Effect of temperature gradients and stress levels on damage of C/SiC composites in oxidizing atmosphere

Strain response of a C/SiC composite, which is cycled with ΔT₁ of 500 °C at 50 MPa, ΔT₂ of 400 °C at 100 MPa and ΔT₃ of 300 °C at 150 MPa, was investigated. Measured thermo-elastic strain ranges are found to retain 0.209% for ΔT₁, 0.168% for ΔT₂, and 0.122% for ΔT₃, independent upon the applied stress level. Non-linear variations of thermal cycling creep strain can reflect damage evolutions of the composites by changing its rate, which depends on temperature gradient and applied stress. After 104 thermal cycles, strength, modulus, and failure strain of the composites retain 60.29%, 84.2%, and 59% of the initial properties, respectively. The coating cracks of the cycled specimens are observed to be perpendicular to the applied stresses and arranged at relatively regular spacing, through which the fibers are oxidized superficially.