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MMPDS-01<br />

31 January 2003<br />

Figure 2.3.1.3.8(a). Best-fit S/N curves for unnotched AISI 4340 alloy <strong>steel</strong> bar, F tu =<br />

125 ksi, longitudinal direction.<br />

Correlative Information for Figure 2.3.1.3.8(a)<br />

Product Form: Rolled bar, 1.125 inch diameter,<br />

air melted<br />

Properties:<br />

TUS, ksi TYS, ksi Temp., EF<br />

125 — RT<br />

(unnotched)<br />

150 — RT<br />

(notched)<br />

Specimen Details: Unnotched<br />

0.400 inch diameter<br />

Surface Condition: Hand polished to RMS 10<br />

Reference:<br />

2.3.1.3.8(a)<br />

Test Parameters:<br />

Loading - Axial<br />

Frequency - 2000 to 2500 cpm<br />

Temperature - RT<br />

Atmosphere - Air<br />

No. of Heat/Lots: 1<br />

Equivalent Stress Equation:<br />

Log N f = 14.96-6.46 log (S eq -60)<br />

S eq = S max (1-R) 0.70<br />

Std. Error of Estimate, Log (Life) = 0.35<br />

Standard Deviation, Log (Life) = 0.77<br />

R 2 = 75%<br />

Sample Size = 9<br />

[Caution: The equivalent stress model may<br />

provide unrealistic life predictions for<br />

stress ratios beyond those represented above.]<br />

2-45

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