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Ultrasonic Signal Processing for Non-Destructive Testing and EvaluationHoseini, Seied Mohammad Reza Unknown Date
No description available.
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Ultrasonic guided wave propagation in pipes coated with viscoelastic materialsZlatev, Zahari January 2014 (has links)
This work studies guided wave propagation in pipes coated with thick highly viscoelastic coating materials. The main motivation for this study is the problems associated with Long Range Ultrasonic Testing (LRUT) of coated pipelines. The results reported in the literature show that the proper determination of the optimum LRUT parameters depends strongly on the bulk acoustic properties of the coating materials. The bulk acoustic properties of coating materials reported in the literature show that they could vary significantly depending on the coating material age, temperature and bonding level. The methods for acoustic characterisation of coating materials reported by other researchers, have been studied and it was found that they do not take into account the temperature changes and bonding level variation. In this work, the bulk acoustic properties of two highly viscoelastic bitumen based coating materials are investigated. The conventional methods for acoustic characterisation are studied and a new method for independent measurement of bulk shear properties of bitumen is developed. The bulk acoustic properties of bitumen based coating materials are also studied by two new characterisation methods. The first method derives the bulk coating material properties from experimental data on guided wave reflection coefficients. The second method derives the coating material bulk properties from experimentally measured guided wave attenuation data. It is demonstrated that these new methods deliver much more accurate values for the bulk acoustic properties when compared to the data measured by conventional methods. The second method is used to study the temperature effect on the bulk acoustic properties and it is demonstrated that temperature has a significant effect. The validity of the acoustic properties for the two bitumen materials is investigated through comparison between numerical predictions and experimental data measured for guided wave reflection coefficients and attenuation of the torsional T(0,1) and longitudinal L(0,2) guided wave modes. Good agreement is achieved in the frequency range between 20 kHz and 100 kHz, which is typical for LRUT of pipes.
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Evaluation non destructive par ultrasons de l'adhésion aux interfaces de joints collés / Ultrasonic non-destructive evaluation of the adhesion at the interfaces of bonded jointsSiryabe, Emmanuel 13 December 2016 (has links)
Cette thèse a pour objectif de développer des méthodes ultrasonores pour l’END de l’adhésion de joints collés. Pour aborder ce problème, les assemblages sont réalisés avec des substrats en aluminium (isotrope, élastique) et un adhésif de type époxy(isotrope, viscoélastique). Selon la géométrie des assemblages, deux méthodes sont proposées pour obtenir une information quantitative sur le niveau d’adhésion. La première est adaptée à des échantillons de type tri-couches avec recouvrement total.Elle consiste à analyser la transmission d’ondes ultrasonores planes de volume à travers l’assemblage immergé dans l'eau.Les conséquences d'un mauvais traitement de surface des substrats sur la mesure des modules de viscoélasticité du joint adhésif sont étudiées. Il a été montré que des interphases dégradées provoquent une anisotropie apparente des modules mesurés pour le joint de colle. Cette anisotropie a été quantifiée à l'aide de deux paramètres β1 et β2 dont les valeurs permettent de révéler la qualité des interphases. Ensuite, les modules élastiques (ou raideurs kL et kT) des interphases ont été estimés, en supposant les propriétés de l'adhésif connues. On montre que leurs valeurs sont maximales lorsque l'adhésion est nominale, et qu’elles diminuent franchement lorsque l'adhésion est dégradée, mais dans des proportions différentes. Des mesures de la contrainte à rupture, réalisées sur des échantillons préparés dans les mêmes conditions, corroborent la chute des modules des interphases. La seconde méthode est adaptée à des échantillons collés avec un recouvrement partiel. Elle es tbasée sur la mesure du coefficient de transmission d'ondes de Lamb se propageant d'un substrat à l'autre, à travers la zone de recouvrement. Une étude de sensibilité numérique (par éléments finis) des coefficients de transmission des modes de Lamb a montré que les propriétés mécaniques des interphases (modélisées par des raideurs surfaciques) peuvent être évaluées si les autres caractéristiques de l’assemblage sont connues. Des mesures expérimentales de ces coefficients de transmission ont ensuite été réalisées avec deux échantillons. L’un d’eux possède des interphases à adhésion nominale et l’autre des interphases dégradées. Une confrontation entre les résultats des mesures obtenus pour les différents modes et les simulations numériques permet de déterminer les valeurs des raideurs d’interfaces pour chaque échantillon. Là encore, il est observé qu’une mauvaise adhésion se traduit par des valeurs faibles des raideurs d’interfaces, qui peuvent être quantifiées, cette fois,grâce aux ondes ultrasonores guidées. / The aim of this thesis is to develop NDT ultrasonic methods for the evaluation of the adhesion at interfaces in bonded joints.To address this problem, the assemblies are made of aluminum substrates (isotropic, elastic) and epoxy adhesive (isotropic,viscoelastic). Depending on the geometry of the studied assemblies, two methods are proposed to obtain quantitativeinformation on the adhesion level. The first method is suitable for three-layered plate-like samples. It consists in analyzingthe transmission of bulk ultrasonic plane waves through the assembly immersed in water. The consequences of a inapropriatesurface treatment of the substrates on the measurement of viscoelastic moduli of the joint are studied. It has been shown thatdegraded interphases cause an apparent anisotropy of the measured elastic moduli of the joint. This anisotropy was quantifiedusing two parameters β1 and β2 whose values can reveal the quality of the interphases. Then, the elastic moduli (or stiffnesseskL and kT) of the interphases were estimated, assuming that the adhesive layer properties are known. It was shown that theirvalues are higher when the adhesion is nominal, and are strongly decreased when the adhesion is degraded. Measurements ofthe mechanical strength, on samples prepared under the same conditions, confirmed the drops in these elastic moduli. Thesecond method is more suitable for lap joint samples. It is based on the Lamb wave transmission coefficient measured fromone substrate to the other, across the overlap zone. A numerical sensitivity analysis (finite element model) of the transmissioncoefficients of Lamb waves showed that the mechanical properties of the interphases (modeled by interfacial stiffnesses) canbe evaluated if the other characteristics of the assembly are well known. Experimental measurements of the transmissioncoefficients were then performed on two samples. One of them has interphases with nominal adhesion and the other hasdegraded interphases. A comparison between the measured results obtained for the different modes and numericalsimulations was used to determine the values of the interfacial stiffnesses for each sample. Again, it was observed that pooradhesion leads to low values of the interfacial stiffnesses of the interphases, that can be quantified using guided ultrasonicwaves.
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