Application of the two-parameter J-A2 description to ductile crack growth

Typical ASTM fracture testing determines the J-integral resistance (J-R) curve or fracture toughness (J(IC)) based on specimens with high-constraint geometry such as those specified in ASTM E 1737-96. A three-term asymptotic solution with two parameters, J and A(2) (a constraint parameter), has been developed for characterizing the constraint effect of various geometries. The present paper extends the J-A(2) characterization of a stationary crack tip to the regime of stable crack growth. Similar to the concept of J-controlled crack growth, the J-A(2) description can be approximately used to characterize ductile crack growth under certain amount of crack extension. The region of J-A(2) controlled crack growth is much larger than that controlled by the J-integral alone. From the relationships between A(2) and the test data, J(IC), and tearing modulus, T-R, the coefficients used to define a J-R curve can de determined. For non-standard specimens or actual structures, once the constraint parameter A(2) is determined, the J-R curves appropriate for these geometries can then be obtained. A procedure of transferring J-R curves determined from the standard ASTM procedure to non-standard specimens or flawed structures is outlined in the paper.