Comparative studies of nondestructive evaluation methods have shown that nonlinear ultrasonic techniques are more sensitive than conventional linear methods to changes in material microstructure and the associated small-scale damage. Many of the material degradation processes such as carbonation in concrete, corrosion in metals, etc., begin at the surface. In such cases, ultrasonic Rayleigh surface waves are especially appropriate for detection and characterization of damage since their energy is concentrated in the top layer of the test object. For the civil engineering infrastructure, only a limited number of field applicable nonlinear ultrasonic techniques have been introduced. In this paper a nonlinear ultrasonic measurement technique based on the use of Rayleigh waves is developed and used to characterize carbonation in concrete samples. Wedge transducer is used for the generation and an accelerometer for detection of the fundamental and modulated ultrasonic signal components. The measurements are made by varying the input voltage and along the propagation distance. The slope of the normalized modulated amplitudes is taken as the respective nonlinearity parameter. Concrete samples with two different levels of damage are examined, and the difference of the two fundamental frequencies is used to quantify damage state.

This research deals with the second harmonic generation of Lamb waves in nonlinear elastic, homogeneous, isotropic plates. These waves find current applications in the field of ultrasonic, nondestructive testing and evaluation of materials. The second harmonic Lamb wave generation is investigated analytically in order to provide information on suitable excitation modes maximizing the second harmonic amplitude. Using an existing solution for the problem of second harmonic generation in wave guides, the solution is explained for the plate and examined as to the symmetry properties of the second harmonic wave, since published results are contradictory. It is shown that the cross-modal generation of a symmetric secondary mode by an antisymmetric primary mode is possible. Modes showing internal resonance, whose conditions are nonzero power flux from the primary wave and phase velocity matching, are shown to be most useful for measurements. In addition, group velocity matching is required. A material-independent analysis of the linear Lamb mode theory provides mode types satisfying all three requirements. Using the example of an aluminum plate, the found internally resonant modes are evaluated with regard to the rate of second harmonic generation and practical issues such as excitability and ease of measurement. Pros and cons of each mode type are presented.

Although the study of the interaction of acoustic and elastic waves with periodic surfaces and structures has a rich history dating back to Lord Rayleigh, it has recently been attracting new research efforts due to its value in the study of phononic crystals and in methods for ultrasonic non-destructive evaluation (NDE). The objective of the research described in this thesis is to provide new numerical and experimental tools capable of capturing important features that occur due to the diffraction of ultrasound on periodic solid surfaces. This thesis is divided into four main parts. First, the Rayleigh-Fourier (R-F) method will be used to simulate diffracted fields generated by structures containing multiple periodic surfaces and/or multiple solid layers. The second part of this thesis examines diffraction effects and compares ultrasonic NDE techniques for surfaces with imperfect periodicities. The third portion of this thesis focuses on one unusual phenomenon that has been observed on periodic surfaces, namely the lateral backward displacement of a bounded ultrasonic beam along the surface. This effect is currently understood to occur due to backward propagating surface waves that result from diffraction and mode conversion on the surface. The fourth and final part of this thesis describes the diffraction of bulk ultrasonic waves that can occur on the surfaces of phononic crystals.

Dans cette thèse, les travaux présentés s’appuient sur une démarche expérimentale utilisant, outre les mesures destructives habituellement mises en œuvre pour la caractérisation des matériaux cimentaires, les techniques non destructives exploitant la propagation des ondes ultrasonores à des fréquences comprises entre 50 kHz et 600 kHz. L’objectif est d’étudier les corrélations entre les propriétés hydrauliques et mécaniques de la pâte de ciment et les paramètres linéaires des ondes ultrasonores (vitesse et atténuation). L’étude concerne plus particulièrement les relations entre la porosité et la vitesse ultrasonore des différents types d’onde (ondes de volume et onde de Rayleigh). Les matériaux étudiés sont des pâtes de ciment à porosité variable, confectionnées avec différents rapports E/C et avec différents dosages en entraineur d’air. Afin de prendre en compte l’effet de la teneur en eau, les mesures sont effectuées à différents états de saturation : état saturée, 70% de saturation, 30% de saturation et l’état sec. Les données recueillies permettent la constitution d’une base des données expérimentale regroupant les caractéristiques physiques, mécaniques et ultrasonores de la pâte de ciment. Dans la dernière partie de cette thèse, les relations entre les vitesses ultrasonores et la porosité basées sur deux approches macroscopique et microscopique sont présentées et confrontées aux mesures / In this thesis, we present an experimental study including, besides the destructive measurements usually implemented for the characterization of cementitious materials, non-destructive techniques using ultrasonic wave propagation in a frequency range from 50kHz to 600kHz. The objective is to study the correlations between hydraulic, mechanical properties and linear ultrasonic parameters (velocity and attenuation) of cement paste. This study specifically addresses the relationship between porosity and ultrasonic velocity of the different types of waves (body waves and Rayleigh wave). The studied materials are cement pastes with variable porosity, made up with different water / cement ratios and with different concentrations of air entrainer. To take into account the effect of water content, measurements are made at different states of saturation: saturated state, 70% saturation, 30% saturation and dry state. The data collected allows the creation of a database of experimental data involving physical, mechanical and ultrasonic parameters of cement paste. In the final part of this thesis, relationships between ultrasonic velocity and porosity based on macroscopic and microscopic approaches are presented and compared with measurements

Conselho Nacional de Desenvolvimento Científico e Tecnológico / The purpose of this study is to explore the use of ultrasonic technique in order to estimate the moisture content during wood drying, from green condition to the end of the drying process. The treatments were based on the combination of two different species (Pinus elliottii Engelm. and Eucalyptus grandis Hill ex Maiden), drying temperatures (20, 40 and 70ºC) and transducers types (plane faces and dry points). The experiment was set up according to a factorial model, with approximately 50 replications. A 50 kHz - transducer (PUNDIT ultrasonic equipment) was used. Samples tested had nominal 3.5 cm thick by 10 cm wide by 25 cm long and the ultrasonic wave speed propagation was measured according to its longitudinal direction. The results indicated increase of ultrasonic speed with reduction of moisture content for both transducers used. This relationship is valid for the wood from green to the end of the drying process. However, low correlation was observed, and the best model adjusted determination coefficients were observed with eucalypt wood (Raj.²= 88%). The use of the transducers of dry points was more practical than the plane faces one. Moreover, they should be used in hard and not much heterogeneous woods. The ultrasonic velocity was also influenced by wood density and drying temperature. The species showed different effects of wood density on the velocity. In the pine wood, velocity increased with increasing density. Opposing effect was observed in eucalypt wood. The ultrasonic speed tended to decrease as drying temperature increased. Nevertheless, this variable s influence was reduced. It was not noticed any defined influence of the species in the ultrasonic speed when the plane face transducers were used. However, the eucalyptus wood provided larger velocity when the dry point transducers were used. The results suggest that this method presents good potential for the control of the drying process. Studies on the influence of the several wood characteristics on the ultrasonic wave s velocity and the development of specific transducers for the use of this alternative in commercial scale are required. / O objetivo deste estudo foi explorar o uso da técnica ultra-sônica para estimar o teor de umidade da madeira durante sua secagem, desde a condição verde até o final do processo. Os tratamentos basearam-se na combinação de duas espécies (Pinus elliottii Engelm. e Eucalyptus grandis Hill ex Maiden), temperaturas de secagem (20, 40 e 70ºC) e tipos de transdutores (faces planas e pontos secos). O experimento foi estabelecido segundo modelo fatorial, com aproximadamente 50 repetições por tratamento. Utilizou-se um equipamento ultra-sônico PUNDIT, com transdutores de 50 kHz. As amostras testadas apresentaram dimensões nominais de 3,5 x 10 x 25 cm de espessura, largura e comprimento, respectivamente e a velocidade ultra-sônica foi determinada considerando-se o plano longitudinal. Os resultados indicaram aumento da velocidade ultra-sônica estimada em função da redução do teor de umidade, para ambos os transdutores. Esta relação apresentou-se válida para a madeira desde verde até o final da secagem. No entanto, foi observada baixa correlação, sendo que os melhores coeficientes de determinação ajustados ocorreram à madeira de eucalipto (Raj.²= 88%). O uso dos transdutores de pontos secos apresentou-se mais prático do que o uso do de faces planas, devendo ser utilizados em madeiras duras e pouco heterogêneas. A velocidade ultra-sônica também foi influenciada pela densidade da madeira e pela temperatura de secagem. As espécies proporcionaram efeitos distintos da densidade sobre a velocidade. Na madeira de pinus, a velocidade aumentou com o aumento da densidade, ao passo que na de eucalipto ocorreu efeito inverso. A velocidade ultra-sônica apresentou tendência de redução em virtude do aumento da temperatura de secagem. No entanto, a influência desta variável foi reduzida. Não foi observada influência definida das espécies sobre a velocidade ultra-sônica quando utilizados os transdutores de faces planas. Porém, a madeira de eucalipto proporcionou maior velocidade quando utilizados os transdutores de pontos secos. Os resultados sugerem que este método apresenta bom potencial para ser usado no controle do processo de secagem. Entretanto, são necessários estudos sobre a influência das diversas características das madeiras sobre a velocidade das ondas ultra-sônicas, bem como o desenvolvimento de transdutores específicos para o uso desta alternativa em escala comercial.

La compréhension de phénomènes physiques complexes tels que la diffusion multiple résonante des ondes nécessite l'étude de systèmes modèles parfaitement contrôlés. Lors de ces travaux de thèse, nous proposons l'utilisation d'émulsions résonantes pour l'étude du transport des ondes ultrasonores en milieux désordonnés fortement diffusants. Les constituants de ces émulsions (gouttetelettes d'huile fluorée dispersées dans un gel aqueux) ont été choisis pour leur caractère très faiblement absorbant et leur propension à engendrer de très forte résonances de type-Mie. De plus, la nature fluide de ces systèmes autorise l'exploration in situ du champ acoustique dans le milieu. Dans un premier temps, nous nous attachons à la description théorique de la propagation des ondes acoustiques dans des émulsions résonantes. Les modes de résonance d'une goutte isolée sont tout d'abord modélisés avant d'étudier la diffusion (simple et multiple) d'une onde acoustique par une population désordonnée d'objets identiques. Les techniques micro-fluidiques employées pour la synthèse de ces systèmes modèles sont ensuite déc rites, de même que les dispositifs acoustiques mis en place pour la caractérisation des ondes cohérentes et incohérentes. Pour des émulsions diluées, les résultats de ces caractérisations sont analysés dans le cadre d'hypothèses de diffusion indépendante, adaptées aux descriptions de la propagation balistique de l'onde cohérente et du transport diffusif de l'intensité incohérente moyenne. L'estimation expérimentale de la vitesse de l'énergie des ondes multiplement diffusées permet d'établir un lien original entre de précédents travaux menés en optique et en acoustique. Enfin, lorsque la concentration en diffuseurs augmente, les approximations évoquées précédemment sont mises en défaut. Nous observons alors des phénomènes physiques plus complexes liés à l'interaction entre diffuseurs, comme le transport "sub-diffusif" de l'intensité moyenne laissant entrevoir des perspectives séduisantes quant à l'étude du phénomène de locations d'Anderson / Complex physical phenomena study, such as resonant multiple scattering of waves, requireswell calibrated model systems. During this study, we suggest the use of resonant emulsions tostudy ultrasonic waves transport in strongly resonant disordered media. Emulsions components(uorinated oil droplets in a water-based gel) were selected for both their weak absorptionand propensity to generate strong Mie-type resonances. Fluid kind of those systems allowsfurthermore in situ acoustic _eld probing.First, we theoretically describe acoustic waves propagation in resonant emulsions. Dropletsresonance modes are calculated just as multiple scattering of an acoustic wave by a disorderedpopulation of identical objects. Then, micro-uidic technics used to make such model systemsare described as well as acoustic devices designed for both coherent and incoherent waves characterization.For diluted emulsions, our experimental observations of both the ballistic propagation ofcoherent wave and di_usive transport of averaged intensity are well described by independentscattering approximations. Energy velocity estimation of multiple scattered waves allows thenan original link between pioneering works in optics and acoustics.Finally, when scatterers concentration increases, previous approximations fail. We thus observefurther complex phenomena, which arise from scatterers interactions, such as\sub-di_usive"transport of averaged intensity suggesting attractive prospects for Anderson localization study.

Cette étude novatrice consiste à mettre en oeuvre dans un même protocole expérimental, trois techniques de caractérisation non destructive en simultané : l’émission acoustique, la thermographie infrarouge et les ultrasons pour la caractérisation de l’endommagement des matériaux Composites à fibres continues et à Matrice Polymère (CMP) à plis croisés [0/90]S. Chaque technique a permis demontrer sa potentialité à révéler l’endommagement dépendant de ses spécificités intrinsèques. L'émission acoustique a été utilisée sous sa forme classique et couplée avec une classification de données obtenue par les k-means et la carte de Kohonen. La thermographie infrarouge a été étudiée selon ses deux formes passive et active, les méthodes ultrasonores ont été exploitées en termes d’amplitude et de vitesse des ondes longitudinales et des ondes de Lamb respectivement. Il a été montré que l’approche multitechnique adoptée dans ce travail est très intéressante pour obtenir un diagnostic complet sur l’état de santé du matériau au repos et sous différents niveaux de chargement mécanique en traction. Il s’est avéré aussi que l’aspect « complémentarité » entre les trois techniques était plus envisageable que celui de la « redondance ». La fusion des données a été utilisée pour avoir une prise de décision fiable, complète et plus crédible sur les différents mécanismes d’endommagement susceptibles d’apparaître dans un matériau CMP. Ceci n’a été possible que pour les deux techniques d’imagerie, le C-scan ultrasonore et la thermographie infrarouge. En conclusion, les résultats montrent que ces trois techniques sont potentiellement capables de qualifier l’état d’endommagement du matériau, mais qu’elles ne le quantifient pas de la même manière / This innovative study consists to implement in the same experimental procedure three non destructive techniques simultaneously: acoustic emission, infrared thermography and ultrasonic waves for the characterization of damage in cross ply Polymer Composite Materials (PCM) [0/90]S. Each technique has demonstrated its potential to reveal the damage that depends on its intrinsic characteristics. Acoustic emission has been used in its classical form and coupled with a data classification obtained by k-means and Kohonen map. Infrared thermography has been studied using both passive and active forms, ultrasonic methods have been used by exploiting amplitude and velocity of longitudinal and Lamb waves respectively. It has been shown that the adopted multi-technique approach is veryinteresting to obtain a full diagnostic of the health state of the material before and after uniaxial mechanical loading. The “complementarity” aspect between the three used techniques is showed more interesting that “redundancy” aspect. The data fusion theory was used to have a reliable, comprehensive and credible decision about the different damage mechanisms may appear in PCM material. This has been possible only for the two imaging techniques, ultrasonic C-scan and infrared thermography. All in all, the results show that these three techniques are potentially able to describe the damage state of the material, but they don’t quantify it with the same manner

[pt] Ondas acústicas, sônicas ou ultrassônicas, podem ser empregadas para a telemetria sem fio como alternativa a sistemas eletromagnéticos, transferindo dados e energia ao longo de um canal formado por uma ou mais camadas de sólidos elásticos ou fluidos acústicos. Um exemplo é a interrogação de sensores passivos através de uma parede metálica. Nesta configuração, pelo menos um transdutor acústico é fixado em um lado da parede (face externa), onde uma fonte de alimentação elétrica é disponível. No lado oposto (face interna), onde os sensores estão instalados, são fixados um ou mais transdutores. Na maioria das aplicações estes transdutores são cerâmicas piezelétricas que geram e recebem sinais ultrassônicos. Ondas acústicas ultrassônicas se propagam ao longo do sólido elástico, transferindo energia e dados entre as duas faces, possibilitando a alimentação e interrogação dos sensores. Este tipo de configuração pode ser empregado em aplicações onde o uso de penetradores elétricos ou ópticos não é recomendado. Entretanto, a resposta das piezocerâmicas pode sofrer influências de variações de temperatura e da própria deformação mecânica da parede metálica na qual são fixados. O presente trabalho procurou quantificar a influência da deformação mecânica e da variação de temperatura na comunicação entre dois transdutores piezocerâmicos ultrassônicos, aderidos à uma placa metálica por meio de adesivo epóxi. No estudo, tomou-se como parâmetro quantitativo o sinal S21, que é o logaritmo da razão entre a potência recebida pela saída do sistema (face interna da parede) pela potência transmitida pela entrada (face externa da parede). O trabalho apresenta comparações entre resultados experimentais e simulados através de um modelo numérico de elementos finitos desenvolvido no COMSOL Multiphysics. Os ensaios experimentais foram realizados com pastilhas piezocerâmicas circulares, do tipo PZT4, com diâmetro e espessura de 25 e 2 mm, respectivamente. Os transdutores foram fixados, de forma concentricamente alinhada e por meio de um adesivo epóxi, nas duas superfícies de uma placa de aço inoxidável AISI 316 L com 6 mm de espessura. O trabalho apresenta tabelas e funções para a amplitude do sinal S21 na frequência onde a transferência de potência é maximizada. Para os casos estudados, observou-se que a frequência ideal muda muito pouco com a temperatura ou a deformação da placa sobre a qual os transdutores são fixados, permanecendo com valores entre 0,988 e 0,995 MHz em todas as condições avaliadas. Em função da deformação da placa metálica, a amplitude do sinal S21 também variou muito pouco, de -3,70 para -3,14 dB, desde a condição indeformada da placa até a máxima deformação aplicada, que foi de 1250 (Micro)m/m. Quanto à variação com a temperatura, na faixa de 30 a 100 Graus C, mais uma vez observou-se apenas um pequeno aumento de 0,8 dB na amplitude do sinal S21. Entretanto, para temperaturas acima de 100 Graus C, o sinal passa a cair rapidamente. Em nenhuma das condições estudadas neste trabalho foi observado prejuízo na transferência de potência entre os transdutores, indicando que este tipo de comunicação pode ser uma alternativa robusta ao uso de penetradores elétricos. / [en] Acoustic, sonic or ultrasonic waves can be used for wireless telemetry as an alternative to electromagnetic systems, transferring data and energy along a channel formed by one or more layers of elastic solids or acoustic fluids. An example of this is the interrogation of passive sensors through a metallic wall. In this configuration, at least one acoustic transducer is attached to one face of the wall (external face) where electrical power supply is available. One or more transducers are also attached to its other side (internal face) where the sensors are installed. In most applications, these transducers are piezoelectric ceramics that generate and receive ultrasonic signals. Ultrasonic acoustic waves propagate along the elastic solid, transferring energy and data between both sides, which enables the power supply and interrogation of the sensors. This type of configuration can be used in applications where the use of an electrical or optical penetrator is not suitable. However, the response of piezoceramics may be affected by temperature variations and mechanical deformations of the metallic wall on which they are attached. The present work sought to quantify the influence of mechanical deformation and temperature changes on the communication between two ultrasonic piezo ceramic transducers, adhered to a metal plate by using an epoxy adhesive. The parameter used to quantify this influence was the S21 signal, which is the logarithm of the ratio between the power received from the output of the system (internal face of the wall) to the power transmitted by the input (external face of the wall). The work presents comparisons between experimental and simulated results obtained by using a finite element model developed through the commercial software COMSOL Multiphysics. In the configuration experimentally tested, two PZT-4 disks with diameter and thickness of, respectively, 25 and 2 mm were concentrically attached to both sides of a 6 mm thick, AISI 316 L stainless steel plate. Amplitudes of the S21 signal measured at the frequency where power transfer is maximized were obtained for different temperature and strain levels. Results for all of the evaluated conditions showed that the impedance matching frequency suffers little influence from temperature variations or strain in the plate on which the transducers are attached, having remained within a range from 0.988 to 0.995 MHz in all tests. As mechanical strains were applied to the metal plate, the amplitude of the S21 signal varied from -3.70 dB to -3.14 dB, from the undeformed condition to the maximum applied deformation (1250 (Micro)m/m). Regarding temperature changes, a small increase of 0.8 dB in the amplitude of the S21 signal was observed when increasing temperature from 30 C Degrees to 100 C Degrees. However, for temperatures above 100 C Degrees, the signal was found to quickly decay. None of the conditions studied in this work brought any impairment to the power transfer between the transducers, indicating that this type of communication can be a robust alternative to electrical penetrators.

In this study the description and development of intensity-based laser interferometric techniques for the detection and measurement of ultrasonic stress waves and their small displacement amplitudes is presented. The dynamic displacement sensitive interferometers described in the following chapters allow the quantitative point-by-point measurement of both in-plane and out-of-plane components of surface displacement motion. These uniquely developed interferometric sensors are: 1) an optical system design for the detection of the surface acoustic wave (Rayleigh wave). The technique is based on the Fourier analysis of coherent light and diffraction imaging properties of an illuminated grating; 2) the design and construction of a two-beam unequal-path laser interferometer for the measurement of out-of-plane surface displacement of ultrasonic waves; 3) extension of a flexible fiber optic probing device which is optically coupled to the test arm of the above two-beam interferometer. This permits scanning of the test surface which may be at some distance from the main optical system components; 4) the design and construction of a laser speckle interferometer for retro-reflective diffusing surfaces in which the in-plane displacements of the ultrasonic wave are interrogated. The inherent advantages of these newly designed optical configurations in terms of their greater simplicity, feasibility, and sensitivity over the conventional counterparts (classical/speckle laser interferometers) are explained. The function-response limitations of these interferometric sensors on lateral displacement resolution, on upper and lower-bound displacement sensitivity (dynamic range), on high-frequency bandwidth probing capability, on low-frequency environmentally associated noise disturbance, and on specularly reflective or diffusively retro-reflective specimen surface preparation are also mentioned. Finally, in a series of experimental observations, the application of a couple of these acoustic sensors in pulsed-excitation ultrasonic Specifically, the optically testing methods is cited. detected ultrasonic signals revealing the true nature of the various surface displacement modes of vibration are presented. / Ph. D.

Structural health monitoring (SHM) is concerned with the continuous, long-term assessment of structural integrity. One commonly investigated SHM technique uses guided ultrasonic waves, which travel through the structure and interact with damage. Measured signals are then analyzed in software for detection, estimation, and characterization of damage. One common configuration for such a system uses a spatially-distributed array of fixed piezoelectric transducers, which is inexpensive and can cover large areas. Typically, one or more sets of prerecorded baseline signals are measured when the structure is in a known state, with imaging methods operating on differences between follow-up measurements and these baselines. Presented here is a new class of SHM spatially-distributed array algorithms that rely on sparse reconstruction. For this problem, damage over a region of interest (ROI) is considered to be sparse. Two different techniques are demonstrated here. The first, which relies on sparse reconstruction, uses an a priori assumption of scattering behavior to generate a redundant dictionary where each column corresponds to a pixel in the ROI. The second method extends this concept by using multidimensional models for each pixel, with each pixel corresponding to a "block" in the dictionary matrix; this method does not require advance knowledge of scattering behavior. Analysis and experimental results presented demonstrate the validity of the sparsity assumption. Experiments show that images generated with sparse methods are superior to those created with delay-and-sum methods; the techniques here are shown to be tolerant of propagation model mismatch. The block-sparse method described here also allows the extraction of scattering patterns, which can be used for damage characterization.