Determination of critical fracture energy, Gfr, from crack tip stretch

Characterization of ductile fracture is a major problem, especially in the nuclear industry where the material behaviour in the upper shelf region is important. Use of the J−Δa curve to cover the risk of ductile fracture is popular among the designers. But, it is well known that the J−Δa curve can be geometry dependent, so, transfer of laboratory test data to the components is a problem. Serious attempts have been made in the recent past to identify a unique material function (independent of geometry) to characterize ductile fracture. Those attempts are partly successful, but there are still many aspects to be solved. The present work aims at the same direction as mentioned above.The paper has three distinct parts, namely a theoretical model, FE simulation and discussions on FE-simulated results. In the theoretical model attempts have been made to relate critical fracture energy, Gfr, with crack tip deformation (stretch) by using the final stretch theory of Michael Wnuk together with a cohesive traction–separation model. The objective of this model is to extract Gfr from local deformation of the crack tip so as to identify it as a crack growth parameter.Next, this model has been successfully implemented in FE simulation of CT specimens and TPBB specimens of ductile materials. Gfr is obtained from the local crack tip stretch together with other associated results.Finally, the results obtained from FE simulation are analysed. It is found that Gfr is a fracture parameter connected to crack tip deformation and it can simulate ductile crack growth process in a steady-state condition.