Robust and versatile metastructures’ manufacturing through fusion-bonding of thermoplastic composites

Fiber-reinforced polymer metastructures, owing to their architectures and material properties, yield unique deformation schemes and load-bearing capabilities. Currently, the prevailing fabrication route of such structures relies on complex tooling to shape and consolidate thermoset-based composites. This study investigates the potential of fusion-bonding thermoplastic-based composites to reduce manufacturing's complexity of composite metastructures, expanding the design freedom, without compromising the load-carrying capabilities. To this end, a welding device specifically developed for the realization of composite metastructures is introduced. A parametric study on mode I fracture toughness at initiation was conducted to determine an ideal processing window. This analysis showed that dual polymer welding approach is key to reduce laminates' distortion, also providing welds with a mode I peeling toughness of 2.1 ± 0.1 kJ/m², a property very close to the one obtained via consolidation, with minor reduction (∼15 %) when curved laminates are welded. The potential of the technique is further showcased by two metastructure modules: a two-dimensional rotating chiral and a three-dimensional structure with compression-twist coupling, successfully manufactured and mechanically evaluated until failure. Furthermore, the demonstrators exhibit a remarkable resilience and showcase the reduction of manufacturing complexity resulting in an expansion of design freedom. The results highlight the potential of the fusion-bonding approach to create lightweight metastructures with high mechanical performance, paving the way for innovative applications in aerospace, automotive, and beyond.