Compute the estimated actual endurance strength for an AISI

Compute the estimated actual endurance strength for an AISI 4118 SOQT 300 steel rod with a diameter of 100.0 mm. It is polished and subjected to a repeated bending stress. A maximum reliability of 99% is specified.

Solution

For the AISI 4118 SOQT 300 steel rod, the folloing data is available from design data books:

1. Ultimate Tensile Strength, S_ut = 986 MPa

2. Reliability factor of 99%, K_c = 0.814

3. Size factor corresponding to 100mm diameter, K_b = 0.75

4. Surface finish factor corresponding to polished rod, K_a = 1

5. Approximate endurance limit for the rotating rod, S_e^\' = 0.5 S_ut = 493 MPa

Actual estimated endurance strength, S_e =  K_a * K_b * K_c * S_e^\' = 1 * 0.75 * 0.814 * 493 = 300.98 MPa