Crack Growth in 18G2A Steels With Different Constraint

A constraint theory in fracture mechanics is used to analyze the test data of 18G2A steels using single edge-notched bend (SENB) specimens with various crack depth to specimen width ratios (a/W). A bending correction factor is included in the two-parameter (J-A₂) asymptotic solution to improve the theoretical prediction of the stress field for deep cracks under large scale yielding condition, where J is the J-integral and A₂ is the constraint parameter, which depends on the in-plane geometry of the cracked body (a/W). As a result, the valid region for a traditional J-controlled crack growth is extended, and the ASTM specimen size requirements for fracture toughness testing can be relaxed. In addition, it is shown that the functional dependence of J-R curves on A₂ for 18G2A steels is established with test data; and the predicted J-R curves agree very well with the experimental curves. This ensures the transferability of laboratory test data to an actual structure provided the constraint level (A₂) of the cracked structure is known or determined. This allows an appropriate J-R curve with the same constraint level to be constructed and used in flaw stability analysis of any cracked body.