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This thesis concerns the structural health monitoring of aeronautical composite structures (SHM) using guided waves generated by piezoelectric transducers. The general objective is to propose and validate experimentally several methods to quantify the size of a delamination type damage present in the structure to be monitored. The first contribution of this thesis is the creation and publication of an open access and reusable database of SHM measurements from fatigue tests of composite structures representative of aeronautics components. The second contribution is the development and validation on damage of unknown size of a purely data-driven quantification approach that consists in training a mathematical model from labeled data and an original mathematical descriptor computed from localization images. The third contribution is the development and validation of a quantification method that relies on the estimation of damage-related parameters from a physical model and does not require reference data. To solve this inverse problem, an analytical model is developed to predict the signal measured by a piezoelectric sensor at the passage of a wave generated by a piezoelectric actuator and scattered by a damage. This model is limited to quasi-isotropic composite material and has been validated by comparison to finite elements method simulations. Based on this theoretical model, an identification tool is proposed to estimate the damage size and severity. These two quantification methods, one based on data and the other on a physical model, have been validated on signals from numerical simulations and on experimental signals from structures with realistic damages., Cette thèse concerne le contrôle de santé des structures composites aéronautiques (en anglais « Structural Health Monitoring » ou SHM) par ondes guidées générées par des transducteurs piézoélectriques. L’objectif général est de proposer et de valider expérimentalement des méthodes permettant de quantifier la taille d’un dommage de type délaminage présent dans la structure à surveiller. La première contribution de cette thèse est la création et la publication d’une base de données libre d’accès et de réutilisation de mesures SHM issues d’essais de fatigue de structures en composite représentatives de composants aéronautiques. La seconde contribution est le développement et la validation sur des dommage de taille inconnue d’une approche de quantification basée purement sur les données qui consiste à entrainer un modèle mathématique à partir de données labélisées et d’un descripteur original calculé à partir d’images de localisation. La troisième contribution est le développement et la validation d’une méthode de quantification qui repose sur l’estimation de paramètres liés au dommage à partir d’un modèle physique et qui ne nécessite pas de données de référence. Pour résoudre ce problème inverse, un modèle analytique est développé pour prédire le signal mesuré par un capteur piézoélectrique au passage d’une onde générée par un actionneur piézoélectrique et diffractée par un dommage. Ce modèle théorique est ensuite utilisé pour remonter à la taille et à la sévérité du défaut. Ces deux méthodes de quantification, basées l’une sur les donnée et l’autre sur un modèle physique, ont été validées sur des signaux issus de simulations numériques et sur des signaux expérimentaux sur des structures comportant des dommages réalistes.

Due to the multiple functionalities of zinc oxide (ZnO), it has been used in a wide variety of applications such as optoelectronics, chemical sensors, piezoelectric transduces and varistors. Composites of piezoelectric ZnO fillers embedded into a polymer matrix offer many potential benefits like high flexibility, low-cost, possible recyclability, tailored properties, adaptable to additive manufacturing, and easy integration to any shapes and dimensions. The goal of this research is to investigate full characterizations of piezoelectric system based on ZnO micro/nano structure in a macroscopic scale. This allows to a better understanding of the electromechanical coupling as well as the intrinsic dielectric, electrical, and mechanical properties of the matrix and filler, when being individual or combined together. Another aspect focuses on the development of optimized strategies based on experimental characterization and finite element method (FEM), with the intention of boosting the piezoelectric performance of ZnO micro/nano composites. Thus, a processive strategy was firstly proposed with ZnO particles incapsulated into polydimethylsiloxane (PDMS) matrix owning to their sample structure, low cost, easy process, and well-controlled elaboration. Experimental results revealed that a higher particle concentration gives rise to a substantial enhancement in the dielectric permittivity, the conductivity, the compressive elastic modulus, and the piezoelectric coefficient. More importantly, significant enhancements in those output performances have been successfully achieved via dielectrophoretic alignment of ZnO microparticles (MP) at moderate concentration. Additionally, a particular emphasis on the shape and size effect of the fillers (i.e., comprising spherical particles, microrods (MR) and nanowires (NW)) on the properties of ZnO composites was thoroughly explored via empirical characterization and numerical simulation. It is pointed out that composites of vertically aligned ZnO NWs grown by chemical bath deposition (CBD) method exhibited the maximum piezoelectric efficiency. FEM modeling was employed to drive the optimization strategies through adjustment of the key parameters such as Young’s modules and dielectric constant of the constituents, together with the density and dimension of NW itself. Furthermore, thanks to the investigation on the crystal defects from spontaneously grown ZnO NWs, two effective strategies including Sb-doping and thermal annealing were confirmed to decrease carrier concentration in ZnO, with the aim of weakening the undesired screening effect. Finally, flexible piezoelectric NWs composites based PDMS polymer substrate instead of the rigid silicon are investigated. Experimental results confirm high potential of the developed material in vivo biosensing and bio-detection applications, especially when flexible and stretchable devices are mandatory for medical uses., Grâce à ses multiples fonctionnalités, l’oxyde de Zinc est déjà utilisé dans de nombreuses applications du domaine de l’optoélectronique, des capteurs physico-chimiques, des composants électroniques ou encore des micro-dispositifs électromécaniques. Un matériau composite utilisant des charges ZnO incorporées dans une matrice polymère offre ainsi de nombreux avantages potentiels tels qu'une flexibilité élevée, un faible coût, une réelle recyclabilité et une intégration aisée, de plus adaptée à la fabrication additive sous toutes formes et dimensions. L'objectif de ces travaux est de mener une caractérisation complète à l’échelle macroscopique de composites piézoélectriques intégrant des structures micro/nano ZnO afin d’aboutir à une meilleure compréhension du couplage électromécanique. Dans ce but, la présente étude s’est d’abord orientée vers la mise au point d’un process de fabrication de composite, à faible cout, à l’élaboration simple et parfaitement maitrisée, basé sur l’utilisation des particules de ZnO encapsulées dans une matrice de polydiméthylsiloxane. Les résultats expérimentaux ont montré qu'une concentration de particule élevée entraîne une augmentation de la permittivité diélectrique, de la conductivité, du module élastique de compression et de la constante piézoélectrique. Plus important encore, une amélioration significative de ces caractéristiques a été obtenue avec succès grâce à l'alignement diélectrophorétique de microparticules de ZnO à concentration plus faible. Une étude de l’influence de la forme et de la taille des charges sur les propriétés des composites a également été menée en utilisant des particules sphériques, des microtubes ou des nanofils. Les composites utilisant un réseau vertical ordonné de nanofils ZnO obtenu par dépôt en bain chimique présente au final le couplage piézoelectrique le plus élevé. Des simulations par la méthode des éléments finis ont été utilisées dans ce sens pour optimiser l’activité piézoélectrique d’un composite à nanofils ZnO en fonction du module d’élasticité et de la constante diélectrique des éléments constitutifs ainsi que de la densité et des dimensions des nanofils. Il a également été établi que l’apparition de défauts cristallins lors de la croissance des nanofils de ZnO génère des porteurs de charges électriques qui ont un effet masquant sur l’effet piézoelectrique. Cette dégradation peut être atténuée par un dopage à l’Antimoine ou par un recuit thermique qui permet de diminuer la concentration de ces porteurs parasites. Au final, des composites flexibles piézoélectriques à nanofils ZnO ont été developpé en utilisant un substrat de type polymère PDMS au lieu d’un substrat rigide silicium. L’ensemble des résultats expérimentaux obtenus confirme l’excellent potentiel des matériaux développés pour toute application de biodétection in vivo nécessitant impérativement des dispositifs médicaux flexibles et extensibles.

CICE 2021, 10th International Conference on FRP Composites in Civil Engineering, Istanbul, TURQUIE, 08-/12/2021 - 10/12/2021; Flax fiber reinforced polymer (FFRP) composites are demonstrating promising outcomes which makes them potential candidates to replace synthetic composites in various industrial applications. However, there is limited information regarding their long-term performance, and it is usually acknowledged that natural fibers are less resistant than their synthetic counterparts. In this context, it is crucial to study their durability before considering their use for structural rehabilitation and strengthening in construction. This study aims to investigate and predict the performance of FFRP composites with a bio-based epoxy matrix.The test program consisted in exposing FFRP laminates and FFRP strengthened concrete slabs to different accelerated ageing conditions over a total period of 2 years, and with various combinations of temperature and relative humidity in the ranges 20-60 °C and 50-100% RH, respectively. Series of tensile, short beam and pull-off tests were periodically performed on ageing samples in order to evaluate their property evolutions over exposure time in the various environments. Finally, collected experimental data were analyzed using statistical tools, in view of developing a degradation model and evaluating the service lifetime performance of this new bio-based composite.

International audience; Au Bénin, les déchets issus de la transformation du bois sont très insuffisamment valorisés dans une perspective de réutilisation par l’industrie du bois. Les technologies de transformation de ces produits connexes, économiquement accessibles aux populations des pays en développement, constituent un domaine très peu abordé dans la littérature internationale. Dans le présent travail, un matériau constitué d’un mélange de sciure de bois de teck et de pâte de polystyrène recyclés, suivant une technologie simple à mettre en œuvre et de type low-tech, a été caractérisé. Les résultats obtenus ont montré que les propriétés du composite varient significativement avec la granulométrie de la sciure utilisée. La masse volumique apparente du matériau est comprise entre 686 à 826 kg/m3, son taux d’absorption d’eau est inférieur à 15 % et son taux de gonflement en épaisseur est inférieur à 5 % après 24 heures d’immersion. Une corrélation élevée a été observée entre ses propriétés physiques et sa porosité qui varie de 34 et 43 % suivant la granulométrie des sciures de bois utilisées. Le composite présente un module d’élasticité en traction compris entre 582 à 1 057 MPa, une résistance en traction comprise entre 2 et 3 MPa et un coefficient de Poisson variant de 0,14 à 0,24. En compression, son module d’élasticité varie entre 270 à 470 MPa et sa résistance entre 6 à 9 MPa. Une mise en œuvre du composite ainsi élaboré peut être envisagée en substitution du bois pour des éléments faiblement chargés comme des pièces de coffrage de construction légère.

The development of composites based on plant fibres has considerably grown in last decades; however, their high sensitivity to moisture limits their use in structural applications. The objective of this study is to determine and understand the impact of moisture variations during one-year cyclic hygrothermal ageing i.e. 52 cycles on the transverse properties of a unidirectional epoxy flax composite. A cycle consists of 3.5 days at 90% RH followed by 3.5 days at 40% RH. Compared to the studies usually carried out to determine the impact of ageing on the longitudinal properties of unidirectional composites, the determination of the transverse mechanical properties during this type of ageing allowed to focus on the contribution of the matrix and the interface on the evolution of the composite properties. The multi-scale analyzes provided identification of the phases responsible for the evolution of transverse mechanical properties induced by ageing. The transverse ultimate tensile strength drops by about 20% after the first week of ageing and slightly decreases up to 2 months. This evolution seems to be induced by the creation of flaws, in particular the phenomena of fibre-fibre and matrix-fibre debonding and the creation of cracks in the fibres initiated at the lumen level, revealed by SEM. The transverse modulus also strongly drops after the first week by about 18% to reach about 45% loss after one year of ageing. These evolutions are mainly linked to the physical plasticization of the epoxy matrix demonstrated by the reversible change of its glass transition temperature, but analyses showed that water does not lead to chemical degradation of the matrix.

International audience; This study deals with the analysis of the propagation of thermal radiation within absorbing and scattering composite materials with rough boundaries. The two-phase system (resin matrix and fibers reinforcement) is treated as an equivalent homogeneous medium characterized by volumetric radiative properties, namely extinction coefficient, scattering albedo, and phase function whereas the interaction of the radiation with the medium boundaries is modeled with boundary scattering properties. The aim is to determine these volumetric and boundary scattering properties by an inverse analysis for parameter identification. It consists of minimizing the sum of the squared difference between calculated and measured bidirectional and normal-hemispherical reflectances and transmittances. The Gauss Newton algorithm is employed for solving this nonlinear least squares problem. The experimental data are obtained by using a visible and near-infrared spectrophotometer equipped with a goniometric system enabling measurements in different scattering directions around a sample between 0.4 and 2.5 µm. The collision-based Monte Carlo method is employed to assess the theoretical values by solving the Radiative Transfer Equation (RTE) along with boundary conditions designed for samples with rough surfaces. The proposed approach is proved to be well appropriate for determining the radiative properties of the rough composite samples. More interestingly, this study demonstrates that the scattering phase function can be modeled by the Henyey and Greenstein approximation and the boundary scattering distributions can be modeled by a Gaussian function and/or a cosine function.

iDICs 2020, Digital image correlation standards, training, and global networking virtual conference, Nantes, FRANCE, 19-/10/2020 - 22/10/2020; Glass fiber composites are preferred as 3D printed materials for aerospace applications for their improved stiffness, strength and toughness. However, the effects of the anisotropy of printed material's microstructure on their mechanical properties are still not fully understood. The microstructure of a printed material is first quantitatively investigated via X-ray computed tomography, in terms of porosity and fibers size and orientation distributions. The DIC and DVC analysis of a complex ex situ compression test is then presented. Several fracture mechanisms are observed.

Following the significant improvement in their properties during the last decade, Distributed Fiber Optics sensing (DFOs) techniques are nowadays implemented for industrial use in the context of Structural Health Monitoring (SHM). While these techniques have formed an undeniable asset for the health monitoring of concrete structures, their performance should be validated for novel structural materials including Ultra High Performance Fiber Reinforced Cementitious composites (UHPFRC). In this study, a full scale UHPFRC beam was instrumented with DFOs, Digital Image Correlation (DIC) and extensometers. The performances of these three measurement techniques in terms of strain measurement as well as crack detection and localization are compared. A method for the measurement of opening and closing of localized fictitious cracks in UHPFRC using the Optical Backscattering Reflectometry (OBR) technique is verified. Moreover, the use of correct combination of DFO sensors allows precise detection of microcracks as well as monitoring of fictitious cracks&rsquo, opening. The recommendations regarding use of various SHM methods for UHPFRC structures are given.

Solar roads are transportation infrastructures able both to generate electricity thanks to solar cells placed under a semi-transparent layer and to ensure heavy traffic circulation. In this paper, a novel transparent top layer made of glass aggregates bonded together using a polyurethane glue is presented. The goal is to design a composite material able to support traffic load, guarantee vehicle skid-resistance, allow the passage of sunlight, and protect the solar cells. For this purpose, the authors investigated the effect of different variables (thickness, glue content, and glass aggregate distribution) on the mechanical and optical performances of the material applying the factorial design method. The semi-transparent layer was characterized by performing the three-point bending test and measuring the power loss. Regarding the vehicle friction, experimental tests with the British Pendulum were conducted in order to measure the skid resistance of the surface and compare it with the specifications of a typical road infrastructure. According to the fraction factorial design and the British Pendulum test, the following mixture was developed: 42.8% of 4/6 mm, 42.8% of 2/4 mm, 14.4% of glue in volume, and a thickness of 0.6 cm. The first results are encouraging, and they demonstrate the feasibility of a semi-transparent layer for future applications in full scale.

The blade/disk interface in turbofan is subject to fretting loading. Fan blade of the new generation of aircraft engines are made of woven composite materials. The introduction of these new kind of materials create the need for a new numerical tool able to simulate the contact between heterogeneous materials. The tribological behavior and the damage mechanism associated with these kind of material are still not well understood. The developpment of new numerical tool able to model the damage in the contact area would allow to predict the life of engines parts and to guarantee the security of passengers. This PhD is about the developpment of semi-analytical methods for modeling the damage in fretting and rolling contact conditions with some applications to heterogeneous materials., Les pieds d’aubes de soufflantes de turboréacteurs étant soumis à des sollicitations de type fretting, l’introduction de matériaux composites dans la nouvelle génération de moteur d’avion a rendu nécessaire le développement d’outils permettant de modéliser le contact entre des matériaux hétérogènes. En particulier, le comportement tribologique et l’endommagement de ces matériaux est encore mal compris. La mise en place de méthodes numériques capable de prédire les endommagements dans le contact permettrait de mieux prédire la durée de vie des pièces en service et de garantir la sécurité des passagers. Cette thèse porte sur le développement de méthodes semi-analytiques pour la modélisation de l’endommagement dans des conditions de fretting et de roulement.

Structure and Dynamics of Polymer Composites and Gels: A Simulation Perspective. Edible Soft Matter – a SoftComp Topical Workshop

Raffia Vinifera L. Arecacea is a type of fast-growing palm, which is found in marshy environments and along rivers. In this study, the “Raffia Bamboo” is the stalk of a Raffia palm widely used in the West Region of Cameroon as a building material. From the litterature review, few informations about its elastic properties are available. Our investigations focused on the elastic moduli and strengths of raffia bamboo and the consequent analysis. The raffia bamboo is a composite material, consisting of a fragile marrow (matrix) inside a thin shell (reinforcement), smooth and hard which protects the marrow. The experimental determination of its elastic properties at 13% moisture content allowed us to evaluate: the shear modulus of the marrow (about 5.8 MPa); the respective longitudinal elastic moduli of the shell, the marrow and the raffia bamboo (17 043 MPa; 959 MPa; 13 008 MPa); the transverse elasticity modulus of the raffia bamboo (about 3 149) ; and finally, the tensile strength of the shell (247 MPa), the respective bending strengths of the marrow and raffia bamboo (738 MPa; 5943 MPa) . From the analysis of the results, the elastic properties of the raffia bamboo Vinifera L. Arecacea allow us to classify this material among the light woods, useful for construction and decoration. Résumé Le raphia est un genre de palmier à croissance rapide, de la famille des Arecaceae que l’on rencontre dans les milieux marécageux et le long des fleuves. Dans cette étude, le « bambou de Raphia » est le pétiole d’une palme de Raphia Vinifera L. Arecacea largement utilisé dans la Région de l’Ouest Cameroun comme matériau de construction. La revue de la littérature montre que très peu d’informations sont disponibles sur ses propriétés élastiques. Dans ce travail, nous présentons des résultats sur les propriétés élastiques du bambou de raphia et l’analyse conséquente. Le bambou de raphia est constitué d’une moelle fragile à l’intérieur d’une coque mince, lisse et dure qui protège cette dernière. Il peut donc être assimilé à un matériau composite dont le renfort est constitué de fibres. La détermination expérimentale des propriétés élastiques à 13% d’humidité a permis de trouver: un module de cisaillement de la moelle d’environ 5,8 MPa, un module d’élasticité longitudinal de l’ordre de 17 043 MPa pour la coque, 959 MPa pour la moelle, 13 008 MPa pour le bambou de raphia ; un module d’élasticité transversale de l’ordre de 3 149 MPa pour le bambou de raphia; et en fin, une résistance en traction de l’ordre de 247 MPa pour la coque, une résistance en flexion 738 MPa pour la moelle et 5 943 MPa pour le bambou de raphia . Il ressort de l’analyse des résultats que les propriétés élastiques du bambou de raphia Vinifera L. Arecacea nous permettent de le classer parmi les bois légers utiles pour la construction et la décoration. &nbsp

Hygromorph biocomposites (HBC) possess moisture-induced actuation from bioinspired designs. The present work describes a large experimental and comprehensive database of the hygro-mechanical and bending actuation properties of flax/maleic anhydride grafted polypropylene (MAPP) HBC composites over a large range of moisture variation (10–90% RH) and water immersion. HBCs exhibit a promising responsiveness and reactivity over the whole relative humidity range (10–90% RH), with acceleration and increase of the actuation observed as soon as a 30% RH value is reached. The experimental data are compared to analogous results from an analytical model based on a modified Timoshenko theory, and a finite element model based on the use of classical laminate theory (CLT). We discuss the effects of the hygroscopic properties (β coefficient) and the design parameters (length/width and thickness ratios) of the composites on the actuation performance.

CICE 2018, Conférence internationale sur les composites à matrice polymère renforcée de fibres en génie civil, PARIS, FRANCE, 17-/07/2018 - 19/07/2018; To characterize the adhesion of FRP composites bonded on concrete, the shear test is frequently used in laboratories studies. Several decades ago, CEREMA developed an experimental device able to perform a single lap shear test on FRP bonded on concrete or steel substrates. With this test, the failure mode of the studied FRP system, its maximum capacity and its anchorage length can be determined. It has also been used to study the durability of different FRP reinforcement systems subjected to hygrothermal ageing. However, this set-up is not suitable for characterization of FRP systems bonded on real structure and at that time, pull-off is the sole test available for onsite testing. Then considering that i) accelerated ageing conditions are always questionable regarding real environmental conditions, ii) that laboratory samples are not fully representative of the substrates of the retrofitted structures iii) that the pull-off test is unable to characterize the shear behavior of bonded joints and iv) that it exists a need for onsite acceptance testing, CEREMA, in collaboration with IFSTTAR, has therefore developed a specific mobile device that can be brought onsite in order to perform a shear test on a real structure.The system is equipped with a jack of capacity 100 kN, which is adapted for the shear characterization of both externally bonded FRP sheets and strips. The machine is connected to a computer equipped with an ergonomic software that controls either the load rate or the displacement rate. It gives, in real time, the stress-displacement curve, the failure force and the anchorage length. Furthermore, the test can be monitored by strain gages, which may give access to cohesive zone model of the interface.Some validation tests have already been carried out successfully on retrofitted RC bridges and the equipment will be fully qualified in 2018. In a near future, application or inspection companies will be offered the possibility to acquire this equipment.

CICE 2018, Conférence internationale sur les composites à matrice polymère renforcée de fibres en génie civil, PARIS, FRANCE, 17-/07/2018 - 19/07/2018; Steel bridges present frequent fatigue problems that reduce their load-carrying capacity and residual life. The mainstream method to strengthen steel bridges, the attachment of steel plates to the tension flange of the girders, has several disadvantages. Carbon Fiber Reinforced Polymers (CFRP) composites, though more expensive than steel plates (price per unit/m2), have relevant advantages for the retrofitting of steel bridges: their application is less intrusive to the existing structure and less time-consuming than traditional. The overall objective of FASSTbridge is to develop and demonstrate a reliable preventive, cost-effective and sustainable solution for steel bridges life-time extension using CFRP instead of steel plates. This paper will present the developed fatigue assessment tool used to determine the remaining fatigue life of steel structures and will introduce the design of reinforcement in fatigue using adhesively bonded CFRP. Finally, the gain in service life using this methodology will be presented.

EU'18, European Geosciences Union General Assembly, Vienne, AUTRICHE, 08-/04/2018 - 13/04/2018; International audience

Natural fibres are a real opportunity to replace conventional synthetic fibres in composite applications. However, even if they have several advantages in comparison to synthetic fibres (lightness, carbon balance, price…), their moisture sensitivity, their poor compatibility with polymer matrices and their low thermal stability and flammability makes their modification by chemical or physical treatments essential. In this chapter, the multiple and multi-scale interfaces in natural fibre based composites is described. The importance and role of the fibre/matrix interface on mechanical performances and durability, and main strategies to enhance the interfacial adhesion is discussed. Finally, an opening towards new functionalities that could be achieved by fibre and interface modifications is addressed.

The growing interest in the preservation of our environment stimulates solutions for developing less impacting materials.Thus, the development of composites from renewable resources and recyclable end-of-life resources seems an interesting alternative. This motivated the reason to focus our work on the use of agricultural by-products and waste recycling. Our purpose is the reprocessing of composites based on polypropylene (PP) reinforced with olive husk flour (OHF) at various load rates with adding PP-g-MA as a compatibilizer by six cycles of extrusion.The Young modulus of the composites has slightly increased with the rise of the OHF rate and the number of cycles. An FTIR analysis shows two types of degradation after reprocessing: thermal degradation characterized by a splitting of chains and thermal oxidation justified by the increase in the carbonyl index even when the intensity of the absorption peak has been noticed at 1690-1640 cm(-1) referring to the vinyl groups after the 6th cycle.Moreover, the TGA analysis showed a better thermal stability of the composites after the 6th cycle compared to the virgin PP. The rate of crystallization increases with the number of extrusion cycle.

The modification of surface properties of synthetic reinforcement fibres to modify composite interphase performance is mostly achieved by chemical functionalization techniques in aqueous media, and in some cases in organic media. In particular, surface treatments of glass fibres are carried out by the use of complex aqueous chemical systems, known as sizings, including one or more organofunctional silane coupling agents, a film former and other additives, i.e. cationic or non-ionic lubricants, anti-static agents, surfactants, wetting agents, chopping aids, and antioxydants). Natural fibres does not yet benefit from such a technological and scientific background. Thereby, many strategies of bulk and surface modifications are currently developed to implement natural fibres in composite materials applications. In this chapter, the different pre-treatments and functionalization treatments and related processes developed to modify natural fibres and interfacial properties in biocomposites will be exposed.

This book is addressed to Master and PhD students as well as researchers from academia and industry. It aims to provide the key definitions to understand the issues related to interface modifications in natural fibre based composites considering the particular supramolecular and micro- structures encountered in plant fibres. A particular emphasis is given to the modification and functionalization strategies of natural fibres and their impact on biocomposites behaviour and properties. Commonly used and newly developed treatment processes are described in view of scaling-up natural fibre treatments for their implementation in industry. Finally, a detailed and comprehensive description of the tools and methodologies developed to investigate and characterize surfaces and interfaces in natural fibre based composites is reviewed and discussed.

As a part of the DECID2 French National Project (2008–2012), construction of a large platform entirely made of smart composites was carried out and two demonstrators were installed. During a previous study, an ABAQUS model of smart composite platform was set up to perform numerical simulations that predict the mechanical behaviour of bolt-fastened platform under static three-point bending load, and a stress concentration is observed around the bolt holes. Unidirectional composites are subjected to delamination at very low stress, and this cannot be tolerated because most of the applications of pultruded structures are in civil engineering, which involves human safety. Therefore, it is essential to study the correlation of delamination onset and find a technology to enhance delamination strength. In this study, a numerical analysis was carried out to enhance the delamination strength around the bolt holes. Bidirectional fiberglass cloths were wrapped around unidirectional pultruded beams to reinforce the structure and to prevent delamination. Due to the high cost of these cloths, a study was also carried out to select an appropriate cloth material by taking into account two aspects: density and number of layers of cloths. The selected cloth was compared with conventional continuous fibreglass mat, and it was found that bidirectional fibreglass cloth material performs well in preventing delamination, even though it is expensive.

Natural fibres are complex hierarchical bio-assemblies built-up of several biopolymers. In this chapter, the main features related to biopolymers organization within natural fibres are described. Then, the specific surface properties and porous structure of natural fibres that are key parameters as regard to fibre and interface modifications are detailed.

An elastic gridshell is a freeform structure, generally doubly curved, but formed out through the reversible deformation of a regular an initially flat structural grid. Building curved shapes that way seems to offer the best of both worlds : shell structures are amongst the most performant mechanically speaking while planar and orthogonal constructions are much more efficient and economic to produce than curved ones. This ability to “form a form” efficiently is of peculiar importance in the current context where morphology is a predominant component of modern architecture, and envelopes appear to be the neuralgic point for building performances. The concept was invented by Frei Otto, a German architect and structural engineer who devoted many years of research to gridshells. In 1975 he designed the Multihalle of Mannheim, a 7500 m2 wooden shell which demonstrated the feasibility of this technology and made it famous to a wide audience. However, despite their potential, very few projects of this kind were built after this major realization. And for good reason, the ressources committed at that time cannot guarantee the replicability of this experiment for more standard projects, especially on the economic level. Moreover, the technics and methods developed by Otto’s team in the 1960s have mostly fall into disuse or are based on disciplines that have considerably evolved. New materials, such as composite materials, have recently emerged. They go beyond the limitations of conventional materials such as timber and offer at all levels much better technical performances for this kind of application. Finally, it should be noted that the regulatory framework has also deeply changed, bringing a certain rigidity to the penetration of innovations in the building industry. Therefore, the design of gridshells arises in new terms for current architects and engineers and comes up against the inadequacy of existing tools and methods. In this thesis, which marks an important step in a personal research adventure initiated in 2010, we try to embrace the issue of the design of elastic gridshells in all its complexity, addressing both theoretical, technical and constructive aspects. In a first part, we deliver a thorough review of this topic and we present in detail one of our main achievements, the ephemeral cathedral of Créteil, built in 2013 and still in service. In a second part, we develop an original discrete beam element with a minimal number of degrees of freedom adapted to the modeling of bending and torsion inside gridshell members with anisotropic cross-section. Enriched with a ghost node, it allows to model more accurately physical phenomena that occur at connections or at supports. Its numerical implementation is presented and validated through several test cases. Although this element has been developed specifically for the study of elastic gridshells, it can advantageously be used in any type of problem where the need for an interactive computation with elastic rods taking into account flexion-torsion couplings is required, Les structures de type gridshell élastique permettent de réaliser des enveloppes courbes par la déformation réversible d’une grille structurelle régulière initialement plane. Cette capacité à “former la forme” de façon efficiente prend tout son sens dans le contexte actuel où, d’une part la forme s’impose comme une composante prédominante de l’architecture moderne, et d’autre partl’enveloppe s’affirme comme le lieu névralgique de la performance des bâtiments. Fruit des recherches de l’architecte et ingénieur allemand Frei Otto dans les années 1960, elles ont été rendues populaires par la construction de la Multihalle de Mannheim en 1975. Cependant, en dépit de leur potentiel, très peu de projets de ce type ont vu le jour suite à cette réalisation emblématique qui en a pourtant démontré la faisabilité à grande échelle. Et pour cause, les moyens engagés à l’époque ne sauraient assurer la reproductibilité de cette expérience dans un contexte plus classique de projet, notamment sur le plan économique. Par ailleurs, les techniques et les méthodes développées alors sont pour la plus part tombées en désuétude ou reposent sur des disciplines scientifiques qui ont considérablement évoluées. Des matériaux nouveaux, composites, ont vu le jour. Ils repoussent les limitations intrinsèques des matériaux usuels tel que le bois et offrent des performances techniques bien plus intéressantes pour ce type d’application. Enfin, notons que le cadre réglementaire a lui aussi profondément muté, apportant une certaine rigidité vis-à-vis de la pénétration des innovations. Ainsi la conception des gridshells se pose-t-elle en des termes nouveaux aux architectes et ingénieurs actuels et se heurte à l’inadéquation des outils et méthodes existant. Dans cette thèse, qui marque une étape importante dans une aventure de recherche personnelle initiée en 2010, nous tentons d’embrasser la question de la conception des gridshells élastiques dans toute sa complexité, en abordant aussi bien les aspects théoriques que techniques et constructifs. Dans une première partie, nous livrons une revue approfondie de cette thématique et nous présentons de façon détaillée l’une de nos principales réalisation, la cathédrale éphémère de Créteil, construite en 2013 et toujours en service. Dans une seconde partie, nous développons un élément de poutre discret original avec un nombre minimal de degrés de liberté adapté à la modélisation de la flexion et de la torsion dans les gridshells constitués de poutres de section anisotrope. Enrichi d’un noeud fantôme, il permet de modéliser plus finement les phénomènes physiques au niveau des connexions et des appuis. Son implémentation numérique est présentée et validée sur quelques cas tests. Bien que cet élément ait été développé spécifiquement pour l’étude des gridshells élastiques, il pourra avantageusement être utilisé dans tout type de problème où la nécessité d’un calcul interactif avec des tiges élastiques prenant en compte les couplages flexion-torsion s’avère nécessaire

SMAR 2017, the fourth International Conference on Smart Monitoring, Assessment and Rehabilitation of Civil Structures, ZURICH, SUISSE, 13-/09/2017 - 15/09/2017; One of the aims of Infravation FASSTbridge (Fast and effective Solution for the Strengthening of existing steel bridges) project is to develop a specific reinforcement system dedicated to the preventive fatigue reinforcement of steel bridges. The proposed system relies on the use of an adhesively bonded composite plate. The adhesive has been specifically formulated within the project to respect the required fulfillments of the studied application. The communication will first give insight of the required properties of the adhesive, the composite plate, and the overall system. Based on these requirements and existing literature and standards on the topic, the chosen experimental plan will be described. It will concern investigations on the adhesive before curing, the adhesive after curing, the composite plate and the whole reinforcing system. Both short term and durability investigations are being considered. This experimental plan is currently carried out by the different partners implied within the projects and first results will be presented, especially regarding the properties of the adhesive and the composite plate and first results obtained on assembly.

SMAR 2017, the fourth International Conference on Smart Monitoring, Assessment and Rehabilitation of Civil Structures, ZURICH, SUISSE, 13-/09/2017 - 15/09/2017; The use of adhesively bonded composite reinforcement is relatively widely used for concrete structures. Yet, some questions remain regarding its use in the case of prestressed concrete structures especially in relation with the influence of existing cracking and the verification of the encountered damage phenomena at real scale. French National Organism Cerema with the help of French motorway bridge owners association ASFA and French National Research Organism IFSTTAR realized several real size experimental investigations of an old prestressed concrete beam coming from a deconstructed bridge to answer these questions (Project CLERVAL). Both flexure and shear tests up to failure were carried out and several measurement methods were used to understand the role of the composite reinforcement on the behavior of the structure and the damage scenario. Acoustic emission was one of these methods and two different systems were investigated. The proposed communication will first describe the two used acoustic systems and their dedication. A specific development will then be presented aiming at optimizing the obtained acoustic phenomena localization. Finally, main results will then be presented for both flexure and shear tests. The obtained results are currently compiled with the results from the other measurement methods. This should allow to better understand the damage process of reinforced prestressed concrete beams and to assess the precision of existing reinforcement design methods.

In this study, we use a bond-based peridynamic approach to investigate the mechanical strength and cracking of composite materials with spherical inclusions. The total volume fraction of particles and the particle-matrix toughness ratio were varied to cover a range of soft to hard inclusions. The mean particle damage was characterized together with crack patterns at a sub-particle scale. Three types of crack patterns are identified depending on the toughness ratio.

This study focuses on the optimization of a manufacturing process adapted to flax fibers based composites in which the components are controlled. Twelve plies unidirectional composites samples were prepared by thermocompression using unidirectional flax fibers and fluid epoxyamine resin. Temperature cycle was chosen to limit fibers degradation during fabrication. Different parameters have been studied to evaluate their influence on the mechanical properties of composites. 0° tensile specimens were tested at a 1mm/min crosshead speed. Measures were performed with a 50mm gauge length extensometer and a 100kN load cell. Furthermore, DSC analyses were performed to obtain information about cross-linking of the matrix. Properties are in accordance with the literature. Using 3bar pressure, fiber content was found to be around 46% (in volume). The density of the composite was measured using Archimedes’ principle and was valued to 1.28 when the fibers’ one was 1.45., Academic Journal of Civil Engineering, Vol 35 No 2 (2017): Special Issue - ICBBM 2017

Du fait de leurs propriétés physiques et chimiques exceptionnelles à haute température par rapport aux métaux, les composites de carbure de silicium (SiC) sont étudiés comme éventuel matériau de gainage du combustible nucléaire dans les réacteurs de fusion ou fission avancée futurs, ainsi que, depuis plus récemment, dans les réacteurs à eau légère existants. Les tubes composites SiC/SiC tressés en 2D, fabriqués par procédé d'infiltration chimique en phase vapeur (CVI), présentent un comportement mécanique anisotrope, faiblement déformable (~ 1%). La maîtrise des relations entre la microstructure, l?endommagement et le comportement macroscopique est essentielle pour optimiser précisément le dimensionnement structurel de ce matériau pour les applications envisagées. Un paramètre de fabrication important est l'angle de tressage, angle entre les torons de fibres et l'axe du tube. L'objectif de ce travail est de fournir une compréhension détaillée de la relation endommagement-microstructure, en particulier des effets de l'angle de tressage sur les mécanismes d?endommagement. Dans ce but, une étude combinant observations expérimentales à macro et micro-échelle et simulations numériques est menée. Les tubes composites sont d?abord étudiés par des essais de traction in situ sous tomographie par rayons X. Les expériences ont été réalisées sur la ligne PSICHE du synchrotron SOLEIL sous faisceau rose polychromatique. Les images tridimensionnelles sont analysées par la technique de corrélation d?image volumique (DVC), complétée par une série d'algorithmes de traitement d'image originaux, développés spécifiquement pour analyser les microstructures 3D, mesurer les déformations à travers l'épaisseur du tube, détecter et caractériser quantitativement le réseau de microfissures créées par le chargement mécanique. De plus, les microstructures réelles, décrites par les images de haute résolution issues des tests in situ, sont utilisées dans les simulations numériques multi-échelle. Les champs de contrainte à l?échelle microstructurale sont calculés en régime élastique par une technique utilisant la transformée de Fourier rapide (FFT). Ils permettent de mieux comprendre l'initiation des fissures et d?interpréter les observations expérimentales par une comparaison directe. Ces approches expérimentales et numériques sont appliquées à trois tubes présentant différents angles de tressage (30 °, 45 ° et 60 °). L?influence de l'angle de tressage sur l'initiation et l'évolution de l?endommagement à c?ur des composites est ainsi mise en évidence Because of their outstanding physical and chemical properties at high temperature, in comparison with metals, silicon carbide (SiC) composite materials are studied as possible nuclear fuel cladding materials either for future advanced fission/fusion reactors, or more recently, for the currently existing light water reactors. 2D-braided SiC/SiC composite tubes, manufactured by chemical vapor infiltration (CVI), exhibit an anisotropic, hardly deformable (~1%) mechanical behavior. Understanding the relations between the microstructure, the damage mechanisms and the macroscopic behavior is essential to optimize the structural design of this material for the considered applications. One important manufacturing parameter is the braiding angle, i.e. the angle between the fiber tows and the tube axis. The objective of this work is to provide a comprehensive understanding of the damage-microstructure relations, in particular of the effects of the braiding angle on the damage mechanisms. For this purpose, an investigation combining experimental observations at macro and micro-scale and numerical simulations is developed. The composite tubes are first studied through in situ tensile testing under X-ray computed tomography. Experiments were carried out on the PSICHE beamline at synchrotron SOLEIL using a pink polychromatic beam. The recorded 3D images are processed using the digital volume correlation (DVC) technique, extended by a series of advanced image processing algorithms specifically developed in order to analyze the 3D microstructures, to measure the deformations through the tube thickness, and to detect and quantitatively characterize the network of micro-cracks created by the mechanical loading. In addition, numerical simulations are performed on the real microstructures as observed in the high-resolution images recorded during the in situ tests. Stress fields are calculated at the microstructural scale in the elastic regime using a numerical tool based on the Fast Fourier Transform (FFT). They help to better understand crack initiation and interpret the experimental observations within one-to-one comparisons. Both the experimental and numerical approaches are applied to three tubes with different braiding angles (30°, 45° and 60°). The effect of the braiding angle on the initiation and evolution of damage in the bulk of the composite materials can thus be highlighted

SMAR 2017, the fourth International Conference on Smart Monitoring, Assessment and Rehabilitation of Civil Structures, ZURICH, SUISSE, 13-/09/2017 - 15/09/2017; Though the use of adhesively bonded composite reinforcement has not been extensively applied on steel structures, it may be a good alternative to existing methods regarding the repair of old cracked steel structures, being mainly built with mild steel or puddled iron. The proposed communication will present investigations led in the framework of a Phd thesis in collaboration with French Railway company SNCF. The studied aimed at first investigating experimentally the reinforcement capabilities of different adhesively bonded composite systems on both mild steel and puddled iron cracked elements. The influence of the length of the crack and the asymmetry of the reinforcement have been studied. In addition, some investigations have also been made on the use of prestressed bonded reinforcement. The obtained experimental results allowed obtaining stress intensity factors modification coefficients that may be used in the design process. These factors have also been compared to numerical results from a developed finite element modeling procedure. Such a procedure could be a basis for the determination of other stress intensity factors for other geometries.

The fiber optic sensors (FOSs) are commonly used for large-scale structure monitoring systems for their small size, noise free and low electrical risk characteristics. Embedded fiber optic sensors (FOSs) lead to micro-damage in composite structures. This damage generation threshold is based on the coating material of the FOSs and their diameter. In addition, embedded FOSs are aligned parallel to reinforcement fibers to avoid micro-damage creation. This linear positioning of distributed FOS fails to provide all strain parameters. We suggest novel sinusoidal sensor positioning to overcome this issue. This method tends to provide multi-parameter strains in a large surface area. The effectiveness of sinusoidal FOS positioning over linear FOS positioning is studied under both numerical and experimental methods. This study proves the advantages of the sinusoidal positioning method for FOS in composite material's bonding.

Poly(vinyl alcohol- co -ethylene) was compounded with 2–10% post-harvest tomato (PHT) plant powder and processed by single-screw extrusion to yield composite films. Upon increasing the filler content, the values of the mechanical properties indicators were found to decrease as follows: Young's modulus from 1797 to 750 MPa, stress at yield from 36 to 15 MPa, maximal stress from 39 to 15 MPa, stress at break from 35 to 14 MPa, and strain at break from 6.6 to 4.3%. The results are discussed in comparison with other composite films containing poly(vinyl alcohol- co -ethylene) and water soluble biopolymers obtained by alkaline hydrolysis of fermented municipal biowastes, and with other commercial materials, such as starch based and low density polyethylene mulch films. Depending on the intended application, the post-harvest tomato blend films may be competitive for cost, performance and sustainability.

The use of multilayer is becoming increasingly important in the field of engineering, first in the industry, and more recently more and more in Civil Engineering. Whether complex blend of polymers, wood or concrete, significant efforts are required for accurate modeling of such materials. Indeed, phenomena induced anisotropy and heterogeneity are associated with these multi-material: edge effects, differential thermal expansion, delamination/detachment or nonlinearities viscosity type damage, plasticity in layers or interfaces. Among the models proposed in the literature, we found for example equivalent monolayer model or of "LayerWise" type (a kinematic per layer). Belonging to the second category, models have been developed in recent years in Navier allow a sufficiently detailed description to address specific issues mentioned above while maintaining a surgical nature. By introducing interface forces as generalized forces of the model, these approaches have demonstrated their effectiveness vis-à-vis the representation of details at inter- and intra-layers. It is then easy to offer behaviors and interfaces criteria and to be effective for modeling delamination or detachment, phenomenom very present in multilayered composites assembled and glued together. Therefore, a finite element program MPFEAP was developed in Navier laboratory. The model was also introduced as a User Element in ABAQUS, in its simplest form (perfect interfaces).A new layerwise model for multilayered plates is proposed in this dissertation, named Statically Compatible Layerwise Stresses with first-order membrane stress approximations per layer in thickness direction SCLS1. The model complies exactly with the 3D equilibrium equations and the free-edge boundary conditions. Also, a refined version of the new model is obtained by introducing several mathematical layers per physical layer. The new model has been implemented in a new version of the in-house finite element code MPFEAP.In parallel, a finite element program based on the Bending-Gradient theory which was developed in Navier laboratory, is proposed here. The model is a new plate theory for out-of-plane loaded thick plates where the static unknowns are those of the Love-Kirchhoff theory, to which six components are added representing the gradient of the bending moment. The Bending-Gradient theory is obtained from the Generalized-Reissner theory: the Generalized-Reissner theory involves fifteen kinematic degrees of freedom, eight of them being related only to out-of-plane Poisson’s distortion and thus, the main idea of the Bending-Gradient plate theory is to simplify the Generalized-Reissner theory by setting these eight d.o.f. to zero and to neglect the contribution of the normal stress σ33 in the plate model constitutive equation. A finite element program called BGFEAP has been developed for the implementation of the Bending-Gradient element. A User Element in Abaqus was also developed for the Bending-Gradient theory, L’utilisation des multicouches prend de plus en plus d’ampleur dans le domaine des sciences de l’ingénieur, tout d’abord dans l’industrie, et plus récemment de plus en plus en Génie Civil. Qu’il s’agisse de complexes mêlant des polymères, du bois ou du béton, des efforts importants sont nécessaires pour la modélisation fine de ce type de matériaux. En effet, des phénomènes induits par l’anisotropie et l’hétérogénéité sont associés à ces multi-matériaux : effets de bords, dilatations thermiques différentielles, délaminages/décollements ou non linéarités de type viscosité, endommagement, plasticité dans les couches ou aux interfaces. Parmi les modèles proposés dans la littérature, on trouve par exemple des modèles monocouche équivalente ou de type "Layerwise" (une cinématique par couche). Appartenant à cette deuxième catégorie, des modèles ont été développés depuis quelques années dans le laboratoire Navier et permettent une description suffisamment fine pour aborder les problématiques spécifiques citées plus haut tout en conservant un caractère opératoire certain. En introduisant des efforts d’interfaces comme des efforts généralisés du modèle, ces approches ont montré leur efficacité vis-à-vis de la représentation des détails au niveau inter- et intra-couches. Il est alors aisé de proposer des comportements et des critères d’interfaces et d’être efficace pour la modélisation du délaminage ou décollement, phénomène très présent dans les composites multicouches assemblés et collés. Par conséquent, un programme éléments finis MPFEAP a été développé dans le laboratoire Navier. Le modèle a également été introduit sous la forme d’un User Element dans ABAQUS, dans sa forme la plus simple (interfaces parfaites).Un nouveau model layerwise est proposé dans ce mémoire pour les plaques multicouches, appelé "Statically Compatible Layerwise Stresses with first-order membrane stress approximations per layer in thickness direction" SCLS1. Le modèle est conforme aux équations d’équilibre 3D ainsi qu’aux conditions aux limites de bord libre. En outre, une version raffinée du nouveau modèle est obtenu en introduisant plusieurs couches mathématiques par couche physique. Le nouveau modèle a été mis en œuvre dans une nouvelle version du code éléments finis MPFEAP.En parallèle, un programme d’éléments finis basé sur la théorie Bending-Gradient développée dans le laboratoire Navier est proposé ici. Le modèle est une nouvelle théorie de plaque épaisse chargée hors-plan où les inconnues statiques sont celles de la théorie Love-Kirchhoff, à laquelle six composantes sont ajoutées représentant le gradient du moment de flexion. La théorie Bending- Gradient est obtenue à partir de la théorie Generalized-Reissner: cette dernière implique quinze degrés de liberté cinématiques, huit d’entre eux étant lié uniquement à la déformation de Poisson hors-plan, et donc l’idée principale de la théorie de plaque Bending-Gradient est de simplifier la théorie Generalized-Reissner en réglant ces huit d.o.f. à zéro et de négliger la contribution de la contrainte normale σ33 dans l’équation constitutive du modèle de plaque. Un programme éléments finis appelé BGFEAP a été développé pour la mise en œuvre de l’élément de Bending-Gradient. Un User Element dans Abaqus a été aussi développé pour la théorie Bending-Gradient

The effect of the type of epoxidation processes of soybean oil on the characteristics of epoxidized soybean oils (ESOs), acrylated epoxidized soybean oils (AESOs), and acrylated epoxidized soybean oil - poly(methyl metacrylate) copolymers (AESO-co-PMMA) has been investigated. Two epoxidation processes were used: an in situ chemical epoxida- tion using hydrogen peroxide and formic acid, and a chemo-enzymatic epoxidation using 2 enzymes: Novozyme ® 435 (CALB) and a homemade lipase/acyltransferase (CpLIP2). ESOs containing different numbers of epoxide groups/molecule were synthesized. A commercial ESO (Vikoflex ® 7170) was employed and it had the highest number of epoxide groups. Acrylation of ESOs was carried out using acrylic acid, and copolymerized with a methyl methacrylate monomer. The chemo-enzymatic epoxidation produced high acid value, particularly from the CpLIP2 (! 46-48%) and indicated the for- mation of epoxidized free fatty acids. In contrast, the ESO synthesized from the chemical epoxidation showed a very low acid value, < 0.6%. The AESOs synthesized from the CALB-based ESO and the chemical-based ESO showed a similar number of acrylate groups/molecule while that from the CpLIP2-based ESO showed a very low number of acrylate groups because the carboxylic groups from the epoxidized free fatty acids impeded the acrylation reaction. The lower the number of acrylate groups the lower was the crosslink density, the Tg, and the gel content in the AESO-co-PMMA copolymer.

The use of adhesively bonded composite reinforcement for steel structures induce a closer study of the adhesive as it is considered the weakest point in the assembly. A reliable numerical damage model has been developed for the adhesively bonded joints and then verified for different types of configurations. A bi- linear traction separation description of a cohesive zone model was used in ABAQUS to simulate the damage evaluation in the adhesive. It was then compared to experimental results for the global structure behavior (local strains, applied load, applied displacement)., L'utilisation des renforcements par composites collés pour des structures métalliques implique une étude plus approfondie des adhésifs puisqu'il s'agit dans ce cas de l'élément le plus faible dans l'assemblage. Un modèle d'endommagement numérique a été développé pour le joint collé étudié et appliqué pour diffèrent type de configurations. Le modèle bi linéaire de traction- séparation (modèle de zone cohésives) est réalisé sur ABAQUS pour visualiser l'évaluation de l'endommagement de l'adhésive et pouvoir réaliser une comparaison avec les investigations expérimentales (déformation locale, effort appliqué, déplacement appliqué).

International audience; Offshore wind energy is one of the main sources of renewable energy that can benefit from new generation materials that exhibit good oxidation resistance and mechanical reliability. Composite materials are the best consideration for harsh environment and deep sea wind turbine manufacturing. In this study, a numerical simulation was implemented to predict the stress distribution over a wind turbineblade and to determine areas with high stress concentration. Finite Element Analysis (FEA) was used to find optimal material and bonding techniques to construct the blade. By using Abaqus commercial software, a finite element model of wind turbine blade was analyzed under bending-torsion coupled with a static-load condition in flap-wise direction. Structural damage in critical zones varies according to ply orientation and stack thickness as a result of composite orthotropic nature. This study leads existing scenarios and techniques which would provide a new and better solutions for wind turbine blade designers. The root section and trailing edge were found to be critical zones in the wind turbine blade. The root section failure can be reduced by (1) adjusting the thickness of the structure or increasing the number of plies in the composites laminate stacking and by (2) adjusting the bonding technique to prevent trailing-edge failure. Transverse-stitch method and the carbon cord tying methods are most effective for trailing edge reinforcement. Both solutions are proposed to reduce failures in wind turbine blades and proven by step-by-step numerical study. The goal of this study is to deliver a good reference for wind turbine blade designers and to improve the accuracy during design phase as well as to avoid failure.

International audience; Passive sampling techniques have been developed as an alternative method for in situ integrative monitoring of trace levels of neutral pesticides in environmental waters. The objective of this work was to develop a new receiving phase for pesticides with a wide range of polarities in a single step. We describe the development of three new composite silicone rubbers, combining polydimethylsiloxane mechanical and sorption properties with solid-phase extraction sorbents, prepared as a receiving phase for passive sampling. A composite silicone rubber composed of polydimethylsiloxane/poly(divinylbenzene-co-N-vinylpyrrolidone) was selected by batch experiments for its high sorption properties for pesticides with octanol-water partition coefficients ranging from 2.3 to 5.5. We named this composite material "Polar/Apolar Composite Silicone Rubber". A structural study by scanning electron microscopy confirmed the homogeneous dispersion of the sorbent particles and the encapsulation of particles within the polydimethylsiloxane matrix. We also demonstrate that this composite material is resistant to common solvents used for the back-extraction of analytes and has a maximal resistance temperature of 350°C. Therefore, the characteristics of the "Polar/Apolar Composite Silicone Rubber" meet most of the criteria for use as a receiving phase for the passive sampling of pesticides.

MCD2016, 8th Rilem International Conference on Mechanisms of Cracking and Debonding in Pavements, Nantes, FRANCE, 07-/06/2016 - 09/06/2016; Old steel bridges made in mild steel or wrought iron were assembled by riveting, an assembly technique which is no longer used today. This one induces stress concentration, residual stresses creation and leads to fatigue prone details in such bridges. Cracking that propagates from a rivet hole, hidden by rivet head, is the typical phenomenon of fatigue damage of riveted members. Thus, especially because of increase traffic, fatigue is among the major issues for old steel highway and railway bridges (over 100 years old). Moreover, these structures are often considered as historical ones and modifications of the original element must be limited. For all these reasons, CFRP composites seem to be a good solution that could lead to fatigue life increase. Fibre-reinforced polymer (FRP) has been widely used to strengthen concrete structures and has a great potential to strengthen steel structures. However, limited amount of research has been done on the application of these materials to old steel materials. This paper deals with the study of cracked steel elements and their reinforcement by adhesively bonded carbon fiber-reinforced polymer (CFRP) under fatigue loading. Studied specimens have typical dimensions encountered in old steelriveted joints. A real crack is propagated at the edge of the hole under fatigue loading and composites materials are then bonded taking into consideration the size of the rivet head. Several different CFRP systems were tested and their efficiency compared. Test results, theoretical and modeling considerations of the different studied configurations are presented in this paper

New PHBV/wheat straw fibres biocomposites were produced in such a way to improve the fibre/matrix interface and modulate functional properties of materials. A torrefaction treatment was applied to wheat straw fibres in such a way to increase their hydrophobicity. This improvement led to a better fibre/matrix interfacial adhesion in resultant composites prepared by melt-extrusion, as revealed by SEM observations. The crystallization process was favoured by the presence of torrefied fibres while molecular weight and crystallinity of matrix polymers remained unchanged as compared to untreated fibres. Fibre torrefaction treatment had no significant effect on the mechanical properties of PHBV/wheat straw fibre composites, except for 30 wt.% of torrefied fibres with materials displaying an increased rigidity. It was concluded that improving fibre/matrix adhesion and increasing fibre aspect ratio did not lead to a better preservation of mechanical properties, due to the inevitable presence of microscopic defects in the composite materials. As regards water vapour permeability (WVP), a 30% decrease was first noticed with torrefied fibre contents up to 20 wt.%, which was ascribed to the hydrophobic nature of fibres and improvement of fibre/matrix adhesion. WVP then increased for a fibre content of 30 wt.%, probably due to the creation of percolating pathway. Keywords: Biocomposite, Torrefaction, PHBV, Wheat straw, Mechanical properties, Water vapour permeability

An innovative experimental device was designed for characterizing the long-term behavior of concrete/composite bonded interfaces subjected to both sustained loading and hydrothermal ageing. This test setup makes it possible to load simultaneously several double shear specimens, by means of flat jacks connected to a hydro-pneumatic accumulator. A prototype involving three double-shear specimens was first designed and built in order to validate the concept. Besides, an analytical model was developed for studying the creep behavior of bonded concrete/FRP interfaces, and validated by comparing the simulations to experimental data. This paper aims at describing the proposed creep setup and its instrumentation, as well as the validation stages and the proposed creep analytical model. In a final part, we introduce an ongoing large scale experimental program involving fourteen test specimens (with two different commercial FRP systems) installed in a climatic room at 40°C and 95% R.H., in order superimpose a hygrothermal ageing to the creep load., Un dispositif expérimental innovant a été conçu pour étudier la durabilité des interfaces collées béton/composite soumises simultanément à une sollicitation de fluage et à un vieillissement hygrothermique. Plusieurs corps d'épreuve peuvent être mis en charge au moyen d'un système hydraulique centralisé. Pour valider ce concept, un prototype à trois corps d'épreuve à double recouvrement a été construit. Les résultats issus du prototype ont permis de développer et de valider un modèle analytique permettant d'étudier le fluage des interfaces collées béton/composite. Cet article se propose de décrire le dispositif de fluage, son instrumentation, les différentes phases de validation et le modèle analytique proposé. Dans la dernière partie, nous décrivons également un vaste programme expérimental, actuellement mené sur un banc de fluage comportant quatorze corps d'épreuve à double recouvrement. Ce banc de fluage complet a été installé dans une chambre climatique à 40°C et 95% H.R., afin de coupler le vieillissement hygrothermique à la charge mécanique de fluage.

International audience; Some studies were performed in the past years regarding the behaviour of geosynthetic clay liners (GCLs) as part of a composite liner, focused on the situation where a GCL is located under a hole in a high density polyethylene (HDPE) geomembrane (GM). In this case, the contact between the GM and the GCL was quantified in terms of flow rate through the composite liner and in terms of interface transmissivity. Various situations were tested in the past in order to evaluate the situation where a smooth GM is used in contact with the GCL. The situation where a textured GM is used in contact with the GCL was also evaluated. More recently, the effect of the nature of the bentonite in the GCL, sodium or calcium bentonite, leading to different flow rates in the GCL was evaluated. In all cases an HDPE GM was used. This choice is linked to the fact that it is the most commonly GM used in composite liners including GCLs for chemical compatibility reasons. However one could imagine that the use of other GMs, like bituminous geomembranes (B-GMs) associated to a GCL, could be adapted for hydraulic applications. A quantification of flow rates was thus performed in laboratory tests at the decimetric scale for the case of a damaged B-GM located on top of sodium or calcium GCLs. This corresponds to an alternative design for a canal projected in France at the moment. Results obtained will be presented in the paper and evaluated depending on the B-GM side (polymeric film or sand layer) in contact with the GCL, the type of GCL tested (sodium or calcium bentonite in the GCL) and also compared to test results obtained from the literature carried out with a HDPE GM associated to a GCL.

International audience; The objective of the discussion is to show the questions arising while reading the paper by Varank et al; especillay as regards the size of the wetted area and the risk for misinterpretation of the conclusions of the paper.

International audience; Some studies were performed in the past years regarding the behavior of geosynthetic clay liners (GCLs) as part of a composite liner, focused on the situation where a GCL is located under a hole in a high density polyethylene (HDPE) geomembrane (GM). In this case, the contact between the geomembrane and the GCL was quantified in terms of flow rate through the composite liner and in terms of interface transmissivity. Various situations were tested in the past in order to evaluate the situation where a smooth GM is used in contact with the GCL. The situation where a textured geomembrane is used in contact with the GCL was also evaluated. More recently, the effect of the nature of the bentonite in the GCL, sodium or calcium bentonite, leading to different flow rates in the GCL was evaluated. In all cases an HDPE GM was used. This choice is linked to the fact that it is the most commonly GM used in composite liners including GCLs for chemical compatibility reasons. However one could imagine that the use of other GMs, like bituminous geomembranes (B-GMs) associated to a GCL, could be adapted for hydraulic applications. A quantification of flow rates was thus performed in laboratory tests at the decimetric scale for the case of a damaged B-GM located on top of a GCL. This corresponds to an alternative design for a canal projected in France at the moment. The effect of the side of the GM (polymeric film or sand layer for the bituminous geomembrane) in contact with a GCL containing calcium bentonite was evaluated. Results obtained are presented in this paper and compared depending on the GM side in contact with the GCL.

International audience; Civil aviation transportation has been growing since the early forties and has become today a massive and unique transport system for people across continents and large countries. First age propeller airliners flew at low altitude and were often subjected to dangerous atmospheric and cloud hazards. Low visibility, heavy precipitation, severe turbulence, wind shear, icing and lightning are common weather hazards that are a challenge for flight safety. Among those weather hazards, lightning was the most unrecognized and misunderstood. Damages to aircraft due to lightning strike were frequently noticed; they range from arc spots on metal to centimeter-size holes in the fuselage, and dielectric radome and antenna destruction. Some cases of catastrophic events are directly attributed to lightning [1], [2]. Experimental in-situ studies were initiated no later than the early sixties [3], but the main in-flight research efforts were undertaken at the beginning of the eighties, when the perspective of a massive use of composite material in aviation was identified for a near future. Three major in-flight test programs were initiated in the USA and Europe by NASA, the Air Force, the FAA and the French Civil and Military Aviation Authorities, associated with Research Organizations. This paper is a review of the in-flight lightning strike experiments performed during that period. Information on aircraft missions, performances and instrumentation is given. Available results and proposed interpretations are presented. The main outcomes of those experiments are emphasized and knowledge gaps and missing information are mentioned.

National audience; Pas de résumé

This paper aims to examine the effectiveness of seismic strengthening of reinforced concrete (RC) columns by externally bonded Fibre Reinforced Polymer (FRP). Particularly, a novel strengthening system, designed for the flexural strengthening of columns is studied. This flexural strengthening is achieved by FRP plates bonded longitudinally and anchored at the column-stub junction. The proposed system is validated through an experimental campaign carried out on full-scale RC columns. Different strengthening configurations have been applied on columns, which were tested under combined constant axial and reversed cyclic lateral load. The experimental results demonstrate that bonded FRP enhance the bending moment capacity and flexural deformation capacity of strengthened columns. Those tests helped us to analyze the behaviour of columns depending on the FRP confinement (FRP jacket) and the coupling of the confinement with the anchored flexural strengthening. It was then found that the proposed anchoring system is a promising constructive dis-position for the seismic strengthening of columns, but this system needs to be improved.

The aim of this paper is to present a specific four-point bending test with a specific model to help investigate the crack initiation and propagation at the interface between layers of composite pavements. The influence of the geometry on the delamination phenomenon in specimens is analyzed. Considering the deflection behavior of specimens, both experimental and analytical results are compared. Two different types of interface (concrete / asphalt and asphalt / concrete) are tested in static conditions. Different failure mechanisms whose mainly delamination is observed. The crack mouth opening displacement is monitoring by means of linear variable differential transducer (LVDT). The strain energy release rate is provided and compared successfully to the literature.