On the application of cohesive crack modeling in cementitious materials

Abstract

Cohesive crack models—in particular the Fictitious Crack Model – are applied routinely in the analysis of crack propagation in concrete and mortar. Bridged crack models—where cohesive stresses are assumed to exist together with a stress singularity at the crack tip—on the other hand, are used typically for multi scale problems such as crack propagation in fiber reinforced composites. Mortar and concrete, however, are multi-scale materials and the question naturally arises, if bridged crack models in fact are more suitable for concrete and mortar as well? In trying to answer this question a model for a centrally cracked sheet is established applying semi-analytical, bridged and fictitious crack modeling. The semi-analytical crack model is compared with a FEM analysis and it is demonstrated, that the standard fictitious crack implementation in FEM packages (in this case DIANA) provides a good approximation. Further, a quantitative condition is established indicating when a bridged crack model can be approximated with a cohesive crack model with smooth crack closure in terms of the ratio between the energy dissipation associated with the crack tip and the process zone.