FRACTURE CHARACTERISTICS OF PITCH BASED-CARBON CARBON COMPOSITES

D pitch based carbon carbon composites with different densities were fabricated by HPIC (High Pressure Impregnation Carbonization) technique, with 1?K PAN based HT carbon fibers as reinforcing materials and modulated coal tar pitch as matrix precursor. Experimental results indicated that the fracture characteristics of composites were closely related to their densities. According to the curves of bending loading versus displacement, carbon carbon composites with high density showed brittle fracture behavior, while low density composites were inclined to tough fracture. Different samples were observed by SEM fractography methods, which reflected that the samples with brittle fracture had almost flat fractured surfaces, but the samples with tough fracture showed that lots of carbon fibers were pulled out. As a fact, the fracturing process of carbon carbon composite was the results of matrix cracks developing and extending. The relevant paths were partly dependent on the interface condition. The crack developing along interfaces would result in debonding between carbon fibers and matrix, and lead to the sliding of carbon fibers. Thus, part of energy absorbed mechanism related to fibers sliding took place, and provided carbon carbon composite with good toughness.