Flexural Behaviour of Unreinforced and Z-Fibre Reinforced 3D Carbon/Epoxy Composites

This study compares the flexural properties of unreinforced and Z-fibre reinforced 3D carbon/epoxy composites. Z-fibre reinforcement is introduced by a novel stitching pattern where uniform distribution of Z-fibres is achieved by inserting linear and angular stitch loops. Flexural tests were performed on both normal and parallel to stitching directions. Z-fibre reinforcement caused reduction in composite density and fibre volume fraction due to local gaps introduced by the needle insertion, which are filled with epoxy resin, resulting in resin rich regions and affecting flexural behaviour. Z-fibre reinforcement reduced the flexural strength and modulus of the composites (up to 27% and 39%, respectively), while the toughness of the Z-fibre reinforced 3D carbon/epoxy system is improved, since damage is more progressive in nature rather than sudden and brittle like fracture. Strain to failure increased from 1.9% to almost 2.8%, a significant improvement, resulting in more damage tolerant behaviour.