Constraint-modified J−R curves and its application to ductile crack growth

The concept of J-controlled crack growth is extended to J−A2 controlled crack growth using J as the loading level and A2 as the constraint parameter. It is shown that during crack extension, the parameter A2 is an appropriate constraint parameter due to its independence of applied loads under fully plastic conditions or large-scale yielding. A wide range of constraint level is considered using five different types of specimen geometry and loading configuration; namely, compact tension (CT), three-point bend (TPB), single edge-notched tension (SENT), double edge-notched tension (DENT) and centre-cracked panel (CCP). The upper shelf initiation toughness JIC, tearing resistance TR and J−R curves tested by Joyce and Link (1995) for A533B steels using the first four specimens are analysed. Through finite element analysis at the applied load of JIC, the values of A2 for all specimens are determined. The framework and construction of constraint-modified J−R curves using A2 as the constraint parameter are developed and demonstrated. A procedure of transferring the J−R curves determined from standard ASTM procedure to non-standard specimens or practical cracked structures is outlined. Based on the test data, the constraint-modified J−R curves are presented for the test material of A533B steel. Comparison shows the experimental J−R curves can be reproduced or predicted accurately by the constraint-modified J−R curves for all specimens tested. Finally, the variation of J−R curves with the size of test specimens is produced. The results show that larger specimens tend to have lower crack growth resistance curves.