Research On Fatigue Characteristics Of Large-volume Half-speed Long Nuclear Power Steam Turbine Blade

Research on fatigue life of steam turbine blade is a major aspect of its strength designand safety evaluation. This paper focuses on the fatigue property of last stage blade ofsteam turbine with high volume nuclear power. Working session of blade can bedivided into three stages according to the speed: starting, stable rotation, stopping.During the process of starting and stopping, blade will experience big centrifugalloading with variable amplitude, as well as steady-state steam dynamic loadingsynchronously. This is low cycle fatigue. While in the high-speed stable rotation,blade will vibrate owing to vibration generated by steam flow disturbance with lowamplitude but high frequency. This is high cycle fatigue. Starting and stoppingsession is the main factor in crack initiation and steady propagation, and thus, it is thekeystone of the working life analysis. In order to study the high and low cycle fatiguelife of long blade, firstly, finite element model of a single blade was analyzed byusing ABAQUS. The ‘Cyclic Symmetry’ was set so as to simulate the whole circlestructure of the blade. The stress distribution was calculated, and regions concerned infatigue calculation were found. Afterwards, fatigue tests were carried out on the bladematerials, and SN curve with corresponding equation was obtained using least squarefitting method. Finally, by combination of finite element results with results of fatiguetests, nSoft code was applied to assess the high/low cycle fatigue life of blade underthe condition without initial crack. In addition, preliminary analysis on cycle fatiguelife under condition with initial crack was studied as well, by setting initialmicro-cracks in the specified locations of blade. All the calculations were assumedunder the most dangerous conditions. The results indicated that the blade withoutinitial crack would not break during its cycle fatigue life. However, the life of theblade with initial crack is extremely low, thus in practical application the crack inspecified locations should be prevented from the crack initiation.