Additive Manufacturing of Continuous Fiber-Reinforced Polymer Composite Sandwich Structures with Multiscale Cellular Cores

The use of composite sandwich structures with cellular cores is prevalent in lightweight designs owing to their superior energy-absorbing abilities. However, current manufacturing processes, such as hot-press molding and mold pressing, require multiple steps and complex tools, thus limiting the exploration of advanced sandwich structure designs. This study reports a novel multi-material additive manufacturing (AM) process that allows the single-step production of continuous fiber-reinforced polymer composite (CFRPC) sandwich structures with multiscale cellular cores. Specifically, the integration of CFRPC-AM and in situ foam AM processes provides effective and efficient fabrication of CFRPC panels and multiscale cellular cores with intricate designs. The cellular core design spans three levels: microcellular, unit-cell, and graded structures. Sandwich structures with a diverse set of unit-cell designs, that is, rhombus, square, honeycomb, and re-entrant honeycomb, were fabricated and their flexural behaviors were studied experimentally. The results showed that the sandwich structure with a rhombus core design possessed the highest flexural stiffness, strength, and specific energy absorption. In addition, the effect of the unit-cell assembly on the flexural performance of the CFRP composite sandwich structure was examined. The proposed design and fabrication methods open new avenues for constructing novel and high-performance CFRPC structures with multiscale cellular cores that cannot be obtained using existing approaches.