A mixed-mode cohesive-zone model accounting for finite dilation and asperity degradation

A cohesive zone model is formulated to describe the mechanics of initiation and propagation of cracks and the associated asperity degradation and nonlinear dilation along structural interfaces of quasi-brittle materials, such as concrete, rocks and masonry, subjected to monotonic or cyclic loading. Using a two-scale approach, a cohesive-law is determined at each point of a smooth macroscale interface by resolving a problem at the micro-scale for a representative interface area (RIA), where the geometry of the asperities is modelled using three differently inclined microplanes. On each microplane a cohesive-frictional cohesive law is then used. In this paper, the finite depth of the asperities is accounted for by considering the progressive reduction in contact area between each couple of interfacing microplanes for increasing opening (macro-scale) relative-displacement. Furthermore, the rupture of the asperities and associated flattening of the fracture surface is captured by a progressive reduction of the inclination angles of the microplanes in the RIA. Numerical examples are reported to assess the sensitivity of the shear-stress slip curves and of the nonlinear dilation upon the geometry of the asperities in the RIA. Numerical-experimental comparisons are then presented to illustrate the predictive capability of the model in simulating granite rock joints subjected to monotonic and cyclic shear loading and the concrete-bar interaction in a pull-out test