Dynamic Combustion of Functionally Graded Additively Manufactured Composite Solid Propellant

Typically, the burning surface of a composite solid propellant is controlled through grain geometry and formulation. However, combustion studies of grains constructed from different propellant formulations at fine scales (nominally 1 mm) are not readily accessible in open literature. With additive manufacturing, such configurations can be investigated easily. Propellants with a faster burning inner layer (enhanced with either 1 wt.% iron oxide or 5 wt.% nanoaluminum) were 3D printed between two layers of slower burning 85 wt.% ammonium perchlorate/hydroxyl-terminated polybutadiene propellant. The dynamic combustion behavior of the layered propellant was investigated at pressures ranging from 3.45 to 10.34 MPa. Overall, an increase in the burning surface area, without interlayer delamination, was observed. The driving force behind the propellant surface area increase was the difference in the burning rate between the layers. In addition, the nanoaluminum propellant layer had a more stable burning rate exponent than the cast nanoaluminum propellant. Overall, only a small addition of catalyzed propellant was needed to increase the burning rate of the bulk material. The results of this study lay the foundation for functionally grading propellant grains, which could tailor the thrust profile of solid rocket motors and gun propellants.