Answer
Impact loading occurs when an axial force is applied suddenly, exceeding the static thrust capacity. This causes the ring to 'dish'—the inner diameter moves axially relative to the outer diameter. This deformation is a result of the moment arm created between the point of load application (the component) and the point of support (the groove). The failure starts with plastic bending of the ring cross-section. Once dished, the ring's effective diameter decreases (for external rings) or increases (for internal rings), leading to premature ejection. Failure analysis usually reveals 'burnishing' on the groove edge and the ring's face. Mitigation involves using a 'heavy-duty' series ring with a larger radial wall ($H$) and increasing the groove depth ($d$) to reduce the moment arm.
