Fracture Assessment Procedure for Structural Components Under Cyclic and Dynamic Loading

摘要

A new fracture assessment method that includes 2 concepts is presented in this paper for structures subjected to large cyclic and dynamic loading. One is a reference temperature concept. The fracture toughness under cyclic and dynamic conditions is replaced by the static toughness without pre-strain at a reference temperature of T - △T_(PD), where T and △T_(PD) are the service temperature and the temperature shift of the fracture toughness. △T_(PD) is related to the flow stress elevation by pre-strain and dynamic loading. The other is a correction of CTOD (Crack Tip Opening Displacement) for constraint loss in structural components in large-scale yielding. The CTOD toughness correction is carried out with the equivalent CTOD ratio β defined on the basis of the Weibull stress criterion. These 2 concepts are implemented in the Japanese Engineering Standard, WES 2808. The procedure for determining β is standardized in the IST project in Japan, discussed below. For integrity assessments of pipelines with a high internal pressure, the effect of biaxial loading on β is addressed by 3-dimensional FE analysis.