Ultrasonic guided wave detection method and system for steel-concrete joint surface defects

Abstract

The invention discloses an ultrasonic guided wave detection method and system for steel-concrete joint surface defects. The method comprises the following steps: S1, selecting an ultrasonic guided wave mode for detection; s2, calibrating an ultrasonic guided wave propagation speed; s3, adopting a twin-crystal probe as an air coupling probe, and rapidly screening defects in a large area by using the twin-crystal probe in a self-transmitting and self-receiving manner; and S4, carrying out quantitative detection on the defects by adopting two air coupling probes in a one-transmitting and one-receiving manner. A cyclic matrix algorithm and a spring model are adopted to calculate ultrasonic guided wave propagation characteristics in a steel-concrete multi-layer plate-shaped structure, an ultrasonic guided wave mode with high steel-concrete joint surface defect recognition sensitivity is selected for detection, and a non-contact air coupling probe is used for scanning imaging. Large-area rapid scanning and local quantitative detection are carried out step by step, efficiency and precision can be taken into account, and efficient and accurate detection of the steel-concrete joint surface defects on the engineering site is achieved.

Description

Technical Field

[0001] The invention relates to the field of non-destructive construction, and in particular to an ultrasonic guided wave detection method and system for defects on a steel-concrete interface. Background Art

[0002] Steel-concrete composite structures such as steel tube concrete, steel plate concrete, and steel-concrete composite beams give full play to the mechanical properties of steel and concrete materials, improve the stiffness, bearing capacity, and seismic toughness of the structure, and are widely used in high-rise and super-high-rise buildings, large-span bridges, cross-sea tunnels and other structures. During the construction process, affected by the construction process, personnel, and environment, the steel-concrete interface is prone to defects such as looseness, voids, and inclusions, which will seriously reduce the mechanical and seismic performance of the steel-concrete composite structure. Therefore, rapid and accurate quantitative identification of defects at the construction site is crucial to evaluating the safety performance of the entire structural system.

[0003] The current methods for detecting defects on the steel-concrete interface mainly include ultrasonic method and ultrasonic phased array imaging method. The ultrasonic method uses two ultrasonic probes placed on both sides of the object to be tested. By measuring the propagation speed, amplitude and phase of ultrasonic waves in the steel-concrete structure, the casting quality of the steel-concrete interface is judged. However, this method requires the addition of coupling agent, and the efficiency of point-by-point detection is low, the scope of application is narrow, and there is no quantitative defect discrimination index. The invention patent "A device and method for detecting the bonding quality of concrete and steel plates" (application number: CN201811492889.4) introduces a method of exciting and receiving ultrasonic waves on the concrete side using an air-coupled probe, and judging the bonding quality of the concrete and steel plate interface by the waveform phase, without the need for coupling agent. However, this method is performed on the concrete side, and the wavelength of the excited ultrasonic wave is large, the defect recognition ability is weak, and the point-by-point detection is inefficient. The ultrasonic phased array imaging method uses a single-side detection method to determine whether there are defects and their locations on the steel-concrete interface through ultrasonic imaging. The invention patents "A method for testing the quality of the interface between new and old concrete for reinforcing concrete structures" (application number: CN202010628895.9) and "An ultrasonic phased array system and steel tube concrete construction method and process" (application number: CN202210434404.6) introduce the ultrasonic phased array imaging method to judge the construction quality of the steel-concrete interface based on ultrasonic images, but the ultrasonic phased array equipment used in this method mostly uses low-frequency ultrasonic waves as the detection carrier, which has a large wavelength and poor defect recognition accuracy, and is detected block by block with low efficiency. At the same time, both the ultrasonic method and the ultrasonic phased array imaging method are local qualitative detections, and it is difficult to accurately identify the area of ​​defects. They cannot meet the needs of refined evaluation of the mechanical properties of steel and concrete composite structures, and there are disadvantages when applied on site. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the present invention provides an ultrasonic guided wave detection method and system for steel-concrete interface defects, which first uses a dual crystal probe B-scan imaging to quickly determine the suspected defect area, and then uses a dual probe to perform local refined B-scan imaging to achieve rapid quantitative detection of steel-concrete interface defects. To achieve the above purpose, the technical solution of the present invention includes:

[0005] An ultrasonic guided wave detection method for steel-concrete interface defects, comprising:

[0006] S1: Select the ultrasonic guided wave mode used for detection;

[0007] S2: Calibrate the ultrasonic guided wave propagation velocity;

[0008] S3: Use dual crystal probe as air-coupled probe to quickly screen defects over a large area with dual crystal probe self-transmitting and self-receiving;

[0009] S4: Two air-coupled probes are used to perform quantitative detection of defects in a one-transmit-one-receive manner.

[0010] A further improvement of the present invention is that step S1 specifically includes:

[0011] S11: The steel-concrete structure is regarded as a multi-layer plate structure of air-steel plate-concrete plate-air. Based on the wave equation of the single-layer medium state space, the cyclic recursive algorithm of the stiffness matrix of the single-layer medium, the spring model and the displacement and stress continuity on the interface between layers, the overall flexibility matrix of the multi-layer plate structure is calculated:

[0012]

[0013] Where: S M is the overall flexibility matrix of the m-layer plate structure, S M-1 is the overall flexibility matrix of the upper m-1 layers, S m is the flexibility matrix of the mth layer; is the matrix S M The second-order submatrix in the upper left corner, is the matrix S M The second-order submatrix in the upper right corner, is the matrix S M The second-order submatrix in the lower left corner, is the matrix S M The second-order submatrix in the lower right corner;

[0014] S12: Based on the zero stress boundary condition, the dispersion equation of the waveguide in the multi-layer dielectric structure is obtained:

[0015] det[S M (k x ,ω) -1 ]=0

[0016] Where: k x represents the wave number in the propagation direction x, ω represents the angular frequency, and det[·] represents the determinant of the matrix;

[0017] S13: The phase velocity dispersion curve of ultrasonic guided waves in steel-concrete structures is obtained by iteratively solving the dispersion equation. The types and thicknesses of the steel plates and concrete in the steel-concrete structures are measured respectively. The low-frequency mode ultrasonic guided waves with weak dispersion effect are selected for steel-concrete interface defect detection. The incident angle θ of this mode is calculated based on Snell's law as:

[0018] θ=arc -1 (C a / C p )

[0019] Where: C p is the phase velocity of ultrasonic guided wave propagation, C a is the speed of sound waves in air;

[0020] S14: Based on the frequency-thickness product of the selected ultrasonic guided wave mode and the thickness of the steel plate and concrete, calculate the wave structure of the ultrasonic guided wave at different frequencies, determine the corresponding frequency f, and select the center frequency f of the air-coupled probe. 0 , and make the frequency f within the operating frequency range of the air-coupled probe.

[0021] A further improvement of the present invention is that step S2 specifically includes:

[0022] S21: respectively adjusting the distance H and the angle θ of the air-coupled probes for receiving and transmitting relative to the steel plate, and adjusting the transmitting voltage of the excitation unit corresponding to the air-coupled probe for transmitting and the gain of the signal amplifier corresponding to the air-coupled probe for receiving, until an ultrasonic guided wave signal with a high signal-to-noise ratio is obtained;

[0023] S22: Based on the one-transmit-one-receive method of two air-coupled probes on the steel plate side of the steel-concrete structure, the received ultrasonic guided wave signals are collected and the average propagation velocity of the ultrasonic guided wave in the steel-concrete structure is calibrated according to the received signals. and the average amplitude Its expression is:

[0024]

[0025] Where: L i H is the horizontal distance between the two air-coupled probes. i A is the vertical distance from the probe to the steel plate surface, i is the horizontal spacing L iThe maximum amplitude of the ultrasonic guided wave signal, N is the number of measurement points selected for calibration, t i Represents the ultrasonic guided wave propagation time at the i-th measuring point.

[0026] A further improvement of the present invention is that step S3 specifically includes:

[0027] S31: Select scanning lines j=1, 2, 3, ... at equal intervals l along the horizontal direction on the surface of the steel plate in the steel-concrete structure, and select measuring points k=1, 2, 3, ... at equal intervals d on each scanning line;

[0028] S32: Use the dual crystal probe to stimulate ultrasonic guided waves at each measuring point, adjust the transmitting voltage and signal amplifier gain, set the sampling length, and collect the ultrasonic guided wave signal S at each measuring point. jk , two-dimensional imaging is performed using the B-scan imaging method based on the amplitude of ultrasonic guided wave signals;

[0029] S33: Set the threshold of the ultrasonic guided wave signal to The area where the ultrasonic guided wave signal amplitude is less than the threshold is judged as a normal area, and the area where it is greater than the threshold is judged as a suspected defect area, and the position P of the suspected defect area is calculated. jk , whose expression is:

[0030]

[0031] Where: t jk represents the propagation time of ultrasonic guided waves at the jkth measuring point in the suspected defect area, H jk is the vertical distance from the dual crystal probe to the steel plate surface at the jkth measuring point;

[0032] S34: Divide the range including the suspected defect area into the suspected defect area of ​​the steel-concrete interface.

[0033] A further improvement of the present invention is that in step S31, the value range of the spacing l is 40 mm to 400 mm, and the value range of the spacing d is 10 mm to 100 mm.

[0034] A further improvement of the present invention is that in step S32, the ultrasonic guided wave signal S jk The intercept of the propagation time is greater than or equal to

[0035] A further improvement of the present invention is that step S4 specifically includes:

[0036] S41: selecting measuring lines m=1, 2, 3, ... at equal intervals Δd in the suspected defect area of ​​the steel-concrete interface determined in step S34, and selecting measuring points n=1, 2, 3, ... at equal intervals Δl on each measuring line;

[0037] S42: Use two air-coupled probes, one for transmitting and one for receiving, to excite ultrasonic guided waves at the measuring point, adjust the transmitting voltage and signal amplifier gain, set the sampling length, scan along the "Z" shape, and collect ultrasonic guided wave signals S at different measuring points. mn , two-dimensional imaging based on B-scan focusing imaging method;

[0038] S43: Extract the defect contour based on the B-scan image, determine the defect area position, and calculate the defect area area.

[0039] A further improvement of the present invention is that in step S41, the value range of the spacing Δl is 1 mm to 20 mm, and the value range of the spacing Δd is 1 mm to 10 mm.

[0040] The present invention also provides an ultrasonic guided wave detection system for steel-concrete interface defects, which is used to perform the above-mentioned ultrasonic guided wave detection method for steel-concrete interface defects, and comprises:

[0041] An ultrasonic guided wave excitation module is used to provide a transmission signal for the air-coupled probe, including a power supply, an excitation unit, a signal amplifier, and the output of the signal amplifier is used to act on the air-coupled probe;

[0042] The ultrasonic guided wave receiving module is used to process the signal received by the air-coupled probe, and includes a signal amplifier, an A / D converter, a data acquisition unit, a signal processing unit, and a display unit connected in sequence; the ultrasonic guided wave receiving module and the ultrasonic guided wave excitation module are synchronously controlled by the control unit through the synchronization unit;

[0043] The mechanical scanning module includes a cross slide structure, which includes a probe bracket. The probe bracket slides on a guide rail driven by a stepper motor; the guide rail slides on another guide rail driven by another stepper motor; the two guide rails are cross-distributed; the two stepper motors are controlled by a control device to drive the probe bracket to scan along a predetermined path.

[0044] The beneficial effects of the present invention include:

[0045] (1) The optimal ultrasonic guided wave mode and frequency are selected through theoretical analysis and calculation of dispersion curves and wave structures for steel-concrete interface defect detection, with high defect identification sensitivity.

[0046] (2) An air-coupled ultrasonic probe is used to receive ultrasonic guided wave leakage signals in the air for defect identification, and a threshold for defect identification is proposed. Compared with traditional ultrasonic testing, no coupling agent is required, and large-scale rapid scanning detection is achieved;

[0047] (3) The dual crystal probe is used to realize the rapid qualitative detection of defects on the steel-concrete interface by self-transmitting and self-receiving, and the dual probe is used to realize the local quantitative detection of defects by one transmitting and one receiving, taking into account the efficiency and accuracy of on-site detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a schematic diagram of the ultrasonic guided wave detection system for steel-concrete interface defects in the present invention;

[0049] Figure 2 It is a schematic diagram of air-coupled ultrasonic guided wave propagation in a steel and concrete structure in the present invention;

[0050] Figure 3 It is a schematic diagram of automatic calibration of ultrasonic guided wave propagation velocity in the present invention;

[0051] Figure 4 It is a schematic diagram of the self-transmitting and self-receiving rapid scanning of the dual crystal probe in the present invention;

[0052] Figure 5 It is a schematic diagram of the double-probe one-transmit-one-receive type fine scanning in the present invention. DETAILED DESCRIPTION

[0053] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0054] It should be noted that the illustrations provided in the following embodiments are only used to illustrate the basic concept of the present invention in a schematic manner, and thus the illustrations only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0055] See also Figure 1 The present invention provides an ultrasonic guided wave scanning detection device, comprising an ultrasonic guided wave excitation module 1, an ultrasonic guided wave receiving module 2, and a mechanical scanning module 3; the ultrasonic guided wave excitation module 1 comprises: a power supply 11, an excitation unit 12, a signal amplifier 13, an air-coupled probe 14, a synchronization unit 15 and a control unit 16; the ultrasonic guided wave receiving module comprises 2: an air-coupled probe 21, a signal amplifier 22, an A / D converter 23, a data acquisition unit 24, a signal processing unit 25 and a display unit 26.

[0056] The mechanical scanning module 3 includes a cross slide structure, which includes a probe holder 37. The probe holder 37 slides on a guide rail 32 driven by a stepper motor 33; the guide rail 32 slides on another guide rail 31 driven by another stepper motor 34; the two guide rails 31 and 32 are cross-distributed. The stepper motors 33 and 32 are controlled by a control device 35. After the ultrasonic guided wave excitation module 1 sets the detection parameters and the scanning path, it sends instructions to the ultrasonic guided wave receiving module 2 and the mechanical scanning module 3 for automatic scanning, quickly collects ultrasonic guided wave signals at each detection point, and automatically images to determine whether there are defects in the scanning area. In this process, the control device 35 controls the two stepper motors to drive the probe holder 37 to scan along a predetermined path, and quickly collects ultrasonic guided wave signals at each detection point, and automatically images to determine whether there are defects in the scanning area.

[0057] In this embodiment, the probe bracket 37 includes an excitation probe fixture 38 and a receiving probe fixture 39; in the one-transmit-one-receive mode, both probe fixtures are installed with probes; in the self-transmit and self-receive mode, the dual-crystal probe can be installed on any one of the two probe fixtures. The two probe fixtures can adjust the angle and position of the corresponding probe respectively. In addition, the cross slide structure of this embodiment is installed on the lifting device 310, and the lifting device 310 is installed on the fixed bracket 311.

[0058] In this embodiment, the scanning modes of the mechanical scanning module are divided into two types, one is to use a dual crystal probe to perform large-area rapid scanning, and the other is to use a dual probe to perform local fine scanning with one transmitting and one receiving.

[0059] In this embodiment, the emission voltage of the excitation unit 12 is adjustable, ranging from 100V to 1000V, and the excitation frequency range is 50kHz to 1MHz; the air-coupled probe is divided into two types, one is a double-crystal planar probe, the center frequency of the probe has three specifications of 100kHz, 200kHz and 400kHz, and the diameters are 30mm, 20mm and 10mm respectively; the other is a single-crystal probe, the excitation probe adopts a planar probe, the center frequency has two specifications of 200kHz and 400kHz, the diameters are 20mm and 10mm respectively, and the receiving probe adopts a focusing probe, the center frequency has two specifications of 200kHz and 400kHz, and the focal length is 38mm.

[0060] In this embodiment, the excitation unit 12 is embedded with automatic calculation software. After inputting parameters such as the steel plate model and thickness, concrete model and thickness, probe frequency, sound speed in air and ultrasonic guided wave propagation speed, the incident angle θ of the selected ultrasonic guided wave mode can be calculated, and the angles of the excitation probe fixture 38 and the receiving probe fixture 39 can be automatically adjusted to the incident angle θ.

[0061] In this embodiment, the signal processing unit 25 has a sampling frequency of 50 MHz and a data storage capacity of 20 GB. It is internally embedded with automatic analysis software, which can automatically collect and store ultrasonic guided wave signals at different measuring points, automatically calculate and correct the initial wave velocity, batch extract the guided wave signal amplitude for B-scan focused imaging, and quantitatively analyze the area of ​​the defect region.

[0062] See also Figure 2 to Figure 5 A method for rapid quantitative ultrasonic guided wave detection of steel-concrete interface defects according to an embodiment of the present invention comprises the following steps:

[0063] S1: Select the ultrasonic guided wave mode used for detection. This step specifically includes:

[0064] S11: The steel-concrete structure is regarded as a multi-layer plate structure of air-steel plate-concrete plate-air. Based on the wave equation of the single-layer medium state space, the cyclic recursive algorithm of the stiffness matrix of the single-layer medium, the spring model and the displacement and stress continuity on the interface between layers, the overall flexibility matrix of the multi-layer plate structure is calculated:

[0065]

[0066] Where: S M is the overall flexibility matrix of the m-layer plate structure, S M-1 is the overall flexibility matrix of the upper m-1 layers, S m is the flexibility matrix of the mth layer; is the matrix S M The second-order submatrix in the upper left corner, is the matrix S M The second-order submatrix in the upper right corner, is the matrix S M The second-order submatrix in the lower left corner, is the matrix S M The second-order submatrix in the lower right corner;

[0067] S12: Based on the zero stress boundary condition, the dispersion equation of the waveguide in the multi-layer dielectric structure is obtained:

[0068] det[S M (k x ,ω) -1 ]=0 (2)

[0069] Where: k x represents the wave number in the propagation direction x, ω represents the angular frequency, and det[·] represents the determinant of the matrix.

[0070] S13: The dispersion equation (2) is solved by programming iteration to obtain the phase velocity dispersion curve of ultrasonic guided waves in the steel-concrete structure. The model and thickness of the steel plate and concrete are measured respectively. The low-frequency mode ultrasonic guided waves with weak dispersion effect are selected for steel-concrete interface defect detection. The incident angle θ of this mode is calculated based on Snell's law as:

[0071] θ=arc -1 (C a / C p ) (3)

[0072] Where: C p is the phase velocity of ultrasonic guided wave propagation, C a is the speed of sound waves in air;

[0073] S14: Based on the frequency-thickness product of the selected ultrasonic guided wave mode and the thickness of the steel plate and concrete, calculate the wave structure of the ultrasonic guided wave at different frequencies, determine the corresponding frequency f, and select the frequency f of the air-coupled probe. 0 , and make the frequency f within the operating frequency range of the probe.

[0074] S2: Please refer to Figure 3 , calibrate the ultrasonic guided wave propagation velocity. This step specifically includes:

[0075] S21: Turn on the transmitting module 1 and the receiving module 2, control the mechanical scanning module 3 to adjust the distance H and angle θ of the air coupling probes 14 and 21 relative to the steel plate in the steel-concrete structure, and adjust the transmitting voltage of the excitation unit 12 and the gain of the signal amplifier 22 until an ultrasonic guided wave signal with a high signal-to-noise ratio is obtained;

[0076] S22: Based on the dual-probe (two air-coupled probes) one-transmit-one-receive method on the steel plate side of the steel-concrete structure, the ultrasonic guided wave signal is stored through the data acquisition unit 24, and the average velocity of ultrasonic guided wave propagation in the steel-concrete structure is automatically calibrated using the embedded software in the signal processing unit 25 and the average amplitude Where L i H is the horizontal distance between the two air-coupled probes. i A is the vertical distance from the probe to the steel plate surface, i is the horizontal spacing L i The maximum amplitude of the ultrasonic guided wave signal, N is the number of measurement points selected for calibration (N = 5 is acceptable), t i represents the ultrasonic guided wave propagation time at the i-th measuring point, and the average velocity value and the average amplitude Save to the signal processing unit.

[0077] S3: Please refer to Figure 4, based on the dual crystal probe's self-transmitting and self-receiving large-area rapid defect screening. This step specifically includes:

[0078] S31: On the steel plate surface in the steel-concrete structure, select scanning lines j = 1, 2, 3, ... at equal intervals l in the horizontal direction, and select measuring points k = 1, 2, 3, ... at equal intervals d on each scanning line, such as Figure 2 As shown;

[0079] S32: Use the dual crystal probe to stimulate ultrasonic guided waves at each measuring point, adjust the transmitting voltage and signal amplifier gain, set the sampling length, and collect the ultrasonic guided wave signal S at each measuring point. jk , performing two-dimensional imaging based on the amplitude of the ultrasonic guided wave signal using the B-scan imaging function of the embedded software in the signal processing unit 25;

[0080] S33: Set the threshold of the ultrasonic guided wave signal to The area where the ultrasonic guided wave signal amplitude is less than the threshold is judged as a normal area, and the area where the ultrasonic guided wave signal amplitude is greater than the threshold is judged as a suspected defect area. The position of the suspected defect area is calculated, and the expression is: where t jk represents the propagation time of ultrasonic guided waves at the jkth measuring point in the suspected defect area, H jk is the vertical distance from the dual crystal probe to the steel plate surface at the jkth measuring point, position P jk It refers to the location where the interface defect between the steel plate and the concrete exists, which can be obtained based on the detection position and propagation time.

[0081] S34: Divide the range including the suspected defect area into the suspected defect area of ​​the steel-concrete interface.

[0082] S4: Please refer to Figure 5 , two air-coupled probes are used to quantitatively detect defects in a one-transmit-one-receive manner. This step specifically includes:

[0083] S41: Select measuring lines m = 1, 2, 3, ... at equal intervals Δd in the suspected defect area of ​​the steel-concrete interface determined in S34, and select measuring points n = 1, 2, 3, ... at equal intervals Δl on each measuring line, such as Figure 3 As shown;

[0084] S42: Use two air-coupled probes, one for transmitting and one for receiving, to excite ultrasonic guided waves at the measuring point, adjust the transmitting voltage and signal amplifier gain, set the sampling length, scan along the "Z" shape, and collect ultrasonic guided wave signals S at different measuring points. mn , performing two-dimensional imaging based on the signal amplitude using the B-scan focus imaging function of the embedded software in the signal processing unit 25;

[0085] S43: Extract the defect contour based on the B-scan focused imaging image, determine the defect area position, and calculate the defect area area.

[0086] Ultrasonic guided waves in plate-like structures are formed by multiple reciprocating reflections of transverse waves and longitudinal waves in the plate, and further superposition interference and geometric dispersion. The wavelength of the sound wave is usually required to be similar to or greater than the thickness of the structure. When ultrasonic guided waves propagate in a plate-like structure, each particle in the plate participates in the vibration (the vibration direction is divided into in-plane and out-of-plane), which can effectively identify defects such as looseness, cracking, and delamination in the structure.

[0087] The ultrasonic guided wave used in this embodiment can be used not only for steel-concrete interface defect detection, but also for concrete internal defect detection. The propagation speed of the ultrasonic guided wave changes with the waveguide frequency and mode, and is more difficult to excite than the Rayleigh surface wave. Therefore, a rigorous theoretical analysis is required to select the appropriate waveguide mode for detection and its corresponding frequency, angle and other parameters. When the ultrasonic guided wave encounters a defect, a defect reflection wave will be generated (the defect position can be located according to this reflection wave), and the amplitude of the original guided wave signal will be reduced (the larger the defect, the smaller the signal amplitude), so it is used for steel-concrete interface and concrete internal defect detection.

[0088] Optionally, in order to minimize the number of ultrasonic guided wave modes, a frequency range that is lower than the cutoff frequency of the higher mode and whose group velocity is as constant as possible needs to be selected for nondestructive testing of the steel-concrete interface, such as the frequency corresponding to the lowest-order antisymmetric mode in ultrasonic guided waves.

[0089] When ultrasonic guided waves encounter defects, reflection, scattering and diffraction will occur. The dual-crystal probe uses one chip to transmit ultrasonic guided waves, and the other chip receives the reflected waves at the defect to perform defect detection. Defect identification uses defect reflected waves and mode conversion. The dual probe uses one probe to transmit ultrasonic guided waves, and the other probe receives the direct waves of the guided waves to perform defect detection. Defect identification uses the direct waves of the guided waves.

[0090] Optionally, in step S21, the height H and angle θ of the air coupling probe are automatically adjusted by the mechanical scanning module 3, the accuracy of the height can reach 0.1 mm, the accuracy of the angle can reach 0.1°, and the value range of H is 5 mm to 25 mm.

[0091] Optionally, in step S22, the signal processing unit 25 is embedded with software developed based on Python language, which has the functions of sound time and signal amplitude extraction, B-scan imaging, defect contour extraction and automatic calculation of defect area, etc., which can quickly give the detection results at the engineering site, and the recognition accuracy of the defect area can reach 1mm 2 .

[0092] Optionally, in step S31, the value range of the spacing l is 40 mm to 400 mm, and the value range of the spacing d is 10 mm to 100 mm.

[0093] Optionally, in step S32, the ultrasonic guided wave signal S jk The interception of propagation time is based on the mean propagation speed and spacing l, should be greater than or equal to

[0094] Optionally, in step S41, the value range of the spacing Δl is 1 mm to 20 mm, and the value range of the spacing Δd is 1 mm to 10 mm.

[0095] The steel-concrete interface defect detection method in this embodiment uses a circulant matrix algorithm and a spring model to calculate the ultrasonic guided wave propagation characteristics in a steel-concrete multilayer plate structure, selects an ultrasonic guided wave mode with high sensitivity for steel-concrete interface defect recognition for detection, uses a non-contact air-coupled probe for scanning and imaging, and gradually performs large-area rapid scanning and local quantitative detection, which can take into account both efficiency and accuracy, and realize efficient and accurate detection of steel-concrete interface defects on engineering sites.

[0096] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. An ultrasonic guided wave detection method for steel-concrete interface defects, characterized in that include: S1: Select the ultrasonic guided wave mode used for detection; S2: Calibrate the ultrasonic guided wave propagation velocity; S3: Use dual crystal probe as air-coupled probe to quickly screen defects over a large area with dual crystal probe self-transmitting and self-receiving; S4: Two air-coupled probes are used to perform quantitative detection of defects in a one-transmit-one-receive manner.

2. The ultrasonic guided wave detection method for steel-concrete interface defects according to claim 1 is characterized in that: Step S1 specifically includes: S11: The steel-concrete structure is regarded as a multi-layer plate structure of air-steel plate-concrete plate-air. Based on the wave equation of the single-layer medium state space, the cyclic recursive algorithm of the stiffness matrix of the single-layer medium, the spring model and the displacement and stress continuity on the interface between layers, the overall flexibility matrix of the multi-layer plate structure is calculated: Where: S M is the overall flexibility matrix of the m-layer plate structure, S M-1 is the overall flexibility matrix of the upper m-1 layers, S m is the flexibility matrix of the mth layer; is the matrix S M The second-order submatrix in the upper left corner, is the matrix S M The second-order submatrix in the upper right corner, is the matrix S M The second-order submatrix in the lower left corner, is the matrix S M The second-order submatrix in the lower right corner; S12: Based on the zero stress boundary condition, the dispersion equation of the waveguide in the multi-layer dielectric structure is obtained: it[S M (k x ,ω) -1 ]=0 Where: k x represents the wave number in the propagation direction x, ω represents the angular frequency, and det[·] represents the determinant of the matrix; S13: The phase velocity dispersion curve of ultrasonic guided waves in steel-concrete structures is obtained by iteratively solving the dispersion equation. The types and thicknesses of the steel plates and concrete in the steel-concrete structures are measured respectively. Low-frequency mode ultrasonic guided waves are selected for steel-concrete interface defect detection. The incident angle θ of this mode is calculated based on Snell's law as: θ=arc -1 (C a / C p ) Where: C p is the phase velocity of ultrasonic guided wave propagation, C a is the speed of sound waves in air; S14: According to the frequency-thickness product of the selected ultrasonic guided wave mode and the thickness of the steel plate and the concrete, the wave structure of the ultrasonic guided wave at different frequencies is calculated, the corresponding frequency f is determined, the center frequency f0 of the air-coupled probe is selected, and the frequency f is within the operating frequency range of the air-coupled probe.

3. The ultrasonic guided wave detection method for steel-concrete interface defects according to claim 2 is characterized in that: Step S2 specifically includes: S21: respectively adjusting the distance H and the angle θ of the air-coupled probes for receiving and transmitting relative to the steel plate, and adjusting the transmitting voltage of the excitation unit corresponding to the air-coupled probe for transmitting and the gain of the signal amplifier corresponding to the air-coupled probe for receiving, until an ultrasonic guided wave signal with a high signal-to-noise ratio is obtained; S22: Based on the one-transmit-one-receive method of two air-coupled probes on the steel plate side of the steel-concrete structure, the received ultrasonic guided wave signals are collected and the average propagation velocity of the ultrasonic guided wave in the steel-concrete structure is calibrated according to the received signals. and the average amplitude Its expression is: Where: L i H is the horizontal distance between two air-coupled probes. i A is the vertical distance from the probe to the steel plate surface. i is the horizontal spacing L i The maximum amplitude of the ultrasonic guided wave signal, N is the number of measurement points selected for calibration, t i Represents the ultrasonic guided wave propagation time at the i-th measuring point.

4. The ultrasonic guided wave detection method for steel-concrete interface defects according to claim 3 is characterized in that: Step S3 specifically includes: S31: Select scanning lines j=1, 2, 3, ... at equal intervals l along the horizontal direction on the surface of the steel plate in the steel-concrete structure, and select measuring points k=1, 2, 3, ... at equal intervals d on each scanning line; S32: Use the dual crystal probe to stimulate ultrasonic guided waves at each measuring point, adjust the transmitting voltage and signal amplifier gain, set the sampling length, and collect the ultrasonic guided wave signal S at each measuring point. jk , two-dimensional imaging is performed using the B-scan imaging method based on the amplitude of ultrasonic guided wave signals; S33: Set the threshold of the ultrasonic guided wave signal to The area where the ultrasonic guided wave signal amplitude is less than the threshold is judged as a normal area, and the area where it is greater than the threshold is judged as a suspected defect area, and the position P of the suspected defect area is calculated. jk , whose expression is: Where: t jk represents the propagation time of ultrasonic guided waves at the jkth measuring point in the suspected defect area, H jk is the vertical distance from the dual crystal probe to the steel plate surface at the jkth measuring point; S34: Divide the range including the suspected defect area into the suspected defect area of ​​the steel-concrete interface.

5. The ultrasonic guided wave detection method for steel-concrete interface defects according to claim 4 is characterized in that: In step S31, the value range of the spacing l is 40 mm to 400 mm, and the value range of the spacing d is 10 mm to 100 mm.

6. The ultrasonic guided wave detection method for steel-concrete interface defects according to claim 4 is characterized in that: In step S32, the ultrasonic guided wave signal S jk The intercept of the propagation time is greater than or equal to 7. The ultrasonic guided wave detection method for steel-concrete interface defects according to claim 4 is characterized in that: Step S4 specifically includes: S41: selecting measuring lines m=1, 2, 3, ... at equal intervals Δd in the suspected defect area of ​​the steel-concrete interface determined in step S34, and selecting measuring points n=1, 2, 3, ... at equal intervals Δl on each measuring line; S42: Use two air-coupled probes to stimulate ultrasonic guided waves at the measuring point, one for transmission and one for reception, adjust the transmitting voltage and signal amplifier gain, set the sampling length, scan along the "Z" shape, and collect ultrasonic guided wave signals S at different measuring points. mn , two-dimensional imaging based on B-scan focusing imaging method; S43: Extract the defect contour based on the B-scan image, determine the defect area position, and calculate the defect area area.

8. The ultrasonic guided wave detection method for steel-concrete interface defects according to claim 7 is characterized in that: In step S41, the value range of the spacing Δl is 1 mm to 20 mm, and the value range of the spacing Δd is 1 mm to 10 mm.

9. An ultrasonic guided wave detection system for steel-concrete interface defects, used to perform the ultrasonic guided wave detection method for steel-concrete interface defects as claimed in any one of claims 1 to 8, characterized in that include: An ultrasonic guided wave excitation module (1) is used to provide a transmission signal for an air-coupled probe, comprising a power supply (11), an excitation unit (12), a signal amplifier (13), and an output of the signal amplifier (13) is used to act on the air-coupled probe; The ultrasonic guided wave receiving module (2) is used to process the signal received by the air-coupled probe, and comprises a signal amplifier (22), an A / D converter (23), a data acquisition unit (24), a signal processing unit (25), and a display unit (26) which are connected in sequence; the ultrasonic guided wave receiving module (1) and the ultrasonic guided wave excitation module (2) are synchronously controlled by the control unit (16) through the synchronization unit (15); The mechanical scanning module (3) comprises a cross slide structure, which comprises a probe bracket (37), wherein the probe bracket (37) slides on a guide rail driven by a stepper motor; the guide rail slides on another guide rail driven by another stepper motor; the two guide rails are arranged in a cross pattern; and the two stepper motors are controlled by a control device (35) to drive the probe bracket (37) to scan along a predetermined path.

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