Comparison of Methods for Predicting Ductile Crack Growth Instability

摘要

Two approaches have been suggested to predict the conditions for instability resulting from ductile crack propagation from a pre-existing defect. These are the T approach of Paris et al., and the I approach of Turner. The Paris T approach is based on the stability of the equilibrium state between the applied value of the J integral and the J versus crack extension material resistance curve. Under linear elastic conditions instability may be interpreted as occurring when the second differential of available energy exceeds that required for crack extension. The Turner approach, on the other hand, is based on the balance between the energies available and required for crack extension. A comparison of the two approaches has been carried out by re-analyzing the instability results of Paris et al., obtained using single-edge-notched, three-point bend specimens under conditions where the J integral can be considered as a crack tip field characterizing parameter. Under these conditions both approaches, although based on different assumptions, are numerically similar and the predicted conditions for instability are in good agreement with experimental results.