EFFECT OF FIBER ARCHITECTURE ON MECHANICAL BEHAVIOR OF SiC(f)/SiC COMPOSITES

We evaluated mechanical properties (first matrix cracking stress, strength, and work-of-fracture) of Nicalon-fiber-reinforced silicon carbide matrix composites with three different fiber lay-up sequences (0"/20"/60", O0/4Oo/6O0, and 0"/45") at various temperatures from room to 1300°C. Up to 1200"C, ultimate strength and work-of-fracture for the 0"/40"/60" and 0"/45" composites increased, but then declined at 1300°C. The decreases were correlated to in-situ Nicalon fiber strength and fibedmatrix interface degradation. However, for the 0"/20"/60" composites, ultimate strength and work-of-fracture reached their a minima at 1200°C. These measured ultimate strengths at room and 1300°C were correlated to the predictions made with an analytical model and to in-situ fiber strength characteristics. The large difference in room-temperature ultimate strengths between the three sets of composites is attributed to the relative contributions of the off-axis fibers to the load-bearing capacity of each composite.