Concrete crack detection method based on infrared thermal field and Rayleigh wave field coupling

Abstract

The invention discloses a concrete crack detection method based on coupling of an infrared thermal field and a Rayleigh wave field, which comprises the following steps of: comprehensively scanning concrete in a target area by adopting an infrared thermal imaging method, and identifying the position of a concrete crack; calculating the depths of a superficial crack, a deep crack and a junction region crack; extracting Rayleigh wave amplitude attenuation characteristics to calculate crack width, and inverting a crack inclination angle based on time domain waveform head wave arrival time difference; superposing an infrared thermal imaging method detection result and a Rayleigh wave detection result, and constructing a three-dimensional visual crack model by adopting a linear interpolation algorithm; the crack position, the crack depth, the crack width, the crack inclination angle and the three-dimensional visual crack model are input, and a mass concrete crack detection report is generated. Through coupling detection of an infrared thermal field and a Rayleigh wave field, seamless connection of a shallow crack and a deep crack is achieved, a three-dimensional visual crack model is constructed, and the problems that a traditional method is low in efficiency, poor in precision and incomplete in coverage are solved.

Description

Technical Field

[0001] The invention relates to the technical field of nondestructive testing of concrete structures, and in particular to a concrete crack detection method based on coupling of infrared thermal field and Rayleigh wave field. Background Art

[0002] As one of the most widely used materials in modern construction, the structural safety of concrete directly determines the lifespan and use function of the project. Cracks, as the most common form of concrete damage, are not only a channel for water and corrosive media to invade, but also a cause of reduced structural bearing capacity.

[0003] Accurate detection and quantitative evaluation of cracks have become a core issue in the field of engineering safety. Although the current mainstream detection technologies all have significant limitations, they are as follows: Infrared thermal imaging is limited by the low thermal diffusion coefficient of concrete and can only detect shallow cracks (<5cm), and is easily affected by ambient temperature and wind speed. The Rayleigh wave method is sensitive to deep cracks, but is affected by the near-field effect and has a low resolution in shallow layers. The impact echo method requires densely arranged grids to ensure coverage, and its efficiency is low and it is difficult to meet the comprehensive detection needs of large volumes of concrete; the ultrasonic method has strict requirements on surface flatness, and the signal attenuation is serious on rough or wet surfaces; the penetration depth of geological radar electromagnetic waves in concrete is limited by the shielding effect of the steel mesh.

[0004] In summary, it is difficult to achieve full-depth, high-precision, non-destructive detection of concrete cracks with existing technologies. This invention aims to break through the limitations of a single method and provide a new generation of solutions for engineering health diagnosis by coupling infrared thermal field with Rayleigh wave field and combining it with three-dimensional modeling technology. Summary of the invention

[0005] In order to solve the problem of accurate detection and quantitative evaluation of concrete cracks, the present invention provides a concrete crack detection method based on the coupling of infrared thermal field and Rayleigh wave field. Through the coupling detection of infrared thermal field and Rayleigh wave field, the seamless connection of shallow cracks and deep cracks is achieved, and a three-dimensional visualized crack model is constructed to solve the problems of low efficiency, poor accuracy and incomplete coverage of traditional methods. The present invention is suitable for the rapid positioning, size measurement and three-dimensional visualization of shallow cracks (<5 cm) and deep cracks (≥5 cm).

[0006] To achieve the above object, the present invention provides the following technical solution: a concrete crack detection method based on infrared thermal field and Rayleigh wave field coupling, comprising the following steps: Step S1: Use infrared thermal imaging to comprehensively scan the concrete in the target area, continuously record the changes in the temperature field on the concrete surface, and identify the location of concrete cracks through sudden changes in temperature gradient; concrete cracks are divided into shallow cracks, deep cracks, and cracks in the boundary area; Step S2: For superficial cracks, calculate the depth of superficial cracks based on the simplified model of the one-dimensional heat conduction equation; Step S3: For deep cracks, arrange multi-channel sensors perpendicular to the trend of deep cracks, excite Rayleigh waves to record the time-domain waveform, determine the cut-off frequency through the mutation point of the spectral ratio curve, and calculate the depth of deep cracks; Step S4: For cracks in the junction area, simultaneously use the infrared thermography method and the Rayleigh wave method to detect the depth of cracks in the junction area. If the depth error < 10%, take the average value detected by the infrared thermography method and the Rayleigh wave method; otherwise, optimize the parameters and re-detect; Step S5: For superficial cracks, deep cracks and cracks in the junction area, extract the amplitude attenuation characteristics of Rayleigh waves and calculate the crack width; based on the time difference of the arrival time of the first wave in the time-domain waveform, invert the crack dip angle; Step S6: Superimpose the detection results of the infrared thermography method and the Rayleigh wave detection results, and use the linear interpolation algorithm to construct a three-dimensional visual crack model; Step S7: Input the crack position in Step S1, the depth of cracks in Steps S2 to S4, the crack width and crack dip angle in Step S5, and the three-dimensional visual crack model in Step S6 to generate a large-volume concrete crack detection report.

[0007] Further, in Step S1, use the infrared thermography method to comprehensively scan the concrete in the target area, continuously record the change of the concrete surface temperature field, and identify the concrete crack position through the mutation of the temperature gradient. The specific process is as follows: Step S11, use the pulsed heat source of the infrared thermograph to instantaneously heat the surface of the concrete in the target area, and immediately start the infrared thermograph after heating to continuously record the change of the concrete surface temperature field; Step S12, extract the data of the change of the concrete surface temperature field after heating, and calculate the temperature gradient of each pixel point through formula (1), expressed as: (1); In the formula, represents the temperature difference of any point on the surface of the concrete in the target area; represents the highest temperature of the point; is the lowest temperature of the point; Step S13, set the threshold as = 3σ T , if it exceeds the set threshold, it is determined as the crack area, where σ T is the standard deviation of the ambient temperature.

[0008] Further, in Step S2, calculate the depth of superficial cracks based on the simplified model of the one-dimensional heat conduction equation, specifically expressed as: (2); Wherein, is the depth of the surface crack; is the concrete thermal diffusivity; is the initial temperature difference, i.e., the temperature difference between the concrete surface and the environment at the end of heating; is the remaining temperature difference in the surface crack area at time t, where t is the time after thermal excitation.

[0009] Further, in step S3, multi-channel sensors are arranged perpendicular to the deep crack direction, Rayleigh waves are excited to record the time-domain waveform, and the cut-off frequency is determined through the mutation point of the spectrum ratio curve to calculate the depth of the deep crack; the specific process is as follows: Step S31, multi-channel sensors are arranged perpendicular to the deep crack direction, the channel spacing is 40 - 60 cm, the number of sensors ≥ 4, and they are symmetrically distributed on both sides of the deep crack; a hammer or a piezoelectric transducer is used to excite Rayleigh waves, and the multi-channel Rayleigh wave time-domain waveform data is synchronously collected through a data acquisition instrument; Step S32, the Fourier transform is used to obtain the spectrum of the signals at all sensor measurement points and the amplitude spectrum is obtained, and the mean value of the spectrum ratios of the signals at all sensor measurement points is calculated according to formula (3), expressed as: (3); Wherein, i is the sensor number, ; n is the total number of arranged sensors, n ≥ 4 and is an even number; is the spectrum ratio between the channel and the i-th channel sensor; is the signal frequency-domain amplitude of the channel sensor, is the signal frequency-domain amplitude of the i-th channel sensor; Step S33, define the mean value of the spectrum ratio = 0.5 corresponding frequency as the cut-off frequency f c , the cut-off frequency f c corresponding to one-third of the Rayleigh wave wavelength is the depth of the deep crack, calculated as formula (4), expressed as: (4); Wherein, is the depth of the deep crack; f c is the cut-off frequency; is the Rayleigh wave velocity; The Rayleigh wave velocity in formula (4) is obtained through the wave velocity calibration test of the concrete in the complete target area, expressed as: (5); Wherein, L is the known sensor spacing, and Δt is the arrival time difference of the first wave of Rayleigh waves.

[0010] Furthermore, in step S4, for cracks in the junction area, the infrared thermography method and the Rayleigh wave method are simultaneously used to detect the depth of cracks in the junction area. If the depth error is < 10%, the average value detected by the infrared thermography method and the Rayleigh wave method is taken; otherwise, the parameters are optimized and the detection is repeated. The specific process is as follows: Perform cross-validation and error correction on cracks in the junction area: Detect using the infrared thermography method and the Rayleigh wave method respectively. If the depth error of the cracks detected by the infrared thermography method and the Rayleigh wave method in the junction area is < 10%, take the average value detected by the infrared thermography method and the Rayleigh wave method as the final result; if the depth error of the cracks detected by the infrared thermography method and the Rayleigh wave method in the junction area is > 10%, adjust the working parameters and repeat the detection, and introduce the impact echo method or the ultrasonic method as a third-party verification. The specific adjustment of the working parameters is to optimize the infrared pulse frequency, correct the concrete thermal diffusion coefficient, use a higher-frequency Rayleigh wave source, and correct the Rayleigh wave velocity.

[0011] Furthermore, in step S5, for surface cracks, deep cracks, and cracks in the junction area, extract the amplitude attenuation characteristics of Rayleigh waves and calculate the crack width; based on the arrival time difference of the first wave in the time-domain waveform, invert the crack dip angle. The specific process is as follows: Step S51, calculate the crack dip angle by calculating the arrival time difference of the first wave signals of adjacent sensors on both sides of the deep crack, expressed as: (6); Wherein, is the crack dip angle, is the arrival time difference of the first wave signals of adjacent sensors on both sides of the deep crack; is the spacing between adjacent sensors on both sides of the deep crack; Step S52, calculate the width of the deep crack through the correlation between amplitude attenuation and crack width. The amplitude attenuation index is calculated by formula (7): (7); Wherein, AI is the amplitude attenuation index; is the amplitude of the sensor behind the deep crack; is the amplitude of the sensor in front of the deep crack; Calibrate the relationship between the amplitude attenuation index and the width of the deep crack through experiments, and represent it using a linear model: (8); Wherein, w is the width of the deep crack; k and b are the fitting parameters of the linear model, k is the slope, and b is the intercept.

[0012] Further, in step S6, the infrared thermography detection results are superimposed on the Rayleigh wave detection results, and a three-dimensional visual crack model is constructed using a linear interpolation algorithm. The specific process is as follows: Based on the detection data of the infrared thermography method and the Rayleigh wave method in steps S1 - S5, the detection data of the infrared thermography method and the Rayleigh wave detection data are unified into the same coordinate system: with the lower left corner of the detection area as the origin, the X-axis along the crack direction, the Y-axis perpendicular to the crack direction, and the Z-axis in the depth direction, a three-dimensional visual crack model is constructed using a linear interpolation algorithm, expressed as: (9); In the formula, is the detection result of the crack position and depth in the concrete of the final target area; and are respectively the detection results of the crack position and depth detected by the infrared thermography method and the detection results of the crack position and depth detected by the Rayleigh wave method; λ is the weight coefficient.

[0013] Further, in step S7, the crack position in step S1, the crack depths in steps S2 to S4, the crack width and crack inclination angle in step S5, and the three-dimensional visual crack model in step S6 are input to generate a large-volume concrete crack detection report. The specific process is as follows: Step S71, integrate the input data, and input the detection result of the crack position and depth in the concrete of the final target area , the deep crack inclination angle θ, the amplitude attenuation index AI, and the deep crack width w; use programming software Python or a typesetting system LaTeX template to automatically generate a detection report; Step S72, the detection report includes the detection time, the target area, the total number of cracks, the scale size information, and includes an infrared temperature gradient thermal map marking the crack contour, a Rayleigh wave spectrum ratio curve marking the cut-off frequency, and a three-dimensional visual crack model diagram showing the spatial distribution of the cracks from multiple perspectives; Step S73, based on steps S71 - S72, use the obtained detection report as the basis for engineering decision-making.

[0014] Compared with the existing technologies, the beneficial effects of the present invention are summarized as follows: Full-depth coverage: A full-depth crack detection scheme for connecting shallow cracks (infrared thermal field) and deep cracks (Rayleigh wave field) is proposed to achieve accurate assessment of crack depth, crack inclination angle, and crack width. Non-destructive: No drilling is required, protecting the structural integrity. High precision: The average error of the fusion data is <5%, supporting three-dimensional visualization and risk quantification assessment. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a schematic diagram of the working process of the present invention; Figure 2Schematic diagram of on-site detection work layout for the present invention; In the figure, 1 is the concrete in the target area; 2 is the deep crack; 3 is the infrared thermal imager; 4 is the multi-channel sensor; 5 is the impact hammer; 6 is the data acquisition instrument. Specific implementation mode

[0016] As Figure 1 shown, the present invention provides a technical solution: a concrete crack detection method based on the coupling of infrared thermal field and Rayleigh wave field, including the following steps: Step S1: Use the infrared thermal imaging method to comprehensively scan the concrete in the target area, continuously record the change of the concrete surface temperature field, and identify the position of the concrete crack through the sudden change of the temperature gradient; the concrete cracks are divided into superficial cracks, deep cracks and cracks in the junction area; Step S2: For superficial cracks, calculate the depth of the superficial cracks based on the simplified model of the one-dimensional heat conduction equation; Step S3: For deep cracks, arrange multi-channel sensors perpendicular to the direction of the deep cracks, excite Rayleigh waves to record the time-domain waveform, determine the cut-off frequency through the sudden change point of the spectral ratio curve, and calculate the depth of the deep cracks; Step S4: For cracks in the junction area, use the infrared thermal imaging method and the Rayleigh wave method simultaneously to detect the depth of the cracks in the junction area. If the depth error < 10%, take the average value detected by the infrared thermal imaging method and the Rayleigh wave method; otherwise, optimize the parameters and re-detect; Step S5: For superficial cracks, deep cracks and cracks in the junction area, extract the amplitude attenuation characteristics of Rayleigh waves and calculate the crack width; based on the time difference of the arrival time of the first wave in the time-domain waveform, invert the crack dip angle; Step S6: Superimpose the detection results of the infrared thermal imaging method and the Rayleigh wave detection results, and use the linear interpolation algorithm to construct a three-dimensional visual crack model; Step S7: Input the crack position in Step S1, the crack depths in Steps S2 to S4, the crack width and crack dip angle in Step S5, and the three-dimensional visual crack model in Step S6 to generate a large-volume concrete crack detection report.

[0017] Furthermore, in Step S1, when using the infrared thermal imaging method to comprehensively scan the concrete in the target area, continuously record the change of the concrete surface temperature field, and identify the position of the concrete crack through the sudden change of the temperature gradient, the specific process is as follows: Step S11, as Figure 2 shown, use the pulsed heat source of the infrared thermal imager to instantaneously heat the surface of the concrete 1 in the target area (pulse width 1 - 2 s, heat flux density controlled at 1 - 2 kW / m²). Immediately after heating, start the infrared thermal imager 3 and continuously record the change of the concrete surface temperature field (sampling frequency ≥ 10 Hz, lasting for 30 - 60 seconds); Step S12, extract the data of the change in the concrete surface temperature field within 0 - 60 seconds after heating, and calculate the temperature gradient of each pixel point through formula (1), expressed as: (1); In the formula, represents the temperature difference at any point on the concrete surface within the target area; represents the highest temperature at the point; is the lowest temperature at the point; Step S13, set the threshold as T = 3σ T , and if it exceeds the set threshold, it is determined as a crack area, where σ

[0018] is the standard deviation of the ambient temperature. (2); In the formula, is the depth of the superficial crack; is the concrete thermal diffusivity ; is the initial temperature difference, i.e., the temperature difference between the concrete surface and the environment at the end of heating; is the remaining temperature difference in the superficial crack area at time t, and t is the time after thermal excitation (60 s in this example).

[0019] Furthermore, in step S3, arrange multi-channel sensors perpendicular to the deep crack trend, excite Rayleigh waves to record the time-domain waveform, and determine the cut-off frequency through the mutation point of the spectral ratio curve to calculate the depth of the deep crack; the specific process is as follows: Figure 2 Step S31, as shown, arrange multi-channel sensors 4 perpendicular to the deep crack trend, with the channel spacing of 40 - 60 cm, and the number of sensors ≥ 4, symmetrically distributed on both sides of the deep crack 2; use a hammer 5 or a piezoelectric transducer to excite Rayleigh waves, and synchronously collect the multi-channel Rayleigh wave time-domain waveform data through a data acquisition instrument 6; Step S32, use Fourier transform to obtain the spectrum of the signals at all sensor test points and obtain the amplitude spectrum, and calculate the average value of the spectral ratios of the signals at all sensor test points according to formula (3), expressed as: (3);In the formula, i is the sensor number, ; n is the total number of arranged sensors, n ≥ 4 and n is an even number; is the spectral ratio between the channel and the i-th channel sensor; is the signal frequency domain amplitude of the th sensor, is the signal frequency domain amplitude of the i-th sensor; is the mean value of the spectrum ratio; Step S33, define the mean value of the spectrum ratio = 0.5, and the corresponding frequency is the cut-off frequency f c , and the cut-off frequency f c corresponding to one-third of the Rayleigh wave wavelength is the depth of the deep crack, which is calculated by the formula (4) and expressed as: (4); In the formula, is the depth of the deep crack; f c is the cut-off frequency; is the Rayleigh wave velocity; The Rayleigh wave velocity in the formula (4) is obtained through the wave velocity calibration test of the concrete in the complete target area, and is expressed as: (5); In the formula, L is the known sensor spacing, and Δt is the arrival time difference of the Rayleigh wave first wave.

[0020] Furthermore, in step S4, for the cracks in the junction area, the infrared thermography method and the Rayleigh wave method are simultaneously used to detect the depth of the cracks in the junction area. If the depth error < 10%, the average value of the infrared thermography method and the Rayleigh wave method is taken; otherwise, the parameters are optimized and re-detected; the specific process is as follows: Cross-validation and error correction are carried out on the cracks in the junction area: the infrared thermography method and the Rayleigh wave method are respectively used for detection. If the depth error of the cracks in the junction area detected by the infrared thermography method and the Rayleigh wave method < 10%, the average value of the detection by the infrared thermography method and the Rayleigh wave method is taken as the final result; if the depth error of the cracks in the junction area detected by the infrared thermography method and the Rayleigh wave method > 10%, the working parameters are adjusted and re-detected, and the impact echo method or the ultrasonic wave method is introduced as a third-party verification. The specific adjustment of the working parameters is to optimize the infrared pulse frequency, correct the concrete thermal diffusion coefficient, use a higher-frequency Rayleigh wave source, and correct the Rayleigh wave velocity.

[0021] Furthermore, in step S5, for the surface cracks, deep cracks and cracks in the junction area, the Rayleigh wave amplitude attenuation characteristics are extracted to calculate the width of the cracks; based on the arrival time difference of the first wave, the crack dip angle is inverted; the specific process is as follows: Step S51, calculate the crack dip angle by calculating the arrival time difference of the first wave signals of the adjacent sensors on both sides of the deep crack, and it is expressed as: (6); In the formula, is the crack dip angle, is the arrival time difference of the first wave signals of adjacent sensors on both sides of the deep crack; is the distance between adjacent sensors on both sides of the deep crack; Step S52, calculate the deep crack width through the correlation between amplitude attenuation and crack width. The amplitude attenuation index is calculated by formula (7): (7); In the formula, AI is the amplitude attenuation index; is the amplitude of the sensor behind the deep crack; is the amplitude of the sensor in front of the deep crack; Calibrate the relationship between the amplitude attenuation index and the deep crack width through experiments, and represent it using a linear model: (8); In the formula, w is the deep crack width; k and b are the fitting parameters of the linear model, k is the slope, and b is the intercept.

[0022] Furthermore, in step S6, superimpose the infrared thermography detection results and the Rayleigh wave detection results, and use the linear interpolation algorithm to construct a three-dimensional visual crack model; the specific process is as follows: Based on the detection data of infrared thermography in steps S1 - S2 and the detection data of Rayleigh wave method in steps S3 - S5, unify the detection data of infrared thermography and the detection data of Rayleigh wave method to the same coordinate system: take the lower left corner of the detection area as the origin, the X-axis along the crack direction, the Y-axis perpendicular to the crack direction, and the Z-axis as the depth direction, and use the linear interpolation algorithm to construct a three-dimensional visual crack model, expressed as: (9); In the formula, is the detection result of the crack position and depth in the concrete of the final target area; , are respectively the detection results of the crack position and depth detected by infrared thermography and the detection results of the crack position and depth detected by Rayleigh wave method; λ is the weight coefficient (in this example, for shallow cracks, λ can be set to 0.8, and for deep cracks, λ can be set to 0.3).

[0023] Furthermore, in step S7, input the crack position in step S1, the crack depth in steps S2 to S4, the crack width and crack dip angle in step S5, and the three-dimensional visual crack model in step S6 to generate a large-volume concrete crack detection report; the specific process is as follows: Step S71, integrate the input data, and input the detection result of the crack position and depth in the concrete of the final target area , the deep crack dip angle θ, the amplitude attenuation index AI, and the deep crack width w; use programming software Python or typesetting system LaTeX template to automatically generate a detection report; Step S72, the inspection report includes inspection time, target area, total number of cracks, size information, and includes an infrared temperature gradient thermal map annotating the crack contour, a Rayleigh wave spectrum ratio curve annotating the cut-off frequency, and a three-dimensional visualization crack model diagram showing the spatial distribution of cracks from multiple perspectives; Step S73, based on Steps S71 - S72, use the obtained inspection report as the basis for engineering decisions.

[0024] The above are the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications that do not depart from the disclosure of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for detecting concrete cracks based on the coupling of infrared thermal field and Rayleigh wave field, characterized in that: It includes the following steps: Step S1: Use the infrared thermography method to comprehensively scan the concrete in the target area, continuously record the change of the concrete surface temperature field, and identify the location of concrete cracks through the sudden change of the temperature gradient; Concrete cracks are divided into superficial cracks, deep cracks and cracks in the junction area; Step S2: For superficial cracks, calculate the depth of the superficial cracks based on the simplified model of the one-dimensional heat conduction equation; Step S3: For deep cracks, arrange multi-channel sensors perpendicular to the trend of the deep cracks, excite Rayleigh waves to record the time-domain waveform, determine the cut-off frequency through the mutation point of the spectral ratio curve, and calculate the depth of the deep cracks; Step S4: For cracks in the junction area, use the infrared thermography method and the Rayleigh wave method simultaneously to detect the depth of the cracks in the junction area. If the depth error < 10%, take the average value detected by the infrared thermography method and the Rayleigh wave method; Otherwise, optimize the parameters and re-detect; Step S5: For superficial cracks, deep cracks and cracks in the junction area, extract the amplitude attenuation characteristics of Rayleigh waves and calculate the crack width; Based on the time difference of the arrival time of the first wave in the time-domain waveform, invert the crack dip angle; Step S6: Superimpose the detection results of the infrared thermography method and the Rayleigh wave detection results, and use the linear interpolation algorithm to construct a three-dimensional visual crack model; Step S7: Input the crack location in Step S1, the crack depths in Steps S2 to S4, the crack width and crack dip angle in Step S5, and the three-dimensional visual crack model in Step S6 to generate a large-volume concrete crack detection report.

2. The concrete crack detection method based on the coupling of infrared thermal field and Rayleigh wave field according to claim 1, characterized in that: In Step S1, use the infrared thermography method to comprehensively scan the concrete in the target area, continuously record the change of the concrete surface temperature field, and identify the location of concrete cracks through the sudden change of the temperature gradient. The specific process is as follows: Step S11, use the pulsed heat source of the infrared thermal imager to instantaneously heat the surface of the concrete in the target area. Immediately start the infrared thermal imager after heating and continuously record the change of the concrete surface temperature field; Step S12, extract the data of the change of the concrete surface temperature field after heating, and calculate the temperature gradient of each pixel point through formula (1), expressed as: （1）； In the formula, represents the temperature difference at any point on the concrete surface within the target area; represents the highest temperature of the point temperature; is the lowest temperature of the point; Step S13, set the threshold value to = 3σ T , and if it exceeds the set threshold value, it is determined as the crack area, where σ T is the standard deviation of the ambient temperature.

3. The concrete crack detection method based on the coupling of infrared thermal field and Rayleigh wave field according to claim 2, wherein: In Step S2, calculate the depth of the superficial cracks based on the simplified model of the one-dimensional heat conduction equation, specifically expressed as: （2）； In the formula, is the depth of the surface crack; is the concrete thermal diffusivity; is the initial temperature difference, i.e., the temperature difference between the concrete surface and the environment at the end of heating; is the remaining temperature difference in the surface crack area at time t, where t is the time after thermal excitation.

4. The method for detecting concrete cracks based on the coupling of infrared thermal field and Rayleigh wave field according to claim 3, characterized in that: In Step S3, arrange multi-channel sensors perpendicular to the trend of the deep cracks, excite Rayleigh waves to record the time-domain waveform, determine the cut-off frequency through the mutation point of the spectral ratio curve, and calculate the depth of the deep cracks; The specific process is as follows: Step S31, arrange multi-channel sensors perpendicular to the trend of the deep cracks, the channel spacing is 40 - 60 cm, the number of sensors ≥ 4, symmetrically distributed on both sides of the deep cracks; Use a hammer or piezoelectric transducer to excite Rayleigh waves, and synchronously collect the time-domain waveform data of multi-channel Rayleigh waves through a data acquisition instrument; Step S32, use the Fourier transform to obtain the spectrum of the signals at all sensor test points and obtain the amplitude spectrum, and calculate the average value of the spectral ratio of the signals at all sensor test points according to formula (3), expressed as: （3）； Where \(i\) is the sensor number, ; \(n\) is the total number of sensors deployed, \(n\geq4\) and \(n\) is an even number; is the spectrum ratio between the th and the \(i\)th sensor; is the signal frequency-domain amplitude of the th sensor, is the mean value of the spectrum ratio; Step S33, define the mean value of the spectral ratio The frequency corresponding to 0.5 is the cut-off frequency f c , the cut-off frequency f c One-third of the Rayleigh wave wavelength corresponding to it is the depth of the deep crack, which is calculated by formula (4) and expressed as: （4）； In the formula, is the depth of the deep crack; f c is the cut-off frequency; is the Rayleigh wave velocity; Rayleigh wave velocity in formula (4) Obtained through wave velocity calibration test on concrete in the complete target area, which means: （5）； In the formula, L is the known sensor spacing, and Δt is the arrival time difference of the first wave of Rayleigh waves.

5. The concrete crack detection method based on the coupling of infrared thermal field and Rayleigh wave field according to claim 4, characterized in that: In step S4, for the cracks in the junction area, the infrared thermography method and the Rayleigh wave method are simultaneously used to detect the depth of the cracks in the junction area. If the depth error is < 10%, the average value detected by the infrared thermography method and the Rayleigh wave method is taken; otherwise, the parameters are optimized and the detection is repeated. The specific process is as follows: Cross-validation and error correction are carried out for the cracks in the junction area: the infrared thermography method and the Rayleigh wave method are respectively used for detection. If the depth error of the cracks in the junction area detected by the infrared thermography method and the Rayleigh wave method is < 10%, the average value detected by the infrared thermography method and the Rayleigh wave method is taken as the final result; if the depth error of the cracks in the junction area detected by the infrared thermography method and the Rayleigh wave method is > 10%, the working parameters are adjusted and the detection is repeated, and the impact echo method or the ultrasonic method is introduced as a third-party verification. The specific adjustment of the working parameters is to optimize the infrared pulse frequency, correct the concrete thermal diffusion coefficient, use a higher-frequency Rayleigh wave source or correct the Rayleigh wave velocity.

6. The concrete crack detection method based on the coupling of infrared thermal field and Rayleigh wave field according to claim 5, characterized in that: In step S5, for the surface cracks, deep cracks and cracks in the junction area, the amplitude attenuation characteristics of the Rayleigh waves are extracted to calculate the crack width; based on the arrival time difference of the first waves in the time-domain waveform, the crack dip angle is inverted. The specific process is as follows: Step S51, the crack dip angle is calculated by calculating the arrival time difference of the first wave signals of the adjacent sensors on both sides of the deep crack, which is expressed as: （6）； In the formula, is the fracture dip angle, is the arrival time difference of the first wave signals of adjacent sensors on both sides of the deep fracture; is the distance between adjacent sensors on both sides of the deep fracture; Step S52, the width of the deep crack is calculated through the correlation between the amplitude attenuation and the crack width. The amplitude attenuation index is calculated by formula (7): （7）； Wherein, AI is the amplitude attenuation index; is the amplitude of the sensor at the rear side of the deep crack; is the amplitude of the sensor at the front side of the deep crack; The relationship between the amplitude attenuation index and the width of the deep crack is calibrated through experiments and is represented by a linear model: （8）； In the formula, w is the width of the deep crack; k and b are the fitting parameters of the linear model, k is the slope and b is the intercept.

7. The concrete crack detection method based on the coupling of infrared thermal field and Rayleigh wave field according to claim 6, characterized in that: In step S6, the detection results of the infrared thermography method and the Rayleigh wave detection results are superimposed, and a three-dimensional visualization crack model is constructed using the linear interpolation algorithm. The specific process is as follows: Based on the detection data of the infrared thermography method and the detection data of the Rayleigh wave method in steps S1 - S5, the detection data of the infrared thermography method and the Rayleigh wave detection data are unified into the same coordinate system: taking the lower left corner of the detection area as the origin, the X-axis is along the crack direction, the Y-axis is perpendicular to the crack direction, and the Z-axis is the depth direction. A three-dimensional visualization crack model is constructed using the linear interpolation algorithm, which is expressed as: （9）； In the formula, is the detection result of the crack position and depth in the concrete of the final target area; , are the detection results of the crack position and depth detected by the infrared thermography method and the detection results of the crack position and depth detected by the Rayleigh wave method, respectively; λ is the weight coefficient.

8. The concrete crack detection method based on the coupling of infrared thermal field and Rayleigh wave field according to claim 7, characterized in that: In step S7, the crack position in step S1, the crack depth in steps S2 to S4, the crack width and the crack dip angle in step S5, and the three-dimensional visualization crack model in step S6 are input to generate a large-volume concrete crack detection report. The specific process is as follows: Step S71, integrate the input data and input the detection results of the position and depth of internal cracks in the concrete of the final target area , the dip angle θ of the deep crack, the amplitude attenuation index AI, and the width w of the deep crack; Use the programming software Python or the typesetting system LaTeX template to automatically generate the detection report; Step S72, the detection report includes the detection time, the target area, the total number of cracks, the scale size information, and includes an infrared temperature gradient thermal map marking the crack contour, a Rayleigh wave spectrum ratio curve marking the cut-off frequency, and a three-dimensional visualization crack model diagram showing the spatial distribution of the cracks from multiple perspectives; Step S73, based on steps S71 - S72, the obtained detection report is used as the basis for engineering decision-making.

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