Strength criterion and failure mechanism of 3D braided joints: from specimen to component design

Joints constitute critical assembly components in large 3D braided skin structure. Optimizing braided architectures to enhance bearing performance is essential for ensuring connection reliability of joints. Nevertheless, quantitative relationships between braided architectures and bearing performance remain poorly characterized. Moreover, the uniaxial loading in joints specimen tensile test differs significantly from the actual biaxial loading in components, leading to an overrated performance of joint. This study investigates the effect of braiding angle, thickness, edge-distance, and lap configuration on bearing performance to elucidating the effect of braided architecture on unidirectional bearing performance. Then, degradation in bearing performance under biaxial loading was analyzed to propose the strength criteria for biaxial bearing performance. Experiment shows that variations in braiding angle, edge-distance, lap configuration and thickness inducing up to 72% degradation in uniaxial bearing strength and transitions in failure modes. Additionally, biaxial loading of joints in components induces up to 35% degradation in bearing stiffness and up to 50% in bearing strength. The proposed criteria quantify the performance degradation relationship between specimens and components, providing more specific design numerical references for specimen to component design of joints.