Fiber effects on minicomposite mechanical properties for several silicon carbide fiber chemically vapor-infiltrated silicon carbide matrix systems

Several different types of SiC fiber tows were coated with BN and composite d using chemically vapor-infiltrated SiC to form single-tow minicomposites. The types of SiC fiber included Nicalon(TM), Hi-Nicalon(TM), and the new S ylramic(TM) polycrystalline SiC fiber. The interfacial shear stresses were determined from unload-reload tensile hysteresis-loop tests, The ultimate s tress and strain properties also were determined for the minicomposites. Th e ultimate strengths of the newer Hi-Nicalon and Sylramic fibers were super ior to that of Nicalon minicomposites with similar fiber volume fractions. The Sylramic minicomposites had the lowest strain to failure and highest in terfacial shear strength, respectively, because of the high modulus of the fiber and the rough surface of this fiber type. The apparent interfacial sh ear strength increased as the stress increased for the Sylramic minicomposi tes, which also was attributed to the surface roughness of this fiber.