Application Of 3D Digital Image Correlation Method In Study Of Material Failure

In practical application,ductile fracture is one of the main failure modes of metallic members.The effect caused in production and manufacturing process in metal components is so large that they affect the using and the performance of the component.The study of the deformation and failure process of notched specimens is of great significance.Three dimensional digital image correlation method(3D-DIC)is a kind of non-contact method for measuring three-dimensional full field deformation.In this paper,the 3D-DIC method is used to study the deformation and failure behavior of notched specimen with defects.The study mainly includes the following aspects:1.Studied and realized the comparison method of three dimensional full field surface data;The finite element analysis results were compared with the data of the corresponding tensile deformation process of the plate specimens,round specimens,flat notched specimens and round notched specimens respectively.The comparison results show that the full field contrast method is suitable for the application of 3D plane,3D surface,3D plane with complex strain distribution and complex 3D surface.2.The regularity of deformation of three kinds of tensile specimen during the tension deformation is studied.As the results show,the strain on the parallel section of the specimen is almost equal in the plastic deformation stage;when the load reaches the maximum value,during the local deformation stage to the test piece occurs obviously neck shrinkage,the magnitude of the load on the specimen remains unchanged;after that,until the material was destroyed that the load was decreased rapidly,and the specimen was necking obviously.3.The influence of different strain calculation area on the true stress and true strain of the material was studied.The true stress-strain relationship that was calculated by the mean strain of maximum area on the surface of necking zoon before the failure of the specimen can fully describe the relationship during the progress of material deformation.The parameters of Johnson-Cook model were determined by the analysis of the corresponding true stress-strain data.The model parameters are added to the finite element model in analyzing the test,and the results of finite element calculation are well agreement with the experimental results by the full field comparison method.But the calculation method is not applicable to the calculation of the true stress-strain relationship of round specimens.4.The regularity of deformation of notched specimen during the tension deformation is studied.Results showed that the deformation of the specimen is mainly occurred on the left and right sides of the circular notch,and the two parts of the notch up and down almost no deformation in the whole process.Finite element method was used to analyze the variation of stress and stress triaxiality on the minimum net section of notched specimen and he results show that the position of the maximum stress and stress triaxiality is not in the gap,but in the vicinity of the gap.In the process of deformation,the yield of the material can cause the stress triaxiality to be changed temporarily,and then gradually recovered.5.The relationship between failure strain and stress triaxiality is studied,and the basic parameters of Johnson-Cook failure model are determined;with the finite element analysis method and the full-field data comparison method,analyzed the test data of the notched specimens which one with initial damage.The results showed that although the test value of ultimate load and the calculation results are similar,but due to the existence of initial damage,the strain data around the damage zone is obviously larger than the finite element analysis results.