Le présent travail de thèse fait suite à une première étude où une stratégie d’identification des paramètres et formes des lois de zones cohésives a été élaborée pour des matériaux homogènes. L’extension au cas de matériaux présentant des hétérogénéités nécessite d’accéder localement aux champs de contraintes.Ainsi, l’objectif principal de cette étude est de mettre au point une méthode de caractérisation locale des propriétés mécaniques et des contraintes. Cette méthode est basée sur l’erreur en relation de comportement combinée à l’exploitation de la richesse des mesures de champs cinématiques planes et plus particulièrement des champs de déformations, obtenus par dérivation numérique des champs de déplacements. Cette mesure cinématique est réalisée par une technique de corrélation d’images numériques enrichie.La méthode d’identification est basée sur la minimisation itérative d’une norme énergétique faisant intervenir le tenseur élastoplastique sécant. Différentes simulations numériques ont illustré la capacité de la procédure à identifier localement des champs de propriétés hétérogènes et sa robustesse et sa stabilité vis-à-vis du bruit de mesure, du choix du jeu de paramètres d’initialisation de l’algorithme et de la finesse du maillage.Pour finir, des essais plans avec différentes géométries d’éprouvettes ont été effectués et un essai a été mis au point pour obtenir de manière maîtrisée un état initial très hétérogène. Les résultats d’identification élastoplastique multilinéaire ont montré la capacité de la méthode à identifier les lois de comportements locales sur ce matériau hétérogène. / The present work follows a first approach where a strategy for identifying the shape and the parameters of cohesive-zone laws has been developed for homogeneous materials. The extension of this method to heterogeneous material requires the knowledge of the local stress state.The study aims at developing a local characterization method for mechanical properties and stresses. This method is based on the constitutive equation gap principles and relies on the knowledge of mechanical kinematic fields and particularly of the strain fields. These fields are obtained by the numerical differentiation of displacement fields measured by digital image correlation.This identification method is based on the iterative minimization of an energy norm involving the secant elastoplastic tensor. Various numerical simulations were used to illustrate the performance of the procedure for locally identifying heterogeneous property fields, and to characterize its robustness and its stability with respect to noise to the values of the algorithm initialization parameter and to the mesh refinement.Finally, various experimental tests with different specimen geometries were performed and a test has been developed to obtain a controlled heterogeneous initial state. The multilinear elastoplastic identification results showed the ability of the method to identify the local behavior properties on heterogeneous materials.

Dans ce travail, nous proposons une approche essentiellement expérimentale. Dans une première partie, nous exposons les résultats obtenus par imagerie rapide et mesures électriques corrélées dans le temps, concernant l’étude de la transition entre des électrodes de cuivre dans l’air et l’argon, et entre des électrodes de tungstène dans l’argon pour des pressions comprises entre 100 mbar et 1 bar. Dans aucun cas une transition à l’arc n’est observée sans constriction quasi-totale de la colonne positive. Dans le cas d’électrodes en tungstène dans l’argon, la vitesse d’extension de la zone filamentaire depuis l’anode vers la cathode a été vue dépendante de la pression et de l’intensité. La durée d’une transition spontanée a été linéairement corrélée à la distance inter-électrode, suggérant un mécanisme propagatif à vitesse constante dans la colonne. Plus la pression est élevée, plus la durée totale des transitions est longue ; par ailleurs, à pression constante, cette durée de transition spontanée décroît à intensité croissante, pour tendre vers une durée limite, correspondant à la durée constante de changement de structure de la zone cathodique. Dans une seconde partie, nous nous intéressons à l’échauffement de surfaces d’anodes et de cathodes en cuivre dans l’air et dans l’argon soumises à des arcs électrique pour plusieurs gammes de courant (de 30 à 120 A). Deux méthodes de mesures sont utilisées. Enfin, nous utilisons les mesures de températures de surface pour proposer deux modèles simples de bilan de puissance à la surface des électrodes (flux de chaleur). L’un considère uniquement le chauffage dû au spot d’arc et l’autre le chauffage supplémentaire de la colonne d’arc. / In this work, an approach which is essentially experimental is proposed. In the first part, results are presented which were obtained by synchronized fast camera imaging and electrical measurements. These concern the study of the transition between copper electrodes in air and in argon, and between tungsten electrodes in argon for gas pressure in the range 100 mbar – 1 bar. In no case was the transition to arc been observed without the quasi-total constriction of the positive column. Considering tungsten electrodes in argon, the propagation speed of the filamentary part of the positive column from the anode to the cathode was found to be dependent on the gas pressure and the discharge current intensity. During spontaneous transition, the transition duration has been linearly correlated to the electrode gap, suggesting a propagative mechanism with a constant speed. The higher the pressure, the longer is the total transition duration. For a constant pressure and discharge current, the duration of spontaneous transition decreases with decreasing gap distance toward a limiting value, which corresponds to the constant duration of the structural change of the cathode root from diffuse to spot. In the second part, heating of copper anodes and copper cathodes submitted to electric arcs in air and in argon and for various current intensity values (from 30A to 120 A) is considered. Two measurement methods are used. Finally, the surface temperature measurements are used to purpose two models of the electrode surface power balance (heat flux). One model only considers the heating due to the arc spot and the second one considers a supplementary heating from the arc column.

Ce travail de thèse aborde les conditions et les mécanismes qui conduisent des fils superélastiques de NiTi à la rupture sous chargement mécanique cyclique. Les alliages à mémoire de forme du type NiTi présentent des propriétés thermomécaniques fonctionnelles comme la superélasticité et l’effet de mémoire de forme simple et double, lesquels sont générées grâce aux transformations de phase martensitiques provoquées soit par un changement de la contrainte ou de la température. Ces transformations de phase sont en principe des processus totalement réversibles et sans endommagement. Cependant, lorsque le NiTi est soumis à des transformations de phase induites par des contraintes cycliques, la performance en fatigue de l’alliage chute considérablement par rapport au NiTi non-transformant. La plupart des courbes S-N de fatigue rapportant cette chute ont été mesurées sur des fils NiTi a section constante dans lesquels les transformations martensitiques se développent de façon hétérogene par nucléation et propagation de bandes de cisaillement. De plus, d'après notre expérience, des essais de fatigue sur des échantillons de fils à section constante entrainent la rupture à l'intérieur des mors de la machine d'essai. Par conséquent, les valeurs de contrainte-déformation rapportées dans les courbes S-N ne sont pas nécessairement représentatives des conditions mécaniques critiques qui conduisent le matériau à la rupture. Dans le but de mieux caractériser les performances en fatigue des fils NiTi, nous avons effectué une série de tests de fatigue en traction-traction, tout en utilisant des échantillons sous forme ≪ diabolo ≫. La géométrie de ces échantillons nous a permis de confiner tous les processus de transformation martensitique et de fatigue dans un volume utile bien défini. La caractérisation du comportement thermomécanique de ces échantillons a été réalisée en combinant plusieurs techniques expérimentales et d'analyse telles que la corrélation d'image numérique(DIC), la thermographie infrarouge, la diffraction des rayons X à source synchrotron, la microscopie optique, la microscopie électronique à balayage et l'analyse par éléments finis. Une attention particulière à été portée à la performance de NiTi dans le régime à grand nombre de cycles (HCF) dans laquelle le matériau présente un comportement élastique ou une transformation de phase intermédiaire (appelée R-phase). Les résultats des tests de fatigue nous ont permis de distinguer les étapes de nucléation et de propagation des fissures pendant la durée de vie totale de nos échantillons. Afin de mieux comprendre les mécanismes qui conduisent à la nucléation des fissures, nous avons appliqué la méthode de l’auto-échauffement, qui a démontré son efficacité dans la prédiction de fatigue dans les cas des alliages d'aluminium et des alliages d'acier. Cette méthode corrèle l'élévation de température d'un échantillon soumis à différentes amplitudes de charge cyclique avec des mécanismes de dissipation d'énergie. Ces mécanismes dissipatifs sont après associés à l’accumulation d’endommagement locale dans le matériau. La méthode d'autoéchauffement a été réalisée en utilisant des mesures de champs thermiques des d'échantillons de NiTi sous forme diabolo pendant de chargement cyclique. / This Ph.D. dissertation thesis addresses the conditions and mechanisms that lead superelastic NiTi wires to fail under cyclic mechanical loads. NiTi shape memory alloys exhibit functional thermomechanical properties (superelasticity, shape memory effect, thermal actuation) due to martensitic phase transformations caused by a change of the applied stress and temperature. These phase transformations are though as fully reversible damage-free processes, however, when NiTi is subjected to repetitive stress-induced phase transformations its fatigue performance drops drastically in comparison to non-transforming NiTi. Most of fatigue S-N curves reporting this drop were measured on straight NiTi wires in which martensitic transformations proceed heterogeneously through nucleation and propagation of shear bands. Moreover, from our experience fatigue testing straight wire samples results in undesired failure inside the testing machine clamps. Hence, the reported stress-strain values in S-N curves are not necessarily representative of the critical mechanical conditions that lead the material to failure. With the aim of better characterize the fatigue performance of NiTi wires, we started by carrying out a series of pull-pull fatigue tests using hourglass-shaped samples. This sample geometry allowed us to confine all martensitic transformation and related material fatigue processes into a well-defined gauge volume. The samples’ characterization was performed by combining several experimental and analysis techniques such as Digital Image Correlation, Infrared Thermography, Synchrotron-source X-ray diffraction, Optical Microscopy, Scanning Electron Microscopy and Finite Element Analysis. A special attention was paid to the High Cycle Fatigue (HCF) performance of NiTi in which the material shows elastic behavior and/or an intermediate phase transformation (so-called R-phase). The results from HCF tests allowed us to distinguish crack nucleation and crack propagation stages during the total life of our NiTi samples. In order to get a better understanding of the mechanisms that lead to crack nucleation, we applied the nonconventional Self-Heating fatigue assessment method, which has shown efficiency in the case of aluminum and steel alloys. This method correlates the temperature elevation of a sample subjected to different cyclic load amplitudes with energy dissipating mechanisms that contribute to accumulating local damage in the material. The Self-Heating method was performed using full-field thermal measurements of cyclically loaded NiTi hourglass-shaped samples.

Ce travail est axé sur l'étude de l'évaporation lente d'un liquide confiné dans un tube capillaire de section carrée, en lien avec l'étude du phénomène de séchage. Dans un tel capillaire, si le liquide est suffisamment mouillant, des films liquides se forment par capillarité le long des coins internes. L'évaporation du liquide en sommet de film engendre un pompage capillaire et l'espèce volatile est alors transportée, sous phase liquide, au plus près du sommet du capillaire. Ce mode de transport dépend de la compétition entre les effets capillaires et les effets visqueux et de gravité qui s'opposent tous deux au mouvement du liquide vers le sommet du capillaire. Ces films liquides sont étudiés en adoptant une approche expérimentale. Le principe des expériences est de laisser un liquide volatil s'évaporer dans un tube capillaire carré. Plusieurs expériences d'évaporation sont réalisées en faisant varier la nature du liquide, la taille du capillaire et son orientation (horizontale et verticale). Une méthode de thermographie infra-rouge permet de mesurer le profil de température le long du capillaire. Le refroidissement induit par le changement de phase liquide-vapeur ainsi que sa position sont alors mesurables. A partir d'une méthode de visualisation par ombroscopie, plusieurs grandeurs sont mesurées : position du ménisque principal, taux d'évaporation et épaisseur relative des films. En s'appuyant sur une analyse simple du transfert de masse, on montre alors que les cinétiques d'évaporation obtenues expérimentalement se divisent en trois principales phases caractéristiques, ressemblant fortement aux trois périodes de la cinétique classique de séchage des milieux poreux capillaires. L'analyse de l'hydrodynamique des films montre qu'il est indispensable de prendre en compte l'arrondi interne des coins des capillaires dans la modélisation de l'écoulement au sein des films. On montre notamment que le phénomène étudié est très sensible à ce paramètre, qui limite l'extension des films. Ce travail expérimental a permis de développer une modélisation du transfert de masse dans la configuration étudiée, couplée à une modélisation de l'écoulement des films, et finalement de proposer un modèle de séchage d'un capillaire carré quantitativement satisfaisant. / In connection with the study of the phenomenon of drying, this work focuses on the study of slow evaporation of a liquid confined in a capillary of square cross section. In such a capillary, if the liquid wetting contact angle is low enough, liquid films are trapped by capillary forces along the capillary inside corners. Evaporation of the liquid at the film top creates a capillary pumping. The volatile species is then transported in liquid phase to the top of the capillary. This efficient mode of transport depends on the competition between the effects of capillarity and the effects of viscosity and gravity both opposing to the liquid flow towards the top of the capillary. In this work, the liquid films are studied experimentally.The principle of the experiments is to leave a volatile liquid evaporate in a square capillary tube. Several evaporation experiments are conducted, varying the liquid, the capillary tube size and its orientation (horizontal and vertical). An infrared thermography method allows to measure the temperature profile along the capillary. The cooling induced by the liquid-vapor phase change and its location is then measured. Owing to an ombroscopy visualization method, the location of the bulk meniscus, the evaporation rate and the relative thickness of the films can be measured. The experimental results show that the evaporation kinetics is similar to the drying kinetics of capillary porous media. This finding allows to study evaporation in a square capillary by analogy with the study of drying of capillary porous media. Based on a simple analysis of mass transfer in the system, it is then shown that the evaporation kinetics obtained experimentally can be divided into three main characteristic phases. The analysis of the hydrodynamic of the films shows that it is essential to take into account the roundeness of the capillary tube inside corners in the modelling of the flow in the films. We show that the phenomenon studied is very sensitive to the degree of roundedness of the tube internal corners, which limits the extension of the films. Modelling of the mass transfer coupled with modelling the film flow lead to a quantitatively satisfactory model of the drying of a square capillary tube.

Les caméras infrarouges modernes permettent d’accéder à la mesure de champs thermiques et de leur évolution temporelle. Le traitement d’images obtenues permet d’analyser la signature thermique d’objets mobiles ou de fluides en écoulement. Dans ce contexte nous avons fait l’étude de trois expériences différentes. La première consiste à suivre des billes mobiles et à évaluer leurs coefficients d’échanges thermiques avec l’environnement par l’estimation de temps caractéristiques. Dans le deuxième cas, nous faisons une comparaison entre deux fluides qui s’écoulent dans un microcanal, afin de déterminer les variations relatives des propriétés thermiques. La dernière application consiste à réaliser une cartographie de diffusivité thermique avec une source de chaleur mobile. / The modern infrared cameras allow the measurement of thermal fields and their temporal evolution. Infrared images processing is suitable to analyze the thermal signature of moving objects or fluid flows. In this context, we made the study of three different experiments. The first one is relative to infrared tracking of randomly moving balls and then estimate their thermal exchanges with the environment by the estimation of some characteristic time. In the second case we made a comparison between two fluids which flow inside a microchannel in order to determine the relative changes of thermal properties. The last application was to estimate a thermal diffusivity field with a mobile heat source.

This study is part of an original approach based on quantitative imaging techniques, such as Infrared Thermography, to study the damage under fretting loadings. The main objective was the establishment of new experimental method for a rapid determination of crack initiation conditions under fretting loadings, based on the analysis of the thermal signal. One other objective was the determination of the different heat sources in order to assess a local analysis of the fretting damage. This work underlined the great potential of Infrared Thermography to study this damage. / Cette étude s'inscrit dans une approche originale basée sur des techniques d'imagerie quantitatives comme la thermographie infrarouge pour étudier l'endommagement sous chargement de fretting. Le premier objectif était de développer une méthode de construction rapide de carte de fretting basée sur l'analyse du signale thermique au cours d'essais de fretting. Un deuxième objectif était de déterminer les sources de chaleurs accompagnant le fretting pour une meilleure compréhension des mécanismes d'endommagement. Ce travail a souligné le grand potentiel de la thermographie infrarouge pour l'étude de c'est phénomènes.

De nombreux phénomènes à l’oeuvre dans le processus de déformation et d’endommagement des élastomères sont étudiés à partir de la réponse mécanique de ces matériaux. Cependant, la plupart de ces phénomènes dépendent de la température et ont des signatures calorimétriques qui pourraient permettre de mieux les comprendre. Dans le contexte industriel de la manufacture de pneumatiques, les élévations de température induites par le chargement peuvent fortement impacter les performances physiques des pneumatiques ainsi que la tenue en fatigue des constituants caoutchoutiques. L’objectif de cette thèse est donc de caractériser le comportement thermomécanique des élastomères chargés et non chargés sous divers types de chargement mécanique. Pour ce faire, des mesures de champs thermiques et cinématiques couplées ont été mises en oeuvre lors d’essais mécaniques à température ambiante. Dans un premier temps, des essais de traction uniaxiale sur éprouvettes indemnes ont permis de confirmer que l’hystérésis mécanique observée lors d’un cycle de traction sur un caoutchouc naturel non chargé est essentiellement due au phénomène de cristallisation et non à des phénomènes dissipatifs. Par ailleurs, la construction de bilans énergétiques sur un cycle mécanique a permis de distinguer la contribution des différents mécanismes dissipatifs (viscosité, effet Mullins) des couplages thermomécaniques (élasticité entropique, cristallisation). Dans un second temps, des essais de cisaillement pur ont été menés sur des éprouvettes préalablement entaillées. Les analyses thermomécaniques menées à l’échelle de la zone d’influence de la fissure ont montré que les phénomènes dissipatifs aux très grandes déformations ne s’expriment pas de la même manière qu’aux déformations plus faibles. En particulier, pour les mélanges considérés dans cette étude, les effets du couplage entropique et de la viscosité sont du même ordre à la décharge, si bien que le matériau n’absorbe pas de chaleur à la décharge. Ces résultats sont très prometteurs à la fois pour la compréhension des phénomènes physiques impliqués dans le processus de déformation et pour la modélisation du comportement thermomécanique des élastomères. / Usually, most of the physical phenomena involved in the deformation of elastomers are studied from purely mechanical approaches. However, almost all of such phenomena depend on temperature and have distinguishable calorimetric signatures, which can enable us to better understand them. Furthermore, in the tire industrial context, the temperature increase induced by loading and self-heating may strongly impact the physical performances of tires as well as the fatigue life of the rubber components. Consequently, the aim of this PHD thesis was to characterize the thermomechanical behavior of rubbers, filled and unfilled, subjected to different mechanical loadings. For this purpose, coupled thermal and kinetic full field measurements have been performed during mechanical tests at ambient temperature. First, homogeneous uniaxial tensile tests have enabled us to confirm that the hysteresis loop in terms of the stress-strain relationship is mainly induced by crystallization phenomenon in natural rubber, not to dissipative phenomena. In the same way, energetic balances over one mechanical cycle have enabled us to distinguish the contribution of different dissipative phenomena (viscosity, Mullins effect) and the thermomechanical couplings (entropic elasticity, crystallization). Second, the analysis of the pure shear tests with pre-cracked specimens has enabled us to analyze, for the first time, the calorimetric response of rubbers in the zone of crack influence. Results have shown that dissipative phenomena at large strains differ from those involved at smaller strains. More especially, for the materials considered in the present study, the effects of the entropic coupling and viscosity are of the same order of magnitude during unloading, so that the material does not absorb any heat during unloading. These results are promising and motivate further work in this field in order to better understand the physical phenomena involved in the deformation processes as well as to more relevantly model the thermomechanical behavior of elastomers.

The aim of this thesis was to validate the use of infrared thermography (IRT) to non-invasively measure stress and/or pain in cattle. The main approach was to measure changes in heat emitted from superficial capillaries around the eye (referred to as eye temperature) in response to various aversive husbandry procedures used routinely on farms. In addition, various exogenous challenges were given to investigate the role of the hypothalamic-pituitary-adrenal (HPA) axis and the autonomic nervous system (ANS) in regulating the eye temperature response. No evidence was found to support the hypothesis that an increase in eye temperature was due to HPA activity in cattle. A rapid drop in eye temperature occurred immediately after disbudding, an electric prod, startling and shouting. It is suggested that this was caused by the redirection of blood from the capillary beds via sympathetically-mediated vasoconstriction. Therefore, the role of the ANS was tested by measuring eye temperature, heart rate variability (HRV) and plasma catecholamine responses simultaneously. Somatic pain from disbudding and initial responses to surgical castration included a synchronised drop in eye temperature, increases in catecholamines and changes in HRV indicative of increased sympathetic activity. The role of the sympathetic nervous system was further confirmed by a drop in eye temperature that occurred following an epinephrine challenge. In contrast, deeper visceral pain from castration caused a more marked increase in eye temperature and changes in HRV indicative of increased parasympathetic tone. The underlying mechanism driving the increase in eye temperature is unknown; however, it is possible that it may be caused by vasodilation due to increased parasympathetic activity. These differences in ANS responses to different procedures, detected by IRT and HRV, may be due to the nature of the pain and the relative fear associated with the procedure. In summary, this research showed that during stress or pain, the heat emitted from superficial capillaries around the eye changes as blood flow is regulated under ANS control and these changes can be quantified using IRT. A combination of IRT and HRV is a non-invasive way to measure ANS activity and assess acute welfare impacts of husbandry practices in cattle. Further research using pharmacological inhibition and stimulation of the ANS activity would be beneficial to fully understand the underlying regulatory mechanisms of the eye temperature and HRV responses in cattle and other species during stress and/or pain. The full capability of IRT and HRV for detection of disease and emotional states and the effects of different intensities of pain, individual traits and previous experience also deserve attention.

Το αντικείμενο της παρούσας διδακτορικής διατριβής είναι η ανάπτυξη μιας εναλλακτικής μεθόδου μη καταστροφικού ελέγχου (ΜΚΕ) για αγώγιμα υλικά, που συνδυάζει την ηλεκτρομαγνητική διέγερση - επαγωγική θέρμανση του υλικού και επιθεώρηση με μεταβατική υπέρυθρη θερμογραφία. Με ένα μεταβαλλόμενο μαγνητικό πεδίο επάγονται δινορρεύματα εντός του εξεταζόμενου δοκιμίου. Η θερμότητα που παράγεται από τα δινορρεύματα, δημιουργεί θερμοκρασιακές διαφορές οι οποίες τείνουν να εξομαλυνθούν μέσω της θερμικής αγωγής. Κάποια ατέλεια στη δομή του υλικού, όπως είναι μια ρωγμή, θα επηρεάσει άμεσα ή έμμεσα τη ροή της θερμότητας και κατ’ επέκταση τη θερμοκρασιακή κατανομή στην επιφάνεια του υλικού. Χρησιμοποιώντας την υπέρυθρη θερμογραφία μπορούμε να απεικονίσουμε σε δύο διαστάσεις τη θερμοκρασιακή κατανομή της επιφάνειας του επιθεωρούμενου δοκιμίου και να εντοπίσουμε την ατέλεια αυτή. Η παρούσα διατριβή επικεντρώνεται στην υπολογιστική και πειραματική διερεύνηση της αποτελεσματικότητας και της αξιοπιστίας της ηλεκτρομαγνητοθερμικής μεθόδου ως μεθόδου ΜΚΕ σε αγώγιμα υλικά. Αφού πραγματοποιηθεί αναλυτική περιγραφή του μοντέλου με το οποίο προσεγγίζονται τα ηλεκτρομαγνητικά - θερμικά φαινόμενα της ηλεκτρομαγνητικής διέγερσης - επαγωγικής θέρμανσης αγώγιμων υλικών, αναπτύσσεται υπολογιστικός κώδικας για την υλοποίηση του μοντέλου. Με τη χρήση του υπολογιστικού προγράμματος διερευνάται η σημασία και η σπουδαιότητα ενός μεγάλου πλήθους παραμέτρων που επηρεάζουν την αποτελεσματικότητα της ηλεκτρομαγνητοθερμικής μεθόδου με απώτερο στόχο τη βελτιστοποίηση της. Στη συνέχεια ακολουθεί πειραματική επαλήθευση των αριθμητικών αποτελεσμάτων, όπου και αποδεικνύεται η αξιοπιστία των υπολογιστικών μοντέλων που χρησιμοποιήσαμε κατά την αριθμητική διερεύνηση της μεθόδου. Κατ’ αυτόν τον τρόπο επαληθεύεται η αποτελεσματικότητα της μεθόδου στον ΜΚΕ έλεγχο αγώγιμων υλικών. Το γενικό συμπέρασμα που προκύπτει είναι ότι η ηλεκτρομαγνητοθερμική μέθοδος αποτελεί μια αξιόπιστη μέθοδο για τον ΜΚΕ αγώγιμων υλικών. Απομένει πλέον να διερευνηθούν οι δυνατότητες της μεθόδου στο έπακρο, ώστε να αναδειχθεί το εύρος των εφαρμογών αυτής και να χρησιμοποιηθεί ενδεχομένως σε περιπτώσεις όπου μέχρι σήμερα κυριαρχούν άλλες διαγνωστικές μέθοδοι. / The subject matter of the present dissertation is the development of an alternative method for non-destructive inspection of conducting materials, which combines electromagnetic excitation – thermal conduction and inspection with transient infrared thermography. A time-varying magnetic field is used to induce eddy currents inside the conducting material under inspection. The Ohmic power generated in the material by the eddy currents creates temperature gradients which tend to be ironed out through thermal conduction. A defect in the material structure, such as a cracking, will affect the heat flow either directly or indirectly and hence the temperature distribution at the surface of the material. By employing infrared thermography, it is then possible to visualize in two-dimensional the temperature distribution over the excited surface of the tested specimen and detect the defect. The present dissertation focuses on computational and experimental investigation of the effectiveness and reliability of electromagnetic-thermal method as a method for non destructive inspection of conductive materials. After have been made a detailed description of the model which describes the electromagnetic-thermal phenomena of electromagnetic excitation - induction heating in conductive materials, it was developed a computer program based on the above model. Using the computer program we investigated the significance and the importance of a large number of parameters affecting the effectiveness of electromagnetic-thermal method, with a view to optimize the method. The experimental verification of numerical results, indicate the reliability of computational model used in the numerical investigation of the method and verifies the method’s effectiveness for non destructive inspection of conducting materials. The general conclusion is that the electromagnetic - thermal method is a reliable method for non destructive inspection of conductive materials. It remains the full potentials of the method to be investigated, in order to extend the range of applications and use the method in cases where today dominate other diagnostic methods.

O estímulo vibratório gerado pela utilização das plataformas vibratórias tem sido aplicado como método eficaz para promover desempenho esportivo e também na reabilitação de pacientes com diversificadas disfunções. Acredita-se que a vibração de corpo inteiro (VCI) é capaz de diminuir os déficits de ativação muscular voluntária através de reflexos de estiramento neuromuscular, tornando-se um meio eficaz e de fácil aplicabilidade para pacientes com maiores incapacitações. Resultados controversos na literatura, com relação aos benefícios dos estímulos vibratórios, tornam a escolha dos parâmetros do equipamento (frequência, amplitude, tempo de exposição e modo de vibração) um desafio na obtenção dos melhores resultados. Assim, o objetivo desta tese visa a avaliação dos efeitos fisiológicos agudos da vibração de corpo inteiro (sensibilidade cutânea tátil e dolorosa, equilíbrio, temperatura superficial da pele, transmissibilidade da vibração) e a construção de um mapa de percepção corporal da VCI. Foram utilizados diferentes parâmetros e marcas desses equipamentos. Para investigar cada variável, quatro diferentes estudos foram realizados separadamente. O primeiro estudo investigou os efeitos da VCI na sensibilidade cutânea vibratória medidos a 30 Hz (corpúsculos de Meissner) e 200Hz (corpúsculos de Pacini) e de toque-pressão dos pés de 20 sujeitos normais e o tempo de duração dos efeitos da vibração nesses receptores. Como principais resultados, foram constatadas que as descargas aferentes dos mecanorreceptores de adaptação rápida foram fortemente afetadas pela vibração assim como a sensibilidade de toquepressão. Após 10 min de exposição à VCI o tempo de recuperação para a sensibilidade voltar aos limiares basais nos pés foi entre 2 e 3 h. Para continuar elucidando os efeitos agudos pós-exercício com vibração, um segundo estudo foi realizado avaliando variáveis fisiológicas em quatro diferentes frequências de exposição de VCI (30, 35, 40, 44 Hz). Foram avaliadas pressão arterial, frequências cardíaca e respiratória, temperatura axilar e a temperatura cutânea através de termografia por infravermelho dos membros inferiores dos 24 participantes avaliados. Por fim, o equilibro desses indivíduos foi avaliado através das análises dos deslocamentos, da velocidade e da área do centro de pressão (COP), em uma plataforma de força. Os dados do segundo estudo mostraram que, para as frequências de 40 e 44 Hz do equipamento, houve uma alteração significativa para as variáveis velocidade e comprimento ântero-posterior do centro de pressão. Além disso, durante a vibração e 10 min após, a temperatura dos membros inferiores foi reduzida, provavelmente em virtude da vasoconstrição gerada. Na investigação da sensibilidade dolorosa um terceiro estudo foi proposto, tendo em vista que as vias dos mecanorreceptores de sensibilidade cutânea tátil diferem daqueles relacionados com a sensibilidade dolorosa. Um modelo de dor crônica com ratos Wistar foi realizado e os animais foram tratados com VCI, esteira e a combinação de esteira com VCI. Como principais resultados deste estudo, os grupos tratados com VCI mostraram redução significativa da sensibilidade de toque-pressão após todas as sessões em comparação aos demais grupos. Efeitos analgésicos através do tempo de latência medidos com o hot plate foram encontrados após o terceiro dia de tratamento com 5 min de exposição por dia à VCI, nos primeiros 5 dias e 10 min nos 5 dias subsequentes. Como finalização das variáveis de interesse, o último estudo combinou dados quantitativos advindos da acelerometria (com medições na cabeça, quadril e tíbia) com dados qualitativos através da escala de Borg. Sessenta e cinco adultosjovens foram avaliados e este estudo propôs um método para escolher os diversificados parâmetros da plataforma vibratória, para alcançar os efeitos desejados na reabilitação ou desempenho esportivo. Este estudo mostrou que os índices de percepção de severidade medidos através da escala de Borg corresponderam com os dados quantitativos da acelerometria e assim os parâmetros do equipamento podem ser escolhidos com base na sensação subjetiva proveniente da escala de Borg. Os níveis de desconforto no equipamento podem estar relacionados com a frequência de ressonância das diferentes partes do corpo. Futuros estudos devem considerar aplicações clínicas da plataforma vibratória em pacientes com dor crônica musculoesquelética utilizando o modelo para escolha dos parâmetros do equipamento proposto nesta tese. / The vibratory stimuli generated by the use of vibrating platforms have been used as an effective method to promote sports performance and also in the rehabilitation of patients with several dysfunctions. It is believed that the whole body vibration (WBV) is able to decrease the deficits in voluntary muscle activation by neuromuscular stretch reflexes making it an efficient and easy exercise method applied to patients with greater disabilities. Controversial results in the literature regarding the benefits of the vibratory stimuli make the choice of the equipment parameters (frequency, amplitude, time of exposure and vibration mode) a challenge in getting the best results. The goal of this dissertation involves the evaluation of the acute physiological effects of whole body vibration (skin tactile and pain sensitivity, balance, skin temperature and vibration transmissibility) and the construction of a WBV perception body map. Parameters settings and different brands of these devices were used. To investigate each variable, four different studies were conducted separately. The first study investigated the effects of WBV on fast adapting mechanoreceptors measured at 30 Hz (Meissner corpuscles) and 200Hz (Pacinian corpuscles) and touch-pressure sensitivity from the right foot of 20 health subjects and the duration of the vibration effects on these receptors. The main results show that the afferent discharges of the fast adapting mechanoreceptors are strongly affected by vibration and sensitivity of touch-pressure was also impaired. After a single 10 minutes exposure to WBV, the time required to recover baseline tactile sensitivity on the feet was between 2 and 3 hours. To further elucidate the acute postexercise vibration effects, a second study was conducted assessing physiological variables at four different WBV frequencies (31, 35, 40, 44 Hz). Blood pressure, heart and respiratory rates, skin temperature and balance were measured. Skin temperature was measured by an infrared thermography of the lower limbs of 24 subjects. Balance was accessed with a force plate through the analysis of the center of pressure (COP) velocity, area and displacements variables. The results from this study show that for 40 and 44 Hz of the device’s frequencies, a significant decrease in balance was found for the center of pressure variables velocity and anterior-posterior displacement. Also, during WBV exposition and 10 minutes post vibration, the temperature of the lower limbs was reduced, probably due to vasoconstriction. To investigate the variable "pain", a third study was proposed, considering that the pathways and receptors of the cutaneous touch-pressure and vibration sensitivity differ from those related to pain sensitivity, the C and A fibers. A chronic pain model was applied in male Wistar rats and the animals were treated with WBV exercise (vibration platform), a low intensity exercise (treadmill) and a combined treatment involving both. The main results show that the groups treated with WBV showed a significant reduction in sensitivity to touchpressure after every session compared to the other groups. Analgesic effects through the time latency measured by the hot plate were found after the third treatment day with 5 min of exposure to WBV during the first 5 days and 10 min next 5 days. As completion of the fourth variable of interest, the last study by deriving quantitative data from accelerometry (with measurements on the head, hip and tibia) was combined with qualitative data arising from the Borg scale. Sixty five health young adults were measured and the study proposes a method for choosing the parameters settings of the vibrating platform, to achieve the desired goals in rehabilitation or sports performance. Discomfort perception ratings measured by the Borg scale corresponded well with the measured acceleration magnitudes and so the parameters settings of the device can be chosen based on the subjective sensation from the Borg scale. The level of discomfort ratings might be related to the frequency resonance phenomena of body parts. Future clinical applications with vibration platform in patients with muscle-skeletal chronic pain should be considered applying the model for choosing the parameter settings of the device proposed in this dissertation.