Some Consequences of Stress Range Dependent Constitutive Models in Creep

Detailed procedures for high temperature design remain elusive, even though advanced material models for creep have been developed over several decades and (some) employed in detailed inelastic finite element analysis. The simplified design approaches which are available have in general been developed on the basis of simple power-law creep models, but most have not been re-assessed if more advanced creep models are adopted. Over many years fairly simple alternatives to the power-law have been available but few have been similarly assessed in the design context. These simple alternatives have usually focussed on the problem of stress range dependency: the form of the constitutive model, even for secondary creep, changes as the stress increases from low through moderate to high stress. In this paper some simplified design approaches are initially re-assessed for such creep laws using two simple structures.