3D-printed continuous and short carbon fibre reinforced composite metamaterials with tailorable negative Poisson’s ratios

Currently, metamaterials have been attracting increasing attention with a wide range of applications, i.e., smart materials, graded materials, shape memory alloys, biomaterials, etc. This study developed an integrated computational design method with 3D printing to endow continuous and short carbon fibre reinforced composite metamaterials with negative Poisson’s ratios. First, continuous carbon fibre (CCF) composites were designed using a multidisciplinary technique integrating homogenisation-based topology optimisation and fibre placement methodology for determining the 3D printing set-up with fused filament fabrication. Second, specimens made of pure polyamide (PA), short carbon fibre reinforced PA (SCF/PA) and CCF reinforced PA (CCF/PA) were fabricated and tested for a comparative evaluation. Lastly, the effects of carbon fibre reinforcement were investigated, showing that a small addition of CCFs (vol% = 0.23) can improve the negative Poisson’s ratio from −0.24 of the PA metamaterials to −0.34. However, other greater CCF volume fraction would reduce the negative Poisson’s ratio