Effect of through-the-thickness areal density and yarn fineness on the mechanical performance of three-dimensional carbon-phenolic composites

An experimental investigation was performed to study the mechanical performance of 3D carbon/phenolic composites subjected to bending and impact forces. T300-3k dry preforms were tufted using carbon threads of 396, 800, and 1600 tex. Also, the tufting densities varied from sparse density (tufted 16x16: areal density=0.37cm(-2)) to moderate density (tufted 11x11: areal density=0.82cm(-2)) and high density (tufted 5.5x5.5: areal density=3.30cm(-2)). The tufted preforms were then infiltrated by phenolic resin through the vacuum pressure infusion process. The three-point bending tests results revealed that the flexural strength loss of tufted composites ranged from 17 to 34%. In untufted composites, the specified crack grew quickly along the composite while through-the-thickness reinforcements stopped the crack growth and led to crack branching along the thickness of composite. With the presence of through-the-thickness yarns, damage behavior changed and the tufted composites exhibited a slower rate of decrease in the level of stress. These composites also showed higher levels of after-failure stress values. The experimental results of the impact test demonstrated that tufting had different effects on the energy absorption of composites. In a number of tufted composites, the energy absorption increased by 14.6% and in the other ones, it reduced by 8%.