| The effect of constituent properties and geometric parameters on the overall behavior of brittle matrix composites was examined by developing and testing model composites. The model composite materials studied included a silicon carbide fiber/barium borosilicate glass system, a polyvinyl-alcohol fiber/epoxy system, and two optic fiber/epoxy systems. Single fiber tests were used to characterize the interfacial bonding and sliding characteristics of each system. The use of a transparent matrix allowed clear observation of the failure mechanisms, i.e., matrix cracking and fiber debonding, under longitudinal tensile loading. The silicon carbide fiber had a rough interface which increased the fiber's sliding resistance and contributed to interfacial wear during pullout. The specimens were fabricated by placing the fibers between pieces of glass and heating the sandwich above the softening point of the glass under slight pressure. Although volume fractions were low, multiple matrix cracking occurred and the general shape of the stress-strain curve was similar to that of commercial ceramic matrix composites. The polyvinyl-alcohol fibers bonded weakly to epoxy although resistance to sliding was high due to fiber roughness and the non-circular nature of the fibers. The matrix crack densities were high for these composites and also for the optic fiber coated with polyimide, which has a high bond strength with epoxy. |
