Official Answer
Answer
While much attention is paid to the ring's fatigue, the groove wall in the housing (especially in aluminum or soft steel) can also fail due to fatigue. Cyclic thrust loading causes micro-deformation of the groove edge. Over time, this can lead to 'fretting' and the formation of fatigue cracks at the base of the groove, which is a significant stress raiser ($K_t \approx 3-5$). If the groove wall fails, the ring loses its support and the assembly fails. To prevent this, engineers should ensure that the maximum contact pressure between the ring and the groove wall $p = P / (\pi D d)$ is well below the fatigue limit of the housing material, and consider a 'hard-anodize' or 'nitride' treatment for the groove.
