数字图像相关方法(DIC)是一种非接触式全场光学测量方法,在许多领域已被用于物体表面位移和应变的测量。传统的DIC全场应变测量通常使用高精度逐点局部位移场最小二乘法,但该方法对于旋转物体的应变测量仍存在显著误差。为此,在传统DIC应变计算方法的基础上,引入变形前后的旋转矩阵,提出一种考虑旋转的局部位移场最小二乘应变计算方法。该方法能够补偿由旋转引起的应变误差,从而实现任意旋转角度下应变的高精度测量。在模拟实验中,分别对多种旋转角度下的同一应变以及同一旋转角度下的不同应变进行测量,由两种实验应变测量获得的均方根误差(RMSE)平均值相对传统DIC方法分别为由0.00498降低到0.00011以及由0.00703降低到0.00027,两种实验结果均证明所提方法能较大程度地提高旋转条件下的应变测量精度。

Digital image correlation (DIC) is a non-contact and full-field optical measurement method used to measure displacement and strain of object surfaces in numerous fields. In traditional DIC, the local displacement pointwise least square method (PLS) is widely used for full-field strain measurement owing to its high accuracy; however, this leads to a significant error when used for strain measurement of rotating object. To address this issue, a PLS strain calculation method that considers the rotation was proposed herein. By introducing a rotation matrix before and after deformation into the traditional PLS method, the proposed method can eliminate the strain error caused by rotation. Consequently, the proposed method can be used to calculate strain at an arbitrary rotation angle without the loss of measurement accuracy. To verify the high accuracy and validity of the proposed method, two simulation experiments of strain measurement were conducted. One considers the same strain under various rotation angles and the other considers different strains under the same rotation angle. In the two respective experiments, the strain measurement results of the root-mean-square error mean value decreased from 0.00498 to 0.00011 and from 0.00703 to 0.00027 compared with the conventional DIC method. Results indicate that the proposed method can significantly improve the strain measurement accuracy under rotating conditions.