The creep behavior of structural materials is often measured using uniaxial tension creep rupture tests. Unfortunately, the time required for austenitic steel samples to rupture under ideal (i.e. elastic stress) conditions is prohibitive. To accelerate creep rupture in these samples, a tensile stress in excess of the material yield strength 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 yield-induced plastic flow that may occur during such accelerated tests.
Using validated finite element models, the effects of creep and yield-induced plastic strain have been decoupled for a series of accelerated creep tests using 316H austenitic steel. The influence of continued yielding after the initial sample loading was predicted to be significant, which suggests the diffuse necking in the samples due to creep is responsible for stress intensification and further yield through the tests. These results suggest the initial plastic loading in accelerated creep tests may significantly influence the measured creep rupture time in these samples.