DIC-AIDED METAL TENSILE TEST TECHNOLOGY USING CHAIN-LIKE SECOND ORDER SUB-REGIONS

Aiming at improving the measurement accuracy and test efficiency of metal tensile tests, the Digital Image Correlation (DIC) technology is introduced upon the conventional tensile test, and the corresponding deformation measurement theory and method are proposed. Based on the necking effect of tensile specimen, a chain-like deformation measurement theory is proposed, and the proposed theory characterizes the deformation of the specimen at each stage through a flexible chain that freely deforms as the surface of specimen does. Further, by setting up multiple equal-sized and continuous DIC second-order sub-regions, the DIC sub-pixel registration algorithm is used to obtain the coordinates of the chain sub-regions corner points at any moment, and the deformation results of the discrete flexible chain along the length of the specimen are determined to indicate strain and necking extremum spot of the specimen, thus a methodology of DIC-aided test method for metal tensile tests is established. Tensile tests of several standard metal specimens were carried out to measure necking effect, elastic modulus, ultimate elongation, and true stress-strain curve using both the proposed method and conventional methods such as extensometer and image targets tracing. Results show that the proposed method has agreeable measurement accuracy and high effectiveness, which indicates that the proposed method can obtain automatic measurement and has a potential prospect to be industrially popularized in the field of metal tensile tests.