SINOPSIS

The cross-bending and shearing behavior of composites made from carbon fibers and a carbon matrix has been investigated. The effect of the ratio of the span length to the specimen thickness on the values of maximum normal stress in cross-bending fracture in composites has been estimated. The limiting values of this parameter at which its variations do not affect the determined values of maximum fracture stress of composites have been specified. It is shown that the standards developed for determining the cross-bending ultimate strength of composites with a polymeric matrix are not always suitable for carbon−carbon composites. A brief analysis of methods for determining the ultimate shearingstrength of composites with a polymeric matrix has been made. The reasons for restricting their use in carbon−carbon composites have been specified. The methods of shearing tests of carbon−carbon composites, allowing the shear fracture in the estimated cross section of specimens, have been proposed. The values of ultimate shearing strength do not depend on the size of the specimens within the range studied. The pattern of stress distribution over the cross section of the specimen in the case of shearing tests of prismatic specimens has been investigated.