高クロムフェライト鋼のクリープ劣化の先進的電磁非破壊試験：特性評価、モデリングおよび物理的解釈

Tohoku University内一　哲哉課

Magnetic non-destructive materials characterization of non-ferromagnetic materials using magnetic susceptibility

International audienceAll materials interact with an external magnetic field to some extent quantified by the magnetic susceptibility χ . There is a correlation between local χ value and local anomalies of material composition, deformation and stress, which makes it interesting to explore related sensor principles with a potential for NDT application. This contribution however concerns a modification over the magnetic force based sensor for laterally resolved susceptibility measurement and demonstrates the possible range of NDT applications on different non-ferromagnetic material samples. This sensor however eliminates the use of cantilever to avoid possible vibrations in the industrial environment

Essais électromagnétiques avancés non destructifs sur les aciers ferritiques à haute teneur en chrome dégradé : Caractérisation, modélisation et interprétation physique

Under constant high temperatures and pressure, the material undergoes mechanical creep degradation which leads to microstructural changes. These microstructural changes if not monitored on time, can lead to some serious fatal accidents such as in power plants. To investigate these microstructural changes, the material has to be shaped in a certain specific shape and size to have the imaging analysis using Scanning electron microscopy, Electron backscatter diffract ion etc. which are destructive in nature and involve high equipment cost. In order to overcome this issue, this thesis work, incorporates three different non-destructive techniques, to study the evolution of magnetic signatures with respect to the level of rupture they are exposed to. It is legitimate to assume that all the microstructural changes that occur in the material can be reflected in the corresponding magnetic signatures measured. The material that has been studied here is high chromium creep degraded steel which is used in the thermal power plant. The magnetic signatures are evaluated in terms of microstructural information to draw the conclusions. Some magnetic parameters from the curves, such as coercivity, magnetic reversibility are derived which show strong correlations with the microstructure. Similarly, techniques based on Hysteresis curves, and magnetic Barkhausen Noise are also implemented. To further quantify the results obtained from the magnetic signatures of the materials, a model has been developed to derive model parameters in order to physically interpret the microstructural changes. The modelling technique will help in overcoming the issue of lack of standards in NDT, irrespective of the experimental set-up involved. The parameters are compared to reveal sensitivity based on the technique. Finally, conclusion has been drawn to check which parameters are correlated to microstructure for a particular NDT technique used.Sous des températures et des pressions élevées constantes, les matériaux métalliques de structure subissent une dégradation mécanique par fluage qui entraîne des changements microstructuraux. Ces derniers, s'ils ne sont pas surveillés à temps, peuvent entraîner des incidents sérieux, notamment dans le domaine de la production d’énergie électrique (centrales électriques). Pour déterminer les changements microstructuraux, le matériau doit avoir une forme et une taille spécifiques pour que l'analyse des images obtenues par microscopie électronique à balayage, diffraction par rétrodiffusion d'électrons, etc. soit effectuée. Cette préparation destructive demande à extraire le matériau à tester du système, et à le modifier pour la mesure. Afin de surmonter ce problème, dans ce travail de thèse sont proposées trois techniques micro magnétiques non destructives, pour étudier l'évolution des signatures magnétiques par rapport aux niveaux de rupture auquel les matériaux sont exposés. Il est légitime de supposer que tous les changements microstructuraux qui se produisent dans le matériau vont se refléter dans les signatures magnétiques mesurées. Le matériau étudié ici est de l'acier à haute teneur en chrome très sensible au fluage et principalement utilisé dans les centrales thermiques. Certains paramètres magnétiques, tels que la coercivité, la réversibilité magnétique, sont dérivés et montrent de fortes corrélations avec la microstructure. De même, des techniques basées sur les courbes d'hystérésis et le bruit magnétique de Barkhausen sont également appliquées. Pour quantifier davantage les résultats obtenus à partir des signatures magnétiques des matériaux, le modèle de Jiles-Atherton a été adapté à la simulation des signaux de contrôle non destructif. A l’inverse, la possibilité de déterminer les paramètres du modèle à partir des seules mesures de contrôle non destructif est démontrée. Cela apporte des éléments complémentaires à l’interprétation physique des changements microstructurels. La technique de modélisation peut aider en outre à résoudre le problème de l'absence de normes dans les essais non destructifs, quel que soit le dispositif expérimental utilisé. Les paramètres sont enfin comparés pour révéler la sensibilité de chacun d’entre eux aux changements microstructuraux, et ce en fonction de chaque technique de contrôle non destructif utilisée

Simulation of Synchronized-Switching Method Energy Harvester Including Accurate Piezoceramic Nonlinear Behavior

Synchronized-switching techniques have significantly enhanced the harvested energy from semipassive and active surrounding ambient mechanical vibration harvesters. They have allowed a large improvement of vibration-control efficiency using piezoelectric devices. Unfortunately, for such techniques, dielectric limitations appear as soon as the piezoceramic operates under external solicitation of higher amplitudes and frequencies. Under extreme conditions, active materials exhibit nonlinear behavior related to dielectric hysteresis that significantly reduces their performance. In this work, we focus on this nonlinear behavior and its consequences in terms of system efficiency. We apply a realistic model including accurate material laws. In such models, a constant piezoelectric coupling d 31 is not suitable as a coefficient anymore and it should be replaced by a function depending on the polarization level through the active material. The response of more realistic systems including hysteresis was taken into account and compared with the basic model, where a constant d 31 was considered

Multiscale Characterization and Model for the Dynamic Behavior of Ferroelectric Materials Using Fractional Operators

International audienceFractional operators are well adapted to model dynamic dielectric losses of ferroelectric materials. Where usual integer derivative operators are always limited to a relatively weak frequency bandwidth, an approach based on fractional derivatives provides good simulation results even beyond working frequency of industrial systems. In this article, we determined the link between a high excitation (> 2 kV/mm), weak frequency (< 100 Hz) dynamic dielectric fractional hysteresis model and the weak excitation stress level (< 5 V/mm) but large frequency bandwidth (40 Hz < f < 40 MHz) well known as dielectric permittivity fractional models (Cole-Cole model and Havriliak-Negami). The good comparison of simulation/measure was obtained considering the same sample and the same dynamic parameters (fractional order together with nonlinear dry friction parametrization) in both cases. This allows attributing

Magnetic Susceptibility Imaging as a New Approach towards Characterization and Testing of Para-and Diamagnetic Materials

International audienceAll materials interact with a magnetic field to some extent. This interaction is generally quantified by the magnetic susceptibility . Non-ferromagnetic materials' group comprises (besides many others) all kinds of plastics, glass, carbon and non-ferrous metals. It is legitimate to assume that there is a correlation between local  value and local anomalies of material composition, deformation and stress, which makes it interesting to explore related sensor principles with a potential for NDT application. This contribution however concerns a novel magnetic force based sensor for laterally resolved susceptibility measurement and demonstrates the possible range of NDT applications on different non-ferromagnetic material samples

Dynamic hysteresis lump model including fractional operators for the incremental permeability nondestructive testing

International audienceMagnetic Incremental Permeability (MIP), represents the effective permeability for a small alternating field superimposed on a larger steady field. A dynamic lump scalar hysteresis model including fractional operator is proposed here to model MIP. The model considers both tangent excitation field H and permanent mechanical stress T as excitation of the material. Numerical results and simulation parameters (fractional order) allow to clarify the MIP mechanisms and to define degradation threshold level for industrial applications

Caractérisation et modélisation phénoménologique locale du bruit de Barkhausen sous contrainte de champs magnétique et mécanique

International audienceAprès traitement et normalisation, il est possible de tracer des cycles d'hystérésis locaux à partir de la mesure du bruit magnétique de Barkhausen. Si le matériau est homogène et dans des conditions d'excitation similaires les cycles obtenus sont comparables aux cycles d'hystérésis magnétiques classiques B(H) (Induction magnétique B en fonction du champ d'excitation tangentiel de surface H). Les cycles locaux du bruit Barkhausen donnent des indices intéressants quant à l'évolution de la microstructure du matériau magnétique (contraintes internes, niveau de dégradation …). Ceci en fait un outil incontournable de l'évaluation non destructive des aciers ferromagnétiques. Dans cet article nous proposons une modélisation phénoménologique du bruit de Barkhausen à partir de la modélisation locale de B soumise à un champ H et/ou une contrainte mécanique unie axiale avec comme objectif ultime une quantification des contraintes internes résiduelles par la mesure Barkhausen

From magnetic Barkhausen noise to quasi-static vector Preisach hysteresis model distribution

International audiencePreisach quasi-static hysteresis model is highly used in the electromagnetic simulation community. To run hysteresis Preisach model, one firstly needs to describe the Preisach triangular distribution followed by experimental results (hysteresis loops). Unfortunately, nondestructive technique control (NDT) situations forbid access to such experimental hysteresis loops. In this article, a new technique based on magnetic Barkhausen noise measurement is proposed to describe Preisach distribution. This technique allows to implement Preisach model without experimental hysteresis loops