An analytical model is presented to predict the progressive failure of reinforced thermoplastic pipes (RTPs) under axial compression, in which the existing homogenization method and a nonlinear stiffness degradation model are combined to predict the continuum damage mechanical response in an iterative and cyclic way. As the homogenization method ignores the effect of the cross‐sectional curvature on the damage sequence, a stress correction factor is defined to consider this effect. Once corrected stresses satisfy Hashin‐Yeh failure criteria, the nonlinear stiffness degradation model is adopted to update the constitutive relationship established by the homogenization method. The proposed model is capable of identifying the damage location and failure mode, analyzing damage accumulation and predicting the ultimate compression. Meanwhile, ABAQUS Explicit quasi‐static analyses calling a user‐defined subroutine were conducted to capture the progressive failure mechanisms in 3D composites and verify the proposed model. The proposed model was found to give accurate prediction on the elastic stiffness, first ply failure, the damaged stiffness, the ultimate compression, and stress distributions. Furthermore, the effects of fiber's winding angles and the thickness‐radius ratios have been discussed, which illustrate that tensile failure mode would appear even when RTPs are under axial compression.

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This paper investigates the bending stiffness and progressive failure of reinforced thermoplastic pipes (RTPs) under bending loads, in which a theoretical method based on the strain energy equivalence of multi‐layered anisotropic cylinders, is proposed. The bending stiffness and stress field was derived from the equilibrium between the work done by bending moments and the strain energy. This new method could consider the hybrid of isotropic and anisotropic materials and improve computation efficiency significantly. To verify the theoretical method, Abaqus/Explicit quasi‐static analysis on 3D composite elements was performed, in which the progressive failure was considered by using a VUMAT subroutine. The degradation of composites was implemented by a nonlinear stiffness degradation model based on the Hashin‐Yeh failure criterion. The comparison showed that the theoretical results are slightly conservative as the theoretical method neglects the contribution of interlayer interactions. Meanwhile, it can accurately predict the dominant stresses of each composite lamina. According to numerical simulations, the fiber tensile failure, the matrix tensile and compressive failure are the dominant failure modes of RTPs under bending loads. Furthermore, the effects of the winding angles of fibers on damage propagation and the effects of the initial ovality on the bending stiffness are also discussed.