Key features arising from structural analysis of the NESC-1 PTS benchmark experiment

Abstract

Interpreting the results of the NESC spinning cylinder test represents a significant challenge for structural integrity specialists. The test was conceived to provide data on the behaviour of underclad defects and a large, through-clad defect under simulated PTS loading conditions. It contained the following structural features, the understanding of which is essential to obtaining a full interpretation of the test results: • cladding effects; • residual stresses; • constraint effect; • effective crack front width; • warm prestressing effect. The paper presents the results of the NESC-1 test with particular reference to the essential features listed above, and their relative importance. The paper notes that the most significant uncertainty factor that influenced the integrity assessment of the test is the variability of material toughness. This is in relation to both intrinsic variability (scatter) and that of the near-surface (clad/HAZ/base metal) region. There is some evidence to suggest that a loss of constraint influenced the near-surface behaviour of the largest underclad defect and the through-clad defect. However, the higher toughness of the HAZ, reduced crack front width (relative to that of a 25 mm CT specimen) and cladding effects are significant factors, too. The paper concludes by pointing out the need to provide (through continued international collaboration) validated procedures for relating fracture test data on specific specimen geometries to local constraint parameters estimated from 3D finite element simulations. Here, it is apparent that significant progress is to be gained from a formal unification of local approach methodology, the master curve description of cleavage toughness and ‘classical’ constraint-based fracture assessment methods.