The mechanical response of a PBX and binder: combining results across the strain-rate and frequency domains

The mechanical response of a polymer bonded explosive (PBX) has been measured using a Split Hopkinson Pressure Bar at a strain-rate of 2000 s(-1), across a range of temperatures from 173 to 333 K, with the aim of observing its behaviour in the glassy regime. The yield stresses increased monotonically with decreasing temperature and no plateau was found. The failure mechanism was found to transition from shear-banding with crystal debonding fracture to brittle failure with some evidence of crystal fracture. Similar experiments were performed on samples of its nitrocellulose-based binder material, at a strain-rate of 3000 s(-1) across a temperature range 173-273 K. The failure stresses of the binder approach that of the composite at temperatures near -70 degrees C. The elastic moduli were estimated from post-equilibrium regions of the stress-strain curves, and compared with those obtained for the composite using 5 MHz ultrasonic sound-speed measurement, and powder dynamic mechanical analysis measurements and quasi-static behaviour reported in a previous paper. The moduli were plotted on a common frequency axis: a temperature shift was applied to collapse the curves, which agreed with the Cox-Merz rule.