Local fracture criteria: lengthscales and applications

Cohesive zone elements for the modeling of fracture generally use fixed cohesive properties to describe the process of material separation. Results of crack growth simulations by the use of the modified Gurson relation demonstrate that in case of ductile fracture the separation parameters cohesive strength and characteristic length, however, do not remain constant throughout a crack growth analysis and their values are not known a priori. This finally leads to the need of further developments in cohesive zone models where both cohesive zone parameters are adjusted by triaxiality. In the present paper such a model is presented, its material parameters are derived and an application to the simulation of crack growth in a ductile metal is demonstrated. This application shows that the ''triaxiality dependent cohesive zone model'' can in detail reflect the changes in lengthscale of separation and cohesive strength as the crack propagates through the ductile metal. (orig.)