Multi ‐Axial Compression Analysis of Novel Three‐Dimensional Six‐Directional Braided Composites by Structural Optimization Design

ABSTRACT This study targets stepwise 3D6d braided composites by establishing a constraint PSO‐SVM surrogate coupled with NSGA‐III optimization and TOPSIS selection to link true geometry and damage evolution with efficient multi‐objective design. A lift rod‐based densification route adjusts yarn insertion direction and preform density, fully parameterizing insertion density, density zone length, braiding pitch, and six directional yarn tension. Across 72 designs, the optimized architecture raises compressive strengths in X , Y , and Z by 26%, 19%, and 14% with concurrent increases in moduli. Measured strengths are 164, 224, and 268 MPa, and measured moduli are 5.9, 8.7, and 9.3 GPa, while coefficients of variation for modulus and strength are 2.5 × 10 ⁻¹ and 4 × 10 ⁻¹ , indicating improved near isotropy. Predictions for the experiment are below 5%. DIC and micro CT reveal a progressive failure governed by interfacial shear and fiber buckling, confirming the reliability of the model and the process strategy. The surrogate‐driven optimization framework offers practical guidance for integrated structure process design of high‐performance 3D braided composites.