A steel sheet was deformed plastically. After unloading, it was found that the principal engineering strains in the plane of the sheet were e1=0.172 and e2=-0.0431. Assume that the ratio of the stresses,α=σ2/σ1,was held constant during the loading and that there was no stress normal to the sheet surface. Also assume the von Mises criterion. (a)Find the ratio,α=σ2/σ1, that prevailed during loading. ─ (b)Find the ratio,σ/σ1, that prevailed during loading. (c)Find the effective strain. (d)Assume that the tensile stress-strain curve for this steel can be approximated by σ=Kε^n with K=650MPa and n=0.22. Find the value of σ1 just before unloading. 请问要如何讲解说明这题，知道怎麽算，但不会讲解 =_= 麻烦版友们，拜托了! 万分感谢!! --

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