A round solid bar having a groove of 0.1-in deep with a 0.1-in radius machined into it. The material of the bar is AISI 1020 cold drawn steel, its diameter is 2.54 cm, and it is exposed to a
purely reversing torque of 1800 lbf. in. For the S-N curve of such material, take f = 0.9.
(a) Estimate the number of cycles to failure.
(b) If the bar is also placed in a 750◦F environment, estimate the number of cycles to failure.