Estimation of the 'mirror constant' in Tyranno~direct R Si-Ti-C-O fibres from fibre strength data measured in situ a 3-D woven SiC/SiC composite

摘要

The strength, S, of ceramic fibres may be estiamted from its fracture surface using the fracture mirror radius, r_m, and the equation S=A_m/(r_m)~1/2, where A_m is known as the "mirror constant". A_m is equal to C_m centre dot K_IC, where C_m is a function of the flaw size and K_IC is the fracture toughness. The present work estiamted the value of A_m for Tyranno~direct R Si-To-C-O fibres in situ a 3-D woven SiC/SiC-based composite to be 2.50 (+-0.9) MPa centre dot m~1/2. This value corresponded well with an estiamte of 2.51 MPa centre dot m~1/2 obtained previously for nominally similar Nicalon~direct R Si-C-O fibres. The unusually low experimental value of tensile strength at 1300 deg C in vacuum was attributed to a 30