Volume 16, Issue 2 (March 1988)
Development of a Miniaturized Specimen Technique for Fracture Toughness JIc Measurement
The effect of specimen thickness on fracture toughness JIc has been investigated with compact tension specimens using the multispecimen R-curve method. HT-9 and A533B-1 steel specimens with thicknesses of 25(1TCT), 10(0.4TCT), 3, and 0.5(0.2TCT) mm were tested. Some of them did not satisfy the ASTM E 813 size requirement for valid JIc. The through-thickness distribution of the plastic energy dissipation or work done within the intense strain region at the crack tip was measured by 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. A new JIc evaluation procedure for invalid specimen size is proposed using rigid plastic analysis and shear fracture measurements with recrystallization-etch or fractographic observations. Predicted JIc values are compared with the JIc values obtained from valid specimen size. This miniaturized specimen technique may be applicable to post-irradiation fracture toughness testing.