FLOW OF RX-08-FK HIGH-ENERGY PASTE IN A CAPILLARY RHEOMETER

The flow of RX-08-FK, a mostly organic, high-energy, paste-extrudable explosive containing about 75% suspended solids, was experimentally st udied. The paste was forced through long capillary tubes in a speciall y designed, double-piston rheometer at temperatures ranging from -54 t o +74 degrees C, and at nominal shear rates at the tube walls from 50 to 40000 s(-1) preconditioned for many hours to achieve the desired ex perimental temperature and the rheometer itself was enclosed in a prec onditioned temperature-controlled chamber. We found the paste to be ps eudoplastic with significant yield stress and entrance effects. The re sults of 176 runs at temperatures of -35 degrees C and higher were fit ted by an empirical model much like the original model suggested by He rschel and Bulkey, modified to include a factor correcting the stress for the substantial entrance loss experienced with this paste. The obs erved stresses at -54 degrees C were substantially higher and less she ar dependent than those extrapolated from the above model; these diffe rences may relate to the fact that the glass-transition temperature of RX-08-FK is approximately -60 degrees C. (C) 1997 The Society of Rheo logy.