Abstract
For digital image correlation to be firmly accepted as a validated displacement measurement system in the industrial arena, a measurement must be captured by the analysis system at time of test which confirms that the image correlation hardware and software system is performing as expected. To this end, a method for validating stereo digital image correlation optical test setups is presented, which is traceable to the length standard. The method employs a screen, on which is displayed a randomized speckle pattern of appropriate pitch for the test in question. This speckle pattern is then artificially translated by a known number of pixels on the screen, and image pairs captured of the original and translated speckles. Processing of these data image pairs with image correlation, and calibration of the pixel pitch of the display screen using a traceable measurement system, allows the image correlation test setup to be traceably calibrated in terms of in-plane displacement. The method is shown to be sufficiently sensitive and repeatable to provide a reasonably accurate, traceable validation in a practical environment.
Highlights
Digital image correlation (DIC) is a powerful optical measurement technique that provides full-field displacement and strain data for a test specimen undergoing deformation
For the purpose of this investigation, the technique was applied to both liquid crystal display (LCD) and electronic paper display (EPD) screens
A linear relationship between the imposed shift and the error is evident for both the EPD and LCD screens
Summary
Digital image correlation (DIC) is a powerful optical measurement technique that provides full-field displacement and strain data for a test specimen undergoing deformation. DIC has been shown to be a powerful technique in both the validation[1] and revision[2] of numerical models, such as finite element simulations, as it can provide a full-field data map contrary to traditional methods of comparing a model to point measurements provided by strain gauges. The most current measurement calibration methods for DIC propose the use of a standardized reference specimen to provide a “known” theoretically predicted displacement or strain field. This data can be compared to the experimental optical measurements in order to quantify an uncertainty value for those measurements. Designed for use in terms of strain measurement, the calibration specimens achieve traceability
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