Dual‐Scale Coupling Model and Experimental Validation of Instantaneous Dynamic Transverse Permeability for Large‐Tow Carbon Fiber

Carbon fiber‐reinforced resin‐matrix composites have emerged as lightweight structural materials for diverse engineering applications, owing to their outstanding specific strength and specific modulus. Large‐tow carbon fibers (filament count ≥ 48K) have accelerated large‐scale deployment of these composites due to their cost advantage over small‐tow counterparts. However, their intrinsic dual‐scale impregnation behavior often causes inhomogeneous impregnation across macro‐ and microscales, leading to defects such as dry spots and voids, which degrade the mechanical performance of the resulting composites. To address this challenge, we established a Navier–Stokes/Brinkman coupled dual‐scale numerical model enabling bidirectional simulation of macroscopic inter‐tow flow and microscopic intra‐tow impregnation. Concurrently, we developed a systematic experimental characterization framework covering key parameters (contact angle, surface tension, viscosity, gel point) and a fitting method for effective average radial permeability ( K p ) based on impregnation time‐radius data. Using experimental data from industrial 48K large‐tow carbon fiber tows, we quantitatively assessed the proposed calculation method for Instantaneous Dynamic Transverse Permeability ( K p ( t )); the predicted values agree with experimental results within the estimated measurement uncertainty. The simulation results qualitatively reproduced the two‐stage impregnation sequence and revealed the coupling mechanism of dual‐scale flows with order‐of‐magnitude velocity differences. Overall, this work provides an analytical approach for predicting K p ( t ) for 48K tows and offers a preliminary theoretical reference for defect suppression in LCM composite manufacturing.