Problem 6: A stepped bar is loaded with a cyclic axial force F that varies from 0 to 500 kN. Dimensions for the bar are given in the figure below. The bar is fabricated from low-strength steel with an ultimate tensile strength of 341 MPa, a yield strength of 240 MPa, and an endurance limit of 170 MPa. Calculate the expected fatigue life (i.e. number of cycles until fatigue failure) for this bar. =20 mm F = 500 kN W₂ = = 130 mm W₁₁ = 90 mm b = 40 mm