Investigation of the Nonlinear Bending Behavior of Thermosetting Unidirectional Prepregs Based on Horizontal Cantilever Bending Experiments and a Bi‐Linear Bi‐Material Model

ABSTRACT The bending stiffness of unidirectional (UD) prepregs is non‐constant and temperature‐dependent, playing a critical role in wrinkle formation during preforming. Therefore, establishing a temperature‐dependent constitutive model to capture the bending behavior is essential for accurately predicting wrinkling defects. In this study, the temperature‐dependent evolution of the mechanical properties of UD prepregs was systematically investigated through experiments. Horizontal cantilever bending tests at different temperatures show that UD prepregs exhibit a strongly nonlinear moment–curvature response and temperature‐dependent bending stiffness, with the highest sensitivity below 45°C. The 90° bending stiffness is significantly lower than that in the 0° direction. Based on the exponential decay model, two independent temperature‐dependent Bi‐Linear Bi‐Material (BLBM) constitutive models were established for the 0° and 90° nonlinear moment–curvature responses of UD prepregs. The models were implemented into ABAQUS via a VUMAT subroutine, enabling integrated simulation of temperature effects, anisotropic stiffness evolution, and nonlinear bending behavior. The model‐predicted moment–curvature and deflection curves show excellent agreement with the experimental results, with coefficients of determination exceeding 0.97, confirming the validity of the proposed model in capturing the nonlinear bending behavior of UD prepregs. This study provides a methodological foundation for wrinkling prediction in composite preforming.