Constraint-corrected failure assessment diagrams based on crack tip plastic zone size

Failure assessment diagram (FAD) is affected by constraints, and it has been corrected by in-plane T-stress (T11) in the R6 defect assessment procedure, but the influence of out-of-plane constraint is usually neglected. The combined effects of in-plane and out-of-plane constraints on FAD are investigated in this work. Crack tip plasticity can characterize the in-plane and out-of-plane constraints comprehensively. Hence, by using plastic zone size (rp0), a new correction model of FAD is proposed theoretically in small scale yielding condition. Then the influences of constraints on failure assessment curves and allowable loads are analyzed in central-cracked unstiffened and stiffened plates, and the failure mechanisms are studied too. The results reveal that, compared with traditional FAD and T11-stress corrected FAD, the new correction model of FAD based on rp0 is more accurate and reasonable; and both in-plane and out-of-plane constraints play important roles in failure assessment curves and allowable loads. Additionally, the new correction model of FAD is an effective approach to analyze the failure mechanisms, and the failure modes depend on crack length and type of structures.