Dynamic Stress Measurement and Data Correlation Analysis for Aircraft Engine Blades

Measuring blade dynamic stress plays a crucial role in forecasting blade high cycle fatigue (HCF) failure during aircraft engine tests. A method to improve the measurement accuracy of blade vibration amplitude is introduced. The gauged blades are calibrated on the shaker to measure dynamic strains and tip amplitudes before being assembled with the rotor. First, a brief strain distribution for each vibration mode is acquired to validate the predicted and measured mode shapes, through which the maximum dynamic strain positions are also identified. Then, the ratios of strain to amplitude for each mode can be established based on Amplitude frequency (AF) techniques to define blade tip amplitude limits during engine tests. Third, the ratios can be substituted into online measured blade tip amplitudes to estimate blade safety, which could make blade vibration monitoring more accurate and thus prevent unnecessary engine shutdowns. To validate the methods, engine test data of a high bypass ratio aircraft engine fan blades are introduced. Results show that dynamic strain and tip amplitude data of the fan blades are with good correlation. It proves that the blade tip timing (BTT) system works well in predicting the occurrences of fan blade resonances and the measured amplitudes are with reasonable uncertainties. The results reveal that BTT could be a useful tool to quantify blade vibration levels based on AF techniques.