| Air hole and shrinkage cavity are easy to occur in the welding of rail weld.The rail weld has to bear the rolling and impact of train wheels for a long time during its service,which makes the rail break easily.At present,in the aspect of rail health detection,the railway department mainly adopts the traditional ultrasonic detection method based on rail flaw detection vehicle.This detection method is used to detect the internal defects of rail,but the detection effect on the surface and near surface of complex parts such as rail weld,rail waist and rail bottom is poor or unable to detect.Structural Health Monitoring(SHM)technology based on Lamb wave has many advantages,such as low frequency,small energy attenuation,easy to pass through the weld area and sensitive to damage and so on.However,the amplitude and phase of Lamb signal fluctuate greatly due to the fixed mode of piezoelectric sensor,pressure and sensor performance,which seriously affects the rail weld damage monitoring.Therefore,the following research has been carried out in this paper.(1)Through a large number of experiments,the amplitude and phase error range of Lamb signal caused by human operation is obtained,which improves the reliability of the experiment.In this experiment,the amplitude and phase error ranges of Lamb wave signal are obtained as(0V,0.08V)and(0 μs,1 μs)respectively by repeatedly collecting Lamb wave signals,which are used as thresholds to judge whether there are differences between amplitude and phase of multiple response signals in subsequent experiments.(2)The effect of magnetic field on Lamb wave response signal is studied.In the process of research,the magnetic field has no effect on the amplitude and phase of the response signal received by piezoelectric sensor by comparing the magnetic field on the aluminum plate.Based on this,a new fixed mode of magnet fixed piezoelectric sensor is proposed for rail welding.It can not only guarantee the magnetic field of the magnet not to affect the Lamb wave signal,but also quantify the force magnitude of the piezoelectric sensor and ensure the simultaneous interpreting of the force of different sensors.The influence of pressure effect on piezoelectric sensor is deduced.The influence of pressure change on the amplitude and phase of the response signal of piezoelectric sensor is studied.The relationship between the amplitude and phase of ultrasonic signal and the change of pressure is obtained through experiments.Then it is concluded that the pressure fixed sensor(0.294 N,0.686 N)should be selected in the test,and the amplitude and phase of the response signal are in a relatively stable state.(3)The methods of compensation principle of sensor performance and pressure are studied.Compensation principle of sensor performance scheme based on mechanical coupling coefficient is proposed.The performance of each sensor in the equivalent path is compensated,and the compensation coefficient matrix of all sensors is obtained.According to the influence of changing pressure on Lamb wave signal,compensation principle of pressure scheme based on Hilbert transform is proposed.The amplitude compensation index is obtained by combining Hilbert transform with the pressure amplitude curve fitted by logistic model,and the phase compensation index is obtained according to the linear relationship between instantaneous phase difference and pressure difference.Finally,the pressure compensation scheme of Lamb wave under variable pressure is established.(4)A non benchmark damage monitoring method based on symmetrical mode is proposed.Experiments on the rail weld show that the method can realize the rail weld damage identification after the compensation principle of sensor performance and pressure processing data. |
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