Answer
Failure of a retaining ring assembly can occur either through the ring shearing or the groove material yielding. Ring shear is a pure mechanical failure of the ring itself, calculated as $P_s = \frac{D T π σ_s}{S}$, where $\sigma_s$ is the shear strength. However, in most engineering designs using aluminum or soft steel housings, 'Groove Deformation' occurs first. This is when the axial load causes the groove wall to yield and 'dish' or wallow out. As the wall deforms, the ring begins to tilt (dish). This changes the loading from shear to a combination of bending and tension, which can cause the ring to 'pop out' of the groove at a fraction of its theoretical shear strength. Engineers must use a safety factor of at least 2:1 for groove yield calculations.
