Modeling the effects of thermal and mechanical load cycling on a C/SiC composite in oxygen/argon mixtures

Analytical solutions of and experimental results on the strain response of a carbon fiber reinforced SiC matrix composite under thermal and mechanical load cycling in O₂/Ar are presented. Thermal strain and mechanical strain were shown to approximately sustain linear relationships with temperature T and stress σ, respectively; whereas baseline strain was considered to be damage-dependent, resulting from a combination of two major contributing mechanisms: (a) a physical mechanism in the form of matrix microcracking accompanied by fiber debonding, sliding or fracture and (b) a chemical mechanism in the form of the fiber oxidation associated with longitudinally increased compliance. Based on these analyses a theoretical model, taking into account the thermal strain, mechanical strain and baseline strain, was theoretically formulated with respect to the contribution of each on the overall total strain and to their generation mechanisms. The proposed model gave correct and reliable predictions.