Research On Electromagnetic Ultrasonic Transducer And Bolt Stress Testing Technology

Bolts are often used in industrial production to fasten equipment connection.The pretightening force affects the connection performance directly.When the bolt is in service,it may be loose or broken due to vibration,impact or other factors,resulting in serious accidents.Therefore,it is of great significance to take a scientific method to detect the stress of the connecting bolt and ensure the reliability of the bolt connection for the normal operation of the equipment.In this paper,the characteristics of various methods for testing bolt stress are compared.Among them,the method based on ultrasonic acoustoelastic effect for testing bolt stress has the advantages of high detection efficiency and less interference.Both piezoelectric ultrasonic technology and electromagnetic ultrasonic technology can stimulate ultrasonic wave.Compared with piezoelectric ultrasonic technology,electromagnetic ultrasonic technology is used to detect the bolt stress,which has the advantages of no coupling agent,more convenient measurement and no damage on the bolt surface.Based on this,this paper studies the use of electromagnetic ultrasonic technology to detect bolt stress.According to the requirements of testing,the design of the research scheme was completed.Aiming at the shortcomings of low energy exchange efficiency and signal-to-noise ratio of electromagnetic ultrasonic transducer,this paper designs the excitation circuit of electromagnetic ultrasonic transducer,and improves the signal-to-noise ratio of the transducer by amplifying and filtering the ultrasonic signal.In addition,the paper focuses on the influence factors of the energy transfer efficiency of the electromagnetic ultrasonic transducer.The finite element software COMSOL Multiphysics was used to build the model of electromagnetic ultrasonic transducer.The influence of permanent magnet placement and size parameters on the energy transfer efficiency was simulated and analyzed.The size parameters of the coil were optimized by orthogonal decomposition method,and the design optimization of the transducer was realized.On this basis,two kinds of electromagnetic ultrasonic probes with spiral coil and butterfly coil are developed.A test system was established in the laboratory,and different coils were used to test the ultrasonic echo of aluminum plate.The test results show that the signal amplitude generated by the butterfly coil is higher than that of the spiral coil,and the energy transfer efficiency is higher.The calibration function between the bolt axial stress and the transit time is established through the test of bolt stress measured by electromagnetic ultrasonic transducer.Compared with the measurement results of piezoelectric ultrasonic transducer,the two can achieve the same measurement accuracy level,but the electromagnetic ultrasonic transducer does not need coupling agent,the measurement process is more convenient,the measurement results are more stable.It lays a foundation for the application of electromagnetic ultrasonic detection of bolt stress.