Journal
OPTICS AND LASERS IN ENGINEERING
Volume 91, Issue -, Pages 62-72Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.optlaseng.2016.11.001
Keywords
Speckle-pattern quality; Digital image correlation; Deformation measurement; Gray intensity; Speckle morphology
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Funding
- Basic Science Research Programthrough the National Research Foundation of Korea (NRF) - Ministry of Science, ICT and Future Planning [NRF2015R1C1A1A02037663]
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In digital image correlation (DIC), speckle patterns are generated on the surface of a specimen to resolve uniqueness issues. Thus, speckle patterns significantly affect the accuracy of image correlation. To assess the quality of speckle patterns, the standard deviation of gray intensities within each speckle (SDGIS) is introduced as a new metric. On the basis of the cumulative distribution of SDGIS, speckle-pattern quality measurement (p) is proposed, which integrates the features of gray intensity and speckle morphology. Twelve speckle patterns are generated by changing the spraying time and nozzle sizes of an airbrush because these are associated with the speckle volume fraction and speckle size, respectively. In addition, three displacement fields are used to investigate the effects of speckle patterns on the accuracy of the DIC results. For the 12 speckle images associated with the three displacement fields, the correlation results demonstrate that the proposed speckle pattern quality measurement is inversely proportional to the averaged error of the subset method. This is statistically confirmed by evaluating the correlation coefficient and p-value. Furthermore, the error of the subset method is more affected by speckle patterns than the subset size when the subset size is sufficiently large.
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