Resetting scheme for plastic strain surface in constitutive modeling of cyclic plasticity

Abstract

Key wordsCyclic plasticity, constitutive model, cyclic hardening, strain range dependence, plastic strain surface.A resetting scheme is proposed for correctly evaluating the plastic strain range to analyze structural components subjected to regular cyclic loading following pre-loading. In this scheme, a plastic strain surface, referred to as the plastic-strainrange surface in the present paper, is reset to a point and re-evolves every cycle, with its size at the end of the last cycle considered to be the plastic strain range of the current cycle. This resetting scheme provides a definite value for the evolution parameter of the plastic-strain-range surface irrespective of the amounts of cyclic hardening, pre-straining, and ratcheting. The resetting scheme is implemented in a cyclic viscoplastic model in finite element methods, and is applied to analyze a notched bar subjected to cyclic loading at its ends. Furthermore, the validity of the resetting scheme for non-proportional cyclic loading is examined by analyzing the cyclic behavior along elliptic and rhombic strain paths. It is shown that the resetting scheme allows the use of a definite value for the evolution parameter of the plastic-strain-range surface in the presence of any cyclic hardening and/or ratcheting. Moreover, it is shown that the resetting scheme can be valid for cyclic loading with a certain degree of non-proportionality.

Effect of cyclic hardening on stress relaxation in SUS316HTP under creep-fatigue loading at 700ºC: experiments and simulations

“…The constitutive model was implemented in Abaqus using a user subroutine UMAT by extending the UMAT program developed by Ohno et al (2016bOhno et al ( , 2017b. From here on, t * denotes the time elapsed after the onset of strain holding, and σ relax indicates the stress attained at the end of stress relaxation under strain holding.…”

“…The resetting thus provides a definite value for the evolution parameter η of the PSR surface irrespective of the amount of cyclic hardening, pre-straining, and ratcheting. In this study, η is set to 0.4, as verified by Ohno et al (2017b). Table 4 gives the material parameters used in this study, which were determined using the following procedure.…”

New formulation of nonlinear kinematic hardening model, Part II: Cyclic hardening/softening and ratcheting

“…The main feature of q and p is that they change in a stepwise manner, providing stepwise dependence of the A and B parameters on accumulated plastic strain. This has been shown to give more certainty in modelling strain range dependence (Ohno et al, 2018). The stepwise change of previously accumulated plastic strain p has also shown improved description of the stress-strain curve shape (Voyiadjis et al, 2012).…”

“…This model has shown good prediction ability of peak stress variation as well as stress-strain curve shape of stabilised hysteresis loops for the low cycle fatigue region. Ohno et al (2018) proposed revisiting the concept of plastic memory surface (Chaboche, 1979), highlighting the uncertainty of the choice of the evolution parameters of the plastic strain surface when cases of variation in mean plastic strain due to pre-straining and ratcheting may arise. A resetting scheme is proposed for plastic memory surface, in which the strain surface is reset to a point every cycle, providing definite values for the evolution parameters.…”

“…It is proposed to consider the change of plastic strain range in a stepwise manner, where transition between strain ranges occurs when the critical distance in plastic strain space stops growing. This can be considered as generalization of the re-setting approach (Ohno et al, 2018). Two hardening parameters of the kinematic hardening rule are formulated as functions of plastic strain range and previously accumulated plastic strain.…”