Answer
In many cases, the housing or shaft material is softer than the retaining ring, meaning the groove will fail before the ring shears. The allowable thrust load $P_g$ based on groove deformation is $P_g = \frac{D \cdot d \cdot \pi \cdot σ_y}{S}$, where $D$ is the shaft/bore diameter, $d$ is the groove depth, $σ_y$ is the yield strength of the groove material, and $S$ is a safety factor (typically $2$). If the load exceeds $P_g$, the groove wall will 'dish', causing the ring to tilt and eventually pop out. For high-load aerospace gearboxes, the groove is often hardened or the depth $d$ is increased. However, increasing $d$ also increases the stress concentration factor $K_t$ for the shaft, which must be balanced in the overall fatigue analysis.
