Numerical study on variation of chord modulus on the springback of high-strength steels

Abstract

The advanced high-strength steels (AHSS) have become an interesting alternative to the automotive industry to reduce vehicle weight and therefore reduce fuel consumption. However, the wide variety of applications in the automotive industry is still limited due to challenges in its formability and unloaded behavior of these steels popularly called as springback. Computational tools for numerical simulation have been employed in the industrial environment to help predict the occurrence of springback and defining the appropriate parameters to eliminate or reduce their magnitude. However, the accuracy of the numerical results for AHSS still failed to reach a satisfactory level. The limitation in predicting the springback of AHSS by means of finite element method (FEM) is assigned to computationally difficult to characterize the mechanical behavior of these steels during the plastic strain. The variation of elastic modulus during plastic strain is considered as a major cause of non-linearity of the behavior of these steels. This work aims to study the declining behavior of the modulus of elasticity with an increasing plastic strain objecting to an improvement in the computational prediction of the springback phenomenon of AHSS. Specimens of various AHSS steels were loaded and unloaded in uniaxial tension in 0°, 45°, and 90° to the rolling direction. For all AHSS, it was found that the elastic modulus decreases during loading and unloading after each acquired plastic strain approximately up to 10% of plastic strain and then saturates at higher strain values. Further, the L-bending test was simulated where the change of elastic modulus with respect to plastic strain as observed in the uniaxial tension test is informed through the user subroutine VUSDFLD material model. The springback results were then compared with the experiments. It was found that predictions are in close agreement with experiments after informing the model with the decline of elastic modulus with respect to plastic strain through user subroutine material model as compared to the baseline model.