Damage-based fretting wear model for life prediction of steel wire ropes

Abstract

Steel wire ropes are designed with different configurations and arrangements to suit various applications. In most manufacturing industries, fatigue test is often conducted to assess the reliability of new wire ropes. The fatigue test is time-consuming and requires a large collection of stress-life data to suit various wire rope designs and stress ratios. Furthermore, during the reliability test, the sample wire rope is subjected to tension-tension fatigue loading and this would induce fatigue damage by fluctuating stresses in the wire material. The current fatigue life prediction method does not take into account the combined bulk fatigue due to tensile stress fluctuations and fretting wear due to relative sliding and contact stress between the stranded wires, which is the dominant damage mechanism in a wire rope. Therefore, the objective of this study is to develop a validated methodology for fatigue life prediction of newly-designed steel wire ropes that incorporates both bulk fatigue and fretting wear conditions. The interaction between wires is explicitly addressed through the friction and fretting wear damage coefficient. Drawn, bare (non-galvanized), as-received high carbon steel wires and steel rods (undrawn) are used as the reference materials. A series of metallurgical and mechanical testing including microstructure analysis, tensile, interrupted fatigue, hardness and sliding wear tests are conducted on the reference materials to obtain the required properties of the wire materials as the model parameters. The model is then integrated into the user material subroutine (UMAT) of the Abaqus finite element analysis (FEA) software to predict the fretting wear and fatigue life of the drawn steel wires. The load cycle block method with each block representing 10,000 cycles is employed for computational efficiency. The associated coefficient of fretting wear damage, cf was determined through calibration with reported experimental data and it was found that when cf = 0.10, the simulated wear depth showed a good agreement with the measured data. The criteria for material removal due to wear and fatigue fracture were established. The material is removed due to wear once the element reaches the terminal value of Dc = 0.90. A new fatigue fracture criterion is proposed based on the total dissipated energy, Ed when the wear depth is 1/3 of the initial wire diameter. Once the energy reaches the critical value of Edc = 32-34 J, fatigue fracture is expected to occur. The number of cycles associated with Edc is taken as the fatigue life of the wire. The calibrated fretting wear damage model was then examined for the reliability of 1x7 steel wire rope samples and the simulated fatigue life showed a good agreement with the measured data by Kiswire. This indicates that the fretting wear damage model is able to quantify the fatigue response of the newly-designed steel wire ropes with various configurations prior to the production of samples for the reliability test. In addition, the design, size, arrangement, and configurations of the wire rope could be improved at an earlier stage based on the reliability requirements. This will increase production productivity and significantly reduce the cost involved in the production and disposal of the steel wire rope that did not achieve the reliability criteria.