Research On Assembly Stress Measurement Method Of Aeroengine Bolted Connection Based On Acoustoelastic Effect

Aeroengine is the core power plant of aircraft,and it is an important embodiment of the state’s cutting-edge technology level.Aeroengine is assembled by multistage rotor stator,and bolt connection is widely used in aeroengine.The assembly quality of bolted connection directly affects the coaxiality and quality characteristics of aero-engine,and then affects the stability and safety of aero-engine.The measurement of assembly stress can evaluate the assembly quality of aero-engine,optimize the assembly process,improve the reliability,stability and safety of aero-engine,and reduce the maintenance time cost of aero-engine.In order to improve assembly quality and aeroengine performance,it is necessary to measure assembly stress of bolted parts.Therefore,the research on assembly stress measurement method of aeroengine bolt connection based on acoustic elastic effect is carried out in this project.In order to solve the problems of large error of assembly stress measurement methods for small size bolts(M6)of aero-engine and imperfection of assembly stress measurement model for flange holes,the assembly stress measurement method for M6 bolts and flange holes based on acoustic elastic effect is studied.Considering the influence of bolt elongation and couplant thickness fluctuation,a model for measuring the assembly stress of M6 bolt by acoustic time difference is established,which effectively reduces the influence of couplant thickness fluctuation and bolt elongation on the measurement accuracy.By analyzing the waveform conversion mode of ultrasonic oblique incidence and combining with the coupling agent attenuation law,the measurement model of flange hole assembly stress based on acoustic elastic effect is established,and the second reflected longitudinal wave is used to measure the flange hole assembly stress.In order to solve the problem that the ultrasonic echo signal is seriously affected by the thread and the echo signal is weak in the stress measurement of small bolt assembly,an ultrasonic echo acquisition method based on pulse repetition frequency optimization is proposed.By optimizing the pulse repetition rate of ultrasonic transmitting circuit,the influence of thread on ultrasonic echo signal is reduced.The optocoupler is used to optimize the ultrasonic transmitting pulse isolation circuit,which effectively suppresses the influence of high-voltage transmitting pulse signal on the echo signal reception,and improves the signal-to-noise ratio of ultrasonic echo signal in small-size bolt assembly stress measurement.Aiming at the problem that the sampling rate of echo signal and noise affect the measurement accuracy of acoustic time difference in assembly stress measurement,a cross-correlation function acoustic time difference measurement method based on sinc function interpolation is proposed.In this method,sinc function is used to interpolate the ultrasonic echo signal,so as to improve the resolution of acoustic time difference,reduce the sampling rate requirement of cross-correlation function acoustic time difference measurement algorithm,and improve the accuracy of acoustic time difference measurement.The influence of signal-to-noise ratio on the accuracy of cross-correlation function acoustic time difference measurement algorithm is studied.The results show that the signal-to-noise ratio of cross-correlation function acoustic time difference measurement algorithm is 10.1 d B.In order to verify the accuracy and effectiveness of the measurement model of bolt connection assembly stress,ultrasonic echo acquisition method and cross-correlation function acoustic time difference measurement method proposed in this paper,the calibration and measurement experiments of M6 bolt assembly stress and flange hole assembly stress were carried out.The accuracy of the cross-correlation function acoustic time difference measurement method based on sinc function interpolation is verified by the assembly stress calibration experiment of M6 bolt.The validity of the ultrasonic echo acquisition method based on pulse repetition rate optimization is verified by the assembly stress measurement experiment of M6 bolt.The maximum error of assembly stress measurement of M6 bolt is 26.5 MPa,and the relative error is 8.8%.The accuracy of the measurement model based on the second reflected P-wave is verified by the flange hole assembly stress measurement experiment.The maximum measurement error is 13.3 MPa and the relative error is 14.8%.