PSI - Issue 77

Esteban Cadavid Gil et al. / Procedia Structural Integrity 77 (2026) 248–255 Cadavid et al. / Structural Integrity Procedia 00 (2026) 000–000

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ing due to platform motions, induced by waves, wind and ocean currents, leading to a higher risk of fatigue failure (Sobhaniasl et al., 2020). Consequently, reliable fatigue life prediction requires a detailed knowledge of the cable’s mechanical behaviour (Fang et al., 2023). Nevertheless, uncertainties remain regarding the accurate characterization of the cable’s mechanical response, making full-scale mechanical testing essential for precise measurement of key properties, such as axial and bending sti ff ness (Thies and Georgallis, 2024). Submarine power cables have a complex mechanical structure, comprising multiple components with distinct ma terial properties arranged in a helical geometry. This configuration enhances their axial and torsional resistance while providing bending flexibility (Hu et al., 2022). The non-linear and hysteretic behavior of multi-component cables under cyclic bending is governed by a combination of factors. These include the non-linear stress-strain response of the constituent materials, the complex helical geometry and internal mechanical interactions, such as intra- and inter layer contact and friction, particularly among the stranded wires of the cable cores (Hu et al., 2022). This non-linear response is characterised by two regimes: stick and slip. At small curvatures, relative displacements between cable components are restrained by friction, leading to maximum bending sti ff ness (stick regime). As curvature increases, progressive slippage develops between the cable components, resulting in a gradual decrease in bending sti ff ness until full slippage occurs and sti ff ness reaches its minimum value (Me´nard and Cartraud, 2023; Foti and Martinelli, 2018). Given this inherent and complex non-linearity, numerical approaches such as finite element (FE) modelling are essen tial for cable design and performance evaluation. However, accurate prediction of the cable’s limit states (e.g., ultimate and fatigue strength) requires models calibrated with experimentally verified mechanical properties, highlighting the need for dedicated experimental testing (Ringsberg et al., 2023). Ringsberg et al., 2023, reported results of static tests performed on dynamic power cables without metallic armors, designed for application in floating wave energy converters. Tensile, bending and torsion tests were performed on cables with outer diameters of 38, 39.7, and 53.3 mm to determine their axial, bending and torsional sti ff ness. Addi tionally, fatigue tests were conducted to investigate the cables’ performance under cyclic loading conditions and to identify the potential failure modes. Me´nard and Cartraud, 2023 developed a numerical approach based on a detailed 3D finite element model to simulate the global mechanical response of a three-core dynamic power cable (101 mm outer diameter) used in a floating o ff shore wind turbine. To validate this model, a four-point bending test was carried out to characterise the cable’s bending response. The experimental data were used to calibrate model parameters, including the friction coe ffi cient between cable components and the initial stress state induced during manufacturing processes. Similarly, Fang et al., 2023 investigated the bending behaviour of a submarine power cable (45.5 mm outer diameter) using both full-scale and short-length finite element models. Validation of the numerical models was per formed by comparing the numerical results with the bending moment-curvature relationships obtained from four-point bending cable tests. In the abovementioned studies, the experimental determination of bending curvature relied on displacement sensors positioned at discrete locations on the cable’s outer surface. This approach may introduce inaccuracies, as it does not directly capture the displacement of the cable’s neutral (mean) axis, which represents its actual deflected shape. To address this limitation, the present study proposes a novel method that employs 3D optical measurements to track the cable’s motion, enabling reconstruction of its neutral axis and an accurate representation of its deflected shape during testing. This technique allows for the determination of bending curvature along the cable’s length. The bending moment-curvature relationship is used to quantify the non-linear bending sti ff ness in both the stick and slip regimes, facilitating the evaluation of mechanical degradation under cyclic bending.

Nomenclature

x

Longitudinal coordinate along the cable length, measured from the left support

M(x) Bending moment at position x along the cable length f(x) Fitted polynomial function ρ Bending radius k Bending curvature F Vertical force exerted by the hydraulic actuator