Answer
Over-expanding a spiral retaining ring occurs when the ring is stretched beyond its elastic limit during installation over a shaft or into a bore. This results in permanent plastic deformation, meaning the ring will not return to its original 'clinging' diameter, leading to a loose fit in the groove. The maximum installation diameter $D_{max}$ should be calculated such that the fiber stress does not exceed the yield strength $\sigma_y$. Prevention involves using a tapered mandrel or a sleeve for installation, which controls the expansion to a specific limit. Additionally, the formula for the stress during expansion is $S = \frac{E \cdot t \cdot (D_s - D_i)}{(D_m^2)}$, where $D_s$ is the shaft diameter and $D_i$ is the ring's free inside diameter. If $S > \sigma_y$, the ring is compromised.
