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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ncf11735155
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Publication Accès libre Evaluation of the state of conservation of mosaics: Simulations and thermographic signal processing(Elsevier, 2017-04-13) Avdelidis, Nicolas P.; Zhang, Hai; Theodorakeas, Panagiotis; Maldague, Xavier; Ibarra Castanedo, Clemente; Perilli, Stefano; Sfarra, Stefano; Nardi, Iole; Koui, MariaNondestructive inspection of mosaic structures is not a novelty in the thermographic scene. Interesting works can be retrieved from scientific literature, some of them dedicated to the use of static active configurations and/or the passive approach for the inspection of plastered mosaics or the assessment of mosaic floors. In the present study, a mosaic made by synthetic tesserae of different colors depicting a dove was inspected by active thermography using a static configuration. The mosaic was manufactured with artificial defects positioned at several depths and locations, where some of them, due to their dynamic nature, enabled the monitoring of their thermal effects over time. In particular, the mosaic contains: a void into which compressed air can be injected, a sponge insert that can be soaked by a known quantity of water through an external tube, and a sub-superficial recirculation circuit from which a stream of cold or hot water can flow. The variability of the nature of these defects, simulating what happens in a real case, was conveniently modeled by numerical simulation approaches. The latter point was assessed through the aid of a simulation software, while the comparison of the results obtained by numerical analysis with those derived by thermographic testing was also performed.Publication Accès libre Enhanced infrared image processing for impacted carbon/glass fiber-reinforced composite evaluation(Molecular Diversity Preservation International (MDPI), 2017-12-26) Avdelidis, Nicolas P.; Zhang, Hai; Osman, Ahmad; Maldague, Xavier; Ibarra Castanedo, Clemente; Sfarra, Stefano; Fernandes, Henrique; Matikas, Theodore E.In this paper, an infrared pre-processing modality is presented. Different from a signal smoothing modality which only uses a polynomial fitting as the pre-processing method, the presented modality instead takes into account the low-order derivatives to pre-process the raw thermal data prior to applying the advanced post-processing techniques such as principal component thermography and pulsed phase thermography. Different cases were studied involving several defects in CFRPs and GFRPs for pulsed thermography and vibrothermography. Ultrasonic testing and signal-to-noise ratio analysis are used for the validation of the thermographic results. Finally, a verification that the presented modality can enhance the thermal image performance effectively is provided.Publication Accès libre An active infrared thermography method for fiber orientation assessment of fiber-reinforced composite materials(Pergamon, 2015-08-28) Zhang, Hai; Maldague, Xavier; Fernandes, HenriqueFiber orientation in composite materials is an important feature since the arrangement or orientation of the fibers relative to one another has a significant influence on the strength and other properties of fiber reinforced composites. In this paper we present a method to assess the fiber orientation on the surface of carbon fiber reinforced polymer (CFRP) laminates. More specifically, a diode-laser beam is used to locally heat a small spot on the surface of the sample. Observation of the heat pattern in the infrared spectrum enables the assessment of the fiber orientation. Different samples and different regions on the surface of the samples are tested in order to estimate the precision of the method.