Official Answer
Answer
The maximum stress occurs at the crests of the waves and is calculated using $S = \frac{3 \pi P D_m}{4 b t^2 N^2}$. This value must be compared against the tensile strength of the material, adjusted by a safety factor for the specific application. For 17-7PH CH900, the yield strength is approximately $1,170$ MPa. If the calculated stress $S$ exceeds $80\%$ of the yield strength during operation, the spring will likely experience a permanent set. In high-cycle applications, the stress should be kept below the endurance limit defined by the Goodman relation $S_a = S_e (1 - \frac{S_m}{S_u})$ where $S_a$ is alternating stress and $S_m$ is mean stress.
