221 research outputs found
Bounds for overall properties of composites with time-dependent constitutive law
No full textThis paper deals with the search, via variational methods, of bounds on the overall mechanical properties of composite materials, with the constitutive laws of the constituents governed by linear operators, generally non-symmetric with respect to the chosen bilinear form. For this types of problems, by virtue of a symmetrization technique derived by Tonti (1984), we provide a minimum formulation, then used to derive bounds for the overall properties of composites having a linear time-dependent constitutive law. Some of the examples already known in the literature prove to be special cases of the theory proposed here, such as the results derived by Cherkaev and Gibiansky (1994) and Milton (1990), those obtained by Rafalski (1969 a, 1969b) and Reiss and Haug (1978), and those provided by Carini and Mattei (2015)
Variational formulations for the linear viscoelastic problem in the time domain
No full textUnder the assumption of small displacements and strains, we formulate new variational principles for the linear viscoelastic hereditary problem, extending the well-known Hu-Washizu, Hellinger-Reissner, Total Potential Energy, and Complementary Energy principles related to the purely elastic problem. In addition, a new global minimum formulation is derived, giving an energetic interpretation. The new formulations are based on a convolutive bilinear form of the Stieltjes type and on the division of the time domain into two equal parts, with the resulting decomposition of the variables and of the equations governing the problem. In particular, the global minimum principle is achieved by virtue of the positive definiteness of a part of the split constitutive law operator and by means of a partial Legendre transform, and is then used to provide bounds of the overall mechanical properties of viscoelastic composite materials
On explicit analytic solutions for the accurate evaluation of the shear stress in sandwich beams with a clamped end
No full textWe focus on analytic solutions for the accurate computation of the shear stress in sandwich beams under flexure. To this purpose, we follow the strategy recently proposed by our group and apply the Jourawski method to the structural beam model based on the zigzag warping. We consider sandwiches whose cross-section is symmetric with respect to the neutral axis and whose skin shear deformation and core longitudinal stress are accounted for (that is, we do not limit our attention to thin skins nor to antiplane sandwiches). We obtain explicit analytic expressions for the cases of cantilever and propped-cantilever beams subject to uniform transverse load. The comparison with numerical solutions obtained through plane stress finite element simulations shows the excellent accuracy of the analytic solution, apart in a region close to the fully clamped cross-section, where the finite element solution itself is unreliable, while the new analytic solutions provide useful estimates
Corrigendum to "On explicit analytic solutions for the accurate evaluation of the shear stress in sandwich beams with a clamped end"
No full textA structural model for plane sandwich beams including transverse core deformability and arbitrary boundary conditions
No full textIn order to model the effect of arbitrary boundary conditions on plane linear elastic sandwich beams, we develop a structural theory relying on a zigzag warping: each layer, of arbitrary thickness and modulus, is described by the Timoshenko kinematics and, for the core, we further consider the transverse strain, which measures the normal deformability along the core thickness. This structural model, dependent on six functions of the beam axis coordinate, builds on the theory put forward by Dusan Krajcinovic in the early Seventies. By following a variational approach, we obtain and discuss the (Euler-Lagrange) balance equations and the (natural) boundary conditions governing the model. In sandwich beams having a soft core, this model can describe relevant features of the stress state due to "severe boundary conditions", including, for instance, loading on a specific skin coupled with constraints realised, at certain cross-sections, on the opposite skin only. In this work we focus on the flexure accompanied with non-uniform shear. In particular, we consider the cases of cantilever and propped-cantilever beams subject to uniform load. We provide accurate shear stress estimates by post-processing, through a Jourawski-like approach, the longitudinal normal stress predicted by the beam model. We demonstrate the capability of the proposed model by comparison of its results, obtained by using the Rayleigh-Ritz method, with those ofThe predictions of the present beam model are shown to be useful at fully clamped cross-sections, where displacement-based FE results are unreliable. continuum plane stress Finite Element (FE) simulations
Bibliografia di Umberto Romagnoli
Get PDFA complete bibliography of Umberto Romagnoli writings, introduced by a few lines by editors of the Journal and completed by an essay by Alberto Mattei dealing with some technical aspects of the collection of the
bibliography interwoven with some scholarly life moments of the author
The obstacle problem in masonry structures and cable nets
Get PDFWe consider the problem of finding a net that supports prescribed forces
applied at prescribed points, yet avoids certain obstacles, with all the
elements of the net under compression (strut net) or under tension (cable web).
In the case of masonry structures, for instance, this consists in finding a
strut net that supports the forces, is contained within the physical structure,
and avoids regions that may be not accessible due, for instance, to the
presence of holes. We solve such a problem in the two-dimensional case, where
the prescribed forces are applied at the vertices of a convex polygon, and we
treat the cases of both single and multiple obstacles. By approximating the
obstacles by polygonal regions, the task reduces to identifying the feasible
domain in a linear programming problem. For a single obstacle we show how the
region available to the obstacle can be enlarged as much as possible
in the sense that there is no other strut net, having a region
available to the obstacle with . The case where some of
the forces are reactive, unprescribed but reacting to the other prescribed
forces, is also treated. It again reduces to identifying the feasible domain in
a linear programming problem. Finally, one may allow a subset of the reactive
forces to each act not at a prescribed point, but rather at any point on a
prescribed line segment. Then the task reduces to identifying the feasible
domain in a quadratic programming problem.Comment: 22 pages, 12 figures, 3 supplemental video
Unilateral Climate Policy and Foreign Direct Investment with Firm and Country Heterogeneity
Get PDFWe contribute to the debate on the impact of unilateral climate policy with a two-country two-firm international oligopoly model accounting for endogenous plant location and heterogeneity in both country size and firms emissions technology. Our results suggest that, if the carbon price differential is moderate as compared to unit transport costs and the relative size of the highly regulated country is big enough, a no relocation equilibrium may prevail also in the long run. A large market asymmetry coupled with a small technology gap emerges as the only configuration in which unilateral climate policy leads to a fall in world emissions irrespective of the optimal location choice. Thus for being effective and not leading to production relocation, unilateral climate policy should be moderate, implemented by a sufficiently large area and complemented by mechanisms for promoting the international transfer of clean technologies. Welfare implications are also discussed
Pairs of foliations and Mattei-Moussu's Theorem
No full textInternational audienceWe prove a reduction of singularities for pairs of foliations by blowing-up, and then investigate the analytic classification of the reduced models. Those reduced pairs of regular foliations are well understood. The case of a regular and a singular foliation is dealt with Mattei-Moussu's Theorem for which we provide a new proof, avoiding Gronwall's inequality. We end-up announcing results recently obtained by the first author in the case of a pair of reduced foliations sharing the same separatrices
Cultura e oro nero. Strategie comunicative e intellettuali nell’Agip e nell’Eni di Enrico Mattei
No full textThe author analyzes the communication strategies in Agip and Eni during Enrico Mattei. In addition to advertising on press, radio and television, Eni producing many documentaries for the cinemas. The best filmmakers and intellectuals collaborate for various Eni’s advertising. In Italy the Sixties represent the era of great collaboration between the intellectuals and government and private industry, led by men like Mattei with excellent management and communication skills. In its advertising Eni presents to the world an image of a modern and competitive company in oil and gas
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