Frequency domain viscoelastic analysis of thermoplastic composite pipes under axisymmetric loading

Thermoplastic Composite Pipes (TCP) have emerged as an alternative for deepwater oil & gas transportation due to their high strength, excellent fatigue life, and corrosion resistance. However, TCP exhibit creep and stress relaxation behaviors, which are significantly influenced by temperature. In this work, the TCP viscoelastic mathematical model is presented by combining the laminate periodic microstructure model and the macroscale pipe model, and a general solution is given for the frequency domain viscoelastic analysis of TCP under axisymmetric loadings. The methodology begins with analyzing the steady-state temperature distribution and establishing an axisymmetric mechanical model. The laminate stiffness tensor is derived based on the fiber and matrix properties, and the viscoelastic behavior of the polymer and laminate layers employs Maxwell elements and Prony series with temperature shift factor. Furthermore, the pipe tension-axial strain, tension-torsion hysteresis loops, equivalent axial stiffness and loss factor under harmonic loading at various frequencies are analyzed. The results show that smaller loading frequencies yield larger hysteresis loop areas and larger maximum and minimum strains. Equivalent axial stiffness increases with increasing frequency, and higher temperature leads to lower equivalent axial stiffness. The loss factors are affected by the frequency and temperature simultaneously. • The TCP viscoelastic mathematical model combines laminate periodic microstructure and macroscale pipe models. • A general solution is given for frequency domain viscoelastic analysis of TCP under axisymmetric loadings. • The tension-axial strain and tension-torsion hysteresis loops of TCP under harmonic loadings are obtained. • The equivalent axial stiffness and loss factor at various frequencies and temperatures of TCP are analyzed.