An innovative system for fretting wear testing under oscillating normal force

Material damage caused by fretting wear is of significant concern in many e ngineering applications. This paper describes the design and performance of a new machine for the laboratory investigation of fretting wear under osci llating normal force (fretting mode II). The test machine uses an electroma gnetic actuator to impose an oscillating normal force between the contactin g bodies at a constant force amplitude over a wide range of frequencies. Th e principle of the actuation mechanism and the fretting wear induced with t his particular wear test configuration are outlined in detail. Normal force and electrical contact resistance were measured on-line during fretting mo de LI wear tests. The performance of the wear test machine is illustrated b y data obtained for different materials combinations, namely, hard material s, such as high-speed steel and (Ti,Al)N coatings oscillating against alumi na ball counterbodies, and soft materials, such as a tin coating oscillatin g against the same. In general, wearing of the counterbodies was observed i n the slip region. It has been observed that hard coatings and bulk ceramic s are prone to fretting fatigue cracking. The evolution of electrical conta ct resistance in the case of the self-mated soft tin coatings tested under fretting mode II conditions is also reported.