Detailed two-dimensional and three-dimensional finite element (FE) analyses of double-edge cracked tension (DE(T)) specimens are carried out to investigate the effect of in-plane and out-of-plane constraint on experimental J testing schemes and crack tip triaxial stresses. FE analyses involve systematic variations of relevant parameters, such as the relative crack depth and plate width-to- thickness ratio. Furthermore, the strain hardening index of the material is systematically varied, including the perfectly plastic (non-hardening) cases. Based on the FE results, a robust experimental J estimation scheme is proposed. It is also found that crack tip constraint states in the DE(T) specimen strongly depend on the relative crack depth, and thus can offer an advantage in investigating constraint effects on toughness. However, the specimen thickness, required to maintain plane strain conditions, is much larger, compared to standard bend type specimens. Detailed results for crack tip stress triaxiality for 3-D DE(T) specimens are given to roughly estimate crack tip constraint in testing DE(T) specimens.
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