A bi-phasic numerical approach for non-linear response and stiffness recovery related to residual thermal stress in UHTCMCs

The tensile properties of sintered Cf-ZrB2/SiC UHTCMCs were investigated for different lamination sequences, revealing ultimate strengths of 570 MPa (0°/0°), 120 MPa (0°/90°), and 40 MPa (90°/90°). The results facilitated modeling the material's non-linear tensile response, characterized by a remarkably prolonged plateau with pseudo-plastic behavior, followed by stiffness recovery before ultimate failure. A simplified analytical model was developed to predict this behavior originated by residual thermal stresses and inelastic phenomena. A complete constitutive law was then developed and implemented in a FE model, utilizing a bi-phasic approach including Drucker-Prager plasticity and orthotropic ductile damage. Two-step analyses were performed, starting with a thermal step to represent the buildup of a self-equilibrating RTS state in the material phases, followed by a mechanical simulation. This demonstrated the model's efficacy in capturing the non-linear response in both homogeneous and cross-ply lay-ups, contributing to advancements in materials engineering and the design of UHTCMCs-based hot structures.