Active thermography gives the possibility to characterize thermophysical properties and defects in complex structures presenting heterogeneities. The produced thermal fields can be rapidly 3D. On the other hand, due to the size of modern thermographic images, pixel-wise data processing based on 1D models is the only reasonable approach for a rapid image processing. The only way to conciliate these two constraints when dealing with time-resolved experiments lies in the earlier possible detection/characterization. This approach is illustrated by several different applications and compared to more classical methods, demonstrating that simplicity of models and calculations is compatible with efficient and accurate identifications. 1. Introduction The evolution of thermophysical properties metrology and nondestructive evaluation (NDE) is characterized by the increased use of refined inverse techniques [1] requiring the establishment of models taking into account many parameters, although among these parameters often only one parameter is of interest for the experimenter. This complexity is particularly important when the analyzed thermal fields are 3D, a situation characteristic of the experiments realized with thermographic systems producing sequences of large thermal images of complex structures presenting important heterogeneities in their thermal properties, internal geometries, and boundary conditions. This approach leads to time-consuming calculations that may be prohibitive for thermographic data processing. Furthermore, it happens that in many situations the reality remains more complex than the sophisticated model used. How to conciliate the existence 3D thermal situations involving numerous parameters and the necessity to have rapid calculations compatible with the very high number of information to process in a thermographic image sequence? A solution lies in the use of 1D thermal models for pixel-wise data processing and the choice of a limited early time domain (for time-resolved techniques) or high frequency domain (for modulated techniques) for which the measured temperatures are essentially depending on the sole parameter to be identified and weakly affected by the 3D heat transfer. To achieve that, the proposed approach consists in performing the identification at the earlier possible time (or at the higher possible frequency) after the thermal stimulation. Here, we will mainly consider time-resolved techniques and early time detection (emerging signal). The present work wants to show the following.(i)A detailed procedure can be defined for
References
[1]
R. B. Orlande, O. Fudym, D. Maillet, and R. M. Cotta, Eds., Thermal Measurements and Inverse Techniques, CRC Press, 2011.
[2]
W. J. Parker, R. J. Jenkins, C. P. Butler, and G. L. et Abbot, “Flash method of determining thermal diffusivity, heat capacity and thermal conductivity,” Journal of Applied Physics, vol. 32, no. 9, pp. 1679–1684, 1961.
[3]
D. Balageas, “Flash Thermal diffusivity measurements using a novel temperature-time history analysis,” in Proceedings of the 1st International Joint Conferences on Thermophysical Properties, no. TP 1981-62, ONERA, Gaithersburg, Md, USA, June 1981.
[4]
D. L. Balageas, “Nouvelle méthode d'interprétation des thermogrammes pour la détermination de la diffusivité thermique par la méthode impulsionnelle (méthode flash),” Revue de Physique Appliquée, vol. 17, pp. 227–237, 1982 (French).
[5]
A. Degiovanni, “Diffusivité et méthode flash,” Revue Générale de Thermique, vol. 16, no. 185, pp. 420–442, 1977 (French).
[6]
A. Degiovanni, “Identification de la diffusivité thermique par l’utilisation des moments temporels partiels,” High Temperatures-High Pressures, vol. 17, pp. 683–689, 1985 (French).
[7]
D. L. Balageas and A. M. Luc, “Transient thermal behavior of directional reinforced composites: applicability limits of homogeneous property model,” AIAA Journal, vol. 24, no. 1, pp. 109–114, 1986.
[8]
A. M. Luc and D. L. Balageas, “Non-stationary thermal behavior of reinforced composites—a better evaluation of wall energy balance for convective conditions,” in Proceedings of the 1st International Joint Conferences on Thermophysical Properties, no. TP 1981-61, ONERA, Gaitherburg, Md, USA, June 1981.
[9]
A. M. Luc-Bouhali, R. M. Pujolà, and D. L. Balageas, “Thermal diffusivity in situ measurements of carbon/carbon composite reinforcements,” in Thermal Conductivity, T. Ashworth and D. R. Smith, Eds., vol. 18, pp. 613–624, Plenum, London, UK, 1984.
[10]
R. M. Pujolà and D. L. Balageas, “Derniers développements de la méthode flash adaptée aux matériaux composites à renforcement orienté,” High Temperature-High Pressure, vol. 17, pp. 623–632, 1985 (French).
[11]
D. L. Balageas, “Détermination par méthode flash des propriétés thermiques des constituants d'un composite à renforcement orienté,” High Temperatures-High Pressures, vol. 16, pp. 199–208, 1984 (French).
[12]
D. L. Balageas, “Détermination de la diffusivité thermique du milieu homogène équivalent à un matériau composite à renforcement orienté,” Comptes-Rendus des Séances de l'Académie des Sciences, vol. 299, no. 4, pp. 143–148, 1984 (French).
[13]
J.-P. Bardon, D. Balageas, A. Degiovanni, and J. Vuiiliermes, “Thermics of composites and interfaces: current status and perspectives,” La Recherche Aérospatiale, no. 1989-6, pp. 37–45, 1989.
[14]
D. Balageas, A. Déom, and D. Boscher, “Composite thermal properties measurements by pulse photothermal radiometry,” in Proceedings of the Eurotherm IV Conference Thermal Transfer in Composite Materials and Solid-Solid Interface, pp. 92–95, Nancy, France, June-July 1988.
[15]
J. C. Krapez, Contribution à la caractérisation des défauts de type délaminage ou cavité par thermographie stimulée [Ph.D. thesis], Ecole Centrale de Paris, Chatenay-Malabry, France, 1991.
[16]
D. L. Balageas, J. C. Krapez, and P. Cielo, “Pulsed photothermal modeling of layered materials,” Journal of Applied Physics, vol. 59, no. 2, pp. 348–357, 1986.
[17]
D. L. Balageas, A. A. Deom, and D. M. Boscher, “Characterization and nondestructive testing of carbon-epoxy composites by a pulsed photothermal method,” Materials Evaluation, vol. 45, no. 4, pp. 461–465, 1987.
[18]
J. C. Krapez and D. Balageas, “Early detection of thermal contrast in pulsed stimulated infrared thermography,” in Proceedings of the Quantitative Infrared Thermography, Editions Europ Thermosonde et Induction (QIRT '94), pp. 260–266, 1994, http://qirt.gel.ulaval.ca/dynamique/index.php?idD=56, paper # QIRT 1994-039.
[19]
D. L. Balageas, “Defense and illustration of time-resolved thermography for NDE,” in Proceedings of the SPIE Thermosense III, vol. 8013, pp. 8013V-1–88013V20, 2011, http://publications.onera.fr/exl-php/cadcgp.php.
[20]
D. Balageas, “Defense and illustration of time-resolved thermography for NDE,” Quantitative InfraRed Thermography Journal, vol. 9, no. 1, pp. 5–38, 2012.
[21]
J. Bontaz, Ch. Fort, and B. Horbette, “Identification de la profondeur et de la valeur de la résistance thermique de contact dans des matériaux stratifiés par la méthode photothermique impulsionnelle,” in Proceedings of the Annual Conference of the Société Fran？aise des Thermiciens (SFT '90), pp. 221–224, Nantes, France, May 1990.
[22]
J. Bontaz, Une méthode photothermique impulsionnelle appliquée au contr？le de matériaux composites [Ph.D. thesis], University of Bordeaux, 1991.
[23]
D. L. Balageas, D. M. Boscher, and A. A. Déom, Temporal Moment Method in Pulsed Photothermal Radiometry. Application to Carbon Epoxy N.D.T., vol. 58 of Springer Series in Optical Sciences, Springer, 1987.
[24]
J. C. Krapez, D. Balageas, A. Deom, and F. Lepoutre, “Early detection by stimulated infrared thermo-graphy. Comparison with ultrasonics and holo/shearo-graphy,” in Advances in Signal Processing for Non Destructive Evaluation of Materials, X. P. V. Maldague, Ed., vol. 262 of NATO ASI Series E, pp. 303–321, Kluwer Academic, 1994.
[25]
J.-C Krapez, F. Lepoutre, and D. Balageas, “Early detection of thermal contrast in pulsed stimulated thermography,” Journal de Physique IV, vol. 4, no. C7, pp. 47–50, 1994.
[26]
S. K. Lau, D. P. Almond, and J. M. Milne, “A quantitative analysis of pulsed video thermography,” NDT and E International, vol. 24, no. 4, pp. 195–202, 1991.
[27]
D. P. Almond and S. K. Lau, “A quantitative analysis of pulsed video thermography,” in Proceedings of the Quantitative Infrared Thermography, Editions Europ Thermosonde et Induction (QIRT '92), pp. 207–211, QIRT, Paris, France, 1992, http://qirt.gel.ulaval.ca/dynamique/index.php?idD=55, paper # QIRT, 1992-031.
[28]
L. D. Favro, X. Han, P. K. Kuo, and R. L. Thomas, “Imaging the early time behavior of reflected thermal wave pulses,” in Proceedings of the Thermosense XVII: An International Conference on Thermal Sensing and Imaging Diagnostic Applications, pp. 162–166, April 1995.
[29]
X. Han, L. D. Favro, P. K. Kuo, and R. L. Thomas, “Early-time pulse-echo thermal wave imaging,” Review of Progress in Quantitative Nondestructive Evaluation, vol. 15, pp. 519–524, 1996.
[30]
R. L. Thomas, L. D. Favro, and P. K. Kuo, “Thermal wave imaging of hidden corrosion in aircraft components,” Report AFOSR-TR-96, 1996.
[31]
H. I. Ringermacher, et al., “Towards a flat-bottom hole standard for thermal imaging,” in Review of Progress in Quantitative Nondestructive Evaluation, D. O. Thompson and D. E. Chimenti, Eds., vol. 17, pp. 425–429, Plenum Press, New York, NY, USA, 1998.
[32]
J. G. Sun, “Analysis of pulsed thermography methods for detect depth prediction,” Journal of Heat Transfer, vol. 128, no. 4, pp. 329–338, 2006.
[33]
S. M. Shepard, T. Ahmed, B. A. Rubadeux, D. Wang, and J. R. Lhota, “Synthetic processing of pulsed thermographic data for inspection of turbine components,” Insight, vol. 43, no. 9, pp. 587–589, 2001.
[34]
S. M. Shepard, J. R. Lhota, B. A. Rubadeux, D. Wang, and T. Ahmed, “Reconstruction and enhancement of active thermographic image sequences,” Optical Engineering, vol. 42, no. 5, pp. 1337–1342, 2003.
[35]
S. M. Shepard, Y. L. Hou, T. Ahmed, and J. R. Lhota, “Reference-free interpretation of flash thermography data,” Insight, vol. 48, no. 5, pp. 298–307, 2006.
[36]
S. M. Shepard, J. Hou, J. R. Lhota, and J. M. Golden, “Automated processing of thermographic derivatives for quality assurance,” Optical Engineering, vol. 46, no. 5, Article ID 051008, 2007.
[37]
S. M. Shepard, “Flash thermography of aerospace composites,” in Proceedings of the 4th Pan American Conference for NDT, Buenos Aires, Argentina, October 2007, http://www.ndt.net/article/panndt2007/papers/132.pdf.
[38]
D. Balageas and J. M. Roche, “Détection précoce et caractérisation de défauts par thermographie stimulée par échelon de flux et comparaison à la méthode impulsionnelle,” in Congrès Annuel de la Société Fran？aise de Thermique, Bordeaux, France, May-June 2012, http://publications.onera.fr/exl-doc/DOC401721_s1.pdf.
