Question $3.$ DYNAMIC FAILURE

A stepped shaft, as illustrated below, has dimensions of $D=50mm,d=25mm,$ and $r=1\mathrm{.}25mm.$

It was machined from steel having tensile properties of $S_u=620$MPa and ${}_{\text{y}\text{i}\text{e}\text{l}\text{d}}=517$MPa.

a$)$ Estimate the value of completely reversed torque, $+-T,$ requireu to produce eventual fatigue failure.

b$)$ Estimate the value of maximum applied torque, $T_{\text{m}\text{a}\text{x}},$ required to produce eventual fatigue failure, if the $T$ is cycled from $0$ to $T_{\text{m}\text{a}\text{x}}.$

c$)$ Comment on your findings.

Ignore $C_T$ and $C_R\mathrm{.}1$MPa$=0\mathrm{.}145$ksi.