26 research outputs found

    Optimisation de transducteurs piézoélectriques pour la génération d'ondes guidées

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    Résumé : Les systèmes de surveillance de santé structurale sont proposés pour la détection d’endommagement dans les infrastructures qui dépassent leur durée de vie en utilisant les ondes guidées (GW). Les ondes guidées peuvent parcourir de longues distances et sont sensibles à une variété d’imperfections. Les transducteurs piézoélectriques sont communément utilisés pour générer et mesurer les ondes guidées dans des structures minces. Comme la détection du défaut et sa localisation sont souhaitées, la nature de la génération des ondes guidées sous forme de plusieurs modes implique une complexité supérieure dans le traitement du signal. Pour remédier à cette limitation, une nouvelle méthode est présentée ici pour la génération des ondes guidées par sélection de mode, et un nouveau transducteur piézoélectrique est ensuite conçu, fabriqué et testé. Tout d'abord, la génération des ondes guidées par optimisation systématique du profil interfacial de la contrainte de cisaillement en mode sélectif est étudiée. En utilisant le principe de superposition, une méthode d'analyse est d'abord développée pour la modélisation de la génération des ondes guidées par un nombre fini de segments de contrainte de cisaillement uniforme, chacun contribuant à un profil élémentaire d’une contrainte constante de cisaillement. Sur cette base, deux fonctions coût sont définies afin de minimiser les modes indésirables et amplifier le mode sélectionné et le problème d'optimisation est résolu avec un cadre d'optimisation d’algorithme génétique parallèle. Les avantages de cette méthode par rapport à d'autres approches de conception de transducteurs classiques sont (1) la contrainte de cisaillement peut être explicitement optimisée à la fois pour exciter un mode et supprimer d'autres modes indésirables, (2) la taille de la zone d'excitation n’est pas limitée et l’excitation en mode sélectif est toujours possible, même si la largeur d'excitation est inférieure à toutes les longueurs d'onde excitées, et (3) la sélectivité est accrue et la largeur de bande est étendue. La méthode analytique et les fonctions coût sont ensuite développées pour concevoir un transducteur piézoélectrique à éléments multiples (MEPT) simple et performant. Une méthode numérique est tout d'abord mise au point pour extraire la contrainte interfaciale entre un seul élément piézocéramique et une structure d'accueil et ensuite utilisée comme entrée d'un modèle analytique pour prédire la propagation des ondes guidées à travers l'épaisseur d'une plaque isotrope. Deux nouvelles fonctions coût sont proposées pour optimiser la contrainte de cisaillement interfaciale pour supprimer le(s) mode(s) indésirable(s) et maximiser un mode désiré. Simplicité et faible coût de fabrication sont deux principales cibles visées dan la conception du MEPT. Un prototype TPEM est ensuite fabriqué à l'aide de micro-usinage laser. Une procédure expérimentale est présentée afin de valider les performances de la TPEM comme une nouvelle solution pour la génération des ondes guidées en mode sélectif. Des essais expérimentaux illustrent la forte capacité du TPEM pour la génération des ondes guidées en mode sélectif, puisque le mode indésirable est supprimé par un facteur allant jusqu'à 170 fois par rapport aux résultats obtenus avec un seul piézocéramique.Abstract : Structural Health Monitoring (SHM) systems are being proposed for damage detection of infrastructures that exceed their life using ultrasonic Guided waves (GWs). GWs can travel over long distances and are sensitive to variety of defects. Piezoelectric transducers (PZTs) are commonly used to generate and measure GWs in plate-like structures. As damage detection and localization is sought, the multi-mode nature of GW generation involves higher complexity in signal processing. To overcome this limitation, a new method is presented here for modeselective GW generation, and a novel mode-selective PZT is then designed, manufactured and tested. First, mode-selective generation of GWs by systematic optimization of the interfacial shear stress profile is investigated. Using the superposition principle, an analytical method is first developed for modeling GWs generation by a finite number of uniform shear stress segments, each contributing with a constant elementary shear stress profile. Based on this, two cost functions are defined in order to minimize the undesired modes and amplify the selected mode and the optimization problem is solved with a parallel Genetic Algorithm (GA) optimization framework. Advantages of this method over more conventional transducers tuning approaches are that (1) the shear stress can be explicitly optimized to both excite one mode and suppress other undesired modes, (2) the size of the excitation area is not constrained and mode-selective excitation is still possible even if excitation width is smaller than all excited wavelengths, and (3) the selectivity is increased and the bandwidth extended. The analytical method and objective functions are then developed to design a novel and costeffective multi-element piezoelectric transducer (MEPT). A numerical method is first developed to extract the interfacial stress between a single piezoceramic element and a host structure and then used as the input of an analytical model to predict the GW propagation through the thickness of an isotropic plate. Two novel objective functions are proposed to optimize the interfacial shear stress for both suppressing unwanted mode(s) and maximizing a desired mode. Simplicity and low manufacturing cost are two main targets driving the design of the MEPT. A prototype MEPT is then manufactured using laser micro-machining. An experimental procedure is presented to validate the performances of the MEPT as a new solution for mode-selective GW generation. Experimental tests illustrate the high capability of the MEPT for mode-selective GW generation, as unwanted mode is suppressed by a factor up to 170 times compared with the results obtained with a single piezoceramic

    Advanced Sensing, Fault Diagnostics, and Structural Health Management

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    Advanced sensing, fault diagnosis, and structural health management are important parts of the maintenance strategy of modern industries. With the advancement of science and technology, modern structural and mechanical systems are becoming more and more complex. Due to the continuous nature of operation and utilization, modern systems are heavily susceptible to faults. Hence, the operational reliability and safety of the systems can be greatly enhanced by using the multifaced strategy of designing novel sensing technologies and advanced intelligent algorithms and constructing modern data acquisition systems and structural health monitoring techniques. As a result, this research domain has been receiving a significant amount of attention from researchers in recent years. Furthermore, the research findings have been successfully applied in a wide range of fields such as aerospace, manufacturing, transportation and processes

    Embedded electronics for intelligent structures

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    Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1991.Includes bibliographical references (leaves 152-156).by David J. Warkentin.M.S

    Air coupled ultrasonic inspection of fiber reinforced composite materials

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    The increase in the use of composite materials in recent years has led the industry into the development of new composite manufacturing processes, like the 3D ultraviolet pultrusion. These new manufacturing processes usually reduce manufacturing costs, cycle time or both. Ensuring the quality of the parts manufactured with these new processes is critical. Therefore, it is necessary to gain knowledge on these manufacturing processes, especially on the behavior of the material during the cure. To monitor these processes, the development of new non-destructive inspection techniques is required. For the 3D ultraviolet pultrusion, the use of non-contact non-destructive testing is necessary. Moreover, for structural parts, ensuring the required mechanical properties gives added value to the part. In this thesis, the viability of air-coupled ultrasonics for plate-like fiber reinforced parts manufacturing is evaluated. At first, isotropic materials are evaluated, considering the ultraviolet cure of a vinyl ester resin. Air-coupled ultrasonics has proved to be fast enough to follow the ultraviolet cure, with quasi-normal ultrasonic spectroscopy. Then, the mechanical properties in fiber reinforced polymers with air-coupled ultrasonics are evaluated. The optimal set-up to generate leaky Lamb waves in plates with different properties is defined. Air-coupled ultrasonics showed that is what difficult to generate Lamb modes with different velocities, although it was possible with a mixed air-coupled laser ultrasonics set-up. Last, leaky Lamb waves where used with air-coupled ultrasonics to evaluate the properties of a fiber reinforced polymer during the thermal cure. The stiffness tensor of the composite was measured during the cure observing the largest variation at the last stages of the cure. The main conclusion of this thesis is that the potential of air-coupled ultrasonics to monitor the fiber reinforced manufacturing processes is elevated. It can presents both the speed required to monitor fast curing processes like ultraviolet cure, with single measurements in less than a second; and the ability to characterize the full matrix of an orthotropic fiber reinforced polymer, through the use of micromechanical models. Air-coupled ultrasonics can be used to characterize the properties of materials with different geometries, like curves or hollow.Material konposatuen erabileraren hazkundeak azken urteetan, material konposatuetarako fabrikazio prozesu berriak garatzera bultzatu du industria, esaterako, 3D pultrusio ultramorea. Fabrikazio prozesu berri hauek, oro har, kostuak, zikloaren denbora edota biak murrizten dituzte. Prozesu berri hauekin fabrikatutako piezen kalitatea bermatzea ezinbestekoa da. Hori dela eta, beharrezkoa da fabrikazio prozesu horien inguruko ezagutza lortzea, batez ere materialak ontzeko garaian. Prozesu horien jarraipena egiteko, suntsitzaileak ez diren ikuskapen teknika berriak garatzea beharrezkoa da. 3D pultrusio ultramorearentzako, beharrezkoa da kontaktu gabeko teknika ez suntsitzaileak erabiltzea. Gainera,pieza estrukturalen kasuan, beharrezkoak diren propietate mekanikoak bermatzeak balio erantsia ematen dio piezei. Tesi honetan zuntzekin indartutako polimerozko plaka motako piezak, airez akoplaturiko ultrasoinuarekin erabiltzeko bideragarritasuna ebaluatu da. Hasieran, material isotropoak ebaluatu dira, binilester erretxina baten ontze ultramorea kontuan hartuta. Airearen akoplamenduarekin egindako ultrasoinuek ultravioleta ontzea jarraitu ahal izateko nahikoa azkarra dela frogatu da, ultrasoinuen espektroskopia bidez, angelu ia normala dela medio. Ondoren, airezko ultrasoinuekin zuntzekin indartutako polimerozko plaken propietate mekanikoak ebaluatzen dira. Airez akoplaturiko ultrasoinuekin Lamb uhinak sortzeko konfigurazio hoberena ebaluatzen da, propietate desberdinak dituzten plakekin. Airearen akoplamenduaerabiltzen duten ultrasoinuek agerian uzten dute zaila dela abiadura ezberdineko Lamb moduak sortzea, baina laser eta airezko ultrasoinuen konfigurazio mistoarekin posible izan zen. Azkenik, airez sorturiko Lamb uhinak erabili dira ontze termikoan zuntzez indartutako polimero baten propietateak zehazteko. Material konposatuko zurruntasuna ontze garaian neurtu zen, ontzearen amaieran aldakuntza handienak ikusiz. Tesi honen ondorio nagusia hauxe da: airez akoplaturiko ultrasoinuekin zuntzekin indartutako polimerozko fabrikazio prozesuak kontrolatzeko duen potentziala handia dela. Bai ultramore ontze prozesu azkarra bezalako prozesuetan, behar den abiadura izan dezake, segundo bat baino gutxiagoko neurketekin; eta zuntz indartutako polimero baten zurruntasunaren matrize neurtzeko gaitasuna, eredu mikromekanikoak erabiliz. airez akoplaturiko ultrasoinuekin geometria ezberdinekin materialen propietateak neurtzeko erabil daitezke, kurbatuak eta hutsak adibidez.El aumento en el uso de materiales compuestos en los últimos años ha llevado a la industria al desarrollo de nuevos procesos de fabricación de maetriales compuestos, como la pultrusión ultravioleta 3D. Estos nuevos procesos de fabricación, generalmente reducen los costes, el tiempo de ciclo o ambos. Garantizar la calidad de las piezas fabricadas con estos nuevos procesos es fundamental. Por lo tanto, es necesario obtener conocimiento sobre estos procesos de fabricación, especialmente sobre el comportamiento del material durante el curado. Para monitorizar estos procesos, se requiere el desarrollo de nuevas técnicas de inspección no destructivas. Para la pultrusión ultravioleta 3D, es necesario el uso de pruebas no destructivas sin contacto. Además, para las partes estructurales, garantizar las propiedades mecánicas requeridas da un valor añadido a la parte. En esta tesis, se evalúa la viabilidad de los ultrasonidos con acoplamiento por aire para la fabricación de piezas reforzadas con fibra de tipo placa. Al principio, se evalúan los materiales isotrópicos, considerando el curado ultravioleta de una resina viniléster. Los ultrasonidos con acoplamiento por aire han demostrado ser lo suficientemente rápidos como para seguir el curado ultravioleta, por medio de espectroscopía ultrasónica en angulo quasi-normal. Después, se evalúan las propiedades mecánicas en los polímeros reforzados con fibra con ultrasonidos con acoplamiento por aire. Se define la configuración óptima para generar ondas de Lamb por aire, en placas con diferentes propiedades. Los ultrasonidos con acoplamiento por aire demostraron que es lo difícil generar modos de Lamb con diferentes velocidades, aunque fue posible con una configuración mixta de ultrasonidos láser y con acomplamiento por aire. Por último, las ondas de Lamb por aire se han utilizado con los ultrasonidos con acoplamiento por aire para evaluar las propiedades de un polímero reforzado con fibra durante el curado térmico. El tensor de rigidez del material compuesto se midió durante el curado observando las mayores variaciones al final del curado. La principal conclusión de esta tesis es que el potencial de los ultrasonidos con acoplamiento por aire para monitorear los procesos de fabricación reforzados con fibra es elevado. Puede presentar tanto la velocidad requerida para monitorizar procesos de curado rápido como el curado ultravioleta, con mediciones en menos de un segundo; y la capacidad de caracterizar la matriz de rigidez ortotrópica de un polímero reforzado con fibra, mediante el uso de modelos micromecánicos. Los ultrasonidos con acoplamiento por aire se pueden usar para caracterizar las propiedades de materiales con diferentes geometrías, tanto curvas como huecas

    Damage identification in FRP-retrofitted concrete structures using linear and nonlinear guided waves

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    Structural health monitoring (SHM) involves the implementation of damage identification methods in engineering structures to ensure structural safety and integrity. The paramount importance of SHM has been recognised in the literature. Among different damage identification methods, guided wave approach has emerged as a revolutionary technique. Guided wave-based damage identification has been the subject of intensive research in the past two decades. Meanwhile, applications of fibre reinforced polymer (FRP) composites for strengthening and retrofitting concrete structures have been growing dramatically. FRP composites offer high specific stiffness and high specific strength, good resistance to corrosion and tailorable mechanical properties. On the other hand, there are grave concerns about longterm performance and durability of FRP applications in concrete structures. Therefore, reliable damage identification techniques need to be implemented to inspect and monitor FRPretrofitted concrete structures. This thesis aims to explore applications of Rayleigh wave for SHM in FRP-retrofitted concrete structures. A three-dimensional (3D) finite element (FE) model has been developed to simulate Rayleigh wave propagation and scattering. Numerical simulation results of Rayleigh wave propagation in the intact model (without debonding at FRP/concrete interface) are verified with analytical solutions. Propagation of Rayleigh wave in the FRP-retrofitted concrete structures and scattering of Rayleigh waves at debonding between FRP and concrete are validated with experimental measurements. Very good agreement is observed between the FE results and experimental measurements. The experimentally and analytically validated FE model is then used in numerical case studies to investigate the scattering characteristic. The scattering directivity pattern (SDP) of Rayleigh wave is studied for different debonding size to wavelength ratios and in both backward and forward scattering directions. The suitability of using bonded mass to simulate debonding in the FRP-retrofitted concrete structures is also investigated. Besides, a damage localisation method is introduced based on the time-of-flight (ToF) of the scattered Rayleigh wave. Numerical case studies, involving different locations and sizes of debonding, are presented to validate the proposed debonding localisation method. Nonlinear ultrasonics is a novel and attractive concept with the potential of baseline-free damage detection. In this thesis, nonlinear Rayleigh wave induced at debondings in FRPretrofitted concrete structures, is studied in detail. Numerical results of nonlinear Rayleigh wave are validated with experimental measurements. The study considers both second and third harmonics of Rayleigh wave. A very good agreement is observed between numerical and experimental results of nonlinear Rayleigh wave. Directivity patterns of second and third harmonics for different debonding size to the wavelength ratios, and in both backward and forward scattering directions, are presented. Moreover, a damage image reconstruction algorithm is developed based on the second harmonic of Rayleigh wave. This method provides a graphical representation for debonding detection and localisation in FRP-retrofitted concrete structures. Experimental case studies are used to demonstrate the performance of the proposed technique. It is shown that the proposed imaging method is capable of detecting the debonding in the FRP-retrofitted concrete structures. Overall, this PhD study proves that Rayleigh wave is a powerful and reliable means of damage detection and localisation in FRP-retrofitted concrete structures.Thesis (Ph.D.) -- University of Adelaide, School of Civil, Environmental and Mining Engineering, 201

    The Real-Time Characterisation of Dry Machine Element Contacts Using Ultrasonic Reflectometry

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    For two components to be in contact, they must be physically touching. If two solids are touching, the contact is by definition inaccessible. How do engineers develop an understanding about a contact if the interface is inaccessible? Load, geometry and material properties govern the contact pressures of touching components. As they move against one another, the result is often wear and this inherently changes the contact behaviour. By understanding how interfaces interact in terms of contact pressure, contact area and wear, components can be optimised to reduce cost and maximise efficiency. Ultrasonic reflectometry has been widely used in medical imaging and non-destructive testing. It is a non-invasive technique that has the ability to probe deep into solid structures and extract information regarding the material and the interface. Two methods have been developed to measure wear in real-time based on ultrasonic time-of-flight and the resonant frequency model. The ultrasonic technique has also been applied to learn more about the contacting parts of machine elements. By analogising the interface asperities as springs, ultrasonic reflectometry can be used to calculate the interfacial stiffness and from this, contact pressure of a tribosystem. Previous work has been limited to laboratory based static measurements. This work builds on this technology to characterise dynamic machine elements with the hopes of developing industrial condition monitoring tools. This thesis is aimed to be a guide for those who wish to use ultrasound as a tool to measure and monitor a dry dynamic tribosystem. More specifically, this work highlights a series of recommendations and pitfalls for ultrasonic measurements of contact pressure and wear in industrial applications

    Enabling wearable soft tactile displays with dielectric elastomer actuators

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    PhDTouch is one of the less exploited sensory channels in human machine interactions. While the introduction of the tactile feedback would improve the user experience in several fields, such as training for medical operators, teleoperation, computer aided design and 3D model exploration, no interfaces able to mimic accurately and realistically the tactile feeling produced by the contact with a real soft object are currently available. Devices able to simulate the contact with soft bodies, such as the human organs, might improve the experience. The existing commercially available tactile displays consist of complex mechanisms that limit their portability. Moreover, no devices are able to provide tactile stimuli via a soft interface that can also modulate the contact area with the finger pad, which is required to realistically mimic the contact with soft bodies, as needed for example in systems aimed at simulating interactions with virtual biological tissues or in robot-assisted minimally invasive surgery. The aim of this thesis is to develop such a wearable tactile display based on the dielectric elastomer actuators (DEAs). DEAs are a class of materials that respond to an electric field producing a deformation. In particular, in this thesis, the tactile element consists of a so-called hydrostatically coupled dielectric elastomer actuator (HC-DEAs). HC-DEAs rely on an incompressible fluid that hydrostatically couples a DEA-based active part to a passive part interfaced to the user. The display was also tested within a closed-loop configuration consisting of a hand tracking system and a custom made virtual environment. This proof of concept system allowed for a validation of the abilities of the display. Mechanical and psychophysical tests were performed in order to assess the ability of the system to provide tactile stimuli that can be distinguished by the users. Also, the miniaturisation of the HC-DEA was investigated for applications in refreshable Braille displays or arrays of tactile elements for tactile maps
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