Fatigue crack growth from small to long cracks in VHCF with surface initiations

In Paris et al. [Paris, Paul C, et al. The relationship of effective stress intensity, elastic modulus and Burgers-vector on fatigue crack growth as associated with “Fish Eye” gigacycle fatigue phenomena. In: Proceedings of the international conference on very high cycle fatigue III, Kyoto, Japan; September 2004], the Paris–Hertzberg–McClintock crack growth rate law, dadN=bΔKeffEb3has been used to demonstrate that crack growth is not of significant portion of total life, when crack initiation is located at the specimen interior, normally termed as “fish-eye”. These kinds of failures only occur at Very High Cycle Fatigue (VHCF) over 106 periods. Between 106 and 108 cycles a transition point is located, where both internal and surface initiations of cracks occurred. Therefore, in this discussion, an estimate will be developed to demonstrate that surface crack growth following initiation is a small portion of the total experimental life if over 107 cycles. Closure effects will be explored for a range of transition crack sizes from small to long as well as for various cyclic load ratios.