A plasticity model with yield surface distortion for non proportional loading

TL;DR

This paper introduces a modified elastic-plastic model with a yield surface distortion to better simulate metallic material behavior under non-proportional loadings, capturing experimentally observed egg-shaped yield surfaces.

Contribution

A new yield criterion incorporating a distorted stress to model non-proportional loading effects, maintaining classical behavior under proportional loading.

Findings

Model accurately predicts egg-shaped yield surfaces.

Experimental validation with 2024 T4 aluminum alloy.

Improves understanding of non-proportional loading behavior.

Abstract

In order to enhance the modeling of metallic materials behavior in non proportional loadings, a modification of the classical elastic-plastic models including distortion of the yield surface is proposed. The new yield criterion uses the same norm as in the classical von Mises based criteria, and a "distorted stress" Sd replacing the usual stress deviator S. The obtained yield surface is then "egg-shaped" similar to those experimentally observed and depends on only one new material parameter. The theory is built in such a way as to recover the classical one for proportional loading. An identification procedure is proposed to obtain the material parameters. Simulations and experiments are compared for a 2024 T4 aluminum alloy for both proportional and nonproportional tension-torsion loading paths.