The main shaft in an industrial bread dough mixer is subjected to an alternating bending stress due to the pulley drive system sigma a and an additional mean bending stress when mixing dough sigma m. The shaft is made from a commercially polished steel Phi 1.5" Times 72", with E = 30 msi, Sy = 80 ksi, Su = 100 ksi Construct the S-N curve for the shaft Construct the 106 and 103 constant-life curves (Goodman Diagram) If on average the ratio of mean stress to alternating stress is 1, sigma a/ sigma m = 1, what is the maxi mu m stress allowable to achieve 106 life? (Estimate from your graph) What surface treatment(s) would you recommend to improve shaft fatigue life?