Capt Peter HsiehReserve Program Manager

Air Force Office of Scientific Research

Armature-rail Electrical Interface in Electromagnetic Launch

3 Nov 2010

DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited.

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Overview

• Electromagnetic launch applications• Railgun physics and engineering• Armature-rail sliding contact– Plasma transition– Hypervelocity gouging– Metallurgical reactions

• Summary

3 Nov 10

I. Newton, A Treatise of the System of the World, ca. 1680

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Electromagnetic launch applications

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0 5 10 15Velocity (km/s)

Kine

tic e

nerg

y (k

J)

Aircraft catapult

Naval railgun

Antitank railgun

Hypervelocity space debris

Space launch

O. Božić and P. Giese (2006)

NASA Ames Research Center (2008)

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Electromagnetic railgun physics

BLIF

C. Meinel, IEEE Spectrum (2007) 40-46

K.A. Schroder et al., IEEE Trans. Magn. 35(1): 95 (1999)

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Railgun engineering issues

• Pulsed power– Energy storage– Pulse shaping network

• Launcher– Armature and rail– Insulators

• PayloadElectromagnetic Launch Facility (EMLF)NSWC Dahlgren Division

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Armature-rail sliding contact

• Electrical contact– Current distribution

• Sliding contact• Hypervelocity gouging– Material properties

• Buried interface• Metallurgical reactions

R.A. Meger, et. al., IEEE Trans. Mag. 41, 211 (2005).

P. G. Slade, Electrical contacts: principles and applications (1999)

M. Ghassemi and R. Pasandeh, IEEE Trans. Mag. 39, 1819 (2003)

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Energy balance at the interface

Electrical current

Friction Joule heating

Air compression

Metallurgical reactions

Conduction

≈ 10 μm

Armature

Rail

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Transition to plasma contact

R. A. Marshall et al. IEEE Trans. Mag. 31(1): 214-218 (1995)

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Hypervelocity gouging

• Phenomenon first reported by AF scientists working with rocket sleds (1969)

• Characteristic tear-drop gouges in rails due to asperity impact

• High-speed asperity impactK. F. Graff and B. B. Dettloff, Wear (1969), 87-97

Rocket sled testing at Holloman AFB

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Gouging and shock loading

K.R. Tarcza and W.F. Weldon, Wear, 209: 21-30 (1997)

F. Stefani and J.V. Parker, IEEE Trans. Mag., 35(1): 312-316 (1999)

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Hydrocode simulation of gouging

J.D. Cinnamon and A. N. Palazotto, Int. J. Impact. Engr. (2009), 254-262

• Analysis of experimental data with CTH hydrocode modeling to extract high-strain rate material parameters

• Validation of CTH model by comparing predicted temperature with alloy microstructure changes

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Interfacial metallurgical reactions

C. Persad, IEEE Trans. Mag. 43(1): 391-395 (2007) ASM Handbook (volume 3): Alloy Phase Diagrams

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Unraveling the problem

• De-couple sliding velocity from electrical current density

• Improve multi-physics modeling of the boundary film on relevant timescale with respect to its electrical and thermal transport mechanisms

• Model and test nonreactive armature-rail material pairs

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Summary

• Electromagnetic launch is a breakthrough technology for hypervelocity research

• The armature-rail interface in railguns experiences conditions far from equilibrium during launch and gives rise to rail wear

• Further basic research to understand energy transport across the armature-rail contact is crucial for materials engineering

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QUESTIONS?

Capt Peter HsiehAir Force Office of Scientific Researchpeter.hsieh@afosr.af.mil

Artist’s concept of NASA lunar base with mass-driver for mined ores.

I.R. McNab, IEEE Trans. Mag. 45(1): 381-388 (2009)