Studies On Time-varying Physical Parameters Identification And Dynamics Analysis Of Cracked Blades

In aero-engine,compressor and turbine blades are very important parts.Because of the function,they work in extremely bad condition.Fatigue crack easily occurs in blades and has a strong impact on the safety in use.So it has engineering meaning that the study on the vibration when the fatigue happens on blades.Due to the crack's open-close process during vibration process,the response has the character of non-stationary.It forwards higher requests for cracked blades of signal pick-up and fault diagnosis.This paper takes aero-engine blades on as the object of the research.A series of research work is developed about the fault diagnosis.The cracked blade was simulated using a cantilever beam.Vibration characteristics and parameter identification were studied using analytical method,numerical analysis and experiments.The works of this article is as follows:1.The dynamic behavior of the cracked transverse beam first-order bending vibration was simulated using a lumped parameter system under harmonic excitation.Here,an experimental system was designed,and the Hilbert transform method was presented to identify the time-varying stiffness and damping based on the response data.The parameter model modified based on the experimental results.The change of parameters' estimation in the new model was obtained in different condition.The responses of the original and modified model were obtained by numerical method and compared with the experimental data.The conclusion is that the response characteristics of modified model are consistent with the experiment.2.The stability domain of the modified model was solved by the perturbation method.The effect of each parameter was analyzed.The periodic solution of steady state vibration response was solved by multiple scales method.At last,the nonlinear response characters were proposed by numerical analysis under different parameters.3.The cracked blade were simplified into a cantilever beam and discretized by 3-D solid element.Meanwhile,a breathing crack model could be simulated as a frictionless contact plane problem.Under a harmonic load,a finite element model was used to study the effects of various factors,such as excitation frequency,crack depth and crack position on the nonlinear dynamic characteristics.The results provided theory and reference for damage identification of cracked structures.This article has a good achievement on research of parameter identification nonlinear dynamics of aero-engine blades,and can be a guide of research on the influence of health monitoring and fault diagnosis.