Study Of Digital Image Correlation Method Based On Crack Tip Function And Its Application

The fracture damage is the prime damage type in structure materials of modern engineering industries. The stress field near the crack tip has great significant effects on the initiation, evolution and damage of the crack. Based on the extended digital image correlation(X-DIC) method, this paper focuses on the theoretical and experimental technologies study accounting for the discontinuity in crack test. Searching for the displacement function characterizing the realistic deformation field in discontinuous zone accurately and applying for the X-DIC, this paper proposed an improved scheme considering the crack tip function and completed relative experiment test study.Firstly, this paper studied the basic theories focusing on X-DIC, discussed the solution to tackling the discontinuous problem and analyzed the X-DIC method considering the displacement function in crack tip, which leading to the improved scheme. The proposal on researching the contribution rate and characterization of deformation made by the crack tip function was emphasized. Through the theoretical study in XFEM, this paper proposed another improved scheme and realized the computer program of X-DIC.Secondly, considering the differences in degrees of freedom of items in displacement functions obtained through X-DIC, the results show that there are differences between the characterization and contribution in every item of deformation in crack tip. the study found the items and combinations has a greater discrimination impact on the different types of crack in the test, and then find out the leading terms to crack tip displacement field in the X-DIC test. The item sin(?/2) in the displacement function of crack tip presents that the displacement field in type I, type II and mix model crack was controlled by this item, and the differences in contribution of other items exist. Moreover, the effects of sub-region in characterization of function in crack tip computed were studied.Lastly, the X-DIC based on the displacement field in crack tip was introduced in the fracture mechanical behavior of super-hard aviation alloy. In which the tensile test was conducted with single side crack in super-hard aviation alloy. The possibility and application of X-DIC were validated as well as the improved method. The reasonable results were obtained accurately. This paper also conducted on the specimen with defect combined with crack and pore well. The results show that the improved X-DIC is more effective in the deformation field with more complex situation, which furthers the application of this method.