The Effect of Particle Size Distribution on Reaction Zone Thickness in Paste Explosives Measured Using a Conical Geometry

The reaction zone thickness of a detonating explosive affects the detonation properties of the explosive material. As the detonation front propagates, momentum is lost via the edges that attenuate the reaction front, which gives rise to curvature. Once the size of the charge reaches a critical size, the energy loss essentially quenches the reactions that sustain detonation, resulting in failure. This phenomenon affects detonation properties such as detonation velocity and critical diameter. Critical diameter and other detonation properties of an explosive material are typically measured using a rate stick. In a rate stick test, rate sticks of decreasing diameter are detonated until a critical diameter is reached where propagation cannot be sustained. The detonation velocity is calculated from each test using a series of probes to track the detonation front; the diameter and velocities are then plotted as a function of inverse diameter. There exists a linear region where the slope is related to the reaction zone thickness. It is hypothesized that the effective reaction zone thickness is influenced by the particle size distribution of the explosive material. In this study, several paste explosives, with varying particle size distribution and solids loading by weight, are tested. Paste explosives based on four different explosives (RDX, PETN, HMX and DAAF) are created by suspending explosive particles of different size distributions within a binder and detonated within a half-cone channel. A high-speed camera captures the detonation front and allows for the detonation velocity to be tracked and calculated as the diameter decreases. Additionally, the half-cone serves as a witness plate, which captures the apparent failure diameter. Using the data collected from these experiments, detonation velocity versus inverse diameter are plotted. Measuring the slope of the linear region for each paste allows for the reaction zone thickness to be inferred and compared to observe the influence of reaction zone thickness on failure diameter and detonation velocity. The particle size distribution will again be varied, and the curvature of the detonation front will be measured.