Torsional failure of a knuckle joint of a universal steel coupling system during operation – A case study

In the present work, the failure investigation of a fractured knuckle joint of a universal coupling system is presented. The coupling system transmits rotational motion to the back-up rolls of an aluminium sheet straightening machine in an aluminium circles production plant. Optical examination of failure surfaces and light microscopy are used as the principal examination techniques to analyze the above failure. Review of the operation conditions and the investigation findings revealed that the abnormal function of lubrication was a major contributor to the failure.