Research On The Forming Characteristics Of Advanced High Strength Steel In Warm Environment

As the improvement of forming technology for the advanced high strength steel (AHSS), the temperature of sheet metal will raise during the forming process. Thus, the research of forming properties of temperature-related for AHSS have an important theoretical significance and practical value because the material mechanical behaviors of AHSS at thermal environment differ greatly with that at room temperature. In this paper, the mechanical properties and forming characteristics of automotive DP590 under warm environment are researched by the combined methods which contain experimental technique, theoretical analysis and numerical simulation.The cruciform specimen central area in the process of biaxial tension test is heated by radiation heating device which is built by the halogen lamp. And the temperature of the sheet metal central area can be adjust by changing the distance between the cruciform specimen center zone and center zone of the quartz tube filament. In addition, the feasibility of radiation heating device is verified by finite element analysis and test.In order to obtain the test stress-strain curves of different loading paths of DP590 sheets at different temperatures, the biaxial tension tests are conducted with radiation heating device at warm environment. Hence, the experimental yield locus of DP590 under different temperatures are calculated using the principle of what equivalent plastic work is equal in a unit volume. It was found that Yld2000-2D yield criterion is suitable to describe the yield behavior of DP590 under warm environment by comparing the experimental yield locus with several commonly used yield criteria. Furthermore, four polynomial function of temperature are used to fit the variation trend of the anisotropic parameters in Yld2000-2d yield function under different temperatures. The temperature-dependent yield criterion is then established by calibrating the dependence of the anisotropic criterion and the temperature. Compared with other commonly used yield criteria, the proposed temperature-dependent yield criterion is more accurate under warm-forming condition.Based on the proposed temperature-dependent Y1d2000-2D yield criterion, the numerical algorithms of forming limit strain are derived from two popular instability theory (M-K model and C-H model). Then theoretical forming limit curve can be obtained. Compared with the experimental forming limit curve which are determined by the forming limit test under different temperature, M-K model is more suitable for prediction of forming limit for DP590 under warm environment, and the characteristics of two instability theory are also analyzed.The proposed temperature-dependent Y1d2000-2D yield criterion and the forming limit curve under warm environment were embedded into ABAQUS through the user-defined subroutine VUMAT. The semi-implicit algorithm was adopted among many stress update algorithms. The numerical simulation of deep-drawing process for DP590 sheet are conducted by using user-defined subroutine VUMAT. The contrasts of the simulation result and test data show that the temperature-dependent Y1d2000-2D yield criterion and the forming limit curve under warm environment established in this paper provides a high accuracy and value in use.