Estimation of the fracture toughness of Tyranno Si-Ti-C-O fibres from flaw size and "fracture mirror" data measured in situ a 3-D woven SiC/SiC composite

The fracture toughness, calculated from the size of initiating flaws, was estimated for Tyranno® LoxM Si-Ti-C-O fibres in situ a 3-D woven SiC/SiC composite that had failed under tensile loading at room temperature. The fibres had been subjected to a surface modification treatment prior to incorporation within the composite. Two distinct flaw populations (internal and surface) were noted within the fibres with associated fracture toughness values of 0.997 (± 0.062) and 1 .428 (± 0.103) Mpam1/2, respectively. The former value was similar to that of nominally similar Nicalon® Si-C-O fibres whereas the latter value was attributed to the presence of an unidentified 80 nm layer surrounding the fibre.