Official Answer
Answer
As an external ring rotates, centrifugal force causes it to expand. If it expands enough to clear the groove, the assembly fails. The maximum RPM is $N = \frac{7220}{D_n} \sqrt{\frac{S_y t}{D_m^3 \rho}}$ where $D_n$ is the outside diameter of the ring, $t$ is the thickness, $D_m$ is the mean diameter, and $\rho$ is the density. For high-speed turbochargers, rings must be 'self-locking'. This involves a tab-and-slot design that mechanically prevents the ring from expanding beyond a specific diameter, effectively making the RPM limit dependent on the material's burst strength rather than centrifugal expansion.
