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

The concept of J-controlled crack growth is extended to J-A(2) controlled c rack growth using J as the loading level and A(2) as the constraint paramet er. It is shown that during crack extension, the parameter A(2) is an appro priate constraint parameter due to its independence of applied loads under fully plastic conditions or large-scale yielding. A wide range of constrain t level is considered using five different types of specimen geometry and l oading 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(I)C, te aring resistance T-R and J-R curves tested by Joyce and Link (1995) for A53 3B steels using the first four specimens are analysed. Through finite eleme nt analysis at the applied load of J(I)C, the values of A(2) for all specim ens are determined. The framework and construction of constraint-modified J -R curves using A(2) as the constraint parameter are developed and demonstr ated. A procedure of transferring the J-R curves determined from standard A STM procedure to non-standard specimens or practical cracked structures is outlined. Based on the test data, the constraint-modified J-R curves are pr esented for the test material of A533B steel. Comparison shows the experime ntal 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.