Research Of The Application Of Digital Image Correlation Method In Mechanical Properties Measurement Of Steel Materials

Digital image correlation method is a test method that can obtain the deformation of the object by calculating the gray information of the surface images of the object before and after the deformation.By comparing the speckle patterns,displacement field and strain field are calculated.DIC method has the characteristics of three-dimensional,full field and non-contact,therefore,it won't be restricted by the shape of the specimen.By DIC method,two-dimensional and three-dimensional deformation test can be carried out using the specimen with different shapes,and obtain the whole information of the deformation field,so,it has been more and more widely used in the testing of mechanical properties of materials.Combined with the tensile experiments,fatigue experiments and fracture mechanics experiment,the application of DIC method in the testing of mechanical properties of materials was researched in this paper,IF steel,321 stainless steel and A508-3 steel were used as the experimental materials.The main work summarized as follows:Measured the strain by DIC method,compared the results measured by DIC method with the results measured by extensometer thus verified the accuracy of DIC method in deformation data testing.Measured the strain-hardening exponent(n-value)and the plastic strain ratios(r-value)of IF steel by DIC method,and researched the influence of the test location of the transverse extensometer on the accuracy of the measurement of r-value.The result showed that the accuracy of the testing results of the r-value depended on the test location of the transverse extensometer,different test locations got different results,and the farther the measurement distance,the greater the difference.Combined the analysis results of DIC method and the experimental process,the validity of fatigue experiments was successfully predicted without adding additional experimental operations by analyzed the strain distribution,and avoided the slow progress and the high cost which is caused by the invalidity experiments.Explored the real-time application during the experiment of DIC method.J integral experiment and CTOD test experiment of A508-3 steel were carried out by DIC method,solved the problem of the negative crack extension,which is common in the measurement by the compliance method,and implemented the direct measurement of CTOD of the specimen.Researched the deformation and the crack propagation rule of the specimen during the experiment by DIC method and obtained the information about the rotation center of crack surface,the location of crack and the crack propagation path by analyzed the changes of the displacement field and the strain field of the specimen.