Accurate Simulation of EMAT Probes for Ultrasonic NDT Based on Experimental Measurements

During the last years, CEALIST has been developing EMATprobes dedicated to liquid sodium ultrasound applications, including telemetry, defect detection in sodium immersed welds, defect sizing, andmore recently using phased array probes, beam forming images and synthetic focusing. At the same time, simulation tools based on the numerical methods available at CEA LIST have been integrated within the CIVA software platform. This paper focuses on the experimental calibration of the simulation models for liquid sodium EMAT transducers. In particular, it tries to answer the questions regarding choices of input data for the developed models with the goal of carrying out realistic simulations. The full system measurement model, including coil impedances, gains and analog filters need to be taken into account to obtain predictive simulations. Physical measurements allow the precise determination of the needed parameters and allow verifying the different aspects of the EMAT probe behavior. The developed model is then used to propose a design that is optimized with respect to the generation of longitudinal waves in liquid sodium

Experimental Validation of an 8 Element EMAT Phased Array Probe for Longitudinal Wave Generation

41st Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE), Boise, ID, JUL 20-25, 2014International audienceSodium cooled Fast Reactors (SFR) use liquid sodium as a coolant. Liquid sodium being opaque, optical techniques cannot be applied to reactor vessel inspection. This makes it necessary to develop alternative ways of assessing the state of the structures immersed in the medium. Ultrasonic pressure waves are well suited for inspection tasks in this environment, especially using pulsed electromagnetic acoustic transducers (EMAT) that generate the ultrasound directly in the liquid sodium. The work carried out at CEA LIST is aimed at developing phased array EMAT probes conditioned for reactor use. The present work focuses on the experimental validation of a newly manufactured 8 element probe which was designed for beam forming imaging in a liquid sodium environment. A parametric study is carried out to determine the optimal setup of the magnetic assembly used in this probe. First laboratory tests on an aluminium block show that the probe has the required beam steering capabilities

Machine-learning based temperature compensation for Guided Wave Imaging in Structural Health Monitoring

International audienceIn Guided Wave (GW) Structural Health Monitoring (SHM), a baseline, i.e. a set of measurements taken on the inspected structure in a pristine state, is often required to separate the contributions of the defect(s) from the other propagating wave packets. Due to the sensitivity of GWs to Environmental and Operational Conditions (OECs), most GW-SHM techniques are limited in terms of range of applicability [1]. More specifically, the inspection of the unknown state must be conducted under the same EOCs as the ones of the pristine state. Besides measuring baselines on the structure under all the EOCs of interest, which is prohibitively expensive, a potential solution is to compensate the EOC effects on the measured signals. Several solutions in the literature, such as Baseline Signal Stretch [2] and Dynamic Time Warping [3], have been proposed to solve this problem, but are somewhat limited in terms of amplitude of compensation or range of application. In this paper, a model-based machine learning procedure to compensate the measured signals in an unknown state and known EOCs is presented. The compensation model is trained on experimental data acquired at various temperatures on a structure representative of the one of interest. In other words, an experiment under various EOCs must be conducted on a simplified version of the structure with at least two transducers. Material and transducers of the simplified experiment must be identical to the ones of the real structure, but the actual geometry might differ. The compensated signals are then used to conduct guided wave imaging, allowing immediate defect detection and localization. Results are shown for both aluminum and composite panels

Assessing performance of flaw characterization methods through uncertainty propagation

International audienceIn this work, we assess the inversion performance in terms of crack characterization and localization based on synthetic signals associated to ultrasonic and eddy current physics. More precisely, two different standard iterative inversion algorithms are used to minimize the discrepancy between measurements (i.e., the tested data) and simulations. Furthermore, in order to speed up the computational time and get rid of the computational burden often associated to iterative inversion algorithms, we replace the standard forward solver by a suitable metamodel fit on a database built offline. In a second step, we assess the inversion performance by adding uncertainties on a subset of the database parameters and then, through the metamodel, we propagate these uncertainties within the inversion procedure. The fast propagation of uncertainties enables efficiently evaluating the impact due to the lack of knowledge on some parameters employed to describe the inspection scenarios, which is a situation commonly encountered in the industrial NDE context

Thermométrie Ultrasonore sur des géométries variables dans le temps, Application à la Fabrication Additive par Fusion sur Lit de Poudre

Les procédés de fabrication additive par fusion sur lit de poudre (PBF) permettent de fabriquer des composants à géométrie complexe. Parmi les différents mécanismes impliqués, la température joue un rôle fondamental, notamment dans les processus de fusion de poudre, de solidification et de formation de la microstructure. Par conséquent, nous proposons d'étudier l'évolution d'un champ de température d'un objet manufacturé à travers un suivi in situ, utilisant la propagation des ondes élastiques et des mesures de temps de vol. On modélise la croissance d'un cylindre obtenu par fusion de poudre, son évolution thermique au cours de la fabrication et le temps de vol d'une onde élastique se propageant en mode impulsion-écho à partir du plateau de fabrication. Une méthode inverse déjà développée [1] est étendue à notre contexte de fabrication additive, et adaptée à une reconstruction de la température en temps réel. Un modèle aux différences finies est utilisé pour calculer le champ de température, lié linéairement à la vitesse de l'onde élastique [2], permettant un calcul de temps de vol. En parallèle, la géométrie spatiale varie avec l'ajout de couches de fabrication. Des résultats sont obtenus sur des données simulées, et confirment le potentiel de notre méthode inverse. Sa sensibilité au bruit est également étudiée. Nous discutons de l'applicabilité de l'algorithme à des données expérimentales, récemment enregistrées en mesurant les temps de vol à l'aide d'un transducteur de 5 MHz placé sous le plateau de fabrication. [1]I. Ihara, T. Tomomatsu, M. Takahashi, A. Kosugi, I. Matsuya, H. Yamada, S. Mukhopadhyayet K. Jayasundera, Ultrasonic thermometry for temperature profiling of heated materials, Advancement in Sensing Technology :New Developments and Practical Applications, 211–236, 2013. [2]T.-F. Chen, K.-T. Nguyen, S.-S. Wen et C.-K. Jen, Temperature measurement of polymer extrusion by ultrasonic techniques, Measurement Science and Technology, Vol. 10, 139–145,1999

Caractérisation d'échantillons représentatifs de soudures austénitiques en 316L par spectroscopie de Résonance Ultrasonore (RUS)

Conference : Cofrend 2023 - Les Journées Cofrend/ COFREND DAYS, Marseille, France, , 06 - 08 June 2023Dans la perspective d'améliorer les procédés d'imagerie ultrasonore sur des assemblages soudés, les caractéristiques mécaniques effectives du matériau et leur variabilité au sein de la soudure sont une donnée nécessaire. De nombreuses techniques reposant sur l'utilisation d'ondes élastiques ultrasonores ont déjà été mises en œuvre afin d'obtenir avec précision les constantes élastiques et ainsi d'évaluer l'anisotropie apparente de ces milieux complexes. Dans le cadre de cette étude, la Spectroscopie de Résonance Ultrasonore (RUS) a été mise en œuvre pour caractériser des échantillons prélevés dans un « mur » fabriqué par soudage dans l'hypothèse d'un comportement élastique orthotrope, homogène à l'échelle de l'échantillon. Les fréquences de résonance mesurées ont permis de résoudre le problème inverse à l'aide de méthodes d'optimisation utilisant le gradient et d'obtenir les constantes élastiques pour chacun des échantillons. Les résultats sont comparés à ceux préalablement obtenus par l'utilisation d'une technique de mesure de vitesse de phase en ondes ultrasonores pulsées dans le cadre du projet ANR MUSCAD

Model based inversion strategy dedicated to non-destructive testing applications

International audienceThis paper presents a global strategy aiming at solving efficiently inverse problems classically faced in the community of non-destructive testing, like flaw characterization and sensors optimization, for instance. The approach is based on intensive use of simulation tools that are obtained from complex physical models developed at CEA LIST and dedicated to ultrasonic and electromagnetic testing applications. Results presented in different physical contexts show not only its efficiency to solve parametric estimation problems, but also its capability to account for variability due to uncertainty in some model parameters and to evaluate the so-called well-posedness of inverse problems considered

Simulation-based performances assessment of FMC-TFM array imaging techniques

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Simulation-based performances assessment of FMC-TFM array imaging techniques

International audienceAdvanced array imaging techniques such as FMC-TFM and derived methods have attracted a great deal of interest and are more and more used in the industry since they allow improved performances in a wide range of situations. However, questions often arise about the quantification of these performances, the relative advantages of different techniques or setups , and the sensitivity to uncontrolled parameters. Thus it is of interest to optimize the technique by reducing the number of ultrasonic salvos while maintaining a good level of performances. To assess the performance of array imaging techniques is not a trivial task since it requires to account for variability of influent parameters. In this communication we demonstrate the potential of simulation tool to fulfil these needs. The present study is based on the use of versatile simulation tools implemented in the CIVA platform which allow to predict results obtained when applying a given processing algorithm to a given acquisition scheme (defined by the subset of simultaneously/successively emitting/receiving elements). Comparing different processing techniques and different acquisition schemes becomes possible. Moreover, statistical analysis of results issued from meta-models derived from CIVA allow to evaluate the sensitivity of the technique to various influent parameters. Probability of detection curves can be extracted and the sizing accuracy can be quantified and compared

Implementation of non destructive testing and in-line monitoring techniques on extra-large structures printed with WAAM technology.

International audienceGrade2XL is a European project funded by the H2020 program that gathers 21 academic and industrial partners. Started in March 2020 for 4 years, the principal objective is to print extra-large structures using the WAAM (Wire Arc Additive Manufacturing) method with a complete control of the fabrication process. Since WAAM is a relatively new technology for printing large specimens, it is important to develop quality assurance methods that can be used during the fabrication and once the structure has been built, which is the focus of CEA List in the project. Regarding methods applied built structures, CEA List has investigated Resonant Ultrasound Spectroscopy (RUS) for the material characterization and more specifically the evaluation of the elastic constants or more conventional ones for the inspection with phased-array ultrasonic techniques (PAUT) or eddy current (EC) for the detection of indications are implemented and optimised them for the inspection of the final structures. Concerning the development of in-line monitoring methods, CEA List has been working on laser Doppler vibrometry (LDV) and X-ray fluorescence (XRF) spectrometry, in order to get structural information during the printing but also detect the appearance of abnormal events and correlate them to the appearance of defects generated during the WAAM process.This proceeding presents the advantages of those methods for the inspection of extra-large structures made by WAAM and discusses the first results obtained in the framework of the project