基于子区投影和Savitzky-Golay滤波的三维数字图像相关法应变场计算方法研究

Strain Field Calculation by 3D Digital Image Correlation Method Based on Subset Projection and Savitzky-Golay Filter

数字图像相关(DIC)法是一种非接触式的全场变形测量方法。三维DIC系统突破二维DIC系统对试验件表面为平面的要求,通过双目或多目相机系统获得试验件表面的三维位移场数据。通过建立局部子区拟合最小二乘平面,将三维空间曲面上的离散点投影到二维平面内,再利用Savitzky-Golay滤波器拟合求解局部应变张量。利用三维DIC法,实现了自由曲面试验件应变场的表征。重点研究了小平面投影算法的误差,结果表明,投影过程导致的应变场计算误差远小于位移场误差的传递量;当应变子区半径M=5时,应变场误差约为30με;当M=10时,应变场误差约为10με。

The digital image correlation(DIC)method is a non-contact,full-field deformation measurement method.The three-dimensional DIC breaks through the requirement that the surface of the test piece is planar in the two-dimensional DIC system,and obtains the three-dimensional surface displacement field data of the test piece through a stereo or multi-view camera system.First,a local subset is used to fit the least square plane,and the discrete points on the three-dimensional spatial curved surface are projected into the two-dimensional plane.Then,the Savitzky-Golay filter is used to solve the local strain tensor.Finally,the characterization of the strain field of a free-form test piece is realized,especially the errors of the small-plane projection method are investigated.The results show that the calculation error of the strain field caused by the projection process is much smaller than the transmission of the systematic error component contained in the displacement field data.When the strain subset size M=5,the strain field error is about 30με.When M=10,the strain field error is about 10με.