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Among various industries, the construction sector has one of the greatest impacts on the environment. Minimizing the resource use and the waste outputs in this sector could be fulfilled by applying circular economy (CE) strategies. Although research on CE in the construction sector has increased in recent years, there have not been remarkable adjustments by applying these strategies to the construction industry. The purpose of this study was to examine the impacts of using CE strategies in the construction sector. A framework was adapted to guide the application of different CE strategies at the end-of-life of buildings. The framework was assessed by a case study of a residential building in mass timber. This study evaluated the application of CE strategies from the environmental aspect with the life cycle assessment (LCA) method. The results confirmed that circular strategies can deliver lower environmental impacts.

The present study is based on the patent FR3052379A1, which consists of rolling and gluing green veneers to form structural size hollow tubes. The objective was to study the drying behavior of circular hollow tubes and investigate the method of crack detection using image correlation from green conditions to equilibrium moisture content. The manufactured tubes are composed of six plies. Three different configurations of global grain angle orientations with respect to the tube longitudinal axis are used: {0, 0, 0}°, {10, 0, 10}°, and {− 10, 0, 10}°. Each grain angle was made up of two plies. The tubes deformation and crack formation due to drying shrinkage were measured using a stereo digital image correlation system. The stereo correlation is suitable for measuring tangential shrinkage and studying the opening and/or closing of cracks on the surface of the tubes subjected to internal moisture variations and blocked deformations. The influence of grain angle was discussedin this paper; however, due to the very few numbers of samples, no conclusive findings can be made. The completion of this study was made possible thanks to the financial support of the Carnot Arts Institute. The authors also thank the Xylomat technical platform of the Xylomat scientific network financed by the ANR-10-EQPX-16 XYLOFOREST which was widely used to carry out this study.

To prevent the occurrence of localized necking, the concept of forming limit diagram is often used, thus playing an important role in sheet metal forming processes. The aim of the present study is to develop a numerical tool for the theoretical prediction of forming limit diagrams, which would be a cost-efective procedure as compared to experimental measurements. The proposed numerical tool is based on the Marciniak and Kuczyński imperfection approach combined with the Gurson–Tvergaard–Needleman damage model, which is implemented into the MATLAB program within the framework of plane-stress conditions. Forming limit diagrams have been predicted by assuming both geometric (thickness) as well as material initial imperfections in the Marciniak and Kuczyński imperfection approach. These forming limit diagrams, for different sizes of geometric or material imperfections, are also compared with the forming limit diagram obtained by using the bifurcation theory. It is shown that the bifurcation-based forming limit diagram provides an upper bound as compared to the Marciniak and Kuczyński imperfection approach predictions. The results also reveal that irrespective of the imperfection type considered in the Marciniak and Kuczyński imperfection approach, the corresponding forming limit diagram tends to that predicted by bifurcation theory when the size of initial imperfection tends to zero. Additionally, the predicted ductility limits are lowered as the magnitude of initial imperfection increases; however, the decrease in the ductility limits at balanced biaxial tension is more signifcant than for the other strain-path ratios. The results for the forming limit diagrams indicate that the predicted ductility limits are more sensitive to the initial imperfection in the thickness and the isotropic hardening coefficient as compared to the other types of material imperfections. Moreover, the initial imperfection in the critical porosity is the most infuential one among the Gurson–Tvergaard–Needleman damage parameters. PAKISTAN HIGHER EDUCATION COMMISSION (HEC)

The present study investigates the effect of the high-speed milling (HSM), grinding and anodizing processes on the high cycle fatigue strength of the AA7050 aluminum alloy. These processes are systematically applied to certain aircraft components as specified by aeronautical standards, to attain a good surface finish. In order to understand the effect of each process on the fatigue strength, a vast experimental campaign consisting of fully reversed plane bending fatigue tests has been conducted on specimens with different surface states. A polished batch, three milled batches with different surface roughness, a grinded batch and two milled then anodized batches with different surface roughness have been tested. The results show that the roughness must be highly degraded (Sa > 3 μm) in order to impact the fatigue strength. It is also shown that anodizing has slight beneficial effect on the fatigue strength in the high cycle fatigue domain studied. The experimental results show a dependence of the fatigue strength on the surface roughness via the parameter √Sa, previously proposed by the authors. This work was carried out within the FUI QUAUSI project (Grant n°FR1307003R on call n°15) with the support of industrial (Dassault Aviation, Europe Technologie, Figeac Aéro, Mecachrome, Spring Technologie, Precise, GEBE2, CETIM) and academic partners (LSN2-IUT Carquefou).

The aim of this contribution is to present numerical comparisons of model-order reduction methods for geometrically nonlinear structures in the general framework of finite element (FE) procedures. Three different methods are compared: the implicit condensation and expansion (ICE), the quadratic manifold computed from modal derivatives (MD), and the direct normal form (DNF) procedure, the latter expressing the reduced dynamics in an invariant-based span of the phase space. The methods are first presented in order to underline their common points and differences, highlighting in particular that ICE and MD use reduction subspaces that are not invariant. A simple analytical example is then used in order to analyze how the different treatments of quadratic nonlinearities by the three methods can affect the predictions. Finally, three beam examples are used to emphasize the ability of the methods to handle curvature (on a curved beam), 1:1 internal resonance (on a clamped-clamped beam with two polarizations), and inertia nonlinearity (on a cantilever beam).

L'économie d'énergie est devenue un véritable enjeu dans la gestion des procédés et a conduit à l'analyse de la consommation d’énergie des machines de forgeage, et ce à des fins d'optimisation. Dans ses travaux, on s’intéresse à la quantité et à la façon dont l'énergie est dissipée par une presse à vis lors d’opérations de forgeage de produits massifs. Un modèle masse-ressort-amortisseur, image du système composé de la machine et de ses outils, est associé au modèle rhéologique du matériau à déformer pour décrire les opérations de forgeage avec ce système de production. Le modèle du système machine-outil est ici caractérisé uniquement pour la phase de forgeage. Les paramètres du modèle sont identifiés grâce à des mesures expérimentales de plusieurs variables du processus lors d'une frappe à vide, c’est-à-dire outil contre outil, sans lopin. Ainsi, les paramètres identifiés sont spécifiquement adaptés au système machine-outil étudié. Ensuite, les prédictions du modèle sont validées par des essais de refoulement de cylindres de cuivre à froid. Le modèle prédit avec précision les variables du processus forgeage pour des frappes consécutives. La diminution de l'efficacité du processus ainsi que la transition de chocs inélastiques vers des chocs élastiques, après plusieurs frappes sur une même pièce sont également prédites par le modèle. Cette méthode offre une nouvelle solution dédiée qui permet aux forgerons de prévoir la quantité d'énergie de forgeage dissipée par leurs machines. L'approche développée dans cet article concerne une presse à vis mais peut être transférée à d'autres machines pilotées en énergie, comme les marteaux pilons.

International audience; This work deals with the multi-scale optimisation of composite structures by adopting a general global-local (GL) modelling strategy to assess the structure responses at different scales. The GL modelling approach is integrated into the multi-scale two-level optimisation strategy (MS2LOS) for composite structures. The resulting design strategy is, thus, called GL-MS2LOS and aims at proposing a very general formulation of the design problem, without introducing simplifying hypotheses on the laminate stack and by considering, as design variables, the full set of geometric and mechanical parameters defining the behaviour of the composite structure at each pertinent scale. By employing a GL modelling approach, most of the limitations of well-established design strategies, based on analytical or semi-empirical models, are overcome. The GL-MS2LOS makes use of the polar formalism to describe the anisotropy of the composite at the macroscopic scale (where it is modelled as an equivalent homogeneous anisotropic plate). In this work, deterministic algorithms are exploited during the solution search phase. The challenge, when dealing with such a design problem, is to develop a suitable formulation and dedicated operators, to link global and local models physical responses and their gradients. Closed-form expressions of structural responses gradients are rigorously derived by taking into account for the coupling effects when passing from global to local models. The effectiveness of the GL-MS2LOS is proven on a meaningful benchmark: the least-weight design of a cantilever wing subject to different design requirements. Constraints include maximum allowable displacements, maximum allowable strains, blending, manufacturability requirements and buckling factor.; This work deals with the multi-scale optimisation of composite structures by adopting a general global-local (GL) modelling strategy to assess the structure responses at different scales. The GL modelling approach is integrated into the multi-scale two-level optimisation strategy (MS2LOS) for composite structures. The resulting design strategy is, thus, called GL-MS2LOS and aims at proposing a very general formulation of the design problem, without introducing simplifying hypotheses on the laminate stack and by considering, as design variables, the full set of geometric and mechanical parameters defining the behaviour of the composite structure at each pertinent scale. By employing a GL modelling approach, most of the limitations of well-established design strategies, based on analytical or semi-empirical models, are overcome. The GL-MS2LOS makes use of the polar formalism to describe the anisotropy of the composite at the macroscopic scale (where it is modelled as an equivalent homogeneous anisotropic plate). In this work, deterministic algorithms are exploited during the solution search phase. The challenge, when dealing with such a design problem, is to develop a suitable formulation and dedicated operators, to link global and local models physical responses and their gradients. Closed-form expressions of structural responses gradients are rigorously derived by taking into account for the coupling effects when passing from global to local models. The effectiveness of the GL-MS2LOS is proven on a meaningful benchmark: the least-weight design of a cantilever wing subject to different design requirements. Constraints include maximum allowable displacements, maximum allowable strains, blending, manufacturability requirements and buckling factor.

In this work, the influence of a compliant hyperelastic polymeric phase infiltrated inside stiff auxetic lattices is studied through experimental and numerical approaches. Samples were fabricated using material jetting technology (MJT). The design principle mimics examples of biological materials which combine stiff and compliant materials to attain high superior mechanical properties exceeding the rule of mixtures of both constituent. Two negative Poisson’s ratio lattice designs are considered, namely Hexaround and Warmuth cell. Their effective elasto-mechanical properties are investigated through finite element method (FEM) using a homogenization strategy with periodic boundary conditions. A comparison of mechanical properties between lattices and composite lattices, for multiple lattice/matrix volume fractions is discussed and numerical models are validated through a series of compression tests. Results suggest that filling lattices could increase Young’s modulus, peak stress, plateau stress and delayed densification of the lattice, hence improving both specific energy absorption (SEA) and absorption efficiency of the considered architectured materials. The improvements are attributed to the presence of the matrix acting as a structural support, modifying lattice failure mode from layerwise to shear band breaking. These results expand the design principles for new energy absorption devices based on architectured materials. France–Australia Science Innovation Collaboration program. ANR JCJC SCOLASTIC project (grant no.16-CE08-0009). Rod Rickards Fellowship from the Australian Academy of Science.

This paper aims at reviewing nonlinear methods for model order reduction of structures with geometric nonlinearity, with a special emphasis on the techniques based on invariant manifold theory. Nonlinear methods differ from linear based techniques by their use of a nonlinear mapping instead of adding new vectors to enlarge the projection basis. Invariant manifolds have been first introduced in vibration theory within the context of nonlinear normal modes (NNMs) and have been initially computed from the modal basis, using either a graph representation or a normal form approach to compute mappings and reduced dynamics. These developments are first recalled following a historical perspective, where the main applications were first oriented toward structural models that can be expressed thanks to partial differential equations (PDE). They are then replaced in the more general context of the parametrisation of invariant manifold that allows unifying the approaches. Then the specific case of structures discretized with the finite element method is addressed. Implicit condensation, giving rise to a projection onto a stress manifold, and modal derivatives, used in the framework of the quadratic manifold, are first reviewed. Finally, recent developments allowing direct computation of reduced-order models (ROMs) relying on invariant manifolds theory are detailed. Applicative examples are shown and the extension of the methods to deal with further complications are reviewed. Finally, open problems and future directions are highlighted., Comment: 64 pages, 8 figures

We compare different models describing the buckling, post-buckling and vibrations of elastic beams in the plane. Focus is put on the first buckled equilibrium solution and the first two vibration modes around it. In the incipient post-buckling regime, the classic Woinowsky-Krieger model is known to grasp the behavior of the system. It is based on the von Kármán approximation, a 2nd order expansion in the strains of the buckled beam. But as the curvature of the beam becomes larger, the Woinowsky-Krieger model starts to show limitations and we introduce a 3rd order model, derived from the geometrically-exact Kirchhoff model. We discuss and quantify the shortcomings of the Woinowsky-Krieger model and the contributions of the 3rd order terms in the new model, and we compare them both to the Kirchhoff model. Different ways to nondi-mensionalize the models are compared and we believe that, although this study is performed for specific boundary conditions, the present results have a general scope and can be used as abacuses to estimate the validity range of the simplified models.

International audience; This work presents a generalized method for robotic mortar extrusion, allowing the fabrication of structural-insulating walls of novel performances. It involves two distinct steps that are to be simultaneously automated: extrusion of a specifically formulated mortar, and assembly of adequately shaped insulating blocks. Here, the layer by layer approach of concrete printing is renewed by using insulating blocks as support for the extrusion. The volumetric space of the wall is divided by an adequate space tessellation, dividing it in polyhedra. They become insulating blocks, on the edges of which mortar is extruded. The set of edges then forms a space truss, of great mechanical efficiency. “Printable” mortar is crucial to the system for the blocks could not withstand the hydrostatic pressure of fresh mortar without additional form-work features, once a few meters height has been reached. This approach renews traditional confined masonry, allowing for geometric complexity and automation.

International audience; Current discrete/lattice methods can simulate a continuous mechanical behavior thanks to a network of bonds. The main drawback of these approaches is the need of a calibration process to link the emerging behavior of the structure and the parameters of the local mechanical bond. It is proposed in this work to use a fast and recent reduction model technique to build once and for all an exhaustive data chart and thus to avoid the calibration process. The proper generalized decomposition technique was used to build a parametric analysis in the case of a lattice beam structure. The results were in the range of the current calibration values found in the literature and extend it by giving a global calibration curve. They also allowed to discuss about the influence, in this specific case of lattice-beam structure, of the density of beams in terms of number of discrete elements and connectivity.

Buckling and wrinkling of thin structures often lead to very complex response curves that are hard to follow by standard path-following techniques, especially for very thin membranes in a slack or nearly slack state. Many recent papers mention numerical difficulties encountered in the treatment of wrinkling problems, especially with path-following procedures and often these authors switch to pseudo-dynamic algorithms. Moreover, the numerical modeling of many wrinkles leads to very large size problems. In this paper, a new numerical procedure based on a double Taylor series is presented, that combines path-following techniques and discretization by a Trefftz method: Taylor series with respect to a load parameter (Asymptotic Numerical Method) and with respect to space variables (Taylor Meshless Method). The procedure is assessed on buckling benchmarks and on the difficult problem of a sheared rectangular membrane. National Research Agency ANR (Labex DAMAS, Grant No.ANR-11-LABX-0008-01). China Scholarship Council.

Non-intrusive methods have been used since two decades to derive reduced-order models for geometrically nonlinear structures, with a particular emphasis on the so-called STiffness Evaluation Procedure (STEP), relying on the static application of prescribed displacements in a finite-element context. We show that a particularly slow convergence of the modal expansion is observed when applying the method with 3D elements, because of nonlinear couplings occurring with very high frequency modes involving 3D thickness deformations. Focusing on the case of flat structures, we first show by computing all the modes of the structure that a converged solution can be exhibited by using either static condensation or normal form theory. We then show that static modal derivatives provide the same solution with fewer calculations. Finally, we propose a modified STEP, where the prescribed displacements are imposed solely on specific degrees of freedom of the structure, and show that this adjustment also provides efficiently a converged solution., Comment: 6 tables, 14 figures, 27 pages

International audience; Since the founding theory established by G. Floquet more than a hundred years ago, computing the stability of periodic solutions has given rise to various numerical methods, mostly depending on the way the periodic solutions are themselves determined , either in the time domain or in the frequency domain. In this paper, we address the stability analysis of branches of periodic solutions that are computed by combining a pure Harmonic Balance Method (HBM) with an Asymptotic Numerical Method (ANM). HBM is a frequency domain method for determining periodic solutions under the form of Fourier series and ANM is continuation technique that relies on high order Taylor series expansion of the solutions branches with respect to a path parameter. It is well established now that this HBM-ANM combination is efficient and reliable, provided that the system of ODE is first of all recasted with quadratic nonlinearities, allowing an easy manipulation of both the Taylor and the Fourier series. In this context, Hill's method, a frequency domain version of Floquet theory, is revisited so as to become a by-product of the HBM applied to a quadratic system, allowing the stability analysis to be implemented in an elegant way and with good computing performances. The different types of stability changes of periodic solutions are all explored and illustrated through several academic examples, including systems that are autonomous or not, conservative or not, free or forced.

International audience; This paper presents the concept of applying life-dependent material parameters to several multiaxial fatigue criteria. This concept reflects the transformation of damage mechanisms in relation to the applied load level, and also in relation to the varying level of plasticity. The goal of this study is to demonstrate the benefit of introducing life-dependent material parameters into stress-based multiaxial fatigue criteria for predicting the fatigue life of materials. New experimental results of fatigue tests on 2124-T851 aluminium alloy confirm the advantage of the life-dependent concept in life assessment over the concept with fixed weight parameters.

International audience; A piezoelectric nanoelectromechanical system (NEMS) with integrated actuation and detection capabilities was fabricated using lead zirconate titanate (PZT) thin films patterned by microcontact printing. PZT-coated cantilever resonators of various dimensions were fabricated to assess the variability in PZT properties as a function of the device dimensions; the microcontact-printed PZT was 281 nm thick. PZT layers of the cantilevers were poled at 107 kV cm−1 and 150 °C to improve their piezoelectric properties. It was demonstrated that PZT piezoelectrics can be utilized for simultaneous actuation and detection of resonance. The PZT cantilevers were analytically modelled to estimate values of their piezoelectric coefficient d31. Mechanical tip displacement detection of the cantilevers by laser vibrometer was also carried out to validate the estimation of d31.

International audience; In this work, a multi-scale optimization strategy for lightweight structures, based on a global-local modelling approach is presented. The approach is applied to a realistic wing structure of a civil aircraft. The preliminary design of the wing can be formulated as a constrained optimization problem, involving several requirements at the different scales of the structure. The proposed strategy is characterized by two main features. Firstly, the problem is formulated in the most general sense, by including all design variables involved at each problem scale. Secondly, two scales are considered: (i) the structure macroscopic scale, where low-fidelity numerical models are used; (ii) the structure mesoscopic scale (or component-level), where enhanced models are involved. In particular, the structural responses are evaluated at both global and local scales, avoiding the use of approximated analytical methods. To this end, fully parametric global and local finite element models are interfaced with an in-house genetic algorithm. Refined models are created only for the most critical regions of the structure, and linked to the global one by means of a dedicated sub-modelling approach.

International audience; In this work, a design strategy for optimising thin-walled structures based on a global-local finite element (FE) modelling approach is presented. The preliminary design of thin-walled structures can be stated in the form of a constrained non-linear programming problem (CNLPP) involving requirements of different nature intervening at the different scales of the structure. The proposed multi-scale optimisation (MSO) strategy is characterised by two main features. Firstly, the CNLPP is formulated in the most general sense by including all design variables involved at each pertinent scale of the problem. Secondly, two scales (with the related design requirements) are considered: (a) the structure macroscopic scale, where low-fidelity FE models are used and (b) the structure mesoscopic scale (or component level), where more accurate FE models are involved. In particular, the mechanical responses of the structure are evaluated at both global and local scales, avoiding the use of approximated analytical methods. The MSO is here applied to the least-weight design of an aluminium fuselage barrel of a wide-body aircraft. Fully parametric global and local FE models are interfaced with an in-house metaheuristic algorithm. Refined local FE models are created only for critical regions of the structure, automatically detected during the global analysis, and linked to the global one, thanks to the implementation of a sub-modelling approach. The whole process is completely automated, and once set, it does not need any further user intervention.; In this work, a design strategy for optimising thin-walled structures based on a global-local finite element (FE) modelling approach is presented. The preliminary design of thin-walled structures can be stated in the form of a constrained non-linear programming problem (CNLPP) involving requirements of different nature intervening at the different scales of the structure. The proposed multi-scale optimisation (MSO) strategy is characterised by two main features. Firstly, the CNLPP is formulated in the most general sense by including all design variables involved at each pertinent scale of the problem. Secondly, two scales (with the related design requirements) are considered: i) the structure macroscopic scale, where low-fidelity FE models are used; ii) the structure mesoscopic scale (or component-level), where more accurate FE models are involved. In particular, the mechanical responses of the structure are evaluated at both global and local scales, avoiding the use of approximated analytical methods. The MSO is here applied to the least-weight design of an aluminium fuselage barrel of a wide-body aircraft. Fully parametric global and local FE models are interfaced with an in-house metaheuristic algorithm. Refined local FE models are created onlyfor critical regions of the structure, automatically detected during the global analysis, and linked to the global one thanks to the implementation of a sub-modelling approach. The whole process is completely automated and, once set, it does not need any further user intervention.

International audience; Improving the energy efficiency of power plants by increasing steam operating temperature up to 700 °C can be achieved using novel engineering design concepts such as coated steam pipe systems. This paper presents an optimised designfor a novel coated dual pipe system to be used in advanced ultra-supercritical power plant. The approach developed in this study uses a combination of an optimisation algorithm and FE simulation, based on the reduction of the hoop stress at top coat/bond coat interface generated by the thermal and mechanical stresses. This allows determination of the optimum dimensions and material properties of the system. A unified viscoplastic model which combines a power flow rule with non-linearanisothermal evolution of isotropic and kinematic hardening has been used for the thermo-mechanical analysis of the coated dual pipe system under the cyclic loading. The results of the optimisation show that the value of the hoop stress at the top coat/bond coat interface is reduced significantly, compared with that in the baseline model. Finally, the potential technical challenges and future works for the proposed steam dual pipe system are discussed.

Under tension low carbon steel exhibits inhomogeneous plastic deformation. This instability called Piobert-Lüders banding creates fronts of localized strain that propagate in the structure. To date, Lüders banding has been studied experimentally and numerically only in simple geometries like sheets, tubes and normalized fracture mechanics specimens. This paper focuses on architectured materials and specifically lattice structures which can be defined as a tessellation of unit-cells periodically distributed in space. This class of advanced materials draws new mechanical properties from its inner architecture. We investigate the effect of the architecture on the global behavior of the structure. Especially, how bands interact with the lattice and how to control initiation and propagation of localized strain using the architecture. An elastoplastic material model is used in order to simulate the Piobert-Lüders band formation and propagation. The model also considers a large deformation framework for elastoplasticity with periodic boundary conditions in order to represent the architectured material. Initiation and propagation of material instabilities depend on the geometry as well as its on the relative orientation with respect to the loading direction. Propagating and non-propagating behaviors are identified for the Piobert-Lüders bands and related to the different types of geometry. Material instabilities affect the mechanical behavior of the structure as far as they are governed by the architecture. These conclusions are compared to experimental results from tensile tests on laser-architectured specimens made of ARMCO steel. ANR-16-CE08-0001 (ANR ALMARIS project)

International audience; During the last decades, a family of assumed-strain solid-shell finite elements has been developed with enriched benefits of solid and shell finite elements together with special treatments to avoid locking phenomena. These elements have been shown to be efficient in numerical simulation of thin 3D structures with various constitutive models. The current contribution consists in the combination of the developed linear and quadratic solid-shell elements with complex anisotropic plasticity models for aluminum alloys. Conventional quadratic anisotropic yield functions are associated with less accuracy in the simulation of forming processes with metallic materials involving strong anisotropy. For these materials, the plastic anisotropy can be modeled more accurately using advanced non-quadratic yield functions, such as the anisotropic yield criteria proposed by Barlat for aluminum alloys. In this work, various quadratic and non-quadratic anisotropic yield functions are combined with a linear eight-node hexahedral solid-shell element and a linear six-node prismatic solid-shell element, and their quadratic counterparts. The resulting solid-shell elements are implemented into the ABAQUS software for the simulation of benchmark deep drawing process of a cylindrical cup. The predicted results are assessed and compared to experimental ones taken from the literature. Compared to the use of conventional quadratic anisotropic yield functions, the results given by the combination of the developed solid-shell elements with non-quadratic anisotropic yield functions show good agreement with experiments.

International audience; In this work, nonlinear dynamic analysis of thin structures is investigated using quadratic solid-shell (SHB-EXP) elements. The proposed SHB-EXP elements are based on a fully three-dimensional formulation using an in-plane reduced-integration scheme along with the assumed-strain method in order to alleviate most locking phenomena. These developments consist of a twenty-node hexahedral element, denoted SHB20-EXP, and its fifteen-node prismatic counterpart, denoted SHB15-EXP. The formulation of these elements is combined with fully three-dimensional behavior models, including elastic behavior as well as anisotropic plastic behavior for metallic materials. The resulting formulations are implemented into ABAQUS explicit/dynamic software package in the framework of large displacements and rotations. First, to assess the performance of the SHB-EXP elements, four representative nonlinear dynamic benchmark tests have been conducted. Then, impact / crash problem and deep drawing of cylindrical cup have been performed to demonstrate the capabilities of the SHB-EXP elements in handling various types of nonlinearities (large strains, anisotropic plasticity, and double-sided contact). Comparisons with results obtained by ABAQUS elements as well as with reference solutions taken from the literature show the good capabilities of the developed quadratic SHB-EXP elements for the explicit dynamic simulation of thin structures.

International audience; Even if the diffusion equation has been widely used in physics and engineering, and its physical content is well understood, some variants of it escape fully physical understanding. In particular, anormal diffusion appears in the so-called fractional diffusion equation, whose main particularity is its non-local behavior, whose physical interpretation represents the main part of the present work.

International audience; In this paper, a method for the quasi-static simulation of flexible cables assembly in the context of automotive industry is presented. The cables geometry and behavior encourage to employ a geometrically exact beam model. The 3D kinematics is then based on the position of the centerline and on the orientation of the cross-sections, which is here represented by rotational quaternions. Their algebraic nature leads to a polynomial form of equilibrium equations. The continuous equations obtained are then discretized by the finite element method and easily recast under quadratic form by introducing additional slave variables. The asymptotic numerical method, a powerful solver for systems of quadratic equations, is then employed for the continuation of the branches of solution. The originality of this paper stands in the combination of all these methods which leads to a fast and accurate tool for the assembly process of cables. This is proved by running several classical validation tests and an industry-like example.

The properties of reinforced polymers strongly depend on the microstructural state, that is, the orientation state of the fibres suspended in the polymeric matrix, induced by the forming process. Understanding flow-induced anisotropy is thus a key element to optimize both materials and process. Despite the important progresses accomplished in the modelling and simulation of suspensions, few works addressed the fact that usual processing flows evolve in confined configurations, where particles characteristic lengths may be greater than the thickness of the narrow gaps in which the flow takes place. In those circumstances, orientation kinematics models proposed for unconfined flows must be extended to the confined case. In this short communication, we propose an alternative modelling framework based on the use of unilateral mechanics, consequently exhibiting a clear analogy with plasticity and contact mechanics. This framework allows us to revisit the motion of confined particles in Newtonian and non-Newtonian matrices. We also prove that the confined kinematics provided by this model are identical to those derived from microstructural approaches (Perez et al. (2016) [1] ).

While modal identification is a mature subject, very few studies address the characterization of errors associated with components of a mode shape. This is particularly important in test/analysis correlation procedures, where the Modal Assurance Criterion is used to pair modes and to localize at which sensors discrepancies occur. Poor correlation is usually attributed to modeling errors, but clearly identification errors also occur. In particular with 3D Scanning Laser Doppler Vibrometer measurement, many transfer functions are measured. As a result individual validation of each measurement cannot be performed manually in a reasonable time frame and a notable fraction of measurements is expected to be fairly noisy leading to poor identification of the associated mode shape components. The paper first addresses measurements and introduces multiple criteria. The error measures the difference between test and synthesized transfer functions around each resonance and can be used to localize poorly identified modal components. For intermediate error values, diagnostic of the origin of the error is needed. The level evaluates the transfer function amplitude in the vicinity of a given mode and can be used to eliminate sensors with low responses. A Noise Over Signal indicator, product of error and level, is then shown to be relevant to detect poorly excited modes and errors due to modal property shifts between test batches. Finally, a contribution is introduced to evaluate the visibility of a mode in each transfer. Using tests on a drum brake component, these indicators are shown to provide relevant insight into the quality of measurements. In a second part, test/analysis correlation is addressed with a focus on the localization of sources of poor mode shape correlation. The MACCo algorithm, which sorts sensors by the impact of their removal on a MAC computation, is shown to be particularly relevant. Combined with the error it avoids keeping erroneous modal components. Applied after removal of poor modal components, it provides spatial maps of poor correlation, which help localizing mode shape correlation errors and thus prepare the selection of model changes in updating procedures.

In this work a multi-scale two-level (MS2L) optimisation strategy for optimising VAT composites is presented. In the framework of the MS2L methodology, the design problem is split and solved into two steps. At the first step the goal is to determine the optimum distribution of the laminate stiffness properties over the structure (macroscopic scale), while the second step aims at retrieving the optimum fibres-path in each layer meeting all the requirements provided by the problem at hand (mesoscopic scale). The MS2L strategy has been improved in order to integrate all types of requirements (mechanical, manufacturability, geometric, etc.) within the first-level problem. The proposed approach relies on: (a) the polar formalism for describing the behaviour of the VAT laminate, (b) the iso-geometric surfaces for describing the spatial variation of both the laminate stiffness properties (macro-scale) and the layers fibres-path (meso-scale) and (c) an hybrid optimisation tool (genetic and gradient-based algorithms) to perform the solution search. The effectiveness of the MS2L strategy is proven through a numerical example on the maximisation of the first buckling factor of a VAT plate subject to both mechanical and manufacturability constraints.

In order to overcome the possible singularity associated with the Point Interpolation Method (PIM), the Radial Point Interpolation Method (RPIM) was proposed by G. R. Liu. Radial basis functions (RBF) was used in RPIM as basis functions for interpolation. All these radial basis functions include shape parameters. The choice of these shape parameters has been and stays a problematic theme in RBF approximation and interpolation theory. The object of this study is to contribute to the analysis of how these shape parameters affect the accuracy of the radial PIM. The RPIM is studied based on the global Galerkin weak form performed using two integration technics: classical Gaussian integration and the strain smoothing integration scheme. The numerical performance of this method is tested on their behavior on curve fitting, and on three elastic mechanical problems with regular or irregular nodes distributions. A range of recommended shape parameters is obtained from the analysis of different error indexes and also the condition number of the matrix system. All resulting RPIM methods perform very well in term of numerical computation. The Smoothed Radial Point Interpolation Method (SRPIM) shows a higher accuracy, especially in a situation of distorted node scheme.

International audience; In standard practice, testing of composites in tension requires the use of stress inducing serrated grips. The low transverse compressive strength of unidirectional non-crimp fabric composites limits the application of high clamping forces. Tabs are therefore essential as they ensure a reduction in grip pressure transmission, surface damage and induced stress damage. Tabs, however, tend to introduce induced stress concentrations at the tab termination region. The objective of this study was to minimise stress concentration by varying tab design configurations to determine the optimal design most suitable for tensile testing of non-crimp fabric composites using finite element and statistical tools. Finite element models generated from experimental data were used for accessing the stress concentrations. A two (2)-level full factorial design was adopted and utilised for statistical analysis. Results revealed that tab stiffness, tab taper angle, adhesive thickness and manufacturing process (bonded or molded) were statistically significant for minimising stress concentration. molded tabs were found to be acceptableif the stiffness of tab was significantly lower than test specimen. The optimal configuration derived from the multiple response optimisation was tab stiffness (20 Gpa), tab Thickness (0.5 mm), tab length (50 mm), tab taper angle (5 o ) and adhesive thickness (1.5 mm).

This study deals with the problem of the least-weight design of a composite multilayer plate subject to constraints of different nature (mechanical, geometrical and technological requirements). To face this problem, a multi-scale two-level (MS2L) design methodology is proposed. This approach aims at optimising simultaneously both geometrical and mechanical parameters of the laminate at each characteristic scale (mesoscopic and macroscopic ones). In this background, at the first level (macroscopic scale) the goal is to find the optimum value of geometrical and mechanical design variables minimising the structure mass and satisfying the set of imposed constraints (on first buckling load, membrane stiffness and feasibility constraints). The second-level problem (mesoscopic scale) aims at finding at least one stacking sequence meeting the geometrical and material parameters provided by the first-level problem. The MS2L optimisation approach is based on the polar formalism to describe the macroscopic behaviour of the composite (in the framework of the equivalent single layer theories) and on a special genetic algorithm to perform optimisation calculations. The optimum solutions provided by the MS2L optimisation strategy are characterised by a weight saving of about 10% with enhanced mechanical properties when compared to conventional symmetric balanced stacks. The effectiveness of the optimum solutions is also proven through an experimental campaign of buckling tests. The experimental results are in excellent agreement with those foreseen by the numerical simulations. PARSIFAL (Prandtlplane ARchitecture for the Sustainable Improvement of Future AirpLanes) project. Grant Agreement n. 723149

International audience; This research work deals with the geometric modelling of 5-axis machine tool based on a standard-ised parameterisation of geometric errors with the aim to decrease the volumetric error in the workspace. The identification of the model's parameters is based on the development of a new standard thermo-invariant material namely the Multi-Feature Bar. Thanks to its calibration and a European intercom-parison, it now provides a direct metrological traceability to the SI metre for dimensional measurement on machine tool in a hostile environment. The identification of three intrinsic parameters of this standard , coupled with a measurement procedure ensures a complete and traceable identification of motion errors of linear axes. An identification procedure of location and orientation errors of axes is proposed by probing a datum sphere in the workspace and minimising the time drift of the structural loop and the effects of the previously identified motion errors. Finally, the developed model partially identified, allows the characterisation of 95% of the measured volumetric error. Therefore, the mean volumetric error not characterised by the model only amounts to 8 µm.; Ces travaux de recherche portent sur la modélisation géométrique de machine-outil 5-axes, basée sur une paramétrisation normalisée des erreurs géométriques en vue de réduire l’erreur volumétrique au sein du volume de travail. L’identification du modèle est passé par le développement d’un nouvel étalon matériel thermo-invariant : la Multi-Feature Bar. Raccordé à la définition internationale du mètre par un étalonnage et une intercomparaison européenne, il permet d’envisager des mesures traçables sur machine-outil dans un environnement hostile. L’identification de trois paramètres intrinsèques à cet étalon, couplée à une procédure de mesure, assure une identification complète et traçable des erreurs de mouvement d’axes linéaires. Ensuite, l’identification des erreurs entre axes est quant à elle baséesur une procédure de palpage de sphère dans le volume de travail en minimisant la dérive temporelle de la structure ainsi que les effets des erreurs de mouvement précédemment identifiés. Au terme de ces travaux, le modèle développé, et partiellement identifié permet d’ores et déjà de caractériser 95 % de l’erreur volumétrique mesurée. Ainsi l’erreur volumétrique moyenne non caractérisée par le modèle ne s’élève qu’à 8 µm.

International audience; This paper presents a general methodology to compute nonlinear frequency responses of flat structures subjected to large amplitude transverse vibrations, within a finite element context. A reduced-order model (ROM)is obtained by an expansion onto the eigenmode basis of the associated linearized problem, including transverse and in-plane modes. The coefficients of the nonlinear terms of the ROM are computed thanks to a non-intrusive method, using any existing nonlinear finite element code. The direct comparison to analytical models of beams and plates proves that a lot of coefficients can be neglected and that the in-plane motion can be condensed to the transverse motion, thus giving generic rules to simplify theROM. Then, a continuation technique, based on an asymptotic numerical method and the harmonic balance method, is used to compute the frequency response in free (nonlinear mode computation) or harmonically forced vibrations. The whole procedure is tested on a straight beam, a clamped circular plate and a free perforated plate for which some nonlinear modes are computed, including internal resonances. The convergence with harmonic numbers and oscillators is investigated. It shows that keeping a few of them is sufficient in a range of displacements corresponding to the order of the structure’s thickness, with a complexity of the simulated nonlinear phenomena that increase very fast with the number of harmonics and oscillators.

International audience; Fully reversed strain controlled low cycle fatigue and creep-fatigue interaction tests have been performed at ±0.7% strain amplitude and at three different temperatures (400°C, 500°C and 600°C) to investigate the cyclic behaviour of a FV566 martensitic turbine steel. From a material point of view, the hysteresis mechanical responses have demonstrated cyclic hardening at the running-in stage and subsequent, hysteresis cyclic softening during the rest of the material life. The relaxation and energy behaviours have shown a rapid decrease at the very beginning of loading followed by quasi-stabilisation throughout the test. A unified, temperature- and rate-dependent visco-plastic model was then developed and implemented into the Abaqus finite element (FE) code through a user defined subroutine (UMAT). The material parameters in the model were determined via an optimisation procedure based on a genetic solver. The multi-axial form of the constitutive model developed was demonstrated by analysing the thermomechanical responses of an industrial gas turbine rotor subjected to in-service conditions. Asub-modelling technique was used to optimise the FEA. A 2D global model of the rotor with a 3D sub-model of the second stage of the low pressure turbine were then analysed in turn. The complex transient stress and accumulated plastic strain fields were investigated under realistic thermo-mechanical fatigue loading (start-up and shut-down power plant loads). The sub-modelwas then used for local analysis leading to identification of potential crack initiation sites for the presented types of blade roots.

International audience; This paper addresses the design of the elastic structure of artificial wings to optimize their dynamical behaviour to reproduce insect wings kinematics. Our bioinspired kinematics is based on the original concept of using the resonant properties of the wing structure in order to combine the motion of two vibration modes, a flapping and a twisting mode, in a quadrature phase shift. Oneway of achieving this particular combination is to optimize the geometry and elastic characteristics of the flexible structure such that the two modes are successive in the eigenspectrum and close in frequency. This paper first proposes a semi-analytical model, based on assembled Euler-Bernoulli beams, to understand, compute and optimize the artificial wing dynamic vibrations. Then, using this model, it is shown that it is possible to obtain several artificial wing structures with a flapping and a twisting mode close in frequency. Finally, experimental validations are performed on micromachined insect-sized prototypes to validatethe model and the concept.

This article investigates the elastic properties of a large panel of lattice architectures using a continuous description of geometry. The elastic constants of the orthotropic material are determined, and discussed in terms of specific stiffness and of its density dependence. Different kinds of topology families are emerging depending on their specific deformation behavior. For some of them, interesting properties in terms of traction-compression were measured, while some other families are predominantly adapted to shear loading. Homogenization technique also allows to quantify the anisotropy of the structures and to compare them. Specific structures having quasi-isotropic properties even at low relative densities were detected. Experimental works demonstrated the validity of the numerical models, and highlighted the necessity to consider carefully the effect of defects on the specific strength, which are not negligible, despite being of the second-order. Finally, this article provides user-friendly maps for selection of optimal architectures for a large variety of specific needs, like a target stiffness or anisotropy. Keywords: Lattice structures, Porous materials, Homogenization, Elastic constants determination, Mechanical behavior

International audience; In this work we study the nonlinear coupling between the transverse modes of nanoresonators such as nanotubes or nanowires in a singly clamped configuration. We previously showed that at high driving, this coupling could result in a transition from independent planar modes to a locked elliptical motion, with important modifications of the resonance curves. Here we clarify the physical origins, associated to a 1:1 internal resonance, and study in depth this transition as a function of the relevant parameters. We present simple formulae that permit to predict the appearance of this transition as a function of the frequency difference between the polarizations and the nonlinear coefficients and give the "backbone curves" corresponding to the elliptical regime. We also show that the elliptical regime is associated with the emergence of a new set of solutions of which one branch is stable. Finally we compare single and double clamped configurations and explain why the elliptical transition appears on different polarizations.

International audience; This paper presents an experimental approach aimed at analyzing and validating a two-scale nonlinear Finite Element (FE 2 ) simulation of a 3D composite structure. The studied composite material consists of polyamide thermoplastic matrix, exhibiting viscoelastic-viscoplastic behavior with ductile damage, reinforced by woven glass fabric whereby inelastic and anisotropicdamage behavior is considered. The multiscale parallel computation is founded on the periodic homogenization at the microscopic scale, which considers the geometric description of the reinforcement’s architecture and accounts for time-dependent and non-linear local behavior of each constitutive phase. For the numerical implementation at microscopic and macroscopic scales, an advanced UMAT subroutine is developed and combined with a parallelization technique in the commercial software Abaqus/Standard. The multilevel computation is achieved simultaneously at both scales (microscopic and macroscopic) through an incremental scheme. Numerical results of the FE multiscale simulation are analyzed and compared with the experimental results obtained for different stacking sequence configurations of a 3D woven composite holed plate subjected to tension. Besides the good agreement between the experimental and the predicted load-displacement global responses, the numerical simulation of the macroscopic strain fields reasonably agrees with those measured experimentally through the Digital Image Correlation (DIC) technique. Furthermore, the performance and the capabilities of the multiscale (FE 2 ) strategy are demonstrated getting access, at the microstructure scale, to the microscopic strain fields and the spatiotemporal distributions of the internal variables as well as the damage evolution in the polymer matrix and the reinforcement (yarns).

In the present paper a new additive manufacturing processing route is introduced for ultra-high performance concrete. Interdisciplinary work involving materials science, computation, robotics, architecture and design resulted in the development of an innovative way of 3D printing cementitious materials. The 3D printing process involved is based on a FDM-like technique, in the sense that a material is deposited layer by layer through an extrusion printhead mounted on a 6-axis robotic arm. The mechanical properties of 3D printed materials are assessed. The proposed technology succeeds in solving many of the problems that can be found in the literature. Most notably, this process allows the production of 3D large-scale complex geometries, without the use of temporary supports, as opposed to 2.5D examples found in the literature for concrete 3D printing. Architectural cases of application are used as examples in order to demonstrate the potentialities of the technology. Two structural elements were produced and constitute some of the largest 3D printed concrete parts available until now. Multi-functionality was enabled for both structural elements by taking advantage of the complex geometry which can be achieved using our technology for large-scale additive manufacturing. Keywords: 3D Printing, Concrete, Cementitious materials, Large-scale additive manufacturing, Architecture design

This work deals with the problem of the optimum design of a sandwich panel made of carbon-epoxy skins and a metallic cellular core. The proposed design strategy is a multi-scale numerical optimisation procedure that does not make use of any simplifying hypothesis to obtain a true global optimum configuration of the system. To face the design of the sandwich structure at both meso and macro scales, a two-level optimisation strategy is employed: at the first level the goal is the determination of the optimum shape of the unit cell of the core (meso-scale) together with the material and geometric parameters of the laminated skins (macro-scale), while at the second level the objective is the design of the skins stacking sequence (skin meso-scale) meeting the geometrical and material parameters provided by the first-level problem. The two-level strategy is founded on the polar formalism for the description of the anisotropic behaviour of the laminates, on the NURBS basis functions for representing the shape of the unit cell and on the use of a genetic algorithm as optimisation tool to perform the solution search. To prove its effectiveness, the multi-scale strategy is applied to the least-weight design of a sandwich plate subject to constraints of different nature: on the positive-definiteness of the stiffness tensor of the core, on the admissible material properties of the laminated faces, on the local buckling load of the unit cell, on the global buckling load of the panel and geometrical as well as manufacturability constraints related to the fabrication process of the cellular core.

International audience; A self-control method of vibrations is presented in this paper. This method combines the passive damping capabilities afforded by viscoelastic materials with the active control properties associated with piezoelectric materials. Active control is introduced, using the piezoelectric properties, in order to improve the reduction in vibration amplitudes that can be obtained by viscoelastic passive damping alone. To this end, a filter has been mounted between the sensors and actuators. The resulting nonlinear problem is discretized using the recently developed solid–shell finite element SHB20E, due to the advantages it offers in terms of accuracy and efficiency, as compared to standard finite elements with the same geometry and kinematics. In order to solve the discretized problem, a resolution method using DIAMANT approach is developed. A set of selective and representative numerical tests are performed on multilayer plates to demonstrate the interest of the proposed damping model.

International audience; [FeII(Htrz)2(trz)](BF4) spin crossover particles of 85 nm mean size are dispersed in an SU‐8 polymer matrix and spray‐coated onto silicon microcantilevers. The subsequent photothermal treatment of the polymer resist leads to micrometer thick, smooth, and homogeneous coatings, which exhibit well‐reproducible actuation upon the thermally induced spin transition. The actuation amplitude as a function of temperature is accurately determined by combining integrated piezoresistive detection with external optical interferometry, which allows for the assessment of the associated actuation force (9.4 mN), stress (28 MPa), strain (1.0%), and work density (140 mJ cm−3) through a stratified beam model. The dynamical mechanical characterization of the films evidences an increase of the resonance frequency and a concomitant decrease of the damping in the high‐temperature phase, which arises due to a combined effect of the thickness and mechanical property changes. The spray‐coating approach is also successfully extended to scale up the actuators for the centimeter range on a polymer substrate providing perspectives for biomimetic soft actuators.

International audience; Separated representations at the heart of Proper Generalized Decomposition are constructed incrementally by minimizing the problem residual. However, the modes involved in the resulting decomposition do not exhibit a clear multi-scale character. In order to recover a multi-scale description of the solution within a separated representation framework, we study the use of wavelets for approximating the functions involved in the separated representation of the solution. We will prove that such an approach allows separating the different scales as well as taking profit from its multi-resolution behavior for defining adaptive strategies.

International audience; Study: Implantation of a Left Ventricular Assist Device (LVAD) may produce both excessive local tissue stress and resulting strain-induced tissue rupture that are potential iatrogenic factors influencing the success of the surgical attachment of the LVAD into the myocardium. By using a computational simulation compared to mechanical tests, we sought to investigate the characteristics of stress-induced suture material on porcine myocardium.Methods: Tensile strength experiments (n = 8) were performed on bulk left myocardium to establish a hyperelastic reduced polynomial constitutive law. Simultaneously, suture strength tests on left myocardium (n = 6) were performed with a standard tensile test setup. Experiments were made on bulk ventricular wall with a single U-suture (polypropylene 3-0) and a PTFE pledget. Then, a Finite Element simulation of a LVAD suture case was performed. Strength versus displacement behavior was compared between mechanical and numerical experiments. Local stress fields in the model were thus analyzed.Results: A strong correlation between the experimental and the numerical responses was observed, validating the relevance of the numerical model. A secure damage limit of 100 kPa on heart tissue was defined from mechanical suture testing and used to describe numerical results. The impact of suture on heart tissue could be accurately determined through new parameters of numerical data (stress diffusion, triaxiality stress). Finally, an ideal spacing between sutures of 2 mm was proposed.Conclusion: Our computational model showed a reliable ability to provide and predict various local tissue stresses created by suture penetration into the myocardium. In addition, this model contributed to providing valuable information useful to design less traumatic sutures for LVAD implantation. Therefore, our computational model is a promising tool to predict and optimize LVAD myocardial suture.

International audience; To date, Several focusing techniques have been proposed to realize localized stimulation on haptic interfaces: phased arrays of actuators with delayed excitation, or time reversal techniques which require a preliminary learning phase. Additionally, these techniques are sensitive to parameters variation and disturbances. Modal decomposition allows to realize arbitrary vibration fields congruent with the boundary conditions and in this paper, Modal decomposition is proposed to realize a desired vibration velocity field in order to have differentiated stimuli. The experimental results validate the ability of the method to approximate satisfactorily a desired reference form. The psychophysical evaluations show that users can differentiate and localize the stimulation while exploring a surface with two fingers.

International audience; In this work, we propose two prismatic piezoelectric solid–shell elements based on fully three-dimensional kinematics. For this purpose, we perform electromechanical coupling, which consists in adding an electrical degree of freedom to each node of the purely mechanics-based versions of these elements. To increase efficiency, these geometrically three-dimensional elements are provided with some desirable shell features, such as a special direction, designated as the thickness, along which the integration points are located, while adopting a reduced integration rule in the other directions. To assess the performance of the proposed piezoelectric solid–shell elements, a variety of benchmark tests, both in static and vibration analysis, have been performed on multilayer structures ranging from simple beams to more complex structures involving geometric nonlinearities. Compared to conventional finite elements with the same kinematics, the evaluation results allow highlighting the higher performance of the newly developed solid–shell technology.

Structural health monitoring offers new approaches to interrogate the integrity of complex structures. The structural health monitoring process classically relies on four sequential steps: damage detection, localization, classification, and quantification. The most critical step of such process is the damage detection step since it is the first one and because performances of the following steps depend on it. A common method to design such a detector consists of relying on a statistical characterization of the damage indexes available in the healthy behavior of the structure. On the basis of this information, a decision threshold can then be computed in order to achieve a desired probability of false alarm. To determine the decision threshold corresponding to such desired probability of false alarm, the approach considered here is based on a model of the tail of the damage indexes distribution built using the Peaks Over Threshold method extracted from the extreme value theory. This approach of tail distribution estimation is interesting since it is not necessary to know the whole distribution of the damage indexes to develop a detector, but only its tail. This methodology is applied here in the context of a composite aircraft nacelle (where desired probability of false alarm is typically between 10−4 and 10−9) for different configurations of learning sample size and probability of false alarm and is compared to a more classical one which consists of modeling the entire damage indexes distribution by means of Parzen windows. Results show that given a set of data in the healthy state, the effective probability of false alarm obtained using the Peaks Over Threshold method is closer to the desired probability of false alarm than the one obtained using the Parzen-window method, which appears to be more conservative.

This study proposes an innovative model based on local grain angle measurements to predict the modulus of elasticity of LVL made from beech. It includes a veneers sorting method industrially compatible thanks to its low computational time. For this study 41 LVL panels were prepared from 123 beech sheets of veneers. Local grain angle was obtained with a two dimensional scanner and veneer density was measured. Several models based on these measurements have been developed and their ability to predict the modulus of elasticity of LVL panels have been compared. The model based only on local grain angle measurements have been proven more efficient than models taking into account the veneer density. The proposed method can be used to sort veneer during the peeling process and grade the production of LVL panels to optimize their mechanical properties even for low-quality veneer. ANR-10-EQPX-16 XYLOFOREST ; Région Bourgogne Franche-Comté ; Brugère

The design and optimisation of lightweight structures is of paramount importance in many industrial fields: from automotive to biomedical ones, from naval to aerospace fields. During the last three decades, new manufacturing processes emerged, e.g. the additive layer manufacturing (ALM) technology applied to different materials (metals, ceramics, composites), the automated fibre placement (AFP) technology for tailoring unconventional composites (both thermoplastic and thermoset ones), the compression moulding compound (CMC) technology (well suited for thermoplastic composites), etc. Therefore, the development of new, modern and well-suited design/optimisation methodologies becomes fundamental. Generally speaking, the design/optimisation strategy should be able to provide an optimised but also manufacturable solution. On the one hand, this methodology must be able to include, since the early stage of the design process (i.e. the preliminary design phase), the specificity of such new technologies (and, mostly, the related technological limitations). On the other hand, the design/optimisation strategy must be able to find a solution when the problem is formulated in the most general sense and when the full set of design variables, involved at different scales, is considered. In order to attain this ambitious goal, the formalisation of new models (or the generalisation of the existing ones) is of capital importance: the problem formulation must be as general as possible and the useless simplifying hypotheses should be totally (or partially) rejected. Of course, the price to pay is an increased problem complexity. This HDR manuscript represents a synthesis of my research activities since September 2013 which are essentially framed into the previous background. This document briefly present my contribution to the development of suitable design strategies for the optimisation of lightweight structures. The work is articulated into four main research axes: - the development of new numerical methods (meta-heuristics) for the resolution of optimisation problems characterised by a variable number of design variables (e.g. the optimisation of modular structures); - the formulation of high-order shear deformation theories based on tensor invariants (for plates and shells) and the development of a multi-scale optimisation strategy for designing unconventional constant stiffness and variable stiffness composites (manufactured through the AFP process); - the development of a new topology optimisation method based on both NURBS hyper-surfaces and density-based schemes (well suited for parts manufactured by ALM technologies); - the development of a general (i.e. problem-independent) optimisation strategy for inverse problems. The effectiveness of these methods has been proven (for each topic) through benchmarks taken from the literature and by means of real-world engineering problems as well. Starting from these encouraging results, some general and meaningful perspectives on both new design/optimisation strategies and new manufacturing process for producing hybrid anisotropic structures (of complex topology) are given at the end of the manuscript.

International audience; In this paper, we investigate the influence of deviations in the design and implementation parameters on the damping properties of multilayer viscoelastic structures. This work is based on a numerical approach, which uses recently developed solid–shell elements that have been specifically designed for the modeling of multilayer structures. The originality in the current study lies in the analysis of variation in the design parameters, which could be of geometric or material type. Indeed, although several models have been proposed to study variability, they remain mostly complex to implement. Our approach is rather simple, and is based on the uncertainty on the actual values of several parameters in some well-defined intervals. The developed method is applied to the vibration modeling of multilayer structures, with elastic faces and viscoelastic core material. The resulting problem is discretized by using quadratic solid–shell finite elements. To solve the associated nonlinear equations, we adopt the method that couples the homotopy technique to the Asymptotic Numerical Method (ANM) as well as the Automatic Differentiation (AD) and path continuation. The obtained results provide useful information on the error tolerance margin that could be allowed without compromising structural integrity.