Fibre orientation-dependent damage modelling and experimental identification for 3D-printed continuous carbon fibre reinforced nylon composites

The complex failure mechanisms induced by the layer-by-layer deposition in additive manufacturing require advanced modelling strategies to ensure reliable structural analysis; however, existing approaches rarely incorporate explicit orientation-dependent damage laws to capture anisotropic degradation. This study presents an effective intralaminar constitutive damage model for 3D-printed continuous carbon fibre-reinforced nylon (Onyx) composites manufactured by fused filament fabrication (FFF), calibrated for a specific specimen architecture and print configuration. An experimental campaign comprising quasi-static tensile, compression, and in-plane shear tests at multiple fibre orientations was conducted to calibrate a thermodynamically consistent continuum damage mechanics (CDM) model, with key parameters identified from cyclic tests to characterise stiffness degradation and define damage evolution as a function of the local fibre angle ( θ ) . The proposed model accurately reproduces the mechanical response across the investigated loading cases and is further validated under three-point bending, demonstrating its predictive capability for orientation-dependent failure in FFF composites.