A Contribution to the Debate on Methods to Determine Δ K th in a Conservative Way

The threshold value for fatigue crack growth Δ K th is considered to be the most important value in the context of damage tolerant design. Therefore, a reliable experimental determination of the threshold value is of great interest. However, it has been shown several times that the standardized approach can lead to non‐conservative values. Therefore, several alternative methods and variants for the determination of Δ K th have been developed. In this article, selected ideas of existing approaches are taken up. Particular attention is paid to the use of minimum crack initiation loads, both in tensile precracking (TPC) and in compression precracking (CPC). It was observed that crack initiation in cyclic compression could be realized with much lower loads than suggested in literature. Furthermore, crack growth behavior directly after crack initiation in compression differed from expectations. Crack growth data in the near threshold region is determined and compared for the standardized method and for a CPC‐based approach. A proposal for the practical application of a CPC‐based approach is made, with the intention to avoid uncertainties in the determination of Δ K th .