Particle Size Modification of Thermally Stable Secondary Explosives for IM Applications

As well as improving the survivability of weapons and platforms, insensitive munitions (IM) reduce both casualty rates and mission losses. Their use also leads to improved safety during storage and transportation. For a munition to fulfil IM criteria, each of its energetic sub‐sections must be IM compliant. The initiator and explosive train are the most critical of these sub‐systems as their safety and reliability are of paramount importance if the weapon is to be suitable for service use, yet they are generally the most difficult part of a weapon to protect from inadvertent initiation. As part of an ongoing study into initiation methods suitable for use in IM systems, an investigation into the behaviour of energetic materials when impacted by laser‐driven flyers was performed. Laser‐based detonators exhibit increased safety characteristics over conventional initiation methods as they can be based on insensitive secondary explosives rather than sensitive primary explosives. Also, they are less susceptible to accidental initiation due to an external hazard threat. Single pulses from a high‐powered Q‐switched Nd:YAG laser were used to launch flyers from substrate‐backed aluminium films to velocities up to 6 km s⁻¹ across a short stand‐off to impact explosive targets. Several novel energetic materials have been selected for investigation as potential candidates for inclusion within flyer‐based initiation systems and explosive train applications. The materials are of interest due to their increased thermal stability and power output over conventional explosives currently in service. Attempts were made to increase the flyer responsiveness of the materials by tuning their particle size using ultrasound. The effect of particle size on the initiation threshold energy was investigated for three materials.