Ultrasonic attenuation is a useful tool in characterizing the damage state of different materials. The attenuation coefficients for the incident longitudinal and transverse waves are both derived from the scattering cross section of the material. Scattering cross section is defined as the ratio of the scattered energy to the incident energy. The incident wave field can be scattered at inclusions, voids and material defects; there is also grain boundary scattering in polycrystalline materials. For accurate material characterization, it is important to distinguish between the different types of scattering and to relate the attenuation to its appropriate source. This study first solves the single scatterer problem using either the Born approximation (for difficult scatterer shapes and for anisotropic scatterers), or the exact solution (in cases where it is necessary to provide an accurate description of the viscoelastic behavior of the surrounding effective medium). Multiple scattering effects are investigated by a differential self-consistent scheme and a self-consistent scheme. Both multiple scattering approaches are applicable for each single scatterer solution. The differential self-consistent scheme describes the scattering cross section dependent on the volume fraction of the scatterers, and is restricted to low volume fractions and materials, where the surrounding material is clearly distinguished from the inclusions. The self-consistent scheme is applicable to high volume fractions of inclusions as well as to polycrystalline materials, where the distinction between surrounding material and inclusions is not possible.

This research aims to develop a method to evaluate the deterioration of the tube material within a boiler, in order to reduce the failure of it. In this thesis, natural frequency measurement method and ultrasonic attenuation method are mainly applied, and it has reached to a conclusion that the ultrasonic attenuation method is more reliable. Traditionally, the inspectors used the ultrasonic thickness measurement machine to evaluate the thickness and track the condition of a boiler. However, besides the thickness, the inspectors could not have clear understanding of the material and situation within a boiler. To improve the inspection effectiveness, the researcher measures the natural frequencies of the tube material in the new and old boilers by using natural frequency measurement. They found that the used tube material has been altered due to the difference between the natural frequencies. The ultrasonic attenuation conditions of the tubes are also evaluated in this thesis. The echoes of the ultrasound propagating through the thickness of the tube can be analyzed by relative comparison and absolute comparison, respectively. The relative comparison compares the echoes of the multiple back reflections of the ultrasound between the tubes of old and new boilers. In addition, the absolute comparison analyzes the amplitude of the echoes of the ultrasonic multiple back reflection to calculate the ultrasonic attenuation of the tube. Besides the two major techniques, the material analysis, metallurgical analysis, internally scale analysis and mechanical property evaluation are also applied in this thesis to help developing a method to evaluate the deterioration of the tube material within a boiler. This research demonstrates that the ultrasonic attenuation measuring methods can offer reliable results to evaluate the quality of the boiler.

Com base em trabalhos tanto teóricos como experimentais, concluiu-se que o Cu+ fica em posição fora de centro em alguns halogenetos alcalinos. Nesse trabalho apresentamos resultados obtidos por técnicas de ultra-som, para verificar as propriedades do dipolo elástico devido a inos Cu+ em posição fora de centro em cristais de KCl. As alturas dos picos de relaxação observados em KCl: Cu+, apresentam proporcionalidade com a concentração de defeitos e a energia de ativação foi encontrada, sendo 0.1755 e V. A partir da teoria do dipolo elástico, e das concentrações de Cu+ achados por absorção ótica, determinou-se a simetria do defeito como sendo trigonal e o fator de forma |&#9551 - &#9552| = (7.7 &#177 0.8) 10-2. Usando valores teóricos para os deslocamentos dos 6 vizinhos (c1&#8254) próximos e a teoria do \"elipsóide de inclusão\", os momentos de dipolo elástico, &#9551, &#9552 e &#9553 puderam ser determinados e apresentam boa concordância com o experimento. Dada a forma do pico de atenuação, comprovou-se que a reorientação dos dipolos segue o modelo clássico com um tempo de relaxação simples &#964o &#8764-13 / With basis on theoretical and work investigation it is possible to conclude that Cu+ occupies an off-center position in several alkali halides. In this work, we report some results obtained for the elastic dipole which results form an off-senter substitutional Cu+ in KCl by ultrasonic techniques. The height of the relaxation peaks observed in KCl: Cu+ are proportional to defect concentrations, and the activation energy is 0.1755 and V. From the theory for elastic dipole, and the defect concentration measured throught optical absorption and the shape factor |&#9551 - &#9552| = (7.7 &#177 0.8) 10-2. By using theoretical values for the six nearest neighbors displacements and the \"Elipsoid inclusion theory\", the elastic dipole moments , &#9551, &#9552 e &#9553 are determined. Using the shape of the attenuation peak, we conclude that the dipole reorientation follows the classical model with a single relaxation time &#964o &#8764-13

Une analyse numérique basée sur la méthode des éléments finis permettant de quantifier les coefficients d'atténuation et de diffusion ultrasonores dans un polycristal en domaine temporel et fréquentiel est présentée. En particulier, une méthode originale basée sur le théorème de réciprocité pour l'évaluation numérique du coefficient de diffusion est proposée. Des formules analytiques bidimensionnelles (2D) pour les coefficients d'atténuation ultrasonore et de rétrodiffusion sont développées en utilisant l'approximation de Born pour valider les évaluations numériques. L'approche numérique proposée est appliquée au titanium, un polycristal monophasé et non texturé. Premièrement, des simulations sont effectuées dans des microstructures idéalisées composées de grains en taille unimodale. Une comparaison cohérente entre les évaluations numériques et les prédictions analytiques 2D est obtenue. Par ailleurs, les effets de l'atténuation induite par la diffusion multiple sur la mesure de rétrodiffusion, qui sont négligés par les modèles théoriques, sont quantifiés. Deuxièmement, l'approche numérique proposée est appliquée aux polycristaux composés de grains en taille bimodale. Les résultats numériques indiquent que les coefficients d'atténuation et de rétrodiffusion en domaine fréquentiel se situent au milieu des coefficients pour les microstructures unimodales et sont principalement déterminés par les fractions volumiques des grains constitutifs. Cependant, ils ne sont que légèrement affectés par la répartition des gros grains. Une étude de la fonction d'autocorrélation spatiale dans des telles microstructures bimodales est proposée afin d’obtenir une interprétation analytique des phénomènes expérimentés numériquement. / A numerical approach based on the finite element method to quantify ultrasonic attenuation and grain-noise scattering coefficients in both time and frequency domains for polycrystalline materials is presented. More particularly, an original method based on the reciprocity theorem for the numerical evaluation of the grain-noise scattering coefficient is proposed. Twodimensional (2D) analytical formulas of ultrasonic attenuation and backscattering coefficients are developed by using the Born approximation to validate numerical evaluations. Then the proposed numerical approach is applied to the single-phase and untextured polycrystalline titanium. Firstly, 2D FE simulations are performed in idealized microstructures composed of equiaxed grains with different unimodal grain sizes. Coherent comparison between numerical estimates and 2D analytical predictions is obtained. Effects of attenuation due to multiple scattering on the backscattering measurement, which are neglected in the theoretical model, are quantified. Secondly, polycrystals with bimodal grain sizes are considered. Numerical results indicate that attenuation and backscattering coefficients in bimodal microstructures are inbetween the ones of unimodal microstructures and are mainly determined by volume fractions of the constituent grains. However they are only slightly affected by the grain location distributions. The spatial autocorrelation function in bimodal microstructures is further quantified to gain an analytical interpretation of the above phenomena.

Com base em trabalhos tanto teóricos como experimentais, concluiu-se que o Cu+ fica em posição fora de centro em alguns halogenetos alcalinos. Nesse trabalho apresentamos resultados obtidos por técnicas de ultra-som, para verificar as propriedades do dipolo elástico devido a inos Cu+ em posição fora de centro em cristais de KCl. As alturas dos picos de relaxação observados em KCl: Cu+, apresentam proporcionalidade com a concentração de defeitos e a energia de ativação foi encontrada, sendo 0.1755 e V. A partir da teoria do dipolo elástico, e das concentrações de Cu+ achados por absorção ótica, determinou-se a simetria do defeito como sendo trigonal e o fator de forma |&#9551 - &#9552| = (7.7 &#177 0.8) 10-2. Usando valores teóricos para os deslocamentos dos 6 vizinhos (c1&#8254) próximos e a teoria do \"elipsóide de inclusão\", os momentos de dipolo elástico, &#9551, &#9552 e &#9553 puderam ser determinados e apresentam boa concordância com o experimento. Dada a forma do pico de atenuação, comprovou-se que a reorientação dos dipolos segue o modelo clássico com um tempo de relaxação simples &#964o &#8764-13 / With basis on theoretical and work investigation it is possible to conclude that Cu+ occupies an off-center position in several alkali halides. In this work, we report some results obtained for the elastic dipole which results form an off-senter substitutional Cu+ in KCl by ultrasonic techniques. The height of the relaxation peaks observed in KCl: Cu+ are proportional to defect concentrations, and the activation energy is 0.1755 and V. From the theory for elastic dipole, and the defect concentration measured throught optical absorption and the shape factor |&#9551 - &#9552| = (7.7 &#177 0.8) 10-2. By using theoretical values for the six nearest neighbors displacements and the \"Elipsoid inclusion theory\", the elastic dipole moments , &#9551, &#9552 e &#9553 are determined. Using the shape of the attenuation peak, we conclude that the dipole reorientation follows the classical model with a single relaxation time &#964o &#8764-13

<p> Working within the framework of the linearized Boltzmann equation for the conduction electrons the existing theoretical treatments of ultrasonic attenuation in metals are extended to include realistic descriptions of the electronic structure and electron-lattice interaction. A variational solution of the Boltzmann equation which allows the inclusion of phonon drag effects is derived. An anisotropic scattering time solution is also presented. Both of these solutions are applied to calculation of the attenuation coefficient in pure metals and dilute alloys. </p> <p> The theory of the effects of electron-electron collisions on the ultrasonic attenuation in metals is also examined. </p> / Thesis / Doctor of Philosophy (PhD)

La dystrophie musculaire de Duchenne (DMD) entraine une perte progressive de la force musculaire. L'objectif de ce présent travail est d'étudier la sensibilité d'une méthode acoustique échographique (50 MHz) et d'une méthode résonante (25 kHz) aux changements de propriétés des tissus musculaires de souris mdx modèles. Les paramètres mesurés sont l'atténuation ultrasonore pour la méthode échographique et le module complexe de cisaillement pour la méthode résonante. Dans ce manuscrit nous exposons le développement de ces deux méthodes adaptées à l'étude de deux tissus musculaires de souris : le diaphragme et la peau. La méthode échographique a permis de quantifier les changements de propriétés biologiques du diaphragme en fonction du pourcentage de zone non musculaire sur des souris âgées de 3 mois à 24 mois. La méthode résonante, génère un champ de pression dans le tissu induisant un cisaillement dans le tissu. Cette méthode a permis d'estimer des différences de propriétés mécaniques sur le diaphragme et sur la peau entre les tissus sains et tissu pathologiques. Les résultats obtenus autorisent à penser que le développement de la méthode résonante pour des applications in vivo chez l'Homme atteint de DMD est possible. / The muscular dystrophy of Duchenne (DMD) lead a progressive loss of the muscular strength. The objective of this present work is to study the sensibility of an ultrasound acoustic method (50 MHz) and a résonant method (25 kHz) to the changes of properties of muscle tissues of mdx mice models. The mesured parameters are the ultrasound attenuation for the echographic method and the complexe shear modulus for the résonant method.In this manuscript we explain the development of these two methods adapted to the study of two muscular tissues of mouse: the diaphragm and the skin. The ultrasound method allowed to quantify the changes of biological properties of the diaphragm according to the percentage of non muscular area on 3-month-old mice in 24 months. The résonant acoustic method, generates a field pressure in the tissue leading a shearing tissue. This method allowed to estimate différences of mechanical properties on the diaphragm and on the skin between healthy tissues and pathological tissues. We think the obtained results authorize the development of the resonant method for in vivo applications to human touched by DMD.