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.
This article illustrates the specialization to infinitesimal perturbations of the geometrically nonlinear formulation describing the macroscopic dynamic behavior of biphasic media presented in (Serpieri and Rosati J Mech Phys Solids 59(4): 2011) where, based on Lagrangian mechanics arguments, a consistent mathematical theory of fluidsaturated poroelastic material is developed accounting for the property that both constituent materials are microscopically compressible. The primary contribution of this work is the employment of the linearized model in the development of a general procedure for the determination of the relevant elastic coefficients on the basis of the data provided by a set of experimental measures analogous to the one originally considered by Biot and Willis consisting of a shear test, an unjacketed compressibility test and two jacketed tests in which drainage is either completely allowed or prevented. The linearization of the formulation is first presented for a generic configuration in which both phases are undergoing a generic motion. Subsequently, a specific study is presented on the case that the media is motionless, homogeneous, and isotropic in the reference configuration, which is typical of common experimental set-ups for static tests. A numerical example is shown and a general relation between the elastic coefficients and Biot's constant is derived which consistently accounts for the compressibility of all materials.
a b s t r a c tThe linearized version of a recently formulated Variational Macroscopic Theory of biphasic isotropic Porous Media (VMTPM) is employed to derive a general stress partitioning law for media undergoing flow conditions under prevented fluid seepage and negligible inertia effects, typically met in biphasic specimens subjected to jacketed tests.The principle of virtual work, relevant to the specialization of VMTPM to such characteristic flow conditions, naturally yields a stress partitioning law, between solid and fluid phase of a saturated medium, that exactly matches with the celebrated Terzaghi's principle. It is also shown that the stress tensor of the solid phase work-associated with the strain measure of the VMTPM naturally corresponds to the Terzaghi's effective stress. Accordingly, under undrained conditions, Terzaghi's law is proved to be a completely general stress partitioning law for a saturated biphasic medium irrespective of its constitutive and/or microstructural features as well as of the compressibility of its constituent phases.Since the developments reported are obtained ruling out thermodynamic constraints and any assumption on the internal microstructure and on the compressibility of the phases, the results obtained indicate that Terzaghi's law could more generally apply to a broader class of biphasic media and be not restricted within the context of geomechanics.
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