Finite element modeling for single-twisted Fi(29) strand that reproduces strand stiffness and wire stress

Wire ropes consisting of strands of twisted steel wires have high flexibility and tensile strength, making them suitable for use in machinery and structures such as cranes and elevators. For their strength evaluation, the wire stress and strain should be measured. However, experimental approaches are limited due to the complex twisted structures of such ropes. Herein, we develop a finite element (FE) modeling scheme for the single-twisted Fi(29) strand used in 6 x Fi(29) rope with an independent wire rope core that reproduces the strand stiffness and wire stress. To validate the FE modeling scheme, we conduct tensile, three-point bending, and bending-over-sheave (BOS) tests. As for the tensile test, the stiffness in the axial direction and torque coefficient are reproduced within 10% and 5% accuracies, respectively. The strain of the outer wire of the strand is reproduced within a 20% accuracy. The strain of the core wire exceeds those of the other wires. Their strains vary because the straight core wire has higher stiffness than the helical inner and outer wires. Regarding the three-point bending test, the bending stiffness and the strain of the outer wire are reproduced within 10% and 5% accuracies, respectively. Moreover, findings indicate that theory based on material mechanics overestimates the bending stiffness by 30% due to the squeezed deformation of the cross section caused by the concentrated contact force from the upper jig in the test setup. Each wire undergoes bending deformation, and the core wire has higher strain than the other wires. As in the tensile test, the larger stiffness of the core wire increases the bending strain. As for the BOS test, the strain of the outer wires is reproduced within a 12% accuracy. Each wire is bent on sheaves. The wire stresses in the axial direction are approximately 1750 MPa for the core wire, 1370 MPa for the inner wire, and 1240 MPa for the outer wire. This tendency is similar to that seen in the three-point bending test. Finally, we estimate the wire fatigue life using FE simulation, and the estimated fatigue life is roughly consistent with the experimental result.