Official Answer
Answer
Fatigue cracking at the inner diameter (ID) of the wave crest is typical of high-cycle fatigue where the tensile stress range $\Delta \sigma$ is too high. The ID is the most stressed region due to the 'tight' radius of curvature. Failure analysis using SEM (Scanning Electron Microscopy) typically reveals striations characteristic of fatigue. Mitigation strategies include: 1) Shot peening the spring to introduce residual compressive stresses on the surface; 2) Using 'Vibro-finishing' to remove burrs and surface imperfections that act as stress risers; 3) Increasing the material thickness $t$ while reducing the wave height to lower the operating stress range.
