Impact of 3d-printing on the mechanical reinforcement and the ballistic response of paraffin-based fuels: The armored grain

The 3D printing is changing the paradigm for manufacturing, thanks to the ability to rapidly produce customized and complex structures. The Space Propulsion Laboratory is exploiting the benefits offered by the 3D printing to create a new family of paraffin-based fuels featuring both mechanical and ballistic performance: the armored grain. In the present study, the armored grains feature a macro-crystalline wax embedding 3D printed structures made of polylactic acid. Four different reinforcing structures are considered: gyroid, Schwarz P, straight honeycomb, and twisted honeycomb with 1/4 turns per inch. The investigation of the armored grain concept involves: the structural assessment of the mechanical behaviors of the 3D printed reinforcements, and the mechanical and ballistic characterization of the armored grains. The results prove that the armored grain approach is successful in increasing both the yield stress and the strain energy of the pristine paraffin, mitigating the typical brittle behavior of the alkane fuel. The firing tests indicate that the presence of the 3D printed reinforcements does not lessen the ballistic performance of the pure paraffin wax.