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198 Ilare Bordeasu et al.
Fig. 1 – The 3D shaft model, obtained with the INVENTOR program [initiation].
2. Estimation of Fatigue Crack Propagation for Variable Stresses
with Constant Amplitudes
For the selected axial hydraulic turbine (Power plant Iron Gates II) the shaft
presents the following characteristics [1]:
a) the initial crack occurs in the joining zone between the shaft flange (for
coupling with the hydraulic runner) and the shaft body, fig. 2;
b) in order to obtain the needed data we choose the AISI 1020 steel [6] instead
of the actual used 20ГC steel [7]; both steels have almost the same mechanical
characteristics but for the AISI 1020 we found all the supplementary
characteristics needed for fatigue tests;
c) the shaft dimensions are: length 7572 mm, maximum diameter 2300 mm,
the main shaft body, between flanges, has an external diameter of 1200 mm and
an internal one of 600 mm;
d) according with the ANSIS program (Fig. 3), till crack initiation, the
minimum number of cycles was 3,0139 10 8 , corresponding to 80,370 running
hours.
a) Deep circumferential cracks b) Cracks network
Fig.2 – Cracks in the joining zone between the runner flange and the main shaft body.