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Step 8. Select a standard wire diameter from the tables, and then determine the design stress and the maximum allowable stress for the material at that diameter. The design stress will normally be for average service, unless high cycling rates or shock indicate that severe service is warranted. The light service curve should be used with care because it is very near to the yield strength. In fact, we will use the light service curve as an estimate of the maximum allowable stress.For this problem, the next larger standard wire size is 0.0625 in, no. 16 on the U.S. Steel Wire Gage chart. For this size, the curves in Figure 18–11 for ASTM A231 steel wire show the design stress to be approximately 145 000 psi for average service, and the maximum allowable stress to be 170 000 psi from the light service curve.Step 9. Compute the actual values of Cand K, the spring index and the Wahl factor:Step 10. Compute the actual expected stress due to the operating force, Fo,from Equation (18–4):Step 11. Compute the number of active coils required to give the proper deflection characteris-tics for the spring. Using Equation (18–6) and solving for Step 12. Compute the solid length, Ls; the force on the spring at solid length, Fs; and the stress in the spring at solid length, τs