Sidebar fatigue occurs when the frequency and magnitude of stress on/stress off cyclic loading causes the sidebar material to fatigue to the point of failure before the chain has reached the end of its normal anticipated service life. The failure normally commences with a small crack at the edge of the pitch hole. With repeated load cycles the crack gradually progresses outwards until the sidebar is sufficiently weakened to realise complete fracture. Consequently a fatigue fracture is characterised by a series of concentric curved lines across the area of the failure having the appearance of a brittle fracture.
In these circumstances it is necessary to review chain loading and carry out a thorough analysis of the operating conditions.