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

Abstract

The concept of J-controlled crack growth is extended to J−A 2 controlled crack growth using J as the loading level and A 2 as the constraint parameter. It is shown that during crack extension, the parameter A 2 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 J IC, tearing resistance T R 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 J IC, the values of A 2 for all specimens are determined. The framework and construction of constraint-modified J−R curves using A 2 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.