A method for controlling propagation modes of ultrasonic guided waves in a steel rail based on excitation mode

Abstract

This invention provides a method for controlling the propagation modes of ultrasonic guided waves in rails based on excitation methods, belonging to the field of non-destructive testing. The method involves constructing a semi-analytical finite element model using the geometric and material parameters of the rail, determining the incident angle, excitation position, and signal phase difference, establishing a three-dimensional finite element model based on the determined incident angle, excitation position, and signal phase difference, calculating and verifying the excitation control effect. This invention employs the aforementioned method for controlling the propagation modes of ultrasonic guided waves in rails based on excitation methods. By controlling the incident angle, excitation position, and signal phase difference, it improves the excitation efficiency of the target mode, suppresses the generation of non-target modes, reduces noise signals and improves detection accuracy in field tests, and has promising application prospects.

Description

Technical Field

[0001] This invention belongs to the field of nondestructive testing, and in particular relates to a method for controlling the propagation mode of ultrasonic guided waves in rails based on excitation methods. Background Technology

[0002] In rail transit structures, steel rails bear alternating loads from trains over long periods, gradually accumulating internal damage that forms macroscopic defects and can even lead to rail breaks, affecting operational safety. Non-destructive testing (NDT), as a method for assessing structural integrity without causing damage, has gained widespread attention in the rail transportation industry in recent years. Among NDT methods, ultrasonic guided wave-based methods use a fixed device to excite ultrasonic guided waves within the rail, receiving and analyzing the signal characteristic changes as the ultrasonic signal passes through the structure. This approach enables full-section, long-distance, and continuous rail inspection, showing promising application prospects.

[0003] Ultrasonic guided waves are a special form of ultrasonic waves that propagate through a long, narrow waveguide medium, constantly undergoing reflection, refraction, and transverse-to-longitudinal wave conversion at the medium boundary. They possess dispersive and multimodal properties. Dispersive properties refer to the variation of the phase velocity and group velocity of the ultrasonic guided wave with frequency as it propagates in the medium. Multimodal properties refer to the property that ultrasonic guided waves can propagate in the medium with multiple modes coexisting within the structure.

[0004] A crucial aspect of ultrasonic guided wave testing is selecting specific modes for excitation based on structural and damage factors to enhance detection sensitivity. Due to the inherent properties of ultrasonic guided waves, target and non-target modes coexist within the structure. Excitation of non-target modes generates noise-like signals in the response signal, affecting damage identification. Therefore, designing appropriate ultrasonic guided wave excitation methods to suppress non-target mode excitation and improve the excitation efficiency of target modes is key to utilizing ultrasonic guided waves for rail structure testing. Summary of the Invention

[0005] The purpose of this invention is to provide a method for controlling the propagation mode of ultrasonic guided waves in rails based on excitation method. By controlling the incident angle, excitation position and signal phase difference, the excitation efficiency of the target mode is improved and the generation of non-target modes is suppressed. This method can reduce noise signals and improve detection accuracy in field tests and has good application prospects.

[0006] To achieve the above objectives, the present invention provides a method for controlling the propagation mode of ultrasonic guided waves in a rail based on the excitation method, comprising the following steps:

[0007] Determine the geometric and material parameters of the rail, and establish a semi-analytical finite element model in numerical simulation software;

[0008] Based on the semi-analytical finite element model, the ultrasonic guiding frequency range is selected, the corresponding frequency-wavenumber relationship, i.e. the dispersion curve, is calculated, and the displacement mode of each point cross section in the dispersion curve is generated. The target mode is determined based on the dispersion curve and the displacement mode.

[0009] The dispersion curve is converted into the relationship between frequency and phase velocity, i.e., the phase velocity curve. Then, the incident angle of the wedge block and the piezoelectric sensor is selected based on the phase velocity curve and Snell's law.

[0010] Based on the properties of ultrasound and the structural design of the rail, the excitation method is determined by the displacement mode of each point in the dispersion curve to obtain the excitation point with the highest efficiency of the target mode. The phase difference of the excitation signal is obtained based on the symmetry or antisymmetry of the displacement mode.

[0011] In numerical simulation software, a three-dimensional finite element model is established according to the determined frequency range, incident angle, and phase difference of the ultrasonic wave for calculation. The displacement distribution of the structural surface and cross-section during ultrasonic wave propagation is extracted to verify the target modal excitation control effect.

[0012] Preferably, the formula for calculating the incident angle is:

[0013] ;

[0014] In the formula, Indicates the angle of incidence. This represents the longitudinal wave velocity within the wedge. This represents the phase velocity of the target mode.

[0015] Preferably, in the method of exciting ultrasonic guided waves by fixing a piezoelectric sensor on the surface of the structure, the size of the excitation source is calculated as follows:

[0016] ;

[0017] In the formula, Indicates the size of the surface excitation source. Representation pattern Along the excitation direction on the rail surface The conjugate complex number of the vibration velocity, Indicates the target guided wave mode. and These represent two excitation directions. Indicates direction directional vector, Indicates rail The magnitude of stress at the location, Indicates rail The magnitude of the velocity at position, Representation pattern n Along the excitation direction on the rail surface The conjugate complex number of the stress, This indicates the range of influence of the excitation source on the rail surface.

[0018] Preferably, the excitation method is to use a pair of excitation methods that are symmetrical about the center.

[0019] Therefore, the present invention employs the above-mentioned method for controlling the propagation mode of ultrasonic guided waves in rails based on excitation method, and the technical effects are as follows:

[0020] Compared with existing technologies, this method can improve the excitation efficiency of target modes and suppress the excitation of non-target modes in ultrasonic guided wave detection, thereby reducing noise components in the response signal and improving detection accuracy.

[0021] Excitation methods for controlling target modes can be verified in numerical simulation software beforehand, which can reduce the trial and error costs of field experiments. Attached Figure Description

[0022] Figure 1 This is the rail phase velocity curve;

[0023] Figure 2 The target mode's frequency and phase velocity;

[0024] Figure 3 The cross-sectional displacement mode of the target mode;

[0025] Figure 4 This is a schematic diagram of the piezoelectric sensor arrangement;

[0026] Figure 5 This is a displacement contour map of the rail surface;

[0027] Figure 6 This is a displacement contour map of the rail cross section.

[0028] Figure Labels

[0029] 1. Rail; 2. Wedge block; 3. Piezoelectric sensor. Detailed Implementation

[0030] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0031] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0032] Example 1

[0033] This embodiment uses a 60kg / m steel rail as an example according to the GB / T2585-2021 standard. A method for controlling the propagation mode of ultrasonic guided waves in the steel rail based on excitation method includes the following steps:

[0034] A semi-analytical finite element (SAFE) model of the rail is established in numerical simulation software, and the corresponding material parameters are specified, such as density ρ, Young's modulus E, and Poisson's ratio µ.

[0035] Select an appropriate frequency range, calculate the corresponding frequency-wavenumber relationship, convert it to a frequency-phase velocity relationship, and then plot the phase velocity curve. In this embodiment, the frequency range is 0-100kHz, and the phase velocity curve is plotted as follows. Figure 1 As shown.

[0036] Based on the calculation results, cross-sectional displacement patterns for each mode are generated. In this embodiment, the rail head of rail 1 is to be inspected. The target modal parameters selected based on the phase velocity curve and displacement pattern are as follows: frequency 20 kHz, wave number 52.158 rad / m, and phase velocity 2409.3 m / s. Figure 2 As shown.

[0037] In this embodiment, a wedge-shaped organic polymer block is fixed on the surface of the rail 1, and a piezoelectric sensor 3 is fixed on the wedge block 2 to control the incident angle of the ultrasonic guided wave. The incident angle is calculated by substituting the parameters of the target mode into the incident angle calculation formula, so the specified angle is 52 degrees.

[0038] ;

[0039] In the formula, Indicates the angle of incidence. This represents the longitudinal wave velocity in wedge 2. This represents the phase velocity of the target mode.

[0040] Due to the inherent properties of ultrasonic guided waves, exciting the target mode will also excite non-target modes. Controlling the incident angle using wedge block 2 can limit the excitation mode within a certain range, but for complex structures, a more precise excitation method design is required. In this embodiment, the wedge block 2 and incident angle can excite both the target mode and some non-target modes. The parameters of the non-target modes are as follows: frequency 20 kHz, wavenumbers 47.739 rad / m, 48.06 rad / m, 52.955 rad / m, and 54.455 rad / m.

[0041] The purpose of designing the excitation method is to improve the excitation efficiency of the target mode while suppressing the excitation of non-target modes. When a single piezoelectric sensor 3 is fixed on the surface of the rail 1 to excite ultrasonic guided waves, the excitation source can be decomposed into a pair of excitations symmetrical along the central symmetry plane and a pair of excitations antisymmetric along the central symmetry plane. Therefore, during single-point excitation, ultrasonic guided waves with symmetrical displacement mode and antisymmetric displacement mode will exist simultaneously in the structure. Since a pair of excitations symmetrical along the central symmetry plane is used, the ultrasonic guided wave modes excited in the structure are also symmetrical modes, which can be used to suppress the excitation of non-target modes.

[0042] In this embodiment, the cross-sectional displacement mode of the target mode is as follows: Figure 3 As shown, the main displacement mode is vertical displacement, with the displacement region concentrated at the rail head of rail 1, and the displacement vector is symmetrical along the central vertical plane. Ultrasonic guided waves are excited by fixing piezoelectric sensors 3 on the structural surface. The size of the excitation source can be calculated using the following formula, thus allowing for the selection of locations with high excitation efficiency on the structural surface.

[0043] ;

[0044] In the formula, Indicates the size of the surface excitation source. Representation pattern Along the excitation direction on the rail surface The conjugate complex number of the vibration velocity, Indicates the target guided wave mode. and Indicates two excitation directions, Indicates direction directional vector, Indicates rail The magnitude of stress at the location, Indicates rail The magnitude of the velocity at position, Representation pattern n Along the excitation direction on the rail surface The conjugate complex number of the stress, This indicates the range of influence of the excitation source on the rail surface.

[0045] In this example, the non-target modes that need to be suppressed include a mode with a frequency of 20 (kHz) and a wave number of 47.739 (rad / m). The main displacement mode is torsional displacement, the displacement region is distributed across the entire cross section, and the vertical displacement vector is antisymmetric along the central vertical plane. The excitation of this mode can be suppressed by using an excitation method that is symmetric along the central vertical plane.

[0046] The non-target modes that need to be suppressed include a mode with a frequency of 20 kHz and a wave number of 48.06 rad / m. The main displacement mode is vertical displacement, the displacement region is concentrated at the bottom of rail 1, and the displacement vector is antisymmetric along the vertical plane of the center of rail 1. This mode can be suppressed by using an excitation method that is symmetric along the vertical plane of the center while the excitation point is far away from the bottom of the rail.

[0047] The non-target modes that need to be suppressed include a mode with a frequency of 20 (kHz) and a wave number of 52.955 (rad / m). The main displacement mode is lateral displacement, and the displacement region is concentrated in the rail head and rail web of rail 1. Furthermore, the displacement vector is antisymmetric along the vertical plane of the center of rail 1. This mode can be suppressed by using a method of symmetric excitation along the vertical plane of the center and vertical excitation.

[0048] The non-target modes that need to be suppressed include a mode with a frequency of 20 (kHz) and a wave number of 54.455 (rad / m). The main displacement mode is vertical displacement, the displacement region is concentrated at the bottom of rail 1, and the displacement vector is symmetrical about the center of rail 1. This mode can be suppressed by using an excitation method where the excitation point is far away from the bottom of the rail.

[0049] In this embodiment, the ultrasonic guided wave is excited by fixing the piezoelectric sensor 3 to the surface of the rail 1. Therefore, the displacement direction of the excitation point is the normal direction. Based on the above analysis, a pair of piezoelectric sensors 3 are arranged symmetrically perpendicularly to the center of the rail 1. The excitation point is located at the lower part of the rail head. The incident angle between the piezoelectric sensor 3 and the rail 1 is controlled to be 52 degrees by the wedge block 2, and the phase difference of the excitation signal is 0. The specific arrangement is as follows: Figure 4 As shown.

[0050] For the designed ultrasonic guided wave excitation mode control method, numerical simulation can be used to simulate the displacement state of the structure when the ultrasonic guided wave propagates in the structure, and to determine whether it is consistent with the displacement mode of the target mode, thereby verifying it in advance and reducing the error between theoretical calculation and field test. In this embodiment, a three-dimensional finite element model is established, and a wedge block 2 and a piezoelectric sensor 3 are established according to the designed excitation method. The excitation signal is input for calculation, and finally the calculation results are extracted for verification.

[0051] The surface displacement calculation results of the three-dimensional finite element model in this embodiment are as follows: Figure 5 As shown, the surface displacement of rail 1 is concentrated at the rail head, consistent with the displacement mode of the target mode. The cross-sectional displacement results are as follows. Figure 6 As shown, the cross-sectional displacement mode is consistent with the displacement mode of the target mode, indicating that the current excitation method is effective.

[0052] After verification by numerical simulation results, the field test can be conducted by arranging piezoelectric sensors 3 on rail 1 according to the design method to excite the target mode and detect the structure.

[0053] Therefore, the present invention adopts the above-mentioned method for controlling the propagation mode of ultrasonic guided waves in rails based on excitation method. By controlling the incident angle, excitation position and signal phase difference, the excitation efficiency of the target mode is improved and the generation of non-target modes is suppressed. It can reduce noise signals and improve detection accuracy in field tests and has good application prospects.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for controlling the propagation modes of ultrasonic guided waves in a rail based on excitation method, characterized in that, Includes the following steps: Determine the geometric and material parameters of the rail, and establish a semi-analytical finite element model in numerical simulation software; Based on the semi-analytical finite element model, the ultrasonic guiding frequency range is selected, the corresponding frequency-wavenumber relationship, i.e. the dispersion curve, is calculated, and the displacement mode of each point cross section in the dispersion curve is generated. The target mode is determined based on the dispersion curve and the displacement mode. The dispersion curve is converted into the relationship between frequency and phase velocity, i.e., the phase velocity curve. Then, the incident angle of the wedge block and the piezoelectric sensor is selected based on the phase velocity curve and Snell's law. Based on the properties of ultrasound and the structural design of the rail, the excitation method is determined by the displacement mode of each point in the dispersion curve to obtain the excitation point with the highest efficiency of the target mode. The phase difference of the excitation signal is obtained based on the symmetry or antisymmetry of the displacement mode. In numerical simulation software, a three-dimensional finite element model is established according to the determined frequency range, incident angle, and phase difference of the ultrasonic wave for calculation. The displacement distribution of the structural surface and cross-section during ultrasonic wave propagation is extracted to verify the target mode excitation control effect. The method for calculating the size of the excitation source in the case of fixing a piezoelectric sensor on the surface of a structure to excite ultrasonic guided waves is as follows: ； In the formula, Indicates the size of the surface excitation source. The mode n represents the direction of excitation on the rail surface. The conjugate complex number of the vibration velocity, where n represents the target guided wave mode, and u and w represent the two excitation directions, respectively. The direction vector representing the excitation direction w. Indicates rail The magnitude of stress at the location, Indicates rail The magnitude of the velocity at position, Let n be the conjugate complex number of the stress on the rail surface along the excitation direction w. This indicates the range of influence of the excitation source on the rail surface.

2. The method for controlling the propagation mode of ultrasonic guided waves in a rail based on excitation method according to claim 1, characterized in that, The formula for calculating the angle of incidence is: ； In the formula, Indicates the angle of incidence. This represents the longitudinal wave velocity within the wedge. This represents the phase velocity of the target mode.

3. The method for controlling the propagation mode of ultrasonic guided waves in a rail based on excitation method according to claim 1, characterized in that, The excitation method is a pair of excitation methods that are symmetrical about the center.

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