Microstructured microstructure: Effects of concentration variations on shock initiation of HMX-based plastic explosives

This project is an experimental study of the effects on shock initiation and growth of changing the concentration of the energetic component in a plastic-bonded explosive (PBX). Here the PBX consists of HMX with PDMS binder where the HMX weight percentage was varied from 10% to 85%. Changing concentrations is a cornerstone of very many experimental studies but with shock initiation and growth the effects can be quite complicated. Varying the HMX concentration does more than simply change the energetic content. It changes the mechanical properties so the PBX ranges from a soft polymer to a brittle composite. It changes the shock impedance and how much energy is transferred to the PBX from a flyer plate impact. Here we kept the input shock pressure approximately constant at 20 GPa. It changes the optical properties of the PBX which is important in this study where the emission is measured after a high-velocity impact. Finally it changes the microstructure in a complex manner. The HMX tends to cluster within the binder, producing a mixture of HMX aggregates and polymer islands. All these effects have been investigated by measure the time-dependent spectral radiance during and after the shock. From the radiance we get time dependent temperatures and time-dependent rates of energy release. The optical emission is explained in terms of the microstructure and cluster behavior, which was characterized by examining thin slices of the PBX and computing the radial distribution function for HMX concentration.