Ce mémoire s'inscrit dans un projet de recherche qui vise à modéliser un matériau composite tissé taffetas dans le cas d'un écrasement. Les industriels sont intéressés à comprendre les mécanismes d'endommagement des matériaux composites et avoir les différents paramètres mécaniques pour faire une modélisation précise qui tend à représenter le mieux possible le comportement de ces matériaux. Il s'agit d'un composite tissé taffetas stratifié à renforts de fibres de carbone et d'une matrice polymérique en époxyde. Des tests sont effectués en quasi-statique et en dynamique afin d'obtenir les propriétés mécaniques dans les directions principales du matériau. Des tests dans le plan, hors plan et en cisaillement ont été effectués afin de pouvoir modéliser le composite en trois dimensions. De plus, le projet vise à développer des outils qui permettent d'avoir des instruments précis pour la mesure de la force et de la déformation lors d'un test d'impact. De nombreuses méthodes ont été développées pour améliorer la mesure de la déformation et du déplacement en utilisant une caméra haute vitesse. Ensuite, une analyse fréquentielle des montages en dynamique permet de mieux cerner le bruit enregistré durant ces tests et d'utiliser un filtre adéquat pour limiter ces vibrations dans les mesures. Des tests ont confirmé la précision des méthodes développées et sont utilisés pour obtenir les propriétés mécaniques du matériau. En résumé, il semble que certaines directions soient plus influencées par la vitesse de déformation. Les propriétés en traction et en compression hors plan ainsi qu'en cisaillement dans le plan et hors plan varient lors d'un impact. Finalement, un modèle de matériau est implanté dans ABAQUS *Explicit* pour améliorer la précision des simulations dans le cas d'un chargement de cisaillement dans le plan. Le modèle permet de bien prédire le comportement en cisaillement dans le domaine élastique et lors de l'endommagement. / This thesis is part of a research project aiming to model a plain weave composite material during a crash event. Industrial partners are interested in understanding the damage mechanisms of composite materials and identifying different mechanical parameters to carry out precise modelling to represent the behaviour of this material. The studied material is a laminated plain weave made from carbon fibres and epoxy polymer matrix. Tests are performed in quasi-static and dynamic in order to obtain the mechanical properties in the main directions of the material. In-plane, out-of-plane and shear properties are identified to model the composite in three dimensions. Furthermore, the project aims to develop tools providing precise instruments for load and strain measurements during impact. Many methods have been developed to improve the accuracy of strain and displacement measurements using a high-speed camera. Moreover, a frequency analysis of the dynamic setups is performed to understand the noise acquired during testing and to use an appropriate filter to limit these vibrations in the measurements. Tests have confirmed the accuracy of the developed methods and are used to obtain the mechanical properties of the material. In summary, it appears that certain directions are dependent on the strain rate. Out-of-plane tension and compression as well as the in-plane and out-of-plane shear properties are different during a dynamic load. Finally, a material model is developed in ABAQUS *Explicit* to improve the accuracy of simulations for in-plane shear loading. The model predicts the shear behaviour in the elastic region and during the damage evolution.

This thesis focuses on the development of a new method for the continuous<p>monitoring of civil engineering structures in order to locate small damages automatically. A<p>review of the very wide literature on Structural Health Monitoring (SHM) points first out that<p>the methods can be grouped in four categories based on their need or not of a numerical model,<p>as well as their need or not of information of the damaged structure to be applied. This state<p>of the art of the SHM methods highlights the requirement to reach each levels of SHM, which<p>is in particular for the localization of small damages in civil engineering structures the needs<p>for a non-model based output-only damage sensitive feature extraction technique. The origin of<p>the local sensitivity of strains to damages is also analyzed, which justifies their use for damage<p>localization.<p>A new method based on the modal filtering technique which consists in combining linearly<p>the sensor responses in a specific way to mimic a single degree of freedom system and which<p>was previously developed for damage detection is proposed. A very large network of dynamic<p>strain sensors is deployed on the structure and split into several independent local sensor networks.<p>Low computational cost and fast signal processing techniques are coupled to statistical<p>control charts for robust and fully automated damage localization.<p>The efficiency of the method is demonstrated using time-domain simulated data on a simply<p>supported beam and a three-dimensional bridge structure. The method is able to detect and<p>locate very small damages even in the presence of noise on the measurements and variability<p>of the baseline structure if strain sensors are used. The difficulty to locate damages from acceleration<p>sensors is also clearly illustrated. The most common classical methods for damage<p>localization are applied on the simply supported beam and the results show that the modal filtering<p>technique presents much better performances for an accurate localization of small damages<p>and is easier to automate.<p>An improvement of the modal filters method referred to as adaptive modal filters is next<p>proposed in order to enhance the ability to localize small damages, as well as to follow their<p>evolution through modal filters updating. Based on this study, a new damage sensitive feature<p>is proposed and is compared with other damage sensitive features to detect the damages with<p>modal filters to demonstrate its interest. These expectations are verified numerically with the<p>three-dimensional bridge structure, and the results show that the adaptation of the modal filters<p>increases the sensitivity of local filters to damages.<p>Experimental tests have been led first to check the feasibility of modal filters to detect damages<p>when they are used with accelerometers. Two case studies are considered. The first work<p>investigates the experimental damage detection of a small aircraft wing equipped with a network<p>of 15 accelerometers, one force transducer and excited with an electro-dynamic shaker. A<p>damage is introduced by replacing inspection panels with damaged panels. A modified version<p>of the modal filtering technique is applied and compared with the damage detection based principal<p>component analysis of FRFs as well as of transmissibilities. The three approaches succeed<p>in the damage detection but we illustrate the advantage of using the modal filtering algorithm as<p>well as of the new damage sensitive feature. The second experimental application aims at detecting<p>both linear and nonlinear damage scenarios using the responses of four accelerometers<p>installed on the three-storey frame structure previously developed and studied at Los Alamos<p>National Labs. In particular, modal filters are shown to be sensitive to both types of damages,<p>but cannot make the distinction between linear and nonlinear damages.<p>Finally, the new method is tested experimentally to locate damages by considering cheap<p>piezoelectric patches (PVDF) for dynamic strain measurements. Again, two case studies are investigated.<p>The first work investigates a small clamped-free steel plate equipped with 8 PVDFs sensors, and excited with a PZT patch. A small damage is introduced at different locations by<p>fixing a stiffener. The modal filters are applied on three local filters in order to locate damage.<p>Univariate control charts allow to locate automatically all the damage positions correctly.<p>The last experimental investigation is devoted to a 3.78m long I-steel beam equipped with 20<p>PVDFs sensors and excited with an electro-dynamic shaker. Again, a small stiffener is added to<p>mimic the effect of a small damage and five local filters are defined to locate the damage. The<p>damage is correctly located for several positions, and the interest of including measurements<p>under different environmental conditions for the baseline as well as overlapping the local filters<p>is illustrated.<p>The very nice results obtained with these first experimental applications of modal filters<p>based on strains show the real interest of this very low computational cost method for outputonly<p>non-model based automated damage localization of real structures. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

A l’heure actuelle où la préservation de notre environnement est primordiale, les constructions en béton font intervenir de plus en plus des ciments comprenant des ajouts minéraux, tels que le laitier, les cendres volantes… En effet, la production des ciments composés permet de réduire le dégagement des gaz à effets de serre et de réutiliser des déchets industriels. Les bétons formulés à base de ciment au laitier de haut-fourneau (CEM III) sont également largement utilisés suite à leur bonne résistance aux réactions alcali-silices, à la diffusion des chlorures et aux attaques sulfatiques… Cependant, certains ouvrages construits avec ce type matériau ont présenté au jeune âge des problèmes de fissuration liés à la restriction de leurs déformations différées, telles que le retrait endogène, thermique et de dessiccation. Suite à cette observation, des essais préliminaires ont été réalisés au laboratoire du service BATir de l’Université Libre de Bruxelles. Ils ont mis en avant plusieurs caractéristiques du comportement de ces matériaux :<p><p>1. Lors du suivi du retrait restreint à l’aide de l’essai à l’anneau en condition de dessiccation, le béton formulé à base de ciment au laitier de haut-fourneau a fissuré bien avant le béton formulé à base de ciment Portland.<p>2. Le retrait total en condition libre du béton formulé à base de ciment au laitier de haut-fourneau est nettement supérieur à celui du béton formulé à base de ciment Portland. Cette différence de comportement est principalement due à l’accroissement rapide et plus élevé du retrait endogène des bétons formulés à base de ciment au laitier de haut-fourneau.<p><p>Au vu de ces résultats expérimentaux, il a semblé intéressant de déterminer quel était l’impact de la déformation endogène des bétons formulés à base de ciments au laitier de haut-fourneau (CEM III) sur leur sensibilité à la fissuration. Afin de répondre à cette question, les déformations différées (retrait endogène, fluage propre en compression et en traction) au jeune âge de trois compositions de béton avec différentes teneurs en laitier (0, 42 et 71%) ont été étudiées expérimentalement en conditions libre et restreinte. Cependant, le suivi du retrait endogène libre et restreint a nécessité le développement de plusieurs dispositifs expérimentaux limitant au maximum les artefacts de mesure, tels que la TSTM (Temperature Stress Testing Machine). De plus, l’interprétation de ces résultats expérimentaux a également nécessité une caractérisation du comportement de ces matériaux à l’échelle macro- et microscopique. <p><p>Finalement, cette étude a montré que malgré une déformation endogène plus élevée, les bétons formulés à base de ciment au laitier de haut-fourneau fissurent après le béton formulé à base de ciment Portland. Ce comportement est dû à :<p>-l’impact du laitier sur la réaction d’hydratation du matériau cimentaire ;<p>-la présence d’une expansion de la matrice cimentaire des bétons formulés à base de ciment au laitier de haut-fourneau au jeune âge qui retarde l’apparition des contraintes de traction au sein du matériau ;<p>-la plus grande capacité de ces matériaux cimentaires à relaxer les contraintes de traction/<p>Today, the use of concretes with mineral additions (fly ash, slag) for civil engineering structures is spreading worldwide. Indeed, the production of blended cements is more respectful of the environment than the production of Portland cement, because it allows reducing greenhouse gas emissions and using industrial wastes. Slag cement concretes are also largely used for their good resistance to alkali-silica reactions, sulphate attacks and chloride diffusion. However, some of constructions built with slag cement concretes have exhibited cracking at early age due to their restrained deformations, such as thermal, autogenous and drying shrinkage. Following these observations, a preliminary experimental study was realized in the laboratory of BATir Department at ULB. It revealed several characteristics of the behaviour of slag cement concretes:<p>1. The study of restrained deformations under drying conditions by means of ring tests showed that the slag cement concretes seem more prone to crack than the Portland cement concretes;<p>2. The total free shrinkage for slag cement concrete is clearly larger than for Portland cement concrete. This difference of behaviour is mainly due to the fast and large increase in the autogenous deformation of the slag cement concrete.<p><p>Following these experimental results, the effect of the autogenous deformation on the cracking sensibility of slag cement concretes seemed interesting to investigate. Their deformations (autogenous deformation, compressive and tensile basic creep) have been studied at early age for three concretes characterized by different slag contents (0, 42 and 71%) under free and restrained conditions. For monitoring free and restrained autogenous deformations, several test rigs aimed at limiting artefacts were designed, like the TSTM (Temperature Stress Testing Machine). Moreover, the behaviour of these concretes was also characterized by a study at a macro- and microstructure scale.<p><p>Finally, this study shows that the slag cement concretes under sealed and fully restrained conditions crack later than the Portland cement concrete, despite the fact that they are characterized by the largest autogenous deformation. This behaviour is due to:<p>- the slag effect on the hydration reaction of cementitious material;<p>- the cement matrix expansion of the slag cement concretes at early age which delays the occurrence of tensile stresses inside the material;<p>- the largest capacity of this concrete to relax tensile stresses.<p> / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished