Shape memory polymer-based hybrid honeycomb structures with zero Poisson's ratio and variable stiffness

This work describes the out-of-plane bending performance, shape memory effect and variable stiffness of a zero Poisson's ratio honeycomb structure made from the tessellation of re-entrant hexagons and thin plates. The re-entrant hexagons are fabricated with ABS plastics and the thin plates are made from thermosetting styrene-based shape memory polymers (SMPs). The hexagons and the SMP plates are bonded within the groove joints in the thickness direction of the re-entrant cell units. The re-entrant hexagons generate out-of-plane flatwise compressive stiffness and in-plane compliance, while the SMPs thin plates support out-of-plane flexibility, the shape memory effect and a variable bending stiffness. Because the ABS plastics possesses a significantly higher glass transition temperature than the SMPs, the ZPR honeycomb structure features a higher out-of-plane flexibility when the environmental temperature rises from room temperature to the glass transition temperature of the SMPs. On the contrary, the flatwise compressive stiffness of the ZPR honeycomb remains unchanged. Three-point bending tests have also been performed to determine the out-of-plane bending performance of the ZPR structures at varying temperatures.