Abstract
A failure investigation was conducted on a shaft-coupling bracket used in mounting horizontal and vertical shafts of a wire-conductor stranding machine. The investigation was conducted using a systematic approach by assembling background information; performing visual, fractographic, and metallographic examinations; performing chemical analysis; and conducting mechanical testing. The result indicates that the bracket was produced from gray cast iron, subjected to cyclic loading, and the fracture surface shows transgranular fracture features with the presence of beach marks ridges and striation markings. The stranding machine cycled 600 times a day, 200 days a year, and the shaft-coupling bracket failed after a period between 4.5 and 5 years. We concluded that the bracket failed as a result of high-cycle, low-load fatigue, which was initiated in a highly stressed graphite flakes region, propagated under the application of reversed stresses, and eventually fractured after it reached between 540 000 to 600 000 cycles. To prevent a future occurrence, it was recommended that the component should be made out of ductile iron and replaced after a life of 500 000 cycles.
