Effect of Through-the-Thickness Yarn Fineness and Distanceon Damage Behavior of Carbon-Phenolic 3D Composites

The effects of through-the-thickness yarn fineness and distance on the damage behavior of vacuum resin infused 3D carbon-phenolic composites were investigated. For this purpose، the carbon/phenolic composites with different tufting thread fineness (count) and distance ranging from 5. 5 mm to 16. 5 mm were produced to determine an optimum distance and count in the composites. Three-point bending test results show that the flexural strength of tufting composites may drop 17% to 34 % while through thickness reinforcements set up a mechanical connection between the plies and bridge over delamination cracks to avoid their penetration. The weakness is attributed to damaging effect of tufting method، misallignments of X-Y fibers in presence of Z direction reinforcement and stress concentration effect of produced holes for tufting. On the other hands، Z direction reinforcements prevent fibers delamination. Therefore، the laminate strength was increased and failure mechanism was changed from brittle to ductile fracture. In addition at the same through-thickness yarn count of tufting composites، with the increase in tufting distance، the flexural strength is reduced. But i in the case of samples with tufting distance of 5. 5 mm، the flexural strength reduced with increase in thorough-the-thickness yarn count، but for samples with tufting distance of 16 mm، showed some increases with the same count variations. After the failure stress in stress-displacement curve was increased for specimens with Z direction reinforcements.