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

Failure mechanisms under uniaxial compressive loading are determined f or several types of two dimensional (2D) carbon-carbon composites. Com pressive strengths ranging from 90 to 180 MPa are observed. As expecte d, under uniaxial compression, a shear band is formed across the speci men 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 p attern 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 f iber bundles. Hitherto unreported values of beta ranging from 50 to 60 -degrees, and the kink inclination angle alpha in the range 35-40-degr ees, are observed. A theoretical analysis relating the peak compressio n load to alpha and beta, with crimp angles as initial imperfections, explains the experimental observations.