CREEP DEFORMATION OF TYPE 316H AUSTENITIC STAINLESS STEEL AT 550℃ AND THE EFFECTS OF ELASTIC FOLLOW-UP

摘要

Elastic follow-up occurs in structures when localized regions in a component undergo non-linear deformation while the surrounding global material remains elastic. Often, elastic follow-up is described as belonging to a set of boundary conditions that lie between load and fixed displacement control. This condition is known to exist in many engineering components operating at high temperature. In this paper conventional creep models are described to illustrate the effects of elastic follow-up, particularly during primary creep of a Type 316H stainless steel operating at 550℃. Experiments to validate the models are explained and compared to the models. The experiments were set up to replicate two bar models subjected to remote fixed displacement. The forces in the experiment were allowed to relax for three different values of elastic follow-up. It is demonstrated that conventional creep stress relaxation (without elastic follow-up) can be described adequately by empirical forward creep equations. However, the predicted response when elastic follow-up is present is highly dependent on whether time or strain hardening behaviour is assumed. A differential strain hardening model, that takes account of prior accumulated strain and the rate of stress relaxation, is shown to provide an improved model.