Research On Assembly Tightness Detection Method For Aeroengine Bolt-jointed Rotor

Aero-engine bolt-jointed rotors are non-continuous rotors that are formed by compression of multiple components by circumferential tie rod bolts.It is widely used in military and civil aviation engines due to its light weight,high strength,good rigidity,convenient processing,easy assembly and disassembly,and flexible material selection.Due to poor consistency of the assembly quality of bolted rotor during assembly and the difficulty in avoiding looseness during service,it is necessary to carry out a research on assembly tightness detection method of aeroengine bolt-jointed rotor.The assembly tightness detection is based on the vibration method.The vibration response signal reflects the structural characteristics and the natural frequency variation to some extent.Therefore,it is necessary to study the influence of the assembly tightness on the natural frequency of bolt-jointed rotor.A simplified model of the bolted joint rotor considering the joint structure is established.The natural frequency of the assembly tightness to the bolted rotor are preliminarily explored,which provides a theoretical guidance for the study of aero-engine bolt-jointed rotor assembly tightness testing technology.Based on wavelet energy entropy,a method for detecting the tightness of the bolted rotor assembly is proposed.The correctness of the assembly detection method is verified by an experiment.The influence of the accelerometer installation position on the assembly tightness detection method is explored,and the assembly tightness quantitative index is also compared with the other two evaluation indexes which are commonly used in fault diagnosis fields(condensation function,fractal box dimension).The results show that the assembly tightness detection method based on wavelet energy entropy is more practical and effective..Compared with multi-wavelet,single wavelet doesn't have good properties such as orthogonality,symmetry,tight support and high-order vanishing moment.The GHM multi-wavelet,which has excellent properties like orthogonality,symmetry,tight support and high-order vanishing moment,is introduced into the assembly tightness detection of the bolted rotor.Considering the definition and properties of GHM multi-wavelet,the pre-processing and post-processing problems are discussed when GHM multi-wavelet is introduced into the bolt-jointed rotor assembly tightness detection method.The experimental results show that the normalized assembly tightness quantitative index based on GHM multi-wavelet can accurately reflect the six assembly tightness states of the bolted rotor from tightness state to looseness state.Traditional one-dimensional signal-based fault diagnosis methods usually use the time domain amplitude or spectrum for damage detection.However,in practical engineering applications,the signal caused by the fault is not necessarily effective.For example,the signals caused by the damaged element are not always available,such as those buried in broadband background noise or the signal-to-noise ratio of the signal components used to detect the fault is too low.Therefore,the simple use of the vibration signal itself for fault detection has great limitations.On the basis of high-order cumulant image features,an assembly tightness detection method for bolt-jointed rotor is proposed.The high-order cumulant image features and grayscale images can reflect the difference and similarity of assembly tightness.The root entropy index can be used as the characteristic parameter to detect the assembly tightness of the bolt-jointed rotor.