Designing and tailoring effective elastic modulus and negative Poisson’s ratio with continuous carbon fibres using 3D printing

Abstract

This research employed an integrated design method with 3D printing to endow a base polymer for unique mechanical properties, i.e., enhanced effective elastic modulus or negative Poisson’s ratio using continuous carbon fibres (CCF). A multidisciplinary technique integrating homogenisation-based topology optimisation and fibre placement methodology is developed for 3D printing set-up with a fused filament fabrication process. Then, the representative section of periodical structures with either enhanced effective elastic modulus or negative Poisson’s ratio, made of pure polyamide (PA) while reinforced by CCF were fabricated. Effects of carbon fibre reinforcement on mechanical performance and negative Poisson’s ratio were investigated. The results show that the effective elastic modulus and compression strength of the PA specimens can be enhanced almost linearly with a slope 135 MPa per 1.0 vol% of CCF and 2.4 MPa per 1.0 vol% of CCF, respectively, when CCF is added in PA. For composites with negative Poisson’s ratio, a small addition of CCFs (VCCF = 0.23%) can increase the effective elastic modulus by 59% and the negative Poisson’s ratio from −0.24 to −0.34 for the PA auxetic specimens. However, other greater CCF volume fractions reduce the negative Poisson’s ratio.