The Cohesive Zone Model Applied to Blunt Cracks

Many practical situations involve blunt cracks, which have a finite tip radius and no stress singularity due to the presence of a notch or self-blunting behavior. In these cases, linear elastic fracture mechanics does not apply. However, the cohesive zone model (CZM) can be used to predict the onset of fracture for blunt cracks. In this paper, the CZM is applied using finite element analysis to study the fracture of blunt cracks. Quasi-static three point bending is modelled, where fracture initiates by decohesion of a thin line of cohesive elements obeying a pre-defined traction-separation law. The effect of modelling with a bilinear traction- separation law is investigated along with the cohesive energy and cohesive stress parameters for different notch tip radii. Using the fracture load and J-integral at crack growth initiation, a non-dimensional critical energy release rate is determined as a function of a non-dimensional notch radius. A comparison is also made to the stress at a distance criteria along a line proposed by Taylor, and to the stress and energy fracture criterion proposed by Williams and Patel.