Inserts are a crucial part of household and industrial furniture. These small plastic parts which often go unnoticed to the naked eye perform crucial functions like providing a base for the furniture, leveling the furniture, safeguarding the user from edges of the tubes used and providing an aesthetic finish. The inserts have a wing like structure on the exterior which enables them to be inserted and securely held in the tubes. The inserts are assembled into the pipes manually or through machines. The force required to install these inserts in the tube is called a push-in force whereas a pull-out force is the force required for removal of the is called a pull-out force. These forces are experienced by someone who assembles the furniture together. Thus, these forces directly define the ease with which the furniture can be assembled. In the first part of the present thesis, these push-in and pull-out forces are predicted using finite element simulations. These finite element simulations were validated by performing physical assembly and disassembly experiments on these inserts. It was found that the finite element simulations of the insert are useful tool in predicting the push-in forces with a high accuracy.   These push-in and pull-out forces for a single insert vary by 2-5 times when the dimensional variations in the tube are considered. The dimensional variations can be a result of the manufacturing processes from which these tubes are produced. The maximum and minimum dimensions that the tube can have are defined by the maximum material condition (MMC) and the least material condition (LMC). To reduce the variation in push-in and pull out forces, a stricter tolerance control can be applied to the manufacturing process. To avoid this cost while having a lower variation in the push-in and pull out forces, the design of the insert was modified. To achieve this enhanced design of the insert, a metamodel based optimization technique was used in the second part of the thesis. For this optimization, the geometrical parameters - wing height, wing diameter and stem thickness the of the insert were identified as the crucial factors which govern the assembly/disassembly forces. The identification of these parameters was done through a design of experiments. These parameters were then varied simultaneously in a metamodel based optimization which had an objective to minimize the variation in forces observed for an insert when the maximum material condition and the least material conditions are considered. The result for the enhanced design of the insert was then stated in terms of the ratio of these identified parameters. The modified design of the insert not only enables the manufacturer to have better performance, but also reduces the amount of plastic material required for manufacturing of the insert.

Les composites thermoplastiques préimprégnés suscitent un intérêt croissant pour l'industrie automobile grâce à leurs excellentes propriétés mécaniques et leur procédé de fabrication rapide. Dans ce contexte, la modélisation et la simulation numérique des procédées de mise en forme de pièces composites à géométries complexes sont nécessaires pour prédire et optimiser les pratiques de fabrication. Cette thèse est consacrée à la modélisation et à la simulation du comportement de consolidation des composites thermoplastiques préimprégnés lors du processus de mise en forme. Un nouvel élément solide-coque prismatique à sept nœuds est proposé: six situés aux sommets et le septième situé au centre. Le champ de cisaillement transverse est supposé afin de réprimer le verrouillage de cisaillement transversal. La méthode de déformation renforcée supposée par addition d'un DOF de déplacement supplémentaire depuis le nœud central et un schéma d'intégration réduit sont combinées offrant un champ de déformation linéaire le long de la direction d'épaisseur pour contourner le verrouillage. De plus, une procédure de stabilisation de sablier est employée afin de corriger le défaut de rang de l'élément pour le pincement. Cet élément utilise un modèle de relaxation viscoélastique pour modéliser le comportement tridimensionnel de composites thermoplastiques préimprégnés avec effet de consolidation. Un modèle de contact intime est également utilisé pour prédire l'évolution de la consolidation et la microstructure du vide présente au sein du préimprégné. A l’aide d’une loi hyperélastique, plusieurs simulations ont été conduites en combinant le nouvel élément fini et les modèles de consolidation. La comparaison des résultats de simulation avec les essais expérimentaux montre l'efficacité de l’élément solide-coque face aux problèmes de déformations dans le plan et en flexion, mais également pour l'analyse du comportement de consolidation. De plus, le degré de contact intime fournit le degré de consolidation par conditions de procédé appliqué, ce qui est essentiel pour l'apparition de défauts dans la pièce finale de composite. / As the pre-impregnated thermoplastic composites have recently attached increasing interest in the automotive industry for their excellent mechanical properties and their rapid cycle manufacturing process, modelling and numerical simulations of forming processes for composites parts with complex geometry is necessary to predict and optimize manufacturing practices. This thesis is devoted to modelling and simulation of the consolidation behavior during thermoplastic prepreg composites forming process. A new seven-node prismatic solid-shell element is proposed: six located at the apexes and the seventh sited at the center. A shear stain field is assumed to subdue transverse shear locking, the enhanced assumed strain method by addition of an extra displacement DOF from the central node and a reduced integration scheme are combined offering a linear varying strain field along the thickness direction to circumvent thickness locking, and an hourglass stabilization procedure is employed in order to correct the element’s rank deficiency for pinching. This element permits the modelling of three-dimensional constitutive behavior of thermoplastic prepreg with the consolidation effect, which is modelled by a viscoelastic relaxation model. An intimate contact model is employed to predict the evolution of the consolidation which permits the microstructure prediction of void presented through the prepreg. Within a hyperelastic framework, several simulation tests are launched by combining the new developed finite element and the consolidation models. The comparison with conventional shell element and experimental results shows the efficiency of the proposed solid-shell element not only dealing with the in-plan deformation and bending deformation problems, but also in analyzation of the consolidation behavior, and the degree of intimate contact provides the level of consolidation by applied process conditions, which is essential for the appearance of defects in final composite part.