Vibration mode shapes visualization in industrial environment by real-time time-averaged phase-stepped electronic speckle pattern interferometry at 10.6    μ m and shearography at 532 nm

Abstract

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. Downloaded From: http://opticalengineering.spiedigitallibrary.org/ on 06/05/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx

High Spatial-Resolution Digital Phase-Stepping Shearography

“…In conventional shearography, a video camera, operating at a video rate, is used to capture the sheared images of the test object. The maximum resolution of the video camera used is of the order of 5 megapixels [7][8][9][10]. This limits the spatial resolution for the generated shearograms and phase maps and, consequently, limits the maximum value of the deformations that can be successfully observed.…”

Digital Holographic Interferometry in the Long-Wave Infrared Range for Measuring Large Deformations of Space Components under Thermal-Vacuum Testing

“…At such long wavelengths, the stability requirements are then also decreased by a factor of 20 compared to visible wavelengths. We already have presented various developments concerning nondestructive testing by LWIR speckle interferometry [2][3][4][5][6], vibration analysis [7] and deformations metrology of space structures by LWIR DHI [8][9][10][11].…”

Fully automated extraction of the fringe skeletons in dynamic electronic speckle pattern interferometry using a U-Net convolutional neural network

“…Fully automated extraction of the fringe skeletons in dynamic electronic speckle pattern interferometry using a U-Net convolutional neural network 1 Introduction Electronic speckle pattern interferometry (ESPI) as a wellknown optical metrology technique has been extensively investigated and widely used in numerous fields. [1][2][3] It is well known that accurate extraction of phase terms is of fundamental importance for the successful application of ESPI. Compared with the static measurement, the extraction of phase terms in real-time and dynamic ESPI measurement is a more challenging problem.…”