Vented Fixture Modeling

Report No. ARL-TR-2952
Authors: Paul Conroy
Date/Pages: April 2003; 24 pages
Abstract: Vented fixtures have been used extensively for erosion/erosivity investigation for many years. The fixtures can assist in quickly assessing materials/propellants and interactions as well as understanding mechanisms of erosion. In this report, two fixtures are modeled?a 37-mm fixture at the U.S. Army Research Laboratory and a 200-mm3 bomb with a 1-mm vent hole, located in Canada. Both fixtures erode a nozzle-type insert. The 37-mm fixture is designed to maintain a steady erosion quantity over repeated firings, with relatively small throat cross-sectional area change, which enables some insight into possible mechanisms. Each interior ballistic model required modifications to the interior ballistic code to enable a variable throat exit for the orifice. The Canadian fixture has a 1-mm vent hole, which has a tendency to enlarge considerably during firing. The dominant erosion mechanism for the Canadian fixture is shown to be melt wipe, while for the 37-mm fixture, it is primarily thermochemical. A redesign of the Canadian fixture to permit a larger exit orifice with a rupture diaphragm would enable thermochemical differences in the propellants to reveal themselves better.
Distribution: Approved for public release
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Last Update / Reviewed: April 1, 2003