Abstract
In the numerical simulation of failure for structures, crack initiation is normally based on a criterion that provides both the stress and the orientation of the material failure plane. Most constitutive models provide reasonably good criteria for stress, but the predictions of orientation are often at variance with experimental data. If a crack initiates in the wrong direction, it is likely that the direction of propagation will also be in error.
The object of this paper is to describe an anisotropic decohesion function that provides predictions of both stress and failure orientation which are in good agreement with basic features of experimental data. The essential new feature is the addition to the decohesion function of components of stress that are not part of the traction vector on the material failure surface. The result is that a given decohesion surface describes two general regimes of failure. For the first, the normal to the material failure surface is in a direction of principal stress, not necessarily the maximum principal stress. The second involves shear for which there exists two or more solutions for the normal. Typically, the normal vector forms positive and negative angles of equal magnitude with a principal direction of stress and the angle varies continuously with stress. Experimental data for concrete and ice are used as representative examples for isotropic and anisotropic materials, respectively. Copyright ยฉ 2006 John Wiley & Sons, Ltd.