Chiral topologies for composite morphing structures - Part II: Novel configurations and technological processes

The article presents the advancements in the technological processes developed to produce chiral honeycombs made of thin composite laminates. An original technological process, which was applied to produce chiral components for aerospace morphing structures, is critically analysed and a new approach is proposed. The objective of such approach is the production of thin-walled chiral composite structures with enhanced strength properties by using a more feasible technology. According to the new methodology, chiral honeycombs with polygonal nodes are obtained by assembling thin-walled prismatic composite tubes. Numerical models are developed to investigate the behaviour of such topologies. A comparison with the performances of chiral honeycombs with cylindrical nodes is presented, showing that the new configuration can provide negative Poisson's ratios that tend to the theoretical limit of −1 as the stiffness of the polygonal nodes is increased. Thereafter, a method to fill partially the nodes is proposed and numerically assessed, to enhance at the same time the auxetic behaviour and the mechanical properties of the chiral honeycomb. Finally a complete manufacturing process is developed. Hexa-chiral structural units are manufactured and subsequently tested to assess the auxetic response. Results are in acceptable agreement with numerical predictions and indicate that the novel technological route provides a significant contribution for the application of composite chiral honeycomb to morphing structures.