The work here presented focuses on the test methodology related to effect of stress concentrators in strain controlled structures. Cable sheathing as used in subsea power cables are investigated by cyclic fatigue testing, Digital Image Correlation (DIC) and 3D Finite Element Analysis. Focus is put on the strain distribution in conventional specimen geometries and under the presence of artificial notches. It is evident that standardized fatigue testing provides limited input to the final fatigue life of strain controlled power cable sheathing both accounting for expected and unintended stress concentrators. The limitations can be explained by measured strain distribution inherent in most fatigue test specimens. The use of DIC and 3D FEM provides valuable insight into both the theoretical and practical stress and strain distribution. This can help in understanding and overcoming geometrical test constraints, when compared to the actual component loading mode.

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The aim of this work is to investigate and define the tensile properties of cable sheathing lead alloy. In particular its strain rate sensitivity due to the pronounced creep already present at room temperature, in relation to the material work hardening and processing is object of study. Therefore, a series of specimens have been manufactured using cable sheathing of three different extrusion thicknesses and tested in displacement control at different strain rates. The practical difficulties generated by the highly plastic behavior have been overcome by the use of Digital Image Correlation (DIC) technique as a tool for measuring the strain field on the specimen surface. The creep behavior has been described, modeled and calibrated using Isight and finally implemented in the FEA code Abaqus. Two different numerical models have been used for modelling the time dependent deformation, a power law and the Anand model. The first predict correctly the response of the alloy in the primary creep region while the second shows better results for secondary creep.

During the extrusion process of subsea power cable sheathing layer it is possible that metallic and/or non-metallic debris present in the processing environment enter the metal lattice originating discontinuities that might have a detrimental effect on the fatigue life and the overall integrity of the sheathing. In order to understand the influence of these production defects on the reliability of installed power-lines, a series of specimens directly retrieved from the extruded sheathing were fatigue tested at different strain rates and range both in presence and absence of a non-passing through notch simulating the geometrical discontinuity induced by a particle. In order to collect the necessary information for the understanding of the failure mechanism, Digital Image Correlation and Scanning Electron Microscopy were used to understand the influence of the testing condition on the material resistance and failure mode.

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