Detection of broken wires in elevator wire ropes with ultrasonic guided waves and tone-burst wavelet

Elevator wire ropes with polymer cores hold and hoist heavy fluctuating loads in a corrosive environment. Such working condition causes metal fatigue, which together with abrasion around pulleys leads to progressive loss of the metallic cross section. This can be seen in the forms of a roughened and pitted surface of the ropes, reduction in diameter, and broken wires. Therefore, their deterioration must be monitored so that any unexpected damage or corrosion can be detected before it causes a fatal accident. Ultrasonic-guided wave-based inspection, which has proved its capability in nondestructive testing of platelike structures such as tubes and pipes, can monitor the cross section of wire ropes in their entire length from a single point. However, guided waves have drawn less attention for defect detection purposes in wire ropes. This article reports the condition monitoring of a steel wire rope from a hoisting elevator with broken wires as a result of corrosive environment and fatigue. Finite element analysis was conducted as a baseline to study guided wave propagation in wire ropes and plot dispersion curves. Guided wave propagation in wire ropes was experimentally investigated on a newly built cable stretching machine equipped with a load sensor under different amount of tensile loading. To expose the indication of broken wires, the recorded signals were analyzed by tailor-made continuous wavelet transform called tone burst wavelet.