A hollow shaft made from AISI 4340 steel has an outer diameter Do of 4 in. and an inner di...

A hollow shaft made from AISI 4340 steel has an outer diameter Do of 4 in. and an inner diameter Di of 2.5 in. The shaft rotates at 46 rpm for one hour during each day. It is supported by two bearings and loaded in the middle with a load W of 5500 lbf. The distance between the bearings L is 78 in. The maximum tensile stress due to bending for this type of cyclic loading is calculated using the following equation:

What is the stress ratio for this type of cyclic loading? Would this shaft last for one year assuming a safety factor of 2?