Surface Flattening Approach for Forming Variable‐Curvature CFRP Stringers

ABSTRACT Variable‐curvature Carbon Fiber Reinforced Polymer (CFRP) stringers are prone to wrinkling defects during forming, and conventional techniques often fail to meet quality requirements. To reduce wrinkling defects during the forming of variable‐curvature CFRP stringers, this study proposes a novel forming method that begins with applying a triangular mesh flattening algorithm for initial flattening, followed by optimization using a mass‐spring (MS) model; based on the optimized results, forming blanks are fabricated via an automated fiber placement (AFP) process; finally, variable‐curvature CFRP stringers are produced on a self‐developed automated roll forming platform. The flattening results and forming experimental results indicate that, compared with the initial flattening method, the MS model–optimized approach achieves higher near‐net shape prediction accuracy, with the effective surface coverage of the stringers increasing from 86% to 98%, the wrinkled area decreasing to 1.21 × 10 ² mm ² from 5.06 × 10 ² mm ² , and the standard deviations of thickness and internal porosity reducing to 1.5 × 10 ⁻² mm and 0.41%, respectively, demonstrating that this method significantly reduces wrinkling defects during the forming of variable‐curvature CFRP stringers and provides a feasible pathway and theoretical support for their high‐quality forming.