Open-hole tensile behaviour, notch sensitivity and failure analysis of 3D-printed onyx-continuous carbon fibre reinforced composites

The structural integrity of Additively manufactured fibre-reinforced polymer composites is critical for lightweight load-bearing components with fastener holes and cut-outs in lightweight aerospace and unmanned air vehicle (UAV) structures. This study investigates the open-hole tensile (OHT) behaviour and notch sensitivity of 3D-printed Onyx–continuous carbon fibre reinforced (CCFR) composites using a Taguchi L9 design of experiments and analysis of variance (ANOVA). The relative influence of infill type, infill density, fibre orientation, and fibre volume fraction (FVF) on OHT strengths were statistically evaluated. The results indicate that FVF (46.94%) and fibre orientation (38.82%) predominantly govern OHT strength, while infill architecture and infill density have comparatively smaller statistical contributions. Nevertheless, infill architecture influences local stress redistribution and damage evolution under notch loading. Comparison of the predicted and experimental OHT strengths for the validation specimens showed good agreement, supporting the reliability of the developed model. Under optimised conditions, the gyroid infill exhibited the highest OHT and specific strengths among the investigated configurations, while retaining approximately 85% of the solid infill strength, indicating improved strength-to-weight efficiency. Notch sensitivity analysis revealed that gyroid and hexagonal infills exhibited improved resistance to stress concentration compared with the rectangular infill. The findings provide useful design guidelines for lightweight additively manufactured aerospace and UAV structural components containing fastener holes and cut-outs.