Probabilistic estimation of the cracked shaft durability
Keywords:
durability, hydroturbine shaft, crack, expected valueAbstract
The paper presents the numerical modeling of the turbine shaft with the extended defect zone. During the inspection of the shaft, there have been discovered numerous cracks disposed in the extended cylindrical domain. The most affected zone is placed near the flange coupling of the shaft with the turbine runner. The analysis of chemical content and mechanical properties of the shaft material was accomplished. The obtained data allow us to obtain the numerical values of the stress intensity factor range, the fatigue crack growth rate. These quantities are used in crack propagation criteria. It was supposed that there will be micro-defects propagated under applied loading. The crack initiation position was analyzed based on the metallographic analysis and the end of the keyway was determined as the crack initiation position of the shaft. The crack propagation was analyzed with the predicted crack initiation position and crack propagation routine. The modified Paris equation was used for setting the dependency between crack growth rate and stress intensity factor range. For stress intensity factor the semi-analytical expression was in use. Using the Paris equation we find the time before cracked shaft failure for each crack with prescribed initial position. The method is proposed to estimate the probabilistic average of time before failure of the cracked turbine shaft. The time failure was estimated necessary for crack hitting unto the defect zone that lead to the shaft failure. In order to avoid important damages, the obtained results are of highest interest because they give the possibility to establish the correct interval between the current inspections.
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Copyright (c) 2017 Е. А. Стрельникова, И. Г. Сирота, А. В. Линник, Л. А. Калембет, В. Н. Зархина, О. Л. Зайденварг
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