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An experimental investigation has been undertaken to improve understanding of the role of the obturator and detonations in
the subdetonative ram accelerator starting process. Ram accelerator start experiments were conducted with various obturator
geometries to determine the obturator dynamics and assess its effect on the outcome of a start attempt. The obturator rapidly
decelerates upon entrance and then moves backwards. Reversal of direction occurs more rapidly after propellant ignition, for
less massive obturators, and solid geometries. Perforated geometries and decreasing obturator mass are less conducive to igniting
a given propellant, as evidenced by the flowfield and start attempt outcome data presented. Wave unstarts were observed to
occur with and without detonations, indicating more than one mechanism responsible for this type of start failure. Piston-initiated
detonation experiments were conducted by firing the obturators without the ram accelerator projectile. The piston experiments
identified the detonation limits for a wide range of propellants, but were found to not always be indicative of the upper
Mach number at which a ram accelerator can be successfully started. In some instances a successful start or wave fall-off
would occur at Mach numbers above which a piston alone detonated the propellant. Thus, the projectile can play a mitigating
role in detonation initiation and use of piston detonation limits to quantitatively define a detonation wave unstart limit
was not realized.
Received 6 April 1998 / Accepted 15 January 1999 相似文献
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Perla N. Peszkin J. M. Schultz J. S. Lin 《Journal of Polymer Science.Polymer Physics》1986,24(12):2617-2630
Small- and wide-angle X-ray scattering (SAXS and WAXS), shrinkage, and density experiments were performed on poly(butylene terephthalate) fibers which had been isothermally crystallized at different temperatures, and at constant tension, for times ranging from 100 to 1050 ms. A consistent correlation among WAXS, SAXS, and the kinetic results is demonstrated. Shrinkage results show that the crystallization process prevails over the chain-re-coiling process. Density measurements show that the rate of crystallization increases with temperature. Pinhole X-ray photos show that the orientation of the chains within the crystals remains constant with time and temperature. WAXS diffractometer scans show the development of wide-angle Bragg peaks. SAXS shows the development of small-angle Bragg peaks, as the annealing time is increased. The two-lobe arced pattern is the characteristic pattern. The value for long spacing ranged from 100 to 120 Å, increasing with temperature. 相似文献
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Thin layers of (25–1000 Å) tin were evaporated onto a highly oriented polypropylene sheet. Two rates of deposition were used: 5 and 20 Å/s. For the more rapid deposition rate, a preferred orientation of tin was found in all cases. Here, the Sn a axis lay parallel to the polymer chain (polymer c axis). The same orientation relationship was found for the slower deposition rate, but only at lower Sn film thicknesses; at the higher film thicknesses, a random orientation of crystallites is found. Scanning electron micrographs show an equiaxed tin grain structure for the case of no preferred orientation and a platelet morphology for the case of preferred orientation, the thin dimension of the platelets lying perpendicular to the polymer chain axis. Although no clearcut evidence either for or against crystallographic epitaxy has been found, a plausible case for geometrical epitaxy is presented. 相似文献