L’objectif de ce travail est d’effectuer une campagne d’essais expérimentaux d’impact et de compression après impact sur chant de stratifiés composites afin d’établir les scénarios d’endommagements. Un dispositif d'essai au poids tombant a été utilisé afin de réaliser les impacts sur chant sur stratifiés avec différents drapages. Des coupes microscopiques, des radiographies aux rayons X et des analyses ultrasonores ont ensuite été effectuées afin de visualiser et de déterminer le scénario d’endommagement. Des essais de compression après impact ont également été réalisés. Les résultats des tests expérimentaux sont comparés avec un modèle numérique composé d'éléments d’interface pour décrire les fissures matricielles et d’éléments volumiques. Enfin, la prédiction numérique de la tenue résiduelle après impact permettra de diminuer les masses, d’éviter des essais coûteux, et donc de raccourcir la durée de développement. / Low velocity / low energy edge impact and quasi-static experiments have been carried out on carbon fiberreinforced plastic (CFRP) structures. A drop-weight testing machine was used to impact four different UDlaminates at 10, 20 and 35 J impact energy levels. In parallel, a quasi-static study has been conducted in order to compare its results with the impact ones. The impact results show that the static and dynamic behaviors are different. An analytical approach, to understand the impact damage scenario, is provided in order to explain the difference between static and dynamic edge impacts, regardless the stacking or impact energy. This approach explains well the dynamic and static initial stiffness and a crushing plateau. The fiber properties control the initial impact stiffness, while in the quasi-static indentation case, the properties of the matrix control the initial indentation stiffness. The crushing plateau is also controlled by the matrix properties. The impact scenario could be simulated easily knowing the material properties, the stacking sequence and the impact energy. In addition, that is crucial to model the residual strength. And all these experimental results have been compared with a finite element analysis that consists of interface elements to describe the matrix cracks and volume elements in order to simulate the impact and compression after impact damage and to predict the residual strength after impact. The model is in good agreement with the experiment. That will avoid expensive tests, and thus shorten the development time.

abstract: Composite materials are now beginning to provide uses hitherto reserved for metals in structural systems such as airframes and engine containment systems, wraps for repair and rehabilitation, and ballistic/blast mitigation systems. These structural systems are often subjected to impact loads and there is a pressing need for accurate prediction of deformation, damage and failure. There are numerous material models that have been developed to analyze the dynamic impact response of polymer matrix composites. However, there are key features that are missing in those models that prevent them from providing accurate predictive capabilities. In this dissertation, a general purpose orthotropic elasto-plastic computational constitutive material model has been developed to predict the response of composites subjected to high velocity impacts. The constitutive model is divided into three components – deformation model, damage model and failure model, with failure to be added at a later date. The deformation model generalizes the Tsai-Wu failure criteria and extends it using a strain-hardening-based orthotropic yield function with a non-associative flow rule. A strain equivalent formulation is utilized in the damage model that permits plastic and damage calculations to be uncoupled and capture the nonlinear unloading and local softening of the stress-strain response. A diagonal damage tensor is defined to account for the directionally dependent variation of damage. However, in composites it has been found that loading in one direction can lead to damage in multiple coordinate directions. To account for this phenomena, the terms in the damage matrix are semi-coupled such that the damage in a particular coordinate direction is a function of the stresses and plastic strains in all of the coordinate directions. The overall framework is driven by experimental tabulated temperature and rate-dependent stress-strain data as well as data that characterizes the damage matrix and failure. The developed theory has been implemented in a commercial explicit finite element analysis code, LS-DYNA®, as MAT213. Several verification and validation tests using a commonly available carbon-fiber composite, Toyobo’s T800/F3900, have been carried and the results show that the theory and implementation are efficient, robust and accurate. / Dissertation/Thesis / Doctoral Dissertation Civil and Environmental Engineering 2016

Manufacturing of thermoplastic composite based on textile preforms made from hybrid yarns is well suited for the production of fiber-reinforced plastic (FRP) in medium- and large-scale production runs. Especially, the consolidation of thermoplastic FRP is currently complicated by the high viscosity of molten material. Woven multilayered and z-reinforced NCF-preforms are very interesting for FRP supposed to withstand threedimensional loading and impact stress. These preforms with z-directional reinforcement improve the FRP delamination behavior and out-of-plane characteristics. The wellknown composite parameters are essential to ensure the use of these materials in a wide range of applications.