Viscoelastic characterisation of additively manufactured composites with nylon matrix: effects of type and orientation of fibres

This study investigates the viscoelastic performance of additively manufactured (AM) nylon and nylon-matrix composites reinforced with short and continuous fibres with three different fibre orientations: longitudinal, transverse, and quasi-isotropic. Dynamic mechanical analysis under a frequency sweep of 1–100 Hz along with tensile tests used to determine the Young's modulus and X-ray micro-CT for evaluation of microstructural porosity were employed to fully describe the viscoelastic behaviour of the composites. Generally, the addition of fibres increased the storage modulus of most composites. The composites revealed increased porosity and fractography using a scanning electron microscope on the tensile specimens demonstrated poor fibre-matrix bonding. These factors, along with the fibre orientation, had a complex effect on the loss modulus of the composite structures. Overall, the addition of fibres reduced the damping factor of the composite specimens compared to pure AM nylon samples. The quantified parameters, including those of the Prony series, can be used in numerical simulations supporting the design and optimisation of AM components.