Abstract
Accurate assessment of plastic anisotropy is essential to many material models used in computer-aided sheet metal forming simulations. In this analysis, the influence of discontinuous yielding (yield point elongation or YPE) on normal anisotropy (R-value) measurements was examined. A laboratory-annealed, non temper-rolled, aluminum-killed drawing quality (AKDQ) steel was considered. It was found that discontinuous yielding significantly influences R-value calculations by imposing an effective offset to the width strain measurement during a sheet tensile test if the R-value is defined in terms of total strains (R=ɛW/ɛT). The effect may be positive or negative and shows considerable variability between tests. For a more accurate and consistent representation of normal anisotropy, the incremental R-value (R’=dɛW/dɛT) should be used in cases of significant YPE. A procedure has been developed to account for the low-strain effects of discontinuous yielding on plastic anisotropy measurements, where the R’-value is determined in a region of stable, uniform deformation on the stress/strain curve. For adequately temper rolled materials (with minimal YPE) and for inherently YPE-free materials, the R-value may be determined in the conventional way.
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Hance, B.M. Influence of discontinuous yielding on normal anisotropy (R-value) measurements. J. of Materi Eng and Perform 14, 616–622 (2005). https://doi.org/10.1361/105994905X64576
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DOI: https://doi.org/10.1361/105994905X64576