Effectiveness of fibre placement in 3D printed open-hole composites under uniaxial tension

The emerging 3D printing technology of continuous fibres enables fibre steering and customised curved fibre paths during the manufacturing process, which could potentially enhance the mechanical properties of composites with geometric singularities. In this paper, the effect of fibre placement on the mechanical performance of open-hole composites under uniaxial tension is comprehensively studied. A hybrid manufacturing technology is presented to enable the fabrication of 3D printed dual-polymer composites with low porosity and customised continuous carbon fibre reinforcement. A concept of placing continuous fibres along the maximum principal stress trajectories is adopted and found to improve the strength of the composites and dramatically postpone the crack initiation, compared with the drilled samples. Additional fibres, along the minimum principal stress trajectories and around the hole, are found to dramatically alter the failure mode and mechanical performance of the samples. Together with the digital image correlation measurement, a finite element model is also developed based on the actual printing paths to understand the stress distributions due to different fibre placement methods. The study offers a very useful tool for the customised design of 3D printed composites with complex shapes and/or geometric singularities.