Strain response of C/SiC composite to thermal and mechanical load cycling in oxidising atmosphere

Strain response of a C/SiC composite simultaneously subjected to thermal cycling (1173–1473 K) and mechanical cycling (60±20 MPa) in an oxygen–argon mixture: 10·4%O₂–89·6%Ar was investigated. Thermal strain with maximum value of ∼0·117% and mechanical strain with maximum value of ∼0·029% were directly measured on a progressively increasing baseline strain from 0·354 to 0·670%. The thermal strain and mechanical strain were found to have an approximately linear relationship with the temperature and stress respectively; and to be in quantitative agreement with the calculated results using the proposed semiempirical formulas. The baseline strain was considered to be damage dependent and could increase with accumulated damage. It is observed that the thermal and mechanical load cycling in an O₂–Ar mixture could cause the coating/matrix cracks, the degradation of the interfaces, fibre oxidation, and an increase in the baseline strain of the composites by widening crack opening displacement due to larger interfacial debonding and fibre sliding, and reducing effective load bearing area of the fibres.