Personne :
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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  • Publication
    Restreint
    Low-rank sparse principal component thermography (sparse-PCT) : comparative assessment on detection of subsurface defects
    (Pergamon, 2019-03-18) Maldague, X.; Ibarra Castanedo, Clemente; Sarasini, Fabrizio; Yousefi, Bardia; Sfarra, Stefano
    Infrared Non-destructive Testing (IRNDT) applications are unequivocally expanded and portend a commodity to improve the quality of defect detection in different fields such as aviation and industrial methods to arts and archaeology. The proposed approach focuses on the application of low-rank sparse principal component thermography (Sparse-PCT or SPCT) to assess the advantages and drawbacks of the method for non-destructive testing. For benchmarking the approach, two types of infrared image sets are tested: the Square Pulse Thermography (SPT) method for two hybrid composites (carbon and flax fiber reinforced epoxy), and passive infrared test of Bell Tower and the University of L’Aquila (AQ) faculty’s wall infrared sets. The quantitative assessment of the approach is also compared for every method and indicate considerable segmentation performance where other similar approaches were not able to detect the defects. SPCT performance was compared to some popular decomposition methods such as principal component thermography (PCT), candid covariancefree incremental principal component thermography (CCIPCT), non-negative matrix factorization (NMF) using gradient descent (GD) or non-negative least square (NNLS). The comparative results demonstrate the considerable performance while the other methods failed.
  • Publication
    Accès libre
    Terahertz amplitude polynomial principle component regression for aramid-basalt hybrid composite laminate inspection
    (IEEE, 2018-09-17) Zhang, Hai; Maldague, X.; 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.
  • Publication
    Restreint
    Non-destructive imaging of marqueteries based on a new infrared-terahertz fusion technique
    (Pergamon, 2022-06-25) Avdelidis, Nicolas P.; Hu, Jue; Zhang, Hai; Gargiulo, Gianfranco; Maldague, X.; Sfarra, Stefano; Zhang, Mingli; Yang, Dazhi
    Detection of subsurface defects has hitherto been regarded as an important element in the course of preserving cultural heritage. To do so, non-destructive imaging approaches for viewing and determining the location of splitting inside the sample under test are required, which constitute the subject of the present study. Both active thermography and terahertz imaging have demonstrated their potential in providing non-destructive inspection on cultural heritage objects. Conventionally, active thermography has been used to retrieve details on the defects as well as morphological data from the surface and subsurface, whereas pulsed terahertz imaging has been applied to record the internal material distribution. Here, the feature extraction, selection and fusion framework is extended to design a fusion process to merge the information obtained by both active thermography and terahertz imaging; in this way, the technique naturally inherits the strengths of both aforementioned imaging technologies. The fusion technique is able to produce images with high-contrast defect information located at different depths. To demonstrate the efficacy of the suggested technique, an experiment has been conducted on an ancient marquetry.
  • Publication
    Restreint
    Analysis of damage in hybrid composites subjected to ballistic impacts : an integrated non-destructive approach
    (Wiley, 2017-02-28) Maldague, X.; 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.
  • Publication
    Restreint
    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, X.; 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
  • Publication
    Accès 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, X.; 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.
  • Publication
    Accès libre
    Holographic interferometry (HI), infrared Vision and X-Ray fluorescence (XRF) spectroscopy for the assessment of painted wooden statues : a new integrated approach
    (Springer, 2013-09-03) Maldague, X.; Ibarra Castanedo, Clemente; Ridolfi, Stefano; Sfarra, Stefano; Cerichelli, Giorgio; Ambrosini, Dario; Paoletti, Domenica
    Wood has been routinely employed in decorative arts, as well as in sculptures and paintings (support) during the Middle Ages, because of its unique aesthetic virtues. It may safely be assumed that wood, as a material for monumental sculpture, was much more commonly employed in the mediaeval period than existing examples would seem to indicate (Bulletin of the metropolitan Museum of Art, 2013). Wood is easily obtainable; it could be carved and put in place with less difficulty than stone, it is chemically stable when dry, and its surface offers a compatible substrate for paint application. However, the use of wood is not without pitfalls, and requires an understanding of its anisotropic and hygroscopic nature. It is also dimensionally unstable and subject to deterioration by fungi and insects. Moisture-related dimensional changes are certainly among the most challenging problems in painting conservation. With the purpose of preventing important damages, the use of non-or microdestructive testing (NDT) techniques is undoubtedly of paramount interest for painted wooden statues of great value. This work has a threefold purpose: (1) to validate the effectiveness of an integrated approach using near-infrared (NIR) reflectography, square pulse thermography (SPT), and holographic interferometry (HI) techniques for discovering old repairs and/or inclusions of foreign materials in a wooden structure, (2) to confirm and approximately date the restoration carried out by x-ray fluorescence (XRF) spectroscopy and energy-dispersive x-ray spectroscopy (EDS) (that is assembled with a scanning electron microscopy—SEM) techniques, and (3) to combine into a multidisciplinary approach two quantitative NDT results coming from optical and thermographic methods. The subject of the present study was a statue named “Virgin with her Child” (XIV century), whose origins are mysterious and not properly documented.
  • Publication
    Accès 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, X.; 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.
  • Publication
    Accès 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, X.; 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.
  • Publication
    Accès 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, X.; 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.