Monitoring low cycle fatigue damage in turbine blade using vibration characteristics

A finite element based approach is used to simulate the evolution of low cycle fatigue damage in a turbine blade. The turbine blade is modelled as a rotating Timoshenko beam with taper and twist. A damage growth model for low cycle fatigue damage developed using a continuum mechanics approach is integrated with the finite element model. Numerical results are obtained to study the effect of damage growth on the rotating frequencies. It is found that low cycle fatigue causes sufficient degradation in blade stiffness for changes in rotating frequency to be used as an indicator to track damage growth. Continuum damage mechanics models in conjunction with finite element analysis are used to develop thresholds for damage indicators. By placing suitable threshold on the frequency change, it is possible to detect the onset of the final stage of damage in the structure before failure occurs.