Experiments to assess structural loads during solid armature contact transition

The objective of the work is to characterize the force developed at the rail-armature interface during contact transition. Solid armatures were accelerated up to 2.5 km/s, with peak currents on the order of 1 MA. The armature contacts were allowed to naturally transition, an event that typically occurred on the decaying portion of the current pulse. Deflections of unsupported steel rods launched with an armature were measured from flash X-ray images taken at muzzle exit. In-bore X-rays were used on a few tests to refine the time at which the maximum rod deflection occurred. The highest velocity tests provided further data on armature deformation. In addition to the experiments, a coupled electromagnetic-structural dynamics code was used to compute the rod and armature deformations based on a range of assumed pressure profiles at the rail-armature interface and under a variety of boundary conditions. Reasonable agreement between the calculations and experiment was obtained with an interface pressure of approximately 550 MPa (80 ksi) applied over the smallest mesh area available at the leading edge of the front contact (25 kN). In future work, this load can then be used as input to structural mechanics calculations to further increase the survivability of hypervelocity long-rod penetrators.