TRANSIENT NONPROPORTIONAL CYCLIC PLASTICITY

A general framework of constitutive relations for transient isotropic cyclic hardening and softening of metals under arbitrary non-proportional biaxial loading is introduced. It is shown that accumulated plastic strain is useful to correlate rate of hardening but not the magnitude of isotropic hardening incurred during nonproportional loading. An evolution equation is introduced which decomposes the isotropic hardening process into nonfading and fading memory of prior cyclically stable states. The current state of the material is a history functional of the maximum plastic strain range and nonproportionality of loading. All constants for evaluation of this history functional are completely obtained from uniaxial tests and several tension-torsion tests of thin-walled tubular specimens. The equations are used to predict the cyclic hardening response of annealed stainless steel 304 to three very different complex biaxial cyclic loading paths.