Official Answer
Answer
Stress at work height is calculated using the formula $S = \frac{3 \pi P D_m}{4 b t^2 N^2}$, where $P$ is the load at work height. For standard applications, the calculated operating stress should not exceed the minimum tensile strength of the material to avoid permanent set. In high-performance alloys like 17-7PH CH900, the allowable stress can reach up to $80\%$ of the tensile strength. However, if the spring is compressed to 'solid height', the stress often exceeds the yield point, leading to plastic deformation. Engineers must use the formula for solid height stress $S_s = \frac{E t N^2 f}{D_m^2}$ to determine if a stop is required in the assembly to prevent over-compression.
