Research On Digital Image Correlation Method For Full-field Deformation Measuremen

With the continuous improvement of science and technology level of our country,industrial manufacturing,aerospace and medicine and other fields all need to be measured for surface deformation of materials.Different from traditional contact measurement,digital image correlation(DIC)method is an optical measurement method developed rapidly in recent years.It can not only realize non-contact measurement of topography,deformation and strain.Moreover,it has high precision and anti-interference,and its research is of great significance.In order to measure full-field deformation,multi-camera DIC system is usually used for measurement,but the current widely used planar calibration plate cannot meet the calibration requirements of multi-camera DIC system,so it is very necessary to study a new multi-camera calibration method.In this paper,the basic principle of DIC and camera calibration is first introduced,the calibration principle of the classical planar calibration plate method is analyzed and verified by experiment,and the calculation method of three-dimensional strain field is also expounded.Secondly,the calibration method of DIC system of multiple cameras was studied.In this paper,multiple cameras were grouped into two groups,and then the internal and external parameters of each group of cameras were calculated by using Zhang Zhengyou’s planar target calibration algorithm.Based on the known parameters,an improved subpixel edge extraction algorithm used in multi-camera calibration was proposed.A high-precision multi-camera calibration method based on polynomial interpolation was proposed.The subpixel edge extraction algorithm improved by polynomial interpolation was used to extract the projection of the sphere on the image plane,and the relationship between the spatial sphere and its projection conic curve was utilized.The spherical projection is solved,and the external parameters between the binocular systems are calculated according to the three-dimensional coordinate relations of different spherical positions in each binocular system.Finally,six cameras,four cameras and two cameras were used respectively to carry out measurement verification experiments,and the measurement results were compared with the measurement instrument data to study the measurement accuracy.The experimental results show that the measurement errors of the proposed method are all within the acceptable range no matter six cameras,four cameras or two cameras are used,and the accuracy is comparable to that of the actual measuring equipment,which verifies that the algorithm can meet the actual measurement requirements when different numbers of cameras are used for measurement,and verifies the accuracy and feasibility of the algorithm.