  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.
