On Simplified Inelastic Method Using Material's Isochronous Stress–Strain Data for Creep Analysis

Design of components or structures at elevated temperature is complex and the use of rigorous time dependent material models may not be practical for many large scale industrial problems. The use of simplified methods permits creep analysis of components that would be impractical by rigorous time dependent models. The isochronous stress–strain method is an approach that has been used extensively for the creep evaluation of elevated temperature components. In practice, the method has been used for the analysis of problems containing both primary and secondary stresses, such as, for pressure vessels with structural discontinuities or creep buckling problems. Although the simplified method has been widely accepted as an alternative to creep analysis, its limitations and accuracy of the method have not been investigated systematically and are not fully understood under complex loading conditions. This study examines the isochronous stress–strain method against a generalized time-explicit creep model. Analytical solutions are developed for three basic loading configurations, including uniaxial tension, pure bending, and torsion, in either load or displacement controlled conditions. Fundamental behaviors of the simplified method are examined and discussed.