Guided Wave Based Non-destructive Method For Measuring Longitudinal Stress Of The High-speed Continuous Welded Rails

The operating mileage of high-speed railways in China has been advancing to a new level,which brings challenges to the sustainable and safe operation of railways.The longitudinal stress detection of continuous welded rails is an important basis for the safe operation of high-speed railways.Excessive longitudinal stress will lead to accidents such as rail expansion and rail breakage.As a new type of non-destructive measuring technology,guided waves have the advantages of being sensitive to stress,large detection range,long transmission,fast speed,etc.,which are very suitable for rail longitudinal stress inspection.In this paper,the influence of longitudinal rail stress on the guided wave characteristics is investigated,and a theoretical method for calculating rail longitudinal stress by using the variation of rail guided wave characteristics is given.The main research contents and conclusions of this paper are as follows:1.Guided wave dispersion curves in plates are solved by the analytical method and semi-analytical finite element method(SAFE)respectively.By comparing the overall and extracted propagation modes,it is proved that the SAFE method has more comprehensive solution results,which verifies the effectiveness of the SAFE method.2.Compensating the influence of temperature on elastic modulus,the SAFE method is used to solve the guide wave characteristics in rail.It is proved that the guide wave in the rail has obvious multi-mode and dispersion properties.All the propagation modes except the four propagation modes at low frequency have a cutoff frequency.And for the same medium propagation mode,its velocity tends to be stable as the frequency increases,which means that the dispersion phenomenon is weakened.3.The method of pattern orthogonality is used to classify the transmission patterns.It is proved that the longitudinal stress of rail does not change the trend of the dispersion curve.The dispersion properties(wave number,phase velocity and group velocity)of the guided wave have measurable variation under the action of stress,which can be used to detect the longitudinal stress of rail.However,the sensitivity of the dispersion properties to the longitudinal rail stress decrease as the frequency increases.4.Considering fully the sensitivity of guided wave dispersion properties to the longitudinal rail stress and the influence of mode shape on stress detection,an optimal mode selection model suitable for longitudinal rail stress detection was established.According to the results of the model calculation,the y direction of mode 3 at 35 k Hz is suitable for guided wave excitation to test longitudinal rail stress,which is consistent with the conclusions in the existing literature.5.Combining the nonlinear perturbation theory of structure with the guided wave characteristic equation,the nonlinear perturbation theory of guided wave was established,and the linear(first-order)approximation method,the high-order approximation method and the precise method of measuring the longitudinal rail stress variation by using the variation of guided wave properties were derived respectively.The error was smaller than the detection data in the existing literature.The longitudinal rail stress can be measured quickly and accurately only by measuring guided wave dispersion properties once,which provides a scientific basis for the longitudinal stress detection of rail.