Tuning Load Bearing Capacities of Flexible Honeycomb with Poisson's Ratio Modulation

Polymeric honeycomb structures are used in impact mitigation applications due to their high specific strain energy dissipation capacity at extended strains. The load bearing and energy absorption capacities of honeycomb lattices can be concurrently improved by tuning their Poisson's ratio. For instance, the inward-facing cavities in reentrant honeycomb geometries result in an auxetic behavior, effectively increasing the impact energy absorption performance. This study investigates the interrelationship between cell wall thickness, the Poisson effect, and load-bearing capacities of hexagonal and reentrant honeycomb lattices fabricated from thermoplastic polyurethane (TPU) by fused filament fabrication (FFF) additive manufacturing technique. The wall thickness of the samples is varied to investigate its effect on the mechanical performance of the honeycomb structures. The fabricated samples are characterized under quasi-static compression. The results indicate that the load-bearing responses of conventional and reentrant honeycomb structures improve with increasing wall thicknesses, while the energy absorption efficiency is inversely related to the cell wall thickness. Hexagonal honeycomb lattices exhibit superior stiffness and strength compared with their reentrant counterparts, whereas reentrant lattices are lighter and show a more compliant nature due to their more open geometry and inward-facing cavities. We observe that the reentrant lattices tend to fail due to shear deformation while honeycomb lattices fail by the bending and stretching of the cell walls. The findings suggest that the honeycomb lattice structure can be optimized by tuning the wall thickness based on the desired mechanical properties informed by a particular application.