On the analysis of mixed-mode failure

The present paper is concerned with the problem of mixed-mode fracture, especially where such failure occurs along a plane of weakness at a bimaterial interface or by interlaminar failure in polymer fiber-composite materials. Firstly, two different schemes for analyzing such mixed-mode failures are discussed. These schemes are: (1) a method based upon a consideration of the local singular field ahead of a crack tip, and (2) a global method based upon a consideration of the applied energy release rates. Secondly, experimental data taken from the literature are reviewed and it is concluded that the latter scheme results in a more consistent interpretation of the data. Indeed, in several cases the global method clearly gives far better agreement between the theoretical predictions and the observed results. The reasons for this are suggested to be the very localized nature of the singular-dominated region ahead of a crack tip in many test specimens and the relatively large damage zone in the materials studied. Finally, the present work has led to the proposal of a general criterion for fracture under mixed-mode loading.