Environmental issues enforce transportation sectors to limit their carbon dioxide emissions in various ways. Automotive manufacturers attempt to reduce carbon dioxide emission by seeking various strategies, e.g., increasing aerodynamic efficiency, using more fuel-efficient engines, reducing friction and wear of transmission systems, and, most importantly, by using lightweight materials and structures. This dissertation is a contribution toward a lightweight design of structures by proposing numerical models suitable for damage prediction of thermoplastic composite materials. In this dissertation, predictive damage models for two different length scales, namely micromechanics, and mesomechanics, were proposed. Micromechanics is used to predict the nonlinear damage behavior of elementary thermoplastic composite ply, while the mesomechanics is used to predict the failure behavior of thermoplastic composite laminates (test coupon or plate scale). For the micromechanics, a representative volume element (RVE) of such materials was rigorously determined using a geometrical two-point probability function and the eigenvalue stabilization of homogenized elastic tensor obtained by Hill-Mandel kinematic homogenization. We proposed a viscoelastic viscoplastic model for the polypropylene matrix to extend the capability of the micromechanics model in predicting the damage behavior of the composite ply at higher rates. At the mesoscale, we improved the classical mesomechanics damage modeling in the off-axis direction by introducing the confinement effect. The pragmatic approach consists of separating the progressive damage into two parts, namely “diffuse damage regime” and “transverse-cracking regime”, were described by two distinct damage parameters. We also enriched the mesomechanics model by proposing a viscoelastic and viscoplastic model to account for the rate-dependent behavior of the thermoplastic composites. We showed that the predictions given by the proposed micromechanics and mesomechanics models were in excellent agreement with the experimental results in terms of the global stress-strain curves, including the linear and nonlinear portion of the response and also the failure point, making it useful virtual testing tools for the design of thermoplastic composites.

La mise en forme des pièces composites par Resin Transfert Molding (RTM) nécessite de maîtriser, en autre, deux étapes clés : la déformation à sec du renfort et l’injection de la résine. Dans une démarche d’optimisation du procédé, la simulation numérique est un outil incontournable. Ces travaux de thèse s’inscrivent dans cette thématique avec deux contributions essentielles : Mésomécanique : les renforts textiles sont des milieux poreux périodiques. Ces caractéristiques incitent à les modéliser à l’échelle mésoscopique, où le modèle géométrique se réduit à un Volume Elémentaire Représentatif (VER). A cette échelle, le problème de référence à résoudre est fortement non linéaire : comportement non linéaire des mèches, grandes transformations et contact entre mèches. La résolution par une méthode élément fini se heurte à une problématique : la formation de surfaces de contact entre le VER et ses voisins. Une partie de la déformation provient de ce contact formé aux frontières de la période. Aucune solution robuste ne permet à l’heure actuelle de prendre en compte ce contact. Le premier objectif de cette thèse est d’apporter une solution à cette problématique. Etude de perméabilité : la qualité des pièces composites en fin de chaîne de production dépend en partie du processus d’assemblage matrice/renfort. L’un des paramètres qui conditionne le bon déroulement de cet assemblage est la perméabilité du renfort. Expérimentalement, c’est une propriété très difficile à estimer. La simulation numérique est un moyen alternatif d’y accéder, avec la possibilité d’imposer des conditions aux limites parfaites au sens mathématique. De nombreuses études ont été réalisées dans le cas 2D. Le second objectif de cette thèse est de proposer en parti une méthode pour estimer par le calcul la perméabilité d’un renfort 3D. / The manufacture of composite parts by Resin Transfert Molding (RTM) requires to control two main phases: the shaping of the dry reinforcement and the injection of the matrix. Numerical simulation is a powerful tool when it comes to find the right set of parameters needed to obtain a part without non conformity. These research works where performed in this specific field with two main contributions: Mesomechanic: textile fabrics are periodic porous media. Modelling these materials at the mesoscale permit to reduce the geometrical model to a Representative Volume Element (RVE). At this scale the boundary value problem to solve is highly nonlinear: non linear behavior of the yarns, large deformations and contact. Solving this problem with a Finite Element Method include dealing with contact surface generation between the RVE and its neighbors. Part of the RVE yarns deformation is coming from these multiple contacts at the borders. There is no methods yet that solve this issue. The first objective of this thesis is to produce one. Permeability: the quality of the composite part at the end of the manufacturing process depends also of the matrix/reinforcement assembly. One of the parameters that influence the efficiency of this linkage is the permeability of the reinforcement. Measuring permeability throughout experiments is not easy. Numerical simulation offers another way to estimate the permeability of a textile fabric. Numerous works have been performed in this subject especially on 2D textiles. The second objective of this thesis is to propose a method for the numerical estimation of the permeability tensor of 2D and 3D textiles.

An extensive review of probabilistic techniques in fatigue analysis indicates that there is a need for new microstructure-sensitive methods in describing the effects of notches on the fatigue life reduction in cyclically loaded components. Of special interest are notched components made from polycrystalline nickel-base superalloys, which are used for high temperature applications in aircraft gas turbine engine disks. Microstructure-sensitive computational crystal plasticity is combined with novel probabilistic techniques to determine the probability of failure of notched components based on the distribution of slip within the notch root region and small crack initiation processes. The key microstructure features of two Ni-base superalloys, a fine and coarse grain IN100, are reviewed and the method in which these alloys are computationally modeled is presented. Next, the geometric model of the notched specimens and method of finite element polycrystalline reconstruction is demonstrated. Shear-based fatigue indicator parameters are used to characterize the shear-based, mode I formation and propagation of fatigue cracks. Finally, two different probabilistic approaches are described in this work including a grain-scale approach, which describes the probability of forming a crack on the order of grain size, and a transition crack length approach, which describes the probability of forming and propagating a crack to the transition crack length. These approaches are used to construct cumulative distribution functions for the probability of failure as a function of various notch root sizes and strain load amplitudes.

Due to a European energy concept for reducing energy consumption and also the concept of sustainable development, there is a growing demand for reduced energy consumption during the operation of the building and hence increasing demands on the thermal and mechanical properties of the building envelope. For this reason, it is necessary to look for materials that could meet both thermal and mechanical properties, as well as mechanical resistance and loadability, especially for the application for the foundations of the house, the base of the house and for application to structural details for elimination of the thermal bridges between interior and exterior boundaries. The main motivation for choosing the topic of thesis was to find materials derived from recycled or secondary raw materials that would be suitable for manufacturing composite applicable for structural details in the envelope of the building and for insulating in humid environment. An economic and environmental aspect plays an important role in the choice of material. The main theme of the thesis is the laboratory manufacturing of a composite with a thermoplastic matrix derived from recycled plastic materials and waste foam as a phase. Has been developed a unique Waste-based Particle Polymer Composite (WPPC) made from recycled foam and polypropylene. However, before WPPC can be reliably used by construction designers, physical properties of WPPC must be accurately identified. Therefore, it was designed laboratory manufacturing system and sample testing system, it was studied thermal, mechanical, thermomechanical and moisture absorptivity of WPPC. Application of finished composite material with satisfying thermal insulation properties to structural details to eliminate the thermal bridge, was the next step. These are details of the unloaded, prefabricated balconies, windows, atics, as well as basement constructions and the heel of the central load-bearing wall, the terrain flooring and the staircase wall

科学研究費補助金 研究種目:基盤研究(B)(2) 課題番号:09450047 研究代表者:田中 啓介 研究期間:1997-1999年度