Official Answer
Answer
The installation stress $\sigma_i$ of an internal ring occurs when it is compressed to fit into the bore. It is calculated as $\sigma_i = \frac{E \cdot b \cdot (D_g - D_f)}{D_m^2}$, where $D_g$ is the groove diameter and $D_f$ is the free diameter. If the radial wall $b$ is too large, the stress during installation can exceed the material's elastic limit, resulting in 'permanent set'. This means the ring won't 'snap back' into the groove, leading to a loose fit. Conversely, a $b$ that is too small reduces the thrust capacity. The design must balance these using the 'ratio of expansion', ensuring $\sigma_i < 0.8 \cdot S_y$ for repeatable installations.
