A 1-inch diameter bar is made of AISI hot-rolled steel with a yield strength of 280 MPa and an ultimate tensile strength of 400 MPa. A fatigue stress concentration factor, Kf, of 1.35 is selected based on a fillet radius at the end of the bar. Estimate the modified endurance limit based on the effect of Kf. (Ignore other factors.) 270 MPa 148 MPa 189 MPa 135 MPa 104 MPa