Elastic-Plastic Fracture Toughness: A Comparison of J-Integral and Crack Opening Displacement Characterizations

The geometry dependence of the J-integral and crack opening displacement at fracture initiation, J_i and (COD)_i, is examined for HY-80 steel using precracked bend specimens having thicknesses ranging from 1.6 to 53mm. The amount of crack growth at selected points on the load-deflection diagram was delineated using an unload-heat tint procedure. Resistance curves of J and COD versus crack extension were constructed to determine critical values of these parameters at incipient crack movement. Results are interpreted in terms of previously proposed minimum size requirements for valid J_i measurement. The adequacy of the Rice-Srawley J-integral formula for the bend specimen and the utility of J and COD values at maximum load are also considered.