Analytical study on the structural responses of the fiber-optic composite submarine cables under coupled tension-torsion loading

Fiber-optic composite submarine cables are typical multilayer helically wound structures. They are subjected to combined axial tension and torsion during installation, retrieval, and service. This paper investigates the mechanical behavior of such cables under coupled tension-torsion loading. Based on Love's thin rod theory, an analytical model is developed to describe the coupling between axial elongation and torsional deformation in helically wound armor wires. A dimensionless tension-torsion coupling parameter ( η ) is introduced to quantify the relative contributions of tensile and torsional deformation. A finite element model of the submarine cable is established, and the numerical results show good agreement with the analytical predictions. Parametric analyses are conducted to investigate the effects of the helical winding angle, armor wire diameter, and coupling parameter η on the mechanical response of the cable. The results show that the tension-torsion coupling effect has a pronounced influence on the overall axial and torsional stiffness compared with pure axial or pure torsional loading. Under coupled loading, both axial and torsional stiffness are higher than those under pure loading conditions. The stiffness varies with the coupling condition: tensile stiffness increases, while torsional stiffness decreases from Case 1 to Case 4 with increasing η .