Determining large-strain metal plasticity parameters using in-situ measurements of plastic flow past a wedge

TL;DR

This paper introduces a novel, assumption-free method using in-situ wedge flow measurements and optimization to determine large-strain metal plasticity parameters, applicable to various materials and high strain rates.

Contribution

The paper presents a new approach combining in-situ flow measurements with an optimization scheme to accurately identify plasticity parameters without relying on computational simulations.

Findings

Successfully characterized copper's strain hardening behavior.

Effectively determined rate sensitivity parameters of a lead-free solder alloy.

Demonstrated robustness of the method across different material types.

Abstract

We present a novel approach to determine the constitutive properties of metals under large plastic strains and strain rates that otherwise are difficult to access using conventional materials testing methods. The approach exploits large-strain plastic flow past a sharp wedge, coupled with high-speed photography and image velocimetry to capture the underlying plastic flow dynamics. The inverse problem of estimating material parameters from the flow field is solved using an iterative optimization procedure that minimizes the gap between internal and external plastic work. A major advantage of the method is that it neither makes any assumptions about the flow nor requires computational simulations. To counter the problem of non-unique parameter estimates, we propose a parameterization scheme that takes advantage of the functional form of the constitutive model and reformulates the problem into a more tractable form to identify plasticity parameters uniquely. We present studies to illustrate the principle of the method with two materials with widely different plastic flow characteristics: copper (strain hardening) and a lead-free solder alloy (rate sensitive and deformation history dependent). The results demonstrate the efficacy of the method in reliably determining the material parameters under high strain/strain rate conditions of relevance to a range of practical engineering problems.