Research On The Method Of Frequency Tracking During The Structural Fatigue Test

Blades is an important part as well as a weak link of the aircraft engine. The failure rate of bladesis extremely high,. According to the statistics over60%of the overall faults are caused by the bladefault.The blade faults are mostly fatigue damage, then crack and final fracture because of vibration.Therefore, the blade fatigue test is important for the estimation of the blade life.The resonance of blades makes the fatigue damage of blades mostly easily, so we simulate thefatigue damage process of blades by the resonance to make the fatifue damage test more efficient.However, with the blade fatigue damage, the natural frequency also changes. So we must achieve thenatural frequency real-time tracking during the test.In order to achieve the natural frequency real-time tracking during the blade fatigue test, thepaper studys the changes of the structural frequency response function before and after the fatiguedamage under the hypothesis of the real model theory and the proportional damping, then studys themethods to achieve the natural frequency real-time tracking during the test according to the changes.The paper also shows the way and the steps of the methods to achieve the natural frequency real-timetracking during the test according to the changes of the amplitude-frequency characteristics and thephase-frequency characteristics, then the paper make some note during the test.In order to verify the feasibility of the methods, the paper proves the feasibility by numericalsimulation and experimental data. The paper establishes the beam finite element model, simulate thestructural damage by reducing the cell modulus and changing the damping, build the mass matrix,stiffness matrix and damping matrix of model before and after the fatigue damage according to thephysical parameters, then prove the feasibility by the comparison between the amplitude-frequencycharacteristics and the phase-frequency characteristics before and after the fatigue damage. Accordingto numerical simulation, the paper also find the advantages and disadvantages of the method andscope; The paper get the frequency response function before and after the fatigue damage by sweep,prove the feasibility by achieving the natural frequency tracking by the way we found. At same tine,the paper shows the attention need pay to the use of the way of the natural frequency tracking duringthe test.