Implementation of the direct evaluation of strains in a frequency-based image analysis code for random patterns

J. Molimard; A. E. Dolinko

doi:10.1117/12.871265

13 September 2010 Implementation of the direct evaluation of strains in a frequency-based image analysis code for random patterns

J. Molimard, A. E. Dolinko

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Proceedings Volume 7387, Speckle 2010: Optical Metrology; 73871M (2010) https://doi.org/10.1117/12.871265
Event: Speckle 2010, 2010, Florianapolis, Brazil

Abstract

A new approach for decoding displacements from surfaces encoded with random patterns has been developed and validated. The procedure is based on phase analysis of little zones of interest. Resolution in standard conditions (32×32 pixels²) is 2/100th pixel, for a spatial resolution of 9 pixels. Here we adapt new concepts proposed by Badulescu¹³ on the grid method to random patterns for the direct measurement of strains. First metrological results are encouraging: resolution is proportional to strain level, being 1/10th of the nominal value, for a spatial resolution of 9 pixels (ZOI 64×64 pixels²). Random noise have to be carefully controlled. A numerical example shows the relevance of the approach. Then, first application on a carbon fibre reinforced composite is developed. Fabric intertwining is studied using a tensile test. Over-strain are clearly visible, and results connect well with previous ones¹⁶.

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J. Molimard and A. E. Dolinko "Implementation of the direct evaluation of strains in a frequency-based image analysis code for random patterns", Proc. SPIE 7387, Speckle 2010: Optical Metrology, 73871M (13 September 2010); https://doi.org/10.1117/12.871265

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KEYWORDS

Spatial resolution

Digital image correlation

Composites

Image analysis

Cameras

Carbon

Image resolution

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