Chapter 59. Effects of 3D-Fiber Architecture on Tensile Stress-Strain Behavior of SiC/SiC Composites.

Summary

The structural performance of ceramic matrix composites for both low and high-temperature applications depends strongly on key properties contained in their tensile stress-strain behavior after fabrication. These include elastic modulus, matrix cracking stress, and ultimate strength. To determine the effects of fiber architecture on these properties, melt-infiltrated SiC/SiC composite panels were fabricated using 3D orthogonal preforms and 2D fabric lay-ups with various weave patterns. To maximize composite performance, all architectures were constructed with Sylramic^TM SiC fibers in the in-plane directions. Where possible, the preforms and fabrics were then subjected to a treatment that in-situ formed Sylramic-iBN fibers, a fiber type which typically yields composites with the highest tensile and rupture strength. For the 3D preforms, three types of low-modulus z-fibers were used to allow high in-plane fiber fractions, equivalent to those for the 2D composites. Even though the 3D-orthogonal panels displayed well-aligned × and y fibers with low crimp and lower matrix porosity, the room-temperature elastic modulus, cracking stress, and ultimate strength of these panels were generally lower than the 2D-woven panels. It is believed that the reduced modulus and cracking stress were primarily related to fiber-rich regions, the reduced strength to matrix-rich regions.