Elimination of Periodical Error for Bi-directional Displacement in Digital Image Correlation Method
A technique for eliminating the periodical systematic error in bi-directional displacements by a digital image correlation method is investigated. The technique is based on a periodical error elimination method for single directional displacements which h
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Elimination of Periodical Error for Bi-directional Displacement in Digital Image Correlation Method Shuichi Arikawa, Manabu Murata, Satoru Yoneyama, Yasuhisa Fujimoto, and Yohei Omoto Abstract A technique for eliminating the periodical systematic error in bi-directional displacements by a digital image correlation method is investigated. The technique is based on a periodical error elimination method for single directional displacements which has been developed by the authors. In this technique, rotated and multiple translated images for the horizontal and the vertical directions are captured before a deformation. Translation amounts are determined from the rotation and the translated images. After the deformation, a single image is captured. The periodical error is eliminated using a calculation based on the translation amounts and the measured multiple displacements from the single deformed state image with the initial translated images. The elimination is applied to a thermal deformation measurement. As a result, periodical errors for bi-directional displacements can be eliminated. Therefore, it is expected that accurate in-plane displacements and strain components can be obtained using the proposed technique. Keywords Deformation measurement • Digital image correlation • Displacement • Error
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Introduction
Recently, digital image correlation method (DIC) [1] is widely used in various fields. Since DIC is an image-based measurement technique, measurements in various scales are possible, such as a bridge diffraction measurement [2] and a micro-scale measurement in a scanning electron microscope [3]. Additionally, the measurement error level has been much reduced by improving the calculation process in DIC [4–6]. In DIC measurement, a window called subset is set on an initial state image and the displacement is calculated by searching a matched pattern with the initial subset in a deformed state image. Then a subpixel calculation by an interpolation in a region between adjacent pixels is performed for obtaining high accurate displacements. The displacement calculation accuracy has been improved by investigating the image correlation coefficient and the interpolation for the subpixel calculation. In the beginning of the research in DIC, a periodical systematic error occurred using bi-linear interpolation for the subpixel calculation. Recently, improving measurement accuracy and reducing the periodical error have been achieved by applying high-order polynomial interpolations or spline interpolations. Incidentally, the measurement accuracy in DIC is increased by an enlargement of subset size, and it leads to the decreased spatial resolution. With the improvement in the measurement accuracy as described above, the spatial resolution has been improved more than before. However, further improvement of the spatial resolution is very important for measuring complicated deformation fields in detail. In displacement field measurements by DIC, it is inappropriate to assume the spatial resolution as the subset size. Spa
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