Nonlinear ultrasonic detection method for micro-damage of concrete

Abstract

The invention provides a nonlinear ultrasonic detection method for micro-damage of concrete, and particularly relates to the technical field of material detection. The method specifically comprises the following steps: S1, defining a scanning area and planning a scanning path; s2, exciting fundamental frequency ultrasonic waves to the signal excitation points in the signal excitation area in sequence through a transmitting probe by using a pulse reversal technology; s3, receiving the fundamental frequency ultrasonic waves and the generated second harmonics at the signal excitation points at the corresponding positions of the signal receiving area at the same time in sequence by using a receiving probe; s4, scanning all signal excitation points on the whole surface of the to-be-detected concrete scanning area according to a set scanning path; s5, nonlinear ultrasonic parameters on all sound paths are calculated; and S6, constructing a nonlinear ultrasonic imaging spectrum and judging the spatial distribution and damage degree of the micro-damage of the to-be-detected concrete. According to the method, the concrete micro-damage is represented by directly utilizing nonlinear ultrasonic parameters, and the detection limit of ultrasonic waves and the resolution of low-frequency ultrasonic waves are effectively improved on the premise that the penetrating power of the low-frequency ultrasonic waves is reserved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of material detection, and particularly relates to a nonlinear ultrasonic detection method for micro-damage of concrete. BACKGROUND

[0002] As one of the most commonly used building materials, concrete is widely used in important engineering structures such as bridges, tunnels, high-rise buildings, and hydraulic structures. With the increase of service life and the cumulative effect of environmental loads (such as freeze-thaw, carbonation, dry-wet cycle, salt spray erosion, etc.), micro-damage may occur inside the concrete, such as micro-cracks, interfacial debonding, and micro-pore expansion. These micro-damages are difficult to be observed by naked eye or found by conventional detection methods in the early stage, but their development may significantly reduce the durability and safety of the structure, and even cause sudden failure.

[0003] At present, conventional non-destructive testing techniques such as rebound method, ultrasonic pulse method, X-ray imaging, and electromagnetic detection are mainly used to identify obvious defects or large-scale damage in concrete, and their sensitivity to micro-damage is insufficient. The linear ultrasonic detection method mainly relies on the changes of wave speed, amplitude or energy, which are greatly affected by material heterogeneity and environmental factors, and often cannot accurately identify subtle damage.

[0004] In recent years, nonlinear ultrasonic detection technology has attracted widespread attention due to its high sensitivity to microstructure changes in materials. This method analyzes the nonlinear effects induced by sound waves during their propagation in the material, such as higher harmonic generation, frequency mixing, envelope modulation, etc., to evaluate the micro-damage state inside the material. In complex multiphase materials such as concrete, nonlinear ultrasonic waves can effectively capture the slight influence of micro-cracks, interfacial cracking and other subtle defects on wave propagation characteristics, showing better detection ability than traditional methods. However, existing nonlinear ultrasonic methods are mainly aimed at metal materials or composite materials, and their application in highly heterogeneous materials such as concrete still faces technical challenges. For example, the background nonlinear response is disturbed, the test repeatability is poor, and the data interpretation is complex, which still limits its engineering promotion.

[0005] Therefore, there is an urgent need for a nonlinear ultrasonic detection method suitable for concrete materials with high sensitivity and high stability to realize accurate identification and quantitative evaluation of micro-damage. SUMMARY

[0006] To overcome the shortcomings of the prior art, the present application provides a nonlinear ultrasonic detection method for micro-damage of concrete, and the specific technical solutions are as follows: A nonlinear ultrasonic detection method for micro-damage of concrete, specifically comprising the following steps: S1. One side of the concrete to be tested is designated as the signal excitation area, and the opposite side is designated as the signal receiving area. A scanning path is planned in a mirror-symmetrical manner in the signal excitation area and the signal receiving area, and several signal excitation points are set at equal intervals along the scanning path. The line connecting a signal excitation point in one of the signal excitation areas and the corresponding signal excitation point in the signal receiving area is regarded as a sound path. S2. Using pulse inversion technology, the fundamental frequency ultrasonic waves are sequentially excited at the signal excitation points within the signal excitation area via a transmitting probe; S3. Using the receiving probe, simultaneously receive the fundamental frequency ultrasonic wave and the generated second harmonic wave at the corresponding signal excitation points in the signal receiving area; S4. Synchronously move the transmitting and receiving probes to the positions on both sides of the concrete to be inspected according to several signal excitation points on the set scanning path, and complete the scanning of all signal excitation points on the entire surface of the concrete to be inspected. S5. Calculate the nonlinear ultrasonic parameters along all acoustic paths; S6. Construct a nonlinear ultrasonic imaging atlas and determine the spatial distribution and degree of micro-damage in the concrete to be detected.

[0007] Preferably, in S2, the transmitting probe uses a driving voltage of 200-800Vpp and a center frequency of Narrowband ultrasound probes; among which, The value range is 20kHz to 200kHz.

[0008] Preferably, in S3, the receiving probe uses a center frequency of broadband ultrasound probe and .

[0009] Preferably, the pulse inversion technique involves transmitting two excitation pulses of opposite polarity sequentially through a transmitting probe, and then adding the response signals received twice by the receiving probe to obtain the signal spectrum.

[0010] Preferably, in step S5, a fast Fourier transform is performed based on the fundamental frequency ultrasonic signal and the second harmonic signal in the signal spectrum of each acoustic path to extract the amplitude at the corresponding fundamental frequency ultrasonic signal. Amplitude at the second harmonic Using nonlinear ultrasonic parametric formulas The nonlinear ultrasonic parameters on all acoustic paths were calculated separately.

[0011] Preferably, the scanning paths in both the signal excitation region and the signal receiving region adopt a serpentine path.

[0012] Further preferably, in S6, the calculated nonlinear ultrasonic parameters on all sound paths are normalized to construct a two-dimensional heat map with several nonlinear ultrasonic parameters as pixel intensity values, for judging the spatial distribution and damage degree of micro-damage; the area with higher pixel intensity value represents higher damage degree.

[0013] More preferably, the center axes of the transmitting probe and the receiving probe are collinear during detection of each sound path.

[0014] The beneficial effects of the present application are: The present application makes full use of the influence of concrete micro-damage on the propagation behavior of nonlinear ultrasonic waves, suppresses linear noise and enhances nonlinear characteristics through pulse inversion, significantly improves detection sensitivity and spatial resolution under the premise of ensuring detection penetration, and is particularly suitable for early damage detection, structural durability evaluation and health monitoring engineering applications. BRIEF DESCRIPTION OF DRAWINGS

[0015] The drawings constituting the specification of the present application are used to provide further understanding of the present application and do not constitute undue limitations on the present application.

[0016] Figure 1 The flowchart of the present application; Figure 2 The scanning path diagram of one side scanning area in the present application; Figure 3 The position distribution diagram of two probes in the detection process of the present application; Figure 4 The schematic diagram of one set of excitation signals and receiving signals with opposite polarities in the detection process; Figure 5 The imaging atlas obtained by the embodiment is shown in the schematic diagram. DETAILED DESCRIPTION

[0017] The specific implementation of the nonlinear ultrasonic detection method for concrete micro-damage provided by the present application is further described in combination with the drawings and embodiments.

[0018] As shown in the drawings, Figure 1 A nonlinear ultrasonic detection method for concrete micro-damage, specifically comprising the following steps: S1. One side of the concrete to be detected is taken as a signal excitation area, and the opposite side is taken as a signal receiving area; mirror-symmetrically arranged scanning paths are planned in the signal excitation area and the signal receiving area (the scanning paths in the signal excitation area and the signal receiving area are both snake-shaped paths, as shown in Figure 2a plurality of signal excitation points are arranged along the scanning path at equal intervals; and a line connecting a signal excitation point in the signal excitation region and a signal excitation point in the corresponding position of the signal receiving region is regarded as an acoustic path; It is worth mentioning here that the central axes of the transmitting probe and the receiving probe are collinear during detection of each acoustic path.

[0019] S2. A base frequency ultrasonic wave is excited in the signal excitation point in the signal excitation region by the transmitting probe using the pulse inversion technique. Preferably, the pulse inversion technique sends two excitation pulses with opposite polarities in sequence by the transmitting probe, and then adds the response signals received by the receiving probe twice to highlight the nonlinear response in the signal and suppress the linear component, thereby obtaining the signal spectrum and reading the corresponding base frequency ultrasonic wave amplitude and second harmonic amplitude.

[0020] Preferably, in S2, the transmitting probe adopts a narrowband ultrasonic probe with a driving voltage of 200-800 Vpp and a center frequency of 1-2 MHz; wherein, the value of f0 is in the range of 20 kHz-200 kHz.

[0021] S3. The base frequency ultrasonic wave and the generated second harmonic are simultaneously received by the receiving probe in the signal excitation point in the corresponding position of the signal receiving region in sequence; preferably, in S3, the receiving probe adopts a broadband ultrasonic probe with a center frequency of 0.5-5 MHz and .

[0022] S4. The transmitting probe and the receiving probe are moved synchronously in the positions on both sides of the concrete to be detected according to a plurality of signal excitation points on the set scanning path, so as to complete the scanning of all signal excitation points on the full surface of the scanning region of the concrete to be detected. S5. The nonlinear ultrasonic parameters on all acoustic paths are calculated. Specifically, based on the base frequency ultrasonic wave signal and the second harmonic signal in the signal spectrum of each acoustic path, fast Fourier transform is performed to extract the amplitude of the base frequency ultrasonic wave and the amplitude of the second harmonic, and the nonlinear ultrasonic parameter formula is used to calculate the nonlinear ultrasonic parameters on all acoustic paths.

[0023] S6. A nonlinear ultrasonic imaging atlas is constructed to determine the spatial distribution and damage degree of the micro-damage of the concrete to be detected.

[0024] ​​Further preferably, in S6, a two-dimensional heat map with several nonlinear ultrasonic parameters as pixel intensity values is constructed according to the calculated nonlinear ultrasonic parameters on all sound paths, for judging the spatial distribution and damage degree of micro-damage; wherein the area with higher pixel intensity value represents the area with higher damage degree.

[0025] In order to better understand the present application, the following will be described in conjunction with examples: The concrete sample to be detected in the present embodiment adopts 42.5-grade ordinary portland cement, and the design meets GB50003-2011 “Masonry Structure Design Specification”, and the water-cement ratio is designed to be 0.6. Among them, the content of sand is 1680 kg / m 3 , the content of cement is 560 kg / m 3 , and the content of water is 336 kg / m 3 . The sample size is 200 mm x 200 mm x 200 mm, and six pieces of organic glass simulating concrete cracks with a size of 10 mm x 7 mm x 1 mm are embedded in the area of 20 mm x 20 mm x 20 mm in the concrete sample to be detected.

[0026] The transmitting probe in the present embodiment adopts a narrow-band ultrasonic transmitting probe with a center frequency of 100 kHz, which is used to excite a narrow-band ultrasonic signal with a fundamental frequency of 100 kHz (the probe has a narrow frequency band and concentrated energy, which is beneficial to enhance the consistency and stability of the excited signal. A signal generator is used to generate a 10-cycle sine signal with a frequency of 100 kHz Hanning window modulation, and the voltage is further amplified to 400 Vpp by a power amplifier to drive the ultrasonic transmitting probe).

[0027] The receiving probe in the present embodiment adopts a center frequency of 200 kHz and a -6dB bandwidth of 70%, so as to effectively receive the fundamental wave and the second harmonic component generated by the nonlinear effect (during detection, the center axis of the receiving probe is collinear with the transmitting probe, as shown in Figure 3 , at the same time, the receiving probe is connected with an oscilloscope, and the ultrasonic wave fundamental wave and the second harmonic signal passing through the concrete sample are recorded. Among them, the sampling rate of the oscilloscope is set to 10 MHz, and the sampling point number is 5000).

[0028] One side of the concrete to be detected is used as a signal excitation area, and the other side opposite to it is used as a signal receiving area, and a scanning path in a snake shape and mirror image symmetry is arranged in the signal excitation area and the signal receiving area, and a plurality of signal excitation points are arranged at equal intervals along the scanning path. The connecting line between the signal excitation point in one signal excitation area and the signal excitation point at the corresponding position of the signal receiving area is defined as a sound path; Using pulse inversion technology, two ultrasonic pulses of opposite polarity (i.e., 180° out of phase) are sequentially excited at each excitation point within the signal excitation region. These pulses penetrate the concrete structure and generate two sets of response signals at the receiving end. In an ideal linear system, the responses of opposite excitations should be negative of each other, and their superposition should be zero. However, in nonlinear materials with micro-damage, a significant second harmonic component is generated. Adding the two received signals effectively suppresses the linear component (fundamental wave), thereby enhancing the harmonic response (mainly the second harmonic) caused by nonlinearity. Figure 4 As shown in the figure, the excitation signals with opposite polarities during the detection process and the signals received by the receiving probe under the same excitation are presented. By adding the two received signals, the time-domain signal with the second harmonic as the main component can be obtained. The fundamental frequency ultrasonic signal of each sound path can be obtained from the signal spectrum. and second harmonic signal .

[0029] Using nonlinear ultrasound parametric formulas: The nonlinear ultrasonic parameters on all acoustic paths were calculated respectively.

[0030] The nonlinear ultrasonic parameters on all calculated acoustic paths are normalized to construct a two-dimensional heatmap with nonlinear ultrasonic parameters as pixel intensity values. Figure 5 The image shows the detection results of this embodiment. The brighter the area, the higher the nonlinear ultrasonic parameter value, which means that the damage is greater at that location. This enables the determination of the spatial distribution and degree of micro-damage in concrete.

[0031] This invention fully utilizes the influence of micro-damage in concrete on the propagation behavior of nonlinear ultrasonic waves. By suppressing linear noise and enhancing nonlinear characteristics through pulse reversal, it significantly improves detection sensitivity and spatial resolution while ensuring detection penetration. It is particularly suitable for engineering applications such as early damage detection, structural durability assessment, and health monitoring.

[0032] In this invention, terms such as "upper," "lower," "bottom," and "top" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are merely used to facilitate the description of the structural relationships of the various components or elements of this invention and do not specifically refer to any particular component or element in this invention, nor should they be construed as limiting the invention. Terms such as "connected" and "linked" should be interpreted broadly, indicating a fixed connection, an integral connection, or a detachable connection; a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can determine the specific meaning of the above terms in this invention based on the specific circumstances, and they should not be construed as limiting the invention.

[0033] Of course, the above description is not a limitation of the present application, and the present application is not limited to the above examples. Changes, modifications, additions or substitutions made by those skilled in the art within the spirit and scope of the present application should also be included in the protection scope of the present application.

Claims

1. A method of nonlinear ultrasonic testing of microdamage in concrete, characterized in that, Specifically comprising the following steps: S1. One side of the concrete to be detected is taken as a signal excitation area, and the opposite side is taken as a signal receiving area; a scanning path is planned in the signal excitation area and the signal receiving area, respectively, and a plurality of signal excitation points are arranged at equal intervals along the scanning path; The line connecting the signal excitation point in one of the signal excitation areas and the signal excitation point at the corresponding position of the signal receiving area is regarded as an acoustic path; S2. The signal excitation points in the signal excitation area are excited by the transmitting probe in turn by using the pulse inversion technique to generate fundamental frequency ultrasonic waves; S3. The receiving probe is used to simultaneously receive the fundamental frequency ultrasonic waves and the generated second harmonic waves at the signal excitation points at the corresponding positions of the signal receiving area; S4. The transmitting probe and the receiving probe are moved synchronously at the positions of the two sides of the concrete to be detected according to the plurality of signal excitation points on the set scanning path, so as to complete the scanning of all signal excitation points on the full surface of the scanning area of the concrete to be detected; S5. The nonlinear ultrasonic parameters on all acoustic paths are calculated; S6. A nonlinear ultrasonic imaging atlas is constructed, and the spatial distribution and damage degree of the micro-damage of the concrete to be detected are determined.

2. The method of nonlinear ultrasonic testing of concrete microdamage according to claim 1, characterized in that, In S2, the transmitting probe adopts a narrowband ultrasonic probe with a driving voltage of 200-800 Vpp and a center frequency of ; wherein, the value range of f is 20 kHz-200 kHz.

3. The method of nonlinear ultrasonic testing of concrete microdamage according to claim 2, characterized in that, In S3, the receiving probe employs a broadband ultrasound probe with a center frequency of and .

4. The method of nonlinear ultrasonic testing of concrete microdamage according to claim 3, characterized in that, The pulse inversion technique sends two excitation pulses with opposite polarities in turn through the transmitting probe, and then adds the response signals received by the receiving probe twice to obtain the signal spectrum.

5. The method for nonlinear ultrasonic testing of concrete microdamage according to claim 4, characterized in that, In S5, based on the fundamental frequency ultrasonic signal and the second harmonic signal in the spectrum of each acoustic path signal, a fast Fourier transform is performed to extract the amplitude at the corresponding fundamental frequency ultrasonic signal and the amplitude at the second harmonic Using the nonlinear ultrasonic parameter formula The nonlinear ultrasonic parameters on all acoustic paths are calculated respectively.

6. The method of nonlinear ultrasonic testing of concrete microdamage according to claim 5, characterized in that, The scanning paths in the signal excitation area and the signal receiving area are both snake-shaped paths.

7. The method of nonlinear ultrasonic testing of concrete microdamage according to claim 6, characterized in that, In S6, the calculated nonlinear ultrasonic parameters on all acoustic paths are normalized to construct a two-dimensional heat map with a plurality of nonlinear ultrasonic parameters as pixel intensity values, which is used to determine the spatial distribution and damage degree of the micro-damage; Wherein, the area with higher pixel intensity value represents higher damage degree.

8. The method of nonlinear ultrasonic testing of concrete microdamage according to claim 1, characterized in that, During the detection of each acoustic path, the center axes of the transmitting probe and the receiving probe are collinear.

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