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Interaction between solid copper jets and powerful electric current pulses
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2011 (English)In: Journal of applied mechanics, ISSN 0021-8936, E-ISSN 1528-9036, Vol. 78, no 2, 021006- p.Article in journal (Refereed) Published
Abstract [en]

The interaction between a solid copper jet and an electric current pulse is studied. Copper jets that were created by a shaped charge device were passed through an electrode configuration consisting of two aluminum plates with a separation distance of 150 mm. The electrodes were connected to a pulsed power supply delivering a current pulse with amplitudes up to 250 kA. The current and voltages were measured, providing data on energy deposition in the jet and electrode contact region, and flash X-ray diagnostics were used to depict the jet during and after electrification. The shape of, and the velocity distributions along, the jet has been used to estimate the correlation between the jet mass flow through the electrodes and the electrical energy deposition. On average, 2.8 kJ/g was deposited in the jet and electrode region which is sufficient to bring the jet up to the boiling point. A model based on the assumption of a homogenous current flow through the jet between the electrodes underestimates the energy deposition and the jet resistance by a factor five compared to the experiments, indicating a more complex current flow through the jet. The experimental results indicate the following mechanism for the enhancement of jet break-up. When electrified, the natural-formed necks in the jet are subjected to a higher current density compared to other parts of the jet. The higher current density results in a stronger heating and a stronger magnetic pinch force. Eventually, the jet material in the neck is evaporated and explodes electrically, resulting in a radial ejection of vaporized jet material.

Place, publisher, year, edition, pages
2011. Vol. 78, no 2, 021006- p.
National Category
Engineering and Technology
URN: urn:nbn:se:uu:diva-197561DOI: 10.1115/1.4002568OAI: oai:DiVA.org:uu-197561DiVA: diva2:613414
Available from: 2013-03-27 Created: 2013-03-27 Last updated: 2013-08-30Bibliographically approved
In thesis
1. Interaction of Cylindrical Penetrators with Ceramic and Electromagnetic Armour
Open this publication in new window or tab >>Interaction of Cylindrical Penetrators with Ceramic and Electromagnetic Armour
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Växelverkan mellan cylindriska penetratorer och keramiska och elektromagnetiska pansar
Abstract [en]

Armoured vehicles have traditionally used steel armour as protection against penetrators such as projectiles and shaped charge jets. The latter produce a thin stretching metal jet, usually of copper, with a tip velocity of about 7-8 km/s. In order to obtain more weight-efficient solutions, there is a search for lighter materials and other protection techniques. In this thesis, ceramic and electromagnetic armours are studied. Ceramic materials are lighter than steel, and their high compressive strength makes them useful as armour materials. Electromagnetic armour consists of two metal plates connected to an electric power supply capable of delivering a strong current pulse. A conductive penetrator passing through both plates is destroyed by the effects of the resulting current.

Tests of the ceramic armour materials alumina and boron carbide were performed with reverse impact technique, which signifies that a target assembly (ceramic confined in a metal cylinder) was launched by a gun towards a projectile placed in front of the gun barrel. By this technique yaw was eliminated, but the geometric scale had to be very small. Therefore, we studied scaling laws for ceramic armour through a series of tests with direct impact technique and projectile diameters from 2 to 10 mm. The small scale has the advantage that flash X-ray photography can be used to photograph the projectile inside the ceramic target. The phenomenon of interface defeat or dwell was also demonstrated. It signifies that the ceramic, at least for a short time, can withstand the impact pressure so that the projectile just flows out onto the target surface. A transition velocity, above which dwell does not occur, was determined. Simulations were performed with the continuum-dynamic code Autodyn and by use of a model for the brittle ceramic materials by Johnson and Holmquist. The simulations reasonably well represented the penetration behaviour above the transition velocity. They also did below, if under this condition the ceramic model was forced to remain undamaged.

The performance of electromagnetic armour was tested against a shaped charge jet. The jet was registered with shadowgraph flash X-ray photography between the plates and after passing through the plates. The current through the jet and the voltage over the plates were also registered. The current caused heating leading to melting and even vaporization. The magnetic Lorentz force compressed the jet radially, and as this effect increases with decreasing jet radius, instability may arise. Explosions in the compressed regions resulted in a fragmented jet with disk-shaped fragments which are less effective penetrators than the elongated fragments obtained in the absence of current. We also performed a theoretical study, in which the penetrator was subjected to small elastic strains only and the current was constant. The magnetic field was determined by FFT, and the stresses due to the Lorentz force were calculated with a semi-analytical method. The velocity skin effect was demonstrated.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. 73 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1032
National Category
Interaction Technologies
Research subject
Engineering Science with specialization in Solid Mechanics
urn:nbn:se:uu:diva-197563 (URN)978-91-554-8633-4 (ISBN)
Public defence
2013-05-17, Polhemssalen, Ångström, Uppsala, 10:15 (Swedish)
Available from: 2013-04-25 Created: 2013-03-27 Last updated: 2013-08-30Bibliographically approved

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