Crack inspection and simulations with Eddy Current Thermography for the aerospace industry

La Thermographie des Courants de Foucault (Eddy Current Thermography, ECT) est une méthode de contrôle non-destructif (CND) sans contact, et de nos jours il est utilisé dans une large gamme d'applications. Cette méthode combine les techniques de courants de Foucault et des techniques de thermographies de type CND afin de fournir une méthode efficace pour la détection des fissures. Dans cette méthode, le courant de Foucault est généré dans les échantillons métalliques. Si l'échantillon contient des fissures, le déplacement du courant et la propagation de la température à l'intérieur des échantillons métalliques seraient affectés par ces fissures. Les changements de la distribution de température sont captés par une caméra infrarouge. L'un des principaux défis de cette méthode est qu'elle nécessite beaucoup de paramètres dans les expériences, tels que l’excitation des bobines: la valeur de la fréquence, le nombre de tours, le matériel de fil, le rayon de la bobine ... Afin d'optimiser les expériences, la simulation numérique est nécessaire, et le logiciel COMSOL Multiphysics® FEM est une solution très appropriée. Pendant le processus de simulation, une limite de détection de fissure a été proposée pour une fissure dans un spécimen métallique donné. Les résultats de la simulation et de la limite de détection des fissures sont également vérifiés au moyen d’expériences en laboratoire. L'objectif final de cette thèse est de fournir une image globale de la Thermographie des Courants de Foucault, la limite de détection des fissures et la manière dont la simulation ainsi que les expériences doivent être effectue afin de détecter les fissures dans les échantillons de plaques métalliques. Ces échantillons ont été fournis par L3-MAS et Pratt & Whitney Canada (PWC), les partenaires industriels impliqués dans ce projet quia été financé par le Conseil de recherches en sciences naturelles et en génie du Canada (CRSNG) et le Consortium de recherche et d'innovation en aérospatiale au Québec (CRIAQ).Eddy Current Thermography (ECT) is a non-contact, non-destructive testing (NDT) method, and nowadays it is used in a wide range of applications. This method combines eddy current and thermographic NDT techniques in order to provide an efficient method for crack detection. In this method, the eddy current is generated into metallic specimens. If the specimen contains cracks, the current flow and temperature propagation inside the metallic specimens would be affected by these cracks. The changes of temperature distribution are captured by an infrared camera. One of the main challenges in this method is that it requires many parameters in the experiments, such as coil excitations: the frequency value, number of turns, material of wire, radius of the coil...In order to optimize the experiments, numerical simulation is necessary, and COMSOL Multiphysics® FEM software is a very suitable solution. During the simulation process, a crack detection limit for a crack in a given metallic specimen has been proposed. The simulation results and crack detection limit are also verified using experiments in the laboratory. The final goal of this thesis is to provide the overall picture of the Eddy Current Thermography, crack detection limit and the manner in which to simulate as well as perform the experiments in order to detect cracks on the metallic plate specimens which were provided by L3-MAS and Pratt & Whitney Canada (P.W.C), the industrial partners involved in this project which was sponsored by the Natural Sciences and Engineering Research Council of Canada (NSERC) and The Consortium for Research and Innovation in Aerospace in Québec (CRIAQ)

Towards the simulation of the whole manufacturing chain processes with FORGE®

International audienceFollowing the metal composition and the microstructure evolution during the whole manufacturing chain is becoming a key point in the metal forming industry to better understand the processes and reach the increasing quality requirements for the parts. Thus, providing a simulation tool able to model the whole chain becomes critical. Physical phenomena occurring during the processes are nowadays better understood, providing always more relevant models for numerical simulation. However, important numerical challenges still exist in order to be able to run those simulations with the required accuracy. This article shows how FORGE® tackles those issues in order to provide highly accurate microstructure and surface treatments simulation features applied on real industrial processes

Multiphysics Structured Eddy Current and Thermography Defects Diagnostics System in Moving Mode

Eddy current testing (ET) and eddy current thermography (ECT) are both important non-destructive testing (NDT) methods that have been widely used in the field of conductive materials evaluation. Conventional ECT systems have often employed to test static specimens eventhough they are inefficient when the specimen is large. In addition, the requirement of high-power excitation sources tends to result in bulky detection systems. To mitigate these problems, a moving detection mode of multiphysics structured ET and ECT is proposed in which a novel L-shape ferrite magnetic yoke circumambulated with array coils is designed. The theoretical derivation model of the proposed method is developed which is shown to improve the detection efficiency without compromising the excitation current by ECT. The specimens can be speedily evaluated by scanning at a speed of 50-250 mm/s while reducing the power of the excitation current due to the supplement of ET. The unique design of the excitation-receiving structure has also enhanced the detectability of omnidirectional cracks. Moreover, it does not block the normal direction visual capture of the specimens. Both numerical simulations and experimental studies on different defects have been carried out and the obtained results have shown the reliability and detection efficiency of the proposed system

Application of HPC in eddy current electromagnetic problem solution

As engineering problems are becoming more and more advanced, the size of an average model solved by partial differential equations is rapidly growing and, in order to keep simulation times within reasonable bounds, both faster computers and more efficient software implementations are needed. In the first part of this thesis, the full potential of simulation software has been exploited through high performance parallel computing techniques. In particular, the simulation of induction heating processes is accomplished within reasonable solution times, by implementing different parallel direct solvers for large sparse linear system, in the solution process of a commercial software. The performance of such library on shared memory systems has been remarkably improved by implementing a multithreaded version of MUMPS (MUltifrontal Massively Parallel Solver) library, which have been tested on benchmark matrices arising from typical induction heating process simulations. A new multithreading approach and a low rank approximation technique have been implemented and developed by MUMPS team in Lyon and Toulouse. In the context of a collaboration between MUMPS team and DII-University of Padova, a preliminary version of such functionalities could be tested on induction heating benchmark problems, and a substantial reduction of the computational cost and memory requirements could be achieved. In the second part of this thesis, some examples of design methodology by virtual prototyping have been described. Complex multiphysics simulations involving electromagnetic, circuital, thermal and mechanical problems have been performed by exploiting parallel solvers, as developed in the first part of this thesis. Finally, multiobjective stochastic optimization algorithms have been applied to multiphysics 3D model simulations in search of a set of improved induction heating device configurations

Polymer bonding by induction heating for microfluidic applications

Microfluidic systems are being used in more and more areas and the demand for such systems is growing every day. To meet such high volume market needs, a cheap and rapid method for sealing these microfluidic platforms which is viable for mass manufacture is highly desirable. In this work low frequency induction heating (LFIH) is introduced as the potential basis of a cost-effective, rapid production method for polymer microfluidic device sealing. Thin metal layers or structured metal features are introduced between the device s substrates and heated inductively. The surrounding material melts and forms a bond when cooling. During the bonding process it is important to effectively manage the heat dissipation to prevent distortion of the microfluidic platform. The size of the heat affected zone (HAZ), and the area melted, must be controlled to avoid blockage of the microfluidic channels or altering the channels wall characteristics. The effects of susceptor shape and area, bonding pressure, heating time, etc, on the heating rate have been investigated to provide a basis for process optimisation and design rules. It was found that the maximum temperature is proportional to the square of the susceptor area and that round shaped susceptors heat most efficiently. As a result of the investigations higher bonding pressure was identified as increasing bond strength and allowing the reduction of heating time and thus the reduction of melt zone width. The use of heating pulses instead of continuous heating also reduced the dimensions of melt zones while maintaining good bond strength. The size of the HAZ was found to be negligible. An analytical model, which can be used to predict the heating rate, was derived. In validating the model by numeric models and experiments it was found that it cannot be used to calculate exact temperatures but it does correctly describe the effect of different heating parameters. Over the temperature range needed to bond polymer substrates, cooling effects were found not to have a significant impact on the heating rate. The two susceptor concepts using thin metal layers (metal-plastic bonds) or structured metal features (plastic-plastic bonds) were tested and compared. While the metal-plastic bonds turned out to be too weak to be useful, the bonds formed using structured susceptors showed good strength and high leakage pressure. Based on the knowledge gained during the investigations a microfluidic device was designed. Different samples were manufactured and tested. During the tests minor leaks were observed but it was found that this was mainly due to debris which occurred during laser machining of the channels. It was concluded that induction bonding can be used to seal plastic microfluidic devices. The following guidelines can be drawn up for the design of susceptors and process optimisation: Materials with low resistivity perform better; For very thin susceptors the effect of permeability on the heating rate is negligible; The cross-sectional area of the susceptor should be as large as possible to reduce resistance; The thickness of the susceptor should be of similar dimensions to the penetration depth or smaller to increase homogeneity of heat dissipation; The shape of the susceptor should follow the shape of the inductor coil, or vice-versa, to increase homogeneity of heat dissipation; The susceptor should form a closed circuit; Higher bonding pressure leads to stronger bonds and allows reduced heating times; Pulsed heating performs better than continuous heating in terms of limited melt area and good bond strength. The drawbacks of the technique are explained as well: introducing additional materials leads to additional process steps. Also the structuring and placement of the susceptor was identified to be problematic. In this project the structured susceptor was placed manually but that is not feasible for mass manufacture. To be able to use the technique efficiently a concept of manufacturing the susceptor has to be found to allow precise alignment of complex designs.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Mesure d'hystérésis magnétique volumique de l'acier 4340 en fonction de la température

RÉSUMÉ Le domaine du chauffage par induction sollicite les propriétés électriques et magnétiques d’une pièce d’acier pour y injecter une puissance par induction électromagnétique, soit des courants de Foucault en surface. Des simulations par la méthode des éléments finis sont couramment employées pour déterminer la distribution de puissance, notamment lorsqu’une géométrie complexe est traitée. Une amélioration de la précision de ces simulations accélère le prototypage du profil de chauffe adapté pour une pièce. En considérant les avancées dans les techniques de calcul numérique, les biais de mesure dans les propriétés magnétiques couramment employées ont un impact considérable sur la précision des résultats. Dans ce mémoire, on propose une méthodologie de mesure des propriétés magnétiques des matériaux magnétiques à haute température. Une approche dite quasistatique à deux bobines est adaptée pour mesurer l’évolution des propriétés jusqu’à la température de Curie, soit une analyse dite «thermomagnétique». Dans la méthode développée, l’analyse recueille une cinquantaine de courbes d’hystérésis distribuées entre 20°C et 850°C en moins de 30 minutes. La rapidité de l’analyse à haute température est cruciale pour éviter toutes transformations de la microstructure de l’acier lors des mesures. On soupçonne que cinq minutes sont suffisantes pour altérer les propriétés magnétiques dans certains cas particulièrement sensibles. De plus, l’usinage de l’échantillon d’acier implique habituellement des techniques qui créent en surface des contraintes mécaniques, de la déformation plastique et de hautes températures. Ces trois phénomènes affectent les propriétés magnétiques. La méthode actuelle emploie des échantillons avec un grand rapport volume/surface pour limiter l’impact des altérations du matériau en surface.Un aspect novateur de ce travail est le développement de bobines adaptées aux hautes températures (900°C) à un faible coût de fabrication. Ce savoir-faire appliqué à l’approche choisie permet, entre autres, une meilleure précision dans la mesure des courbes d’hystérésis.----------ABSTRACT The field of induction heating relies on the electrical and magnetic properties of a material to transfer electromagnetic power inside the work piece by means of eddy currents. With complex geometries, finite element simulations are commonly used to determine the magnetic field distribution, and thus the power distribution. Better predictions of the transferred power accelerate the prototyping scheme used to obtain the optimal heating profile. Considering the advances in numerical techniques, measurement bias in magnetic properties can have a relatively large impact on the precision of the results. In the present work, we propose an approach to magnetic property measurements at high temperature. A two windings quasistatic approach is used to monitor the evolution of the properties up to the Curie temperature, i.e. a thermomagnetic analysis (TMA). The developed setup can acquire approximately 50 hysteresis curves spread between 20°C and 850°C within 20 minutes. This rapid TMA is crucial to avoid any microstructural transformation in the steel over the course of the heating. An exposure of five minutes to high temperatures is suspected to be enough to alter the magnetic properties in some sensitive steels. Furthermore, the sample’s machining, prior to the measurements, most often implies cutting techniques that create residual stress, plastic deformation and high temperatures. These three phenomenon can alter the microstructure and therefore permanently change the initial material’s magnetic properties. The chosen magnetic measurement method favours samples with a large volume to surface ratio to reduce the impact of material alteration at the surfaces. A contribution of this work is the development of a high temperature winding (900°C) at low cost. This expertise applied to our method can increase the precision in the magnetic measurement of hysteresis curves by allowing the windings to be part of the sample and therefore inside the oven. This enables the use of closed samples (toroids) with a diameter of approximately 5 cm and a 5 mm cross-section diameters, which is impractical with traditional windings