Charles Owens

The Effect of Surface Heterogeneities in Exploding Metallic Foils

During the electrical explosion of bridge-wires and bridge-foils, the metal bridge undergoes rapid resistive-heating. The metal is rapidly expanded through solid, liquid, vapour and plasma phases. This study uses ALEGRA MHD, a Sandia National Laboratory magneto-hydrocode, to predict the formation of these metallic phases during the explosion process and determine the effects of surface heterogeneities on the spatial distribution of these phases. The simulations are compared against x-ray phase contrast radiographs of electrically exploded bridge-foils. From comparison of these data, it is evident that the meso-structure of the metallic foil dominates the explosion process and is something that should be controlled during the manufacturing processes for detonator designs.During the electrical explosion of bridge-wires and bridge-foils, the metal bridge undergoes rapid resistive-heating. The metal is rapidly expanded through solid, liquid, vapour and plasma phases. This study uses ALEGRA MHD, a Sandia National Laboratory magneto-hydrocode, to predict the formation of these metallic phases during the explosion process and determine the effects of surface heterogeneities on the spatial distribution of these phases. The simulations are compared against x-ray phase contrast radiographs of electrically exploded bridge-foils. From comparison of these data, it is evident that the meso-structure of the metallic foil dominates the explosion process and is something that should be controlled during the manufacturing processes for detonator designs.

SPALL AND DAMAGE BEHAVIOR OF S200F BERYLLIUM

We have performed a series of plate impact experiments to study the strength and spall damage behavior of S200F Be. Peak stresses achieved were in the range from 5.6–19.2 GPa. VISAR data show long rise times in the approach to the shocked state believed to be the result of twinning occurring alongside or in deference to slip in this hep material, with its free surface never achieving a steady velocity. These data indicate brittle spall behavior with spall strengths in the range of 0.8–0.9 GPa. In experiments where target thickness is varied, we see evidence of precursor decay and present calculations of the Hugoniot Elastic Limit (HEL).

Dynamic Initiator Experiments using IMPULSE (Impact system for Ultrafast Synchrotron Experiments) at the Advanced Photon Source

Submitted for the SHOCK15 Meeting of The American Physical Society Dynamic Initiator Experiments using IMPULSE (Impact system for Ultrafast Synchrotron Experiments) at the Advanced Photon Source NATHANIEL SANCHEZ, BRIAN JENSEN, KYLE RAMOS, Los Alamos Natl Lab, ADAM IVERSON, National Security Technologies, MICHAEL MARTINEZ, GARY LIECHTY, Los Alamos Natl Lab, KAMEL FEZZAA, Argonne National Laboratory, STEVEN CLARKE, Los Alamos Natl Lab — We have successfully imaged, for the first time, the operation of copper slapper initiators that are used to initiate high explosive detonators. These data will aid in model development and calibration in order to provide a robust predictive capability and as a design tool in future applications. The initiation system consists of a copper bridge fixed to a parylene flyer. The copper bridge functions when a capacitor is discharged causing current to flow through the narrow bridge. As this happens, a plasma forms due to the high current densities and ohmic heating, which launches the parylene flyer that impacts a high explosive pellet producing detonation. Unlike traditional measurements, x-ray phase contrast imaging can see “inside” the process providing unique information with nanosecond time resolution and micrometer spatial resolution. The team performed experiments on the IMPULSE system at the Advanced Photon Source to obtain high resolution, in situ images of this process in real-time. From these images, researchers can examine the formation of the plasma instabilities and their interaction with the flyer, determine the flyer velocity, and obtain crucial information on the spatial distribution of mass and density gradients in the plasma and flyer. Nathaniel Sanchez Los Alamos Natl Lab Date submitted: 29 Jan 2015 Electronic form version 1.4

Enhancing impact velocity with shock interactions in a restricting die

Shock compression and impact studies could benefit from the ability to increase impact velocities that can be achieved with gun systems. Single-stage guns have modest performance (0.2-2 km/s) that limits their utility for high-pressure and high-velocity studies, while more capable systems are expensive and complex. We are developing a technique that uses a low-strength sabot with a tapered die to increase the impact velocity without modifying the gun itself. Impact of the projectile with the die generates a converging shock wave in the sabot that acts to accelerate the front of the projectile, while decelerating the rear portion. Preliminary experiments using this technique have observed a velocity enhancement of up to a factor of two.