Ply and interlaminar behaviours of 3D printed continuous carbon fibre-reinforced thermoplastic laminates; effects of processing conditions and microstructure

Taking advantage of an extended design and manufacturing space for composites, the technology of fused filament fabrication (FFF) of continuous fibre-reinforced thermoplastics shows great potential for the production of the next generation of lightweight structural parts. This process still has room for development. Moreover, knowledge of the mechanical behaviour of the resulting 3D printed composites is still limited. In this work, the intra- and inter-laminar behaviours of carbon fibre/polyamide printed laminates were extensively characterised to determine ply elastic and strength properties, as well as interface strength and fracture characteristics. Moreover, the effects of eventual production defects on these properties were analysed, putting in evidence some of the present shortcomings of the FFF process. Such defects include non-homogeneous fibre distribution, large amounts of intra- and interlaminar voids, and weak interlayer bonding, which are likely to be due to insufficient thermo-mechanical consolidation of the material during the FFF process, and have significant influence on the matrix-dominated mechanical properties. As a result, the transverse and interlaminar properties were found to be lower than those obtained through hot compression moulding of carbon fibre/polyamide laminates. Besides highlighting possible process improvements, the mechanical characterisation carried out in this work promises a significant contribution to the abilities of designing and simulating general 3D printed composite parts