THE BEHAVIOR OF CERAMIC MATRIX FIBER COMPOSITES UNDER LONGITUDINAL LOADING

Failure mechanisms were studied by reflection light microscopy in a unidirectional silicon carbide/glass-ceramic composite loaded in longitudinal tension. The material behaves linearly up to the point where the first transverse matrix cracks appear. Thereafter, it undergoes a rapid stiffness decrease corresponding to matrix crack multiplication and saturation. These matrix cracks increase in density with applied stress up to a limiting level of 28 cracks/mm or a minimum crack spacing of 36 mum (0.0014 in), which corresponds approximately to two fiber diameters. Fiber breaks and fiber debonding, which start before matrix crack saturation, continue until final failure. In the last stage the material exhibits quasi-linear behavior with small stiffness variation. Experimental results of crack density and stress/strain behavior were compared with predictions based on a modified shear lag analysis.