HIGH-STRAIN RATE IMPACT IGNITION OF RDX WITH ETHYLENE VINYL-ACETATE (EVA) COPOLYMERS

The effects of vinyl acetate content and molecular weight of ethylene-vinyl acetate (EVA) copolymers on the high strain rate impact ignition sensitiveness of RDX/EVA (95:5) physical mixtures, explosive molding powders, and compacted charges were evaluated. In a drop-weight impact test on physical mixtures and molding powders, the high strain rate mechanical properties and thermal properties of the polymers, and the way the polymer is distributed, affect impact sensitiveness. Localized viscous flow occurs in copolymers with high vinyl acetate contents and this sensitizes some physical mixtures. The response of the compacted molding powders was studied using a Hopkinson Bar. Those containing copolymers with high vinyl acetate contents and high molecular weights have the best high strain rate mechanical properties and are least sensitive to impact ignition. Increasing the binder level from 5 to 10 or 15 wt. % decreases the impact sensitiveness and changes the mode of failure from brittle to ductile. The relative ease of impact ignition of some pressed compositions was determined using a Hopkinson Bar test, and these results are compared with shock sensitivity data for the same charges.