We performed a failure investigation on a 6x36G IWRC Grade, non-galvanized wire rope using visual, metallurgical and hardness testing.
Metallographic and Vickers 500gr micro-hardness results identified the wires as cold drawn and exhibited converted Rockwell C values of 54 to 56 HRC, typical for this grade of wire rope. The approximate ultimate tensile strength (UTS) of the steel wires – estimated from the hardness results, was 307 ksi UTS.
Visual examinations found numerous locations with heavy deformation (crushing) on the outer strand wires that also exhibited fatigue fractures. The observed crushing deformation likely resulted from: a) simple overload events, b) uneven drum winding with heavy loads, or c) shock/dynamic loading that locally deformed the outer wires in the strands.
The wire deformation introduced laps and seams that are favorable fatigue initiation sites. Most fractures were observed at the deformed wire locations. Repeated bending during operation after wire deformation propagated numerous fatigue cracks – resulting in catastrophic overload failure after the load bearing capability of the wire rope was reduced due to the numerous fractured wires.
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