Eddy current induced dynamic deformation behaviors of aluminum alloy during EMF: Modeling and quantitative characterization

Unveiling the quantitative influence of the induced eddy current in electromagnetic forming (EMF) is of great significance to realize the precision control of the forming process. To this end, a semi-phenomenological model for predicting the current-carrying dynamic deformation behaviors of aluminum alloy is established by introducing a rate-dependent electroplasticity (EP) model and an elastic thermal expansion model into the high-strain-rate constitutive model. In the modeling process, the electroplastic energy density (EPED), which is a function of prestrain and current density, is defined as the dominant factor of EP-induced stress drop and its threshold value is determined. Moreover, a rate-dependent factor is formulated to consider the effect of wide-range strain rate variation on EP-induced stress drop. Applied to uniaxial-stress EMF process, the present model exhibits preferable prediction accuracy by comparing the predicted results of analytical calculation with experimental ones. The present model captures the characteristic stress responses of EMFed samples, i.e. monotonic strain hardening followed by long-range flow softening. It is found that the peak stress and EP softening ratio both increase with EPED, which can be attributed to the combined influences of increased current density, electric resistivity and acceleration on the competition between strain rate hardening and EP induced softening.