Failure assessment of the shaft of a pumped storage unit

Abstract

The paper is focused on failure assessment of the shaft of a pumped storage unit. The shaft failure occurred during normal operation of the hydropower unit after 35 years of service. Three different methods are applied in order to assess its lifetime. Firstly, a finite element analysis was performed in order to obtain the static stress distribution and to apply a strain‐based crack initiation for the shaft under torsion load. The number of cycles for crack propagation was obtained using the Paris law for mode III. More precisely, the lifetime assessment of the shaft is obtained based on a low‐cycle fatigue analysis for estimating the number of cycles for crack initiation and then followed by that for fatigue crack propagation. Secondly, an analytical estimation based on failure assessment diagram is carried out for circumferential crack in order to determine the safe/unsafe region, where the shaft can operate with a crack. The failure assessment diagram for mode III loading was plotted in order to obtain the critical circumferential crack using the stress intensity factor solution and three analytical solutions for plastic zone. Thirdly, the theory of critical distance is employed for estimating the shaft life under torsional loading. A good agreement is obtained between the estimated results and experimental data for the shaft life and the crack length.

Fatigue crack initiation prediction of cope hole details in orthotropic steel deck using the theory of critical distances

“…The TCD is a new perspective in fracture mechanics, which is initially proposed by Neuber 23 and Peterson, 24 and then developed by Taylor and other researchers. [25][26][27][28][29][30][31][32] The concept behind the TCD is that the fatigue behaviour of the notches or other structural details depends on the stress distribution within a certain critical distance around the stress concentration. 22 This distance is a characteristic À6.0% À0.8% À5.5% À7.0% À2.6% À2.8% À0.7% À4.9% Fig.…”

“…The efficiency and accuracy of the TCD methods for fatigue prediction of notched components and welded joints were tested extensively by Taylor and other researchers . The investigations and validations were carried out on a wide range of notch geometries in various components with different materials. Righiniotis et al .…”

“…[25][26][27][28] The efficiency and accuracy of the TCD methods for fatigue prediction of notched components and welded joints were tested extensively by Taylor and other researchers. [25][26][27][28][29][30][31][32] The investigations and validations [25][26][27][28][29][30][31][32] were carried out on a wide range of notch geometries in various components with different materials. Righiniotis et al 33 applied the TCD methods to the fatigue assessment of stringer-to-cross-girder connections in riveted railway bridges.…”

Vibration analysis of coupled bending-torsional rotor-bearing system for hydraulic generating set with rub-impact under electromagnetic excitation

“…However, it is indicated from engineering practice that the torsional loads are endured by shaft system of hydraulic generating set for long time, because of manufacturing or human factors. The minor result for that is the amplitude augment of torsional vibration, while the worst consequence is the crack or even fracture of the shaft system [42], which may engender immeasurable economic loss for hydropower plant. Therefore, from the perspective of safety operation for unit and plant, the investigation about the effect of parameters or excitations, especially those which are closely related to torsional vibration, on the dynamic characteristics of torsion oscillation is necessary.…”

Analysis of multiaxial low cycle fatigue of notched specimens for type 316L stainless steel under non-proportional loading

“…Smith-Watson-Topper (SWT) [7]. Other authors instead, focused on energetic approaches for the fatigue life assessment under non-proportional loadings and, more in general, under localized plastic phenomenon [8][9][10][11][12][13][14]. Critical plane and energy approaches found good applicability of fatigue life evaluation in multiaxial high cycle and LCF under proportional loading condition.…”