Low-Cycle Fatigue and Ratcheting Responses of Elbow Piping Components

Abstract

The objective of this study was to investigate low-cycle fatigue and ratcheting responses of elbows through experimental and analytical studies. Low-cycle fatigue and ratcheting damage accumulation in piping components may occur under repeated reversals of loading induced by earthquake and/or thermomechanical operation. Ratcheting and fatigue damage accumulation can cause failure of piping systems through fatigue cracks or plastic buckling. However, the ratcheting damage induced failures are yet to be understood clearly; consequently, ASME Code design provisions against ratcheting failure continue to be a controversial issue over the last two decades. A systematic set of piping component experimental responses involving ratcheting and a computational tool to simulate these responses will be essential to rationally address the issue. Development of a constitutive model for simulating component ratcheting responses remains to be a challenging problem. In order to develop an experimentally validated constitutive model, a set of elbow experiments was conducted. The loading prescribed in the experiments involved displacement-controlled or force-controlled in-plane cyclic bending with or without internal pressure. Force, displacement, internal pressure, elbow diameter change, and strains at four locations of the elbow specimens were recorded. This article presents and discusses the results from the experimental study. A sister article evaluates seven different constitutive models against simulating these elbow ratcheting and fatigue responses.