Research On Approach For Corrosion And Wear Cumulative Damage Assessment Of Chain Links

The mooring chains, under the combined influence of marine wind, waves and currents as well as the floating bodies, are inevitably corroded and worn. The integrity of the mooring system will be adversely affected provided such cumulative damage. The reliable assessment of the damages of the mooring chains in the life-cycle is therefore quite necessary.This paper is aimed to build the engineering numerical mode by studying the analysis method on the responses of the interfaces between the adjacent links and the internal structure of chains under the combined influence of marine dynamic factors and the platform movement. It will have a further research on how the corrosion and the friction of interfaces between the adjacent links are affected and their coupling mechanism on the basis of the numerical simulated results. The engineering evaluation mode of the corrosion and wear coupling accumulative damage on the interfaces between the adjacent links is therefore built. Finally, this paper is also the ground of the evaluation on the residual strength of the mooring chains and its accumulative damages during the life-cycle.Firstly, as regards to the research aims above, numerical simulative studies on the mechanics behavior of the Grade R4stud-less chains of92mm bar diameter with axial tension and twists have been extensively executed with the software ANSYS14.0. A detailed discussion is given for the configuration of the parameters of the key basic numerical simulative technique of the interfacing of the mooring chain. The constructive non-linearity and interfacing non-linearity as well as the impact of the residual stresses caused by the proof test loads on the fatigue life of the mooring chain are considered in the elastoplastic FEA.Secondly, the stretch and twist characteristics of the chains are researched by numerical analysis. It points out that the torsional responses (torque and end-shorting) of links behaves non-linear manner under axial load as well as the twist angle. This non-linear relation is strengthened with the increase of axial load and the twist angle. Great horizontal reacting forces are caused by high axial loads with low-level torsion as well as low axial loads with high-level torsion. Simplified formula on the basis of a great deal of numerical simulated data is presented for the stud-less chains which allow the prediction of torque for values of twist in the range0to19degree per link.At last, the uniform corrosion and the fretting wear of the stud-less links in the life-cycle is researched in accordance with non-linear numerical simulative technique, corrosion rate mode built on the long-term corrosion data and the quantitative formula of the fretting wear of the chains based on Archard wear theory and fretting wear mechanism. The assessment method on the accumulative damages of corrosion and wear is presented with the example of the numerical simulation analysis. The results show that the corrosion and wear cumulative damage of links increases the stress levels and the range of plastic deformation region which makes the overall resistance level of the mooring chains decreased. Accurate assessment for corrosion and wear cumulative damage of chain links is significant for the safety in the life-cycle.