It has long been appreciated that plastic dissipation contributes significantly to the total work of fracture in metals and polymeric solids. To quantify this dependence, the fracture process may be represented in terms of a traction- separation law, for which the work of separation per unit area and the peak normal stress are characteristic parameters, while the material around the growing crack is elastic-plastic. Thus, the near tip fracture toughness is fixed, while the fracture toughness corresponding to the remote applied load is calculated.
In some of the studies to be presented this type of cohesive zone modeling is used to determine resistance curves for crack growth under small scale yielding conditions. The cases studied include crack growth in a homogeneous material, T-stress effects on the toughness, mixed mode crack growth along the interface to a rigid solid, and mixed mode crack growth between dissimilar elastic-plastic solids.
Results are also presented, where a cohesive zone model is used to represent the strength of the fibre-matrix interface in a metal matrix composite. This is also interface crack growth under various mixed mode conditions, but the conditions here are full scale yielding in configurations determined by the fibre geometries and spacings.
For some cases of interface failure the work of separation and the peak stress may be estimated by a micromechanical analysis. Such an analysis is illustrated for ductile failure under normal separation.