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

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Answer: 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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