A physically based thermo-elastoplastic constitutive model for braided CMCs-SiC at ultra-high temperature

Complex microstructure and multiple internal microcrack propagation of braided silicon carbide ceramic matrix composites (CMCs-SiC) make their mechanical behavior remarkably nonlinear. Still, few models have been developed at ultra-high temperature due to the challenge to incorporate detailed micromechanisms of nonlinearity into the formulation. Based on the observations of fracture morphologies of previous experiments of CMCs-SiC under different stress states and current on-axis tensile experiments of 2D C/SiC composites at ultra-high temperature, some assumptions are proposed. Then, a physically based constitutive model at ultra-high temperature is established within the thermo-elastoplastic framework. The novelty of this model is that we proposed a thermal yield criterion, which considers the material orthotropy, tension-compression asymmetry, unilateral crack closure effect, and temperature effect. The thermal hardening effect is a distinctive phenomenon for CMCs-SiC in vacuum and is described using an improved Johnson–Cook model. The proposed model is implemented using a return mapping algorithm. The results show that the model predictions of stress–strain relationships agree well with experimental data at different stress states and different temperatures.