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An important aspect of any safety analysis of pressurized components is estimating the in-service fracture toughness and structural stability of these components.Of particular interest in the power generation and process industries is the assurance of leak-before-break for any pressurized components. The fracture toughness values of these components are determined using standard ASTM specimens and testing procedures. For internally-pressurized tubes, the fracture toughness values are used in combination with theoretically-derived crack driving forces to determine the unstable, or critical, crack length. The fracture toughness value of the tubes are found using compact toughness specimens (CTS) removed from the tube wall. Elastic and elastic-plastic, three-dimensional, finite element analyses of standard CTS and axially-cracked, internally pressurized tubes have been performed to examine the various constraint methodologies that can correlate the CTS and pressurized tube fracture values. The stress-based methodologies, viz, J-T/J-Q, von Mises equivalent and principle stress zone volumes, and a stress-strain technique were applied to the analysis results. A direct correlation between the planer CTS crack tip stress fields and the complex three-dimensional stress field at the crack tip of an axially-cracked, internally pressurized tube could not be found.
zirconium, compact toughness specimen, pressure tube, finite element, fracture determination, J-integral, constraint evaluation
Research engineer, Atomic Energy of Canada Limited, Chalk River Laboratories, Ontario,