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Carbon Fiber Reinforced Polymers (CFRPs) have been increasingly employed for structural strengthening, and are attached to structures using bonding adhesives. The aim of this work is to characterize defects in the bond between CFRP and concrete (after they are located by pulse infrared thermography), and assign the defects a “numerical value” (ranging from 0 for a complete air–gap to 1 for a fully glued bond). Quantitative characterization is performed by measuring the thermal impedance, and then identifying the thermophysical parameters of the system through fitting the measured impedance to a theoretical model. An inversion procedure is carried out to estimate the unknown parameters, without prior knowledge of sample properties. In particular, it is possible to estimate more accurately both the amount of glue within a defect and the thermal contact resistance.

This paper presents a NDT by infrared thermography with excitation CO2 Laser, wavelength of 10.6 μm. This excitation is the controllable heating beam, confirmed by a preliminary test on a wooden plate 1.2 m x 0.9 m x 1 cm. As the first practice, this method is applied to detecting the defect in CFRP heated by the Laser 300 W during 40 s. Two samples 40 cm x 40 cm x 4.5 cm are prepared, one with defect, another one without defect. The laser beam passes through the lens of a deviation device, and heats the samples placed at a determinate position and area. As a result, the absence of adhesive can be detected. This method displays prominently its application as NDT with the composite materials. This work gives a good perspective to characterize the laser beam, which is very useful for the next detection campaigns., {"references":["Ch. Maierhofer, A. Brink, M. Röllig, H. Wiggenhauser, \"Transient thermography for structural investigation of concrete and composites in the near surface region,\" Infrared Physics & Technology, vol. 43, pp. 271-278, 2002.","Jeff R. Brown, H. R. Hamilton, \"Quantitative infrared thermography inspection for FRP applied to concrete using single pixel analysis,\" Construction and Building Materials, 2010.","Akbar Darabi, Xavier Maldague, \"Neural network based defect detection and depth estimation in TNDE,\" NDT & E International, vol. 35, pp. 165-175, 2002.","C. Ibarra-Castanedo, F. Galmiche, A. Darabi, M. Pilla, M. Klein, A. Ziadi, S. Vallerand, J.-F. Pelletier, X. Maldague, \"Thermographic nondestructive evaluation: overview of recent progress,\" in SPIESociety of Photo-Optical Instrumentation Engineers, Procedures Thermosense XXV, 2003.","Hernán D. Benítez, Humberto Loaiza,Eduardo Caicedo,Clemente Ibarra- Castanedo,AbdelHakim Bendada,Xavier Maldague, \"Defect characterization in infrared non-destructive testing with learning machines,\" NDT & E International, vol. 42, pp. 630-643, 2009.","M. R. Clark, D. M. McCann, M. C. Forde, \"Application of infrared thermography to the non-destructive testing of concrete and masonry bridges,\" NDT & E International, vol. 36, pp. 265-275, 2003.","XAVIER P.V. MALDAGUE, Theory and Practice of Infrared Technology for Nondestructive Testing. Canada, 2001.","Manyong Choi, Kisoo Kang, Jeonghak Park, Wontae Kim, Koungsuk Kim, \"Quantitative determination of a subsurface defect of reference specimen by lock-in infrared thermography,\" NDT & E International, vol. 41, pp. 119-124, 2008.","S. Vallerand, X. Maldague \"Defect characterization in pulsed thermography: a statistical method compared with Kohonen and Perceptron neural networks,\" NDT & E International, vol. 33, pp. 307- 315, 2000. [10] U. Galietti, D. Palumbo, G. Calia and F. Ancona, \"New data analysis to evaluate defects in composite materials using microwaves thermography,\" presented at the 11th International Conference on Quantitative InfraRed Thermography, University of Naples Federico II, Naples, Italy, 2012. [11] Hongjoon Kim, Kyungyoung Jhang, Minjea Shin, Jaeyeol Kim \"A noncontact NDE method using a laser generated focused-Lamb wave with enhanced defect-detection ability and spatial resolution,\" NDT & E International, vol. 39, pp. 312-319, 2006. [12] J. Schlichting, Ch. Maierhofer, M. Kreutzbruck, \"Crack sizing by laser excited thermography,\" NDT & E International, vol. 45, pp. 133-140, 2012. [13] S. E. Burrows, S. Dixon, S.G. Pickering, T. Li, D.P. Almond, \"Thermographic detection of surface breaking defects using a scanning laser source,\" NDT & E International, vol. 44, pp. 589-596, 2011. [14] Teng Li, Darryl P. Almond, D.Andrew S. Rees, \"Crack imaging by scanning pulsed laser spot thermography,\" NDT & E International, vol. 44, pp. 216-225, 2011. [15] L. De Lorenzis and J. G. Teng, \"Near-surface mounted FRP reinforcement: An emerging technique for strengthening structures,\" Composites Part B: Engineering, vol. 38, pp. 119-143, 2007. [16] M. J. Chajes, et al., \"Durability of concrete beams externally reinforced with composite fabrics,\" Construction and Building Materials, vol. 9, pp. 141-148, 1995"]}

Ce travail présente une méthode inverse pour déterminer la diffusivité thermique et l’épaisseur du béton d’enrobage de deux poutres expérimentales, l’une en béton et l’autre en mortier. L’armature métallique centrale est sollicitée à l’aide d’un chauffage par induction et l’évolution des températures de surface est mesurée à l’aide d’une caméra infrarouge. Une modélisation numérique mettant en oeuvre un schéma ADI permet de résoudre l’équation de transfert thermique. Il est intégré à une procédure d’identification qui conduit à la détermination des paramètres d’épaisseur et de diffusivité thermique. Une étude de sensibilité montre que ces paramètres peuvent être déterminés simultanément durant la phase de chauffage de la barre. 29ème rencontre de l’AUGC Tlemcen (29-31 Mai 2011).