Abstract
A commercial AZ31 magnesium alloy sheet has been tested under proportional,biaxial tensile loading using cruciform specimens. In order to quantitatively determine the,elastic-plastic deformation behavior of the test material, the contours of plastic work and the,directions of plastic strain rates were measured over a range of equivalent plastic strain,,0.001 p,≤ε 0 ≤ 0.008. The measured work contours and the directions of plastic strain rates have,been compared with those predicted using the von Mises, Hill’48 and the Yld2000-2d yield,functions. The validity of these yield functions is discussed from viewpoints of the yield surface,shape and normality flow rule in the first quadrant of the stress space. The r-value of AZ31 was,found to increase with plastic strain. The effect of the changes in r-value on the shape of the,calculated yield locus has been discussed. Furthermore, biaxial unloading tests following biaxial,loading were carried out for several stress ratios. The nonlinearity of the stress-strain curves,during uniaxial and biaxial unloading was measured and quantitatively evaluated.
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