Two-dimensional digital image correlation (2D-DIC) is increasingly being used in a wide variety of applications. This technique is capable of measuring the in-plane deformations and strains of planner surfaces. A basic condition for using this technique is having the camera to observe the target surface perpendicularly. If the camera is not perpendicular to the surface, errors will be introduced in the measured displacements and strains. Small amounts of camera misalignment can easily go undetected during the initial setting of the experimental setup. In this paper, a novel approach for verifying the perpendicularity of the camera with respect to the target surface in 2D-DIC experiments is introduced. If the camera is not perpendicular to the surface, the tilt angles about both of the two in-plane axes can be calculated using this novel approach. A simple in-plane rigid-body-translation of the specimen in any of the two in-plane directions (horizontal or vertical direction relative to the camera image), is used for detecting camera non-perpendicularity and calculating the tilt angle(s). This approach uses the normal and shear strain errors, induced in DIC results due to camera non-perpendicularity, to determine the surface tilt angle(s), if any is present. The tilt angle(s) are calculated using simple analytical equations that are developed based on the pinhole camera model. The proposed approach is validated using experiments performed while the target surface is tilted at angles ranging from 0.5° to 4°. The experimental results show that this approach is able to confidently detect camera misalignment for tilt angles of 1° or larger and the tilt angles can be calculated with less than 0.3° error.

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在二维数字图像相关实验中确定表面倾斜角的新方法

二维数字图像相关 (2D-DIC) 越来越多地用于各种应用。该技术能够测量平面的平面变形和应变。使用这种技术的一个基本条件是让相机垂直观察目标表面。如果相机不垂直于表面，则会在测量的位移和应变中引入误差。在实验设置的初始设置期间，少量的相机未对准很容易被检测到。在本文中，介绍了一种在 2D-DIC 实验中验证相机相对于目标表面的垂直度的新方法。如果相机不垂直于表面，则可以使用这种新颖的方法计算关于两个平面内轴的倾斜角。样品在两个平面内方向（相对于相机图像的水平或垂直方向）中的任何一个的简单平面内刚体平移，用于检测相机的非垂直性并计算倾斜角. 这种方法使用法向和剪切应变误差，由于相机非垂直而在 DIC 结果中引起，以确定表面倾斜角（如果存在）。使用基于针孔相机模型开发的简单分析方程计算倾斜角。所提出的方法通过在目标表面以 0.5° 到 4° 的角度倾斜时进行的实验进行验证。实验结果表明，这种方法能够自信地检测倾斜角度为 1° 或更大的相机未对准，并且可以用小于 0 的角度计算倾斜角度。