SUMMARYA thermodynamics-based cohesive-zone interface formulation combining adhesion, friction and interlocking is illustrated. Interlocking is modeled exploiting a macroscopic description, which represents the geometry of the interface in the form of a periodic arrangement of distinct microplanes, denoted by Representative Interface Element (RIE). The interaction within each of these surfaces is governed by the combined damage-friction interface formulation proposed by Alfano and Sacco (Int. J. Numer. Meth. Engng 68(5):542-582). Although a simple damage law combined with Coulomb friction and no dilatancy is introduced on each individual microplane, the overall dilatant and hysteretic nature of the bond-slip is predicted as a result of the interaction induced by the presence of the microstructure of the RIE. The formulation is investigated by performing sensitivity analyses and is validated by evaluating its performance in the simulation of pull-out tests under controlled confining pressure. The results of a structural simulation of a pull-out test under variable amplitude repeated loading are also reported.
The present paper deals with the derivation of an interface model characterized by macroscopic fracture energies which are different in modes I and II, the macroscopic fracture energy being the total energy dissipated per unit of fracture area.It is first shown that thermo-dynamical consistency for a model governed by a single damage variable, combined with the choice of employing an equivalent relative displacement and of a linear softening in the stress-relative displacement law, leads to the coincidence of fracture energies in modes I and II. To retrieve the experimental evidence of a greater fracture energy in mode II, a micro-structured geometry is considered at the typical point of the interface where a Representative Interface Element (RIE) characterized by a periodic arrangement of distinct inclined planes is introduced. The interaction within each of these surfaces is governed by a coupled damage-friction law.A sensitivity analysis of the correlation between micromechanical parameters and the numerically computed single-point microstructural response in mode II is reported. An assessment of the capability of the model in predicting different mixed mode fracture energies is carried out both at the single microstructural interface point level and with a structural example. For the latter a double cantilever beam with uneven bending moments has been analyzed and numerical results are compared with experimental data reported in the literature for 1 different values of mode mixity.
a b s t r a c tA 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 twoscale 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.
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