THE INFLUENCE OF DEFECTS ON THE RESPONSE OF TITANIUM SIC FIBER COMPOSITES TO THERMAL EXPOSURE/

The effect of thermal exposure on the mechanical properties of Timetal 1100/SCS-6 (SiC) fiber composites has been evaluated. Unidirectional composites were exposed and tensile tested in the transverse (90-degre es) and longitudinal (0-degrees) orientation. Two panels were sectione d into samples, thermally exposed, and tested in the transverse orient ation; one contained well-spaced fibers, while the other had a high de gree of fiber-fiber contact. Likewise, two groups were tested in the l ongitudinal orientation. These panels all had good fiber spacing, but some contained large regions of poor matrix-ply bonding, while others were predominantly well-consolidated. The poor spacing in the transver se samples and the poor matrix-ply bonding in the longitudinal samples strongly affected the residual properties of the composite following exposure. In effect, these defects increased the volume of the matrix that was embrittled by the environment during exposure in air, thereby resulting in degradation of the matrix and the fiber-matrix interface . Well--consolidated composites with good fiber spacing retained a lar ge percentage of their as-fabricated properties following exposure.