Effects of fiber volume fraction and thermal treatment on the properties of C/C composites

The hardness of C/C composites is reinforced with the increasing of the fiber volume fraction. When the carbon fiber volume fraction is over 30%, the hardness of C/C composites keeps constant. The bending strength of C/C composites is reinforced with the increasing of the fiber volume fraction. High fiber volume fraction results in smaller holes in preforms which can not be well filled by pyrocarbon, so the bending strength will decline. Therefore, there is an inflexion with the increasing of the fiber volume fraction. There are three fracture mechanisms-brittle fracture, pseudo plastic fracture by which whole bundle fiber are drawn, and pseudo plastic fracture by which portion fiber are put out, in accordance with the variation of the thermal treatment temperature of fibers. C/C composites with excellent mechanical properties were obtained after heat treatment of carbon fibers at 1600℃.