| Blades are the most critical and vulnerable parts of aero engine, and the fault rate is very high. According to the statistics, over 60% of the overall faults are caused by engine vibration. Furthermore, the blade fault has accounted for more than 70% of vibration fault. So fatigue test is essential for the estimated life of aero-engine blades.The thesis starts with the vibration differential equations based on equivalent stiffness and equivalent softness. According to these equations, the analytical solutions of natural frequency and forced vibration response are deduced. By 3D finite element method in consideration of blade's geometrical nonlinear deformation, the influence of depth, location and shape of crack are studied. The results indicate that the influence of depth and the location of fatigue crack on natural frequencies are large. The deeper the crack is, the lower the blade's natural frequencies are. When crack depth is constant but the crack location goes far from the blade end, the first order natural frequency increases. The crack not only makes the blade's natural frequencies decreased, but also causes non-linear characteristics of forced vibration response.A model of an aero-engine blade is built by finite element software Ansys, and dynamics analysis is also conducted with software Ansys. The existence of crack causes the amplitude of harmonic response changed. When crack location is constant but the crack depth increases, the amplitude of harmonic response increases. The amplitude of harmonic response drops with the same crack depth, while the crack location goes far from the blade's end. In the mean time, the crack caused the blade's phase changed. It provides a basis for the establishment of fatigue test monitoring system. At last, according to the theoretical and experimental results, a fatigue test monitoring system is programmed by Visual C++ based on NI instruments.
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