Effects of the polymer matrix density on the shock, bullet impact and high strain‐rate ignition sensitivity of polymer bonded explosives

Abstract

Four HMX/polymer cast‐cured explosive compositions containing a constant volume percentage (24%) of acrylate polymers ranging in density from 0.93 Mg/m3–1.65 Mg/m3 were evaluated in shock sensitivity, bullet impact sensitivity and high strain‐rate impact ignition tests. It was observed that shock sensitivity and bullet impact sensitivity, measured for flat‐ended projectiles impacting the bare face of elsewhere confined charges, increased with the density of the polymer matrix in the compositions. This correlation between the tests occurs because the detonations observed in the bullet impact test are initiated by shock, with shock initiation presumably occurring more readily when there is less impedance mismatch (i.e. a smaller density difference) at the polymer matrix/HMX crystal interface. In the Hopkinson Bar test a poorer correlation of ignition sensitivity with polymer density was observed because at these lower impact energies other initiation mechanisms such as macroscopic shear and plastic heating, viscous flow, etc. also play an important role.