Research On Springback For High-Strength Steel Based On Elastic Modulus

As an important defect in sheet metal forming, springback is considered mostly for getting a good compensation in mould design. With the widely using of high-strength steel sheet, the problem of springback is increasingly prominent. And the higher the strength of steel is, the more significant the springback will be. The modulus of elasticity is one of the important factors that influence springback amount, and usually modulus of elasticity is taken as a constant value in engineering applying, while actually the elastic modulus changes coupled with increasing of plastic deformation, therefore, it is not accurate to get the springback amount with numerical simulation taking no account of changing of modulus, which exists big difference between the actual amount of springback with that.This paper discussed the relationship of DP590between the elastic modulus with strain in the conditions of loading-unloading cycles and usual loading in uniaxial tensile test. The result was found that the stress reduced nonlinearly with changing of strain during unloading. The results of concerned data processing and fitting indicated that the elastic modulus decreased with increasing of plastic deformation, and finally it tended to a constant value; In addition, it was also found that the changing tendency of elastic modulus was related to loading ways. The reason why elastic modulus changed was analyzed from the results of the experiment and was described in this paper, and the models of relation between elastic modulus with strain were achieved in the condition of two different loading ways.Taking the forming and springback of U-shaped part as an example, using the finite element analysis software, ABAQUS, for its powerful nonlinear analysis function and different algorithm, such as the dynamic explicit algorithm and static implicit algorithm, rewriting the input file to assign the different material properties to the corresponding analysis steps, the model can be applied in ABAQUS to simulate the stamping and springback of U-shaped part in the condition of usual loading. While in the condition of cyclic loading, the corresponding model was realized successfully through the information transmission between analysis steps during the same simulation above.The results of simulation above and the results of simulation based on constant elastic modulus were compared with the results achieved by physical test of U-shaped bending springback. It was shown that the springback amount of numerical simulation was smaller than that come out of physical experiment; The phenomenon that springback in condition of cyclic loading was more significant than that in condition of usual loading happened both in experiments and numerical simulations; Compared with the numerical simulation based on the initially constant Young’s modulus, the results of simulation adopted the models achieved were more accurate and consistent with the real testing results. The conclusion was made that considering the effect of plastic deformation on elastic modulus for high-strength steel can help improve the accuracy of the springback prediction and contribute to guide mold design. Besides, the models of elastic modulus based on the two loading ways above were accurate to some extent, and the numerical simulation method described in this paper was also feasible.