1,327 research outputs found
Applications of a micro-structured brittle damage model to laboratory tests on rocks
No full textA multiscale microstructured brittle damage model is used to describe the behavior of confined rock materials. Plane strain and triaxial tests conducted
at the laboratory scale are simulated in terms of boundary value problems. Simulations reveal good predictive qualities of the model to describe the macroscopic features of specimens at failure. The microstructures, oriented in different directions, allow the localization of the macroscopic strain along straight lines, emerging at the macroscale in the form of shear bands. The microstructured material model, characterized by recursive equidistant parallel cohesive-frictional faults, is fully defined by six elastic and inelastic material constants. The model was originally developed in a finite kinematics framework to simulate the dynamic behavior of confined brittle materials (Pandolfi et al. in J
Mech Phys Solids 54:1972–2003, 2006). In linearized form, it has been extended and used for the simulation of in-field excavations (De Bellis et al. in: Eng
Geol 215:10–24, 2016). The performance of the model in predicting the behavior of small scale rock tests in the laboratory, the object of the present study, has
never been investigated. Numerical simulations show that the model is able to capture several important features observed in rocks, in particular the reduction
of the overall stiffness for increasing deterioration of the material, fragile to ductile transition, strain localization, shear band formation, and more general size effect
Prestation indue et enrichissement in?quitable : ? propos de deux quasi-contrats dans l\u27avant-projet d\u27ordonnance r?formant le droit fran?ais des obligations
No full textLes quasi-contrats constituent une institution juridique discr?te mais durable en m?me temps que passionnante. Pourtant, dans le cadre de la r?forme du droit des obligations, peu d?analyses doctrinales ont port? sur cette mati?re. La pr?sente ?tude consiste alors en une analyse des dispositions relatives ? ce qui est appel? le ? paiement de l?indu ? et ? l?enrichissement injustifi? ? dans le dernier ?tat du projet de r?forme.
D?une mani?re g?n?rale, l?heure n?est pas ? la refonte totale des quasi-contrats, si tant est qu?elle e?t ?t? n?cessaire. Par cons?quent, nous proposons principalement des modifications d?ordre terminologique, en axant notre analyse sur la s?mantique et sur la linguistique juridique en g?n?ral
NURBS-Based Collocation Methods for the Structural Analysis of Shells of Revolution
No full textIn this work we present a collocation method for the structural analysis of shells of revolution based on Non-Uniform Rational B-Spline (NURBS) interpolation. The method is based on the strong formulation of the equilibrium equations according to Reissner-Mindlin theory, with Fourier series expansion of dependent variables, which makes the problem 1D. Several numerical tests validate convergence, accuracy, and robustness of the proposed methodology, and its feasibility as a tool for the analysis and design of complex shell structures
A virtual element approach for micropolar continua
No full textIn this work we propose a novel virtual element approach for solving boundary value problems in 2D linear isotropic micropolar elasticity. Following the basic idea of the Virtual Element Method (VEM), the degrees of freedom of each material point, i.e. the displacement and rotation fields, are decomposed into both a polynomial space, either linear or quadratic, and a remaining space that is kept virtual in the formulation. Generalized consistency and stabilization terms are consistently derived. Different patch tests, properly conceived for micropolar continua, are proposed and compared to reference solutions present in literature. The obtained results are in good agreement with these solutions, confirming the capability of the proposed elements in the modelling of the expected responses. The expected applications of this methodology concern the mechanical study of microstructured materials, inherently characterized by nonlocal response, which has been widely proven to be effectively represented by micropolar continua
Las redes reguladoras transnacionales diez años después de la crisis: caracteres y problemas
No full textAuxetic anti-tetrachiral materials: equivalent elastic properties and frequency band-gaps
No full textA comprehensive characterization of the novel class of anti-tetrachiral cellular solids, both considering the static and the dynamic response, is provided in the paper. The heterogeneous material is characterized by a periodic microstructure made of equi-spaced rings each interconnected by four ligaments. In the most general case, rings and ligaments are surrounded by a softer matrix and the rings can be filled by a different material. First, the first order linear elastic homogenized constitutive response is estimated resorting to two different microstructural models: a discrete model, in which the ligaments are modeled as beams and the presence of the matrix is neglected and the equivalent elastic properties are evaluated through a simplified analytical approach, and a more detailed continuous model, where the actual properties of matrix, ligaments and rings, varying in the 2D domain, are considered and the first order computational homogenization is adopted. Special attention is given to the dependence of the 2D overall Cauchy-type elastic constants on the mechanical and geometrical parameters characterizing the microstructure. The results, indeed, show the existence of large variations in the linear elastic constants and degree of anisotropy. A comparison with available experimental results confirms the validity of the analytical and numerical approaches adopted. Finally, the rigorous Floquet–Bloch approach is applied to the periodic cell of the cellular solid to evaluate the dispersion of propagation waves along the orthotropic axes in the framework of elasticity and to detect band gaps characterizing the material. A numerical approach, based on the first order computational homogenization, is also adopted and the rigorous and approximate solutions are compared
Continuum versus micromechanical modeling of corneal biomechanics
No full textTwo alternative numerical models of the human cornea are used to simulate the mechanical response under the action of a physiological intraocular pressure (IOP). The first model is continuum or macromechanical, considering the stromal tissue as a bulk material with stochastic distribution of the spatial variability of reinforcing collagen fibers. The second model is discrete or micromechanical, considering the sole collagencrosslink stiffening micro-structure. The geometry of the two models is reconstructed from corneal topographer images. Simulations consider the behavior of a healthy cornea and of a keratoconus cornea. For the keratoconus the material properties of a portion of the cornea are reduced to 1/8 of the values used for the healthy tissue. It is found that, for suitable choice of the material parameters for the discrete model, in the healthy case the mechanical responses of the two models are fully comparable. In the keratoconus case, both models capture with comparable accuracy the anterior shape of the conus; in addition, the discrete model is able to describe the tissue thinning typical of the pathology. Despite the inclusion of stochastic material properties, starting from a healthy condition, continuum models of the cornea are not able to predict the thinning of a keratoconus cornea, while the inclusion of the underlying collagen microstructure allows for a proper description of pathologic mechanical behaviors
Comment on "self-expandable metal stents for malignant colonic obstruction: data from a retrospective regional SIED-AIGO study" by R. Di Mitri, F. Mocciaro, M. Traina et al. [Digestive and Liver Disease 2014;46:279-82].
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