Constraint effects on ductile crack growth in cladded components

摘要

This report describes results of a research program which is seeking an improved understanding of some issues that may significantly influence the fracture risk of cladded components. It has been shown that crack-tip constraint (degree of stress triaxiality) is an important issue in transferring fracture toughness data from laboratory specimens to structures. Shallow cracks and multiaxial loading are two important factors which influence crack-tip constraint in reactor pressure vessels. These two issues are investigated and addressed independently as Part A and Part B in this work. In Part A, a two-parameter approach based on the J-integral and the constraint parameter h was examined for ductile crack growth in cladded specimens. In Part B, the crack-tip fields of some surface crack configurations through the cladding were investigated in two types of reactor pressure vessel subjected to severe pressurized thermal transients, which introduced biaxial loading on the cracks. From these two studies, it can be concluded that any increase in crack-tip constraint conditions resulting from biaxial loading would act in opposition to the relaxations of crack-tip constraint that have been demonstrated for shallow cracks. These opposite trends indicate that the conventional one-parameter description (K or J) may be applicable with sufficient accuracy for integrity assessments of the actual crack configurations. However, further investigations are required to better understand the biaxial loading effects on initiation and propagation of ductile crack growth. Some general conclusions and a procedure for engineering fracture assessment of cladding cracks are outlined in Part C. 44 refs, 42 figs. (Atomindex citation 26:052203)