Research On Digital Image Correlation Method Based On Improved Sub-pixel Registration

Digital image correlation(DIC)is a newly developed optical measurement method,whose main purpose is to study the stress and strain of the object to be measured.At present,the research on digital image correlation mainly focuses on measurement accuracy and calculation efficiency.In this paper,the basic principle,correlation coefficient function,whole pixel search and sub-pixel registration of digital image correlation method are studied.In terms of calculation efficiency,several commonly used correlation coefficient functions are discussed and the correlation coefficient functions in this paper are determined.Then the improved cuckoo search method is introduced into the whole pixel search stage,and its search strategy is introduced in detail.After verifying by computer simulation speckle patterns with controllable parameters,it is concluded that the improved cuckoo search method is the best of the three algorithms in terms of both computational efficiency and reliability.In view of measurement accuracy,since the accuracy of the gray gradient has an important impact on the measurement accuracy and calculation efficiency of sub-pixel registration,and the traditional method of calculating the gray gradient is susceptible to noise interference when calculating the gradient,a large calculation error occurs Therefore,this paper proposes a NR method based on Huber function regularized gray gradient.The algorithm uses Huber function regularization to calculate the gray gradient,and then uses the Newton iterative algorithm to perform sub-pixel registration.By simulating the speckle pattern,the anti-noise ability of the new algorithm is verifiedunder the two conditions of the same noise with different displacements and different noise with the same displacement.Then the measurement accuracy,calculation efficiency and anti-noise performance of the gradient method,N-R method and the new algorithm are compared.Finally,the algorithm proposed in this paper is applied to the measurement of concrete surface deformation,which verifies the feasibility and accuracy of the algorithm in practical application.Then,combining the digital image correlation method with the concrete CT image,the internal deformation of concrete is measured,and the failure process of concrete is analyzed.The experimental results show that the combination of CT technology and digital image correlation method can provide a visual means for the internal stress-strain analysis of concrete.