Procédé composite à grandes cadences pour l'allégement des pièces mécaniques

Le CETIM développe des procédés pour la mise en oeuvre à grandes cadences et à bas coût de pièces mécaniciennes en matériaux composite thermoplastique. Un triangle de suspension définie par PSA a été développé et testé à titre de démonstration. Les performances et la cadence de production sont satisfaisantes, mais pas le coût de revient. C'est pourquoi le CETIM a développé un nouveau procédé, le QSP®, permettant de fabriquer des pièces composites à coût réduit. Ce développement procédé repose sur la pultrusion thermoplastique pour l'imprégnation des fibres, puis sur le thermoformage de préforme multi-épaisseur et multi-orientation. De nouvelles méthodes de conception sont mise au point pour optimiser les conceptions de pièces QSP

Autonomous Takeoff and Flight of a Tethered Aircraft for Airborne Wind Energy

A control design approach to achieve fully autonomous takeoff and flight maneuvers with a tethered aircraft is presented and demonstrated in real-world flight tests with a small-scale prototype. A ground station equipped with a controlled winch and a linear motion system accelerates the aircraft to takeoff speed and controls the tether reeling in order to limit the pulling force. This setup corresponds to airborne wind energy (AWE) systems with ground-based energy generation and rigid aircrafts. A simple model of the aircraft's dynamics is introduced and its parameters are identified from experimental data. A model-based, hierarchical feedback controller is then designed, whose aim is to manipulate the elevator, aileron, and propeller inputs in order to stabilize the aircraft during the takeoff and to achieve figure-of-eight flight patterns parallel to the ground. The controller operates in a fully decoupled mode with respect to the ground station. Parameter tuning and stability/robustness aspect are discussed, too. The experimental results indicate that the controller is able to achieve satisfactory performance and robustness, notwithstanding its simplicity, and confirm that the considered takeoff approach is technically viable and solves the issue of launching this kind of AWE systems in a compact space and at low additional cost

Mixed multilayered plate elements for coupled magneto-electro-elastic problems

Finite Elements FE based on the Reissner's Mixed Variational Theorem RMVT, for the analysis of multilayered plates subjected to magneto-electro-elastic MEE fields, are developed in this work. Accurate description of the various field variables has been provided by employing a variable kinematic model which is based on the Carrera's Unified Formulation CUF. Displacements, transverse shear/normal stresses, magnetic and electric potentials have been chosen as independent unknowns. Interlaminar continuity of mechanical variables is "a priori" guaranteed by the RMVT application. Layer-wise plate elements with linear up to fourth order distribution in the thickness direction have been compared. FE governing equations, according to CUF, are presented in terms of fundamental nuclei whose form is not affected by kinematic assumptions. Results show the effectiveness of the proposed elements, the superiority of mixed FEs with respect to the classical ones, as well as their capability, by choosing appropriate kinematics, to accurately trace the static response of laminated plates subject to magneto-electro-elastic fields

Coupled stress and energy analysis of crack onset in textile composites at the mesoscopic scale

International audienceA coupled stress and energy criterion is used to analyze crack initiation at the mesoscopic scale in a four-layer plain weave glass-epoxy composite. The choice of possible crack configurations is restricted based upon optical microscope observations of damage mechanisms on a specimen edge during tensile testing. It is found that transverse yarn cracking accompanied by yarn-yarn decohesions around the crack tips is the first damage that occurs in the composite. For the stress condition in the yarns, a criterion developed for modeling failure of unidirectional plies in a laminate is applied. For the energy condition, the difference between the potential energies of an undamaged and a cracked unit cell is calculated, using identical mesh topologies. The energy criterion is found to be dominant in the studied case. It leads to an estimation of the crack initiation strain much closer to experimental observations by acoustic emission than the stress criterion alone and allows to determine crack length and orientation at damage onset. The coupled criterion leads to the conclusion that the yarn-yarn decohesions are a direct consequence of the transverse yarn cracks, and its length can be determined through the energy criterion

Comparison between voxel and consistent meso-scale models of woven composites

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Mesures de champs de déformations par corrélations d'images pour l'identification de modèles mécaniques microscopiques de composites à matrice polymère

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Optimisation de stratifiés composites sous contrainte fiabiliste à travers un double espace de design

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Optimisation Aéroélastique Fiabiliste des Plaques Composites par Metamodélisation à Double Espace

International audienceComposite materials are essential in aerospace engineering due to their superior strength-to-weight ratio. This work explores the reliability-based design optimisation of composite plates under aeroelastic constraints with a focus on cost efficiency. We utilise a simplified approach focusing on generating surrogate models through conditioned Gaussian Processes, which predict various aeroelastic responses like flutter speed, gust loads, and static forces. These models help in the effective navigation of the composite design space. We introduce a 5 step optimisation algorithm in which we prioritise minimising the gust response and structure mass while adhering to predefined limits on flutter and strain. The proposed approach not only simplifies the optimisation process but also enhances the understanding and reliability of composite material design in aerospace applications, aiming for improved safety and performance.Les matériaux composites sont essentiels dans le domaine de l'ingénierie aérospatiale en raison de leur rapport résistance/poids supérieur. Ce travail explore l'optimisation de la conception basée sur la fiabilité des plaques composites sous des contraintes aéroélastiques, en mettant l'accent sur l'efficacité des coûts. Nous utilisons une approche simplifiée en nous concentrant sur la génération de modèles de substitution via des processus gaussiens conditionnés, qui prédisent diverses réponses aéroélastiques telles que la vitesse de flutter, les charges de rafales et les forces statiques. Ces modèles aident à naviguer efficacement dans l'espace de conception des composites. Nous introduisons un algorithme d'optimisation en 5 étapes dans lequel nous priorisons la minimisation de la réponse aux rafales et de la masse de la structure tout en respectant des limites prédéfinies sur le flutter et la déformation. L'approche proposée non seulement simplifie le processus d'optimisation, mais elle améliore également la compréhension et la fiabilité de la conception des matériaux composites dans les applications aérospatiales, visant à améliorer la sécurité et les performances