Development of a novel constitutive model for improved structural integrity analysis of piping components

摘要

Elbows are critical components of piping systems in the nuclear power industry, however, existing constitutive models are unable to simulate the low-cycle fatigue and ratcheting responses of this component. This study developed a constitutive model, incorporating a novel and various advanced uniaxial and multiaxial modeling features for successful response simulations of stainless steel (SS) 304 short and long radius elbows subjected to internal pressure and opening-closing displacement-controlled cycles. Simulated results demonstrate that if an existing advanced constitutive model is calibrated solely based on the material level responses, it is not able to simulate the elbow responses with acceptable accuracy. This drawback is primarily attributed to the fact that the prior loading and loading histories at different locations in an elbow are different and not represented by the loading histories of the material experiments performed for model parameter determination. Hence, model development and simultaneous experimental verification at the material and component levels trace the drawbacks of the constitutive modeling features effectively. Such evaluation of the simulated responses at two levels provided a novel modeling concept in improving the elbow response simulations quite satisfactorily. The implemented modeling features and response simulations at both levels are presented and critically analyzed for providing insights in developing robust constitutive models for structural integrity analysis.