Empirical Equations for Fatigue Limit

Many empirical equations have been proposed that relate fatigue limit to the mechanical properties of materials. T. Svensson et al. [6] working on a base of 166 data collected in Japan and relative to carbon steel, Cr-Mo steel and ferritic stainless steel proposed the diagram of Fig. 5.2. 

5 Stress-Based Fatigue Analysis High Cycle Fatigue 

Alternatively, knowing the steel hardness or yield strength Cy, the Svensson et al. [6] equations are available 

The second of Eq. (5.4) is somewhat unusual since it introduces the yield strength in relation with the fatigue limit that, usually, is related to the ultimate strength of the material. Another empirical relationship that makes use of the Vickers hardness has been proposed by Murakami and Endo [7] for hardness less than 400 HV 

Equation (5.7) is valid up to 40/50 HRC afterwards the fatigue limit stabilizes owing to inclusions always present in metals. Equations (5.6) and (5.7) are plotted in Fig. 5.3 on the Garwood et al. diagram [8]. It may be useful the diagram of 

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