Fatigue Behavior of CFRP Cables Under Tensile and Bending Loads for Offshore Applications
Composite cables have many advantages over wire ropes and synthetic ropes because of their high specific tensile strength and specific stiffness, as well as an outstanding fatigue behavior and chemical resistance when carbon fiber reinforced polymers (CFRP) are used. This paper investigates a novel technology for cable-moored platforms, such as semi-submersible and Tension Leg Platforms (TLPs) in deep waters, aiming to reduce the total structure weight and maintenance costs for these platforms, and taking into account cumulative fatigue damage due to fluctuating axial stresses. The present analysis focused on a 1×7 CFRP helix cable, with a 3.5 mm diameter core rod and an external layer containing other 6 rods of the same diameter. The cable tensile behavior was investigated by numerical modeling using FEM, whose results were compared to experimental data. The longitudinal Young modulus of a single rod was experimentally measured in tensile tests of specimens instrumented with strain-gages, while the remaining engineering constants were obtained through micromechanics. To simulate the service conditions of platforms, the 1×7 CFRP cables were tested under static tension, cyclic bending and tensile-tensile fatigue. The cyclic bending test was carried out for 1500 cycles under a stress level of 20% of minimum breaking load (MBL) and the tensile-tensile fatigue test was run for 12000 cycles under a stress level of 50% of MBL. The residual strength of the cables after cyclic bending and fatigue tests was evaluated under static tensile testing. The 1×7 CFRP cables showed very good mechanical performance and potential to be applied for mooring offshore platforms.
Authors: Laís V. Silva, Eduardo A.W. Menezes, Carlos A. C. Junior, Sandro C. Amico
Conference: CAMX 2016 – Anaheim