A combined numerical/experimental study of ductile crack growth after a large unloading, using T∗, J and CTOA criteria

The J-integral is commonly used to determine the resistance of plastically deformed structures to continued crack growth. This approach is only valid for monotonic loading and small crack growth; yet it is believed conservative for all general loadings. Another parameter, T∗ , has been formulated, which is theoretically valid under a wide range of conditions. These two plastic fracture criteria, along with CTOA (crack tip opening angle), were examined after a cycle of loading/unloading to zero load followed by reloading. The results of the numerical/ experimental study showed that the T∗ parameter accurately predicted the behavior (crack growth after 50% reloading), while the other parameters (J and CTOA) were seriously anticonservative.