Above that critical 1. In other 2 0. Gouging includes dynamic phenomena like 2 0. Impacts that are 3 0. This concept of a threshold is 10 0. Model of rail tolerances. Thirty combinations of discontinuity heights and face angles were simulated in CTH over computational hours on a mas- sively parallel bit computer cluster with 32 nodes to determine the affect of these parameters on the initiation of hypervelocity gouging. It became clear almost immediately that there were threshold values for both face angle and discontinuity height that would cause either wear to the rail or a hypervelocity gouge.
For instance, with a face angle of 1. This established Fig. For a discontinuity height of 0. This established a discontinuity height limit for gouging. The results of this modeling effort appear in Table 2. Therefore, this face angle and discontinuity heights that lead to hypervelocity rail height change can occur as a sharp discontinuity in height or as gouging in the CTH simulation. If the seam was smoothed further over a longer distance , a smaller angle could be achieved.
The effect of surface indentations on gouging in railguns
Seams that are better than standards are the goal, but only those which do not meet this tolerance are re-accomplished. Note that the rail seam tolerance wherever possible. This concept is illustrated in Fig. Wear impact case, no visible damage, at 20 ms. Wear impact case, no visible damage, at 20 ms, comparison to rail sample.
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These experimentally exam- change in the rail, yet did not measurably plastically deform the ined rail sections provide us with valuable validation points to rail. In these cases, the post-impact rail would only exhibit erosion which we can compare the CTH simulations. In each damage. Case 1: rail wear without visible surface damage steel K [17—19]. A comparison of the depth of austenized In order to understand the gouging phenomenon at the HHSTT, material and the subsequent alteration of the microstructure is many sections of rail were examined to ascertain whether micro- made with the HHSTT rail specimens in Fig.
The investigation initially Fig.
Wear impact case, visible damage, at 20 ms, comparison to rail sample. The primary goal of this study was to duplicate this phenomenon of hypervelocity goug- ing within CTH simulations, and then ascertain the parameters critical to its initiation. By varying the impact parameters within the CTH simulation, gouging events were readily replicated.
The hypervelocity gouging events yielded rail damage — both physical material removal and microstructural alteration — that matched closely the experimental examination [17—19] of a gouged rail specimen. This material mixing continues as the event develops. In this case, the discontinuity was 0. As the impact event progresses, the material mixing and Fig. Gouge initiation, 15 ms. In some cases in which the damage depth is [17—19]. The gouges predicted by CTH were shown to match greater , the rail is replaced in response to these observations.
A rail section that experienced a scrape This representative case illustrates that the rail damage evident and was replaced was metallurgically examined.
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A more at the HHSTT can be accurately predicted by the simulation of the pronounced case of rail material microstructural alteration was impact event with CTH. Of primary importance is that these hy- observed . This, of course, makes it were not attained. The CTH model resulted in a 0.
Conclusions 3. Hyperve- model constants for both VascoMax and steel are applied locity gouging is differentiated from material removal and gross within CTH to model the HHSTT sled impact scenario. The goal of Fig. Gouge impact case, 40 ms, material mixing and pressure development. Gouge impact case, 40 ms, strain-rate and temperature development. All of the visibly dam- compare CTH simulation results to available post-impact rail aged sections of rail exhibited microstructural changes due to specimens.
In some of the rail samples, attempt to determine the probable cause of the hypervelocity no visible damage was present but a small amount of microstruc- gouging during HHSTT test runs. During this analysis, the vertical tural alteration was observed. The CTH simulations were able to impact case was determined to be highly unlikely due to the re- accurately duplicate each of these cases, with variations of impact quired vertical velocity to initiate gouging. Based on the Therefore, a model within CTH has been developed and vali- simulation series, a new rail alignment tolerance was determined dated against experimentally observed phenomenon at the HHSTT.
These tolerances are being applied to the HHSTT, and test model both hypervelocity gouging impacts and impacts charac- runs of greater than 3. Gouge impact case, 40 ms, comparison to rail sample. Material characterization and development of a constitutive relationship for hypervelocity impact of hypervelocity gouging impacts. International Journal of Impact Engineering December ;33 1—12 —9.
- Hypervelocity Gouging Impacts.
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John Schmisseur, monitors. Also, Dr. Additionally, investigation of a scaled hypervelocity gouging model and validation of material constitutive models. Reston, Institute of Technology was instrumental to the research. In- vestigation of a scaled hypervelocity gouging model and validation of material References constitutive models. Failure of steel during high material models for hypervelocity gouging impacts. Wear ;— Effects of temperature on the process of hypervelocity Newport, RI, 1—4 May.
AIAA Journal ;41 11 — Gouge development during hypervelocity sliding and validation of material models for hypervelocity gouging impacts. AIAA impact. International Journal of Impact Engineering ;30 2 — Journal February ;46 2 — Further validation of a general ap- hypervelocity test sled slipper-rail impacts. International Journal of Impact proximation for impact penetration depth considering hypervelocity gouging Engineering ;32 6 — International Journal of Impact Engineering August ;34 8 — Metallographic examination of thermal effects in the mitigation of hypervelocity gouging.
Palm Springs, CA, 19—22 April. Johnson , Terry M. Haran , F. Moon , Wram Robinson. Critical velocity for rails in hypervelocity launchers Nicholas V. Nechitailo , K. Elastic waves and solid armature contact pressure in electromagnetic launchers A. Johnson , F. Cinnamon , Anthony N.
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Szmerekovsky , A. Wave formation in a high-velocity symmetric impact of metal plates V.
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