1. Capt Peter Hsieh Reserve 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.

2. Overview Electromagnetic launch applications Railgun physics and engineering Armature-rail sliding contact – Plasma transition – Hypervelocity gouging – Metallurgical reactions Summary 3 Nov 10 2 I. Newton, A Treatise of the System of the World, ca. 1680

3. Electromagnetic launch applications 3 10 0 10 1 10 2 10 3 10 4 10 5 10 6 10 7 10 8 051015 Velocity (km/s) Kinetic energy (kJ) Aircraft catapult Naval railgun Antitank railgun Hypervelocity space debris Space launch O. Božić and P. Giese (2006) NASA Ames Research Center (2008)

4. Electromagnetic railgun physics 4 C. Meinel, IEEE Spectrum (2007) 40-46 K.A. Schroder et al., IEEE Trans. Magn. 35(1): 95 (1999)

5. Railgun engineering issues Pulsed power – Energy storage – Pulse shaping network Launcher – Armature and rail – Insulators Payload 5 Electromagnetic Launch Facility (EMLF) NSWC Dahlgren Division

6. Armature-rail sliding contact Electrical contact – Current distribution Sliding contact Hypervelocity gouging – Material properties Buried interface Metallurgical reactions 6 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)

7. Energy balance at the interface 7 Electrical current Friction Joule heating Air compression Metallurgical reactions Conduction ≈ 10 μm Armature Rail

8. Transition to plasma contact 8 R. A. Marshall et al. IEEE Trans. Mag. 31(1): 214-218 (1995)

9. 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 impact 9 K. F. Graff and B. B. Dettloff, Wear (1969), 87-97 Rocket sled testing at Holloman AFB

10. Gouging and shock loading 10 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)

11. Hydrocode simulation of gouging 11 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

12. Interfacial metallurgical reactions 12 C. Persad, IEEE Trans. Mag. 43(1): 391-395 (2007)ASM Handbook (volume 3): Alloy Phase Diagrams

13. 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 13

14. 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 14

15. QUESTIONS? Capt Peter Hsieh Air Force Office of Scientific Research peter.hsieh@afosr.af.mil 15 Artist’s concept of NASA lunar base with mass-driver for mined ores. I.R. McNab, IEEE Trans. Mag. 45(1): 381-388 (2009)