Personne :
Zhang, Hai

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Zhang
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Hai
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Université Laval. Laboratoire de vision et systèmes numériques
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2015 - 201828
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Résultats de recherche

Voici les éléments 1 - 10 sur 28
  • Publication
    Restreint
    Qualitative assessments via infrared vision of sub-surface defects present beneath decorative surface coatings
    (Springer, 2017-11-24) Lopez Rodriguez, Fernando; Zhang, Hai; Maldague, X.; Ibarra Castanedo, Clemente; Sfarra, Stefano; Fernandes, Henrique
    In this work, the potentialities of the infrared vision to explore sub-superficial defects in polychromatic statues were investigated. In particular, it was possible to understand how the reflector effect of the exterior golden layers could be minimized, applying advanced statistical algorithms to thermal images. Since this noble metal is present as external coating in both artworks, an in-depth discussion concerning its physicochemical properties is also added. In this context, the principal component thermography technique and, the more recent, partial least squares thermography technique were used on three different datasets recorded, providing long thermal stimuli. The main images were compared both to phasegrams and to the thermographic signal reconstruction results in order to have a clear outline of the situation to be debated. The effects of view factors on the radiation transfer linked to the specular reflections from the surface did not falsely highlight certain features inadvertently. Indeed, the raw thermograms were analyzed one by one. Reflectograms were used to pinpoint emissivity variations due to, e.g., possible repainting. The paper concludes that, as it is possible to understand from a physical point of view, the near-infrared reflectography technique is able to examine the state of conservation of the upper layers in cultural heritage objects, while the infrared thermography technique explores them more in-depth. The thesis statement is based on the thermal and nonthermal parts of the infrared region, therefore, indicating what can be detected by heating the surface and what can be visualized by illuminating the surface, bearing in mind the nature of the external coating.
  • Publication
    Restreint
    Optimised Dynamic line scan thermographic detection of CFRP inserts using FE updating and POD analysis
    (Elsevier, 2017-10-20) Peeters, Jeroen; Mokhtari, Mohammed-Yacine; Zhang, Hai; Maldague, X.; Ibarra Castanedo, Clemente; Khodayar, Fariba; Sfarra, Stefano; Dirckx, Joris; Steenackers, Gunther
    The detection of delaminations in composite laminates using automated thermographic scanning is a quite challenging task. The set-up parameters are not only dependent on the equipment, but on the inspected component as well. In this work, a methodology is discussed to use Finite Element (FE) model updating to automatically establish the most suitable inspection parameters for a given combination of the structure and the investigated delamination depths. The optimised results are compared using binary Probability of Detection analysis and are benchmarked with parameter sets retrieved by an expert using the regular trial & error approach. The results show an improvement of the accuracy and scanning speed which significantly increases as the POD decreases and the complexity of the samples increases.
  • Publication
    Accès libre
    Comparative study of microlaser excitation thermography and microultrasonic excitation thermography for submillimeter porosity in carbon fiber reinforced polymer composites
    (Society of Photo-optical Instrumentation Engineers, 2016-09-30) Zhang, Hai; Maldague, X.; Hassler, Ulf; Ibarra Castanedo, Clemente; Robitaille, François; Genest, Marc; Fernandes, Henrique; Joncas, Simon
    Stitching is used to reduce incomplete infusion of T-joint core (dry-core) and reinforce T-joint structure. However, it may cause new types of flaws, especially submillimeter flaws. Thermographic approaches including microvibrothermography, microlaser line thermography, and microlaser spot thermography on the basis of pulsed and lock-in techniques were proposed. These techniques are used to detect the submillimeter porosities in a stitched T-joint carbon fiber reinforced polymer composite specimen. X-ray microcomputed tomography was used to validate the thermographic results. Finally an experimental comparison of microlaser excitation thermography and microultrasonic excitation thermography was conducted.
  • Publication
    Accès libre
    Pulsed micro-laser line thermography on submillimeter porosity in carbon fiber reinforced polymer composites : experimental and numerical analyses for the capability of detection
    (Optical Society of America, 2016-08-08) Fleuret, Julien; Zhang, Hai; Maldague, X.; Hassler, Ulf; Ibarra Castanedo, Clemente; Robitaille, François; Djupkep Dizeu, Frank Billy; Genest, Marc; Fernandes, Henrique; Joncas, Simon
    In this article, pulsed micro-laser line thermography (pulsed micro-LLT) was used to detect the submillimeter porosities in a 3D preformed carbon fiber reinforced polymer composite specimen. X-ray microcomputed tomography was used to verify the thermographic results. Then, finite element analysis was performed on the corresponding models on the basis of the experimental results. The same infrared image processing techniques were used for the experimental and simulation results for comparative purposes. Finally, a comparison of experimental and simulation postprocessing results was conducted. In addition, an analysis of probability of detection was performed to evaluate the detection capability of pulsed micro-LLT on submillimeter porosity.
  • Publication
    Accès libre
    An experimental and analytical study of micro-laser line thermography on micro-sized flaws in stitched carbon fiber reinforced polymer composites
    (Elsevier, 2016-04-01) Sheng, Yunlong; Yu, Ling Yao; Hassler, Ulf; Zhang, Hai; Maldague, X.; Robitaille, François; Genest, Marc; Joncas, Simon; Fernandes, Henrique; Holub, Wolfgang
    Stitching is used to reduce incomplete infusion of T-joint core (dry-core) and reinforce T-joint structure. However, it might cause new types of flaws, especially micro-sized flaws. In this paper, a new micro-laser line thermography (micro-LLT) is presented. X-ray micro-computed tomography (micro-CT) was used to validate the infrared results. The micro-LLT and micro-CT inspection are compared. Then, a finite element analysis (FEA) is performed. The geometrical model needed for finite element discretization was developed from micro-CT measurements. The model is validated for the experimental results. Finally a comparison of the experiments and simulation is conducted. The infrared experimental phenomenon and results are explained based on the FEA results
  • Publication
    Accès libre
    Comparative study on submillimeter flaws in stitched T-joint carbon fiber reinforced polymer by infrared thermography, microcomputed tomography, ultrasonic c-scan and microscopic inspection
    (Society of Photo-optical Instrumentation Engineers., 2015-10-15) Zhang, Hai; Hassler, Ulf; Maldague, X.; Ibarra Castanedo, Clemente; Robitaille, François; Genest, Marc; Fernandes, Henrique; Joncas, Simon
    Stitching is used to reduce dry-core (incomplete infusion of T-joint core) and reinforce T-joint structure. However, it may cause new types of flaws, especially submillimeter flaws. Microscopic inspection, ultrasonic c-scan, pulsed thermography, vibrothermography, and laser spot thermography are used to investigate the internal flaws in a stitched T-joint carbon fiber-reinforced polymer (CFRP) matrix composites. Then, a new microlaser line thermography is proposed. Microcomputed tomography (microCT) is used to validate the infrared results. A comparison between microlaser line thermography and microCT is performed. It was concluded that microlaser line thermography can detect the internal submillimeter defects. However, the depth and size of the defects can affect the detection results. The microporosities with a diameter of less than 54  μm are not detected in the microlaser line thermography results. Microlaser line thermography can detect the microporosity (a diameter of 0.162 mm) from a depth of 90  μm. However, it cannot detect the internal microporosity (a diameter of 0.216 mm) from a depth of 0.18 mm. The potential causes are given. Finally, a comparative study is conducted.
  • Publication
    Accès libre
    Automated assessment and tracking of human body thermal variations using unsupervised clustering
    (The Optical Society of America, 2016-11-17) Fleuret, Julien; Zhang, Hai; Maldague, X.; Yousefi, Bardia; Watt, Raymond; Klein, Matthieu
    The presented approach addresses a review of the overheating that occurs during radiological examinations, such as magnetic resonance imaging, and a series of thermal experiments to determine a thermally suitable fabric material that should be used for radiological gowns. Moreover, an automatic system for detecting and tracking of the thermal fluctuation is presented. It applies hue-saturated-value-based kernelled k-means clustering, which initializes and controls the points that lie on the region-of-interest (ROI) boundary. Afterward, a particle filter tracks the targeted ROI during the video sequence independently of previous locations of overheating spots. The proposed approach was tested during experiments and under conditions very similar to those used during real radiology exams. Six subjects have voluntarily participated in these experiments. To simulate the hot spots occurring during radiology, a controllable heat source was utilized near the subject’s body. The results indicate promising accuracy for the proposed approach to track hot spots. Some approximations were used regarding the transmittance of the atmosphere, and emissivity of the fabric could be neglected because of the independence of the proposed approach for these parameters. The approach can track the heating spots continuously and correctly, even for moving subjects, and provides considerable robustness against motion artifact, which occurs during most medical radiology procedures.
  • Publication
    Accès libre
    Experimental evaluation of pulsed thermography, lock-in thermography and vibrothermography on foreign object defect (FOD) in CFRP
    (Molecular Diversity Preservation International (MDPI), 2016-05-21) Liu, Bin; Zhang, Hai; Maldague, X.; Fernandes, Henrique
    In this article, optical excitation thermographic techniques, including pulsed thermography and lock-in thermography, were used to detect foreign object defect (FOD) and delamination in CFRP. Then, vibrothermography as an ultrasonic excitation technique was used to detect these defects for the comparative purposes. Different image processing methods, including cold image subtraction (CIS), principal component thermography (PCT), thermographic signal reconstruction (TSR) and Fourier transform (FT), were performed. Finally, a comparison of optical excitation thermography and vibrothermography was conducted, and a thermographic probability of detection was given.
  • Publication
    Accès libre
    Weak magnetic flux leakage : a possible method for studying pipeline defects located either inside or outside the structures
    (Butterworth-Heinemann, 2015-06-04) Liu, Bin; Zhang, Hai; Cao, Y.; Lin, Y. R.; Sun, W. R.; Xu, B.
    Magnetic leakage distribution results from linear defects of oil–gas pipelines in a weak magnetic field, which is modeled by the magnetic dipole theory. The analysis is useful for the identification of defects located either inside or outside the pipelines. The results indicate that the radial signals of inside–outside defects can be clearly distinguished, and the axial signals are basically the same in a weak magnetic field. The theoretical and the experimental results are very consistent.
  • Publication
    Accès libre
    Carbon fiber composites inspection and defect characterization using active infrared thermography : numerical simulation and experimental results
    (Optical Society of America, 2016-09-23) Zhang, Hai; Maldague, X.; Figueiredo, Alisson; Ibarra Castanedo, Clemente; Fernandes, Henrique; Guimarares, Gilmar
    Composite materials are widely used in the aeronautic industry. One of the reasons is because they have strength and stiffness comparable to metals, with the added advantage of significant weight reduction. Infrared thermography (IT) is a safe nondestructive testing technique that has a fast inspection rate. In active IT, an external heat source is used to stimulate the material being inspected in order to generate a thermal contrast between the feature of interest and the background. In this paper, carbon-fiber-reinforced polymers are inspected using IT. More specifically, carbon/PEEK (polyether ether ketone) laminates with square Kapton inserts of different sizes and at different depths are tested with three different IT techniques: pulsed thermography, vibrothermography, and line scan thermography. The finite element method is used to simulate the pulsed thermography experiment. Numerical results displayed a very good agreement with experimental results.