High-frequency guided wave detection system and method for crack defects of anchoring anchor rod

Abstract

The invention discloses a high-frequency guided wave detection method for crack defects of an anchoring anchor rod, belongs to the field of nondestructive testing of anchor rods, and aims to carry out nondestructive testing on defect degrees and positions of the anchoring anchor rod and construct a high-frequency ultrasonic guided wave nondestructive testing system. A frequency scanning method is adopted for carrying out high-frequency guided wave detection on an anchor rod-resin-surrounding rock three-layer anchoring anchor rod test piece, the echo signal state and distribution characteristics are analyzed, the optimal excitation frequency, system gain and head wave width are optimized, nondestructive detection is carried out on anchoring anchor rods with different defect degrees, and the purpose of detecting the defect degrees and defect positions is achieved. According to the high-frequency ultrasonic guided wave nondestructive testing method and the built testing system, nondestructive testing can be conducted on a large-size three-layer anchoring anchor rod structure, and an efficient and reliable method is provided for nondestructive testing of anchoring anchor rods in actual engineering. The constructed ultrasonic guided wave nondestructive testing system can detect the defect degree and position of the anchoring anchor rod, and the defect position detection error is smaller than or equal to 2%.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for detecting crack defects of an anchor rod, and in particular to a high-frequency guided wave detection system and method for detecting crack defects of an anchored anchor rod. BACKGROUND

[0002] When low-frequency guided waves propagate in a free anchor rod under vacuum conditions, the guided waves will only attenuate due to the material damping of the anchor rod itself, so the attenuation of the free anchor rod is small, and thus the guided waves can propagate for a long distance. However, when the anchor rod is embedded in other media, if the phase velocity of a certain guided wave mode is higher than the bulk wave velocity of the surrounding medium, the anchor rod cannot completely constrain the propagating energy, which will be radiated to the surrounding medium in the form of waves. The guided wave energy gradually converts into radiated energy, resulting in a leakage attenuation of the signal amplitude in the free anchor rod. Low-frequency guided waves can be used for detection under the condition that the thickness of the anchoring layer is small, but boundary multiple reflection problems will occur. With the increase of the anchoring layer, not only will the low-frequency guided waves leak, but also they will be severely attenuated due to the scattering of structures such as pores and cracks in the surrounding medium of the anchor rod, resulting in that the guided wave signal becomes very weak after a short distance of propagation, and it is difficult to detect the effective signal. Existing researches have shown that although high-frequency guided waves contain multiple modes, there are still low-attenuation guided wave modes suitable for anchored anchor rod detection, and the short wavelength characteristics of the low-attenuation high-frequency modes can be more sensitive to small defects of the anchor rod.

[0003] Under laboratory conditions, an anchored anchor rod system is usually composed of an anchor rod and an anchoring medium, wherein the anchoring medium is usually cast with mortar or concrete, and the radial casting size is often small, so the guided waves cannot propagate to the far distance semi-infinite space, resulting in multiple reflection echoes of the guided waves at the anchoring boundary. At the same time, the actual anchoring support system is mainly composed of three layers of anchor rod, anchoring agent and surrounding rock. The existing double-layer model composed of anchor rod and anchoring medium assumes that the anchor rod is directly cast in the surrounding rock layer, ignoring the influence of the waveguide characteristics of the anchoring agent layer. Therefore, it is of great significance to establish a three-layer anchored anchor rod structure that maps the real conditions. SUMMARY

[0004] The purpose of the present application is to provide a high-frequency guided wave detection method for crack defects of an anchored anchor rod, in order to solve the problem that the current technology for detecting crack defects of an anchored anchor rod using high-frequency guided waves is not mature and is easily affected by external factors during the detection process.

[0005] To achieve the above-mentioned purpose, the present application provides, in one aspect, a high-frequency guided wave detection system for crack defects of an anchored anchor rod, comprising: a nonlinear high-energy ultrasonic testing system, a digital oscilloscope, a signal amplifier, an attenuator, a duplexer, a probe, and a computer control system.

[0006] The nonlinear high-energy ultrasonic testing system excites a high-frequency guided wave excitation signal.

[0007] The attenuator attenuates the signal by 6dB to prevent the damage of high-power signal peak burst to the test equipment;

[0008] The combination of the duplexer and the probe can realize that a single sensor probe is used for transmitting and receiving signals simultaneously;

[0009] The digital oscilloscope collects and stores signals and transmits the signals to the computer control system;

[0010] One end of the probe is a piezoelectric transducer.

[0011] Further, the piezoelectric transducer comprises a piezoelectric crystal, a matching layer, an electrode layer, an acoustic absorption material, a cable joint and a shell.

[0012] The piezoelectric crystal converts an electric signal into an ultrasonic guided wave when transmitting and converts an ultrasonic guided wave into an electric signal when receiving;

[0013] The matching layer effectively enables the ultrasonic guided wave radiated by the crystal to enter the waveguide structure to be detected, and realizes the acoustic impedance matching between the transducer and the anchor rod;

[0014] The electrode layer is used to realize the piezoelectric effect;

[0015] The acoustic absorption material absorbs the ultrasonic radiation from the back of the crystal, eliminates the interference of multiple reflections of ultrasonic waves at both ends, increases the damping of the crystal, narrows the transmitting pulse to improve the resolution;

[0016] The cable joint is used to connect the probe and the host computer to realize the transmission of electric signals.

[0017] Further, the probe is a straight probe for longitudinal wave detection, adopts a high-damping narrow pulse with a specification N4, the basic frequency is 2.25MHz, the diameter of the circular piezoelectric wafer is 13mm, and the piezoelectric material is lead zirconate titanate ceramic.

[0018] Another aspect of the present application provides a high-frequency guided wave detection method for anchoring an anchor rod crack defect, the anchor rod comprises an insertion section inserted into an anchor hole and an exposed section exposed to the anchor hole, and comprises the following steps:

[0019] S1: Assemble a high-frequency ultrasonic guided wave detection system, connect the probe with the exposed section, perform high-frequency guided wave scanning on the anchor rod, and determine the optimal high-frequency guided wave frequency;

[0020] S2: Test the defect-free anchoring anchor rod under the condition that the system gain is 50dB-80dB, determine the optimal system gain by analyzing the advantages and disadvantages of the bottom echo and the overall guided wave signal;

[0021] S3: Detect the defect-free anchoring anchor rod sample, analyze the time-domain waveforms of different first wave widths, and determine the optimal frequency bandwidth;

[0022] S4: using the optimal values of the high-frequency guided wave frequency, system gain and frequency bandwidth obtained in steps S1-S3, performing nondestructive testing on the defective anchoring anchor rod, and calculating the defect position of the anchoring anchor rod;

[0023] S5: using the reflection coefficient C Re and the crack defect degree H to determine the defect degree.

[0024] Further, in step S1, the frequency of the high-frequency guided wave scanning is 2.00-3.50 MHz.

[0025] Further, in step S3, the first wave width is 0.015-0.025 ms.

[0026] Further, in step S5, the relative reflection coefficient C Re and the crack defect degree H are in a nonlinear relationship, and are expressed by a polynomial fitting formula as follows:

[0027] C Re = 0.00425H 3 - 0.06462H 2 + 0.32173H.

[0028] In summary, the present application has the following beneficial effects over the prior art:

[0029] In order to nondestructively test the defect degree and position of the anchoring anchor rod, the present application constructs a high-frequency ultrasonic guided wave nondestructive testing system, uses the frequency scanning method to perform high-frequency guided wave testing on the "anchor rod-resin-surrounding rock" three-layer anchoring anchor rod specimen, analyzes the echo signal state and distribution characteristics, optimizes the best excitation frequency, system gain and first wave width, and nondestructively tests the anchoring anchor rod containing different defect degrees, thereby achieving the purpose of testing the defect degree and defect position.

[0030] The high-frequency ultrasonic guided wave nondestructive testing method and the testing system constructed by the present application can nondestructively test large-size three-layer anchoring anchor rod structures, and provide an efficient and reliable method for nondestructive testing of anchoring anchor rods in actual engineering.

[0031] The ultrasonic guided wave nondestructive testing system constructed by the present application can detect the defect degree and position of the anchoring anchor rod. The defect position detection error is not more than 2%; with the increase of the crack defect degree, the amplitude peak value of the crack defect echo presents an upward trend, and the bottom echo presents a downward trend. BRIEF DESCRIPTION OF DRAWINGS

[0032] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings:

[0033] Figure 1 This is a schematic diagram of a high-frequency ultrasonic guided wave detection system.

[0034] Figure 2 This is a diagram of the probe structure.

[0035] Figure 3 The structure of the anchor bolt test specimen;

[0036] Figure 4 The frequency response curve of the ultrasonic sensor;

[0037] Figure 5 The signal distribution characteristics of high-frequency guided wave scanning anchor bolts;

[0038] Figure 6 Typical echo type for defect-free anchor bolt specimens;

[0039] Figure 7 The trend of the peak amplitude of the bottom echo in the signal aggregation state as a function of frequency;

[0040] Figure 8 Guided wave detection results under different system gains;

[0041] Figure 9 Time-domain waveforms for different first-wave widths;

[0042] Figure 10 The variation of bottom echo packet parameters with the width of the first wave;

[0043] Figure 11 Guided wave signals for non-destructive testing of anchor bolts;

[0044] Figure 12 The echo signal amplitude varies with the degree of defect;

[0045] Figure 13 This represents the variation of the relative reflection coefficient with the degree of defect.

[0046] The above figures include the following reference numerals:

[0047] 1. Electrode layer; 2. Matching layer; 3. Piezoelectric crystal; 4. Absorbing material layer; 5. Cable connector. Detailed Implementation

[0048] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0049] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, the singular form may also include the plural form unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0050] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0051] See Figure 1 As shown, the present invention provides a high-frequency guided wave detection system for anchor bolt crack defects, comprising: a nonlinear high-energy ultrasonic testing system, a digital oscilloscope, a signal amplifier, an attenuator, a duplexer, a probe, and a computer control system;

[0052] A nonlinear high-energy ultrasonic testing system excites a high-frequency guided wave excitation signal;

[0053] The attenuator attenuates the signal by 6dB to prevent damage to the test equipment from high-power signal peak bursts.

[0054] The combination of a duplexer and a probe enables a single sensor probe to be used for both transmitting and receiving signals simultaneously.

[0055] Digital oscilloscopes acquire and store signals and transmit them to a computer control system;

[0056] like Figure 2 As shown, the probe is a straight probe used for longitudinal wave detection, employing a high-damping narrow pulse of specification N4, with a fundamental frequency of 2.25MHz, a circular piezoelectric crystal with a diameter of 13mm, and the piezoelectric material is lead zirconate titanate ceramic.

[0057] A piezoelectric transducer comprises a piezoelectric crystal, a matching layer, an electrode layer, sound-absorbing material, a cable connector, and a housing. The piezoelectric crystal primarily converts electrical signals into ultrasonic guided waves during transmission and vice versa. The matching layer effectively guides the ultrasonic guided waves radiated by the crystal into the waveguide structure under test (anchor end face), achieving acoustic impedance matching between the transducer and the anchor. The electrode layer is used to realize the piezoelectric effect. The sound-absorbing material absorbs the ultrasound radiated from the back of the crystal, eliminating multiple reflections at its ends and increasing crystal damping, thus narrowing the transmitted pulse and improving resolution. The cable connector connects the probe to the main unit, enabling electrical signal transmission.

[0058] This invention provides a high-frequency guided wave detection method for crack defects in anchor bolts, wherein the anchor bolt includes an insertion section inserted into the anchor hole and an exposed section exposed outside the anchor hole, comprising the following steps:

[0059] S1: Assemble the high-frequency ultrasonic guided wave detection system, connect the probe to the exposed section, perform high-frequency guided wave scanning on the anchor bolt, and determine the high-frequency guided wave frequency;

[0060] As a preferred option, the frequency of the high-frequency guided wave scanning is 2.00MHz to 3.50MHz.

[0061] S2: Test the defect-free anchor bolt with a system gain of 50dB to 80dB. Determine the optimal system gain by analyzing the bottom echo and the overall signal of the guided wave.

[0062] S3: Test the defect-free anchor bolt specimens and analyze the time-domain waveforms with different first wave widths to determine the optimal frequency bandwidth;

[0063] As a preferred option, the initial waveform width is 0.015ms to 0.025ms;

[0064] S4: Use the high-frequency guided wave frequency, system gain and frequency bandwidth obtained in steps S1 to S3 to perform non-destructive testing on the defective anchor rod and calculate the location of the defect in the anchor rod.

[0065] S5: Use reflection coefficient C Re The degree of defect is determined by a polynomial fitting formula between the defect degree H and the crack defect degree.

[0066] As a preferred option, the relative reflectance coefficient C Re The relationship between the crack defect degree H and the nonlinearity is expressed by a polynomial fitting formula as follows:

[0067] C Re =0.00425H 3 -0.06462H 2 +0.32173H (1)

[0068] Example:

[0069] I. Anchor Bolt Test Model

[0070] Anchor bolt specimens consist of three parts: anchor bolt, anchoring agent, and surrounding rock. The dimensions of each part of the model include radial and axial dimensions, and the relative positional relationships of each layer need to be arranged according to the actual situation.

[0071] Regarding the radial dimensions of the anchor bolt, the bolt diameter is 20mm. To ensure anchoring quality, the difference between the bolt diameter and the anchoring agent diameter is generally 6-10mm. Therefore, an anchoring agent layer with an inner diameter of 20mm and an outer diameter of 30mm is designed. To simulate an infinite surrounding rock in a laboratory setting, this paper designs a surrounding rock layer with an inner diameter of 30mm and an outer diameter of 180mm, the cross-section of which is shown in the diagram. Figure 3 As shown in (a). Regarding the axial dimensions of the anchor bolt, the length of the anchor bolt and the surrounding rock mass are both 1000 mm, the length of the anchoring agent is 900 mm, and the bottom of the anchor bolt and the anchoring agent is 100 mm from the bottom of the surrounding rock mass. The length and relative position of each layer of the model are shown in (a). Figure 3 (b)

[0072] II. Fabrication of Defective Anchor Bolts

[0073] (1) Surrounding rock strata and borehole construction

[0074] Cylindrical PVC pipes of the specified anchoring model dimensions were selected as the surrounding rock layer molds, placed vertically, and their bottoms sealed. For the pre-drilled holes to create the anchor bolt insertion points, PVC pipes with an outer diameter of 30mm were selected based on the dimensions, with a length of 1.5m for easy removal after pouring. The pipes were fixed in position along the center of the model's axis. Before pouring, a release agent was applied to the mold's contact surface, stirred, and then concrete was gradually poured in. After pouring, a vibrator was used to shake for 1-2 minutes to remove air bubbles. Before complete solidification, the pre-drilled pipes were removed. The demolded specimens underwent a 28-day curing period.

[0075] (2) Anchor bolt specimen processing

[0076] Based on the designed anchor bolt length, two types of specimens were prepared: one without defects and one with cracks. One specimen was prepared without defects, and one specimen had three different degrees of defects. For cracks, wire cutting was used at a distance of 0.5m from the end of the anchor bolt, with a width of 1mm and depths of 5mm, 10mm, and 15mm respectively.

[0077] (3) Anchor bolts are anchored into the surrounding rock.

[0078] First, the defects of each anchor rod are sealed with bandages to prevent the anchoring agent from seeping into the cracks. Then, anchor rods with different degrees of crack defects are fixed in the reserved holes, so that they coincide in the axial direction and maintain a fixed distance at the bottom. Then, the resin material is prepared according to the material ratio. For the filling of the resin material, the resin filling volume is designed. According to the theoretical calculation formula of the anchor rod anchoring length, considering the amount loss in the test anchoring process, the coefficient k is used for correction. The length of the resin anchoring agent used in the test can be calculated by formula (2):

[0079]

[0080] In the formula, L r L represents the length of the anchoring agent, in meters (m). a D is the maximum anchorage length (m); D is the borehole diameter (mm); d is the threaded anchor diameter (mm). r is the diameter of the anchoring agent, in mm; k is the correction factor, taken as 1.1.

[0081] According to formula (2), the MSZ2875 medium-speed resin anchoring agent with a diameter of 28 mm and a length of 70 cm designed and manufactured meets the requirements.

[0082] Finally, after cleaning the pre-drilled holes in the specimen, a customized resin anchoring agent was placed inside. The anchor rod end was fixed to the drilling head using a connecting structure. The drilling machine was driven vertically and rotated at a certain rate to drill in, so that the anchor rod could continuously anchor into the bottom while stirring the resin material. The overall anchoring time was limited to within 25 seconds, and the gelation time was 180 seconds to ensure complete anchoring. Excess resin was cleaned up, and the specimen was placed indoors at room temperature for 3 days before testing.

[0083] III. Determining the Optimal Excitation Frequency

[0084] To obtain the propagation characteristics of high-frequency guided waves in anchored bolts and the optimal excitation frequency, scanning tests are usually performed near the peak frequency of the sensor to determine this.

[0085] The frequency response curve of the contact longitudinal wave straight probe sensor used in this invention is as follows: Figure 4 As shown, its peak frequency is 2.47MHz. Therefore, high-frequency guided wave scanning is performed on the defect-free anchor bolt specimen in the frequency range of 1.50MHz to 3.50MHz with a step size of 0.05MHz.

[0086] Statistical analysis of signal distribution characteristics of anchor bolts using various high-frequency guided wave scanning results is as follows: Figure 5 As shown, the signal is mainly absent in the frequency range of 1.50MHz to 1.95MHz. In the frequency range of 2.00MHz to 3.50MHz, the bottom echo packets exhibit two forms: signal convergence and signal separation, which are distributed alternately in frequency.

[0087] like Figure 6 As shown, a detailed analysis is conducted using three typical signal states as examples: a no-signal state at 1.70MHz, a signal aggregation state at 2.40MHz, and a signal separation state at 3.10MHz.

[0088] Depend on Figure 6 (a) It can be seen that when the frequency of the high-frequency guided wave is 1.70MHz, no obvious bottom echo appears. The echo near the anchoring boundary of the high-frequency guided wave excitation end is obvious. The axial propagation of the high-frequency guided wave at this frequency is greatly affected by the anchoring boundary. Most of the high-frequency guided wave energy will form a reflected echo and undergo boundary leakage attenuation when it propagates to the interface between the anchor rod and the anchoring agent. The energy propagating along the anchor rod axis will have no echo signal because the attenuation is too large and the propagation distance is too small.

[0089] Depend on Figure 6 (b) It can be seen that the bottom echo can be clearly detected when the frequency of the high-frequency guided wave is 2.40MHz, which is a typical signal convergence state. This indicates that the high-frequency guided wave energy propagates along the anchor rod axis under this frequency state, and less energy is reflected or leaked on the anchor rod surface, resulting in a clear bottom echo.

[0090] And by Figure 6 (c) It can be seen that when the frequency of the high-frequency guided wave is 3.10MHz, the bottom echo packet separation occurs, which is a typical signal separation state. The reason is that although the energy of the corresponding high-frequency guided wave is concentrated inside the anchor rod, it is not distributed along the axial center of the anchor rod. The bottom echo packet generates a large energy dispersion, and the echo signal cannot be used as an effective detection signal.

[0091] Therefore, it can be seen that the signal convergence state can receive valid signal packets, and the corresponding frequency can be used as the excitation wave frequency for detecting anchor bolts. To determine the optimal excitation frequency, the peak amplitude of the first bottom echo in the signal convergence state within the range of 2.00MHz to 3.50MHz was extracted and analyzed as a function of frequency, as shown below. Figure 7 As shown, the peak value of the bottom echo amplitude fluctuates with increasing frequency, reaching its maximum at 2.40MHz, indicating minimal attenuation at this frequency. This frequency can be considered the optimal excitation frequency for the high-frequency guided wave test of the anchor bolt specimen in this paper.

[0092] IV. Determining the Optimal System Gain

[0093] Due to the high attenuation characteristics of high-frequency guided waves, signal amplification is usually required during guided wave testing. However, while amplifying the effective signal, the amplifier also amplifies the background noise in the system. When the signal is excessively amplified, the signal-to-noise ratio decreases. Furthermore, the amplifier in the test system has a dynamic range; exceeding this limit will lead to signal distortion or the risk of multimode guided wave aliasing, making it impossible to accurately calculate the propagation speed of the high-frequency guided wave in the anchor bolt. Therefore, it is necessary to compensate by increasing the system gain and selecting the optimal system gain parameters. This invention uses a high-frequency guided wave with an excitation frequency of 2.40MHz to test defect-free anchor bolts with system gains of 50dB, 60dB, 70dB, and 80dB. By analyzing the bottom echo and the overall guided wave signal, the optimal system gain is determined.

[0094] Depend on Figure 8 It can be seen that when the system gain is 50dB, the first bottom echo can be clearly received, but the second bottom echo cannot be received; when the system gain is 60dB, both bottom echoes can be clearly received; when the system gain is 70dB, the change in the amplitude of the bottom echo signal is not significant, but the amplitude of the reflected echo at the anchorage boundary is significantly enhanced, and the appearance time of the bottom echo packet is prolonged, accompanied by dispersion; when the system gain is 80dB, although both bottom echoes can be clearly received, the influence of the echo at the anchorage interface is more significant, and the first bottom echo signal shows signal saturation, which is very unfavorable for close-range defect detection. Therefore, the optimal system gain of the test system of this invention is determined to be 60dB.

[0095] V. Determining the Optimal Frequency Bandwidth

[0096] The frequency bandwidth of the excitation wave determines the range of frequency components during transmission. A wider bandwidth means the high-frequency guided wave contains more frequency components, which, due to dispersion effects, arrive at the receiver at different speeds, resulting in waveform elongation and energy diffusion. Therefore, controlling the frequency bandwidth of the excitation wave is a method to reduce the effects of dispersion.

[0097] Since frequency bandwidth is a mapping of the first wave width in the frequency spectrum, this invention directly studies the first wave width of the excitation wave of high-frequency guided waves. The center frequency is set to 2.40MHz and the system gain to 60dB. The first wave widths are 0.005ms, 0.015ms, 0.025ms, 0.050ms, and 0.075ms, respectively. Defect-free anchor bolt specimens are tested, and the time-domain waveforms of different first wave widths are analyzed to determine the optimal frequency bandwidth.

[0098] from Figure 9It can be seen that obvious bottom echoes are visible at all first wave widths. When the first wave width is 0.005ms, the bottom echo dispersion is severe, the wave packet shows multi-peak separation, and the echo amplitude does not reach the normal size. The second bottom echo cannot be received. When the first wave width is 0.015ms to 0.025ms, the bottom echo energy is obviously concentrated, and two clear echo wave packets are observed. When the first wave width is 0.050ms to 0.075ms, the bottom echo wave packet energy is concentrated, but wave packet superposition occurs. The two wave packets are severely elongated, and multiple places show a wave superposition pattern, making it impossible to accurately determine the position of the bottom echo peak.

[0099] To optimize the frequency bandwidth, a detailed analysis of the peak amplitude and packet width of the bottom echo packet is performed, such as... Figure 10 As shown, the peak amplitude of the bottom echo packet initially increases and then gradually stabilizes with the increase of the first wave width. The first wave width of 0.025ms and beyond can more accurately reflect the amplitude level of the bottom echo. Meanwhile, the packet width increases linearly with the increase of the first wave width, and the dispersion characteristics of the high-frequency guided wave gradually become more significant, corresponding to the actual signal conditions. Therefore, 0.025ms is determined to be the optimal first wave width.

[0100] VI. Calculate the location of defects in the anchor bolt.

[0101] Based on the previous research, a high-frequency guided wave with a center frequency of 2.40MHz, a system gain of 60dB, and a first wave width of 0.025ms was used to perform non-destructive testing on anchor bolts with prefabricated defects.

[0102] The results of guided wave signal detection are as follows Figure 11 As shown, primary and secondary bottom echoes can be detected in defect-free anchor bolts, while primary defect echoes and bottom echoes can be detected in anchor bolts with prefabricated defects, although secondary defect echoes and bottom echoes are not very obvious.

[0103] To detect the location of defects, the times corresponding to the peak amplitudes of the defect echo and the first bottom echo were extracted, as shown in Table 1. Based on the time-length relationship, the locations of defects of different degrees in the anchor bolt can be calculated, with an error of less than 2.0% compared to the actual defect location (0.5m from the end).

[0104] Table 1 Defect Location Detection Results

[0105]

[0106] VII. Determine the degree of anchor bolt defects

[0107] The variation of wave packet amplitude of the defect echo and bottom echo in the first echo with the depth of the defect damage was statistically analyzed. Figure 12It can be seen that as the depth of the defect increases, the ultrasonic guided wave is reflected at the defect damage interface, which causes the amplitude of the defect echo to gradually increase, while the amplitude of the bottom echo gradually decreases.

[0108] When the crack defect is 10mm, that is, when the defect area accounts for half of the anchor bolt cross-sectional area, the defect echo is basically the same as the bottom echo.

[0109] like Figure 13 As shown, the relative reflection coefficient at different defect depths is calculated, and numerical fitting is performed on the data points to obtain the relative reflection coefficient C. Re The relationship between the crack defect degree H and the nonlinearity is determined by a polynomial fitting formula:

[0110] C Re =0.00425H 3 -0.06462H 2 +0.32173H (3)

[0111] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-frequency guided wave detection system for crack defects in anchor bolts, characterized in that, Includes a nonlinear high-energy ultrasonic testing system, digital oscilloscope, signal amplifier, attenuator, duplexer, probe, and computer control system; A nonlinear high-energy ultrasonic testing system excites a high-frequency guided wave excitation signal; The attenuator attenuates the signal by 6dB to prevent damage to the test equipment from high-power signal peak bursts. The combination of a duplexer and a probe enables a single sensor probe to be used for both transmitting and receiving signals simultaneously. Digital oscilloscopes acquire and store signals and transmit them to a computer control system; One end of the probe is a piezoelectric transducer.

2. The high-frequency guided wave detection system for anchor bolt crack defects according to claim 1, characterized in that, The piezoelectric transducer includes a piezoelectric crystal, a matching layer, an electrode layer, a sound-absorbing material, a cable connector, and a housing; The piezoelectric crystal converts electrical signals into ultrasonic guided waves when transmitting and converts ultrasonic guided waves back into electrical signals when receiving. The matching layer effectively allows the ultrasonic guided waves radiated by the crystal to enter the waveguide structure under test, thereby achieving acoustic impedance matching between the transducer and the anchor. The electrode layer is used to achieve the piezoelectric effect; The sound-absorbing material absorbs ultrasound radiated from the back of the crystal, eliminates multiple ultrasound reflections at both ends, increases crystal damping, and narrows the emitted pulse to improve resolution. The cable connector is used to connect the probe and the host to achieve electrical signal transmission.

3. The high-frequency guided wave detection system for anchor bolt crack defects according to claim 1, characterized in that, The probe is a straight probe for longitudinal wave detection, using a high-damping narrow pulse of specification N4, with a basic frequency of 2.25MHz, a circular piezoelectric crystal with a diameter of 13mm, and the piezoelectric material is lead zirconate titanate ceramic.

4. A high-frequency guided wave detection method for crack defects in anchor bolts, wherein the anchor bolt comprises an insertion section inserted into the anchor hole and an exposed section exposed outside the anchor hole, characterized in that, Including the following steps: S1: Assemble the high-frequency ultrasonic guided wave detection system, connect the probe to the exposed section, perform high-frequency guided wave scanning on the anchor bolt, and determine the optimal high-frequency guided wave frequency; S2: Test the defect-free anchor bolt with a system gain of 50dB to 80dB. Determine the optimal system gain by analyzing the bottom echo and the overall signal of the guided wave. S3: Test the defect-free anchor bolt specimens and analyze the time-domain waveforms with different first wave widths to determine the optimal frequency bandwidth; S4: Use the optimal values ​​of high-frequency guided wave frequency, system gain and frequency bandwidth obtained in steps S1 to S3 to perform non-destructive testing on the defective anchor rod and calculate the location of the defect in the anchor rod. S5: Use reflection coefficient C Re The degree of defect is determined by a polynomial fitting formula between the defect degree H and the crack defect degree.

5. The high-frequency guided wave detection method for anchor bolt crack defects according to claim 4, characterized in that, In step S1, the frequency of the high-frequency guided wave scanning is 2.00MHz to 3.50MHz.

6. The high-frequency guided wave detection method for anchor bolt crack defects according to claim 4, characterized in that, In step S3, the first wave width is 0.015ms to 0.025ms.

7. The high-frequency guided wave detection method for anchor bolt crack defects according to claim 4, characterized in that, In step S5, the relative reflection coefficient C Re The relationship between the crack defect degree H and the nonlinearity is expressed by a polynomial fitting formula as follows: C Re =0.00425H 3 -0.06462H 2 +0.32173H。

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