Fiber test development for ceramic composite thermomechanical properties

Many of the key thermomechanical tensile properties of continuous-fiber ceramic composites (CFCC), such as ultimate fast-fracture strength and long-term rupture strength, are controlled by the dl:formation and fracture properties of the reinforcing fibers. For this reason, research efforts are ongoing at NASA to develop fiber test procedures and composite property models that will allow use of the fiber data to accurately predict these CFCC strength properties for a variety of potential application conditions. Because of the current interest in two-dimensional woven composites, emphasis is being placed on the testing of single small-diameter fibers and single-ply fabrics. The primary objective of this paper is to review the status of these efforts. It is shown that the fabric tests and procedures need further development in order to use bundle strength theory to predict the fast-fracture strength of as-fabricated CFCC. On the other hand, the single-fiber tests using simple composite rupture models yield predictions in good agreement with available data for CFCC rupture strength at high temperatures.