Characterization of stable crack growth through AISI 4340 steel using cohesive zone modeling and CTOD/CTOA criterion

The criteria based on cohesive zone model (CZM) and CTOD/CTOA have been employed for analysis of stable crack growth (SCG) through AISI 4340 steel. Investigations have been reported first concerning characterization of mode I SCG using the CZM and a particular crack size in a CT specimen 8 mm thick. The characteristic data is then verified considering other mode I crack sizes and the same specimen geometry. Similar verifications have also been done considering cracks under mixed mode (I and II) loading. The same mode I cases have been studied later considering some variations of crack tip opening displacement/angle (CTOD/CTOA) with crack extension. Load-load-line displacement (LLD) predictions based on these two approaches have been compared with experimental results reported in the literature. The predictions based on the CZM are found to be closer to the experimental results. The results include the traction-separation law suitable for characterization of SCG through AISI 4340 steel under mode I and mixed mode (I and II). Similarly a CTOD/CTOA variation with crack extension for the similar purpose under only mode I loadings has been reported. Other observations on modeling of crack tip constraint effects by mixed (plane strain core plus plane stress outer domain) discretisation scheme, crack tip element size and J integral, are presented.