Conception optimisée de structures constituées de matériaux composites thermoplastiques à fibres continues

Les matériaux composites à matrice thermoplastique et fibre continue (TPFC) connaissent depuis quelques années un essor important. Les raisons de cette évolution tiennent aux besoins d'optimisation de certaines industries comme l'automobile ou l'aéronautique. Paradoxalement, peu d'études leur sont consacrées. La quasi totalité des essais et des études scientifiques publiées sur les TPFC ont été réalisés sur des composites AS4/PEEK, un matériau d'excellence, reconnu pour ses performances mécaniques proches des composites carbone-époxy classiques. Dans un premier temps, un ensemble de publications est exploité pour mettre en évidence les principales caractéristiques du comportement mécanique de TPFC unidirectionnels (UD). Suite à cette étude, nous proposons un modèle multi-échelle qui reproduit convenablement la réponse d'un stratifié tout en limitant l'effort expérimental et numérique. Cette étude a permis de simuler fidèlement un ensemble d'essais tirés de la littérature et ainsi conforter les hypothèses faites. Une seconde étape du travail de cette thèse concerne l'optimisation de structures composites. La riche bibliographie sur cette thématique nous a permis de cerner les principales exigences industrielles, et de choisir un algorithme génétique, adapté à la spécificité des problèmes traités. Des problèmes simples sont exploités pour comparer les mérites respectifs de divers choix algorithmiques et pour évaluer l'influence des paramètres mécaniques sur les solutions optimales. Enfin, des analyses structurelles sont menées par la méthode des éléments finis intégrant des contraintes technologiques. Ce travail met en évidence l'importance des choix méthodologiques sur la qualité de la solution finale. Les méthodes proposées permettent d'obtenir des solutions quasi-optimales performantes tout en limitant la durée des procédures grâce à une évaluation comparative rigoureuse qui justifie les hypothèses retenues.Composite materials with thermoplastic matrix and continuous fibre (TPCF) progressed considerably over the past few years. This stems from the needs for optimization of certain industries such as the automotive and aeronautic industries, which are seeking to improve certain design features. Paradoxically, few studies have investigated these products. Nearly all the tests and the scientific studies published on the TPCF were conducted on composites AS4/PEEK composites, an excellent material ,that is recognised for its mechanical performances close to the traditional carbon-epoxy composites. First, the research in this area is reviewed to highlight the main characteristics of unidirectional TPCF. Following this study, we propose a multi-scale model which suitably reproduces the response of a laminate while limiting the experimental and numerical effort. This study made it possible to accurately simulate a whole of tests drawn from the literature and thus to consolidate the made assumptions. The second stage of the work of this thesis investigates the optimization of composite structures. A review of the abundant bibliography on this topic provided the principal main industrial requirements, which led to the choice of the genetic algorithm adapted to the specificity of the problems involved. Thereafter, simple problems were tested to compare the respective merits of various algorithmic choices and to evaluate the influence of the mechanical parameters on the optimal solutions. Lastly, the structural analyses were carried out by using the finite element method integrating technological constraints. This work highlights the importance of the methodological choices on to the quality of the final solution. The methods suggested make it possible to obtain good quasi-optimal solutions while limiting the duration of the procedures thanks to a rigorous comparative evaluation which justifies the assumptions selected.CHAMBERY -BU Bourget (730512101) / SudocSudocFranceF

Single- and multi-objective optimization of composite structures: the influence of design variable

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Optimization of blended composite structures: parametric study

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Yield criterion for porous media with spherical voids

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Torsional behavior of a wood-based composite beam

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Multi-sequence dome lay-up simulations for hydrogen hyper-bar composite pressure vessels.

International audienceThe aim of this study is to propose a calculation method for predicting the geometrical characteristics of the end-closures of composite pressure vessels used in gaseous hydrogen storage applications. We present here a method for predicting the characteristics of domes made by multi-sequence lay-up and subject to changes in winding angle and thickness. In the proposed model, winding angle and thickness calculations are based on two existing methods that have been investigated in a single dome lay-up context. Using them for multi-sequence dome lay-up calculation is the originality of this work. The first predictive results are compared with experimental pressure vessel data and discussed. A good correlation between the theoretical approach and the experiments was found, indicating that the predictions could be helpful in a procedure of overall optimisation

Comparison of optimal design methods for type 3 high-pressure storage tanks.

International audienceThis study compares different optimal design methods for producing two-angle filament-wound structures able to withstand under internal pressure. In recent years, studies have concentrated on materials and their damage behaviour as well as winding optimisation techniques in relation to vessel geometry and manufacturing processes, but none of these studies has established a definitive design rule. In the present paper, two developed methods, one based on a basic CPT with gradual damage and enumerative optimisation, the other a more sophisticated finite element (FE) method with Reddy's progressive damage law and genetic algorithm (GA) optimisation are compared to recent results based on CDM theory and a 3D FE technique incorporating a modified GA. The results were used to compare the advantages and limitations of each method and to derive simple design rules and calculation strategies that would reliably obtain a very good CPU cost/efficiency ratio

Ductile failure of cylindrically porous materials : Part II: next term other cases of symmetry

In a companion paper (previous termPartnext term I) we investigated the plane stress case in order to compare it with specific tensile tests. In the present paper, the Gurson problem is investigated in other cases of symmetry, including the most general 3D-plane case. Once the problem is outlined, we will present its formulation in terms of limit analysis (LA), then a new method to obtain a linear programming (LP) problem very suitable for modern LP codes based on Interior Point algorithms. The results indicate that a Gurson-like formulation cannot correctly represent the general solution, as in the plane stress case of previous termPartnext term I. A realistic global formulation could be specified in terms of all loading parameters, without using the restriction induced by an equivalent stress form

A progressive failure analysis of a 700-bar type IV hydrogen composite pressure vessel

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Validation of a low inertia mold with rectangular heating channels for injection process

International audienceCurrent molding processes for high performance composite materials do not meet future expectations of composite manufacturers in terms of cadence, particularly for aeronautics and automotive [1]. Researches are currently being carried out on resin, reinforcements and process automation, with the aim of increasing composite production line productivity for being competitive in terms of cost-quality-cadence. However, current molds are designed according to rules from the field of plastic injection, which leads to massive structures and low thermal performances [2]. For efficiency on the complete production line, it is essential to conduct research on molds to increase their thermomechanical responses. In a previous study [3], it was demonstrated that the transition from circular to rectangular heating channels, with consideration of technological aspects (pump and pressure drops) could significantly increase heating rates of the structure. The main purpose of this study is to experimentally validate thermal performances of an innovative low inertia mold with rectangular channels compared to a massive reference RTM mold as presented in Figure 1