Defect characterisation of 3D printed composites with high spatial resolution

Abstract

The development of 3D printing technology has made it feasible to manufacture fibre-reinforced composites with complex internal geometries and customized mechanical properties. However, the layer-by-layer manufacturing method of fused filament fabrication (FFF) produces various microstructural defects, such as pores and fibre misalignment, which significantly affect the mechanical properties and reliability of the printed composites. This paper aims to characterise these defects and visualise the internal structure of continuous carbon fibre (CFRP) and glass fibre (GFRP) reinforced nylon composites with high spatial resolution using computed tomography (CT), and then analyse their impact on the failure mechanism under compressive load. This study takes into account the defects before the experiment and the failure mode after the experiment, and porosity and length and angle-based waviness are utilised as indicators to quantitatively describe the degree of composite defects. The results show that the CFRP sample with more ideal fibre alignment dispersion (5.6° vs 6.54°) exhibits earlier shear failure due to its relatively higher porosity (4.49% vs 3.64%). These findings indicate that composite failure is governed by the interaction of multiple defects. In addition, fibre fracture and local buckling frequently appear near the notch, emphasising the role of stress concentration in failure initiation. Therefore, the optimisation of compressive strength should consider the coupling effects of multiple factors and focus on strengthening regions particularly near geometric discontinuities such as notches.