Required information 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 Sut of 113 kpsi. Each rod is to have a size giving an equivalent diameter de of 0.32 in. Determine the endurance limit for each material. Is there any advantage of using the alloy steel for this fatigue application

Yes, there is advantage.

Explanation:

Step 1 of 3

For AISI 4340 Cr-Mo-Ni steel

The tensile strength(S) = 260kpsi.

Step 2

Endurance limit for (S') for 260kpsi is 100 kpsi

From table parameters for As-forged surface finish

a= 39. 9, b=-0. 995

Step 3

Find the surface factor by using

aS^b

S is tensile strength is 260kpsi.

Therefore

Surface factor =

39, 9(S)^-0.995 = 0.1578

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