Consider an isotropic material loaded so that the principal stresses coincide with the x, y, and z axes. Assuming the von Mises yield criterion applies, make a plot of \sigma_{y} versus \sigma_{x} yield locus with \sigma_{z} = 0.
Let \sigma_{x} =\sigma_{1} , \sigma_{y} =\sigma_{2} , and \sigma_{z} =0. Now \alpha =\sigma_{2}/ \sigma_{1} . Figure 6.3 results from substituting several values of \alpha into Equation (6.12),
\sigma_{1} = Y/(1-\alpha +\alpha^{2} )^{1/2}. (6.12)
solving for \sigma_{x} /Y and \sigma_{y} /Y = \alpha \sigma_{x} /Y, and then plotting.