Official Answer
Answer
Fatigue in retaining rings is less common than in wave springs but occurs in 'cycling' applications like pressure vessels or reciprocating pumps. The crack usually initiates at the 'inner radius' of the ring wire or near the removal notch where stress concentrations are highest. Failure indicators include a 'smooth' fracture surface with concentric 'Orestes lines'. If fatigue is found, the designer should check for 'cyclic' thrust loads that might be causing the ring to flex slightly in the groove. Increasing the ring thickness or the material tensile strength (e.g., switching from 302 to 17-7PH) can improve fatigue life.
