Given below are the material properties and fatigue test dat

Given below are the material properties and fatigue test data for three steels. The fatigue data were generated using fully reversed axial loading on notch-free polished specimens. How do these data compare to the estimated S-N curve for rotating bending shown in Fig. 1.5? Determine a possible method or relationship to modify the estimated rotating bending S-N curve to account for axial loading. How well does the modification factor for endurance limit given in Eq. (1.15) work for these data? (Data taken from Ref.20.)

Solution

The given data given for axial laoding will be somehow different than as in case of rotation and bending because in rotation and bending one layer of element goes under pure tensile and shear loading. Thus axial stress and endurance strength given in the table cane be taken as allowable stress and should be equal to or greater than amplitude of principal stress due to this normal and shear stress in rotation and bending case for safe design.

Principal Stress = (Normal stress/2) + 0.5[(normal stress)² + 4*(shear stress)²]^1/2

Modification factors can be taken same for axial load case and rotation and bending case.