Progressive‐Curvature Bending Model and Forming Mechanism of <scp>3D</scp> Angle‐Interlock Woven Preforms Based on the Variable Micro‐Element Method

ABSTRACT Nonuniform deformation of the preform in complex components can lead to variations in the mechanical properties of composite materials, thereby reducing their strength and stiffness and potentially inducing localized failure, especially under complex loading conditions. To investigate the effects of structural parameters on the bending formability of 3D angle‐interlock woven preforms (3DAWPs), a variable microelement method was adopted. Based on the analysis of the deformation mechanism, a progressive‐curvature bending model was established using the representative volume element (RVE). The geometric characteristics after deformation and the distribution of fiber volume fraction (FVF) within the preform were predicted. The results show that the warp inclination angle is positively correlated with the cross‐sectional deformation coefficients of warp and weft yarns. The RVE length and fiber volume fraction are positively correlated with the weft deformation coefficient but show an opposite trend for the warp deformation coefficient. The fiber volume fraction increases from the outer layer to the inner layer, with a maximum difference of about 9% forming a clear hierarchical distribution. At forming angles of 45°, 60°, 90°, and 120°, the thickness difference between the outermost and innermost unit cells accounts for about 22%, 16%, 11%, and 7% of the initial thickness, respectively, and the deviation of the fitted thickness curves gradually decreases. Bending forming experiments were conducted on 3DAWPs, and the experimental results validated the theoretical analysis and the proposed model. This research provides theoretical support for enhancing the reliability and durability of composite materials in complex components.