Effect of Manufacturing Defects on Damage Initiation and Propagation in Gapped UD Carbon Fibre Composite Laminates

Resin Transfer Moulding (RTM) is widely used to manufacture high-quality CFRP components for aerospace applications. Recently, a novel gapped unidirectional (UD) carbon fibre material has been developed, offering new opportunities for composite design and manufacturing. However, the damage mechanisms and defect sensitivity of RTM-manufactured laminates based on this material system remain largely unexplored. The novelty of this work lies in the investigation of damage initiation, propagation, and compressive performance in RTM-manufactured laminates produced from this newly developed gapped UD material, with particular emphasis on the role of manufacturing-induced defects. Thin Teflon films were embedded at the laminate mid-plane to introduce controlled artificial delaminations, enabling a systematic assessment of their influence on damage initiation, damage propagation, and interlaminar stress redistribution. Progressive tensile and compressive testing, combined with stepwise microscopic inspection, was employed to track damage evolution. The results showed that crack initiation under tensile loading is governed primarily by ply orientation, with matrix cracks consistently initiating in the central 90° plies at strains of 0.4–0.5%. Cracking in the ± 45° plies occurred only at the maximum applied strain (1.2%), indicating a higher resistance to failure. Resin-rich areas and binder-related inclusions were not observed to act as preferential crack initiation sites. In contrast, porosity had a pronounced effect on compressive performance. An overall decrease in compressive strength was observed with increasing void content, with the most porous specimens exhibiting reductions of up to approximately 35–40% compared with specimens containing negligible porosity. Artificially induced delaminations reduced the strain threshold for damage initiation and promoted more extensive damage propagation. These results provide new insight into the role of manufacturing defects in damage initiation, propagation, and compressive failure of RTM-manufactured gapped UD CFRP laminates. The findings contribute to the understanding of defect-sensitive damage mechanisms in this emerging material architecture and support the development of more reliable aerospace-grade composite structures.