19:31 Nov 18, 2011 

Based on this approach, I suppose it would have been better if the sentence had stated that a longer crack length is "allowed", resulting in the possibility of narrowing the blade root.

18:36 Nov 18, 2011 

Hi Patrick, what this sentence is trying to say is that the crack longer propagates in a stable/incremental state before reaching the unstable propagation phase / catastrophic failure or rupture stage / critical crack size.
Maybe this http://www.probabilistik.de/vortrag/Vortrag0404_Mueller_UStu... helps.

18:24 Nov 18, 2011 

And yes, your suggestion "failure crack length" is what I would use as a translation for "Versagensrisslänge".

18:16 Nov 18, 2011 

I agree. The 2nd part of the sentence should probably read "..., wodurch bei gleichen Belastungen eine Verschmälerung des Schaufelfusses möglich ist."