Optimizing C _f /ZrB ₂ –SiC Composites for Aerospace TPS via Density‐Normalized Performance

ABSTRACT In this study, the mechanical performance of ZrB 2 –SiC‐based carbon fiber‐reinforced composites was evaluated using a design‐oriented framework, focusing on the effects of fiber architecture (long/short fibers) and rheology modifier (RM) addition. Elastic modulus, Vickers hardness, and fracture toughness were first assessed using raw experimental data, followed by density‐normalized metrics to decouple density‐related effects. The relationships between density‐normalized properties were qualitatively assessed to clarify interproperty synergies, and a trade‐off analysis using a multiobjective selection approach was subsequently employed to evaluate performance pathways among the investigated design cases. The results show that mechanical performance cannot be explained solely by relative density; instead, fiber architecture and RM addition introduce clear trade‐offs among stiffness, hardness, and toughness through microstructural arrangement. Short‐fiber systems incorporating RM exhibit more stable and efficient mechanical performance without a density penalty. Based on these findings, design rules are proposed to guide the selection of optimal fiber architecture and reinforcement strategies for ZrB 2 –SiC‐based advanced ceramics for specific application objectives.