A viscoplasticity model with an enhanced control of the yield surface distortion

TL;DR

This paper introduces a comprehensive viscoplasticity model for metals that incorporates isotropic, kinematic, and distortional hardening, ensuring convex, smooth yield surface evolution and thermodynamic consistency, validated with aluminum alloy data.

Contribution

The paper presents a novel viscoplasticity model with enhanced control over yield surface distortion, combining multiple hardening mechanisms and ensuring convexity and thermodynamic consistency.

Findings

Model captures arbitrary yield surface shapes with sharpening and flattening.

Yield surface evolves smoothly and remains convex during hardening.

Model validated with experimental data for aluminum alloy 1100 Al.

Abstract

A new model of metal viscoplasticity, which takes combined isotropic, kinematic, and distortional hardening into account, is presented. The basic modeling assumptions are illustrated using a new two-dimensional rheological analogy. This demonstrative rheological model is used as a guideline for the construction of constitutive relations. The nonlinear kinematic hardening is captured using the well-known Armstrong-Frederick approach. The distortion of the yield surface is described with the help of a so-called distortional backstress. A distinctive feature of the model is that any smooth convex saturated form of the yield surface which is symmetric with respect to the loading direction can be captured. In particular, an arbitrary sharpening of the saturated yield locus in the loading direction combined with a flattening on the opposite side can be covered. Moreover, the yield locus evolves smoothly and its convexity is guaranteed at each hardening stage. A strict proof of the thermodynamic consistency is provided. Finally, the predictive capabilities of the material model are verified using the experimental data for a very high work hardening annealed aluminum alloy 1100 Al.