Quasi-static compression performance of material extrusion enabled re-entrant diamond auxetic metamaterial: Fabrication, tuning the geometrical parameters and fibre reinforcements

Auxetics are the class of cellular structures which possess a negative Poisson's ratio. Negative Poisson's ratio is achieved through the careful design of the structures. Generally, auxetic structures are not feasible to manufacture using the conventional manufacturing processes due to the unit cell's complex geometry, additive manufacturing help in alleviating this issue. Material extrusion/Fused Filament Fabrication (FFF) is the most simple, reliable, and low-cost additive manufacturing process in use. The mechanical performance of FFF processed auxetics is influenced by both geometrical parameters of auxetics and printing parameters. The careful selection of these parameters is of prime priority to avoid premature failure of printed structures. In the present work, the re-entrant diamond auxetic mechanical metamaterial is fabricated via FFF using the most commonly used FFF feedstock material, Acrylonitrile Butadiene Styrene (ABS). Initially, efforts are made to fine-tune the FFF process parameters to process these complicated geometrical structures. The ideal deformation parametric zone is defined with preliminary experiments to avoid premature failure of the re-entrant diamond structure. Experimental investigation of the effect of auxetic geometrical parameters and FFF process parameters on the quasi-static in-plane compressive performance is systematically evaluated using the design of experiments. The grey-based optimisation method is considered to optimise influential parameters for combined responses. Further, the re-entrant diamond auxetic metamaterial is reinforced with short carbon and glass fibre, and studied at optimal parametric levels. Reinforcements have enhanced the specific strength and stiffness of the structure with the loss of energy absorption characteristics. Microscopic studies confirm the predominant failure modes as a bond failure for CF-ABS and fibre breakage for GF-ABS. This study also aims to serve as fabrication guidelines to process complicated cellular composite structures via FFF.