PSI - Issue 5

H. Lopes et al. / Procedia Structural Integrity 5 (2017) 1205–1212

1212

H. Lopes et al. / Structural Integrity Procedia 00 (2017) 000 – 000

8

5. Conclusions

A method for the evaluation of noise was successfully applied to the determination of modal rotations of a beam. The first four modal rotation fields were experimentally obtained with an in-house digital shearography system. Two sets of measurements were carried out to investigate the influence of the shearing amount and the vibration amplitude of rotations on the noise. The results show that the best measurements are obtained for the first modal rotation field with the largest values of the shearing amount and maximum vibration amplitude. The present study gives important and useful information about the improvement of measurements of modal rotations, allowing us to define a set of optimal parameters. Further studies are underway with the objective of investigating the influence on noise of other parameters, such as methods to evaluate the phase and the numerical aperture of the imaging system.

Acknowledgements

This work was supported by FCT, through IDMEC, under LAETA, Project UID/EMS/50022/2013 and LAETA Interinstitutional Project “Advanced materials for noise reduction: modeling, optimization and experimental validation”.

References

Abdullah, W. S. W., Petzing, J. N.,2005. Development of speckle shearing interferometer error analysis as an aperture function of wavefront divergence. Journal of Modern Optics, 52, 1495–1510. Aebischer, H. A., Waldner, S., 1999. A simple and effective method for filtering speckle-interferometric phase fringe patterns. Optics Communications, 162, 205–210. Araújo dos Santos, J. V., Lopes, H., 2017. Damage localization based on modal response measured with shearography, in “Vibration based structural health monitoring methods” . In: Nobari, A. S., Aliabadi, F. M. H. (Eds.). World Scientific Publishing, (In press) Creath, K., Schmit, J., 1996. N-point spatial phase-measurement techniques for non-destructive testing. Optics and Lasers in Engineering, 24, 365– 379. Ghiglia, D. C., Pritt, M. D., 1998. Two-dimensional phase unwrapping : theory, algorithms, and software. Wiley, New York. Kreis, T., 2005. Handbook of holographic interferometry: Optical and digital methods”, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. Lopes, H., Araújo dos Santos, J. V., Moreno-García, P., 2017. Evaluation of noise level in speckle interferometry measurements. Mechanical Systems and Signal Processing (Submitted). Lopes, H., Ferreira, F., Araújo dos Santos, J. V., Moreno-García, P., 2014. Localization of damage with speckle shearography and higher order spatial derivatives. Mechanical Systems and Signal Processing, 49, 24–38. Mininni, M., Gabriele, S., Lopes, H., Araújo dos Santos, J. V., 2016. Damage identification in beams using speckle shearography and an optimal spatial sampling. Mechanical Systems and Signal Processing, 79, 47–64. Pandey, A., Biswas, M., Samman, M., 1991. Damage detection from changes in curvature mode shapes. Journal of Sound and Vibration, 145, 321– 332. Picart, P., Pascal, J. C., Breteau, J. M., 2001. Systematic errors of phase-shifting speckle interferometry. Applied Optics, 40, 2107–2116 Schnars, U., Jueptner, W., 2005. Digital holography: Digital hologram recording, numerical reconstruction, and related techniques. Springer, Berlin. Seara, R., Gonçalves, A. A., Uliana, P. B., 1998. Filtering algorithm for noise reduction in phase-map images with 2π phase jumps. Applied Optics, 37(11), 2046–2050. Steinchen, W., Yang, L. X., Maeckel, G., Maeckel, P., Voessing, F., 1998. Digital shearography for strain measurement: an analysis of measuring errors, Proc. SPIE, 3479, 235–246. Steinchen, W., Yang, L., 2003. Digital shearography: Theory and application of digital speckle pattern shearing interferometry, SPIE Press.