Prediction of Impact Stress Concentration in Octagonal Hollow <scp>3D</scp> ‐Woven <scp>CFRP</scp> : An <scp>ISCF</scp> ‐Coupled Physical Model for Multi‐Scale Synergistic Weaving

ABSTRACT This research focuses on the stress concentration issue of octagonal hollow three‐dimensional woven carbon fiber reinforced polymer (CFRP) preforms under impact loads. A coupled analytical prediction model of the impact stress concentration factor (ISCF) was developed. The collaborative effects of parameters such as geometric curvature radius and fiber arrangement were quantitatively analyzed. Moreover, under the corresponding conditions, the model was verified through low‐velocity impact experiments, and the predictive error of ISCF is less than 3%. For cases where the error exceeded 3%, a corrective model was proposed. An innovative multi‐scale synergistic weaving process is proposed; the in‐plane reinforcement framework is constructed by means of 0°/90° orthogonal yarn placement, and Z ‐axis yarn is introduced to achieve overall reinforcement in the three‐dimensional space. Moreover, a representative volume element (RVE) model with an elliptical cross‐section was constructed to achieve high‐precision cross‐layer prediction of the fiber volume fraction ( V f ), the predictive error of V f pred is around 1.1%. The results indicate that the stress concentration in the dihedral angle regions of the preform is significantly higher than that in the straight regions. In the present study, when V f fraction reached 51.06%, the damage safety factor exceeded the safety threshold, suggesting that the material was susceptible to irreversible damage at this volume fraction. This study provides theoretical underpinnings for the optimized design of 3D‐Woven CFRP, thus holding great value for engineering applications.