Investigation of Additively Manufactured Layered Composite Solid Propellant

Abstract

Typically, the burning surface profile of a composite solid propellant is controlled through grain geometry and formulation. However, the combustion of propellants with different burning rates that are layered at a small scale (~1 mm) has not been previously studied due to manufacturing limitations and cost. With the emergence of new additive manufacturing techniques, particularly vibration assisted printing (VAP), it is possible to layer different propellant formulations at this scale and to investigate the fundamental combustion behavior of such configurations. In this study, a cast layered propellant was compared to two printed layered propellants. In addition, the combustion behavior was investigated at different pressures. It was found that the cast layered propellant catastrophically failed at high pressure (>200 psi) due to the cast-cure technique used. The printed layered propellant was able to survive at high pressure (1500 psi). A major finding in this study was that the 3D printed layered propellant exhibited burning surface profiles that developed into an U- or V-shape over time. This result is consistent with those obtained from recent simulations of layered propellant using a combustion code called RocFire. The quality of the printed layered propellant was investigated via microscopic imaging which showed that although there was some slight variation in layer thickness, the variation was within acceptable limits given the thinness of the propellant layers. There was also minimal mixing between the propellant layers. The results of this study will lay the foundation for integrating different propellant formulations into functionally graded propellant grains, which can potentially be used to further tailor the thrust profile of solid rocket motors.