THE LANL SPIFFY TEST FOR EVALUATION OF SHOCK BEHAVIOR OF EXPLOSIVES AND PROPELLANTS

The small planar impact Fritz flyer (SPIFFY) test was previously developed at the Los Alamos National Laboratory (LANL) as a low-cost method for probing the unreacted equation of state (EOS) and shock sensitivity of new propellants and explosives before committing the material to more costly and higher-precision gas gun experiments. This test utilizes 3D-printed "Fritz" plane wave lenses (PWL), which include an inert wave shaper paired with a cast-cure formulation to generate a planar output shock. These PWLs are guided by Fritz's original parameters and simulations, and are iteratively refined to improve planarity after testing and analysis with a streak camera and a shock lighting paint. The scale-up of the previous 25.4 mm design to 50.8 mm followed guidelines by Fritz and uses the polymethylmethacrylate (PMMA) Hugoniot as an adequate stand-in for the chemically similar 3D-printed methacrylate and acrylate commercial printing formulation. Based on similar cutback tests, the designed SPIFFY test apparatus uses the printed PWL with an output explosive that launches a metal flyer (Al 1100) a controlled distance into a metal acceptor plate. Variation in the flyer material, thickness, and separation distance allows for tuning the shock pressure and input profile into the material. Output curvature characterization of the 50.8 mm-diameter lenses showed reliable planarity below 100 ns across the entire breakout surface, and ~20 ns across the center 38 mm. Following this characterization, the plane wave generators were used to launch flyers at varying materials to investigate shock and particle velocities and chemical reactions. Us-up curves are determined with simple cut-back tests constructed of right cylinders, and the shock to detonation transition can be determined at various pressures by firing into targets of cast 30° wedges. This test was applied to cast propellants that utilize high-nitrogen/high-hydrogen ingredients designed to have low shock sensitivity.