Challenging the paradigm for reactive material's ignition from shear to pressure: Thermomechanical study of Al-PTFE

Structural reactive materials (SRMs) are attracting growing interest in the warheads industry, while the Al-PTFE system is probably the most popular. Due to their final application, high-strain rate (impact) testing is the most realistic method for SRMs. For this purpose, a synchronized Split Hopkinson (Kolsky) Pressure Bar with high-speed infrared and optical cameras is used to characterize the sintered Al-PTFE system, thus enabling the simultaneous investigation of its thermal energy release and mechanical properties under impact. The characteristic specimen heating rates during such experiments are of the order of 3.85 x 10(8) degrees C/min, which most likely caused evaporation of the reaction products, that were therefore not identified in a post-mortem analysis of the remaining fragments. Whereas the conventional wisdom has it that shear loading causes SRM ignition, the main result of this work just points to the opposite, showing unambiguously that pressure is the reaction-triggering loading mode, with the potential involvement of a pore collapse mechanism.