Question

a A beam with a square cross-section of linch x 1inch is cantilevered at one end, and subjected to force that fluctuates from F = 120lbf (downward) to F = -600lbf (upward) at its tip. The length of beam is L = 25 inches. The selected steel material has mechanical properties as shown in the following S-N fatigue diagram. Hint: neglect any stress concentration at the support end. (a) (4 points) Calculate the midrange stress Om and alternating stress oa at point A and point B of the beam. (b) (6 points) Estimate the fatigue life of material at point A and point B of the beam using the modified Goodman criterion, and find which point will fail earlier. 25" А B Sut (N = 1) = 125 S. S; (N = 103) = 90 100 Fatigue strength, Sp,kpsi Se(N = 106) = 50 s, 10 10 102 10 109 10 10" 10 10 Number of stress cycles, N

Answer 1

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