Influence of specimen size on I-III mixed mode fracture, fracture toughness JIC and plastic dissipation with crack growth dWp/da

Abstract The effect of thickness on the fracture toughness, plastic energy dissipation or work at the crack tip and stretch zone has been investigated with compact tension specimens. A533B-1 steel specimens with thicknesses of 25 (1TCT), 10(0.4CT), 5, 3 and 0.5 (0.2CT) mm were tested. Some did not satisfy the ASTM E813 size requirement for fracture toughness J IC . J IC was determined from a multi-specimen resistance curve. The through-thickness distribution of the plastic energy dissipation or work done within the intense strain region at the crack tip was measured using a recrystallization-etch technique. Fractographic examinations of the variation of stretch zone width and fracture modes along the specimen thickness were performed by scanning electron microscopy (SEM), where flat fracture and shear fracture regions have been distinguished. This indicated how changes in specimen thickness affect plastic deformation, fractography and the overall fracture toughness. This investigation also finds that plastic energy absorbed at the crack growth dW p /da in the mid-section of a specimen has a constant value irrespective of specimen geometry and size during the steady progagation stage of crack growth.