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Research Papers

Disruption Mechanisms in Electrified Solid Copper Jets

[+] Author and Article Information
Patrik Appelgren1

 Swedish Defence Research Agency (FOI), SE-164 90 Stockholm, Sweden

Melker Skoglund, Patrik Lundberg, Lars Westerling, Anders Larsson, Tomas Hurtig

 Swedish Defence Research Agency (FOI), SE-164 90 Stockholm, Sweden

1

Present address: Division of Space and Plasma Physics, School of Electrical Engineering, Royal Institute of Technology, SE-100 44 Stockholm, Sweden.

J. Appl. Mech 78(2), 021014 (Nov 10, 2010) (5 pages) doi:10.1115/1.4002569 History: Received September 09, 2009; Revised February 25, 2010; Posted September 16, 2010; Published November 10, 2010; Online November 10, 2010

Interaction between a solid copper jet and an electric current pulse is a complex process that has been experimentally studied by letting a jet created by a shaped charge device pass through an electrode configuration consisting of two aluminum plates with a separation distance of 150 mm. When the jet bridged the electrodes, which are connected to a charged pulsed power supply, current pulses with amplitude up to 250 kA were passed through the jet. By using flash X-ray diagnostics, the disruption of the electrified jets could be studied. In this paper, the disruption of the electrified jets is discussed and compared with disruption phenomena observed in electrically exploded metal rods in a static setup. Necks are naturally formed along a stretching jet, and in the experiments with current interaction these necks explode electrically. In the static experiments, the metal rods have small notches distributed along the rod to resemble the necks of the jet. When two neighboring necks or notches explode, the shock of the explosion compresses the intermediate jet or rod segment axially and the material is forced out radially. The disruption phenomena in the jet and rod experiments are similar with rapid expansion of the metal at explosion and at comparable velocities.

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Figures

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Figure 1

Rod with machined notches

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Figure 2

Current pulse in static experiments. Dashed vertical lines mark the times for flash X-rays in Fig. 3.

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Figure 3

(a) Montage of X-ray pictures of a copper rod with notches (axial positions indicated by the arrow) subjected to a current pulse. (b) X-ray pictures of a smooth (left) copper rod and a rod with notches (right) at times 75 μs and 100 μs.

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Figure 4

Position-time diagram for the jet with the current pulse

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Figure 5

X-ray pictures of jet disruption at different energies. From top: 96 kJ, 39 kJ, and 0 kJ stored in the capacitors. The pictures are taken 86 μs after contact is made by the tip with electrode 2 except for the lower picture taken 81 μs after contact. The jet tip has moved a distance of 620 mm from electrode 2 at time 86 μs.

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Figure 6

(a) The X-ray pictures of the segmented rod at times 50 μs, 62.5 μs, and 75 μs and (b) the X-ray picture of the 39 kJ shaped charge jet experiment at time 86 μs divided in portions with axial velocities in the ranges 3.5–4.2 km/s, 4.2–4.9 km/s, and 4.9–5.7 km/s. Note that the flash X-ray is placed in line with electrode 2 and hence depicts the 3.5 km/s fragment from the side at right angle while the fragments close to the tip depicts at an angle from above, revealing the ring shape.

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Figure 7

The disruption along the jet in the 39 kJ experiment at time 86 μs. The circles qualitatively indicate how the spherically shock wave from the exploding necks may compress the fragment to eventually form rings. The portions have axial velocities in the ranges 3.5–4.2 km/s, 4.2–4.9 km/s, 4.9–5.7 km/s, and 5.7–6.4 km/s.

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Figure 8

The radial velocities of the expanding spheres, assuming that the electrical explosion occurs at the position of electrode 2. The exact location at which the explosion occurs is unknown. The average radial velocity is 120 m/s, i.e., close to the value estimated from the maximum radius of fragments identified in two X-ray pictures taken at different times (2).

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Figure 9

A qualitative description of the jet disruption process, where the explosions of the necks force material radially outward to eventually form a ring

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