Empirical FCP Equations

10 Fracture Mechanics Apjmjach to Fatigue Crack Propagation 

Thus the FCGR becomes infinite as K ax approaches the toughness of the material Kc, which actually means final fracture, Stage III of fatigue. Note that in the Foreman Eq. (10.13) A and m are material characteristic whose value is different from C and n of the Paris law (10.10). Weertman [11] proposed an alternative equation for Regions II and III 

The AK exponent in the Weertman Eq. (10.14) may be variable and not necessarily four. Klesnil and Lucas [12] proposed an equation for Regions I and II modifying Eq. (10.10) to account for the threshold AKth 

McEvily [13] developed another equation that can be fit to the entire sigmoidal 

An interesting equation that describes the entire sigmoidal curve was developed by Newman [15] 

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