USE OF A COMBINED ISOTROPIC NON-LINEAR KINEMATIC HARDENING MODEL TO PREDICT EVOLUTIONARY CYCLIC STRESS-STRAIN BEHAVIOUR IN AN AUSTENITIC STAINLESS STEEL

摘要

Evaluation of fatigue damage in components is commonly carried out using power law deformation equations to define stress and strain ranges for the applied loading conditions. These equations are generally based on cyclically stabilised hysteresis loops defined for a particular strain range. Where loading conditions change or an assessment of a complex geometry is required, the component may be subjected to a range of loading conditions and variations of strain range through the component thickness. In addition, some components are subjected to relatively few, but severe, loading cycles during their lifetimes. It follows that accurate representation of the evolutionary stress-strain behaviour, prior to obtaining the cyclically stable material response, can give rise to benefits for structural integrity assessments. This paper gives details of a non-unified combined isotropic non-linear kinematic hardening model, the fast reactor state variable (FRSV) model. The specific advantage of this type of model is that it provides a good representation of the cyclic evolution of material hardening or softening behaviour. The model is used to predict the evolutionary cyclic stress-stain behaviour in an austenitic stainless steel over a range of strain ranges. The cyclic stress-strain data are obtained on standard uniaxial cylindrical test specimens. Details of the constitutive model are outlined together with the methodology used to derive the six material constants required to characterise the evolutionary cyclic plastic behaviour. Additionally, the quality of the derived parameters is assessed through comparison of the numerically calculated results with the experimental data over the strain ranges of interest.