Abstract
According to the Paris–Hertzberg crack growth law, an analytical model shows that cracks grow from a flaw very quickly from the short to the long cracks regime, during gigacycle fatigue. The location of the initiation, at the surface or inside, has a small effect. This means that the key problem is the nucleation of the crack around the flaws as it is shown by Lukas et al. and Mughrabi and Stanzl [Lukas P, Kunz L, Svoboda M, Bokuvka O. Fatigue behaviour of ultra fine-grain copper in VHCF regime. In: VHCF4, Ann Arbor; 2007. p. 265–70, [1]; Mughrabi H, Stanzl S. Fatigue damage evolution in ductile single phase FCC metals in the UHCF regime. In: VHCF4, Ann Arbor; 2007. p. 75–82, [2]]. This approach is applied to a PM Ni alloy which is used for aircraft turbine. It is concluded that the damage tolerance concept is to be applied with cautiousness for VHCF prediction, in PM alloys.
Highlights
We found that the 'K thresholds for R = -1, R = 0, R = 0,8 are respectively 5,5 8 and 4,2
In the gigacycle regime of PM N18 nickel based alloy used for turbine disks, the fatigue strength is related to the initiation of permanent slip bands around defects more than crack growth.Comparing the effect of inclusions and porosities in the N18, it is interesting to point out the following: The role of the inclusions is sometimes hidden by the role of porosities when the R load ratio is equal to -1 or to 0
The scattering of the results for R = 0 in a N18 seeded with ceramic inclusions is important, since for a N18 standard, the scattering is low
Summary
The fatigue life of an automobile engine is ranging in the gigacycle 109, regime and the aircraft turbine is of the order of 1010 cycles, according to rotation of several thousands per minute. 2 -5 September,2008, Brno, Czech Republic a0 a Estimating the life for a crack of this type beginning just above threshold it is appropriate to consider the growth law as: da dN
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