The trend towards substituting higher density metals with lower density ones, while maintaining optimum strength, dent and crash resistance, has been a motivation to develop light metals with higher strength to weight ratio, because this impacts vehicle fuel efficiency and, accordingly, CO_2 emission. Magnesium alloys are one of such metals that have drawn significant attention recently. Kelley and Hosford analyzed the deformation behavior of magnesium thorough a number of plain strain channel-die compression. In through thickness compression tests it is difficult to obtain accurate stress-strain relationship at small strains due to friction. Therefore, biaxial tensile test using cruciform specimens is preferred. Recent studies focus on modeling the mechanical behavior of Magnesium using crystal plasticity based approaches. Since in press forming processes a sheet metal is subjected to multiaxial stresses, this necessitates the use of an appropriate material model to be applied in simulation, whose accuracy depends on a number of material parameters determined experimentally. One of such material parameters is the r-value, which indicates the state of anisotropy in materials. In this study the variation of r-value of Magnesium AZ31 has been measured by strain gauges at certain strain levels of plastic strain. The effect of the variable r-value on the shape of the yield locus calculated using Hill's quadratic and the Yld2000-2d is evaluated and discussed. The experimental data for biaxial stresses are those reported in [5].
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