A study on the theories of unstable crack extension for the prediction of crack trajectories

The paper deals with the prediction of the unstable crack trajectory from the stress field existing just before the onset of extension. A criterion termed as the criterion of zero shear stress has been introduced. Some finite element and experimental studies have been carried out. The crack trajectories based on the criteria of zero shear stress, minimum strain energy density (SED), and maximum tangential stress have been compared. All the three criteria appear to be useful for predicting the complete unstable trajectory of an internal crack in tensile panels. The SED criterion is unsuitable for the edge crack examples. The usefulness of the criteria of maximum tangential stress and zero shear stress for edge crack examples are shown. The latter is noted to have some computational advantages.