Parametric Modeling and Micro‐ CT Validation of the Braiding Process for a Rectangular Carbon‐Fiber Preform With Yarn Addition

Accurately modeling structural evolution during yarn addition is essential for 3D braided composites. Based on an existing virtual fiber (VF) framework, this study develops a continuous braiding‐process model for a rectangular 3D preform with single‐yarn addition, covering the pre‐addition, transition, and yarn‐added regions. One extra yarn is introduced alongside each main braiding yarn, increasing the physical yarn count and altering spatial occupancy and contact relationships, which induce yarn‐path deflection, rearrangement, and cross‐sectional evolution. A segmented axial pulling strategy controls geometric continuity across these regions. Micro‐CT reconstruction is used to evaluate yarn cross‐sectional parameters, projected braiding angles, and three‐dimensional centerline trajectories. Relative errors in cross‐sectional parameters and projected braiding angles are below 5%, while the model captures the principal spatial‐path characteristics with noticeable local positional deviations. Increasing the axial pulling displacement in the yarn‐added region from 0.5 to 1.5 mm/step reduces preform width and braiding angle by 18.8% and 60.8%, respectively. At 1.0 mm/step, the braiding‐angle difference before and after yarn addition is 0.63°. These results identify axial pulling displacement as a key parameter for coordinating local yarn‐count variation and preform geometry, and provide a process‐modeling approach for analyzing geometric evolution in the investigated rectangular preform with single‐yarn addition.