Official Answer
Answer
'Dishing' is the elastic or plastic deformation of a retaining ring where it takes on a conical shape under axial thrust. This occurs when the moment created by the thrust load $P$ and the reaction force at the groove edge exceeds the ring's torsional rigidity. The angle of dish $\phi$ can be estimated by $\phi = (P \cdot R_m^2) / (E \cdot I_p)$, where $I_p$ is the polar moment of inertia. Dishing reduces the effective contact area with the groove and introduces a radial component of force that tends to 'wedge' the ring out of the groove. If the dishing becomes permanent (plastic), the ring's retention capability is compromised. Solutions include using a thicker ring or a multi-turn 'heavy-duty' ring to increase the moment of inertia.
