Comparative behavior of Ti and 304 stainless steel in a magnetically-driven implosion at the Pegasus-II facility

摘要

The PEGASUS-II facility, a pulsed power capacitor bank capable of delivering several megamperes of current to a cylindrical conducting liner, was used for the magnetic implosion of a thick-walled cylinder to study two-dimensional high-strain-rate flow in different materials. Boundary conditions of loading (dynamic pressure) were monitored by the measurement of magnetic field outside of the composite cylinder. The kinematics of flow were measured using three radial x-ray radiographs at different azimuthal angles and different times after the start of current through the cylinder. The composite liner consisted of separate stacked cylinders of 304L stainless steel or Ti between Cu cylinders. It was demonstrated that a magnetically-driven composite thick-walled cylinder is able to preserve cylindrical symmetry at the level of strain large enough to initiate material instability and at the same time avoid typical geometric instability for thin walled cylinders. The results are contrary to the expected behavior based on uniform plastic flow of these materials. This is explained based on the plastic flow instability and formation of multiple shear bands in Ti.