1 Australian Nuclear Science and Technology Organisation

Predicting the High-Temperature Creep Rupture Behaviour of Austenitic Steel using Finite Element Analysis

C.J. Hamelin1, W. Payten1 1Australian Nuclear Science and Technology Organisation, Lucas Heights NSW 2234, Australia e: [email protected]

The high-temperature creep behaviour of austenitic steel is often measured using uniaxial tension creep rupture tests. An ideal test would be conducted under the application of an elastic tensile stress, to eliminate the influence of material plasticity. Unfortunately, the time required for austenitic samples to rupture under these conditions is typically prohibitive. To accelerate creep rupture in these samples, a tensile stress in excess of the yield strength of the material is often applied and the post-load deformation is assumed to be largely creep-based. There is currently no method of measuring the creep deformation separately from the plastic deformation that may be applied during testing. In the present study, numerical simulations of uniaxial tension creep rupture tests in AISI 316H austenitic stainless steel have been conducted using finite element analysis (FEA). Representative FE models have been constructed using the ABAQUS commercial finite element package. The first stage in model validation was to compare the predicted plastic deformation in the models to experimental data. The plasticity model used was found to predict the plastic behaviour of the steel to within measurement uncertainty. The next stage of model validation was to assess the accuracy of the creep deformation model used; as this model was based on design code, it was found to be conservative and required calibration to improve model accuracy. Finally, the increased deformation due to damage accumulation during tertiary creep was simulated using a strain energy ductility exhaustion (SEDE) model, which had been calibrated using the measured data set. Numerical solutions were found to be in good agreement with measurements. Using these validated FE models, it was possible to decouple the effects of creep and plastic deformation during testing. Significant plastic deformation was predicted following the initial sample loading, which suggests the diffuse necking in the samples due to creep is responsible for local stress concentration and further plasticity. It was also determined that since the SEDE model was calibrated to test data, the predicted creep damage accumulation is a function of the total inelastic strain rate, and not the creep strain rate as is often assumed. As such, considerable damage is predicted to accumulate during the initial plastic loading of the sample; such predictions suggest this loading may significantly influence the measured creep rupture time in these samples. The authors wish to acknowledge M.W. Spindler (EDF Energy) for the provision of an extensive creep rupture database for model validation.