Study on Multiaxial Inelastic Deformation under Ratcheting and Nonproportional Loading Conditions Based on Viscoplasticity Theory.

Inelastic deformation of 316 FR stainless steel under biaxial ratcheting and nonproportional straining is discussed based on viscoplasticity theory by Krempl. It is pointed out that the multiaxial ratcheting can be regraded as a special case of nonproportional loading and that the simultaneous modeling is necessary for the both behaviors. In the one of the author's previous study a viscoplastic constitutive equation was developed for nonproportional loading based on the viscoplasticity theory proposed by Krempl. An idea similar to Ohno-Wang model for ratcheting is used to extend this previous model and a viscoplastic constitutive model is developed for biaxial ratcheting and nonproportional loading. A critical value is assumed for the dynamic recovery of thekinematic hardening parameter. It is also assumed that the activating the dynamic recovery of the kinematic hardening reduces the additional hardening under nonproportional loading. It is shown that the developed model well reproduces both biaxial ratcheting and stress response under nonproportional loading.