Analyzing Bending Damage Mechanical Properties of Multi‐Layered Wound Composite Pipes

ABSTRACT An accurate analysis of bending properties is essential for understanding the damage behavior of multi‐layered composite pipes. Currently, two‐dimensional (2D) theoretical models based on the Lekhnitskii stress function or complex expressions with unknowns are primarily used to analyze the bending characteristics of composite pipes. These approaches cannot accurately predict the stress distribution of every layer and initial damage in composite pipes under bending conditions. In accordance with nonlinear cylindrical shell theory, this study parameterizes the ellipticity deformation in each layer and establishes the constitutive equation of pipes while considering material nonlinearity and the stiffness degradation model. The virtual work principle and failure criterion are applied to develop a 3D mechanical analysis model to assess the bending properties of pipes. A four‐point bending test and numerical simulation are carried out to validate this theoretical model. On this basis, the stress distribution, stiffness degradation mechanism, and damage failure characteristics of pipes under bending conditions are analyzed. The research findings show that axial stress, radial stress, and shearing stress are largely controlled by bending deformation, while hoop stress is primarily affected by elliptical cross‐section deformation. The initial failure mode is mainly matrix tensile failure in the outermost reinforced layer. When the winding angle is less than or equal to 45°, fiber/matrix shear failure occurs first. When the winding angle exceeds 45°, matrix tensile failure becomes the primary failure mode. This study enhances the understanding of multi‐layered wound composite pipes' behavior under bending conditions and provides insights for improving design and reliability in offshore applications.