Application And Numerical Simulation Of 3D Digital Image Correlation Method In Carbon Steel Stretching

Traditional extensometers and resistance strain gauges have problems in strain measurement such as complicated operation process and inability to perform real-time measurement,which cannot meet the application requirements in complex environments.With the rapid development of binocular stereo vision technology and image recognition technology,the 3D digital image correlation method,with its simple operation process,high accuracy and reliability,had been highlighting its advantages in engineering applications and had become one of the most common methods used in deformation detection.In this paper,based on the 3D digital image correlation method,we conducted experiments related to the deformation process of carbon steel materials,which are most used in engineering,and the main research work is as follows:To further understand the displacement and strain distribution at the neck shrinkage of commonly used carbon steel bars under tensile conditions,tensile experiments were conducted on three carbon steels,Q235B steel,45 steel and T8 steel at a tensile speed of 4mm·min^-1.The strain,radius and stress triaxiality changes at the neck shrinkage during the tensile process were determined based on the digital image correlation method.At the same time,the Johnson-Cook principal structure model was used to calibrate the true stress-true strain relationship,and the ABAQUS finite element software was used to simulate the tensile process of 45 steel.The results showed that the absolute values of strains in the x-axis and y-axis directions of the three steels showed a slow and then fast increasing trend,and the radius values at the necking point showed a decreasing trend.The strain measurement accuracy of the digital image correlation method was better than 0.05%,which was basically comparable to the results measured by the force-displacement transducer.The true stress-true strain curve derived from ABAQUS finite element simulation is basically consistent with the experimental curve,and the actual deviation between the two is 0.48%.The trend of the triaxial degree of stress at the necking is basically consistent with the experiment.The strain variation and strain field clouds of 45steel obtained from the simulation are in good agreement with the results measured by 3D digital image correlation method in the x-axis and y-axis directions,and there are differences in the xy-plane.As a result,the deformation failure process of materials is often abrupt and requires regular wear testing and reliability assessment of workpieces in engineering applications.To understand the effect of notch factor on the mechanical properties of carbon steel plates and the distribution of strain field at the notch during the tensile process,quasi-static tensile experiments were performed on notched plates of different sizes of 20,45 and 60steel,and the parameters related to the Johnson-Cook principal structure model were calibrated using the transformed true stress-true strain curves.Determination of strain changes and strain field distribution at the corresponding points of notches during tension based on digital image correlation method.The deformation process of 45 steel notched plates was simulated by finite element method and get its strain field distribution cloud map.The results showed that the deformation process of the three carbon steel plates conforms to the Johnson-Cook model stress-strain law,and the tensile strength and notch sensitivity of the material increase and then decrease with the increase of the notch size,reaching the maximum atρ=0.2 mm.The measurement results of the digital image correlation method are in high agreement with the finite element simulation results,and the strains are mainly concentrated near the root of the notch in the x-axis and y-axis directions.The strains in the xy-plane direction are roughly symmetrically distributed in a 45°shear shape with the central axis,mainly concentrated at the edge of the notch.Therefore,during engineering failure analysis,the stress concentration factor can be reduced by adding additional notches of appropriate size and shape in the stress concentration region to reduce the occurrence of part failure conditions.