S-N Curve From Hardening and Grain Size Data

2 S-N Curve From Hardening and Grain Size Data 

The corresponding point is marked by letter A in Fig. 5.21. The second value to find is the fatigue limit oy. The simplest equation to use is (5.1) that yields 

But we also know that the measured mean hardness is 157 HV so that Eq. (5.6) yields 

Moreover, knowing that ferritic grain size is about 40 qm we may use the HPM Eq. (5.20) that yields 

The four values obtained with different equations are close to each other, but not exactly equal. We may decide to take the average of the four obtaining 

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