Fiber Reinforced Polymer (FRP) sheets can provide incredible structural strength while weighing only a fraction as much as steel. When applied to piles the FRP provides strengthening through both concrete confinement and tensile reinforcement. Mainly used in structural repair, its application is relatively simple in theory. However, many factors(some avoidable, some not) can interfere with the bond between FRP and concrete. When this bond is interrupted the strength of the repair becomes compromised.This thesis examines 2 new methods of improving FRP bond to concrete piles during the time the resin is curing. These methods are compared using 3 types of testing, both nondestructive and otherwise: acoustic analysis, infrared thermography, and pull-off testing. Therefore not only FRP bond improvement techniques are compared but also the techniques for bond evaluation. Findings have shown a definite correlation between non destructive testing and destructive pull-off testing, as well as bond improvement both above and below the waterline when a pressure bag system is used.

The study of mechanical energy and electrical energy dissipation in cementitious materials can lead to development of high damping concrete for structural applications, and new non-destructive testing techniques for use on existing concrete structures. This research aims to improve mechanical damping properties of cementitious materials and determine durability parameters from complex permittivity measurements. Damping was improved by utilizing poromechanical effects, and by adding viscoelastic and nanometric inclusions. Poromechanics was utilized to model and predict damping on specimens designed to maximize poromechanical effects, and composite theory was used to predict composite bounds for the loss tangent, i.e. modeling the effects on damping due to the addition of viscoelastic inclusions. Experimental results indicated that substantial damping improvement can be realized by both poromechanical effects and adding novel inclusions into cement pastes. The models were able to predict experimentally measured damping as a function of loading frequency. The electrical energy dissipation in cementitious materials was studied by dielectric spectroscopy as a function of moisture state and pore structure/permeability. The results were compared to predictions from multiphase composite modeling, where the properties of the confined water was inversely determined and used to predict moisture content. It was found that moisture state of cementitious materials has a linear relation to the complex permittivity over a wide variety of frequency ranges. Composite model prediction indicated that permeability of saturated cementitious materials studied in this research is likely dependent on the amount of free water in the pores. Permeability can be inferred from the pore structure of the cement paste via complex permittivity measurements by conditioning cement paste at different levels of relative humidity.

Le développement des produits à base de polysaccharides issus de microalgues implique une étude poussée des voies biotechnologiques de culture. Afin d'optimiser ces nouveaux produits dès la formation des microalgues, un nouveau système de contrôle non-destructif en ligne et sans contact a été développé dans le cadre de cette thèse. Il s'appuie sur la mesure par induction des propriétés diélectriques (conductivité et permittivité) dans le domaine des radiofréquences (1-400MHz). Ce document montre, qu'à l'échelle d'investigation correspondante, il est possible de suivre aussi bien l'évolution du milieu de culture que la formation d'exopolymères via la mesure de la permittivité complexe de ces matériaux. La preuve de concept a nécessité la mise au point d'un circuit résonant bas coût particulièrement sensible, utilisé en émission-réception, et la résolution théorique et expérimentale d'un problème inverse adapté aux champs proches. Ce système implanté dans un photobioréacteur prototype a permis d'extraire l'évolution de grandeurs caractéristiques propres au suivi de culture de microalgues. Cette thèse s'inscrit dans un projet collaboratif plus large de valorisation d'actifs issus de microalgues avec les sociétés Phycosource, Pronovalg, Bio-EC, et LVMH dans le cadre d'un FUI. / The development of products based on polysaccharides from microalgae involves extensive study of biotechnological ways of cultivation. In order to optimize these new products, from the formation of microalgae, a new non-destructive testing system online and without contact has been developed as part of this thesis. It is based on the measurement by induction of dielectric properties (permittivity and conductivity) in the field of radio frequency (1-400MHz). This document shows that inside the corresponding scale of investigation, it is possible to follow both the evolution of the culture medium and the exopolymer formation, via the measurement of complex permittivity of these materials. The proof of concept, required the development of a resonant low cost system particularly sensitive, used as a transceiver, and theoretical and experimental solution of an inverse problem in near fields. This system that operates in a photobioreactor prototype, was used to extract the evolution of characteristics variables of microalgae cultivation. This thesis is part of a larger collaborative project valuation of assets derived from microalgae with Phycosource companies Pronovalg, Bio-EC, and LVMH as part of a FUI.

The aim of this work has been to apply the techniques of non-destructive testing and evaluation to the graphite fuel channel bricks which form the core of an Advanced Gas-Cooled reactor. Two modes of graphite degradation have been studied: subsurface cracks originating from the keyway corners of the bricks and the reduction in material density caused by radiolytic oxidation. This work has focused on electromagnetic inspection techniques. Brick cracking has been studied using a multi-frequency eddy current technique with the aim of determining quantitative information. In order to accurately control the crack dimensions this work has used radially machined slots as an analogue. Two sensor geometries were studied and it was determined that slots of at least 10 mm through-wall extent could be located. A novel, empirical method of determining the slot size is presented using a brick machined with a series of reference slots. Machined slots originating from a keyway could be sized to within 2 mm using this method. A parametric 3D finite element study was also carried out on this problem. These simulations could distinguish the location of the slots and had some sensitivity to their size, however, the model was found to be overly sensitive to the specific mesh used. Two new contributions to the inverse problem are presented. The first is a minor extension to the usual adjoint problem in which one system now contains a gradiometer. The second is a proposed solution to the ambiguous nature of the inner product required by the sensitivity formulation. This solution has been validated with finite element modelling. Density reduction has been studied via its relationship with electrical conductivity using a technique based on impedance spectroscopy. An inverse eddy current problem has been solved using the regularised Gauss-Newton method to determine the conductivity of the brick over its cross section. The associated forward problem has been solved using the finite element method on a simplified geometry. Tikhonov regularisation has been employed to overcome the ill-posed nature of the inverse problem. This method has been applied to a range of sample and sensor geometries and found to produce excellent results from laboratory data provided the finite element model is well calibrated. Bore or surface conductivity values can be reproduced to better than 1% with the accuracy reducing with distance from the sensor. The sensitivity of the algorithm to the regularisation parameter has been studied using the L-curve method and the effect of two regularisation operators has also been examined. A new method of choosing the regularisation parameter a priori is proposed and tested. Data taken during reactor outages produces physically realistic profiles although the results appear off-set from electrical resistivity values measured using the four-point method. The focus of future work should be to remove this effect which will likely require improvements to the forward model.

AbstractThis thesis describes research on the use of eddy current techniques for nondestructivetesting of carbon fibre reinforced plastic (CFRP). The research hasinvolved bulk conductivity testing, fibre direction characterization and 3D FEMmodeling of the CFPR and eddy current probes geometry. In the conductivity testing,how the sample thickness, fibre volume content and fibre conductivity affects thesignal from the eddy current has been evaluated. Eddy current testing shows gooddirectionality as CFRP is an anisotropic material, thus is very suitable to characterizethe fibre orientation. Direction sensitive probes have been developed and tested toreveal information about the fibre direction and layer. Computer FEM software hasbeen used to analyze the magnetic field inside the sample and probes. Specific probegeometries have been designed depending on the electrical properties of thecomposites and testing requirement. The experiment, simulation and analysis resultsshow very good agreement. However, when the measuring frequency increases, noisesand parasitic capacitance inevitably become significant and have a negative influenceon the results. Improvements and further research are proposed which are believed tomake eddy-current techniques a more feasible and efficient measurement method, willcontribute to the development and maintenance of light weight CFRP composites.

Le contrôle non destructif (CND) de pièces pour des applications dans l'industrie a mené au besoin de modèles rapides et précises. Tels modèles servent au développement des méthodes d'inspection, à l'optimisation des capteurs utilisés aux essais, à l'évaluation des courbes de Probabilité de Detection (POD) ainsi qu'à la caractérisation de défauts. Cette thèse se focalise au CND par Courants de Foucault (CF) de pièces cylindriques avec des discontinuités selon z et contenant un défaut fin. Un modèle pour l'inspection de telles pièces a été développé afin de traiter des applications comme l'inspection des pièces alésées trouvées en aéronautique et des tubes des générateurs de vapeur utilisés dans l'industrie nucléaire. Ce modèle est basé sur une formulation d'équation intégrale. Plus précisément, la variation de l'impédance du capteur, dit signal CF, est calculée à partir d'une équation intégrale sur la surface du défaut. La formulation suivie est basée sur la méthode d'intégration surfacique (SIM). Cette formulation nécessite, d'un côté, le calcul du champ électrique en absence du défaut et, de l'autre côté, l'expression d'une fonction de Green qui correspond à la géométrie de la pièce sans défaut. Les deux problèmes électromagnétiques sont résolus en utilisant la méthode Truncation Region Eigenfunction Expansion (TREE). La méthode TREE est un outil performant pour la résolution des problèmes électromagnétiques qui prend en compte la décroissance rapide de l'intensité du champ afin de tronquer le domaine d'intérêt à une distance, où le champ est négligeable.Le modèle est validé en comparant le signal CF calculé avec des résultats obtenues par une approche combinant la méthode d'intégration volumique (VIM) et SIM, dite l'approche VIM-SIM (implémentée dans la plateforme CIVA) ainsi qu'avec le modèle d'éléments finis (FEM). Nous avons traité trois configurations différentes : un demi-espace conducteur alésé avec un défaut fin, une plaque conductrice avec un alésage et un défaut, et un tube semi-infini avec un défaut fin à la proximité de son bord. La comparaison des résultats montre un très bon accord entre les trois modèles. Le temps de calcul avec le modèle SIM est considérablement inférieur aux temps de calcul des autres modèles. En outre, le modèle SIM donne la possibilité d'effectuer le balayage du capteur dans le tube ou l'alésage dans le cas des pièces alésées. / Nondestructive Testing (NDT) of parts for industrial applications such as in nuclear and aeronautical industry has led to the need for fast and precise models. Such models are useful for the development of the inspection methods, the optimisation of probes, the evaluation of the Probability of Detection (POD) curves or for the flaw characterisation.This PhD thesis focuses on the eddy-current NDT of layered cylindrical pieces with discontinuities in the z direction and containing a narrow crack. A model for the inspection of such pieces is developed in order to be applied on the inspection of fastener holes met in aeronautics and of steam generator tubes in nuclear sector.The model is based on an integral equation formalism. More precisely, for the calculation of the impedance change one needs to solve an integral equation over the surface of the narrow crack, which is represented by a surface electric dipole distribution. This is the method known as surface integration method (SIM). This formulation requires, on the one hand, the calculation of the electric field in the absence of the flaw, the so-called primary field, and, on the other hand, the Green's function expression corresponding to the geometry of the flawless piece. Both electromagnetic problems are solved by means of the Truncation Region Eigenfunction Expansion (TREE) method. The TREE method is a powerful tool for the solution of electromagnetic problems which uses the rapid decrease of the field in order to truncate the region of interest at a distance where the field is negligible.The model is validated by comparing the results of the coil impedance variation with those obtained by an approach that combines the volume integral method (VIM) with SIM, known as VIM-SIM method, implemented in the commercial software CIVA and the finite element method (FEM) implementation in COMSOL software. Three different configurations have treated. The more general geometry of a conducting half-space with a borehole, a conducting plate with a borehole and a crack and a conducting semi-infinite tube with a crack near the edge. The results of the three models show good agreement between them. The computational time of the SIM model is significantly lower compared to previous models. Furthermore, another advantage of the SIM model is that it provides the possibility of a scan inside the borehole.

Composite materials have increasingly been used as an alternative to metals and other isotropic materials for primary structural components in aerospace industries. Unlike traditional isotropic materials, composite materials are known to have complex internal microstructures. Therefore, it is essential to develop methods for the inspection, evaluation, and monitoring of composite materials. Ultrasonic-guided waves and, more precisely, Lamb waves have proven to be an efficient and accurate technique for the non-destructive testing. Since guided waves are dispersive and multimodal, it is important to develop a practical method to manipulate Lamb waves to achieve better structural health monitoring and non-destructive inspection results. There are minimal studies involving manipulating guided waves for the inspection of composite materials. Moreover, the currently proposed methods to manipulate Lamb waves are complex and costly. The objective of this dissertation research is to offer practical and straightforward methods with a simple design to control Lamb waves using additively manufactured lenses used as superstrates on composite plates. This dissertation is organized in three major parts. Part I focuses on the Lamb wave propagation in composite plates with different lay-up and plate orientations. Finite element simulations were performed to investigate the behavior of Lamb wave propagation in different plates. A semi-finite element approach was used to derive the dispersive curves in each plate. In Part II, a lap-joint study was conducted to investigate the interaction of Lamb waves in the lap joint regions. Two different lap joints were considered, composite-aluminum and composite-plastic. In each lap joint the thickness of the top surface (aluminum or plastic) is continuously increased. In Part III, additively manufactured lenses are designed to modulate the wavefront of Lamb waves in thick composite plates. The first design is a prism-shaped lens proposed to steer Lamb waves to a targeted direction. Multiple prism designs are considered to offer a flexible steering direction by either changing the prism thickness or the wedge angle. The second design is a plano-concave shaped lens designed to focus the Lamb wave at a targeted focal point. This dissertation research will provide a clear understanding of Lamb wave propagation in anisotropic material, anisotropic-isotropic lap joints, and wavefront modulation on anisotropic material using additively manufactured lenses. This approach contributes to the development of better quality SHM for online monitoring systems.

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