INCREASED DUCTILITY IN HIGH-VELOCITY ELECTROMAGNETIC RING EXPANSION

Thin rings have been rapidly expanded using large, transient magnetic fields to study the effect of deformation velocity on strains to failu re of ductile metals. A classical electrodynamics analysis similar to one developed previously by Gourdin was employed to estimate sample ve locities. Within expansion velocities studied (50 to 300 m/s), the exp erimental results show that ductility of Al 6061 and OFHC Cu increases monotonically with increasing velocity. In each case, sample strain a t failure is almost twice as great at 300 m/s as in the static conditi on. Comparison to a one-dimensional rigid-viscoplastic dynamic finite element method analysis suggests that inertial effects are mainly resp onsible for enhanced ductility over a wide range of velocity.