An energetic approach for large ductile crack growth in components

The practical prediction of ductile crack growth for the evaluation of component integrity is based on the characteristic value of J at crack initiation, J(0.2) or J(IC), and on the J-Deltaa curve that characterizes the crack propagation. However, the J-Deltaa curve was shown to be scale dependent when crack propagation becomes important (more than few mm): for instance, it is not transposable from small specimens to structures. In this context, a proposition applicable to large ductile crack propagation in components is made. It is founded on energetic parameters such as the J integral proposed by Rice or the modified J(M) proposed by Ernst. A fracture energy dissipation rate. related to the dissipated plastic strain energy and noted G(fr), is proposed and is shown to be a material characteristic. The paper shows with two examples how the material G(fr) value is deduced from fracture tests and how it can be used for the prediction of the behavior of the structure, for more than 90 mm of crack propagation.