Development of an Expandable HE Formulation for an Explosive Train Interrupter Module

Realization of a reliable interrupter device in an explosive train to prevent unintended detonation is a potentially powerful strategy for enhanced safety in high explosives (HE). We present an interrupter concept that relies on an expandable HE part containing Expancel® microspheres, which are commercially available blowing agents that can expand up to 60 times in volume when heated. These thermally expandable microspheres (TEMs) consist of a thermoplastic shell that encapsulates an inert hydrocarbon that gasifies upon heating, exerting pressure on the softened shell to expand it. We developed and tested a new HE formulation consisting of erythritol-1,3,4-trinitrate-2-acrylate (ETriN A), pentaerythritol tetranitrate (PETN), trimethylolethane trinitrate (TMETN), and TEMs. This formulation remains pliable enough after cast curing to expand dramatically, unlike other formulations that were tested. We present a successful proof of concept for an interrupter module that consists of an unexpanded HE part placed directly below the detonator. In the "inactive" state, an air gap separates the interrupter from the detonator to inhibit shock propagation. In order to complete the explosive train, the HE is expanded to fill the air gap, allowing shock propagation through the expanded HE.