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Research Papers: Applications

Simple Thermal Model to Select Electromagnetic Launcher Tribomaterials

[+] Author and Article Information
Edin E. Balic

Department of Mechanical, Aerospace
and Nuclear Engineering,
Rensselaer Polytechnic Institute,
Troy, NY 12180

Thierry A. Blanchet

Department of Mechanical, Aerospace
and Nuclear Engineering,
Rensselaer Polytechnic Institute,
Troy, NY 12180
e-mail: blanct@rpi.edu

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received July 15, 2015; final manuscript received October 13, 2015; published online July 26, 2016. Editor: Michael Khonsari.

J. Tribol 138(4), 041102 (Jul 26, 2016) (8 pages) Paper No: TRIB-15-1269; doi: 10.1115/1.4032913 History: Received July 15, 2015; Revised October 13, 2015

Lab-scale electromagnetic launcher (EML) tests for the baseline case of an aluminum armature spanning a pair of copper rails reproduced excessive aluminum melt wear depth leading to loss of conductive contact and resultant electrical transition before completion of launch. A simple thermal model partitioning interfacial Joule heat input between conduction into the rails and melting of the armature provided compact expressions describing armature wear behavior. A quantity from this expression, termed the armature melt resistance (AMR), predicts a decrease of armature wear and the likelihood for resultant electrical transition with increasing rail thermal conductivity and heat capacity, as well as armature heat capacity, latent heat, and melt point. With this AMR metric to guide materials' selection, in subsequent tests, a slight increase in wear indeed occurred upon substitution of stainless steel rails, with more dramatic order of magnitude decreases in wear and avoidance of electrical transition instead realized upon substitution of solid molybdenum armatures.

FIGURES IN THIS ARTICLE
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Copyright © 2016 by ASME
Topics: Wear , Rails , Aluminum , Copper
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References

Figures

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Fig. 1

Armature transmitting current I prescribed at one rail to the return rail, with induced magnetic field B between the rails out of plane of page resulting in Lorentz force F accelerating conducting armature

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Fig. 2

(a) Assembly of aluminum armature (12.33 mm armature width into page) with platform insert of tungsten to support nylon bore rider and weight armature to 19 g and (b) armature/platform retrieved from catch tank following launch showing rectangular worn contact patch over leg surface

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Fig. 4

Thermal model of stationary rail at far-field temperature To as it is traversed by high-speed (V) armature contacting it over a length 2b. A flux  q˙r partitioned into the rail from the total interfacial power results in a maximum surface temperature Tm at the trailing edge of the high-speed contact.

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Fig. 3

(a) Copper rails showing the start location and initial 0.2 m distance traversed and deposited upon by an aluminum armature; (b) normalized EDXS intensity of aluminum deposit and underlying copper rail as a function of increasing rail position over which deposit diminishes; and (c) voltage as a function of time during launch of aluminum armature on copper rails indicating transition by t = 2000 μs

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Fig. 5

(a) Armature wear volume averaged from two repeat tests for each of four combinations of armature (Al or Mo) and rail (Cu or stainless steel) materials and (b) armature wear volume as a function of AMR

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Fig. 6

Normalized EDXS intensity of armature deposit and underlying rail as a function of increasing rail position at various armature/rail combinations: (a) aluminum/copper; (b) aluminum/304 stainless steel; (c) molybdenum/copper; and (d) molybdenum/304 stainless steel

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Fig. 7

Voltage as a function of time at four combinations of armature (Al or Mo) and rail (Cu or stainless steel) materials

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Fig. 8

Prescribed current as a function of time at four combinations of armature (Al or Mo) and rail (Cu or stainless steel) materials

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Fig. 9

Al armature with Mo cladding attached over legs (a) as assembled, (b) as retrieved post-launch from catch tank, and (c) voltage as a function of time for Mo-clad Al armature on Cu rails, remaining lower than solid Mo armature while not transitioning like solid Al armature (Fig. 3(c))

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