Method for controlling propagation mode of ultrasonic guided wave in steel rail based on excitation mode

Abstract

The invention provides a method for controlling an ultrasonic guided wave propagation mode in a steel rail based on an excitation mode, which belongs to the field of nondestructive testing, and comprises the following steps: constructing a semi-analytical finite element model through geometric parameters and material parameters of the steel rail, and then determining an incident angle, an excitation position and a signal phase difference; and establishing a three-dimensional finite element model according to the determined incident angle, excitation position and signal phase difference, and calculating and verifying an excitation control effect. According to the method for controlling the propagation mode of the ultrasonic guided wave in the steel rail based on the excitation mode, the mode of controlling the incident angle, the excitation position and the signal phase difference is adopted, the excitation efficiency of a target mode is improved, generation of a non-target mode is restrained, noise signals can be reduced in a field test, the detection precision can be improved, and the method is suitable for popularization and application. Good application prospects are realized.

Description

Technical Field

[0001] The present invention belongs to the field of non-destructive testing, and in particular relates to a method for controlling ultrasonic guided wave propagation modes in rails based on an excitation mode. Background Art

[0002] In rail transit structures, rails bear constant alternating loads from trains, gradually accumulating damage within them, forming macroscopic defects and even causing breakage, impacting operational safety. Nondestructive testing, a non-destructive method for assessing structural integrity, has garnered widespread attention in the rail transit industry in recent years. Among nondestructive testing methods, those based on the principle of ultrasonic guided waves use a fixed device to excite ultrasonic guided waves within the rails, receiving and analyzing changes in the ultrasonic signal's characteristics as it passes through the structure. This allows for full-section, long-distance, and uninterrupted testing of rails, and holds great promise for future applications.

[0003] Ultrasonic guided waves are a special form of ultrasonic wave propagation in a long waveguide medium, resulting from continuous reflection, refraction, and conversion between transverse and longitudinal waves at the medium's boundaries. They exhibit both dispersive and multimodal properties. Dispersion refers to the frequency-dependent variation of the phase and group velocities of ultrasonic guided waves. Multimodality refers to the coexistence of multiple modes within a structure.

[0004] A key step in ultrasonic guided wave testing is selecting specific modes for excitation based on factors such as structure and damage, thereby improving detection sensitivity. Due to the inherent properties of ultrasonic guided waves, both target and non-target modes coexist within a structure. Excitation of non-target modes can generate noise-like signals in the response signal, hindering damage identification. Therefore, designing appropriate ultrasonic guided wave excitation methods to suppress the excitation of non-target modes and improve the excitation efficiency of target modes is crucial for using ultrasonic guided waves to inspect rail structures. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for controlling the propagation mode of ultrasonic guided waves in rails based on the excitation method. By controlling the incident angle, excitation position and signal phase difference, the excitation efficiency of the target mode is improved, the generation of non-target modes is suppressed, and the noise signal can be reduced and the detection accuracy can be improved in field tests. The method 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 an excitation mode, comprising 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 frequency range of the ultrasonic waveguide is selected, the corresponding frequency-wavenumber relationship, i.e., the dispersion curve, is calculated, and the displacement pattern of the cross section at each point in the dispersion curve is generated. The target mode is determined based on the dispersion curve and the displacement pattern. The dispersion curve is converted into the relationship between frequency and phase velocity, i.e., the phase velocity curve. Then, the incident angles of the wedge block and the piezoelectric sensor are selected based on the phase velocity curve and Snell's law. According to the properties of ultrasonic waves and the excitation mode of the rail structure design, the excitation point with the highest target modal efficiency is obtained through the displacement pattern of the cross section at each point in the dispersion curve, and the phase difference of the excitation signal is obtained according to the symmetry or antisymmetry of the displacement pattern; In the numerical simulation software, a three-dimensional finite element model is established for calculation according to the determined frequency range, incident angle, and phase difference of the ultrasonic wave. The displacement distribution of the structure surface and cross-section during the propagation of ultrasonic guided waves is extracted to verify the target mode excitation control effect.

[0007] Preferably, the calculation formula of the incident angle is: ; Where, represents the angle of incidence, represents the longitudinal wave velocity in the wedge, represents the phase velocity of the target mode.

[0008] Preferably, in a method of fixing a piezoelectric sensor on the surface of the structure to excite ultrasonic guided waves, the size of the excitation source is calculated as follows: ; Where, represents the size of the surface excitation source, Representation Mode On the rail surface along the excitation direction The conjugate complex number of the vibration velocity, represents the target waveguide mode, and represent the two excitation directions, Indicates direction The direction vector, Indicates rail The stress magnitude at the location, Indicates rail The velocity of the position, Representation Mode n On the rail surface along the excitation direction The conjugate complex number of the stress, Indicates the range of action of the excitation source on the rail surface.

[0009] Preferably, the excitation mode is a pair of excitation modes that are symmetrical along the center.

[0010] Therefore, the present invention adopts the above-mentioned method for controlling the propagation mode of ultrasonic guided waves in rails based on the excitation mode, and the technical effects are as follows: Compared with existing technologies, the proposed method can improve the excitation efficiency of target modes in ultrasonic guided wave detection and suppress the excitation of non-target modes, thereby reducing the noise component in the response signal and improving detection accuracy.

[0011] The excitation method used to control the target mode can be verified in advance in numerical simulation software, which can reduce the trial and error cost of field tests. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is the rail phase velocity curve; Figure 2 are the frequency and phase velocity of the target mode; Figure 3 is the cross-sectional displacement pattern of the target mode; Figure 4 Schematic diagram of the piezoelectric sensor layout; Figure 5 is the displacement cloud map of the rail surface; Figure 6 It is the displacement cloud diagram of rail cross section.

[0013] Reference numerals 1. Rail; 2. Wedge block; 3. Piezoelectric sensor. DETAILED DESCRIPTION

[0014] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0015] Unless otherwise defined, technical or scientific terms used in the present invention shall have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

[0016] Example 1 In this embodiment, a method for controlling the propagation mode of ultrasonic guided waves in the rail based on an excitation method is implemented using a 60 kg / m rail in the GB / T2585-2021 specification, including the following steps: A semi-analytical finite element (SAFE) model of rail 1 is established in the numerical simulation software, and the corresponding material parameters, such as density ρ, Young's elastic modulus E, and Poisson's ratio µ, are specified.

[0017] Select an appropriate frequency range to calculate the corresponding frequency-wave number relationship and convert it into a frequency-phase velocity relationship, and then draw a phase velocity curve. In this embodiment, the frequency range is 0-100kHz phase velocity curve, as shown in FIG. Figure 1 shown.

[0018] The cross-sectional displacement patterns of each mode are generated based on the calculation results. In this embodiment, the rail head of rail 1 is tested. The target modal parameters selected by combining the phase velocity curve and the displacement pattern are as follows: frequency 20 (kHz), wave number 52.158 (rad / m), phase velocity 2409.3 (m / s), as shown in the following figure. Figure 2 shown.

[0019] This embodiment uses a wedge-shaped organic polymer block fixed on the surface of the rail 1 and a piezoelectric sensor 3 fixed on the wedge block 2 to control the incident angle of the ultrasonic guided wave. The incident angle calculation formula is substituted into the parameters of the target mode to calculate the matching incident angle, so the specified angle is 52 degrees.

[0020] ; Where, represents the angle of incidence, represents the longitudinal wave velocity in wedge 2, represents the phase velocity of the target mode.

[0021] Due to the inherent properties of ultrasonic guided waves, exciting the target mode also excites non-target modes. Controlling the incident angle using wedge 2 can keep the excited modes within a certain range, but complex structures require more sophisticated excitation design. The wedge 2 and incident angle used in this embodiment can excite modes including the target mode and some non-target modes. The parameters of the non-target modes are as follows: a frequency of 20 kHz, and wavenumbers of 47.739 rad / m, 48.06 rad / m, 52.955 rad / m, and 54.455 rad / m, respectively.

[0022] 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 the ultrasonic guided wave, the excitation source can be decomposed into a pair of symmetrical excitations along the central symmetry plane and a pair of antisymmetric excitations along the central symmetry plane. Therefore, when a single point is excited, ultrasonic guided waves with symmetrical displacement modes and antisymmetric displacement modes will coexist in the structure. However, by using a pair of excitations along the center, it can be seen that the ultrasonic guided wave mode excited in the structure is also a symmetrical mode, which can be used to suppress the excitation of non-target modes.

[0023] The cross-sectional displacement pattern of the target mode in this embodiment is as follows: Figure 3 As shown, the primary displacement mode is vertical, concentrated at the head of rail 1, and the displacement vector is symmetrical along the central vertical plane. By fixing a piezoelectric sensor 3 on the structure surface to excite ultrasonic guided waves, the size of the excitation source can be calculated using the following formula, allowing for the selection of a location on the structure surface with high excitation efficiency.

[0024] ; Where, represents the size of the surface excitation source, Representation Mode On the rail surface along the excitation direction The conjugate complex number of the vibration velocity, represents the target waveguide mode, and represents two excitation directions, Indicates direction The direction vector, Indicates rail The stress magnitude at the location, Indicates rail The velocity of the position, Representation Mode n On the rail surface along the excitation direction The conjugate complex number of the stress, Indicates the range of action of the excitation source on the rail surface.

[0025] 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 area is distributed over 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.

[0026] The non-target modes that need to be suppressed include the 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 area is concentrated at the bottom of rail 1, and the displacement vector is antisymmetric along the vertical plane at the center of rail 1. The excitation of this mode can be suppressed by using an excitation method that is symmetric along the vertical plane at the center and the excitation point is far away from the bottom of the rail.

[0027] The non-target modes that need to be suppressed include the modes 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 area is concentrated on the rail head and rail waist of rail 1. The displacement vector is antisymmetric along the vertical plane of the center of rail 1. The excitation of this mode can be suppressed by using a method of symmetry along the vertical plane and simultaneous vertical excitation.

[0028] The non-target modes that need to be suppressed include the 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 area is concentrated at the bottom of rail 1, and the displacement vector is symmetrical along the vertical plane of the center of rail 1. The excitation method of moving the excitation point away from the bottom of the rail can be used to suppress the excitation of this mode.

[0029] In this embodiment, the ultrasonic guided wave is excited by fixing the piezoelectric sensor 3 on the surface of the rail 1, so the displacement direction of the excitation point is normal. According to the above analysis, a pair of piezoelectric sensors 3 are arranged symmetrically along the vertical plane of the center of the rail 1, and the position of the excitation point is the lower part of the rail head. The incident angle between the piezoelectric sensor 3 and the rail 1 is controlled by the wedge block 2 to be 52 degrees, and the phase difference of the excitation signal is 0. The specific arrangement is as follows: Figure 4 shown.

[0030] The designed ultrasonic guided wave excitation modal control method can be verified in advance using numerical simulation methods to simulate the displacement state of the structure as the ultrasonic guided waves propagate through the structure. This method can then be used to determine whether the displacement pattern matches the target modal pattern. This method is then used to reduce the error between theoretical calculations and field tests. In this embodiment, a three-dimensional finite element model is established. The wedge block 2 and piezoelectric sensor 3 are constructed according to the designed excitation method. The excitation signal is then input for calculation, and the calculated results are extracted for verification.

[0031] 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 on the rail head, which is consistent with the displacement mode of the target mode. The cross-sectional displacement results are as follows: Figure 6 As shown in Figure 3, the cross-sectional displacement pattern is also consistent with the displacement pattern of the target mode, and it can be considered that the current design excitation method is effective.

[0032] After verification by the numerical simulation results, the field test can arrange the piezoelectric sensor 3 on the rail 1 according to the design method to stimulate the target mode to detect the structure.

[0033] Therefore, the present invention adopts the above-mentioned method of controlling the propagation mode of ultrasonic guided waves in the rail based on the excitation method, and adopts the method of controlling the incident angle, excitation position and signal phase difference to improve the excitation efficiency of the target mode and suppress the generation of non-target modes. It can reduce noise signals and improve detection accuracy in field tests, and has good application prospects.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements 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 ultrasonic guided wave propagation modes in rails based on an excitation method, characterized in that: The following steps are involved: 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 frequency range of the ultrasonic waveguide is selected, the corresponding frequency-wavenumber relationship, i.e., the dispersion curve, is calculated, and the displacement pattern of the cross section at each point in the dispersion curve is generated. The target mode is determined based on the dispersion curve and the displacement pattern. The dispersion curve is converted into the relationship between frequency and phase velocity, i.e., the phase velocity curve. Then, the incident angles of the wedge block and the piezoelectric sensor are selected based on the phase velocity curve and Snell's law. According to the properties of ultrasonic waves and the excitation mode of the rail structure design, the excitation point with the highest target modal efficiency is obtained through the displacement pattern of the cross section at each point in the dispersion curve, and the phase difference of the excitation signal is obtained according to the symmetry or antisymmetry of the displacement pattern; In the numerical simulation software, a three-dimensional finite element model is established for calculation according to the determined frequency range, incident angle, and phase difference of the ultrasonic wave. The displacement distribution of the structure surface and cross-section during the propagation of ultrasonic guided waves is extracted to verify the target mode excitation control effect.

2. The method for controlling ultrasonic guided wave propagation modes in rails based on an excitation method according to claim 1, characterized in that: The formula for calculating the angle of incidence is: ； Where, represents the angle of incidence, represents the longitudinal wave velocity in the wedge, represents the phase velocity of the target mode.

3. The method for controlling ultrasonic guided wave propagation modes in rails based on excitation mode according to claim 1, characterized in that: The method of fixing the piezoelectric sensor on the surface of the structure to excite the ultrasonic guided wave, the size of the excitation source is calculated as follows: ； Where, represents the size of the surface excitation source, Representation Mode On the rail surface along the excitation direction The conjugate complex number of the vibration velocity, represents the target waveguide mode, and represent the two excitation directions, Indicates the excitation direction The direction vector, Indicates rail The stress magnitude at the location, Indicates rail The velocity of the position, Indicates that mode n is on the rail surface along the excitation direction The conjugate complex number of the stress, Indicates the range of action of the excitation source on the rail surface.

4. The method for controlling ultrasonic guided wave propagation modes in rails based on an excitation method according to claim 1, characterized in that: The excitation method is to use a pair of excitation methods that are symmetrical along the center.

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