STRESS INTENSITY FACTORS OF SLANTED THROUGH-WALL CRACKS IN PLATE AND CYLINDER

摘要

For Leak-Before-Break (LBB) analysis of nuclear piping, a circumferential through-wall crack (TWC) with the crack front parallel to the cylinder radius is typically postulated, i.e., an idealized TWC. Such assumption simplifies the LBB analysis significantly. However, in reality, an internal surface crack grows through the wall thickness and penetrates through the wall thickness at the deepest point. Hence, a TWC with different crack lengths at inner and outer surfaces is formed. Such a TWC is referred to as a "slanted TWC" in the present study. Leak rates as well as SCC and fatigue crack growth rates of slanted TWC are expected to be quite different from those of postulated idealized TWC. In this context, characterization of the actual TWC shape during crack growth due to fatigue or stress corrosion cracking is essential for accurate LBB analysis. Based on detailed 3-dimensional (3-D) elastic finite element (FE) analyses, the present paper provides stress intensity factors (SIFs) for plates and cylinders with slanted TWCs. As for loading conditions, axial tension was considered for the plates, whereas axial tension and global bending were considered for the cylinders. In order to cover the practical range of crack sizes, the geometric variables affecting the SIF were systematically varied. Based on FE analysis results, SIFs along the crack front, including the inner and outer surface points, were provided. The SIFs of slanted TWC can be used to evaluate the fatigue crack growth of a TWC and to perform detailed LBB analysis considering a more realistic crack shape.