THE EFFECT OF SURFACE FLAWS ON SIC FIBER STRENGTH IN AN SIC TI-ALLOY COMPOSITE/

The strength distribution of SiC fibers has been measured after chemic al extraction from a titanium-alloy matrix composite both in the as-co nsolidated state and after heat-treatment at 950 degrees C for 430 hou rs. The strength and fracture mode of fibers extracted from the as-con solidated composite was comparable to that of virgin fiber. However, f ibers from the heat-treated composite demonstrated lower tensile stren gth and fractured from surface flaws created by chemical reaction betw een the fiber and matrix. A fracture mechanics analysis of the relatio nship between the size of these surface flaws and fiber tensile streng th enabled the calculation of the fiber fracture toughness (2.2 MPa ro ot m). The validity of this toughness value for internally-initiated t ensile failures was verified by comparison of observed and predicted f law sizes.