Defects in a plastic floor material produced in Tarketts factory in Ronneby are causing waste of time and material since it is noticed too late in the production line. The objective of this thesis is to investigate if the nondestructive test method NAW®, which is developed by Acoustic Agree in Ronneby, can be a solution to find the defects at an earlier stage. Nondestructive testing mainly means what the name says; quality tests of a material can be made without causing any damage. One simple example of a nondestructive testing tool is the human eye. By looking at a product defects on the surface can be found. The method used in this thesis, NAW®, is a nonlinear acoustical method. By listening to the material, information about disturbances inside the material can be gathered and interpreted to get a picture of the quality status. Although by listening it does not in this case mean by a human ear but with special equipment since the sound used is high frequent ultrasound. For several material samples, experiments were made both for the references and with introduced defects. It was hard to get definitive results since, for example, even the results for the different reference samples were differing a lot. Nevertheless there are some results pointing in the same direction which means that there is still hope for the possibility to use NAW® as a tool in the production at Tarkett. One important problem in this work is the fact that the defect material is not actually a real defect material but an imitated one with defects made by hand in the experiments. This is a possible error and has to be considered in case of further experiments. Either the imitated defects have to be “improved” or, in the ideal case, real defective material from the factory should be used to get as reliable results as possible. / Defekter i golvmaterial i tillverkningen hos Tarkett i Ronneby orsakar slöseri med tid och material eftersom de upptäcks sent i produktionslinjen. Syftet med detta examensarbete är att undersöka om den oförstörande provningsmetoden NAW®, som utvecklats av Acoustic Agree i Ronneby, kan vara en lösning för att hitta defekterna på ett tidigare stadium. Oförstörande provning är helt enkelt materialprovning där föremålet som undersöks inte förstörs. Ett enkelt exempel på verktyg för oförstörande provning är ögat. Genom att undersöka ett föremål med synen kan man enkelt kvalificera ytan. Den metod som används i detta arbete, NAW®, är en olinjär akustisk metod. Genom att lyssna på materialet kan mycket information om störningar inuti materialet samlas ihop och tolkas för att få en bild av kvaliteten. För flera materialbitar har experiment genomförts både för referensmaterial och för material med imiterade defekter. Det var svårt att se entydiga resultat då exempelvis till och med resultaten för referensmaterialet var väldigt olika sinsemellan. Dock pekar vissa av resultaten åt samma håll vilket gör att hoppet lever kvar för att NAW® kan vara ett möjligt verktyg i produktionen hos Tarkett. Ett stort problem i arbetet var frånvaron av trovärdiga defekter. Defekterna tillverkades och introducerades i materialet för hand, och viss tveksamhet finns gällande likheten mellan imiterade och riktiga defekter. Detta ses som en möjlig felkälla och måste tas i beaktan för eventuellt fortsatt arbete. Antingen måste de imiterade defekterna ”förbättras” eller, som vore idealt, så kan riktigt defekt material från tillverkningen användas för att ge så trovärdiga och pålitliga resultat som möjligt.

Les différents processus de dégradation des structures de génie civil induisent une micro, puis macro- fissuration du béton. Celle-ci génère alors une réduction des propriétés mécaniques de l'ouvrage et, à terme, sa perte d'étanchéité. Il est donc nécessaire de fournir des informations quant à la présence et à la taille de fissures pour procéder aux réparations nécessaires et conserver l'intégrité de l'ouvrage. Dans un premier temps, le contrôle du béton ainsi que la morphologie de la fissure réelle sont présentés. La notion de contacts entre ses lèvres est introduite pour définir la problématique de sa caractérisation. La bibliographie montre que les méthodes acoustiques standards ne sont pas adaptées à la caractérisation d'une fissure dans le béton. Deux pistes sont alors identifiées : les ultrasons diffus et l'acoustique non linéaire. Nous présentons dans un second temps la caractérisation de la fissure par analyse du transport de l'énergie suivant une équation de diffusion. Les paramètres associés (diffusivité et dissipation) sont déterminés expérimentalement sur des éprouvettes fissurées sur différentes profondeurs. Nous introduisons et définissons le temps d'arrivée du maximum de l'énergie (ATME) qui s'avère être le paramètre le plus sensible à la partie ouverte d'une fissure. Son évolution au regard des incertitudes de mesure ne permet toutefois pas de caractériser totalement la partie fermée. Une simulation numérique en différences finies est réalisée. Elle met en évidence le rôle des contacts au sein de la partie fermée de la fissure et confirme les observations expérimentales. / The various processes of deterioration of the building structures lead to a micro and macro-cracking of the concrete. Consequently, the mechanical properties of the structure are reduced and, eventually, the building is no longer airtight. It is therefore necessary to supply information regarding the presence and size of cracks to carry out the necessary repairs and keep the integrity of the structure. First, the control of concrete as well as the morphology of the actual crack are presented. The notion of contacts between its lips is introduced to define the problem of its characterization. The bibliography shows that the standard acoustic methods are not adapted for characterizing of a crack in concrete. Two tracks are then identified: the diffuse ultrasound and the nonlinear acoustics. Subsequently, we present the characterization of the crack by analyzing the transport of the energy with a diffusion equation. The associated parameters (diffusivity and dissipation) are experimentally determined on test tubes cracked at different depths. We introduce and define the arrival time of the maximum energy (ATME), which turns out to be the most sensitive parameter to the open part of a crack. Its evolution with regard to the measurement uncertainties does not allow a full characterization of the closed part. A digital modeling in finite differences is performed. It highlights the role of the contacts within the closed part of the crack and confirms the experimental observations. Then, we present the nonlinear acoustics and the associated methods applied to concrete.

Cette thèse porte sur la propagation d’ondes non-linéaires dans des métamatériaux acoustiques unidimensionnels. Plus précisément, nous voulons étudier les interactions entre les non-linéarités, les pertes et la dispersion. Ce travail combine des calculs analytiques, des simulations numériques et des résultats expérimentaux. En particulier, nous concentrons notre analyses sur deux phénomènes : la génération du second harmonique et la formation de solitons acoustiques. Deux types différents de métamatériaux sont étudiés : (i) un guide d’onde chargé par une distribution périodique de trous latéraux (milieu à densité effective négative) et (ii) un guide d’onde chargé périodiquement par des  plaques élastiques encastrées (milieu à masse effective négative). En s’appuyant sur une analogie électroacoustique et sur la théorie des lignes de transmission, un modèle discret de la propagation est développé pour chaque système. L’approximation des grandes longueurs d’ondes est ensuite utilisée pour obtenir une modèle continu permettant d’établir une équation non-linéaire, dispersive et dissipative pour la propagation. Cette dernière est analysée à l’aide de la méthode des perturbations conduisant à une expression analytique pour la génération du second harmonique. De plus, la méthode des échelles multiples est utilisée pour obtenir les diverses solutions de solitons d’enveloppe (bright, dark et gray) présents dans les systèmes. Les prédictions analytiques sont corroborées par des simulations numériques directes et des mesures de la génération de second harmonique sont effectuées mettant en lumière un bon accord avec le modèle théorique. / The subject of this PhD thesis is the propagation of nonlinear waves in 1D acoustic metamaterials. More specifically we aim to study the interplay between nonlinearity, loss and dispersion. Our studies combine analytical calculations, numerical simulations and experimental results. In particular we focus our analysis on two main phenomena: the second harmonic generation and the formation of solitary waves. Two different acoustic metamaterials are studied: (i) A waveguide loaded with a periodic distribution of side holes (featuring negative effective bulk modulus) and (ii) a waveguide periodically loaded with clamped elastic plates (featuring negative effective mass density). Relying on the electroacoustic analogy and the transmission line approach, we derive a discrete lattice model for each system. The corresponding long wavelength, continuum approximation of the lattice models, leads to a nonlinear, dispersive and dissipative wave equation. From the latter, by utilising a perturbation method, we obtain analytical results regarding the second harmonic generation. Furthermore with the use of a multiple scale analysis we find various envelope (bright, gap, black and gray) soliton solutions supported by the acoustic metamaterial. The analytical predictions are corroborated by direct numerical simulations. We finally perform experiments on an acoustic waveguide loaded with a periodic distribution of side holes and measure the second harmonic generation in close agreement with our theoretical predictions.

Le choix de la filière SFR (Sodium Fast Reactor : Réacteurs à neutrons rapides refroidis par du sodium liquide), par la France conduit à la réalisation d’un prototype de quatrième génération nommé ASTRID. Le développement de ce type de réacteurs présente plusieurs défis, en particulier du point de vue de l’amélioration de la démonstration de la sûreté et de la surveillance du fonctionnement. Cette dernière passe, entre autres, par la caractérisation de l’engazement du sodium liquide (présence de microbulles de gaz). La caractérisation de l’engazement est l’objet de cette étude, elle implique la détermination du taux de vide (fraction volumique de gaz) et de l’histogramme des rayons des microbulles. Le travail bibliographique réalisé a montré que les techniques acoustiques linéaires de caractérisation des nuages de bulles ne permettaient pas de répondre pleinement à cette problématique, en revanche des pistes prometteuses ont été identifiées en étudiant les techniques acoustiques non linéaires. Cette dernière voie a par conséquent été explorée. Un banc expérimental en eau permettant la génération et le contrôle optique de nuages de microbulles nous a permis de valider finement la reconstruction d’histogrammes des rayons grâce à une technique de mixage nonlinéaire d’une haute fréquence avec une basse fréquence. La potentialité du mixage de deux hautes fréquences, plus intéressante d’un point de vue industriel, a par ailleurs été démontrée. Enfin, les bases de la transposition originale d’une technique de spectroscopie de résonance non linéaire appliquée à un nuage de bulles ont été posées, grâce à la mise en place de résonateurs acoustiques. Les résultats obtenus offrent de nombreuses perspectives, tant du point de vue des applications industrielles que du point de vue plus fondamental de la compréhension du comportement acoustique non linéaire d’une bulle excitée par plusieurs fréquences et d’un nuage de bulles excité à basse fréquence. / The SFR system chosen (Sodium Fast Reactor: fast neutron reactors cooled by liquid sodium) by France led to afourth-generation prototype named ASTRID. The development of this kind of reactors presents several challenges, particularly in terms of improving the safety and monitoring operation. This involves, among other things, characterization of the bubbles presence in liquid sodium. The characterization of the bubbles presence is the subject of this thesis. It involves the determination of void fraction (gas volume fraction) and histogram of the radiiof bubbles. The bibliographic work done has shown that linear acoustic techniques for the characterization of bubble clouds are inadequate to achieve this. However promising leads have been identified by studying nonlinear acoustic techniques. This last idea has therefore been explored. An experimental water bench for the generation and optical control of microbubbles cloudallowed us to validate finely the reconstruction of histograms of radii through a technique of nonlinear mixing of a high frequency with a low frequency. The potential of the mixing of two high frequencies, more interesting for the industrial point of view has also been demonstrated. Finally, the bases of the transposition of an original technique of nonlinear resonance spectroscopy applied to a bubbles cloud were explored through the introduction of acoustic resonators. The results offer many interesting opportunities, both in terms of industrial applications and formore fundamental understanding of non-linear behavior of a bubble excited by multiple frequencies and of bubbles clouds excited at low frequency.

Les géomatériaux tels les roches et le béton ont la particularité de s’amollir sous chargement dynamique, c.-à-d. que la vitesse du son diminue avec l’amplitude de forçage. Afin de reproduire ce comportement, un modèle de milieu continu à variables internes est proposé. Il est composé d’une loi de comportement donnant l’expression de la contrainte, et d’une équation d’évolution pour la variable interne. La viscoélasticité non linéaire de type Zener est prise en compte par l’ajout de variables internes supplémentaires. Les équations du mouvement forment un système de lois de conservation non linéaire et non homogène. Le système d’équations aux dérivées partielles est résolu numériquement à l’aide de la méthode des volumes finis. Une solution analytique du problème de Riemann de l’élastodynamique non linéaire est explicitée. Elle est utilisée pour évaluer les performances des méthodes numériques. Les résultats numériques sont en accord qualitatif avec les résultats expérimentaux d’expériences de résonance (NRUS) et d’acousto-élasticité dynamique (DAET). Des méthodes similaires sont développées en 2D pour réaliser des simulations de propagation d’ondes. Dans le cadre des méthodes de continuation reposant sur la décomposition en harmoniques, une méthode numérique est développée pour le calcul de solutions périodiques. Sur la base d’une discrétisation éléments finis des équations du mouvement, cette méthode fréquentielle donne des simulations de résonance rapides, ce qui est utile pour mener des validations expérimentales. / Geomaterials such as rocks and concrete are known to soften under a dynamic loading, i.e., the speed of sound diminishes with forcing amplitudes. To reproduce this behavior, an internal-variable model of continuum is proposed. It is composed of a constitutive law for the stress and an evolution equation for the internal variable. Nonlinear viscoelasticity of Zener type is accounted for by using additional internal variables. The equations of motion write as a nonlinear and nonhomogeneous system of conservation laws. This system of partial differential equations is solved numerically using finite-volume methods. An analytical solution to the Riemann problem of nonlinear elastodynamics is provided, which is used to benchmark the performances of the numerical methods. Numerical results are in qualitative agreement with experimental results from resonance experiments (NRUS) and dynamic acousto-elastic testing (DAET). Similar methods are developed in 2D to perform wave propagation simulations. In the framework of harmonic-based continuation methods, a numerical method is developed for the computation of periodic solutions. Based on a finite element discretization of the equations of motion, this frequency-domain method provides fast resonance simulations, which is useful to carry out experimental validations.

Welded steel pipes are an essential structural part of any power plant. Longer lifetimes and higher pressures in the pipes cause an increased probability of failure due to creep damage. To maintain safe operation, nondestructive evaluation techniques to detect creep damage are needed. Nonlinear acoustic techniques employing longitudinal waves have been proven to be sensitive to creep damage. The objective of this research is to develop a robust experimental procedure to reliably measure the acoustic nonlinearity parameter using longitudinal waves, and then to validate the procedure on samples of different materials and sizes. Finally the technique is applied to characterize creep damage levels around the weld of a welded steel pipe. While the experimental technique presented can only measure the relative nonlinearity, it is accurate enough to detect changes in nonlinearity due to creep damage. Measurements show an increase in nonlinearity in the heat affected zone (HAZ). Experiments after annealing the creep damaged specimen show a decrease in nonlinearity in accordance with a decrease in dislocation density. Measurements on an undamaged welded A36 steel component suggest that the heat itself is not responsible for the increase in nonlinearity.

Nonlinear mixing of two collinear, initially monochromatic, Rayleigh waves propagating in the same direction in an isotropic, nonlinear elastic solid is investigated: analytically, by finite element method simulations and experimentally. In the analytical part, it is shown that only collinear mixing in the same direction fulfills the phase matching condition based on Jones and Kobett 1963 for the resonant generation of the second harmonics, as well as the sum and difference frequency components caused by the interaction of the two fundamental waves. Next, a coupled system of ordinary differential equations is derived based on the Lagrange equations of the second kind for the varying amplitudes of the higher harmonic and combination frequency components of the fundamentals waves. Numerical results of the evolution of the amplitudes of these frequency components over the propagation distance are provided for different ratios of the fundamental wave frequencies. It is shown that the energy transfer is larger for higher frequencies, and that the oscillation of the energy between the different frequency components depends on the amplitudes and frequencies of the fundamental waves. Furthermore, it is illustrated that the horizontal velocity component forms a shock wave while the vertical velocity component forms a pulse in the case of low attenuation. This behavior is independent of the two fundamental frequencies and amplitudes that are mixed. The analytical model is then extended by implementing diffraction effects in the parabolic approximation. To be able to quantify the acoustic nonlinearity parameter, β, general relations based on the plane wave assumption are derived. With these relations a β is expressed, that is analog to the β for longitudinal waves, in terms of the second harmonics and the sum and the difference frequencies. As a next step, frequency and amplitude ratios of the fundamental frequencies are identified, which provide a maximum amplitude of one of the second harmonics as well as the sum or difference frequency components to enhance experimental results. Subsequently, the results of the analytical model are compared to those of finite element method simulations. Two dimensional simulations for small propagation distances gave similar results for analytical and finite element simulations. Consquently. this shows the validity of the analytical model for this setup. In order to demonstrate the feasibility of the mixing technique and of the models, experiments were conducted using a wedge transducer to excite mixed Rayleigh waves and an air-coupled transducer to detect the fundamentals, second harmonics and the sum frequency. Thus, these experiments yield more physical information compared to the case of using a single fundamental wave. Further experiments were conducted that confirm the modeled dependence on the amplitudes of the generated waves. In conclusion, the results of this research show that it is possible to measure the acoustic nonlinearity parameter β to quantify material damage by mixing Rayleigh waves on up to four ways.

Thesis (M.S.)--Brigham Young University. Dept. of Physics and Astronomy, 2007. / Includes bibliographical references (p. 99-106).

High intensity focused ultrasound (HIFU) provides a wide range of noninvasive therapies ranging from drug delivery to the destruction of kidney stones. In particular, thermal ablation by HIFU presents an effective noninvasive method for the treatment of deep seated solid tumours. HIFU’s further uptake is limited by a need for improved treatment planning and monitoring. Two nonlinear acoustic phenomena that play key roles in HIFU treatment: finite amplitude effects that lead to the generation of harmonics and steepening of wavefronts, and acoustic cavitation. The former must be taken into careful consideration for treatment planning purposes, while the latter has the potential to provide fast, real-time, cost effective treatment monitoring. The first half of this thesis provides new measurements for the nonlinear acoustic properties of tissue, assesses the validity of two common modelling techniques for simulating HIFU fields. The second half develops a new method for combining passive acoustic mapping- an ultrasound monitoring technique- with MR thermometry, to assess estimates of cavitation enhanced heating derived from passive acoustic maps. In the first results chapter B/A was measured in ex-vivo bovine liver, over a heating/ cooling cycle replicating temperatures reached during HIFU ablation, adapting a finite amplitude insertion technique (FAIS), which also allowed for measurement of sound-speed and attenuation. The method measures the nonlinear progression of a plane-wave through liver and B/A was chosen so that numerical simulations matched measured waveforms. Results showed that attenuation initially decreased with heating then increased after denaturation, sound-speed initially increased with temperature and then decreased, and B/A showed an increase with temperature but no significant post-heating change. These data disagree with other reports that show a significant change and suggest that any nonlinear enhancement in the received ultrasound signal post-treatment is likely due to acoustic cavitation rather than changes in tissue nonlinearity. In the second results chapter two common methods of modelling HIFU fields were compared with hydrophone measurements of nonlinear HIFU fields at a range of frequencies and pressures. The two methods usedwere the KZK equation and the commercial package PZFlex. The KZK equation has become the standard method for modelling focused fields, while the validity of PZFlex for modelling these types of transducers is unclear. The results show that the KZK equation is able to match hydrophone measurements, but that PZFlex underestimates the magnitude of the harmonics. Higher order harmonics in PZFlex are not the correct shape, and do not peak around the focus. PZFlex performs worse at higher pressures and frequencies, and should be used with caution. In the final two chapters a system for estimating cavitation-enhanced heating from acoustic maps is developed and benchmarked against magnetic resonance thermometry methods. The first chapter shows that the ultrasound and MR monitoring systems are compatible, and registers the two imaging systems. The HIFUfocus is clearly visible in passive maps acquired in the absence of cavitation and these coincide with the centre of heating in MR temperature images. When cavitation occurs, it coincides spatially and temporally with the appearance of a clear spike in temperature, especially when the passive maps are processed using the Robust Capon Beamformer algorithm. The final chapter shows how passive maps can be converted into thermal heating inputs, and used to estimate cavitation-enhanced temperature increases. These estimates have the potential to closely match maximum temperature rise, and estimated thermal dose after the estimated temperature rise is spatially averaged. However, themethod is not always successful. This is partly due to uncertainties in MR thermometry estimates, partly due to uncertainties in the acoustic properties of tissue.

Avant leur lancement dans l'espace, les satellites font l'objet de tests afin d'éprouver leurs comportements à diverses sollicitations (thermiques, acoustiques, etc.). Pour les essais acoustiques, la société Intespace soumet les satellites à de forts niveaux sonores (de l'ordre de 145 dB SPL dans la chambre réverbérante) comparables à ceux existant lors du décollage du lanceur. Elle utilise pour cela des sources électropneumatiques couplées à des pavillons débouchant dans une chambre réverbérante. Ce système acoustique assure sa mission avec succès mais la société Intespace s'interroge sur ses possibilités d'amélioration. Deux prototypes de sources pneumatiques (à disque oscillant ou rotatif, à l'échelle 1 sur 5) sont développés et construits. Les prédictions théoriques avec vena contracta sont comparées aux données expérimentales issues d'un banc de mesure. Leurs différences concernant les niveaux sonores à la sortie de la source n'excèdent pas 1 dB pour des pressions d'alimentation de 1 à 3,5 bars absolus. Un prototype de pavillon de géométrie optimisée a été construit à l'échelle 1 sur 5. Les mesures montrent des performances intéressantes. Compte tenu des niveaux sonores générés par la source, une étude de la propagation dans le pavillon met en évidence des phénomènes non linéaires, qui s'avèrent peu influencés par la présence d'un écoulement moyen pour les vitesses envisagées dans l'étude. Finalement, des mesures sont réalisées sur l'ensemble du système à l'échelle 1 sur 5, afin d'en évaluer les performances. Les niveaux sonores mesurés sont comparés aux prédictions d'un modèle issu de la théorie de Sabine. Les différences n'excèdent pas plus ou moins 3 dB. / Before their launch in space, satellites are the object of tests in order to test their behaviors with diverse constraints (thermal, acoustic, etc.). In terms of acoustic qualification, the Intespace company submits the satellites to high sound levels (of the order of 145 dB SPL in the reverberating room) comparable to those existing during the take-off phase of the launcher. For this purpose, it uses electropneumatic sources coupled to horns opening into a reverberating room. This acoustic system ensures its mission successfully but Intespace is wondering about the possibilities of improving the system. Two prototypes of pneumatic sources (oscillating or rotating disk, 1 on 5 scale) are developed and constructed. Theoretical predictions taking into account the vena contracta are compared with the experimental data from an instrumented measuring bench. Their differences in the sound levels at the source outlet do not exceed 1 dB at supply pressures of 1 to 3.5 bars absolute. A horn prototype whose shapes have been optimized was built on a 1 on 5 scale. The measurements show interesting performances. Considering the sound levels generated by the source, a study of the propagation in the horn highlights nonlinear phenomena. The latter are not influenced by the presence of an average flow for the velocities envisaged in the study. Finally, measurements are realized on the whole system at 1 on 5 scale, in order to evaluate their performance. The measured sound levels are compared to the predictions of a model derived from the Sabine theory. The differences do not exceed 3 dB or less.