| The Digital Image Correlation Method(DIC)is a non-contact full-field optical measurement method.Compared with other optical measurement methods and traditional testing methods,DIC has the advantages of strong anti-interference,high test accuracy and simple equipment.So the DIC method has been widely used in various engineering surveys since its introduction in the 1980 s,and one of the hot trends is to study the material damage mechanism using digital image correlation methods.Nevertheless,there are still some shortcomings in this method.In order to better apply it to various research fields,it is necessary to conduct research on the accuracy and consistency of the method deeply.This article is based on the basic principles of DIC,and some of related issues are discussed.The research contents and results mainly include:(1)In the case of the water transfer speckle field,the reliability of the test system using 3D digital image correlation method was evaluated from the two aspects,which are displacement test accuracy and consistency of test results.The displacement accuracy proofreading experiment and DIC test result consistency analysis experiment were designed..Among them,in the displacement accuracy analysis,the displacement of the displacement table is taken as the reference.The results show that the relative error of the in-plane displacement and the out-of-plane displacement can be less than 0.1% under a certain loading displacement,which meets the engineering test requirements.When evaluating the consistency of the test results,the author repeated the pure bending test of carbonic acid polyester beam several times,the study found that the DIC method has good consistency in both displacement and strain tests.(2)Taking the three-point bending test on plain concrete as an example,the whole process of material failure is analyzed through the displacement field and the first principal strain field using digital image correlation,and the propagation path of crack on the surface of the structure is extracted.At the same time,the parameters such as crack length and opening displacement are calculated,which provides a new and effective method for relevant engineering applications.After statistical analysis,(3)Three-point bending experiments of prefabricated I-type cracked cast iron beams were carried out.The stress intensity factor and J-integral near the crack tip were calculated with the theoretical formula of fracture mechanics.The results were compared with the standard results of E399-74 test.The results show that the calculation accuracy of stress intensity factor is less than 10%,and the calculation error of J-integral is less than 20%,which basically meets the needs of engineering application.Simultaneously,it is found that the accuracy of SIF can be improved by increasing the number of terms of least squares fitting coefficients and by reasonably selecting data points.At the same time,the experimental results also verify the path independence of J-integral.(4)In the case of artificial spray spotting,the CFRP plate-steel interface slip test was designed.The comparison between the strain by DIC test and strain gauge results verified that the strain measurement results were in good agreement,and the DIC calculation parameters were also analyzed.The effect of the strain results shows that in the uniform deformation,increasing the strain window can make the strain result convergent to the true value better,and the calculation step size and calculation template should be formulated according to the actual situation.At the same time,the displacement process and strain field obtained by DIC are used to analyze the whole process of CFRP plate-steel interface failure.Two typical failure modes are summarized,namely CFRP plate strength failure and rubber layer detachment failure. |
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