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Two steels are being considered for the manufacture of as$-$forged connecting rods subjected to bending loads. One is AISI $4340$ Cr $-$Mo$-$Ni steel capable of being heat$-$treated to a tensile strength of $260$ kpsi $.$ The other is a plain carbon steel AISI $1040$ with an attainable $S_{ut}$ of $113$ kpsi $.$ Each rod is to have a size giving an equivalent diameter $d_e$ of $1\mathrm{.}190$ in $.$ Determine the endurance limit for each material. Is there any advantage of using the alloy steel for this fatigue application?

What are the estimated values of the endurance limits for the $4340$ and $1040$ steels?

The endurance limit for the $4340$ steel is $$ kpsi.

The endurance limit for the $1040$ steel is $\backslash$times kpsi.