19 July 1996 Three-dimensional displacement analysis by projected fringes and speckle correlation
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Abstract
For comparison to model predictions, measurement of the true response of weak polymeric materials requires that a non- contacting method be use. In particular, for compression tests on weak polymers it is necessary to obtain the full 3D displacement field for the specimen. In this work, the full 3D displacement field was measured using a combination of white light speckle correlation and projected fringes. To obtain the out-of-plane displacement field, a fringe pattern with frequency of 0.30 lpmm was projected onto the specimen surface using a standard slide projector. A phase-stepping algorithm was used to convert the optical fringe pattern in a contour map for the surface. Due to reflections and noise in the fringe pattern, the authors developed a robust phase unwrapping methodology based on fuzzy logic principles. Baseline tests have shown that the algorithm produces accurate contour maps even when noise and poor fringe contrast are present. For the measurements of the in-plane displacement field the polymer foam material was illuminated with a white light source and the natural character of the reflected light was used to obtain speckle images of the polymer. The images were acquired at various load levels and stored in digital form. The digital images were correlated to obtain the speckle deformation field. To increase the range of measurement and to deal with high strain, additional processing of the images using fuzzy logic algorithms was completed.
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Thomas Wolf, Bernd Gutmann, H. Weber, "Three-dimensional displacement analysis by projected fringes and speckle correlation", Proc. SPIE 2861, Laser Interferometry VIII: Applications, (19 July 1996); doi: 10.1117/12.245153; https://doi.org/10.1117/12.245153
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