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A nonlinear acoustic method to assess the damage level of a complex medium is discussed herein. Thanks to the highly nonlinear elastic signatures of cracks or, more generally, internal solid contacts, this method is able to distinguish between contributions from linear wave scattering by a heterogeneity and contributions from nonlinear scattering by a crack or unbounded interface. The coda wave interferometry (CWI) technique is applied to reverberated and scattered waves in glass plate samples featuring various levels of damage. The ultrasonic coda signals are recorded in both the absence and presence of an independent and lower-frequency elastic “pump” wave, before being analyzed by CWI. The monitored CWI parameters quantifying changes in these coda signals, which therefore quantify the nonlinear wave-mixing effects between the coda and pump waves, are found to be dependent on the damage level in the sample. A parametric study is also performed to analyze the influence of sensor positions and average temperature on the method’s output. The reported results could be applied to the non-destructive testing and evaluation of complex-shape materials and multiple scattering samples, for which conventional ultrasonic methods show strong limitations.

Electrical resistivity is sensitive to various properties of concrete, such as water content. Usually used on the surface of old structures, devices for measuring such properties could also be adapted in order to be embedded inside the constitutive concrete of the linings of new tunnels or in new bridges, to contribute to structural health monitoring. This paper introduces a novel multi-electrode embedded sensor for monitoring the resistivity profile over depth in order to quantify concrete durability. The paper focuses on the design of the sensor as a printed circuit board (PCB), which brings several advantages, including geometric accuracy and mitigation of wiring issues, thus reducing invasiveness. The study also presents the numerical modeling of the sensor electrical response and its ability to assess an imposed resistivity profile, together with experimental validations using (i) saline solutions of known conductivity and (ii) concrete specimens subjected to drying. The results demonstrate the capability of the sensor to evaluate resistivity profiles in concrete with centimeter resolution.

International audience; We consider a simplied model of a coupled parabolic PDE-ODE describing heat transfer within buildings. We describe an identication procedure able to reconstruct the parameters of the model. The response of the model is nonlinear with respect to its parameters and the reconstruction of the parameters is achieved by the introduction of a new vectorial descent stepsize, which improves the convergence of the Levenberg-Marquardt minimization algorithm. The new vectorial descent stepsize can have negative and positive entries of different sizes, which fundamentally differs from standard scalar descent stepsize. The new algorithm is proved to converge and to outperform the standard scalar descent strategy. We also propose algorithms for the initialization of the parameters needed by the reconstruction procedure, when no a priori knowledge is available.

One of the principal causes of deterioration in reinforced concrete structures is steel corrosion caused by the penetration of aggressive agents into the protective cover concrete layer (particularly water containing chlorides). Electromagnetic non- destructive evaluation (EM NDE) techniques are sensitive to these aggressive agents and can be used to assess concrete durability in terms of corrosion risk. The electromagnetic (EM) properties that are the focus of the study presented here are electrical resistivity and dielectric permittivity-inherent material properties that are both sensitive to degree of saturation and the salinity of the pore solution. Three EM NDE techniques suitable for the in situ investigation of concrete are used to obtain these EM properties: electrical resistivity tomography, capacimetry and ground penetrating radar. Experimental work is conducted on in a controlled laboratory environment with the aim of comparing the ability of the three EM NDE techniques to monitor the ingress of saline solutions into concrete slabs and discern between their chloride content. All three methods are found to be capable of detecting variation in water and chloride content and therefore show promise for the in situ monitoring of water and chloride ingress. However, more research is needed on the quantification of the EM properties over depth as well as on the combination of these methods in order to separate the influence of these two parameters on the EM responses.

The purpose of this paper is to investigate the static behavior of helical structures under axial loads. Taking into account their translational invariance, the homogenization theory is applied. This approach, based on asymptotic expansion, gives the first-order approximation of the 3D elasticity problem from the solution of a 2D microscopic problem posed on the cross-section and a 1D macroscopic problem, which turns out to be a Navier–Bernoulli–Saint-Venant beam problem. By contrast with earlier references in which a reduced 3D model was built on a slice of the helical structure, the contribution of this paper is to propose a 2D microscopic model. Homogenization is first applied to helical single wire structures, i.e. helical springs. Next, axial elastic properties of a seven-wire strand are computed. The approach is validated through comparison with reference results: analytical solution for helical single wire structures and 3D detailed finite element solution for seven-wire strands.

International audience; Implementation of periodic thermal excitation to identify thermal properties (conductivity, heat capacity, diffusivity) of complex composite materials at different investigation scales (from micrometer to millimetre) presents many advantages. These methods are usually based on the thermal waves phase lag observation compared to a reference signal. In fact, phase lag evolution versus distance to the heating source or versus excitation frequency is quite informative about numerous material characteristics. For example, considering that a structural defect can modify heat propagation inside a material, diagnosis can be performed from phase lag observations and comparisons between samples with and without defects. Numerous studies have been performed considering global heating (a quite large surface of the investigated composite material is heated and defect depth or size can be detected). The proposed approach is original since periodic heating is local and aims to detect defects in the periphery of the excitation. Based on a mathematical model for thermal waves propagations and introducing complex temperature for numerical resolution (finite element method), a feasibility study has allowed a sensitivity analysis. This preliminary study also provides information on the operating protocol, for heating(frequency, power, size of the source), and observation (transmission or reflection). Then, experimental device and early experimental results are briefly exposed.

To improve the modeling of friction between the ground and reinforcing inclusions, such as steel strips in reinforced earth walls, a specific type of finite element was introduced in the CESAR-LCPC finite element code. Simulations were carried out, in which these elements were used in combination with a linear elastic-perfectly plastic model to describe the interaction between the ground and the inclusions. With this simple interaction model, however, it was not possible to reproduce the observed behavior of a full-scale, experimental wall or the results of pull-out tests carried out on the same wall under the same set of parameters. Therefore, two more complex models were introduced for the soil–inclusion interaction, which led to a much better agreement between the numerical results and the experimental observations. Strip-backfill interaction

The objective of this paper is threefold. First, dielectric permittivity measurements on concrete specimens are compared among the different variants of Jonscher's model. Each of these variants considers just a limited number of parameters (two or three), based on certain material-dependent and/or bandwidth-related simplifying assumptions. According to this set-up, these variants affect the inherent "universality" of the model by imposing a tradeoff between representativeness and practicality. Such an effect becomes more pronounced for concrete mixtures with a high moisture content. Next, we propose a computationally efficient, two-step procedure for estimating the four model parameters; this procedure filters the linear parameters that contribute to model deviation from the frequency power law by applying the Kramers-Krönig relations. Only two parameters therefore need to be estimated numerically, whereas the filtered parameters can be estimated in closed form as the solution to a simple linear least-squares problem. All of these variants are applied to an array of concrete mixtures and then evaluated by their goodness of fit. The results obtained demonstrate that accounting for all model parameters via the proposed procedure yields the smallest fitting error, thus enhancing the data interpretation stage. Moreover, a parametric study has been carried out in order to correlate the dispersion parameter n present in each variant of the frequency power law with the physical and hydric characteristics of the concrete mixtures. This procedure has made it possible to derive trends providing information on the conditioning state of the studied media.

This paper is concerned with the numerical simulation of quasi-static evolutions in shape memory alloys structures. In micromechanical models of shape memory alloys, the phase transformation is described by an internal variable representing the volume fractions of the different variants of martensite. In contrast with the framework of standard plasticity, that internal variable is physically constrained to satisfy a set of inequalities at each point. From a structural simulation point of view, handling such local constraints in the evolution problem is not obvious. Robustness and computational time are particularly sensitive issues. In this paper is proposed a new approach which essentially consists in reformulating the non-linear incremental problem as a linear complementarity problem. That approach notably calls for an easy implementation in FEM codes. Comparison with some experimental and numerical results from literature shows the relevancy of the proposed approach.

The seismic imaging methods currently in the development stage need to be tested for experimental validation under controlled conditions. Yet natural media are very complex, and moreover, the parameters along the measurement profile prove difficult to evaluate independently of the seismic method itself. To satisfy this need, the ultrasonic measurement laboratory (MUSC) presented in this research has been devised to experimentally model seismic field measurements by using reduced-scale models. This facility is composed of small-scale models of the underground, an optical table with two moving arms, a laser interferometer, and adapted piezoelectric transducers used as the seismic sources. The source system has been adapted to simulate the behavior of a point-surface seismic source. This is essential to reproduce the spatial energy distribution of a surface seismic source and supersedes the sources used in the past for other reduced-scale seismic experimental models. The comparisons of experimental data collected with MUSC and numerical data simulated by means of finite-element viscoelastic modeling indicate very good agreement of time arrivals and amplitudes for a range of propagation distances until the amplitude has decreased to the system noise level. These results demonstrate that the MUSC laboratory is a system with plenty of promise for validating seismic imaging methods through testing on a perfectly known propagation model prior to field application.

Nous proposons une méthode de contrôle non destructif de durabilité des matériaux cimentaires. La méthode est fondée sur l'analyse de la microporosité par des micro-transducteurs ultrasoniques haute fréquence. Nous présentons des éléments de réalisation et de caractérisation de tels dispositifs. Leur design repose sur les performances mécaniques exceptionnelles des nanotubes de carbone. Les dispositifs sont modélisés dans un environnement fluide. Leur modélisation valide de façon préliminaire leur intérêt pour le suivi de durabilité.

International audience; no abstract

Carbonation depth-profiles have been determined by thermogravimetric analysis and by gammadensitometry after accelerated carbonation tests on ordinary Portland cement (OPC) pastes and concretes. These methods support the idea that carbonation does not exhibit a sharp reaction front. From analytical modelling, this feature is explained by the fact that the kinetics of the chemical reactions become the rate-controlling processes, rather than the diffusion of CO2. Furthermore, conclusions are drawn as to the mechanism by which carbonation of Ca(OH)2 and C–S–H takes place. Carbonation gives rise to almost complete disappearance of C–S–H gel, while Ca(OH)2 remains in appreciable amount. This may be associated with the CaCO3 precipitation, forming a dense coating around partially reacted Ca(OH)2 crystals. The way in which CO2 is fixed in carbonated samples is studied. The results indicate that CO2 is chemically bound as CaCO3, which precipitates in various forms, namely: stable, metastable, and amorphous. It seems that the thermal stability of the produced CaCO3 is lower when the carbonation level is high. It is also shown that the poorly crystallized and thermally unstable forms of CaCO3 are preferentially associated with C–S–H carbonation.

International audience; In civil engineering, ground-penetrating radar is widely used for road pavement survey. In contrast to the existing literature, this paper takes account of the influence of interface roughness (surface and interlayer roughness) within the scope of the data processing of radar signals. The rigorous electromagnetic method PILE (propagation inside layer expansion) provides the simulated data that show the influence of the interface roughness on the backscattered primary echoes of stratified media, the interface roughness provides a continuous frequency decay of the magnitude of the echoes. The observed frequency variations of the radar magnitude introduce some shape distortion on the radar waveform. The latter variations can be modelled by exponential function, which provides satisfactory results for a narrow bandwidth (2 GHz). An adaptation of the root-MUSIC algorithm is proposed. As a result, it is allowed to jointly estimate the time delay and the interface roughness. Then, the algorithm is tested on the data simulated by the PILE method, and numerical examples are provided to assess the performance of this algorithm. The associated results show that the proposed algorithm can estimate both the time delay and roughness parameters with a small relative error.

A ground-penetrating radar (GPR) has been developed for civil engineering applications. Ultra-wide band (UWB) bowtie slot antennas operating at frequencies from 460 MHz to beyond 4 GHz have been designed to be integrated in a ground-penetrating radar (GPR) positioned very close to the soil surface. FDTD modeling has allowed to define the optimal geometrical parameters associated with the ground-coupled radar system that has been studied in two polarization configurations TE and TM. The ability of the GPR system in detecting small discontinuities using polarization diversity has been analyzed considering several buried canonical objects with different dielectric characteristics. Measurements in a sand box have been compared to full-wave simulations.

National audience

In this paper, we present a software architecture that enhances the 3D visualization of sensors' data. We aim to better explore and analyze sensors' data dealing with atmospheric pollutants. Hence, our software architecture provides two techniques to interact with our geospatial data : a light web application for an easy access and visualization of this data, and a 3D GIS that allows an enhanced analysis of the geospatial data as well as the atmospheric pollutants. In consequence, this work helps at proposing better civil and urban engineering strategies in order to reduce pollution rates, and hence, enhance urban life quality.

Les murs en sol renforcé présentent de nombreux avantages, mais le comportement de ces ouvrages sous des sollicitations dynamiques est relativement mal connu, ce qui freine leur emploi dans le domaine ferroviaire, notamment pour les lignes à grande vitesse. On se propose d'étudier le comportement de ce type d'ouvrages par voie numérique, en effectuant une étude paramétrique. Celle-ci porte sur un remblai simplifié modélisé par éléments finis, en 2 dimensions, soumis à une seule impulsion à son sommet et sous les hypothèses de comportement élastique linéaire pour la partie dynamique des différentes variables. Le sol renforcé est modélisé soit en considérant des barres discrètes soit en utilisant un modèle homogénéisé prenant en compte à la fois les caractéristiques du matériau de remblai et des armatures. De plus l'interface armature-remblai est supposée parfaitement adhérente. On compare ces deux modèles au remblai non armé. On considère également plusieurs types de sollicitations, de durées variables et de directions horizontale ou verticale. Les réponses en déplacements et contraintes pour les trois modèles de remblai sont analysées. On s'intéresse à trois problématiques différentes : - quelle est la différence d'amplitude de déplacements et de contraintes, pour une même sollicitation, entre un massif armé et non-armé ? - pour les phénomènes dynamiques, les modélisations des barres de renforcement par une approche discrète ou par une approche homogénéisée donnent-elles des résultats différents ? - un déphasage entre contraintes de compression et contraintes de cisaillement est-il constaté ? Les résultats indiquent que le fonctionnement global d'un massif de sol amé est donné principalement par la géométrie et les caractéristiques mécaniques du remblai. Les barres augmentent la raideur globale du massif et influent sur les déplacements horizontaux et la contrainte de cisaillement au sein du remblai. Par ailleurs, les résultats semblent indiquer que la modélisation homogénéisée des barres peut être envisagée en dynamique dans la mesure où la différence entre modèle homogénéisé et modèle discret est comparable à celle présente dans le cas d'un chargement statique. Enfin, des déphasages entre contraintes sont mis en évidence au cours de la propagation des ondes générées par l'impulsion dans le massif. Ces déphasages, notamment au niveau des barres de renforcement, posent la question du fonctionnement de l'interface au cours du chargement.

Reliable GPS positioning in city environment is a key issue: actually, signals are prone to multipath, with poor satellite geometry in many streets. Using a 3D urban model to forecast satellite visibility in urban contexts in order to improve GPS localization is the main topic of the present article. A virtual image processing that detects and eliminates possible faulty measurements is the core of this method. This image is generated using the position estimated a priori by the navigation process itself, under road constraints. This position is then updated by measurements to line-of-sight satellites only. This closed-loop real-time processing has shown very first promising full-scale test results.

High frequency mechanical impact is a recent improvement method which is probably one of the most effective for treating welded assemblies. A number of experimental results relating to this process are presented in this article. These results lead to better understand the mechanisms of the process, to outline the influence of the operating parameters and to confirm the role played by the initial quality of treated welds. In addition, a process is proposed in order to numerically estimate the fatigue life improvement reached after treatment. All these results were obtained in the scope of a study whose long-term aim is to propose an approach that can be industrially applicable for fatigue design of welded assemblies treated by high frequency mechanical impact.

Autonomous Navigation Systems used in missiles and other high dynamic platforms are mostly dependent on the Global Positioning System (GPS). GPS users face limitations in terms of missile high dynamics and signal interference. Receiver’s tracking loops bandwidth requirements to avoid these problems are conflicting. The paper presents a novel signal frequency and phase tracking algorithm for very high dynamic conditions, which mitigates the conflicting choice of bandwidths and reduces tracking loop measurement noise. It exploits the flexibility of fuzzy control systems for directly generating the required Numerically Controlled Oscillator (NCO) tuning frequency using phase and frequency discriminators information and is labeled Fuzzy Frequency Phase Lock Loop (FFPLL). Because Fuzzy Systems can be computationally demanding and an Inertial Navigation System (INS) is often onboard the vehicle, an assisted INS Doppler version has been designed and is also proposed. Assessment of the new GPS tracking method is performed with both simulated and experimental data under jamming conditions. The main enhancements of the proposed system consist in reduced processing time, improved tracking continuity and faster reacquisition time.

Dans ce travail, un matériau composite à fibres de verre et à matrice vinylester, obtenu par pultrusion, est soumis à un chargement en flexion 3 points, d'abord sous chargement quasi statique, et ensuite en fatigue à fréquence relativement faible. La technique d'émission acoustique est utilisée lors des essais afin de préciser le seuil d'endommagement et de suivre son développement. Les résultats ont montré que le seuil d'endommagement survient bien avant la fin de proportionnalité permettant de préciser l'intervalle de contrainte le long duquel les essais de fatigue sur ce matériau seront pratiqués, à savoir entre la contrainte correspondant au seuil d'apparition d'endommagement et la contrainte de fin de proportionnalité. Jusqu'à la fin de proportionnalité, le scénario d'endommagement du matériau étudié suggère un mode d'endommagement gouverné principalement par les divers micro mécanismes d'endommagement de la matrice (microfissuration de la matrice longitudinalement et transversalement aux fibres). A un niveau de contrainte plus élevé, les ruptures de fibres en nombre engendrent l'activation concomitante de multiples autres mécanismes d'endommagement. Le réarrangement du matériau composite lors du rechargement s'accompagne d'une activité acoustique importante. Ceci est prouvé par une distribution très large des amplitudes des événements acoustiques.

Les performances des matériaux composites doivent être les meilleures possibles et adaptées à différents environnements (expositions prolongées en environnement extérieur, température, humidité et rayonnement solaire), afin d’être utilisés comme composants structuraux dans le génie civil ou comme matériaux de construction. A l’aide d’une installation spécifique, des échantillons en résine vinylester monolithique, ainsi qu’en matériau composite vinylester/fibre de verre ont été exposés à un rayonnement UV très dense. Afin d’évaluer l’impact de cette exposition aux UV, les techniques de nanoindentation instrumentée et de microscopie confocale ont été utilisées. Cette dernière a permis la visualisation 3D et la quantification de la rugosité du vinylester due à l’exposition aux UV alors que la technique de nanoindentation mesure le module d’Young local et la dureté sur la surface exposée. Sur les échantillons exposés aux UV, une surface très escarpée a été obtenue et dans ces circonstances, l’hypothèse d’une pression hydrostatique lors de l’essai de nanoindentation ne peut plus être vérifiée. Le but de cette étude est de mettre en oe½uvre une technique d’investigation contournant ce problème.

Matériaux bitumineux et comportement rhéologique; - Problématique et objectifs; - Techniques expérimentales et matériaux utilisés; - Faisabilité de la technique de propagation d’ondes pour la détermination de la rigidité d’enrobés secs; - Evolutivité de la rigidité d’enrobés humides en cours de séchage par propagation d’ondes

Travel time information is easy to be perceived by users and has the potential to reduce congestion on both temporal and spatial scales thanks to traveller assistance systems. This thesis addresses the problem of estimating the travel time in city, where traffic is characterized by variable flow and also significant perturbation from/to mid-link source/sink that are not equipped with traffic sensors. This flow disturbs the equation of conservation of vehicles. The bibliography contains deterministic and stochastic approaches, using, in specific experimental situations, either inductive loops or probe vehicles, or both. We propose a stochastic approach based on unscented Kalman filtering. Its dynamic model is based on the classical analytical procedure that considers the time difference between the total of incoming and outgoing vehicles for each segment of the network. The formulation of this model is not explicit, which justifies the use of an unscented filter. The observations are both loop counters at the exit sections and probe vehicles map-matched to the network. The algorithm is applicable in real time, without prior information on the percentage of turning movements at intersections, and under any condition of perturbation. The variance estimation output by the filter measures the confidence in the estimated travel time and allows the rejection of outliers. The validation was shown based on simulations on a simple network with three intersections, variable entering flows, variable percentage of perturbation, and a variable percentage of probe vehicles.; La notion de temps de parcours est une information simple à intégrer par les usagers des transports et a le potentiel, via des systèmes d’assistance, de réduire la congestion aussi bien de manière temporelle que spatiale. Cette thèse porte sur la problématique de l’estimation du temps de parcours en ville, où la circulation se caractérise par un débit variable et un flux significatif de/vers des voies transversales non équipées de capteurs de trafic, flux qui agit comme perturbation de l’équation de conservation des véhicules. La bibliographie présente des approches déterministes et stochastiques, utilisant, selon les situations expérimentales, soit des boucles inductives, soit des véhicules traceurs, soit les deux. Nous proposons une méthode stochastique du type filtrage de Kalman sans parfum. Son modèle dynamique est basé sur la méthode analytique classique des stocks qui considère le décalage temporel entre les cumuls de véhicules entrants et sortants dans chaque tronçon du réseau. La formulation de ce modèle n’est pas explicite, ce qui justifie l’utilisation d’un filtre sans parfum. Les observations utilisées sont à la fois les boucles magnétiques à la sortie des tronçons et les véhicules traceurs après map-matching sur le réseau. L’algorithme est applicable en temps réel, sans connaissance a priori des affectations aux carrefours, et sous conditions éventuelles de perturbation. En sortie de filtre, on dispose des variances d’estimation, ce qui mesure la confiance dans le temps de parcours estimé et permet de rejeter des mesures aberrantes. La validation a été montrée sur la base de simulations sur un réseau simple à trois intersections, avec des flux variables et des perturbations, et pour quelques pourcents de véhicules traceurs.

The paper addresses the reconstruction of a Navier-Stokes flow in water pipes at low Reynolds numbers. A classical strategy consists of identifying optimal boundary velocities that minimize the data misfit, which is normally expressed in L2-norm. Herein, we take full advantage of the knowledge of velocity spatial shape in water pipes. As a consequence, we only determine the time evolution of the boundary velocities by the inverse approach. The minimization procedure is realized by means of the adjoint method. In a 2D water pipe junction test case, we show that the discretization error of the direct and adjoint problems can significantly deteriorate the quality of the reconstructed velocity. Then, the modeling error is analyzed in this paper. By using unsteady Stokes equations to reconstruct a Navier-Stokes flow, we may obtain an L2 error on the reconstructed velocity of about 5% for a computational cost reduced by 2 orders of magnitude.

Antennas with broadband characteristics have recently found various applications in modern ultra wide band (UWB) communication systems and in ground penetrating radar (GPR). Our applications are focused on imaging the subsurface of a large range of civil engineering structures at several depths using a bistatic GPR positioned on or close to the ground surface. The development of a compact (34*29 cm2) broadband pair of antennas operating in the frequency band from 0.27 to 3.1 GHz, whose radiation characteristics have been preliminary studied theoretically in details in different configurations, is to allow the probing of the subsurface in several frequency sub-bands using a step frequency (SF-GPR) acquisition mode. Microstrip patch antennas (MPAs) are one of the most basic and important types of planar antennas because they offer many advantages such as compact size, low-cost, ease of fabrication, light weight, and various shapes design. However, a low bandwidth and a low gain are the main shortcomings for such planar structure. The microstrip antenna has now reached maturity and many techniques have been suggested for achieving a high bandwidth such as using more complex shapes, parasitic elements, multilayer configurations and the tuning of the feed line. In this paper, an original printed rectangular slot antenna fed by a 50 Ohms CPW (coplanar waveguide) transmission line tuned by a E-shaped patch is presented. Presently, little work has been made to lower the operating frequency band of microstrip antennas at frequencies less than 0.8 MHz and to reduce the antenna size at these frequencies because major applications concern UWB wireless communications. By choosing a relative combination of a E-shaped patch, a linear feed line and a rectangular slot, we have designed an antenna structure on a FR4 substrate ( h=1.5 mm) with a very wide operating bandwidth whose nearly half of the spectrum covers frequencies lower than 1 GHz. A partial shield, only opened towards the ground, and coated with an inner layered absorbing material has been added to eliminate undesirable reflections from the upper environment particularly at low frequencies; moreover, in a GPR system, the antenna shielding will allow to reduce the coupling between the transmitting and the receiving units. The proposed rectangular slot antenna has been designed and simulated using the 3D commercial software EMPIRE based on the finite difference time domain (FDTD) technique. A detailed parameter study has allowed to define the several geometrical parameters of the unshielded slot antenna which are the result of a compromise on the frequency bandwidth (S11

International audience

In this paper, we present first a fabrication process of suspended graphene stripes. This process is done on two types of graphene sheets. One is a reduced graphene oxide and the second is a few layer graphene grown by CVD. In the second part, we introduce a new method to derive the value of the local Young’s modulus of ultrathin films using atomic force microscopy for experimental measurements and a continuum mechanics model for analytical fitting. Measurements are performed on few nanometers thick suspended graphene sheets grown by CVD.

ISBN: 978-84-695-3472-4; International audience; Using a 3D urban model to forecast satellites visibility in urban contexts in order to monitor GPS localization is the main topic of the present article. A virtual image processing is at the core of this method. A preliminary proof of concept has been presented in IEEE ITST 2011, where the theoretically visible satellites were computed with respect to the true position of the vehicle computed off-line from the data of a much more sophisticated equipment. This article addresses now the closed-loop real-time processing of the method, i.e. using the position estimated by the navigation process itself.

NDE, SEATTLE, ETATS-UNIS, 22-/05/2012 - 24/05/2012; This paper is concerned with the implementation of FO sensors in reinforcement bars (rebars) for strain measurement in reinforced concrete (RC) structures made of Ultra High Performance Fiber Reinforced Concrete. In the proposed technique, the FO sensor is embedded into a drilled cavity in the rebar using suitable adhesive. The measurement chain consists of an OBR interrogation unit (Optical Backscatter Reflectometer, based on relative Rayleigh measurements) paired with FO sensors. The validation of the proposed technique has been performed successfully through a series of experiments. In a first validation step, uniaxial tensile tests were carried out on steel rods instrumented with FO sensors. The second validation step was to demonstrate the feasibility of embedding FOsensors in RC structures (embedded into the groove of rebars or bonded on the rebars surface) without damaging them during pouring of the concrete. For this purpose, pullout samples were fabricated by partially embedding instrumented rebars in concrete blocks. Results obtained so far indicate that the sensors perform adequately for the strain measurement of rebars tested in tension and for the strain measurement of rebars embedded in a loaded RC structure.

Nanosensors dedicated to the structural health monitoring of concrete structures have been only marginally studied. They would however be particularly well-suited to monitor durability-related processes, as these phenomena involve transport of gas and liquids through micro and nano-porosity. In this paper we discuss the relevance and feasibility of embedding rela-tive humidity nanosensors within concrete. It appears that the localized, continuous knowledge of relative humidity within a concrete structure could provide a useful insight into drying shrinkage; it could also contribute to improved intrinsic permeability measurements, leading to improved assessment of structural durability. For the task, we propose a low-cost, downscalable resistive device made of a 10 nm graphene sheet grown directly on glass and atop which are ink-jet printed silver electrodes. The device resistance increases significantly with relative humidity (RH), especially above 40% RH. Relative amplitude of variations are only of about 3% for the two tested devices, but absolute variations (80 Ohms/sq and 480 Ohms/sq) appear measurable by a low-cost and robust signal conditioning electronics. Thus, the idea of using our graphene-based resistive device for embedded humidity monitoring in concrete ap-pears quite promising.

International audience; Nanoporosities play a most significant role in the durability of cementitious materials, so that nanoscale features are a promising target for SHM. However, to this day, no sensor features the resolution required to investigate non-destructively these nanofeatures. To fill in this loophole, we are devising a SHM-targeted, carbon nanotubes and graphene based capacitive ultrasonic nanotransducer for microporosity assessment in concrete. In this paper, we report on the feasibility of the key building block of the proposed sensor: we have fabricated ultra-thin graphene and single-walled carbon nanotubes membranes. A breakthrough laser vibrometry experiment shows that the membranes can feature above-nanometer amplitudes of vibration over a large range of frequencies spanning from 100 kHz to 5 MHz. A detailed numerical model of the nanotransducer shows that upon embedding in a cementitious material it could determine the volume and content of the porosity in its vicinity. Such information would be invaluable in the evaluation of structural durability.

Hipermat, KASSEL, ALLEMAGNE, 07-/03/2012 - 09/03/2012; In the frame of the French national R&D project Orthoplus, an experimental program has been carried out to assess the influence of a UHPFRC topping layer on the behaviour of orthotropic decks and their fatigue resistance. This project aims at improving the design rules for orthotropic decks and developing a UHPFRC-based innovative solution to improve the durability. Bendings tests were carried out on four specimens, consisting in a realistic steel orthotropic deck model, 2.4 x 4m, with different types and thicknesses of topping layers: traditional bituminous concrete, thin layer of UHPFRC or no topping layer. The load application has been chosen as representative of real situations and of idealised cases considered in design codes. The loads were first applied through static tests with different configurations in accordance with Eurocode 1 and then through a fatigue test representative of traffic loads during bridge lifespan.

Mode-locked vertical-extended-cavity-surface emitting lasers (ML-VECSEL) are promising candidates for the generation of stable short pulses at multi-GHz rate. However, the poor thermal behavior of quaternary InP-based semiconductor compounds often limits the performance of ML-VECSELs operating at 1.55 μm. In this work, we report on a specific approach using downward heat sinking to optimize the heat dissipation out of the active region. VECSEL chips with a low thermal resistance are fabricated using a hybrid metal-metamorphic GaAs/AlAs mirror and bonding to a highly thermally conductive host substrate. We show that superior performance can be obtained with a CVD diamond substrate, while electroplated copper host substrate can afford a flexible and low cost alternate approach for moderate (~100 mW) output power. The VECSEL chip assembled with a 1.55μm fast InGaAs(Sb)N/GaAsN semiconductor saturable absorber mirror (SESAM) produces nearly Fourier transform-limited mode-locked pulses at ~ 2 GHz repetition frequency, and the RF linewidth of the free running laser is measured to be less than 1000 Hz. When the resonance and group delay dispersion of the SESAM microcavity are tuned by selective etching of specific top phase layers, the modelocked pulse width is reduced from several picoseconds to less than 1 ps.

Residual stresses inside optical fibers can impact significantly on Brillouin spectrum properties. We have analyzed the importance of internal stresses on the Brillouin Gain Spectrum (BGS) for a conventional G.652 fiber and compared modeling results to measurements. Then the residual internal stresses have been investigated for a set of trench-assisted fibers: fibers are coming from a single preform with different draw tensions. Numerical modeling based on measured internal stresses profiles are compared with corresponding BGS experimental results. Clearly, Brillouin spectrum is shifted linearly versus draw tension with a coefficient of -20MHz/100g and its linewidth increases.

In spite of numerous efforts for developing the applications of graphene, it remains difficult to put the remarkable physical properties of this material into devices. This is mainly due to the fact that large-area (industrial) graphene includes in its structure and on its surfaces a significant density of defects that make as many traps and scattering centres for charge carriers. The idea of the present work, contrary to diminishing the defect density, is to use the defects and the very large surface to volume ratio of that 2D material, to transform it into high sensitivity sensors. When defects are useful, low-temperature growth becomes the method that best satisfies both physical and financial demands. Here, we further decrease preparation costs by performing growth not only at low temperature directly on the final insulating substrate (glass), but also by printing the device contacts by ink-jet printing. Graphene layers actually develop at the interface between a metallic catalytic film and the insulating substrate during plasma-enhanced chemical vapour deposition (PE-CVD).1,2. Resistivity of the graphene foils was measured by the four-point methods using ink-jet printed electrods, and a resistivity as low as 820 ohms/sq were obtained. Moreover, the sensitivity of such graphene foils to water vapour was evaluated, with the prospect to use them in humidity sensors for civil engineering. In this presentation, we explain how graphite may precipitate at the interface in addition to the surface.2,3 Then we show examples of graphene obtained at temperatures in between 450 and 550°C, on glass (Fig.), fused silica, alumina and SiO2//Si. Transmission electron microscopy indicates that the structure is nanocrystalline. We finally show the humidity response of the fabricated device. Results seem to indicate that high-defect density, thin deposits are more sensitive to water vapour than thicker ones.

Le procédé CASC (contrôle acoustique pour la surveillance des câbles) est un système de surveillance de structures comprenant des câbles tendus (notamment les ponts suspendus, ponts à haubans, structures à précontrainte intérieure ou précontrainte extérieure). Une fois en place, il permet la détection et la localisation des ruptures des fils constituant ces câbles, par l'énergie et les ondes acoustiques qu'ils libèrent lorsqu'ils se rompent. Le système, muni de moyens de transmission, permet la mise en oeuvre d'alarmes et la télésurveillance des structures concernées. Le présent guide décrit le procédé, à travers les phénomènes physiques sur lesquels il se base et l'appareillage qu'il mobilise. Il donne à son utilisateur tous les conseils nécessaires pour la bonne mise en oeuvre de cette méthode sur les ouvrages d'art, de la réflexion préalable jusqu'à l'interprétation des résultats servant à la prise des décisions relatives à la gestion de l'ouvrage.

This paper presents two automated devices for conducting non-contact ultrasonic measurements (with air coupling and laser interferometry) for the purpose of recovering mechanical properties (porosity) on a series of concrete slabs using surface waves. The devices employed herein as part of an extensive laboratory experimental campaign are also intended to be operational onsite. The ultrasonic frequencies applied lie in the range of 40-300 kHz; moreover, according to surface wave (SW) properties, the investigation depth of a few centimetres corresponds to the cover concrete investigation target. The measurements of SW velocity and attenuation are described and used to characterise various concrete mixes. The efficiency of such measurement devices is demonstrated, within the scope of the French research project SENSO, by means of laboratory measurements carried out on manufactured cement slabs.

In this paper, we developed a numerical modeling of a sensor composed of a single mode optical fiber inserted between two thin steel ribbons that are embedded in a polyurethane-type material. The different steps of calculation are performed using the method of finite element discretization. From a mechanical view point, the ribbon transfers its applied external loading to the fiber in the unidirectional form. This transmission causes birefringence in the optical fiber by modifying the opto-geometrical parameters related to the difference between principal stresses in the fiber core. The polarization phase shift enables to evaluate the applied load. The application of this study is about the development of an instrumentation dedicated to the analysis of road traffic (vehicle WIM). The numerical results presented, show the behavior of the sensor as a function of the ribbon geometry for elastic massive under load. These results should be validated from experiments taking into account environmental characteristics and conditions of use.

A large scale equipment project, the Sense-City Equipex has received support from the French government in the framework of the 'Programme d’Investissement d’Avenir'. This project is led by the French Institute of Science and Technology for Transport, Development and Networks (IFSTTAR) with ESIEE-Paris, the Laboratory of Physics of Interfaces and Thin Films (LPICM) and the Scientific and Technical Centre for Building (CSTB) as consortium partners. Starting in 2012, Sense-City will offer a suite of high-quality facilities for the design, prototyping and performance assessment of innovative, micro- and nanotechnology based sensors devoted to urban instrumentation. Acknowledging the shortcomings of evaluating sensors performances in laboratory conditions only or in the ever-changing environment of our cities, Sense-City will provide a realistic urban test space in climatic conditions, far more complex than clean rooms and far less complex than actual cities. Sense-city revolves around the 'mini-city' concept, a large, fully customizable climatic hall able to host full- and reduced-scale models of essential urban components. The design of the models will allow for the simulation in climatic conditions of numerous scenarios of sustainable cities. The scenarios to be implemented will correspond to different research topics related to urban sustainability: energy performances in buildings, quality of air, water and soils, quality of fluid distribution networks (gas, sewage, drink water), control of waste disposal areas, durability and safety of infrastructures.

La pérennité des performances des ouvrages en béton précontraint repose sur la double vérification du maintien de l'intensité de la force de précontrainte et de la section restante des câbles. EDF R&D et le LCPC ont construit un programme de recherche articulé autour de questions pratiques : - quel est l'intensité de la contrainte dans le béton ou dans les câbles ? - combien y a-t-il de fils rompus dans les câbles et où ? - où sont les zones de défaut de protection des câbles ? - les câbles sont-ils le siège d'une activité corrodante qui compromettrait leur durée de vie ? Ce programme nommé ACTENA (pour Auscultation des Câbles Tendus Non Accessibles) a tenté de relever le défi de l'évaluation de l'état de la précontrainte à travers l'exploration et le développement de méthodologies non-destructives : acousto-élasticité du béton et de l'acier, réflectométrie ultrasonore et électromagnétique, impact-echo, imagerie infra-rouge, émission acoustique. Cet ouvrage présente les avancées réalisées au cours des quatre années (2006-2009) du programme ACTENA soutenu financièrement par l'Agence nationale de la Recherche, EDF R&D et la contribution des 15 laboratoires partenaires de ce programme. L'ouvrage est complété par la présentation de la méthode capacitive LCPC pour l'auscultation des conduits de précontrainte extérieure.

A problem arises when uniaxial tensile tests are conducted on UD composite materials in the fiber direction, that is the failure starts in the clamping area and hence the tensile strength is underestimated. In this study, uniaxial tensile tests in the fiber direction on specimens from unidirectional E-Glass fiber/Vinyl ester matrix composite material are analyzed. The effect of use of end tabs on tensile strength of specimens are investigated and finally the best configuration, including the geometry and the material of end tabs and also the clamping pressure on end tabs, is obtained through numerical simulations. mention the results.

A coplanar rectangular slot antenna operating in the very wide frequency band from 0.27 to 3.1 GHz (bandwidth over 166%) has been designed for GPR applications. The antenna, which is supposed to be positioned on the soil surface, appears particularly compact (34 £ 29 cm2) and exhibits a low cross-polarization in the E-plane. 3D FDTD simulations have allowed to make a detailed parametric study associated with the antenna dimensional parameters in order to optimize the radiating performances. The slot antenna has also been studied with a shield to be further integrated in a bistatic subsurface radar positioned on the soil surface. Simulated results of the link in the presence of a homogeneous soil then including buried objects met in civil engineering structures are presented and discussed. First experimental results on a sandy soil have been compared to numerical ones.Une antenne coplanaire rectangulaire à fente fonctionnant dans la bande de fréquence très large de 0,27 à 3,1 GHz (bande passante plus de 166%) a été conçue pour des applications GPR. L'antenne, qui est censée être positionnée sur la surface du sol, apparaît particulièrement compacte (34 par 29 cm2) et présente une faible polarisation croisée dans le plan E. Des simulations FDTD en 3D ont permis de conduire une étude paramétrique détaillée relative aux paramètres dimensionnels de l'antenne pour optimiser ses performances de rayonnement. L'antenne à fente a également été étudiée en présence d'un blindage pour être intégrée dans un radar bistatique de sub-surface positionné à la surface du sol. Les résultats simulés de la chaîne de transmission, en présence d'un sol homogène et d'objets enterrés rencontrés dans les structures de génie civil, sont présentés et discutés. Les premiers résultats expérimentaux en présence d'un sol sableux ont été comparés à des résultats numériques.

Cette etude presente le comportement vis-a-vis de la corrosion par piqure et de la fragilisation par hydrogene de deux nuances d’aciers inoxydables a hautes caracteristiques mecaniques. Ceci a pour objectif de verifier si, pour ces aciers, un ecrouissage important associe a un detensionnement thermomecanique engendre une baisse notable de leur comportement en corrosion. L’etude electrochimique « a contrainte œ nulle » montre que le potentiel de piqure E pit de la nuance austeno-ferritique (duplex) est plus faible que celui de la nuance austenitique, contrairement a ce que prevoit le Pitting Resistant Equivalent Number (PREN). La presence de precipites de nitrure de chrome semble pouvoir expliquer ce resultat. Les observations realisees apres les essais de fragilisation par hydrogene montrent que la fissuration s’amorce sur des piqures. La nuance duplex presente cependant une duree de vie plus importante que celle de la nuance austenitique. Le piegeage de l’hydrogene aux joints de grains α /γ pourrait expliquer la grande resistance de la nuance duplex.

Tuned mass dampers (TMDs) are widely used in civil engineering. the performance of this device depends on their state parameters and therefore the evolution of the bridge may pull down the efficiency of this kind of device. Active tuned mass damper (ATMD) have been explored widely for applications in damping response control of bridges under construction. This paper presents a new semi-active control based on an electromechanical device. This semi-active tool consists of a pendulum coupled to an alternator. The alternator converts the mechanical energy of the oscillating pendulum into electric energy to be dissipated through an exterior resistor via Joule effect. In order to damp the torsional mode of a bridge during successive construction phases, the electromechanical actuator was connected to the bridge and its parameters were changed in real time by using a new semi-active control law. This control law, once applied to the resistor, permits to modify in real time the damping coefficients and the stiffness of the TMD with the aim of obtaining an optimal configuration for the actuator at each construction phase. Numerical and experimental validations on a small-scale bridge dynamical behaviour confirm the interest of the approach., Les amortisseurs de masse accordés (PTM) sont largement utilisés dans le génie civil. Le fonctionnement de cet appareil dépend des paramètres d'état et donc l'évolution du pont peut tirer vers le bas l'efficacité de ce type de dispositif. L'amortisseur actif de masse accordé (ATMD) a été exploré largement pour des applications dans le contrôle de la réponse d'amortissement des ponts en cours de construction. Cet article présente un nouveau contrôle semi-actif basé sur un dispositif électromécanique. Cet outil semi-actif est constitué d'un pendule couplé à un alternateur. L'alternateur transforme l'énergie mécanique du pendule oscillant en énergie électrique destinée à être dissipée par une résistance extérieure par l'intermédiaire de l'effet Joule. Afin d'amortir le mode de torsion d'un pont au cours de phases successives de la construction, l'actionneur électromécanique est relié au pont et ses paramètres ont été modifiés en temps réel en utilisant une nouvelle loi de commande semi-active. Cette loi de commande, une fois appliquée à la résistance, permet de modifier en temps réel les coefficients d'amortissement et la raideur de la DMT dans le but d'obtenir une configuration optimale de l'actionneur à chaque étape de la construction. Les validations expérimentales et numériques sur un pont à petite échelle de comportement dynamique confirment l'intérêt de la démarche.

The assessment of an Excavating Damaged Zone (EDZ) due to underground works is important in the context of radioactive waste disposal within a geological formation. Seismic surveys can pro- vide, in a non-destructive manner, information directly related to the mechanical properties of this damaged zone. However, the classical refraction method is unusable for galleries where a concrete layer caps the top surface. Moreover, other possible seismic methods like surface wave analysis can become complex to implement in such a context since guided waves are present and pass through a high-velocity concrete layer. For these reasons, the present paper will focus on an experimental feasibility study of the MASW (Multi Channel Analysis of Surface Waves) method for assessing an EDZ below a concrete layer in the specific context of the Tournemire experimental platform, which was drilled into an argillaceous formation in the Aveyron department of central France. This facil- ity is operated by IRSN (French institute for Radiological Protection and Nuclear Safety). This experimental study has been conducted in conjunction with a modelling results analysis. During an initial stage, the measurements carried out in situ are analysed and it is demonstrated that a receiv- ing profile longer than 8 m is required to distinguish the various modes. Moreover, the comparison of a hammer source and a sweep signal generated by a vibrator source shows that the latter is more appropriate when building the dispersion diagram, particularly for fundamental and first higher mode curves. A second stage shows that according to the analysis of theoretical curves for profiles with similar seismic velocities of the Tournemire platform medium, the dispersion curves are sensi- tive to EDZ characteristics. In the paper's final part, the dispersion curves obtained from the experimental seismic data are inverted using a global approach. Results of the inversion of the fundamental mode only and of both the fundamental mode and the first higher mode are com- mented upon, evidencing an improved quality for this last approach.

The aim of the study reported in this paper was to provide rational aid tools to quantify the performance of nondestructive testing (NDT) tools. This study focused on the quantification of the performance of impact–echo sources (steel balls of varied diameters), applied with a new, con-tactless robot, for duct void detection and thickness measurements in a reinforced concrete wall. Because of uncertainties during the testing, the data were analyzed in a probabilistic context, with the knowledge that on-site inspections were affected by uncertainties. The αδ method was used in this regard, where the probabilities of detection and false alarm rates were used to build receiver operating characteristic curves. The methodology was applied to data measured on the same wall with two steel ball diameters: 0.16 and 0.125 m. The quantity analyzed here was the impact–echo method (resonance) frequency. This methodology could be extended to other parameters of the impact–echo setup as well as to other NDT methods.

En France, EDF gère un important parc d’ouvrages hydrauliques en terre dédié à la production hydroélectrique, avec des enjeux économiques et sécuritaires conséquents. D’autres ouvrages à charge permanente sont présents sur le territoire, par exemple le grand linéaire de voies navigables (transport, tourisme). Du côté des digues "sèches" (digues de protection contre les inondations), 7500 km de digues protégeant plus de 15000 km2 de zones inondables où vivent 2 millions d’habitants sont recensés. Pour ces ouvrages particuliers, il n’y a pratiquement pas d’année sans rupture et plus de 70 incidents ont été recensés en 25 ans par le Comité Français des Grands Barrages. L’érosion interne et la surverse sont les principales causes de ruptures et d’incidents de levées, digues et barrages en France et dans le Monde. L’Imagerie de Résistivité Électrique (IRE) est une méthode d’imagerie très sensible aux paramètres d’état d’un sol : la nature du sol et son contenu argileux, sa teneur en eau et la salinité de l’eau, son état de compacité et sa température. Elle fait donc partie des méthodes pertinentes pour la reconnaissance et la surveillance des ouvrages hydrauliques en terre. Ainsi, elle est complémentaire de méthodes de reconnaissance à grand rendement (ex : Profilage par méthodes électromagnétique à basses fréquences) en offrant localement des images du corps de digue et de sa fondation. En surveillance, alors que les méthodes basées sur les Potentiels Spontanés ou les mesures de température par Fibre Optique sont particulièrement sensibles aux écoulements d’eau (donc aux fuites à travers le corps de digue), l’IRE peut contribuer à imager les variations des propriétés d’état dans le temps de la structure interne de l’ouvrage (phénomène évolutif d’infiltration combiné ou non à de l’érosion interne). Cependant, dans l’utilisation conventionnelle de l’IRE, le manque d’information provenant des mesures, ainsi que la mauvaise prise en charge de ces mesures et de l’information a priori, entraînent la formation d’artéfacts dans les résultats d’imagerie. Dans ce sens, de nouvelles démarches d’acquisition et d’inversion sont développées, intermédiaires entre les techniques plus classiques 2D et 3D. Ces nouvelles approches, dont le but est de tirer le meilleur compromis entre coût d’acquisition et robustesse (fiabilité) du modèle final sont le fruit du développement d’un problème direct par éléments finis et d’un algorithme d’inversion 3D de type Gauss-Newton. Enfin, des campagnes d’auscultations sur ouvrage semi-contrôlé et sur ouvrage réel ont été réalisées afin de confronter ces développements à la complexité de cas réelles. Ces études révèlent que la qualité de la reconstruction et la capacité d’interprétation peuvent être considérablement améliorées par l’utilisation des approches développées.

Dans le cadre du contrôle non destructif et de la caractérisation de divers ouvrages du génie civil à l’aide d’ondes électromagnétiques, nous étudions des géométries d’antennes planaires ultra large bande dans la bande [0.25;2.6] GHz, de faible coût, aux dimensions les plus réduites possibles, et qui doivent être adaptées à diverses impédances de sol. Ces antennes doivent être blindées pour s’affranchir des réflexions multiples induits par les objets de la surface et pour constituer un système émetteur-récepteur (radar de surface bistatique). Les géométries d’antennes proposées de type dipôle magnétique (antenne à ouverture) ont été développées à partir de simulations 'full wave 3D' fondées sur l’approche FDTD. Des études paramétriques détaillées relatives à la géométrie des différentes antennes ont été conduites afin d’optimiser leur rayonnement en présence de sols de permittivité variée et aussi de réduire leur polarisation croisée. Par la suite, l’intégration des antennes dans un système radar bistatique en présence d’un sol comprenant une ou plusieurs hétérogénéités est modélisée afin d’optimiser la configuration du radar en vue de détecter et de caractériser des modifications de propriétés diélectriques, des défauts ou des objets enfouis.