| Digital image correlation method is widely used in the field of civil engineering for its advantages of high precision,non-contact and full field measurement.The software of 3D non-contact strain measurement system developed on this basis can quickly calculate the strain and displacement of the test object.As an efficient measurement method for sensing structural deformation and obtaining structural deformation parameters,its accuracy is often the preferred measurement index.In the process of actual data processing and analysis,the selection of calculation parameters often becomes an important factor affecting the accuracy.Therefore,it is very necessary to determine the optimal range of calculation parameters to ensure the accuracy of digital image correlation method applied to the actual engineering measurement or monitoring.Firstly,this paper studies the influence of calculation parameters on the accuracy of digital image correlation method.Starting from the calculation parameters of sub-region,calculation step and strain window size,a sub-pixel translation speckle simulation program is designed based on MATLAB platform.20 digital speckle patterns with 0.05 pixel translation are generated,and then random Gaussian white noise is applied to draw the relationship curve of SSSIG（sum of square subset intensity gradients）-RMSE（root mean square error）.The range of the optimal sub region is obtained theoretically.At the same time,based on the 3D printing speckle tensile test,the sub region,step size,and strain window size are selected according to the noise level at no-load time,thus a series of calculation parameters are optimized.The optimization results show that when the calculation subset（template size）is in the range of 27pixel～33pixel,the calculation step size is in the range of19pixel～23pixel,and the strain window size is in the range of 21pixel～25pixel,they would have little influence on the DIC measurement results with high accuracy and less error.To prove the effectiveness of the optimized parameters and test the actual calculation accuracy,an aluminum alloy plate-rod composite structure with rise span ratio of 1:4 and section size of 4400 mm × 1530 mm × 1100 mm was designed,and the ultimate bearing capacity and instability analysis for the aluminum alloy honeycomb plate cylindrical reticulated shell were carried out.From the perspective of digital image correlation method and nonlinear finite element（ABAQUS）simulation,the errors between the displacement results obtained by these two methods and the test results（electrical measurement method）are compared.The results show that: the maximum midspan displacement of cylindrical reticulated shell calculated by digital image correlation method is61.28 mm,and the error is 1.16% compared with the measured value;the maximum midspan displacement simulated by finite element model considering double nonlinear effect is 65.92 mm,and the error is 6.32% compared with the measured value;the maximum midspan displacement simulated by finite element model considering the jump instability and the structural buckling is 66.89 mm,and the error is 7.89% compared with the measured value.It can be seen that the digital image correlation method has higher accuracy in the displacement measurement for the structure compared with the finite element simulation method,which also demonstrates the reliability and effectiveness of the optimal range for the optimized calculation parameters. |
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