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RESEARCH PAPERS

Metallographic Examination and Validation of Thermal Effects in Hypervelocity Gouging

[+] Author and Article Information
John D. Cinnamon

 Air Force Institute of Technology, Department of Aeronautics and Astronautics, Wright-Patterson AFB, OH 45431john.cinnamon@afit.edu

Anthony N. Palazotto

 Air Force Institute of Technology, Department of Aeronautics and Astronautics, Wright-Patterson AFB, OH 45431

J. Pressure Vessel Technol 129(1), 133-141 (Jun 01, 2006) (9 pages) doi:10.1115/1.2389030 History: Received August 01, 2005; Revised June 01, 2006

In this work, a gouged section of 1080 railroad rail steel is examined using metallographic techniques to characterize the nature of the damage. The gouging was performed by a rocket sled at Holloman Air Force Base, riding on VascoMax 300 steel shoes at 2.1kms. The damaged rail is evaluated in detail to examine material phase changes, shear bands, and heat effects. The results are compared to samples of the virgin material, machined and prepared exactly as they are prior to the Holloman AFB High Speed Test Track (HHSTT) runs. The gouged section was examined using optical microscopy, scanning electron microscope (SEM), and other techniques. The resulting microstructure is presented and compared to the virgin material. Material mixing, shear band formation, and significant thermal damage, consistent with a high energy gouging event, are confirmed. In addition, the material phase change evident in this approach allows us to estimate the thermal conditions present during the formation of the gouge. This thermal history establishes a profile by which related research in gouge simulation can be validated against. A one-dimensional heat conduction model is presented that validates the cooling rates required to generate the presented microstructure.

Copyright © 2007 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

HHSTT rocket sled

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Figure 2

Sled shoe, with typical gouge, on rail

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Figure 3

Section of gouged rail

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Figure 4

Depiction of specimen location, which are approximately cubic, with 25mm sides

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Figure 5

Specimens, velocity vector of sled oriented, as shown, by the arrows

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Figure 6

Specimens A4 and B4, sled velocity vector shown by arrows

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Figure 7

Specimen B4, etched, sled travel is left to right (16×)

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Figure 8

Top of deformed specimen, as polished, SEM, BSE (2000× and 10,000×)

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Figure 9

Top split transformation zone, electropolished, SEM, BSE (2000× and 10000×)

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Figure 10

Transition from split transformation to fine pearlite, electropolished, SEM, BSE (5000×)

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Figure 11

Fine pearlite, electropolished, SEM, BSE (2000× and 10,000×)

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Figure 12

Shear band, martensite band, electropolished, SEM, BSE (50× and 2000×)

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Figure 13

Split transformation at edge of heat affected zone, as polished, SEM, BSE (2000×)

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Figure 14

Coarse pearlite, as polished, SEM, BSE (2000×)

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Figure 15

Coarse pearlite, specimen A4, as polished, SEM, BSE (2000×)

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Figure 16

Continuous cooling curve for 1080 steel, adapted from Ref. 8

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Figure 17

Proposed thermal history of hypervelocity gouge

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Figure 18

One-dimensional slice of cooling gouge

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Figure 19

1080 steel specimen cooling

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Figure 20

Specimen cooling through austenizing temperature

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Figure 21

Specimen cooling gradient and resulting microstructure

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