Energy Release Rate Cannot Predict Crack Initiation Orientation in Domains with a Sharp V-notch Under Mode III Loading

The energy release rate (ERR) proposed by Irwin based on a theory by Griffith [1, 2] has been extensively used as a fracture criterion in 2D for brittle domains. Under in-plane mixed mode loading (modes I+II), the direction of crack initiation from cracks and sharp V-notches was determined by the orientation at which the ERR attains its maximum. Using the newly developed asymptotic expansion presented in [3] verified by direct results from finite element analyses we demonstrate that the ERR under mode III cannot predict the fracture initiation direction correctly. The ERR maximum value is always obtained along the V-notch bisector, contrary to experimental observations. This forbids the ERR to be applied as a failure initiation criterion in cases where mode III is dominant.