Theoretical Prediction of the Bending Stiffness of Reinforced Thermoplastic Pipes Using a Homogenization Method

The accurate prediction of bending stiffness is important to analyze the buckling and vibration behavior of reinforced thermoplastic pipes (RTPs) in practical ocean engineering. In this study, a theoretical method in which the constitutive relationships between orthotropic and isotropic materials are unified under the global cylindrical coordinate system is proposed to predict the bending stiffness of RTPs. Then, the homogenization assumption is used to replace the multilayered cross-sections of RTPs with homogenized ones. Different from present studies, the pure bending case of homogenized RTPs is analyzed, considering homogenized RTPs as hollow cylindrical beams instead of using the stress functions proposed by Lekhnitskii. Therefore, the bending stiffness of RTPs can be determined by solving the homogenized axial elastic moduli and moment of inertia of cross sections. Compared with the existing theoretical method, the homogenization method is more practical, universal, and computationally stable. Meanwhile, the pure bending case of RTPs was simulated to verify the homogenization method via conducting ABAQUS Explicit quasi-static analyses. Compared with the numerical and existing theoretical methods, the homogenization method more accurately predicts the bending stiffness and stress field. The stress field of RTPs and the effect of winding angles are also discussed.