SUMMARYWe introduce the notion of time continuity for the analysis of cohesive zone interface ÿnite element models. We focus on 'initially rigid' models in which an interface is inactive until the traction across it reaches a critical level. We argue that methods in this class are time discontinuous, unless special provision is made for the opposite. Time discontinuity leads to pitfalls in numerical implementations: oscillatory behavior, non-convergence in time and dependence on nonphysical regularization parameters. These problems arise at least partly from the attempt to extend uniaxial traction-displacement relationships to multiaxial loading. We also argue that any formulation of a time-continuous functional traction-displacement cohesive model entails encoding the value of the traction components at incipient softening into the model. We exhibit an example of such a model. Most of our numerical experiments concern explicit dynamics. Copyright
COHESIVE ZONE MODELINGCohesive zone modeling is one of the most widely used techniques for modeling fracture. It is predicated on the fact that a process zone forms ahead of the crack front, in which material softening takes place. In the spirit of Dugdale [1] and Barenblatt [2] cohesive zone modeling idealizes the process zone with a weak interface of thickness zero. A material point on this interface is initially undamaged, but when the traction across the interface reaches some critical level it starts losing cohesion and gradually softens until a stress-free surface is created. In one dimension, softening is manifested as a gradual drop in traction with increasing relative displacement. Decohesion is usually modeled by a pointwise relationship between the traction across the interface and the relative displacement between the two faces of the interface.We formulate the problem in the following setting. Let the initial conÿguration of the body be denoted B 0 , and let M(X; t) : B 0 × [0; T ] → R 3 be its deformation map. The ÿrst argument to M is a coordinate X in the undeformed body, and the second argument is time. This map is * Correspondence to: