Influence of polymer properties on the mechanical behaviour of 3D-printed auxetic metamaterials and honeycomb structures under bending load

Metamaterials with auxetic behaviour have great potential for a new generation of load-bearing lightweight sandwich structures due to their outstanding energy absorption capabilities. As a result of their negative Poisson's ratio, component cross-sections increase under tensile loading transverse to the loading direction and decrease conversely under compressive loading. This paper describes experimental and numerical investigations with the finite element method on the load-deformation behaviour of sandwich structures under bending featuring differently oriented auxetic cores and honeycomb cores with varying specifications and degrees of crystallisation. A star-shaped auxetic structure was chosen and compared with hexagonal honeycomb cores. The fabrication of the specimens was carried out by fused deposition modelling and the materials were characterised by infrared spectroscopy, differential scanning calorimetry, melt flow index determinations, dilatometer measurements, tensile tests, and nanoindentation. The bending results exhibited that the advantages of the auxetic structures in energy absorption were clearly evident for certain orientations to the loading direction and that the material properties significantly influenced the structural deformation behaviour.