Study of springback effect of AHS steels using a microstructure based modeling

In sheet metal forming process of automotive parts, springback effect is crucial, in particular, for advanced high strength (AHS) steels, by which local interactions between different phases play an important role on macroscopic response. Otherwise, most structural components with highly complex shapes required multi-step forming procedures. Better understanding and more precise description of plastic deformation behavior and springback occurrence of such formed steel sheets are thus necessary. In this work, the springback of AHS steel grades 780 and 1000 was investigated, for which tension-compression tests were firstly carried out. Then, finite element (FE) modeling was done on both macroscale and microscale using representative volume elements (RVEs) in order to predict the cyclic stress-strain responses. Hereby, the kinematic hardening Yoshida-Uemori (Y-U) model was applied to consider the elastic recovery of material. The material parameters of the Y-U model were identified for the investigated steels as well as their phase constituents. It was verified that the calculated flow stress curves fairly agreed with the experimental ones. Afterwards, hat-shape stamping tests were performed and the results showed that occurred springback angles determined from the experiments and FE simulations were in accordance. Additionally, RVE simulations were conducted for local area of deformed sheet sample. The plastic deformation of various phases in the microstructure of examined steels under load-unloading behavior during the forming process was characterized. This approach can be further used to incorporate the effects of microstructure on the springback effect of AHS steel sheet. (C) 2017 Elsevier Ltd. All rights reserved.