Abstract. Two-dimensional digital image correlation (2D-DIC) has the advantages of high computation efficiency and simple experimental setup compared to three-dimensional DIC (3D-DIC). However, 2D-DIC is sensitive to out-of-plane motion, which leads to rather poor strain results. Recently, optical extensometers realized by dual-reflector imaging have been proposed, which can self-compensate the strain errors introduced by out-of-plane motion of the specimen. We will extend strain measurement from an extensometer to full-field deformation measurement. To this end, first, two corresponding areas of interest (AOIs) are created based on the symmetrical axis of the reference image. Second, the displacement and strain fields of these AOIs are computed with a common 2D-DIC algorithm, respectively. Subsequently, high-accuracy deformation results are obtained by taking the average of the deformation of the corresponding calculation points in two AOIs. Two types of uniaxial tensile tests that correspond to uniform and nonuniform strain fields were conducted to validate the feasibility of the proposed self-compensation method. The first experiment indicates that the strain results obtained using the proposed method are in good agreement with those with strain gauges and that the proposed method can achieve higher strain accuracy than 3D-DIC with a small stereo-angle. The results of the second experiment are basically in agreement with those of the ANSYS numerical simulation, which demonstrates the feasibility of the proposed method for the measurement of nonuniform strain fields. Both of the experiments demonstrate that rigid out-of-plane motion will lead to a global strain field error for common 2D-DIC. With no external compensation device, the proposed self-compensation method has the potential in 2D-DIC for accurate strain measurement due to its high level of accuracy.

中文翻译：

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二维数字图像相关中平面外运动应变误差的自补偿方法

摘要。与三维 DIC (3D-DIC) 相比，二维数字图像相关 (2D-DIC) 具有计算效率高和实验设置简单的优点。然而，2D-DIC 对平面外运动很敏感，这会导致相当差的应变结果。最近，已经提出了通过双反射器成像实现的光学引伸计，它可以自我补偿由样品的平面外运动引入的应变误差。我们将应变测量从引伸计扩展到全场变形测量。为此，首先，基于参考图像的对称轴创建两个相应的感兴趣区域 (AOI)。其次，这些 AOI 的位移和应变场分别使用常见的 2D-DIC 算法计算。随后，取两个AOI对应计算点的变形平均值，得到高精度的变形结果。进行了两种对应于均匀和非均匀应变场的单轴拉伸试验，以验证所提出的自补偿方法的可行性。第一个实验表明，使用所提出的方法获得的应变结果与应变片的结果非常吻合，并且所提出的方法可以实现比具有小立体角的 3D-DIC 更高的应变精度。第二个实验的结果与ANSYS数值模拟的结果基本一致，证明了所提出的非均匀应变场测量方法的可行性。这两个实验都表明，刚性的平面外运动将导致普通 2D-DIC 的全局应变场误差。由于没有外部补偿装置，所提出的自补偿方法由于其高精度水平而具有在 2D-DIC 中进行精确应变测量的潜力。