Stress Analysis and Fatigue Testing of Large-Diameter Z-Type Locked Coil Cables

Through the optimization of the twisting process for high-vanadium locked coil cables， a domestic high-vanadium 165 mm large-diameter Z-type locked coil cable was successfully developed. To investigate its mechanical properties and fatigue durability， axial tensile， fatigue， and salt spray tests were carried out. This study focused on the evolution of the equivalent elastic modulus of the cable with increasing fatigue cycles， as well as the change rule of the strain ratio between the outermost wire and the cable body under increasing stress. Experimental results demonstrated that the cable endured two million fatigue cycles without significant degradation in mechanical properties， and the wire breakage rate met standard specifications. Broken wires were predominantly observed on both sides of the initial fracture， located 50–72 mm inside the anchor within the outer layer. The initial equivalent elastic modulus was 107520 MPa， which first increased and then decreased with accumulating fatigue cycles. Meanwhile， the strain of the outermost wire gradually converged with that of the cable body. Finite element analysis confirmed that stress concentrations under different numbers of wire breaks aligned well with the actual fracture distribution. After a certain number of wire breaks， the maximum stress in the wires stabilized and did not increase with additional breaks. Furthermore， it was found that when wires were broken but not pulled out， the cable could still transfer loads through the full cross-section beyond a certain distance from the break point. No red rust was observed in the salt spray test. The findings indicate that the developed 165 mm large-diameter Z-type locked coil cable exhibits excellent fatigue durability， corrosion resistance， mechanical adaptability， and damage tolerance.