FAILURE MECHANISMS OF LAMINATED CARBON-CARBON COMPOSITES .1. UNDER UNIAXIAL COMPRESSION

Failure mechanisms under uniaxial compressive loading are determined for several types of two dimensional (2D) carbon-carbon composites. Compressive strengths ranging from 90 to 180 MPa are observed. As expected, under uniaxial compression, a shear band is formed across the specimen diagonal. Remarkably, no inelastic deformation, either in the form of micro-buckling or microcrack nucleation was observed prior to the terminal shear failure. The crimp angles associated with the weaving pattern are significant not only in pre-setting the angle of the shear band but also in regard to the local kink boundary angle beta in the fiber bundles. Hitherto unreported values of beta ranging from 50 to 60-degrees, and the kink inclination angle alpha in the range 35-40-degrees, are observed. A theoretical analysis relating the peak compression load to alpha and beta, with crimp angles as initial imperfections, explains the experimental observations.