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This study explores the possibility of using J-Q-related constraint concepts to describe the nature of the crack-tip loading in a reactor pressure vessel (RPV) under pressurized thermal shock (PTS) conditions. The fracture response of an RPV subjected to three postulated PTS transients that incorporate effects of loading, unloading and reloading (via repressurization) of the crack tip has been examined. Analysis results indicate that minimal loss of constraint relative to conditions of K-dominant small-scale yielding (SSY) is observed during the monotonic-loading phase of the transients. The extent of constraint loss upon reloading is sensitive to the time of repressurization, with minimal (significant) loss of constraint observed for the transient with “early” (“late”) repressurization. The nature of the constraint loss, when it occurs, corresponds to a spatially varying hydrostatic field relative to K-dominant SSY conditions. Based on an assumed correlation between loss of crack-tip constraint and fracture toughness, preliminary analysis results indicate that inclusion of constraint effects could provide significant reduction in the value of the calculated conditional probability of vessel failure relative to their exclusion.
PTS, J-Q theory, crack-tip constraint, fracture toughness, warm prestress, unloading
Senior Research Engineer, Saint-Gobain/Norton Industrial Ceramics Corporation, Northboro, MA