6-1 6-6 6-10 A 10-mm steel drill rod was heat-treated and ground. The measured hardness was found to be 300 Brinell. Estimate the endurance strength in MPa if the rod is used in rotating bending. A steel rotating-beam test specimen has an ultimate strength of 1100 MPa. Estimate the fatigue strength corresponding to a life of 150 kcycles of stress reversal. A rotating shaft of 25-mm diameter is simply supported by bearing reaction forces R and R2. The shaft is loaded with a transverse load of 13 kN as shown in the figure. The shaft is made from AISI 1045 hot-rolled steel. The surface has been machined. Determine (a) the minimum static factor of safety based on yielding. 6-12 (b) the endurance limit, adjusted as necessary with Marin factors. (c) the minimum fatigue factor of safety based on achieving infinite life. (d) If the fatigue factor of safety is less than 1 (hint: it should be for this problem), then estimate the life of the part in number of rotations. 200 mm 25 mm 13 kN 50 mm R Not to scale. Problem 6-10 A 1-in-diameter solid round bar has a groove 0.1-in deep with a 0.1-in radius machined into it. The bar is made of AISI 1020 CD steel and is subjected to a purely reversing torque of 1800 lbf. in. Estimate the number of cycles to failure. (a) (b) If the bar is also placed in an environment with a temperature of 750F, estimate the number of cycles to failure.