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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 18
  • 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.
  • 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.
  • PublicationAccès 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.
  • PublicationAccès libre
    Monitoring of jute/hemp fiber hybrid laminates by nondestructive testing techniques
    (De Gruyter, 2014-11-28) Maldague, Xavier; Ibarra Castanedo, Clemente; Santulli, Carlo; Sfarra, Stefano; Paoletti, Domenica
    Damage following static indentation of jute/hemp (50 wt.% total fiber content) hybrid laminates was detected by a number of nondestructive testing (NDT) techniques, in particular, near (NIR) and short-wave (SWIR) infrared reflectography and transmittography, infrared thermography (IRT), digital speckle photography (DSP), and holographic interferometry (HI), to discover and evaluate real defects in a laminate with a complex structure. A comparative study between thermographic data acquired in the mid- (MWIR) and long-wave infrared (LWIR) spectrum bands, by pulsed (PT) and square pulse (SPT) thermography, is reported and analyzed. A thermal simulation by COMSOL® Multiphysics (COMSOL Inc., Burlington, MA, USA) to validate the heating provided is also added. The robust SOBI (SOBI-RO) algorithm, available into the ICALAB Toolbox (BSI RIKEN ABSP Lab, Hirosawa, Japan) and operating in the MATLAB® (The MathWorks, Inc., Natick, MA, USA) environment, was applied on SPT data with results comparable to the ones acquired by several thermographic techniques. Finally, segmentation operators were applied both to the NIR/SWIR transmittography images and to a characteristic principal component thermography (PCT) image (EOFs) to visualize damage in the area surrounding indentation.
  • PublicationAccès libre
    Terahertz amplitude polynomial principle component regression for aramid-basalt hybrid composite laminate inspection
    (IEEE, 2018-09-17) Zhang, Hai; Maldague, Xavier; Osman, Ahmad; Sfarra, Stefano; Szielasko, Klaus; Stumm, Christopher; Sarasini, Fabrizio; Santulli, Carlo
    As an emerging non-destructive diagnostic and monitoring technique, terahertz time-domain spectroscopy (THz-TDS) imagery is attracting more attention. In this regard, new THz image processing algorithms based on infrared thermography (IRT) concepts are greatly needed, since most IRT imagery modalities are fast for in-line industrial inspection. However, this scenario is difficult due to some phisical constraints to be reached, although this idea should be followed to avoid the loss of useful information during image processing. In this paper, a novel THz amplitude polynomial principle component regression (APPCR) algorithm is proposed for the inspection of aramid-basalt hybrid composite laminates. This algorithm segments THz amplitude-frequency curves to simulate heatingup and cooling-down behaviors as in IRT; in addition, it uses an empirical orthogonal functions-based principle component regression modality to simplify the THz image analysis procedure. This experimental and analytical study shows that APPCR can: 1) simplify the THz image analysis procedure, and 2) enhance image contrast and spatial resolution. A theoretical analysis was conducted as experimental explanation, while the IRT imagery results were used for comparative purposes. In addition, signalto-noise ratio analysis was used to evaluate quantitatively the image enhancement. Finally, it is possible to conclude that THz is more suitable to inspect transparent or semi-transparent materials. Advantages and disadvantages of THz-TDS and IRT are summarized into the text.
  • PublicationAccès libre
    The multi-dimensional ensemble empirical mode decomposition (MEEMD) : an advanced tool for thermographic diagnosis of mosaics
    (Kluwer Academic Publishers, 2017-01-12) Yao, Yuan; Maldague, Xavier; Ibarra Castanedo, Clemente; Sfarra, Stefano; You, Renchun
    With a view to map the health status of mosaics, non-destructive testing methods ought to be used for data collection. Among these, the infrared thermography is highly recommended since it is non-contact, non-intrusive, non-invasive and able to convert the invisible thermal energy, into a video signal, in which the energy level are usually correlated to a color or a gray scale. The need to provide the position of sub-superficial defects in the clear way is of paramount importance when the diagnostician is not the final client. In the cultural heritage field, raw thermograms, sometimes, do not provide interesting results for the restorer, since they are affected by an undesirable content of noise that limits the detection of what is present beneath the surface. In this work, the multi-dimensional ensemble empirical mode decomposition (MEEMD) technique was used – to the best of our knowledge for the first time – as regards to the thermographic diagnosis of mosaics. It seems to overcoming the thermal barrier of the tessellatum layer, composed by aggregates of different natures, as typical in the Roman era. The results obtained after the inspection via a very long pulse are encouraging, above all whether compared with other algorithms applied in the recent past. The use of intelligent sensors placed inside and outside the mosaic sample, which measured the temperature evolution along the heating up and cooling down phases, helped in the understanding the optimal heat flux to be provided.
  • PublicationAccès libre
    Santa Maria di Collemaggio Church (L’Aquila, Italy) : historical reconstruction by non-destructive testing techniques
    (Taylor and Francis, 2014-02-28) Maldague, Xavier; Ibarra Castanedo, Clemente; Bendada, Abdelhakim; Ambrosini, Dario; Sfarra, Stefano; Paoletti, Domenica
    The main goal of this work was the non-destructive testing (NDT) of an ancient fresco (15th century) preserved in the Santa Maria di Collemaggio Church (L’Aquila, Italy) and damaged after the 2009 earthquake. Active infrared thermography (IRT), near-infrared (NIR) reflectography and ultraviolet imaging (UV) were used. In addition, the state of the fresco prior to the earthquake was analyzed by electronic speckle pattern interferometry (ESPI), digital speckle correlation (DSC), raking light, tap, and chemical NDT techniques. The use of these techniques was important for the monitoring of new damages and for a comparison between the results over the years. Square heating thermography (SHT) data were processed using principal component thermography (PCT) and pulsed phase thermography (PPT) algorithms, in order to improve the defects’ signature and to reduce the impact of non-uniform heating and emissivity variations due to the painting’s pigments. A multi-analysis approach, segmentation operators and a specific data correlation method emphasize the overall study of the fresco. Furthermore, the facade and the high altar area were inspected by passive thermography and ground-penetrating radar (GPR), respectively. In the present case, the combined use of NDT techniques was useful to fill in the gaps in the construction history of the building.
  • PublicationAccès libre
    Evaluation of defects in panel paintings using infrared, optical and ultrasonic techniques
    (British Institute of Non-Destructive Testing, 2012-01-01) Avdelidis, Nicolas P.; Theodorakeas, Panagiotis; Maldague, Xavier; Ibarra Castanedo, Clemente; Bendada, Abdelhakim; Paoletti, Alfonso; Sfarra, Stefano; Paoletti, Domenica; Hrissagis, Kostas; Koui, Maria
    The increasing deterioration of panel paintings can be due to physical processes that take place during exhibition or transit, or as a result of temperature and humidity fluctuations within a building, church or museum. In response to environmental alterations, a panel painting can expand or contract and a new equilibrium state is eventually reached. These adjustments though, are usually accompanied by a change in shape in order to accommodate to the new conditions. In this work, a holographic method for detecting detached regions and micro-cracks is described. Some of these defects are confirmed by Thermographic Signal Reconstruction (TSR) technique. In addition, Pulsed Phase Thermography (PPT) and Principal Component Thermography (PCT) allow to identify with greater contrast two artificial defects in Mylar which are crucial to understand the topic of interest: the discrimination between defect materials. Finally, traditional contact ultrasounds applications, are widely applied for the evaluation of the wood quality in several characterization procedures. Inspecting the specimen from the front side, the natural and artificial defects of the specimen are confirmed. Experimental results derived by the application of the integrated methods on an Italian panel painting reproduction, called The Angel specimen, are presented. The main advantages that these techniques can offer to the conservation and restoration of artworks are emphasized.
  • PublicationAccès libre
    Surface and subsurface defects detection in impacted composite materials made by natural fibers, using nondestructive testing methods
    (Scientific & Academic Publishing, 2014-01-01) Avdelidis, Nicolas P.; Maldague, Xavier; Ibarra Castanedo, Clemente; Santulli, Carlo; Bendada, Abdelhakim; Theodorakeas, Panagiotis; Sfarra, Stefano; Paoletti, Domenica; Koui, Maria
    In the present study, infrared vision and optical nondestructive testing (NDT) techniques were applied for the evaluation of emerging defects after artificially impacting composite materials reinforced with natural fibers. The samples were manufactured using wool felts and jute fibers inserted in an epoxy matrix. Infrared vision was applied by means of pulsed thermography (PT) and square pulsed thermography (SPT), evaluating two different thermal stimulation procedures; while the algorithms referred to as principal component thermography (PCT) and pulsed phase thermography (PPT) were used in order to enhance the information retrieval from the respective thermographic inspections. For comparison purposes, near-infrared reflectography (NIRR) and transmittography (NIRT), as well as laser speckle imaging techniques were also included. Additionally, ultraviolet (UV) imaging technique was used on the laminates both as complementary approach and as reference for future inspections. Two particular zones highlighted by the latter technique were characterized using an XRF spectrophotometer revealing a reverse concentration of the Al, Si and Cl elements. The results produced from the above comparative study confirmed the synergy of the applied techniques and further indicated that the methodology followed in the present research work can be considered as an innovative approach for the characterization of eco-friendly laminates after an impact loading.
  • PublicationAccès libre
    How to reveal subsurface defects in Kevlar® composite materials after an impact loading using infrared vision and optical NDT techniques?
    (Elsevier, 2013-03-07) Talmy, Étienne; Maldague, Xavier; Ibarra Castanedo, Clemente; Paoletti, Domenica; Bendada, Abdelhakim; Genest, Marc; Rott, Sébastien; Sfarra, Stefano
    An integrated system between infrared vision and optical non-destructive testing techniques can be considered a viable, robust and reliable approach for both aerospace manufacturing and in-service inspections. In this paper, infrared vision is applied in different spectral bands on two impacted panels made of aramid–phenolic composite by applying two different methods, respectively: (1) near and short-wave infrared reflectography and transmittography, and (2) mid-wave active infrared thermography. Furthermore, optical methods, namely digital speckle photography and holographic interferometry, are used as well to highlight the damages due to the impacts on the samples. Some techniques provide more straightforward detection capabilities than others for different defect types.