We present our investigations on two interferometric methods suitable for industrial conditions dedicated to the visualization of vibration modes of aeronautic blades. First, we consider long-wave infrared (LWIR) electronic speckle pattern interferometry (ESPI). The use of long wavelength allows measuring larger amplitudes of vibrations compared with what can be achieved with visible light. Also longer wavelengths allow lower sensitivity to external perturbations. Second, shearography at 532 nm is used as an alternative to LWIR ESPI. Both methods are used in time-averaged mode with the use of phase-stepping. This allows transforming Bessel fringes, typical to time averaging, into phase values that provide higher contrast and improve the visualization of vibration mode shapes. Laboratory experimental results with both techniques allowed comparison of techniques, leading to selection of shearography. Finally a vibration test on electrodynamic shaker is performed in an industrial environment and mode shapes are obtained with good quality by shearography.
Speckle interferometry with CO2 laser (10 micrometers) and microbolometer array has been developed and the final
outcome is a mobile interferometer. The long wavelength allows to measure large deformations and is well immune
against external perturbations, so as it can be used in field conditions. The technique is based on specklegram recording
on the microbolometer array. The background of the specklegram is constituted by the thermal image of the object.
Consequently the technique allows simultaneous observation of deformation and temperature difference when an object
undergoes a given stress. We show several applications in aerospace nondestructive testing.
We present the development of a speckle interferometer based on a CO 2 laser and using a thermal infrared camera based on an uncooled microbolometer array. It is intended to be used for monitoring deformations as well as detecting flaws in aeronautical composites, with a smaller sensitivity to displacement compared to an equivalent system using visible (VIS) lasers. Moreover the long wavelength allows working with such interferometers outside the laboratory. A mobile system has been developed on the basis of previous laboratory developments. Then it is validated in a variety of industrial nondestructive testing applications in field working conditions.
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