Viscoelastic Solutions and Investigation for Creep Behavior of Composite Pipes under Sustained Compression

Composite pipes, which are widely used for transporting fluids, have a high strength, good impermeability and strong resistance to external pressure. Because the pipe bears a sustained load, and its constituent materials usually possess time-dependent properties, the creep phenomenon unavoidably occurs in the composite pipes in the long run. The aim of this study is to propose analytical viscoelastic solutions, which are then applied to a composite pipe structure to explore the creep behavior of composite pipes under sustained compression. The pipe layers and the bonding interlayer both exhibit viscoelastic properties, which are the novelty of this study. The governing equations for the viscoelastic composite pipe are built on the basis of exact elasticity theory combined with the viscoelastic theory. General solutions are derived by means of a Fourier series expansion in which the coefficients are further determined by a Laplace transform. The research results indicate that the present solution has a higher computational efficiency than the finite element solution, because of the latter involving the time discretization method. In addition, for the viscoelastic pipe, if the modulus degradation of the neighboring laminar layers is proportional, the stresses can keep constant with time, as in a purely elastic material.