Fretting wear is one of the leading causes of failure in industrial machinery. As many of the predominant failure modes are dealt with, machines last longer making fretting wear and fretting fatigue a more likely mechanism of failure. The number of incidences of fretting and the number of industries where fretting failures occur has been increasing since the Second World War. Even though more resources are being invested in understanding and reducing fretting, this trend will probably not change in the foreseeable future.
What type of machine is at risk for a fretting failure? Any machine which has vibrations. Any machine which has joints which are nominally fixed although allowing some movement. Fretting is a phenomenon that occurs whenever two contacting bodies experience small scale motion.
The motion required for fretting wear is very small. Although fretting is generally thought of as having motion on the order of microns, it can occur when the magnitude of displacement is only a few nanometers. By this point it should be clear that fretting is a problem which can afflict any industry. The question is not if you have fretting problems, but when your fretting problems become important enough to address.
Fretting is generally addressed using one of two approaches. Either the normal load on the contact is increased along with the coefficient of friction or the normal load is reduced along with the coefficient of friction. The reasoning behind these two opposing approaches is to either prevent motion from occurring or increase the amplitude of motion enough to lubricate the contact.
The dual nature of these approaches to fretting problems means that one must have a good understanding of both the application and theory before trying to solve a fretting problem. There are also many ways in which the two opposing strategies can be implemented; the only limitation of an educated engineer is his imagination (and his budget).
