The electric Joule heating of solid materials through direct current excitation can be used to generate a temperature profile throughout a powdermetallic (P/M) compact. When recording the surface temperature distribution with an infrared (IR) camera important information regarding the integrity of the sample can be gained. This research will concentrate on the formulation of a mathematical model capable of predicting the temperature distribution and heat flow behavior in P/M parts and its relations to the supplied current, injection method, geometric shape as well as the thermo-physical properties. This theoretical model will subsequently be employed as a tool to aid in the actual measurements of infrared signatures over the sample surface and their correlation with the detection of surface and subsurface flaws. In this work we will develop the theoretical background of IR testing of green-state and sintered P/M compacts in terms of stating the governing equations and boundary conditions, followed by devising analytical and numerical solutions. Our main emphasis is placed on modeling various flaw sizes and orientations in an effort to determine flaw resolution limits as a function of minimally detectable temperature distributions. Preliminary measurements with controlled and industrial samples have shown that this IR testing methodology can successfully be employed to test both green-state and sintered P/M compacts.

Este trabalho apresenta duas técnicas de ensaios não-destrutivos por ultra-som realizados em um tanque com água para determinar as constantes elásticas de materiais compostos de fibra de vidro/epóxi. A primeira técnica é a transmissão direta utilizando um par de transdutores. A segunda é a técnica de pulso-eco, utilizando um único transdutor. A água do tanque atua como um acoplante para transferir a energia mecânica do transdutor para a amostra. Como o transdutor não fica em contato direto com a amostra, pode-se garantir um acoplamento constante. O sistema de medição dota de um dispositivo que permite medir a velocidade da onda elástica sob diferentes ângulos de incidência, através da rotação manual da amostra. Devido ao fenômeno de conversão de modos com incidência oblíqua na interface amostra-água, ensaios por ultra-som em tanques com água fornecem as informações necessárias para o cálculo das constantes elásticas em amostras de materiais anisotrópicos, numa dada direção, a partir das medições das velocidades longitudinal e de cisalhamento. Numa dada direção de propagação em um meio anisotrópico, existem três ondas elásticas distintas: uma longitudinal e duas de cisalhamento. Se as constantes elásticas do material são conhecidas, é possível obter as três velocidades em uma dada direção bastando resolver a equação de Christoffel. Invertendo a equação de Christoffel, obtém-se as constantes elásticas a partir das velocidades medidas em uma dada direção. Os experimentos são realizados com amostras de fibra de vidro/epóxi unidirecionais e bidirecionais, utilizando transdutores com freqüências de 0,5 MHz, 1 MHz e 2,25 MHz. Os resultados experimentais obtidos utilizando ambas as técnicas são comparados com um modelo denominado “Regra das Misturas" e com resultados da literatura. / In this work, two ultrasonic non destructive techniques were implemented in a water tank and used to determine the elastic constants of glass-epoxy composites samples. The first is the through-transmission technique implemented with a pair of ultrasonic transducers. The second is the back-reflection technique that uses a single transducer in pulse-eco mode. The water acts as a couplant and transfers the mechanical energy from the transducer to the sample. As the transducer is not in direct contact with the sample, we can guarantee a good coupling with the immersion technique. With the system device, it is possible to measure the velocities of the elastic waves in different angles by manually rotating the sample. Due to wave mode conversion phenomenon at the sample-water interface with oblique incidence, ultrasonic immersion testing provides information to calculate the elastic constants of the specimen by measuring longitudinal and shear wave speeds. There are three different modes of waves, one longitudinal and two shear waves, for any given direction of propagation in an anisotropic medium. If the elastic constants of a medium are known, it is possible to obtain the three wave speeds in particular propagations directions by solving the Christoffel equation. Inverting the Christoffel equation, it is possible to obtain the elastic constants from the measured wave speed in several specific directions of the anisotropic material. Measurements were carried out on unidirectional and bidirectional glass-epoxy composite samples, using transducers with central frequency of 0.5 MHz, 1 MHz, and 2.25 MHz. The experimental results obtained with both techniques are compared with a model denominated “Rule of Mixture" estimation and with the literature.

Air borne or liquid-laden solid particle transport is a common phenomenon in various industrial applications. Solid particles, transported at severe operating conditions such as high flow velocity, can cause concerns for structural integrity through wear originated from particle impacts with structure. To apply Acoustic Emission (AE) in particle impact monitoring, previous researchers focused primarily on dry particle impacts on dry target plate and/or wet particle impacts on wet or dry target plate. For dry particle impacts on dry target plate, AE events energy, calculated from the recorded free falling or air borne particle impact AE signals, were correlated with particle size, concentration, height, target material and thickness. For a given system, once calibrated for a specific particle type and operating condition, this technique might be sufficient to serve the purpose. However, if more than one particle type present in the system, particularly with similar size, density and impact velocity, calculated AE event energy is not unique for a specific particle type. For wet particle impacts on dry or wet target plate (either submerged or in a flow loop), AE event energy was related to the particle size, concentration, target material, impact velocity and angle between the nozzle and the target plate. In these studies, the experimental arrangements and the operating conditions considered either did not allow any bubble formation in the system or even if there is any at least an order of magnitude lower in amplitude than the sand particle impact and so easily identifiable. In reality, bubble formation can be comparable with particle impacts in terms of AE amplitude in process industries, for example, sand production during oil and gas transportation from reservoir. Current practice is to calibrate an installed AE monitoring system against a range of sand free flow conditions. In real time monitoring, for a specific calibrated flow, the flow generated AE amplitude/energy is deducted from the recorded AE amplitude/energy and the difference is attributed to the sand particle impacts. However, if the flow condition changes, which often does in the process industry, the calibration is not valid anymore and AE events from bubble can be misinterpreted as sand particle impacts and vice versa. In this research, sand particles and glass beads with similar size, density and impact velocity have been studied dropping from 200 mm on a small cylindrical stepped mild steel coupon as a target plate. For signal recording purposes, two identical broadband AE sensors are installed, one at the centre and one 30 mm off centred, on the opposite of the impacting surface. Signal analysis have been carried out by evaluating 7 standard AE parameters (amplitude, energy, rise time, duration, power spectral density(PSD), peak frequency at PSD and spectral centroid) in the time and frequency domain and time-frequency domain analysis have been performed applying Gabor Wavelet Transform. The signal interpretation becomes difficult due to reflections, dispersions and mode conversions caused by close proximity of the boundaries. So, a new signal analysis parameter - frequency band energy ratio - has been proposed. This technique is able to distinguish between population of two very similar groups (in terms of size and mass and energy) of sand particles and glass beads, impacting on mild steel based on the coefficient of variation (Cv) of the frequency band AE energy ratios. To facilitate individual particle impact identification, further analysis has been performed using Support Vector Machine (SVM) based classification algorithm using 7 standard AE parameters, evaluated in both the time and frequency domain. Available data set has been segmented into two parts of training set (80%) and test set (20%). The developed model has been applied on the test data for model performance evaluation purpose. The overall success rate of individually identifying each category (PLB, Glass bead and Sand particle impacts) at S1 has been found as 86% and at S2 as 92%. To study wet particle impacts on wet target surface, in presence of bubbles, the target plate has been sealed to a cylindrical perspex tube. Single and multiple sand particles have been introduced in the system using a constant speed blower to impact the target surface under water loading. Two sensor locations, used in the previous sets of experiments, have been monitored. From frequency domain analysis it has been observed that characteristic frequency for particle impacts are centred at 300-350 kHz and for bubble formations are centred at 135 – 150 kHz. Based upon this, two frequency bands 100 – 200 kHz (E1) and 300 – 400 kHz (E3) and the frequency band energy ratio (E3E1,) have been identified as optimal for identification particle impacts for the given system. E3E1, > 1 has been associated with particle impacts and E3E1, < 1 has been associated with bubble formations. Applying these frequency band energy ratios and setting an amplitude threshold, an automatic event identification technique has been developed for identification of sand particle impacts in presence of bubbles. The method developed can be used to optimize the identification of sand particle impacts. The optimal setting of an amplitude threshold is sensitive to number of particles and noise levels. A high threshold of say 10% will clearly identify sand particle impacts but for multiparticle tests is likely to not detect about 20% of lower (impact) energy particles. A threshold lower than 3% is likely to result in detection of AE events with poor frequency content and wrong classification of the weakest events. Optimal setting of the parameters used in the framework such as thresholds, frequency bands and ratios of AE energy is likely to make identification of sand particle impacts in the laboratory environment within 10% possible. For this technique, once the optimal frequency bands and ratios have been identified, then an added advantage is that calibration of the signal levels is not required.

Dans le secteur du génie civil, le renforcement structural et la réparation des ouvrages en béton par collage de polymère renforcé de fibres de carbone (PRFC) sont des techniques désormais répandues. Les performances et la durabilité du système de renforcement sont intrinsèquement liées à la qualité du collage entre le matériau composite et le béton. Or, en pratique, les conditions environnementales et les contraintes liées au chantier ne permettent pas d’assurer l’intégrité de ce collage, dont les propriétés évoluent par ailleurs dans le temps en raison des phénomènes de vieillissement. La vérification in-situ par une méthode non-destructive de l’état du collage est donc une étape importante pour garantir les propriétés d'usage tout au long de la vie du renforcement.Une méthode d’évaluation non-destructive est développée dans le cadre de cette étude. Elle s’inspire de l’essai standard d’arrachement en traction directe bien connu sur le terrain. La méthode repose sur un essai mécanique qui caractérise le comportement en charge – déplacement de l’assemblage, et permet d’exprimer un critère d’évaluation appelé raideur d’assemblage qui dépend notamment du module d’Young de l’adhésif utilisé.La faisabilité en laboratoire de cette méthode est vérifiée sur un dispositif d’essai entièrement conçu pour les fins de l’étude. Un travail d’analyse et de dimensionnement basé sur une modélisation numérique par éléments finis permet de sélectionner des capteurs et une chaîne d’acquisition adaptés. Une formulation analytique partielle de la raideur d’assemblage est énoncée.Une campagne expérimentale sur des éprouvettes de béton renforcées par lamelles de PRFC avec trois adhésifs époxy différents est ensuite mise en œuvre. Les résultats sont interprétés en suivant une approche statistique qui prend en compte les variations de tous les paramètres d’influence. Les performances de détection de l’essai dans le cadre de notre application en laboratoire peuvent ainsi être exprimées.Des éléments contribuant à l’élaboration d’une méthodologie d’essai applicable in-situ sont enfin apportés, et les performances de l’essai sont rediscutées en vue de cette transposition sur le terrain / Over the last 30 years, repairing and strengthening techniques of concrete structures using externally bonded carbon fiber reinforced polymer (CFRP) composites have gained much popularity and are now widespread. The effectiveness of the strengthening systems highly depends on the level of adhesion between the composite material and the concrete surface. Therefore, on-site evaluation of the bond quality is crucial to assess the performance and predict the durability of the reinforcement system.It is proposed to determine the bond properties of the adhesive layer within the reinforcement system by using a nondestructive test (NDT) method derived from the standard and well-known pull-off test. This method consists in analyzing the linear load vs displacement behavior of the adhesive joint, in order to determine an assembly stiffness which can be related to the Young’s modulus of the adhesive layer.In order to investigate the feasibility of the test method, a laboratory implementation is carried out on a mechanical device fully designed for the purpose of the present study. Suitable displacement sensors and an appropriate measurement chain are chosen based on a finite element modeling and a mechanical analysis of the test. A partial analytical form of the assembly stiffness is also expressed.The test method is then applied to concrete slabs reinforced with CFRP plates using three different epoxy adhesives. A statistical assessment of all identified parameters of influence sheds light on the results. In the end, the performances of the test performed in laboratory conditions are discussed.Finally, foundations for a relevant test methodology on real field conditions are laid, and the above-mentioned performances are reviewed

No presente trabalho se estuda a correlação de diferentes parâmetros de sinais de Ruído Magnético de Barkhausen (RMB) e de fluxo magnético com o comportamento elastoplástico em chapas de aço carbono, visando à aplicação dos resultados como técnica de Ensaio Não-Destrutivo. Comprovou-se que o comportamento de parâmetros como a energia (RMBenegia), o valor quadrático médio(RMBrms) e a envolvente dos sinais de RMB com os diferentes estados elastoplásticos do material resultou fortemente dependente da anisotropia de laminação, quantidade de Carbono e fases, gerados no processo de produção das chapas. Como novidade introduziu-se o parâmetro chamado de Área em baixo da curva da distribuição de pulsos do sinal de Barkhausen. A evolução deste parâmetro com a deformação identificou com boa aproximação a região de transição elasto-plástica do material. Harmônicos não lineares (HNL) do fluxo magnético apresentaram uma melhor correlação com a anisotropia do que com os estados elasto-plásticos do material, mas com alta dependência ao acoplamento sonda-amostra. Enquanto que o RMB apresentou elevados níveis de reprodutibilidade. Propriedades mecânicas e comportamentos característicos de ensaios de tração em regime discreto e contínuo foram reproduzidos e identificados com um alto grau de aproximação pelo RMB e os HNL. Outros métodos magnéticos e não magnéticos usados neste trabalho não apresentaram níveis altos de sensibilidade às mudanças microestruturais devido às deformações elasto-plásticas no material, no entanto o RMB e os HNL identificaram tais mudanças microestruturais dando margem a novas soluções nos campos de ensaio e inspeção não-destrutivos. / The present work studies the relationship between different parameters of the Magnetic Barkhausen Noise (MBN) and non-linear harmonics of the magnetic flux signals (NLH) with the elastic-plastic behavior in carbon steel plates, in an effort to use the results as a non-destructive testing technique. MBN parameters such as the envelope of the MBN signal, and the scalar parameters MBNenergy, MBNrms were found to be highly dependent on the lamination processes, carbon content and phases originated during the fabrication of the samples. A new parameter entitled area under the MBN jump distribution was defined. The behavior of this parameter as strain evolved provided a good approximation of the elastic-plastic transition region. Non-linear harmonics offered a good correlation with both anisotropy and the elasticplastic states of the material, nevertheless depending heavily on the sensor coupling with the sample surface, while at the same time MBN provided good reproducibility. The characteristic behavior as well as the mechanical properties obtained from discrete and continuous tensile strength tests were reproduced by both MBN and HNL. Other magnetic and non-magnetic methods did not show the same level of sensibility to microstructure changes due to elastic-plastic strains when compared to the results obtained using MBN and HNL, giving room to new solutions in the nondestructive inspection and testing fields.

Ce travail de thèse est une contribution au développement des méthodes d’acoustique non linéaire pour le contrôle non destructif et l’imagerie de défauts de type contact dans les solides.Dans ce travail, des modifications sont proposées pour deux méthodes récentes de contrôle non destructif par acoustique non linéaire : l’interférométrie de coda couplée au retournement temporel, et l’imagerie non linéaire par ultrasons aériens. Le principal avantage de la première méthode est sa sensibilité extrême liée à l’accumulation des effets induits par des changements, même faibles, des propriétés de l’échantillon durant la formation de la coda. La deuxième méthode apporte une approche complémentaire en permettant de réaliser un contrôle sans contact. Les techniques développées ont été testées sur des échantillons présentant des défauts artificiels à des emplacements connus. Les performances de chacune des méthodes ont été étudiées.La deuxième partie de ce travail porte sur la description théorique des non-linéarités acoustiques de contact et leur utilisation pour le développement d’une boite à outils numériques permettant la simulation d’ondes acoustiques dans des structures complexes contenant des contacts internes. Un model physique décrivant le décalage tangentiel de deux corps en contact en présence de friction est proposé. Il aboutit à une solution analytique pour la relation présentant une hystérésis entre les déplacements de contact normal et tangentiel et les chargements. Ce modèle est utilisé comme condition aux frontières pour les surfaces de contact internes (défauts) dans un modèle de propagation d’ondes acoustiques utilisant un logiciel d’éléments finis commercial / This PhD thesis work contributes to the development of nonlinear elastic methods for non-destructive testing and imaging of contact-type defects in solids.In this work, two modifications of recent nonlinear nondestructive testing methods are suggested: the coda wave interferometry combined with the nonlinear time reversal principle and air-coupled nonlinear ultrasonic imaging. The principal advantage of former technique is in its extremely high sensitivity owing to the fact that weak changes in sample's parameters are accumulated and finally greatly amplified during the formation of the coda wave. The other technique has a complimentary strength and offers a possibility of a remote detection. The developed techniques are tested on samples with artificially fabricated defects at known locations. The performance of each method is accessed and the potential for obtaining robust nonlinear images is demonstrated.The second part of the work is concerned with a theoretical description of contact acoustical nonlinearity and its use for creating of a numerical toolbox capable of simulating wave propagation in complex structures containing internal contacts. A physical model describing the tangential shift of two contacting bodies in the presence of friction has been proposed. Its result is an analytical computer-assisted solution for hysteretic relationships between normal and tangential contact displacements and loads. The contact model and derived load-displacement relationships are used as boundary conditions posed at the internal boundaries (contact surfaces) in a finite element wave propagation model programmed via commercial software

<p>This thesis is concerned with detection of transient signal families and detectors in nonlinear static sensor systems. The detection problems are treated within the framework of likelihood ratio based binary hypothesis testing.</p><p>An analytical solution to the noncoherent detection problem is derived, which in contrast to the classical noncoherent detector, is optimal for wideband signals. An optimal detector for multiple transient signals with unknown arrival times is also derived and shown to yield higher detection performance compared to the classical approach based on the generalized likelihood ratio test.</p><p>An application that is treated in some detail is that of ultrasonic nondestructive testing, particularly pulse-echo detection of defects in elastic solids. The defect detection problem is cast as a composite hypothesis test and a methodology, based on physical models, for designing statistically optimal detectors for cracks in elastic solids is presented. Detectors for defects with low computational complexity are also formulated based on a simple phenomenological model of the defect echoes. The performance of these detectors are compared with the physical model-based optimal detector and is shown to yield moderate performance degradation.</p><p>Various aspects of optimal detection in static nonlinear sensor systems are also treated, in particular the stochastic resonance (SR) phenomenon which, in this context, implies noise enhanced detectability. Traditionally, SR has been quantified by means of the signal-to-noise ratio (SNR) and interpreted as an increase of a system's information processing capability. Instead of the SNR, rigorous information theoretic distance measures, which truly can support the claim of noise enhanced information processing capability, are proposed as quantifiers for SR. Optimal detectors are formulated for two static nonlinear sensor systems and shown to exhibit noise enhanced detectability.</p>

This thesis is concerned with detection of transient signal families and detectors in nonlinear static sensor systems. The detection problems are treated within the framework of likelihood ratio based binary hypothesis testing. An analytical solution to the noncoherent detection problem is derived, which in contrast to the classical noncoherent detector, is optimal for wideband signals. An optimal detector for multiple transient signals with unknown arrival times is also derived and shown to yield higher detection performance compared to the classical approach based on the generalized likelihood ratio test. An application that is treated in some detail is that of ultrasonic nondestructive testing, particularly pulse-echo detection of defects in elastic solids. The defect detection problem is cast as a composite hypothesis test and a methodology, based on physical models, for designing statistically optimal detectors for cracks in elastic solids is presented. Detectors for defects with low computational complexity are also formulated based on a simple phenomenological model of the defect echoes. The performance of these detectors are compared with the physical model-based optimal detector and is shown to yield moderate performance degradation. Various aspects of optimal detection in static nonlinear sensor systems are also treated, in particular the stochastic resonance (SR) phenomenon which, in this context, implies noise enhanced detectability. Traditionally, SR has been quantified by means of the signal-to-noise ratio (SNR) and interpreted as an increase of a system's information processing capability. Instead of the SNR, rigorous information theoretic distance measures, which truly can support the claim of noise enhanced information processing capability, are proposed as quantifiers for SR. Optimal detectors are formulated for two static nonlinear sensor systems and shown to exhibit noise enhanced detectability.

Cold rolled carbon steel 1018C is widely used in pressurized fuel pipelines. For those structures, stress corrosion cracking (SCC) can pose a significant problem because cracks initiate late in the lifetime and often unexpectedly, but grow fast once they get started. To ensure a safe operation, it is crucial that any damage can be detected before the structural stability is reduced by large cracks. In the early stages of SCC, microstructural changes occur which increase the acoustic nonlinearity of the material. Therefore, an initially monochromatic Rayleigh wave is distorted and measurable higher harmonics are generated. Different levels of stress corrosion cracking is induced in five specimens. For each specimen, nonlinear ultrasonic measurements are performed before and after inducing the damage. For the measurements, oil coupled wedge transducers are used to generate and detect tone burst Rayleigh wave signals. The amplitudes of the received fundamental and second harmonic waves are measured at varying propagation distances to obtain a measure for the acoustic nonlinearity of the material. The results show a damage-dependent increase in nonlinearity for early stages of damage, indicating the suitability for this nonlinear ultrasonic method to detect stress corrosion cracking before structural failure.

An automated method in damage state assessment of reinforced concrete columns for the purpose of establishing a rapid and quantitative post-earthquake safety and structural evaluation procedure is proposed. Several techniques from the fields of computer vision and image processing are employed in order to develop a set of methods capable of automatically detecting spalled regions on the surface of reinforced concrete columns as well as the properties of cracks and spalled regions on these surfaces. The resulting properties of the observed visible damage on the reinforced concrete column surfaces are then utilized to automatically estimate the existing condition and safety of the column. The damage state is quantified according to the maximum drift capacity of the column. The methods proposed in this research were implemented in a Microsoft Visual Studio .NET environment, and tested on real images of damaged columns. The test results indicated that the methods could automatically detect spalled regions and retrieve the properties of spalling and cracks on reinforced concrete column surfaces in images or video frames, and further, that this retrieved information could be accurately translate to a meaningful assessment of the column's existing damage state in the form of the maximum drift capacity.