Toughening of thermoset composites using glass/polypropylene commingled stitching yarns

This paper investigates the damage resistance and tolerance of thermoset composite laminates stitched by glass and hybrid glass/polypropylene commingled yarns. Different impact energies (10-70 J) were applied to stitched composite laminates before compression after impact (CAI) tests were conducted. The results showed that, except for 70J, commingled yarn-stitched laminates absorbed more energy than glass-stitched laminates. Compression tests revealed that glass-stitched and commingled composites had, respectively, 2 % and 5 % higher compressive strengths than unstitched laminates. After being impacted to 10-70J energies, glass yarn stitched laminates kept 83-36 % of their compressive strength, while commingled yarn stitched laminates retained 73-40 %, showing that the commingled yarns were more efficient at higher energies. The study found that integrating plastically deformed fibres into hybrid stitching yarns increased energy absorption and composite fracture mechanism by encouraging fibre/matrix debonding, resulting in fewer fibre breakages.