The role of gross plastic fretting in serviceability and deterioration of power contacts

The deterioration caused by fretting of silver coated copper contacts for power applications has been investigated in a number of projects, dealing with different central aspects of the problem. Fretting mechanisms under circumstances of massive plastic deformation have been classified and studied in detail. Fretting under such conditions can be considered as a separate mechanism for wear and surface damage and the label gross plastic fretting has been proposed. The serviceability (contact resistance and mating forces) and tribological deterioration is closely related to the regime of fretting prevailing. Most of the factors defining the deterioration of a contact were investigated during each test or on each tested sample. These factors include: the contact resistance variations; the damage to the contact surfaces; the friction between the contacts; the tendency to welding between the contact members. In particular the previous work has included investigations on how these factors are influenced by: fretting vibration amplitude; normal force; silver coating thickness; contact grease; relatively thick (pre-grown) corrosion films; corrosive atmosphere; atmospheric humidity; current load (direct current). The following paper present a comprehensive summary of the most important findings and their practical consequences. It is concluded that fretting often dominates the contact deterioration.