Optimization And Engineering Application Research Of Digital Image Correlation

With the upgrading of Chinese manufacturing industry,the deformation and residual stress testing of related products or structures will be put forward higher requirements,in order to ensure high efficiency of the manufacturing process and high quality of the final product.Digital image correlation?DIC?as a new deformation measurement method,has the advantages of non-contact measurement,full field deformation measurement,easy operation,high precision and low cost,which make it will play an increasingly important role in the upgrading of Chinese manufacturing industry.In this work,a series of researches about optimization of classical algorithms,measurement error correction and valuable engineering applications of DIC were developed.The purpose of this work was to develop a DIC software with the strengths of high precision,high speed and wide application,then applied DIC to many valuable engineering measurements.Optimization algorithms of initial value transfer mode of deformation based on zero normalized cross correlation?ZNCC?coefficient and interpolation calculation based on the global table of interpolation coefficients were introduced to improve the accuracy and speed of the DIC correlation calculation.The optimization effect of these optimization algorithms in calculating precision and speed was evaluated by the simulation of speckle pattern experiments.In the rigid body translation experiment,the maximum absolute error of measurement results of optimization algorithm was 1×10^-4 pixel,and the absolute value of relative error was less than 0.30%.The accuracy of calculation was consistent with the classical algorithm.At the same time,calculation speed of the optimization algorithm was about 120-180 times faster than that of the classical algorithm without loss of calculation precision,which greatly reduces the computation time.Average gray level gradient was used to assess the quality of speckle pattern.The general characteristics of high quality speckle pattern and the optimal focus position were studied.The experiment results showed that the high quality speckle pattern always had the speckles with regular shape,moderate size and uniform distribution,and the speckle pattern should have high brightness.The turning point of the square value of average gray gradient of the speckle patterns at different focus positions was the best focusing position.The measurement errors introduced by out-of-plane motion,out-of-plane rotation and in-plane rotation were corrected by the correction method with region of compensation.The correction results were evaluated by a series of experiments.It was found that the correction effect of the correction method with region of compensation on the size and fluctuation of the displacement field was very good.The correction effect of the size and fluctuation of the strain field was no as good as the displacement field.DIC was applied to measure full field strain of compact tension specimen,mechanical properties of materials and welding deformation.One of the purposes of this work was to expand DIC to more engineering applications,and hope that DIC can make a contribution to the upgrading of Chinese manufacturing industry.