1,356,378 research outputs found
Closed-form expressions for the macroscopic elastic constants of Flemish bond masonry walls
No full textThe problem of obtaining reliable closed-form expressions for the macroscopic elastic coefficients of Flemish bond brickwork according to the mechanical properties and the geometry of joints and units is dealt with. Unlike most similar existing works, which are limited to single-wythe walls, here the coexistence of headers and stretchers is taken into account, together with the presence of collar joints. Similarly to the so-called Method of Cells for fiber-reinforced composites, any Representative Volume Element (RVE) of the wall is divided into sub-cells. A piecewise-differentiable 3D strain-periodic displacement field, depending on a limited number of degrees of freedom (d.o.f.s), is formulated over the RVE. Suitable boundary conditions are prescribed at the interfaces between the sub-cells, thus reducing the number of independent d.o.f.s. The remaining d.o.f.s can be related to the macroscopic strains of the RVE. Upon integration of the microscopic stress and strain fields, the homogenized elasticity matrix can be obtained. The accuracy of the theoretical predictions is assessed by comparison with the results of Finite Element analyses of the RVE subjected to elementary macroscopic stresses, and with other benchmarks available in the literature
Optimal fiber-reinforcement of no-tension masonry walls through a stress-based formulation
No full textA topology optimization problem is dealt with, which aims at distributing a prescribed amount of fiber-reinforcement over any masonry wall, so as to maximize the overall stiffness of the strengthened element. A no-tension (NT) model is adopted to account for the negligible tensile strength of brickwork. The equilibrium of the NT body is enforced through an energy-based method, which replaces brickwork by an equivalent orthotropic medium with constraints on the stress state. The inability if the reinforcement to carry compressive stresses is also taken into account in a similar way. The stress analysis of the reinforced NT body can be straightforwardly embedded within the topology optimization formulation, with no need for demanding incremental approaches. Both the regions to be strengthened and the local orien-tation of the optimal FRP strips are identified. To improve accuracy in the enforcement of the stress constraints, an efficient formulation that uses stresses as main variables of the elastic problem is implemented. Also, the structural compliance is computed through the evaluation of the complementary strain energy. A preliminary numerical example is shown, to assess the capabilities of the proposed procedure
C. Valerio Flacco Argonautiche, libro VII Introduzione, testo e commento a cura di Annamaria Taliercio
No full textAnalisi storico -letteraria e linguistico-stilistica del libro VII delle Argonautiche di Valerio Flacc
Flemish bond brickwork: Macroscopic elastic properties and nonlinear behaviour
No full textAssuming Flemish bond brickwork to be periodic, a finite element model of a Representative Volume Element (RVE) is developed to predict its macroscopic behavior using a homogenization approach. In linear elasticity, the numerical results are used to assess the reliability of recently proposed closed-form expressions for the macroscopic elastic properties (Taliercio, 2018). Assuming that both mortar and units experience plastic strains and damage effects, the macroscopic strength domain under in-plane principal stresses parallel to the joints is identified and compared with that predicted by Drougkas et al. (2016). Eventually, the model is applied to predict the homogenized strength of Flemish bond brickwork under elementary macroscopic in-plane stresses and transverse shear. The effect of the collar joint on the macroscopic response is pointed out by comparing the numerical results with those obtained on header bond brickwork. This effect is shown to be particularly significant under horizontal, transverse shear
Macroscopic strength estimates for metal matrix composites embedding a ductile interphase
No full textThe influence of an interphase region on the macroscopic strength of unidirectional fiber-reinforced metal-matrix composites (MMCs) is investigated. The three phases of the composite are supposed to be elastic-perfectly plastic and to conform with J2-plasticity. First, theoretical bounds to the macroscopic strength are derived, according to homogenization theory for heterogeneous periodic media: the gap between these bounds is quite narrow for certain stress conditions, volumetric proportions of the constituents, and ratios of the interphase-to-matrix strength. Then, a numerical model previously developed by Taliercio (2005) is employed to predict the macroscopic response of three-phase MMCs under any 3D stress through the analysis of a single representative unit cell. The model is applied to the numerical identification of the macroscopic strength properties of MMCs under uni-, bi- and triaxial stresses, in cases where the theoretical bounds are not sufficiently close to identify the actual macroscopic yield surface. The influence of the weakening interphase on the predicted macroscopic strength is critically discussed. A decrease in interphase strength is found to affect the transverse tensile and shear strength of the composite to a moderate extent, whereas the macroscopic longitudinal shear strength is extremely sensitive to the interphase strength
Certamen Capitolinum
No full textIl saggio affronta uno dei temi più controversi nella poesia virgiliana (l'origine del labor umano). L'autrice, attraverso una sottile analisi testuale e un'acuta valutazione dei rapporti fra Virgilio e i suoi modelli, presenta una nuova intrepretazione atta a garantire e dimostrare l'originalità e la coerenza del pensiero virgilian
Creep Behaviour of Brickwork: A Parametric Investigation
No full textThe prediction of the creep behavior of periodic brickwork subjected to in-plane loads is dealt with in this paper. Analytical approximate expressions for the macroscopic relaxation and creep coefficients are proposed, according to simple statically or kinematically admissible solutions in which the joint thickness is neglected, units are assumed to be either rigid or elastic, and creep phenomena are confined in the interfaces between units. A parametric analysis is carried out to investigate the effect of several parameters on the global and local creep behavior of brickwork, namely: i) mortarto- brick thickness ratio; ii) ratio of the mortar Young's modulus to the brick Young's modulus; iii) brickwork texture (running vs header bond). A finite element model of a single representative volume element (RVE) is also analyzed under sustained macroscopic stresses, to numerically evaluate the creep coefficients and assess the accuracy of the analytical estimates. The creep coefficients are found to be very sensitive to the block stiffness for thin joints. Also, the agreement between numerical and analytical predictions is better for thicker mortar joint
Predicting the macroscopic behaviour of metal-matrix composites embedding an interphase
No full textA numerical model previously developed by Taliercio is applied to the prediction of the macroscopic nonlinear behaviour of unidirectional metal-matrix composites (MMCs), considering the presence of an interphase region between the fibres and the matrix. Special 2D finite elements are formulated, capable of describing Generalized Plane Strain conditions for a representative unit cell of the composite, that is, 3D deformation modes invariant along the fibre axis. Periodicity conditions at the boundary of the cell complete the kinematic formulation. The three phases of the composite are supposed to be elastic-perfectly plastic and to conform with J2-plasticity. Some numerical applications are carried out to investigate the influence of the interphase material on the macroscopic strength of the composite under elementary stress states
A comparison between numerical and analytical homogenized models for visco-elastic brickwork
No full textThe creep behaviour of periodic brickwork is dealt with. An analytical model is proposed, in which units are assumed to be either rigid or elastic and creep effects are confined to mortar joints. Closed-form expressions for the creep coefficients under elementary macroscopic stresses are obtained. A parametric study is carried out to investigate the sensitivity of the analytical creep coefficients to the material parameters. The accuracy of the theoretical predictions and the reliability of the simplifying assumptions is assessed through comparisons with the numerical results obtained discretizing any representative volume element by finite elements and taking the creep behavior of both component materials (bricks and mortar) into account. Experimental data available in the literature for calcium silicate bricks and mortar were used to calibrate the model. The analytical creep coefficients are found to be accurate as the ratio of the elastic modulus of the units to the elastic modulus of mortar is greater than 20
Hierarchical Infills for Additive Manufacturing Through a Multiscale Approach
No full textA numerical method is presented to generate hierarchical infills for additive manufacturing, using homogenization and optimization. Given the shape and the allowed stages of grading, the macroscopic properties of each level of the hierarchical infill are computed through numerical homogenization. Then, a multi-material optimization problem is formulated to find the distribution of the prescribed discrete set of candidates that maximizes the structural stiffness of the object to be printed for a limited volume fraction. The formulation is endowed with an additional overturning constraint to achieve objects that resist gravity in a stable configuration. Numerical simulations, addressing the design of a self-supporting orthotropic rhombic infill and a stiff isotropic triangular one, are shown
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