(6-27 Using the Goodman criterion for infinite life, repeat Problem 6-25 for each of the following loading conditions: (a) 0 kN to 28 kN (b) 12 kN to 28 kN (c)-28 KN to 12 kN 6-25 The cold-drawn AISI 1040 steel bar shown in the figure is subjected to a completely reversed axial load fluctuating between 28 kN in compression to 28 kN in tension. Estimate the fatigue factor of safety based on achieving infinite life and the yielding. factor of safety. If infinite life is not predicted, estimate the number of cycles to failure. em 6-25 25 mm 10 mm 6-mm D.
I am only interested in part 6-27(a). Why is the yielding factor of safety calculated as ( n=Sy/sigma_max), but not as ( n=Sy/Kt*sigma_max )? Since there is a stress concentration factor and the sigma_max is technically considered the nominal stress.
My understanding is that when a ductile material is subjected to a static load the effects of stress concentration near the discontinuity are reduced to local yielding and for this reason not considered in the yielding factor of safety? Because under the static load, when the stress near the discontinuity reaches the yield point, local plastic deformation takes place and increases the yield strength hence sustaining higher loads.
Here the the ductile material is subject to a dynamic load, Would the yielding factor of safety be the same reasoning as for static load? and take the stress concentration factor into consideration in the fatigue factor of safety due to the cyclic loading causing local yielding that gradually propagate cracks over time.
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