Answer
The primary failure mechanism is fatigue fracture initiated by tensile stresses at the wave crests and troughs. In high-frequency applications, 'wave-clash' or dynamic surging occurs if the operating frequency approaches the spring's natural frequency $\nu = \frac{1}{2 \pi} \sqrt{\frac{k g}{W}}$. This leads to localized over-stressing. Analysis of failed springs often reveals 'beach marks' on the fracture face, indicative of fatigue. Mitigation involves ensuring the operating stress $\sigma$ remains below the fatigue limit on a Goodman diagram, where $\sigma = \frac{3 π P D_m}{4 b t^2 n^2}$. Using shot-peening on materials like SAE 1070 or 17-7PH can introduce compressive residual stresses on the surface, effectively shifting the mean stress downward and extending the cycle life by an order of magnitude.
