Beach marks found on the fracture surface prove that the failure mechanism of blades is fatigue.
Gaps between endless laces or between bosses resulted from improper assembly of blades or other condition,
lead to the occurrence of vibration,
other kind of stress superimposed promoting the cracking,
during blades operating.
Therefore, further stress analysis is necessary to study the cause for vibration,
so much as for cracking.
Through the examination of corrosion products on the fracture surface it could not be confirmed that the corrosion
fatigue control the blade cracking for exposure in the atmosphere could also result in oxygen corrosion.
Furthermore, corrosion pits were not found at the crack initiation point. Therefore, only the conclusion can be
drawn that fatigue with the influence of corrosion controls the failure of blades.