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Experimental Study of Electromagnetic Effects on Solid Copper Jets
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
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2010 (English)In: Journal of applied mechanics, ISSN 0021-8936, E-ISSN 1528-9036, Vol. 77, no 1, 011010- p.Article in journal (Refereed) Published
Abstract [en]

In this paper we present a study of the interaction between all electric current pulse and a solid copper jet. Experiments were performed using a dedicated pulsed power supply delivering a current pulse of such amplitude, rise little, and duration that the jet is efficiently affected. The copper jet was created by using a shaped charge warhead. All electrode configuration consisting of two aluminum plates with a separation distance of 150 mm was used. The discharge current pulse and the voltages at the capacitors and at the electrodes were measured to obtain data oil energy deposition in and the resistance of the jet and electrode contact region. X-ray diagnostics were used to radiograph the jet, and by analyzing the radiograph, the degree of disruption of the electrified jet could be obtained. It was found that a current pulse with an amplitude of 200-250 kA and a rise time of 16 mu s could strongly enhance the natural fragmentation of the jet. In this case, the initial electric energy was 100 kJ and about 90% of the electric energy was deposited in the jet and electrodes. At the exit of the electrode region, the jet fragments formed rings with a radial velocity of up to 200 m/s, depending oil the initial electric energy in the pulsed power supply. [DOI: 10.1115/1.3172251]

Place, publisher, year, edition, pages
2010. Vol. 77, no 1, 011010- p.
National Category
Engineering and Technology
URN: urn:nbn:se:uu:diva-127434DOI: 10.1115/1.3172251ISI: 000271574200010OAI: oai:DiVA.org:uu-127434DiVA: diva2:330041
Available from: 2010-07-14 Created: 2010-07-13 Last updated: 2016-04-18Bibliographically 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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