Suitability of the electromagnetic ring expansion test to characterize materials under high strain rate deformation

Abstract

Characterisation of materials under high strain rate is always challenging, and requires sophisticated apparatus. Magnetic pulse forming techniques can involve high strain rate deformation and the electromagnetic ring expansion test (ERET) is considered here to determine its suitability to characterise materials at high strain rate. The multi-physics and high speed nature of the process requires advanced numerical modelling techniques to gain insight and understanding of stress development when used as a material characterisation technique. In order to evaluate the suitability of the ERET to fully characterise the material behaviour at high strain rate, stress states were investigated using 3D coupled mechanical-electromagnetic simulations on a validated numerical model. The numerical simulations were performed in LS-Dyna® with a modified Johnson-Cook (MJC) material model in this study. Albeit the preliminary results show the development of biaxial stress during the test, a shielding mechanism is proposed to eliminate the axial component of the stress on the rings. This study indicates that the ERET has a potential to be used for characterisation of the material parameters under the influence of high strain rate.