NONLINEAR CONSTITUTIVE MODEL FOR 2D-C/SiC COMPOSITES AT ELEVATED TEMPERATURES

High-temperature anisotropic nonlinear constitutive relationship is of great scientific and engineering significance for thermal structure design of ceramic matrix composites. In order to analyze and predict the stress-strain behavior of 2D-C/SiC composites under plane stress state at elevated temperatures, a thermal-mechanical coupled damage constitutive model was developed based on the damage decoupling characterization method, considering the damage coupling effect and material nonlinearity and orthotropy. Meanwhile, by application of the strain segmentation method, and taking into consideration of the effects of thermal mismatch stress, matrix cracking, interface debonding and fiber bridging on the unloading modulus and residual strain, the analytical models of on-axis tension and in-plane shear stress-strain relationships of the material were presented, and preliminary experimental validation were performed. On the basis of basic property characterization, the tensile stress-strain behavior of 2D-C/SiC composites under different off-axis angles, i.e., 15°, 30° and 45°, and at elevated ambient temperatures (27 °C, 973 °C, 1273 °C and 1473 °C) were simulated and predicted. The results show that the strain response of 2D-C/SiC composites depends significantly on environmental temperature. The degree of material nonlinearity decreases with the increase of temperature, while it increases with the increase of off-axis angle. Meanwhile, the apparent modulus of the material tends to increase with the increase of temperature at different off-axis angles. Besides, the developed theoretical model can reasonably predict the stress-strain behavior of 2D-C/SiC composites, and the simulated curves are in good agreement with the experimental data.