Failure analysis in tribology: two case histories involving contact fatigue of metal components

This paper deals with two case studies of failure analysis in sliding/rolling contacts between metallic components. The investigated tribosystems belong to two different fields and involve different contact conditions, but in both of them contact fatigue plays a main role. The first case history comes from earth moving equipment, where the non-conformal contact between a rotating pin and its bearing leads to evidence of large surface damage of the cylindrical pin, with spalling, typical of contact fatigue. However, failure analysis highlighted a dominant role of the first crack nucleation by torsion fatigue. The second case history comes from packaging devices, where the non-conformal contact between a rotating compression roll and the punches for powder pressing led to the formation of macro- and micro-pitting on the surface of both the punches and the roll, indicating that the main damage mechanism is surface-origin contact fatigue.