The low-cycle fatigue life assessment method for online monitoring of steam turbine rotors

The paper presents a simple method for the low-cycle fatigue life monitoring of steam turbine rotors. The method makes use of the equivalent strain energy density rule of notch stress-strain analysis proposed by Molski and Glinka. The method is applied to low-cycle fatigue analyses of steam turbine rotors operating at non-isothermal conditions. A strain energy correction factor is introduced to include the distortion strain energy density. Assessment of the proposed method was done by comparing their estimations with the strain amplitudes obtained from the finite element analysis employing elasitc-plastic material model. The inclusion of energy correction factor obtained from the elastic-plastic finite element analysis significantly improves the accuracy of strain amplitudes and fatigue life estimations. The strain calculation algorithm is based on an analytical solution of the equivalent strain energy equation what makes it very useful for real time fatigue calculations.