Inspection of materials and structures by infrared thermography: signal processing techniques for defect enhancement and characterization

Inspection of materials and structures by infrared thermography: signal processing techniques for defect enhancement and characterization

ND T abstracts unidirectional CFRP laminates. Based on recent developments involving the influence of the underlying layers, the program is adapted. T...

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ND T abstracts unidirectional CFRP laminates. Based on recent developments involving the influence of the underlying layers, the program is adapted. Then, it is shown that for high loadings, the interpretation of the Spate image is not straightforward due to the damage development inside the specimen. This gives also rise to a Spate "error" signal. Through adaptation of the Spate system, it is possible to monitor the surface temperature change as a result of the damage process and an example of this is shown. 50010 Vavilov, V.P.; DeGiovanni, A.; Didierjean, S.; Maillet, D.; Sengoulier, A.A.; Houlbert, A.-S. T h e r m a l flaw detection and tomography of carbon fiberreinforced plastic articles Soviet Journal of Nondestructive Testing, Vol. 27, No. 9, pp. 609-619 (May 1992) A detailed theoretical and experimental analysis of one- and two-sided active thermal inspection of a standard specimen of carbon fiber- reinforced plastic with a thickness of 2 mm was carried out by means of computer thermographic system jointly with a group of French ~ h e r s (University of Nancy). A statistical estimate of the detectability of defects by operators by the Tanimoto test is given. All main relations between the informative paran~tcrs and characteristics of the defects are discussed. The prospects of thermal tomography of carbon fiber-reinforced plastic are discussed.

Lucia, A.C.; Melvin, A.D. Non-destructive evaluation of composite materials: t h e r m a l r e s p o n s e to deformation of laminates

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Commission of the European Communities, EN-36514-ORA (1991) The thermnelastic response to deformation of carbon fibre/epoxy resin composite laminates has been considered theoretically and compared with experimental results. It is found that the surface temperature is strongly dependent on the near-surface layup. The total thermal response to tensile testing to failure is also reported. The results indicate that a simple but accurate estimation of the yield strength in composites is possible by measuring the thermoelastic-plastic limit strength, and that mierostructural "events" are detectable by measuring the surface temperature with sufficiently high resolution. It is anticipated that thermal response analysis will be developed into a damage assessment tool complementary to acoustic emission.

Maldague, X.; Poussart, D.; Drapez, J.C.; Cielo, P. Inspection of materials and structures by infrared thermography: signal processing techniques for defect enhancement and characterization 49743

Laval Univ., Quebec (Canada), N92-12291/0/GAR, 26 pp. (1990) Active infrared thermography is a nondestructive evaluation technique whereby heat perturbation is used to stimulate the thermal response of a given part. Appropriate signal processing techniques must be developed in order to detect subsurface defects or to obtain quantitative information from the raw data. Because of the limited heating temperatures (of the order of 10C) and other diffusion-based propagation of thermal waves, the contrast of thermal features in a thermographic image is relatively low. Image processing must he based on blurred feature recognition rather than on the detection of edges and contours as is usually the case for video images. In this paper some recent developments on thermographic inspection at the Industrial Materials Research Institute (IMRI) are described. A substantial amount of effort has been devoted to image processing and thermal modelling as required for rapid image analysis, signal enhancement, and noise removal from the thermograph, as well as for a quantitative sizing of defects. Examples are presented concerning the inspection of graphiteepoxy structures and of aluminium bonded panels with foam or honeycomb core.

Kageyama, K.; Kikuchi, M.; Nonaka, K. Fatigue damage analysis of notched carbon/epoxy composite by spate and finite element method

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Developments in the Science and Technology of Composite Materials, 4th European Conference, Stuttgart (Germany), 25-28 Sep. 1990. pp. 207- 212. Edited by J. Fuller, G. Gruninger, K. Schulte, A.R. Bunsell, A. Massiah. Elsevier Applied Science (1990) Damage-threshold analysis of notched [0/9012s and [90/012s carbon/epoxy laminates is carried out by using thermoelastic technique (SPATE) and a three dimensional finite element method. Fatigue strength and damage extension is examined experimentally and the process of transverse lamina cracking is analyzed numerically in the framework of Linear Elastic Fracture Mechanics.

Degiovanni, A.; Lamine, A.S.; Houlbert, A.--S.; Maillet, D. Identification of s u b s u r f a c e defects by a thermal method using a sensibility analysis

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Developments in the Science and Technology of Composite Materials, 4th European Conference, Stuttgart (Germany), 25-28 Sep. 1990. pp. 691- 696. Edited by J. Fuller, G. Gruninger, K. Schulte, A.R. Bunsell, A. Massiah. Elsevier Applied Science (1990) A subsurface defect in a composite material can be characterizedin term of depth and thermal resistance after a heat pulse - "flash" - perturbation on its front side. A sensitivity analysis of the rear- side contrast thermogram is done and various methods of identification of these two parameters are reviewed. The use of exporimental Laplace transforms seems to bring better results than the classical one-point evaluation. 49274 Hobbs, C. T h e inspection of aeronautical structures using t r a n s i e n t

thermography NDT for Corrosion in Aerospace Structures. 10 pp. Royal Aeronautical Society (1992). ISBN 0903409 99 2 Thermal imaging enables the observation and resolution of structural defects based on the visualisation of temperatures of components. The technique is improved by generating a steep momentary temperature gradient in the material. Any flawed regions will inhibit the passage of heat, causing the flaw to be contrasted against its surrounding when viewed using a thermal imager. This technique, called transient thermography, was developed at Harwell, and has been shown to be capable of detecting delamiuations, disbonds and lack-of-adhesion in a wide diversity of coated and uncoated materials. This paper describes the technique in relation to the inspection of aircraft for corrosion. The principles of the technique, and the equipment required to facilitate it are reviewed. Examples that show how transient thermography can produce a single pictorial respresentation of the available information are drawn from materials important to the industry. The abilities of the techniqne to detect corrosion is discussed in detail, and is supported by a specific example of a lap- joint inspection performed on an aircraft during scheduled maintenance. Recent developments pertinent to the use of transient thermography for the inspection of aircraft are detailed.

Reifsnider, K.L.; Bakis, C.E. Adiabatic thermography of composite m a t e r i a l s

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Characterization of Advanced Materials. pp. 65-76. Edited by W. Altergott and E. Henneke. Plenum Press (1990). The present paper describes the thermoelastic effect in composite materials, and the manner in which that phenomenon can he used to characterize global strain distributions, local strain distributions, stress relaxation associated with damage development, strain rate dependance, and the dependence of mechanical response on micro- constituent arrangement and behavior. In general, it is found that the thermoelastic effect provides a significant opportunity for the nondestructive evaluation of composite materials, and offers some unique opportunities, especially with regard to the investigation of the manner in which the properties and performance of composites depends upon the properties, performance, and arrangement of micro- constituents. 49027 Orlove, G. I n f r a r e d t h e r m a l imaging in the aerospace industry Sensors, Vol. 9, No. 2, pp. 37-42 (Feb. 1992) Modem application of thermography, or infrared thermal imaging, to nondestructive applications in the aerospace industry form the basis of this article. Thermography has become faster and more cost effective than some traditional test methods. The lnframetrics Model 760 infrared imaging system is described in various applications. The system ThermaGRAM image processing, for analysis of test results.

Gordaninejad, F. Directional thermal conductivity enhancement of fiber reinforced composite materials

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Enhancing Analysis Techniques for Composite Materials, Atlanta, Georgia (United States), 1-6 Dec. 1991. pp. 151-157. Edited by L. Schwer, J.N. Reddy and A. Mal. NDE-Vol. 10. ASME (1991) In this study a three-dimensional unit-cell model which consists of a polymer matrix, metal-coated fibers and metal-coated microspheres is analyzed to assess the enhancement of the overall thermal conductivities of the material. A transient heat transfer analysis based on the flash pulse method is employed to estimate the thermal conductivity of the composites. The performance of the model is examined through digital simulation studies by employing the finite element method. It is found that the thermal conductivities in the longitudinal and the radial directions are highly dependent on the fiber and microspheres volume fractions as well as the thermal conductivities of fiber, matrix microspheres and coatings.

N D T & E International Volume 26 Number 2 1993

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