A procedure for fracture toughness testing using a chevron-notched crack-arrest specimen

A new chevron-notched crack-arrest (CNCA) specimen has been developed for determining the fracture toughness of metals in a more cost-effective manner. The specimen is a hybrid design that incorporates features from the standard K-Ia and K-Ic specimens. Details of the specimen geometry and associated test procedures are described. Strain gages record the stress state in the specimen, and a clip gage measures the crack mouth opening displacement. The method for extracting arrest and initiation toughness from the measured data is presented. Fracture experiments using the CNCA specimen were conducted to determine K-a and K-c for A533-B reactor grade steel at 23 degrees C. The K-a and K-c results from this study were consistent with similar data established for the same material by other researchers. A fractographic analysis identified cleavage as the dominant failure mode during crack propagation, with a conversion to ductile tearing just before arrest.