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Sfarra, Stefano

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Sfarra

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Stefano

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Université Laval. Département de génie électrique et de génie informatique

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ncf11899554

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Résultats de recherche

Voici les éléments 1 - 10 sur 36
  • PublicationAccès libre
    Thermographic non-destructive evaluation for natural fiber-reinforced composite laminates
    (Basel : MDPI, 2018-02-05) Avdelidis, Nicolas P.; Zhang, Hai; Sarasini, Fabrizio; Maldague, Xavier; Santulli, Carlo; Ibarra Castanedo, Clemente; Sfarra, Stefano; Fernandes, Henrique
    Natural fibers, including mineral and plant fibers, are increasingly used for polymer composite materials due to their low environmental impact. In this paper, thermographic non-destructive inspection techniques were used to evaluate and characterize basalt, jute/hemp and bagasse fibers composite panels. Different defects were analyzed in terms of impact damage, delaminations and resin abnormalities. Of particular interest, homogeneous particleboards of sugarcane bagasse, a new plant fiber material, were studied. Pulsed phase thermography and principal component thermography were used as the post-processing methods. In addition, ultrasonic C-scan and continuous wave terahertz imaging were also carried out on the mineral fiber laminates for comparative purposes. Finally, an analytical comparison of different methods was given.
  • PublicationAccès 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, Maria
    Nondestructive 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.
  • PublicationRestreint
    Evaluation of the state of conservation of mosaics : simulations and thermographic signal processing
    (Ed. scientifiques et médicales Elsevier, 2017-04-13) Avdelidis, Nicolas P.; Zhang, Hai; Theodorakeas, Panagiotis; Maldague, Xavier; Ibarra Castanedo, Clemente; Perilli, Stefano; Sfarra, Stefano; Nardi, Iole; Koui, Maria
    Nondestructive 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.
  • PublicationAccès libre
    Non-destructive investigation of paintings on canvas by continuous wave terahertz imaging and flash thermography
    (Springer, 2017-04-05) Avdelidis, Nicolas P.; Fleuret, Julien; Saluja, Karan; Zhang, Hai; Peeters, Jeroen; Maldague, Xavier; Ibarra Castanedo, Clemente; Duan, Yuxia; Sfarra, Stefano; Fernandes, Henrique
    Terahertz (THz) imaging is increasingly used in the cultural heritage field. In particular, continuous wave (CW) and low frequency THz is attracting more attention. The first application of the THz technique inherent to the cultural heritage field dates back 10 years ago. Since 2006, tangible improvements have been conducted in the refinement of the technique, with the aim to produce clear maps useful for any art restorer. In this paper, a CW THz (0.1 THz) imaging system was used to inspect paintings on canvas both in reflection and in transmission modes. In particular, two paintings were analyzed: in the first one, similar materials and painting execution of the original artwork were used, while in the second one, the canvas layer is slightly different. Flash thermography was used herein together with the THz method in order to observe the differences in results for the textile support materials. A possible application of this method for the detection of artwork forgery requires some parameterization and analysis of various materials or thickness influence which will be addressed in a future study. In this work, advanced image processing techniques including principal component thermography (PCT) and partial least squares thermography (PLST) were used to process the infrared data. Finally, a comparison of CW THz and thermographic results was conducted.
  • PublicationRestreint
    Robust quantitative depth estimation on CFRP samples using active thermography inspection and numerical simulation updating
    (Elsevier, 2017-02-14) Peeters, Jeroen; Maldague, Xavier; Ibarra Castanedo, Clemente; Sfarra, Stefano; Dirckx, Joris; Steenackers, Gunther
    A quantitative evaluation of delaminations in composite laminates encounters multiple difficulties due to the anisotropic behaviour of the laminate. Extensive calibrations for each structure are required and each depth needs certain manual modifications for optimal performance of the estimation routines. In this manuscript, a robust technique is developed using a numerical model to estimate the thermal diffusivity through the anisotropic material which improves defect depth estimation between each layer. Three different calibration depths are necessary to compute the diffusivity through a certain stacking sequence of a multi-layered composite laminate. The results are compared with the state-of-the-arts experimental evaluation techniques and with a regular numerical model. It is seen that especially for deeper defects, the optimised numerical model delivers more accurate results due to the considered anisotropic diffusivity.
  • PublicationAccès libre
    Thermography data fusion and non-negative matrix factorization for the evaluation of cultural heritage objects and buildings
    (Springer, 2018-08-24) Avdelidis, Nicolas P.; Maldague, Xavier; Ibarra Castanedo, Clemente; Yousefi, Bardia; Sfarra, Stefano
    The application of the thermal and infrared technology in different areas of research is considerably increasing. These applications involve nondestructive testing, medical analysis (computer aid diagnosis/detection—CAD), and arts and archeology, among many others. In the arts and archeology field, infrared technology provides significant contributions in terms of finding defects of possible impaired regions. This has been done through a wide range of different thermographic experiments and infrared methods. The proposed approach here focuses on application of some known factor analysis methods such as standard nonnegative matrix factorization (NMF) optimized by gradient-descent-based multiplicative rules (SNMF1) and standard NMF optimized by nonnegative least squares active-set algorithm (SNMF2) and eigen-decomposition approaches such as principal component analysis (PCA) in thermography, and candid covariance-free incremental principal component analysis in thermography to obtain the thermal features. On the one hand, these methods are usually applied as preprocessing before clustering for the purpose of segmentation of possible defects. On the other hand, a wavelet-based data fusion combines the data of each method with PCA to increase the accuracy of the algorithm. The quantitative assessment of these approaches indicates considerable segmentation along with the reasonable computational complexity. It shows the promising performance and demonstrated a confirmation for the outlined properties. In particular, a polychromatic wooden statue, a fresco, a painting on canvas, and a building were analyzed using the above-mentioned methods, and the accuracy of defect (or targeted) region segmentation up to 71.98%, 57.10%, 49.27%, and 68.53% was obtained, respectively.
  • PublicationRestreint
    Infrared vision : visual inspection beyond the visible spectrum
    (Springer, 2015-09-25) Maldague, Xavier; Ibarra Castanedo, Clemente; Genest, Marc; Sfarra, Stefano
    Infrared (IR) vision for the nondestructive testing (NDT) of materials has considerably grown in the last few years as a results of the continual technological progress and the development of advanced signal processing techniques. Typical applications can be divided into two groups: (1) reflectography/transmittography in the near (NIR) and short-wave (SWIR) infrared spectra, which have been recently applied in the inspection of semitransparent composite materials such as glass, aramid–phenolic, and a variety of natural fibers; and (2) infrared thermography, which involves the detection of surface and subsurface defects based on the differences in thermal signatures in the mid-wave (MWIR) and long-wave (LWIR) infrared bands. Infrared reflectography and thermography have shown interesting complementarities between them as well as with other NDT methods such as ultrasound testing, eddy current testing, and holographic interferometry. In this chapter, a review of classical and recent applications of infrared vision is provided and discussed in detail with examples.
  • PublicationRestreint
    Analysis of damage in hybrid composites subjected to ballistic impacts : an integrated non-destructive approach
    (Wiley, 2017-02-28) Maldague, Xavier; López, Fernando; Ibarra Castanedo, Clemente; Sarasini, Fabrizio; Sfarra, Stefano; Tirillò, Jacopo; Ferrante, Lucas; Perilli, Stefano; Paoletti, Domenica; Lampani; Barbero, Ever J.; Sánchez-Sáez
    In this chapter infrared (IR) vision has been used as non-destructive testing (NDT) method for the detection of damage occurred in hybrid composites subjected to high velocity impacts. In particular, carbon and basalt fibers have been used in the fabrication of the laminates with an intercalated and a sandwich-like structure. Near-infrared reflectography (NIRR) and infrared thermography (IRT) techniques have shown interesting complementarities, as well as the integrated image processing by using advanced algorithms, such as Partial-Least Square Thermography (PLST) and Principal Component Thermography (PCT). The laminates have been subjected to a long square pulse in order to make possible the acquisition of both the heating and the cooling phases, while the prediction of the damage due to the impacts has been evaluated by finite element (FE) analysis. Preliminary results inherent to the numerical simulation approach are reported. Finally, the damage state has been compared with a detailed fractographic analysis of the laminates’ cross-sections, and qualitatively estimated by segmentation algorithms, thus confirming the potential of the proposed integrated approach.
  • PublicationRestreint
    The use of flax fiber reinforced polymer (FFRP) composites in the externally reinforced structures for seismic retrofitting monitored by transient thermography and optical techniques
    (Wiley, 2017-03-01) Maldague, Xavier; Ibarra Castanedo, Clemente; Paoletti, Domenica; Bendada, Abdelhakim; Sfarra, Stefano
    Natural fibers constitute an interesting alternative to synthetic fibers for the production of composites due to their environmental and economic advantages. Even though their strength is on average lower compared to their synthetic counterparts, natural fibers such as flax, among other bast fibers (jute, kenaf, ramie, and hemp), are serious candidates for seismic retrofitting applications given that their mechanical properties are more suitable for dynamic loads. Strengthening of structures is performed by impregnating flax fiber reinforced polymers (FFRP) fabrics with epoxy resin and applying them to the component of interest, increasing in this way the load and deformation capabilities of the building, while preserving its stiffness and dynamic properties. The reinforced areas are however prompt to debonding if the fabrics are not properly mounted. Nondestructive testing is therefore required to verify that the fabric is installed uniformly and that there are no air gaps or foreign materials that could instigate debonding. In this Chapter, the use of active infrared thermography was investigated for the assessment of a laboratory specimen with artificial defects, an actual FFRP retrofitted beam, and a part of an external masonry wall. Results coming from the academic specimen were compared to digital speckle photography and holographic interferometry images
  • PublicationRestreint
    Solar loading thermography : time-lapsed thermographic survey and advanced thermographic signal processing for the inspection of civil engineering and cultural heritage structures
    (Elsevier, 2017-05-01) Maldague, Xavier; Klein, Matthieu; Ibarra Castanedo, Clemente; Sfarra, Stefano
    The experimental results from infrared thermography surveys over two buildings externally exposed walls are presented. Data acquisition was performed on a static configuration by recording direct and indirect solar loading during several days and was processed using advanced signal processing techniques in order to increase signal-to-noise ratio and signature contrast of the elements of interest. It is demonstrated that it is possible to detect the thermal signature of large internal structures as well as surface features under such thermographic scenarios. Results from a long-wave microbolometer compared favorably to those from a mid-wave cooled infrared camera for the detection of large subsurface features from unprocessed images. In both cases, however, advanced signal processing greatly improved contrast of the internal features.