Effects of stacking thickness on the failure mechanisms of 3D-printed continuous fibre reinforced composite laminates

This study investigates the flexural behavior and failure mechanisms of 3D-printed continuous carbon fibre-reinforced polylactic acid (CCF/PLA) composites with varying thicknesses under three-point bending. Experimental results show that the peak load increases exponentially with increasing thickness, while the displacement at failure decreases, indicating a transition from ductile to brittle behavior. Macroscopic observations and X-ray tomography reveal a progressive change in failure modes, from matrix deformation and localized stress concentration in thin specimens to extensive matrix cracking, fibre pull-out, and fibre fracture in thicker specimens. The proportion of the damaged region through the thickness increases from approximately 27 % in 4-layer specimens to nearly 86 % in 20-layer specimens. A finite element model incorporating anisotropic material properties and interlayer interfaces is developed to simulate the bending response. Numerical results agree well with experiments and provide insight into stress redistribution and shear-dominated deformation in thick specimens. These findings highlight the critical role of thickness in flexural performance and failure evolution, offering guidance for the design and optimization of additively manufactured fibre-reinforced composites.