Flexural behavior of three-axis woven carbon/carbon composites

This work examines the processing characteristics and flexural behavior of 3D woven carbon/carbon composites. Two types of the composites have been ma de, both having 3-axis orthogonal structures. The first combines solid rods along the axial direction. The rod, 1 mm in diameter, is composed of unidi rectional carbon fibers and a phenolic resin. The second is a conventional type composed of carbon yarns in all axes. Both preforms were then impregna ted by the phenolic resin. Matched molds were used to enhance fiber packing and to cure the resin under a hot press. The green composites were then he at-treated at various temperatures ranging from 200 degrees through 1000 de grees C. The second set of specimens was made by applying multi-cycle impre gnation and carbonization. Flexural tests were carried out for these two se ts of specimens. Their responses to the load and the induced damage behavio r have been examined. The use of rods enhances fiber packing and reduces fi ber crimp, leading to higher material performance. Decomposition of the res in due to the heat-treatment results in weak interfacial bonding and compre ssive failure in axial yarns. The efficiency of densification has been exam ined. The induced damage configurations vary significantly in these specime ns, as a result of the processing. Some unique modes associated with the 3D structure are discussed. (C) 2001 Kluwer Academic Publishers.