Official Answer
Answer
A sharp corner at the bottom of the retaining ring groove is a significant stress raiser, but a large radius can lead to ring failure. If the radius $r$ at the bottom of the groove is too large, it prevents the ring from seating fully against the groove wall. This creates a 'ramp' effect: when an axial load is applied, the ring is forced up the radius, leading to a radial expansion and eventual 'pop-out' failure. The standard engineering rule is that the maximum radius on the groove should not exceed $0.1$ times the ring thickness $t$. If a larger radius is required for shaft fatigue strength, a 'back-up washer' with a sharp corner must be placed between the component and the ring to ensure even load distribution.
