Determination of the critical initiation curve for HMX using laser-driven flyers

Optimizing the design of an optical fibered detonator, relying on the initiation from a shock induced by laser-driven flyers, requires knowledge of the energetic material’s critical initiation curve, shock pressure as a function of shock duration, above which detonation occurs. Go-no go tests were conducted on an HMX explosive charge with a density of 1.65 g/cm³. 0.5 mm diameter aluminum flyers were generated using an Nd:YAG laser (1064 nm, 650 mJ, 7 ns pulse duration) in confined interaction, from metallic coatings deposited onto 1 mm-thick H-K9L glass windows. Shock duration and shock pressure were varied using different flyer thicknesses and flyer impact velocity respectively. Flyer velocity varied with energy input and flight distance. Flyer velocity was recorded using photon Doppler velocimetry (PDV) and flyer planarity was checked using a high-speed framing camera. HMX detonation was inferred from PDV measurement of a metallic flyer in contact with the explosive. The resulting critical initiation curve was modeled using an analytical criterion and the threshold laser energy that leads to detonation was identified.