Effect of infill density, build direction and heat treatment on the tensile mechanical properties of 3D-printed carbon-fiber nylon composites

This work investigates the effect of infill density with various fill patterns and build direction with composite type on the tensile mechanical properties of carbon fiber reinforced 3D printed nylon composites. Additionally, it evaluates the impact of heat treatment on the pure and reinforced build direction composites. Results demonstrated that infill density with 50 % and triangular fill pattern showed the highest tensile strength of 153 MPa, Young's modulus of 7188 MPa, and toughness of 5.37 MJ m⁻³ than the rectangular and hexagonal infill densities and fill patterns owing to better performance of triangular fill or lower void content in the struts and therefore greater interface bonds were formed. Side build direction of pure and reinforced composites performed greater tensile strength and Young's modulus, whereas lower toughness compared to flat build composites. Since more layers were available for side build printing, and hence more material and time, it has consumed for printing. Furthermore, after heat treatment, it was found that the pure and reinforced side build direction composites presented the highest tensile strength and Young's modulus but lower toughness compared to flat build composites as the matrix is entirely penetrated by fiber and thus porosity becomes negligible due to consolidated interfaces.