COMBINATION OF LOADING MODES Suppose part is loaded in different modes: axial, bending, torsion. Then you may have nominal stresses (i.e., before any correction factors are used) From axial load: σaaxialσmaxial(nominal)From bending load: σabendingσmbending(nominal)From torsional load: τatorsionτmtorsion(nominal) To estimate fatigue life: 1. Compute Snfrom using CnS′LCS and CG, i.e., Sn= CLCS CGnS′2. If present, apply stress concentration factors to both the Kfaxial,Kfbending,Kftorsionalternating and the nominal component of the stresses. Recall that Kf=1+q(Kt−1)where qis the notch sensitivity and Ktis the theoretical stress concentration factor (from static analysis). Also, apply the safety factor SF here. Thus nominalnominal()()axialaxialaxialaxialaxialaxialafamfmSFKSFKσσσσ=×=×nominalnominal()()bendingbendingbendingbendingbendingbendingafamfmSFKSFKσσσσ=×=×nominal
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