An efficient positioning and detection method for small-size defects on rail bottom

Abstract

The invention discloses an efficient positioning detection method for small-size defects on the bottom of a rail, comprising manufacturing a PZT flexible sensor array that can be attached to the surface of the bottom of the rail, combining a laser ultrasonic rail bottom waveguide dispersion curve, optimizing the rail bottom detection area of ​​the laser-PZT array through simulation, using a laser-PZT array system to detect lossy array waveguide signals and lossless array waveguide signals in the same rail bottom surface area, and performing wavelet packet decomposition and noise reduction filtering on the collected multi-path waveguide signals, comparing the waveguide signals under the same path with and without loss, and making a difference based on the maximum wave packet peak-to-peak value, the path with the maximum difference value is where the damage is located, performing wavelet packet filtering and noise reduction on the collected multi-path waveguide signals, and making a difference based on the maximum wave packet peak-to-peak value, judging the path where the damage is located by the difference value, and realizing efficient detection of small-size damage on the rail bottom surface without relying on multi-modal differentiation of waveguides and measurement of wave velocity, thereby providing a reference for efficient and automated detection of rail bottoms.

Description

Technical Field

[0001] The invention relates to the technical field of nondestructive testing, and in particular to a method for efficiently positioning and detecting small-size defects on a rail bottom. Background Art

[0002] The rail bottom is one of the most important parts of railway infrastructure. Harsh working environment can easily cause damage to the rail bottom. Among them, smaller defects are more dangerous than common transverse cracks because they are more difficult to detect due to their small size. As the defects expand, they will seriously affect the safety of train operation. Therefore, it is necessary to conduct non-destructive testing of small-scale damage on the rail bottom in a timely manner to ensure the safety of railway operation. Existing flaw detection vehicles have a blind spot for the outer area of ​​the rail bottom (because the ultrasonic wave of the flaw detection vehicle fails to propagate to this area, it cannot detect the damage in this area).

[0003] Traditional guided wave detection mainly uses low-frequency guided waves to achieve long-distance and large-scale detection, but it is only sensitive to large defects and cannot identify pitting defects. Therefore, it is urgent to combine the advantages of different detection technologies to study an efficient method for detecting small-size defects on the rail bottom to ensure rail safety. Summary of the invention

[0004] The purpose of this section is to summarize some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the specification abstract and the invention title of this application to avoid blurring the purpose of this section, the specification abstract and the invention title, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0005] In view of the above and / or existing problems in the existing rail bottom wave detection, the present invention is proposed.

[0006] Therefore, the purpose of the present invention is to provide a method for efficiently locating and detecting small-sized defects on the bottom of a rail, which can collect damage characteristics of small defects on the bottom of the rail under a certain area, and realize efficient detection of small-sized damage on the surface of the bottom of the rail.

[0007] To solve the above technical problems, according to one aspect of the present invention, the present invention provides the following technical solutions:

[0008] An efficient positioning and detection method for small-size defects on the bottom of a rail, comprising:

[0009] S1. Make a PZT flexible sensor array that can be attached to the bottom surface of the rail;

[0010] S2, combining the dispersion curve of laser ultrasonic rail bottom guided wave, and optimizing the laser-PZT array rail bottom detection area through simulation;

[0011] S3, using a laser-PZT array system to detect lossy array waveguide signals and lossless array waveguide signals in the same rail bottom surface area;

[0012] S4. Perform wavelet packet decomposition and noise reduction filtering on the collected multi-path waveguide signals, compare the waveguide signals under the same path with and without damage, and make a difference with the maximum wave packet peak-to-peak value, draw a fitting curve of the path-difference value, and the path with the maximum difference value is where the damage is.

[0013] As a preferred solution of the method for efficiently locating and detecting small-size defects on the bottom of a rail described in the present invention, the conductors of the PZT flexible sensing array are a non-crossed single-layer electrode structure with a line spacing of 1 mm, and the line width of the conductors is 1 mm.

[0014] As a preferred solution of the method for efficiently locating and detecting small-size defects at the bottom of a rail according to the present invention, in step S2, the specific steps of combining the dispersion curve of laser ultrasonic guided waves and optimizing the bottom detection area of ​​the laser-PZT array rail by simulation are as follows:

[0015] S201. Draw the dispersion curve of the rail bottom according to the damage size requirements of the rail bottom, and select the appropriate central frequency band of the guided wave detection;

[0016] S202. Based on the lateral length of the rail bottom surface and combined with laser pulse excitation, multiple excitations can be achieved in a short time. A 10x5 laser sensor array is designed, in which 10 laser excitation points are arranged in a row and 5 sensors are designed in the same row.

[0017] S203. Through simulation, a three-dimensional model of the rail is established to simulate the interaction between the laser ultrasonic guided wave and the rail bottom damage, and optimize the layout of the laser-PZT detection array.

[0018] As a preferred solution of the method for efficiently locating and detecting small-size defects at the bottom of a rail according to the present invention, the laser-PZT array system comprises:

[0019] PZT flexible sensor array collects the lossy array waveguide signal and lossless array waveguide signal at the bottom of the rail;

[0020] An ultrasonic preamplifier is connected to the PZT flexible sensor array to amplify the lossy array waveguide signal and the lossless array waveguide signal collected by the PZT flexible sensor array;

[0021] The NI acquisition card is connected to the ultrasonic preamplifier and the control unit, and receives the amplified lossy array waveguide signal and the lossless array waveguide signal or the signal output by the control unit;

[0022] The terminal is connected to the NI acquisition card and the control unit, and receives data transmitted by the NI acquisition card or the control unit;

[0023] A control unit, connected to the laser and the galvanometer, for sending a control signal to the laser or controlling the deflection angle of the galvanometer;

[0024] The laser receives the control signal from the control unit and emits a laser beam to the galvanometer;

[0025] The galvanometer receives the laser beam emitted by the laser and focuses the laser beam at the position collected by the PZT flexible sensor array.

[0026] As a preferred solution of the method for efficiently locating and detecting small-size defects on the bottom of a rail according to the present invention, in step S4, the specific steps of performing wavelet packet decomposition and noise reduction filtering on the collected multi-path waveguide signals are as follows:

[0027] S401, selecting Dmey wavelet as the wavelet packet basis function to perform 5-layer decomposition on the waveguide signal to obtain 32 components with different frequencies;

[0028] S402, solve the ratio p of each sub-band energy value to the total energy value at different decomposition scales according to the following formula i ,

[0029]

[0030] Among them, E i is the energy of the mth node in the jth layer, m represents the total number of sub-bands, E sum is the total signal energy;

[0031] S403, selecting the first n signal frequency bands whose energy ratio sum is greater than 95%, and adding the n signals to obtain the final waveguide signal f after noise reduction filtering.

[0032] Compared with the prior art, the present invention has the following beneficial effects: the present invention combines the advantages of laser ultrasonic technology and the lateral dimensions of the rail bottom to establish a laser-PZT array rail bottom detection system, and optimizes the laser-PZT array rail bottom detection area through simulation, collects the guided wave signals of small-sized damage on the rail bottom surface, and finally performs wavelet packet filtering and noise reduction on the collected multi-path guided wave signals, and makes a difference with the maximum wave packet peak-to-peak value, and judges the path where the damage is located by the differential value, and can realize efficient detection of small-sized damage on the rail bottom surface without relying on guided wave multi-modal differentiation and wave velocity measurement, providing a reference for efficient and automated detection of rail bottom. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the present invention will be described in detail below in combination with the accompanying drawings and detailed embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative labor. Among them:

[0034] Figure 1 This is a flow chart of a method for efficiently locating and detecting small-size defects at the bottom of a rail according to the present invention;

[0035] Figure 2 A schematic diagram of the structure of a PZT flexible array sensor for a high-efficiency positioning detection method for small-size defects at the bottom of a rail according to the present invention;

[0036] Figure 3 A laser ultrasonic guided wave dispersion curve of a rail bottom of the present invention for a highly efficient positioning detection method for small-size defects of a rail bottom;

[0037] Figure 4 A simulated cloud diagram of the interaction between guided waves and rail bottom damage at the same time of a high-efficiency positioning detection method for small-size defects at the bottom of a rail according to the present invention;

[0038] Figure 5 A schematic diagram of the optimized layout of the laser-PZT array sensor at the rail bottom of the present invention for a high-efficiency positioning detection method for small-size defects at the rail bottom;

[0039] Figure 6 This is a diagram of a laser-PZT array detection experimental system for a highly efficient positioning detection method for small-size defects at the bottom of a rail according to the present invention;

[0040] Figure 7 The time domain and frequency domain diagrams of the laser-PZT waveguide signal of the high-efficiency positioning detection method for small-size defects at the bottom of a rail according to the present invention;

[0041] Figure 8 It is a diagram showing the energy proportions of different frequency bands after wavelet packet decomposition of a high-efficiency positioning detection method for small-size defects on the bottom of a rail according to the present invention;

[0042] Fig. 9 It is a time domain response comparison diagram of E3 corresponding to S1-S5 in non-destructive and destructive conditions of an efficient positioning detection method for small-size defects on the rail bottom of the present invention. DETAILED DESCRIPTION

[0043] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0044] Secondly, the present invention is described in detail with reference to schematic diagrams. When describing the embodiments of the present invention in detail, for the sake of convenience, the cross-sectional diagrams showing the device structure will not be partially enlarged according to the general scale, and the schematic diagrams are only examples, which should not limit the scope of protection of the present invention. In addition, in actual production, the three-dimensional dimensions of length, width and depth should be included.

[0045] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0046] The present invention provides a highly efficient positioning and detection method for small-sized defects on the rail bottom, which can collect damage characteristics of small defects on the rail bottom under a certain area, and realize highly efficient detection of small-sized damage on the rail bottom surface.

[0047] See also Figure 1-Figure 9 The specific steps of this method for efficiently locating and detecting small-size defects on the bottom of rails are as follows:

[0048] S1. Prepare a PZT flexible sensor array that can be attached to the bottom surface of the rail, wherein the flexible sensor array is a single-layer node array structure, including a PZT sensor, a flexible printed circuit (FPC) and a polyimide film, such as Figure 2 As shown. In order to improve the signal-to-noise ratio, all wires in the array are designed as non-crossing single-layer electrode structures with a line spacing of 1mm. The wire width is designed to be 1mm. In addition, 150μm polyimide flexible material is used as a substrate because of its strong heat resistance, which is conducive to the welding of PZT piezoelectric sensors. The electrode is a copper disc with a diameter of 2.5mm and a thickness of 35μm. In order to stabilize the contact impedance between the electrode and the sensor electrode, the electrode surface is plated with a 2μm thick nickel layer and a 0.035μm thick gold layer. Finally, the FPC technology is used to make the electrode array. At the same time, in order to reduce bending deformation, rolled copper is used to make surface pads and traces, and the PZT chip is fixed to the wire contacts of the circuit layer by solder. Then, epoxy adhesive is placed around the sensor for insulation and mechanical protection. After determining the relative position of the excitation sensor, the array is adhered to the bottom surface of the rail with epoxy adhesive. The flexible array board is connected to the signal amplification module through FPC, and the interface is reinforced with PCB wiring to make the interface width reach 0.25mm, so that the electrode can be tightly connected to the buckle.

[0049] S2. Combining the dispersion curve of the laser ultrasonic rail bottom waveguide, and optimizing the laser-PZT array rail bottom detection area through simulation, in this embodiment, the specific steps include:

[0050] S201. According to the requirements of the damage size of the rail bottom, draw the dispersion curve of the rail bottom and select the appropriate central frequency band of the guided wave detection; the rail bottom can be regarded as a thick steel plate with a thickness of 15 mm, and the dispersion curve is as follows: Figure 3The dispersion curve is used to obtain the phase velocity c in the guided wave. p and group velocity c g , the speed of the wave packet composed of multi-modal waves is c g , and the velocity of a particle at a fixed phase on the wave packet is c p .c g and c p Can be converted to each other:

[0051]

[0052] Substitute ω=2πf into the above formula:

[0053]

[0054] Where fd represents the frequency-thickness product, c g When it approaches zero, it is the cut-off frequency.

[0055] Since the size of the small damage to be detected is 1mm, according to the principle that the minimum size that can be detected by ultrasound is half of the wavelength, a high-frequency ultrasonic signal of 2-3MHz is selected as the detection center frequency band, such as Figure 3 As shown, at this time, the guided wave signal tends to be a surface wave and there is no dispersion phenomenon.

[0056] S202. Based on the lateral length of the rail bottom surface and combined with laser pulse excitation, multiple excitations can be achieved in a short time. A 10x5 laser sensor array is designed, in which 10 laser excitation points are arranged in a row and 5 sensors are designed in the same row.

[0057] S203. Through simulation, a three-dimensional model of the rail is established to simulate the interaction between the laser ultrasonic waveguide and the rail bottom damage, and optimize the layout of the laser-PZT detection array. In this embodiment, Abaqus software is used to assist in this research. The simulation model is an A60 rail with a length of 20 cm. An artificial pitting defect, i.e., a circular defect with a diameter of 1 mm, is preset at the bottom of the rail to study the interaction between the waveguide and the defect and optimize the layout of the array. Figure 4 As shown in the figure, Gaussian pulse laser is applied as excitation at the center of the rail bottom, the laser spot radius is 0.5 mm, and the laser power density is 1×10 12 W / m 2 , the material light absorption coefficient is 0.37. Mesh division includes mesh size, dense mesh size and transition mesh size. The minimum mesh size is 0.08mm and the maximum mesh size is 0.5mm. Dense mesh is used to divide the laser action area and the main sound wave propagation area. Other non-main areas are wide meshes, and transition meshes are used between the two. The simulation time step is 2ns, the total time is 20us, and the initial value of the temperature during the simulation is set to 300K.

[0058] Figure 4 The cloud diagram of the interaction between guided waves and damage at two different times is shown. During the propagation of waves, there is a difference between the propagation of lossy guided waves and lossless guided waves, and the change of transmitted waves is quite different. As shown by the dotted box in the figure, when there is loss, the attenuation of the transmitted wave is more obvious. Therefore, if the sensor is installed on the side of the transmitted wave, it is easier to detect the guided waves induced by defects. In addition, the wires will also take up a certain amount of space. Considering the limited space at the bottom of the rail, for each row of sensors, 5 PZT sensors are densely arranged, such as Figure 5 As shown in Figure 1, this can ensure the detectability of the proposed array layout for early extended damage. In addition, since high-frequency ultrasonic signals decay quickly, the distance between the excitation and receiving points should not be too large. Combined with the advantages of pulsed laser excitation, the final array detection range is as follows: Figure 5 As shown in (b), the detection range is a rectangle of 45mm*50mm, there are 10 laser excitation points in a row, the distance between points is 4.5mm, there are 5 sensors in a row, and the starting end E1 and the terminal end E2 of the laser excitation source are consistent with the center positions of sensors S1 and S5 respectively.

[0059] S3. Use the laser-PZT array system to detect the lossy array waveguide signal and the lossless array waveguide signal in the same rail bottom surface area. In this embodiment, the laser uses a pulsed laser with a wavelength of 1064nm, a repetition frequency of 10Hz, and a pulse width of 8ns. The flexible sensor array contains 5 PZT sensors, which are attached to the rail bottom surface with epoxy adhesive, and then connected to an ultrasonic preamplifier to amplify the waveguide signal, and finally received by a NI acquisition card with a sampling frequency of 100MHz. The system controls the output of the laser, the movement of the galvanometer, and the acquisition of the acquisition card through a single-chip microcomputer control circuit. There are 10 excitation points in a row, with a spot diameter of 0.2mm and a distance of 4.5mm between points. The starting end E1 and the terminal end E2 of the laser excitation source are consistent with the center positions of sensors S1 and S5 respectively. Each time the laser is excited, the five PZT sensors receive signals at the same time. The laser-PZT array system is as follows Figure 6As shown, it includes a PZT flexible sensor array, an ultrasonic preamplifier, a NI acquisition card, a terminal, a control unit, a laser and a galvanometer. The PZT flexible sensor array collects lossy array waveguide signals and lossless array waveguide signals at the bottom of the rail. The ultrasonic preamplifier is connected to the PZT flexible sensor array to amplify the lossy array waveguide signals and lossless array waveguide signals collected by the PZT flexible sensor array. The NI acquisition card is connected to the ultrasonic preamplifier and the control unit to receive the amplified lossy array waveguide signals and lossless array waveguide signals or the signals output by the control unit. The terminal is connected to the NI acquisition card and the control unit to receive data transmitted by the NI acquisition card or the control unit. The control unit is connected to the laser and the galvanometer to send a control signal to the laser or control the deflection angle of the galvanometer. The laser receives the control signal of the control unit and sends a laser beam to the galvanometer. The galvanometer receives the laser beam sent by the laser and focuses the laser beam on the position collected by the PZT flexible sensor array.

[0060] S4, performing wavelet packet decomposition and noise reduction filtering on the collected multi-path waveguide signals, comparing the waveguide signals under the same path with and without damage, and taking the maximum wave packet peak value as the difference, and drawing a fitting curve of the path-difference value. The path with the maximum difference value is where the damage is. In this implementation mode, the frequency domain analysis is performed on the experimentally acquired signals. Figure 7 It is the original signal of laser ultrasonic guided wave under a certain path. It can be clearly seen that the time domain signal of the guided wave is disordered and there is high-frequency noise. Therefore, the wavelet packet decomposition algorithm is further used to filter and reduce the noise of the collected signal. Figure 8 It is the distribution of energy ratio of each frequency band after wavelet packet decomposition. The frequency band with total energy ratio greater than 95% is the first 16 sub-bands. Therefore, the subsequent analysis signal is obtained by superposition and recombination of the first 16 sub-band signals. The wavelet packet filtering algorithm used in this study specifically includes: selecting Dmey wavelet as the wavelet packet basis function to decompose the waveguide signal in 5 layers to obtain 32 components of different frequencies, and solving the ratio of each sub-band energy value to the total energy value at different decomposition scales according to the following formula: i ;

[0061]

[0062] Among them, E i is the energy of the mth node in the jth layer, m represents the total number of sub-bands, E sum is the total signal energy.

[0063] The first n signal frequency bands whose energy ratio sum is greater than 95% are selected, and the n signals are added together to obtain the final waveguide signal f after noise reduction filtering.

[0064] After obtaining the noise-reduced signal, compare the changes in the corresponding lossy and lossless waveguide signals under the same path, such as Fig. 9As shown in the figure, it is obvious that after the defect exists, the waveguide signals of each path are disturbed, which is reflected in the obvious reduction of the amplitude. Therefore, the peak-to-peak value of the wave packet of the waveguide signal of each path can be obtained, and lossy and lossless differences can be made. By drawing the path-difference value fitting curve, it can be known that the path corresponding to the maximum value is the main location of the small-size damage, thereby realizing the rapid positioning of the damage.

[0065] The present invention combines the advantages of laser ultrasonic technology and the lateral size of the rail bottom to establish a laser-PZT array rail bottom detection system, and optimizes the laser-PZT array rail bottom detection area through simulation, collects the guided wave signals of small-sized damage on the rail bottom surface, and finally performs wavelet packet filtering and noise reduction on the collected multi-path guided wave signals, and makes a difference with the maximum wave packet peak-to-peak value, and judges the path where the damage is located by the differential value. In addition, it can realize efficient detection of small-sized damage on the rail bottom surface without relying on guided wave multi-modal differentiation and wave velocity measurement, providing a reference for efficient and automated detection of rail bottom.

[0066] Although the present invention has been described above with reference to the embodiments, various modifications may be made thereto and parts thereof may be replaced by equivalents without departing from the scope of the present invention. In particular, as long as there is no structural conflict, the various features in the embodiments disclosed in the present invention may be used in combination with each other in any manner, and the fact that these combinations are not exhaustively described in this specification is only for the sake of omitting space and saving resources. Therefore, the present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. An efficient positioning and detection method for small-size defects on the bottom of a rail, characterized in that: include: S1. Make a PZT flexible sensor array that can be attached to the bottom surface of the rail; S2, combining the dispersion curve of laser ultrasonic rail bottom guided wave, and optimizing the laser-PZT array rail bottom detection area through simulation; S3, using a laser-PZT array system to detect lossy array waveguide signals and lossless array waveguide signals in the same rail bottom surface area; S4, performing wavelet packet decomposition and noise reduction filtering on the collected multi-path waveguide signals, comparing the waveguide signals under the same path with and without damage, and taking the maximum wave packet peak value as the difference, and drawing a fitting curve of the path-difference value, the path with the maximum difference value is where the damage is; In step S2, the specific steps of combining the laser ultrasonic guided wave dispersion curve and optimizing the laser-PZT array rail bottom detection area through simulation are as follows: S201. Draw the dispersion curve of the rail bottom according to the damage size requirements of the rail bottom, and select the appropriate central frequency band of the guided wave detection; S202. Based on the lateral length of the rail bottom surface and combined with laser pulse excitation, multiple excitations can be achieved in a short time. A 10x5 laser sensor array is designed, in which 10 laser excitation points are arranged in a row and 5 sensors are designed in the same row. S203, establishing a three-dimensional model of the rail through simulation, simulating the interaction between the laser ultrasonic guided wave and the rail bottom damage, and optimizing the layout of the laser-PZT detection array; The laser-PZT array system comprises: PZT flexible sensor array collects the lossy array waveguide signal and lossless array waveguide signal at the bottom of the rail; An ultrasonic preamplifier is connected to the PZT flexible sensor array to amplify the lossy array waveguide signal and the lossless array waveguide signal collected by the PZT flexible sensor array; The NI acquisition card is connected to the ultrasonic preamplifier and the control unit, and receives the amplified lossy array waveguide signal and the lossless array waveguide signal or the signal output by the control unit; The terminal is connected to the NI acquisition card and the control unit, and receives data transmitted by the NI acquisition card or the control unit; A control unit is connected to the laser and the galvanometer, and sends a control signal to the laser or controls the deflection angle of the galvanometer; The laser receives the control signal from the control unit and emits a laser beam to the galvanometer; The galvanometer receives the laser beam emitted by the laser and focuses the laser beam at the position collected by the PZT flexible sensor array; In step S4, the specific steps of performing wavelet packet decomposition and noise reduction filtering on the collected multi-path waveguide signals are as follows: S401, selecting Dmey wavelet as the wavelet packet basis function to perform 5-layer decomposition on the waveguide signal to obtain 32 components with different frequencies; S402, solve the ratio p of each sub-band energy value to the total energy value at different decomposition scales according to the following formula i , Among them, E i is the energy of the mth node in the jth layer, m represents the total number of sub-bands, E sum is the total signal energy; S403, selecting the first n signal frequency bands whose energy ratio sum is greater than 95%, and adding the n signals to obtain the final waveguide signal f after noise reduction filtering.

2. The method for efficiently locating and detecting small-size defects at the bottom of a rail according to claim 1, characterized in that: The conductive wires of the PZT flexible sensor array are non-crossed single-layer electrode structures with a line spacing of 1 mm and a line width of 1 mm.

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