The investigation of primary creep regeneration for 10%Cr martensitic steel: Unified constitutive modelling

Abstract

An elastic-viscoplastic constitutive material model is developed for the representation of the creep response of a 10%Cr steel under cyclic loading conditions. It has been shown that the model is able to describe primary creep regeneration (PCR), i.e. the incidence of a period of high creep strain rate following a stress reversal. The developed model is a variant of the well-known Chaboche viscoplastic constitutive model, and employs a bi-term power-law equation to represent the stress-regime dependence of the viscoplastic strain rate response. Back stress and drag stress are used to describe the kinematic and isotropic hardening/softening behaviour of the material, respectively. The evolutions of back stress and drag stress consider contributions from strain hardening, dynamic softening, static recovery and cyclic hardening/softening. The effectiveness of the developed model for describing the sensitivity of the PCR behaviour to different loading parameters (e.g. reverse-loading magnitude and duration) and to represent the effect of PCR activation on the overall strain accumulation behaviour of the material is discussed. Furthermore, the predictive capability of the model is demonstrated for describing the response of the material during two independent benchmark tests; a stress-varying creep and a low-cycle fatigue experiments.