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Abstract. The mechanical response of a polymer bonded explosive 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 of 173-273 K. The failure stresses of the binder approach that of the composite at temperatures near -70°C. The elastic moduli were estimated from post-equilibrium regions of the stress-strain curves, and compared to those obtained for the composite using 5 MHz ultrasonic soundspeed measurement, and powder DMA 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.

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Soft materials have seen continued growth in industrial importance, but are difficult to test at relevant, particularly at high, rates of deformation and relevant temperatures. This is mainly due to the low stresses supported by these materials, which mean that very sensitive force measurements are required. In this paper, a split-Hopkinson pressure bar method for testing very soft materials and elastomers at high rates of deformation is presented and applied. Experiments are conducted in compression on hydroxyl terminated polybutadiene, a very soft rubber, at strain rates of about 2000 s−1. Titanium alloy bars are used, and in addition to the usual strain gauges on the bars, forces at both ends of the specimen are measured using a piezoelectric material, lead zirconium titanate (PZT), which is much more sensitive than the quartz crystal gauges typically used in previous literature. The piezoelectric constant of PZT ranges between 290–630 × 10−12 C N−1, making it 100 times more sensitive than quartz crystal (2.3 × 10−12 C N−1). Results obtained from the experiments show that the gauges are able to measure the forces on both ends of the specimen with excellent signal to noise ratios.

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