Due to its simplicity in instrumentation and data analysis, uniaxial tensile tests are commonly used for determining the plastic stress-strain relation of a sheet metal. However, such a stress-strain relation is valid only up to the moderate strain level just before the onset of diffuse necking in the specimen gage section. Once diffuse necking starts, the plastic deformation of the specimen becomes increasingly non-homogenous. Questions arise regarding the validity of extrapolating such a uniaxial stress-strain relation to large strains when one analyses the forming failure of the sheet metal occurring at much larger strains. Here we report our effort in investigating an alternative technique for obtaining uniaxial stress-strain curves of sheet metals at large strains. A tapered tensile testing specimen originally used by Dr. Owen Richmond and his colleagues [1] will be evaluated via a combination of three-dimensional finite element analysis and whole-field in-plane plastic strain mapping experiments. Specifically, the criterion for determining the onset of localized necking and the suitability of a Bridgman-type correction will be assessed in this talk.
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