SOPHISTICATED CREEP-FATIGUE LIFE ESTIMATION SCHEME FOR PRESSURE VESSEL COMPONENTS BASED ON STRESS REDISTRIBUTION LOCUS CONCEPT

摘要

High temperature components are operated under cyclic thermal transient. Creep-Fatigue is the most dominant failure mode to be considered in Elevated Temperature Design of these components. Design limit for computed thermal stress is allowed to exceed yielding, because thermal stress is generally regarded as a displacement controlled one. Since creep deformation is considered as additional inelastic behavior, methodology to estimate inelastic strain concentration should be prepared in a design standard. Though inelastic FEM analyses can be applied to calculate inelastic strain concentration magnitude, it is well known that prediction is affected by applied constitutive model. Current design codes recommend to apply elastic FEM and to estimate inelastic strain behavior by simplified method. This paper presents sophisticated technique to estimate inelastic strain behavior based on Stress Redistribution Locus (SRL) method. Applicability of SRL concept is discussed with a help of FEM results for representative components of pressure vessel components such as nozzle, skirt and tube sheet.