Chapter 12: Application of Continuous Velocity of Detonation Diagnostics to PE4 Cylinder Tests

Velocity of detonation (VoD) is an important and often measured parameter for characterising explosive materials. This is traditionally measured using discrete time of arrival probes; time of arrival is plotted against position and a line of best fit used to find the VoD. This necessitates the use of a large amount of explosive material to allow steady state detonation to be reached prior to taking the measurement and provides no information on detonation propagation prior to this state being reached. A continuous method of measuring the VoD would allow smaller sample sizes to be used and would provide data from initiation through to steady state detonation. One diagnostic technique which has the potential to provide such continuous VoD measurements uses fibre Bragg gratings (FBGs). To assess their suitability, FBGs were tested on a series of PE4 cylinder tests. Cylinder tests are a commonly used characterisation test from which the expansion of the cylinder wall is also measured, thus it was also important to confirm that the presence of a FBG did not affect the expansion. Two types of gratings, uniform and chirped, were tested and the results compared to the traditional diagnostics. The measured detonation velocities are consistent with those obtained using the traditional electrical contact probes, and the effect the fibres have on the expansion of the copper cylinder has been assessed using heterodyne velocimetry and a high-speed framing camera and confirmed to be negligible. This shows that FBGs are a suitable replacement for, and improvement on, traditional diagnostics.