EXTREME shearography: development of a high-speed shearography instrument for measurements of the surface strain components during an impact event

Abstract

EXTREME shearography Development of a high-speed shearography instrument for measurements of the surface strain components during an impact event Anisimov, Andrei G.; Groves, Roger M.

EXTREME shearography: high-speed shearography instrument for in-plane surface strain measurements during an impact event

“…When shearography is used for monitoring of dynamic events, the phase corresponding to the deformation of the object can be extracted from each captured interferogram by using a spatial phase shift 7 with Mach-Zehnder 8 or Michelson interferometers 9 . This work presents the design and recent results on the EXTREME shearography development with the analysis of the in-and out-of-plane surface strain components, which is a continuation of the previously reported results 10 when only the out-of-plane surface strain components were measured. The previous paper 10 also includes the literature overview of the application of shearography and speckle interferometry techniques to vibration and impact monitoring.…”

“…Two portions of the single pulse with energy from 100 up to 500 mJ sequentially illuminate the object under the control of a Pockels cell with the minimum separation time of 1 μs. The synchronisation in real-time is based on the approaching impactor using a set of 20 optical interrupters which results in a reliable prediction of the impact event with the accuracy up to 1 μs 10 . In each interferometer, two slits were placed at the front focal planes of the imaging lenses to achieve a better quality of the phase maps in comparison with a circular aperture 17 .…”

“…The trade-off between the interferometer parameters (Equation 3) was made as follows: a) the distance between the camera and the object of 500-600 mm was based on safety measures; b) the focal length was maximised up to 50 mm (Xenoplan 2.8/50 by Schneider) and was also defined by the specimen size of 200×200 mm with the visible area of Ø150 mm; c) each slit was shifted from the joint axis by 1.9 mm (β=2.3°) resulting in the offset frequency close to a half of the maximum one, see Figure 2 (b, c); d) the 1.8 mm slit was chosen as a rational compromise resulting in the absence of the overlap of the central and side maximums of the Fourier spectra and the average subjective speckle size of 7 pixels (corresponding to 0.35 mm; along with the x-axis). e) the shear distance x d was set at 17 to 21 pixels (0.9..1.1 mm) and calibrated over the field of view for both cameras as in 10 by processing a checkerboard image captured through the reference and the sheared field of views.…”

“…The previous paper 10 also includes the literature overview of the application of shearography and speckle interferometry techniques to vibration and impact monitoring. The previous configuration 10 of the shearography instrument realised measurements of the out-of-plane surface strain components (  w x,   w y) during the impact using the double frame approach. The spatial phase shift was based on a modified Michelson interferometer with 4f system.…”

Non-destructive testing and evaluation of composite materials/structures: A state-of-the-art review

“…Aggelis et al 299 Sfarra et al 300 Rahani et al 301 Arora et al 302 Quantitative strain monitoring Anisimov and Groves 303 Elhajjar and Shams 202 Sui et al 304 Wang et al 237 Mechanical analysis specimens have to be analysed using radiation facilities which are inconvenient compared to other NDT techniques. Also, locations and availability of synchrotron facilities are very limited, which further constrain their accessibility and costs.…”