Potentiel de la robotique pour l'inspection thermographique par chauffage inductif

La thermographie par courants de Foucault (ECT) est une méthode de thermographie active. L’excitation inductive génère des courants de Foucault dans les spécimens conducteurs. En présence de défauts, la circulation des courants est affectée par ces discontinuités produisant un changement dans la distribution de la température autour des défauts. Ces changements sont observés avec une caméra infrarouge. Dans ce travail, on présente une application robotique de la thermographie par courants de Foucault. Une interface robotique a été développée et tous les capteurs utilisés ont été intégrés à la plateforme. Des simulations ont été achevées avec COMSOL Multiphysics en variant différents paramètres. Des expériences ont été menées sur plusieurs spécimens (de différents matériaux) avec des défauts de différents types et tailles. La linescan thermographie est principalement étudiée et d’autres modes d’inspections ont été explorés. Les images résultantes sont reconstruites avec un algorithme dédié. Finalement, les résultats de la méthode sont comparés à ceux de la thermographie optique (par halogène) pour montrer les capacités de la méthode.Eddy current thermography (ECT) is an active thermography method. The inductive excitation generates Eddy currents in electrically-conductive specimen. In a presence of defects, the eddy current flow is affected by these discontinuities leading to changes in the temperature distribution in the specimen around the defects. These changes are observed by an infrared camera. In this work, we present a robotic application of the method. A robotic interface is developed and all the sensors needed are integrated to the platform. Simulations are performed using COMSOL Multiphysics by varying different parameters. Experiments are realised on different specimens (made of different materials) with defects of different sizes. The linescan Eddy current thermography is studied and other modes are explored. The resulting images are reconstructed with a dedicated algorithm. Finally, the method’s results are compared to optical thermography to show the capability of the method

Characterisation and probability of detection analysis of rolling contact fatigue cracks in rails using eddy current pulsed thermography

PhD ThesisWith transportation volumes continuously increasing, railway networks are now facing problems of greater axle loads and increasing vehicle speeds. The most direct consequence is the initiation of rolling contact fatigue (RCF) defects in rails, which have become safety issues for all types of railway systems and received more attention due to lack of timely examination and management. Among different RCF defects, the RCF crack probably presents the biggest hazard in rails. Detection and characterisation of RCF cracks aim to provide detailed guidelines for safety management and preventative grinding. Unfortunately, current nondestructive testing and evaluation techniques are still facing several challenges and research gaps. One outstanding challenge is the characterisation of RCF cracks under their complex geometries and clustered distributions. One major research gap is how to evaluate the probabilistic performance in crack characterisation via a proper framework. By combining the advantages of eddy current pulse excitation and infrared thermography, this thesis proposes the use of eddy current pulsed thermography (ECPT) technique to address the detection and characterisation of RCF cracks in rails. To quantitatively investigate the ECPT’s performance in crack characterisation, a performance evaluation framework based on probability of detection (POD) analysis is proposed. The major contributions of the thesis are summarised as follows: (1) implementations of three-dimensional FEM models and a lab-based ECPT system for investigating the characterisation of RCF cracks under clustered distributions and geometric influences; (2) temporal/spatial-thermal-feature-based ECPT for angular slots and RCF cracks detection and characterisation; (3) investigations into the capability and the performance of ECPT for characterising angular slots and natural RCF cracks via a POD analysis framework. The thesis concludes that the proposed feature-based ECPT system can characterise RCF cracks in both light and moderate stages. Based on feature comparison and POD evaluation, tempo-spatial-based patterns are better fits for pocket length characterisation. Temporal domain-based features show better performances for inclination angle characterisation. A spatial domain-based feature, SST, can characterise vertical depths with reasonable POD values. One tempo-spatial-based pattern at the early heating stage, IET-PCA, gives the best performance for characterising surface lengths. Still, several issues need to be further investigated in future work, such as feature selection for crack characterisation, three-dimensional reconstruction of RCF cracks, model-assisted POD frameworks for improving the effectiveness of POD analysis with a limited number of physical specimens

Automated dynamic inspection using active infrared thermography

Active thermography is a proven technology used in a wide variety of applications. In the most common approach using a static configuration, the elements involved in the inspection do not move. This presents serious drawbacks when it is applied to the inspection of large products and machines. An alternative approach is the dynamic inspection, which enables the inspection of large and complex products with better resolution, but it is also extremely challenging as data reconstruction is necessary. This work analyzes two methods for dynamic inspection using active infrared thermography: the thermal photocopier and the line scan. Automatic robust methods are proposed to calculate the temperature-time history, producing a pseudostatic sequence that can be further processed using advanced data processing algorithms to improve defect detection. Results demonstrate the robustness of the proposed methods and the ability to inspect large products with excellent results.Peer reviewed: YesNRC publication: Ye