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-effect ive manner. The specimen is a hybrid design that incorporates features from the standard K-Ia and K-Ic specimens. Details of the specimen ge ometry and associated test procedures are described. Strain gages reco rd the stress state in the specimen, and a clip gage measures the crac k mouth opening displacement. The method for extracting arrest and ini tiation toughness from the measured data is presented. Fracture experi ments 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 result s from this study were consistent with similar data established for th e same material by other researchers. A fractographic analysis identif ied cleavage as the dominant failure mode during crack propagation, wi th a conversion to ductile tearing just before arrest.