Large strain constitutive behavior of OFHC copper over a wide range of strain rates using the shear compression specimen

Abstract

A new specimen geometry, the shear compression specimen (SCS), has been developed and validated for large strain testing of metals over a wide range of strain rates. A detailed numerical analysis of this specimen is presented to assess its range of applications and limitations. The dominant deformation mode of the gage section of the SCS is found to be shear. The stress and strain state in the gage section is necessarily three-dimensional, in contrast with commonly assumed situations of simple shear. Yet, considerable simplification is gained through the introduction of simple approximations for the Mises equivalent stress and plastic strain. These fields are found to be uniformly distributed over the gage section. The SCS framework is applied to the characterization of the large strain behavior of OFHC copper over a range of strain rates ε_ε = 10^(-3) to 3.2×10^4 s^(−1). The strain rate sensitivity of the material is noted, in accord with previous observations. The mechanical tests are complemented by microstructural characterization of the material which corroborate the numerical predictions of uniformity of the equivalent strain. The grains in the gage section are discernable for true strains less than 2. At larger strains, of the order of 3.5, the individual grains are no longer discernable and small equiaxed grains are observed, using scanning electron microscopy. These grains are characteristic of recrystallized material. The use of a single specimen geometry coupled to simple data reduction procedures is expected to promote constitutive characterization at large strains over a seamless range of strain rates.

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