Ensemble Joint Sparse Low Rank Matrix Decomposition for Thermography Diagnosis System

Composite is widely used in the aircraft industry and it is essential for manufacturers to monitor its health and quality. The most commonly found defects of composite are debonds and delamination. Different inner defects with complex irregular shape is difficult to be diagnosed by using conventional thermal imaging methods. In this paper, an ensemble joint sparse low rank matrix decomposition (EJSLRMD) algorithm is proposed by applying the optical pulse thermography (OPT) diagnosis system. The proposed algorithm jointly models the low rank and sparse pattern by using concatenated feature space. In particular, the weak defects information can be separated from strong noise and the resolution contrast of the defects has significantly been improved. Ensemble iterative sparse modelling are conducted to further enhance the weak information as well as reducing the computational cost. In order to show the robustness and efficacy of the model, experiments are conducted to detect the inner debond on multiple carbon fiber reinforced polymer (CFRP) composites. A comparative analysis is presented with general OPT algorithms. Not withstand above, the proposed model has been evaluated on synthetic data and compared with other low rank and sparse matrix decomposition algorithms

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

Unsupervised Sparse Pattern Diagnostic of Defects With Inductive Thermography Imaging System

This paper proposes an unsupervised method for diagnosing and monitoring defects in inductive thermography imaging system. The proposed method is fully automated and does not require manual selection from the user of the specific thermal frame images for defect diagnosis. The core of the method is a hybrid of physics-based inductive thermal mechanism with signal processing-based pattern extraction algorithm using sparse greedy-based principal component analysis (SGPCA). An internal functionality is built into the proposed algorithm to control the sparsity of SGPCA and to render better accuracy in sizing the defects. The proposed method is demonstrated on automatically diagnosing the defects on metals and the accuracy of sizing the defects. Experimental tests and comparisons with other methods have been conducted to verify the efficacy of the proposed method. Very promising results have been obtained where the performance of the proposed method is very near to human perception

Comparative study of infrared thermography, ultrasonic C-scan, X-ray computed tomography and terahertz imaging on composite materials

L’évaluation non destructive (NDT) des matériaux composites est compliquée en raison de la vaste gamme de défauts rencontrés (y compris délaminage, microfissuration, fracture de la fibre, retrait des fibres, fissuration matricielle, inclusions, vides et dommages aux chocs). La capacité de caractériser quantitativement le type, la géométrie et l’orientation des défauts est essentielle. La thermographie infrarouge (IRT), en tant que technique de diagnostic d’image, peut satisfaire le besoin industriel croissant de NDT&E. Dans la thèse, la thermographie par excitation optique et mécanique a été utilisée pour étudier différents matériaux composites, dont 1) des préformes sèches en fibres de carbone, 2) des composites de fibres naturelles, 3) des composites hybrides de basalte-fibres de carbone soumis à une charge d’impact (séquence de type sandwich et séquence d’empilement intercalé), 4) des défauts micro-dimensionnés dans un composite polymère renforcé de fibre de carbone (CFRP) en 3D avec une couture de type « joint en T », et 5) des peintures sur toile qui peuvent être considérées comme des matériaux composites. Une nouvelle technique IRT de thermographie de ligne par micro-laser (micro-LLT) a été proposée pour l’évaluation des porosités submillimétriques dans le CFRP. La microscopie de points par micro-laser (micro-LST) et la micro-vibrothermographie (micro-VT) ont également été présentées avec l’utilisation de microlentilles. La thermographie pulsée (PT) et la thermographie modulée « à verrouillage » (LT) ont été comparées à la tomographie par rayons X (TC) pour validation. Le C-scan ultrasonore (UT) et l’imagerie par ondes tera-hertziennes en onde continue (CW THz) ont également été réalisés à des fins comparatives. L’inspection par techniques thermographiques est une question ouverte à discuter pour le public scientifique. En fait, la thermographie par impulsions (PPT) basée sur la transformation de phase a été utilisée pour estimer la profondeur des dommages. Pour traiter les données thermographiques, on a également utilisé la reconstruction de signal thermographique de base (B-TSR), la thermographie des composants principaux (PCT) et la thermographie des moindres carrés partiels (PLST). Enfin, une analyse complète et comparative basée sur le diagnostic d’images thermographiques a été menée en vue d’applications industrielles potentielles.Non-destructive testing (NDT) of composite materials is complicated due to the wide range off laws encountered (including delamination, micro-cracking, fiber fracture, fiber pullout, matrix cracking, inclusions, voids, and impact damage). The ability to quantitatively characterize the type, geometry, and orientation of flaws is essential. Infrared thermography (IRT), as an image diagnostic technique, can satisfy the increasing industrial need for NDT&E. In the thesis, optical and mechanical excitation thermography were used to investigate different composite materials, including 1) carbon fiber dry preforms, 2) natural fiber composites, 3) basalt-carbon fiber hybrid composites subjected to impact loading (sandwich-like and intercalated stacking sequence), 4) micro-sized flaws in a stitched T-joint 3D carbon fiber reinforced polymer composite (CFRP), and 5) paintings on canvas which can be considered as composite materials. Of particular interest, a new IRT technique micro-laser line thermography (micro-LLT) was proposed for the evaluation of submillimeter porosities in CFRP. Micro-laser spot thermography (micro-LST) and micro-vibrothermography (micro-VT) were also presented with the usage of a micro-lens. Pulsed thermography (PT) and lock-in thermography (LT) were compared with x-ray computed tomography (CT) for validation. Ultrasonic C-scan (UT) and continuous wave terahertz imaging (CW THz) were also conducted for the comparative purpose. The inspection by thermographic techniques is an open matter to be discussed for the scientific audience. In fact, pulse phase thermography (PPT) based on phase transform was used to estimate the damage depth. Basic thermographic signal reconstruction (B-TSR), principal component thermography (PCT) and partial least squares thermography (PLST) (another more recent advanced image processing technique) were also used to pro-cess the thermographic data. Finally, a comprehensive and comparative analysis based on thermographic image diagnostics was conducted in view of potential industrial applications

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