High Cycle Fatigue (HCF) of turbine blades is one of the major design concerns in an Aero Gas turbine engine developmental program. Resonance induced High Cycle Fatigue (HCF) failure of blades may result in engine catastrophe having expensive consequences leading to program delays and cost overruns in a project. Even though, the resonance regimes in operating envelope can be predicted using FE tools, there are uncertainties involved in theoretical prediction of blade vibratory amplitudes. If these blade amplitudes cross the allowable limits during operation, HCF failures are expected to occur. The purpose of this paper is to assess the safety of the blades from HCF point of view. An integrated approach using test data and analytical model was employed to evaluate the vibratory behavior of a Low Pressure turbine rotor blade of an Aero-Gas Turbine engine. Correlation factors between blade tip amplitudes and dynamic stresses during critical modes of vibration were established using the data from strain gages, Non Intrusive Stress Measurement System (NSMS) and FE Model. Good agreement was found between the predicted stresses using FE/NSMS and measured vibratory stresses from strain gages. Fine tuned FE model was generated for evaluation of vibratory stresses from NSMS data.
Results have shown up to 300% scatter in the dynamic responses across the blades and 2% scatter in natural frequency for a particular resonance. Amplitude–stress relationship shows linearity and is observed to be invariant across the blades. All these statistical variations in responses along-with established correlation factors were considered for the safety assessment of blades from HCF point of view.
