Application of nonlinear continuous damage model on low cyclic fatigue analysis of steam turbine rotor

For big error in the life assessment of low cycle fatigue of turbine rotor, a nonlinear continuous damage mechanics model is employed to analyze the life and damage of low cyclic fatigue of turbine rotor. Te transient temperature and thermal stress fields of 600 MW turbine under typical cold start and sliding parameter stop operations are calculated by applying finite element method. In the thermal stress analysis, the elastic-plastic finite element method is employed. Linear accumulation theory and a nonlinear continuous damage model are respectively employed to calculate the low cycle fatigue damages caused by thermal stress. The compare of these two method results show that for the linear damage accumulation theory widely used in present engineering life assessment is under uniaxial assumption and the effects of multiaxial stress are not taken into account, the turbine rotor life is overestimate in life prediction. Not only the effects of complex multiaxial stress are taken into account but also the nonlinear accumulation process of low cycle fatigue damage is described correctly in the nonlinear continuous damage mechanics model. Therefore, the results from nonlinear continuous damage mechanics model are in better agreement with the facts than the results from linear accumulation theory.