| With the continuous improvement of the industrial level,the operating conditions of rotating machinery become more complex,which can easily improve the probability of failure and reduce its service life.As the foundation and core equipment of modern industry,the running state of rotating machinery is directly related to the safety and stability of the whole mechanical system.Therefore,timely perception of the running state of rotating machinery is of great significance to ensure the safe operation of mechanical system.Acoustic emission(AE)sensor is the front-end and core component of AE status monitoring system.Its basic structure includes piezoelectric ceramics,matching layer,backing layer and built-in circuit.This paper studies the perception mechanism of piezoelectric AE sensors to determine the basic structure,then the parts structure mathematical model is established,the influence law of different parameters on its performance are studied,at last,through more than physical field numerical simulation and experiment verify the validity of the model,for the research and development of high sensitivity ae sensor provides a theoretical basis.The main research contents of this paper are as follows:(1)Study on the sensing mechanism of piezoelectric AE Sensor.The common damage phenomenon and motion behavior of bearings are analyzed,and the impact signal characteristics of bearings are studied.The AE signal of early damage has high frequency and small amplitude.Then the propagation characteristics of AE signal are studied.The electromechanical coupling model of piezoelectric materials is established,and the constitutive relation of electromechanical transformation of piezoelectric ceramics is revealed.(2)Study on structure and mathematical model of AE sensor.The basic structure of the sensor is analyzed and determined,and the working mode of piezoelectric ceramic is d33.Based on the analysis of impedance matching theory,the built-in circuit of the sensor is designed,and the mathematical model of AE sensor is established,including the size parameter model of piezoelectric ceramics based on aperture effect and resonant frequency,the vibration model of piezoelectric ceramics,and the matching layer thickness design model based on acoustic attenuation.Then the influence of the structure of each part on the sensor performance under different parameters is analyzed.(3)Numerical simulation of AE sensor.The finite element model of AE sensor is established and simulated.Through modal analysis,steady-state analysis and frequency domain analysis of piezoelectric ceramics,natural frequencies,mode shapes and impedance of piezoelectric ceramics are determined,and the correctness of the size parameter model of piezoelectric ceramics is verified.The validity of the matching layer thickness design model based on acoustic attenuation is verified by studying AE sensors in time domain and frequency domain.The matching layer can enhance the acoustic transmission ability and improve the sensitivity of the sensor,while the backing layer can play an effective sound absorption effect,reduce the trailing time of the signal received by the sensor and improve the resolution of the sensor.(4)Study on packaging and performance of AE sensor.The test and verification of the built-in circuit are completed,and the packaging process of the AE sensor is determined and packaged.In order to verify the correctness of the developed AE sensor,an experimental scheme is designed.Firstly,the consistency of the sensor is compared and analyzed,and then the validity of the matching layer thickness design model based on acoustic attenuation is verified.Finally,the AE sensor is applied to the AE test of high-speed train bearings damage.The test shows that the AE sensor can realize the early damage perception of mechanical equipment. |
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