element simulations to analyze how plastic yielding initiates and propagates in duplex stainless steel under various biaxial stress conditions.

Contribution

It introduces a multiaxial strength-to-stiffness parameter and an equation to predict local stress for yielding initiation and propagation in polycrystalline duplex stainless steel.

Findings

Model accurately predicts local stress states during deformation.

Yielding initiation correlates with the multiaxial strength-to-stiffness parameter.

Propagation of yielding can be estimated from the local stress equation.

Abstract

The elastoplastic behavior of a two-phase stainless steel alloy is explored at the crystal scale for five levels of stress biaxiality. The crystal lattice (elastic) strains were measured with neutron diffraction using tubular samples subjected to different combinations of axial load and internal pressure to achieve a range of biaxial stress ratios. Finite element simulations were conducted on virtual polycrystals using loading histories that mimicked the experimental protocols. For this, two-phase microstructures were instantiated based on microscopy images of the grain and phase topologies and on crystallographic orientation distributions from neutron diffraction. Detailed comparisons were made between the measured and computed lattice strains for several crystal reflections in both phases for scattering vectors in the axial, radial and hoop directions that confirm the model's ability to accurate predict the evolving local stress states. A strength-to-stiffness parameter for multiaxial stress states was applied to explain the initiation of yielding across the polycrystalline samples across the five levels of stress biaxiality. Finally, building off the multiaxial strength-to-stiffness, the propagation of yielding over the volume of a polycrystal was estimated in terms of an equation that provides the local stress necessary to initiate within crystals in terms of the macroscopic stress.