Imaging with Optically Generated Thermal Waves

Busse, G.

doi:10.1109/t-su.1985.31603

Cited by 34 publications

(3 citation statements)

References 53 publications

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“…Photothermal techniques [7][8][9] are a rapidly expanding research field for the inspection of industrial materials. The part is surface-heated by a laser or similar radiative source and the temperature evolution is monitored to evaluate the thermal parameters of the material such as the thermal diffusivity.…”

Section: Description Of the Methodsmentioning

confidence: 99%

A rapid test for evaluating the degree of cure in CFRP composites

Krapez

Cielo

Cole

et al. 1987

Journal of Thermal Analysis

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A noncontact optothermal method is described for possible application to routine industrial evaluation of the degree of cure in polymeric composites. The surface of the part is heated by a laser beam or other radiative source while its temperature evolution is continuously monitored with an infrared detector. A strong exothermal peak is observed when the material is partially or totally uncured. Changes in the signal shape related to variations of the part geometry or environmental conditions are minimized by a differential approach comparing subsequent heat cycles on the same area. Results obtained with cured or uncured graphite-epoxy prepreg sheets are presented.Quality control of composite materials and structures is a very active research field [1,2]. Graphite-epoxy composites are particularly subject to strict inspection procedures because of their increasing utilization as primary structures in safetysensitive fields such as in the aircraft industry. The mechanical properties of carbonfiber-reinforced-plastics (CFRP) structures are much affected by the degree of cure of the resin matrix both before and after processing. Before processing, the slightly precured prepreg sheets which are shipped to the manufacturer in refrigerated cells are normally inspected to verify, that the required pre-cure level has not been exceeded [3]. After lay-up and autoclave curing, the degree of polymerization must be sufficiently high to assure the required mechanical performance.A number of approaches are possible to evaluate the degree of polymer cure, including spectroscopic, calorimetric, mechanical, electromagnetic or ultrasonic methods [1,4,5], the most widely used being the spectroscopic and the thermal techniques. Infrared spectroscopy can provide quantitative data concerning the amount of unreacted epoxy groups. For best results measurements must be made in transmission and, in the case of cured composites, this requires destruction (grinding) of the sample. The diffuse reflectance method has the advantage of being noncontact and nondestructive, but is of limited value for quantitative work [4].

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Section: Description Of the Methodsmentioning

confidence: 99%

A rapid test for evaluating the degree of cure in CFRP composites

Krapez

Cielo

Cole

et al. 1987

Journal of Thermal Analysis

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“…For non-destructive material analysis, photoacoustic and photothermal methods can be applied [16] . In photothermal interferometry the thermal expansion of the specimen is measured rather than the thermal wave itself [17] .…”

Section: Phase-locked Techniquementioning

confidence: 99%

Optical methods for precision measurements

Tiziani

1989

Opt Quant Electron

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Contactless measuring techniques are becoming increasingly important for industrial applications . The use of a laser, solid-state detector arrays and powerful small computers leads to a very efficient fringe analysis in holography as well as in Moire and speckle techniques . Due to the computer analysis, much more information can be extracted from interferograms, leading to higher sensitivities and accuracies . The application of different fringe analysis procedures is discussed, together with some potentials of the application of interferometry, holography, and speckle and Moire techniques . . IntroductionInterferometry, holography, speckle and Moire techniques are becoming useful tools for precision measurements in research and for industrial applications . Computer analysis is increasingly important for fringe analysis . The use of solid-state detector arrays . image memory boards together with microprocessors and computers for the extraction of the information from the interferograms and high-resolution graphic hoards finds important application in optical metrology . Much more information can he extracted from the interferograms, leading to higher sensitivities and accuracies .Fringe analysis procedures including fringe peak detection and fringe order determination are tedious and time-consuming . Automatic fringe analysis and precision phase measuring techniques are very important in applying interferometric techniques . Automatic quantitative evaluation of interferograms requires accurate interference phase measurements . independent of fringe position and intensity variations superposed onto the interferograms . In many interferometric arrangements . phase shifting or heterodyne techniques have been introduced for automatic fringe analysis .In the phase shifting technique or quasi-heterodyne technique the relative phase is changed continuously or stepwise, using at least three phase shifts of 90° or 120°, for instance . The phase of the interference patterns can then he computed from the different measured intensity values . The phase shifting technique is very appropriate for digital processing and TV techniques . Interferometry and two-reference-beam holography together with video electronic processing lead to a sensitivity of 1 100 of a fringe at any point of the fringe pattern in the TV image . In heterodyne methods the relative phase increases linearly

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“…Throughout the development of thermal wave NOE techniques the most common application has been the imaging of subsurface structure of coated and bulk materials [1]. The use of thermal wave imaging for the detection of coating adhesion defects was first proposed by Luukkala and penttinen [2], and Busse and Ograbek presented the first experimental results on the detection of artificial adhesion defects of a graphite coating on aluminum [3].…”

Section: Introouctionmentioning

confidence: 99%