Correlation of makeup wire fracture modes and mechanical properties with fatigue life of large diameter cables

The samples of cable used for bend over sheave fatigue testing were subjected to fracture analysis of the individual broken wires. Fractures were classified according to appearance under 50X microscope examination. High magnification was used to determine which fractures involved fatigue. After cataloguing fractures from samples of four diffent cable lots, it was found that the principal wire layer in which fatigue cracks originate can vary with the quality of the wire used for construction. A strong correlation was found between bend cycle life and fatigue crack initiation with tensile ductility of the wire as measured by reduction in area. There was also some evidence indicating that surface decarburization might also exert some significant effect.