From Architectured Materials to Large-Scale Additive Manufacturing

The classical material-by-design approach has been extensively perfected by materials scientists, while engineers have been optimising structures geometrically for centuries. The purpose of architectured materials is to build bridges across themicroscale ofmaterials and themacroscale of engineering structures, to put some geometry in the microstructure. This is a paradigm shift. Materials cannot be considered monolithic anymore. Any set of materials functions, even antagonistic ones, can be envisaged in the future. In this paper, we intend to demonstrate the pertinence of computation for developing architectured materials, and the not-so-incidental outcome which led us to developing large-scale additive manufacturing for architectural applications

Computational Homogenization of Architectured Materials

Architectured materials involve geometrically engineered distributions of microstructural phases at a scale comparable to the scale of the component, thus calling for new models in order to determine the effective properties of materials. The present chapter aims at providing such models, in the case of mechanical properties. As a matter of fact, one engineering challenge is to predict the effective properties of such materials; computational homogenization using finite element analysis is a powerful tool to do so. Homogenized behavior of architectured materials can thus be used in large structural computations, hence enabling the dissemination of architectured materials in the industry. Furthermore, computational homogenization is the basis for computational topology optimization which will give rise to the next generation of architectured materials. This chapter covers the computational homogenization of periodic architectured materials in elasticity and plasticity, as well as the homogenization and representativity of random architectured materials

Transverse shear stiffness of a chevron folded core used

International audienceUsing Kelsey et al. (1958) unit load method, upper and lower bounds for the effective transverse shear moduli of a chevron folded core used in sandwich construction are analytically derived and compared to finite element computations. We found that these bounds are generally loose and that in some cases chevron folded cores are 40% stiffer than honeycomb-like cores

A Bending-Gradient model for thick plates, Part II: Closed-form solutions for cylindrical bending of laminates

In the first part (Lebée and Sab, 2010a) of this two-part paper we have presented a new plate theory for out-of-plane loaded thick plates where the static unknowns are those of the Kirchhoff-Love theory (3 inplane stresses and 3 bending moments), to which six components are added representing the gradient of the bendingmoment. Thenewtheory, calledBending-Gradientplatetheoryisanextensiontoarbitrarilylayered plates of the Reissner-Mindlin plate theory which appears as a special case when the plate is homogeneous. Moreover, we demonstrated that, in the general case, the Bending-Gradient model cannot be reduced to a Reissner-Mindlin model. In this paper, the Bending-Gradient theory is applied to laminated plates and its predictions are compared to those of Reissner-Mindlin theory and to full 3D Pagano’s exact solutions. The main conclusion is that the Bending-Gradient gives good predictions of deflection, shear stress distributions and in-plane displacement distributions in any material configuration. Moreover, under some symmetry conditions, the Bending-Gradient model coincides with the second-orderapproximationof the exact solution as the slenderness ratio L/h goes to infinity

Collecte des ordures ménagères en milieu rural par conteneurs de moyenne capacité: rapport final d'étude

A new method for salvaging household waste appeared in 1986 on the SIRTOM of Merlerault in the Orne department. Designed and developed by the "Société Normande de Nettoiement", the innovation relies in the combination of three patented interfaces: container-crane-bucket that can be handled by one person. This is an analysis during winter conditions of the operation of this salvaging system developed for rural population. The conclusions of this study: an important productivity gain, improvements in terms of cleanliness, sanitation and safety conditions for the employees and more ease in the salvaging process. For consumers, this is a 24 hour service, but with a one constraint: displacement. Although it does require high investments, this method must be more economical than the other existing mechanized methods. / Un nouveau mode de collecte des ordures ménagères a fait son apparition en 1986 sur le SIRTOM du Merlerault dans le département de l'Orne. Conçu et réalisé par la Société Normande de Nettoiement, l'innovation de ce nouveau système réside dans l'agencement des trois interfaces brevetées : conteneur-grue-benne qui permettent une manipulation unipersonnelle. L'étude de "la collecte des ordures ménagères en milieu rural par conteneur de moyenne capacité" analyse, en situation hivernale, le fonctionnement de ce dispositif de collecte mis en oeuvre pour la desserte de la population rurale éparse. Il en ressort un gain important de productivité, une amélioration de la propreté, des conditions d'hygiène et de sécurité incomparable pour le personnel et une latitude plus grande pour le ramassage. Pour les usagers, la servitude des dates de passage a disparue au profit d'un service offert 24 heures sur 24, mais avec une contrainte de déplacement. Quoique nécessitant des investissements importants, le mode de collecte doit s'avérer plus économique que les autres systèmes mécanisés existants

Émergence d'effets de strain-gradient en élastostatique par optimisation topologique

Practical examples of microstructures producing so-called strain-gradient effects in elastostatics are not very common. Therefore, the topological optimization of strain-gradient effects for two-dimensional periodic media in elastostaic regime is considered in the present article, in order to obtain new microstructures featuring these effects. The periodic unit cell is made of a mixture of stiff and soft materials. The optimization process is carried out through the solution of a shape optimization problem. On the one hand, the design variable is the distribution of material inside the unit cell. On the other hand, the shape functional depends on this distribution through related first and second-order homogenized tensors, which are defined from a homogenization scheme based on the two-scale asymptotic expansion. The adopted method used to tackle numerically the optimization problem is based on the topological derivatives of the homogenized tensors, which measure how the homogenized elasticity tensors change when a small circular inclusion endowed with different material property from the background is introduced at the microscopic level. With this approach, new microstructures with macroscopic strain-gradient effects are obtained. In particular, we retrieve well-known microstructures such as the pantographic material

Justification of the Bending-Gradient theory through asymptotic expansions

Abstract In a recent work, a new plate theory for thick plates was suggested where the static unknowns are those of the Kirchhoff-Love theory, to which six components are added representing the gradient of the bending moment [1]. This theory, called the Bending-Gradient theory, is the extension to multilayered plates of the Reissner-Mindlin theory which appears as a special case when the plate is homogeneous. This theory was derived following the ideas from Reissner [2] without assuming a homogeneous plate. However, it is also possible to give a justification through asymptotic expansions. In the present paper, the latter are applied one order higher than the leading order to a laminated plate following monoclinic symmetry. Using variational arguments, it is possible to derive the Bending-Gradient theory. This could explain the convergence when the thickness is small of the Bending-Gradient theory to the exact solution illustrated in [3]. However, the question of the edge-effects and boundary conditions remains open. 1.