Investigation of Propagation Failures of Flexible Linear Shaped Charges at Cryogenic Temperatures
The NASA Centaur vehicle utilizes Flexible Linear Shaped Charges (FLSC) containing 7 to 15 grains of RDX/ft to perform various separation functions (Fig. 1). Although the systems have consistently performed satisfactorily on flight vehicles, a few unexplained propagation failures occurred during early development tests in environments intentionally more severe than those encountered in light. All of these were in areas of low temperature (-400°F), high thermal gradients (~ 100°F/in.), and small bend radii (< 1/2 in.). In addition to the possibility of random damage of the test specimens during installation into the test assembly, where they were mechanically worked to conform to complex curves, it was felt that the possibility also existed that extreme temperature changes during testing could have caused intolerable dimensional changes at the points of failure. In linear charges, critical dimension effects exist where propagation velocity, normally a function of the type of explosive only, becomes dependent on geometry (because of edge energy losses), and propagation eventually fails if cross sections fall below minimum values for a particular set of circumstances. The results of a NASA Lewis Research Center sponsored program to compare room-temperature propagation velocities with those at cryogenic temperature for these materials have already been reported in the literature . No gross changes were indicated, and no effects were seen to which the original test failures could be attributed.
KeywordsCrack Width Cryogenic Temperature Propagation Failure Neutron Radiography High Thermal Gradient
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