The effect of blank holder gap on yarn local buckling during forming of woven CFRP preform with complex geometries

Abstract

Fabric forming is widely recognized for its efficiency in producing fiber-reinforced composite preforms, but defect suppression in preforms with double-curvature geometries are limited. This study investigates the effect of the blank holder gap (BHG), defined as the distance between the blank holder and the die, on yarn local buckling by developing a forming testbench with adjustable BHG for experimental analysis. Furthermore, a macroscopic finite element model was established to analyze the influence mechanism. With the BHG decreasing, in-plane friction force exerted on the fabric by the blank holder and die increases, which hinders the passive drawing of the warp yarns by the weft yarns. This elevated friction reduces the in-plane bending deformation of the warp yarns and lowers the likelihood of local buckling. However, the increased friction force also intensifies the slippage between adjacent yarns, enlarging the gaps between them and consequently reduces the fiber volume fraction of the component. These findings offer valuable guidance for optimizing BHG to achieve a balance between yarn local buckling suppression and slippage in the forming of complex composite preforms.