Reduction of Young’s modulus for a wide range of steel sheet materials and its effect during springback simulation

Abstract

Springback is among the key issues to be addressed in order to facilitate the application of AHSS in the automotive body. Since numerical simulations have become a standard tool during process design in automotive panel production, advanced material models considering springback-related material properties are increasingly getting into the focus. Next to the Bauschinger-Effect, describing early re-yielding during load reversal, also a reduction of Young’s modulus with increasing plastic strain is depicted in several material models implemented in different FEM codes. Herein, we focus on this Young’s modulus reduction. The initial Young’s modulus as well as its reduction are measured from uniaxial tensile tests with multiple unloading-reloading cycles without load reversal. Results are shown for steel sheet materials ranging from mild steels to AHSS containing retained austenite. Differences of the Young’s modulus decrease among the different steel grades are discussed with respect to their respective microstructure. Material models, depicting the Young’s modulus reduction, are fitted to the obtained data. The consequence of considering this effect during forming simulation is shown for bending-under-tension tests of DP600, representing the largest reduction.