Beam stress measurement method and device based on multi-frequency ultrasound

Abstract

The invention discloses a beam stress measuring method based on multi-frequency ultrasound and a corresponding measuring device. Ultrasonic probe pairs are arranged on the two opposite side faces of a beam, and each ultrasonic probe pair comprises an ultrasonic transmitter and an ultrasonic receiver which are located on the two opposite side faces of the beam respectively. During measurement, the ultrasonic transmitter is used for transmitting multi-frequency ultrasonic waves, and the ultrasonic receiver is used for receiving the multi-frequency ultrasonic waves. And the main control equipment calculates the stress borne by the beam according to the received multi-frequency ultrasonic waves. According to the invention, frequency dispersion integration is adopted, single-frequency noise is suppressed, and the method has the advantages of strong anti-interference performance, wide applicability and improved precision, and is suitable for health monitoring of concrete structures such as bridges and buildings.

Description

Technical Field

[0001] This invention relates to the field of civil engineering health monitoring and non-destructive testing technology, and in particular to a method and device for measuring beam stress based on multi-frequency ultrasound. Background Technology

[0002] In the health monitoring of civil engineering structures (such as concrete beams, bridges, and buildings), stress measurement is a key step in assessing structural safety and durability.

[0003] In existing technologies, common stress measurement techniques include strain gauge methods and fiber optic sensing methods. Traditional beam stress measurement methods mostly rely on direct sensor installation or external load testing. These methods typically require destructive testing of the structure or depend on complex sensor arrangements, making their implementation complex and limiting. Furthermore, existing measurement technologies struggle to accurately reflect the distribution of normal and shear stresses within beams in real time, especially in the monitoring of large-scale structures (such as bridges and buildings), where the application of traditional methods is significantly restricted.

[0004] Furthermore, strain gauge methods are susceptible to environmental humidity and temperature fluctuations, and can only acquire data at a single point, making it difficult to reflect the stress distribution across the entire cross-section. While fiber optic sensing offers high accuracy, it is complex to install, expensive, and requires strict surface preparation of the object being measured. These existing stress measurement technologies suffer from structural influences, installation difficulties, and low accuracy during application. Especially in complex structures like concrete beams, achieving accurate stress distribution measurement without compromising structural integrity remains a significant technical challenge.

[0005] In recent years, ultrasonic technology has been used for stress monitoring due to its advantages such as non-contact and full-range penetration, but existing research still has the following shortcomings:

[0006] • Single frequency band: It relies solely on the wave velocity variation of a single frequency (such as 0.5MHz) and cannot utilize dispersion characteristics to enhance sensitivity.

[0007] • Ignoring amplitude information: Focusing only on wave velocity while ignoring amplitude attenuation makes it impossible to quantify the damage to microcracks in the tensile zone.

[0008] • Temperature interference is not decoupled: The thermal expansion effect of concrete can mask the wave velocity changes caused by stress, and existing methods lack an effective compensation mechanism.

[0009] • Gap in shear stress detection: Traditional ultrasonic setup methods (such as the through-hole method) are difficult to capture oblique shear deformation and cannot achieve shear stress measurement. Summary of the Invention

[0010] (a) Technical problems to be solved

[0011] The technical problem to be solved by this invention is that existing methods for measuring stress in beams are not sensitive enough and cannot account for amplitude damage caused by microcracks.

[0012] Another technical problem that this invention aims to solve is the inability to effectively measure the shear stress of a beam.

[0013] (II) Technical Solution

[0014] This invention proposes a method for measuring beam stress based on multi-frequency ultrasound, which includes the following steps:

[0015] Step S1: Arrange a pair of ultrasonic probes on two opposite sides of the beam. The ultrasonic probe pair includes an ultrasonic transmitter and an ultrasonic receiver, which are located on opposite sides of the beam respectively. During measurement, the ultrasonic transmitter is used to emit multi-frequency ultrasonic waves, and the ultrasonic receiver is used to receive multi-frequency ultrasonic waves.

[0016] Step S2: Calculate the stress borne by the beam based on the received multi-frequency ultrasonic waves.

[0017] According to a preferred embodiment of the present invention, in step S1, the ultrasonic transmitter and the ultrasonic receiver are located on the same horizontal plane, and their connection is perpendicular to the axis of the beam. During measurement, the ultrasonic transmitter and the ultrasonic receiver are set at multiple positions at different heights of the beam. In step S2, the wave velocity of the multi-frequency ultrasonic wave is calculated, the amplitude of the multi-frequency ultrasonic wave is detected, and the normal stress distribution of the beam section is calculated based on the normal stress calculation formula.

[0018] According to a preferred embodiment of the present invention, the formula for calculating normal stress is:

[0019] in,

[0020] σ b V is the normal stress of the beam section, in MPa; E is the dynamic elastic modulus of the beam, in GPa; V p0 (f) is the reference wave velocity corresponding to frequency f of the beam under stress-free conditions, in km / s and V. p (f) represents the measured wave velocity under stress, in km / s, A0(f) mid A(f) represents the amplitude of the first peak of the beam at the intermediate frequency when the beam is stress-free. mid C represents the amplitude of the first wave peak measured when the beam is under stress. u The wave velocity stress sensitivity coefficient of the beam is expressed in MPa⁻¹, C. a Let be the amplitude damage coefficient of the beam, which is dimensionless.

[0021] According to a preferred embodiment of the present invention, the method further includes step S0: determining the reference wave velocity V corresponding to the frequency f of the beam under stress-free conditions. p0 (f) Calibrate the amplitude A0(f) of the first peak of the beam at the intermediate frequency when the beam is under no stress. mid The beam's wave velocity stress sensitivity coefficient C is calibrated. u Calibration is performed on the beam's amplitude damage coefficient C. a Perform calibration.

[0022] According to a preferred embodiment of the present invention, in step S1, the ultrasonic transmitter and the ultrasonic receiver are located on the same vertical plane, and their connection is at a 45-degree angle to the axis of the beam. Furthermore, during measurement, the ultrasonic transmitter and the ultrasonic receiver are positioned at multiple locations at the same height of the beam.

[0023] In step S2, the wave velocity of the multi-frequency ultrasonic wave is calculated, the amplitude of the multi-frequency ultrasonic wave is detected, and the shear stress distribution of the beam section is calculated based on the shear stress calculation formula.

[0024] According to a preferred embodiment of the present invention, the formula for calculating shear stress is:

[0025] Where τ is the shear stress of the beam section, in MPa, and G is the shear modulus of the beam, in GPa. Δφ is the rate of change of the oblique propagation wave velocity of the beam, in km / s; Δφ is the phase shift of the first wave peak measured under stress, in radians; β and γ are the shear sensitivity coefficients of the beam, dimensionless.

[0026] According to a preferred embodiment of the present invention, the method further includes step S0: calibrating the shear sensitivity coefficients β and γ of the beam.

[0027] According to a preferred embodiment of the present invention, the method further includes step S3: measuring the current temperature of the beam and correcting the calculated stress distribution of the beam section according to the following formula:

[0028] Where, σ means The measured normal or shear stress is η, the thermal expansion coefficient of the beam is T, the current temperature of the beam is T0, and the reference temperature is T0.

[0029] A second aspect of the present invention provides a beam stress measurement device based on multi-frequency ultrasound, comprising: an ultrasonic probe pair, including an ultrasonic transmitter and an ultrasonic receiver, respectively located on two opposite sides of a beam, wherein the ultrasonic transmitter is used to emit multi-frequency ultrasonic waves and the ultrasonic receiver is used to receive multi-frequency ultrasonic waves; and a main control device for controlling the operation of the ultrasonic transmitter and the ultrasonic receiver, and simultaneously calculating the stress borne by the beam based on the received multi-frequency ultrasonic waves.

[0030] In this method, when the beam stress measuring device is used to measure the normal stress of a beam, the ultrasonic transmitter and ultrasonic receiver are located on the same horizontal plane, and their connection is perpendicular to the axis of the beam; the main control device calculates the normal stress according to the following formula:

[0031] in,

[0032] σ b V is the normal stress of the beam section, in MPa; E is the dynamic elastic modulus of the beam, in GPa; V p0 (f) is the reference wave velocity corresponding to frequency f of the beam under stress-free conditions, in km / s, V. p (f) represents the measured wave velocity under stress, in km / s, A0(f) mid A(f) represents the amplitude of the first wave at the intermediate frequency of the beam when it is stress-free. mid C represents the amplitude of the first wave measured under stress on the beam. u The wave velocity stress sensitivity coefficient of the beam is expressed in MPa⁻¹, C. a Let be the amplitude damage coefficient of the beam, which is dimensionless;

[0033] When the beam stress measuring device is used to measure the shear stress of a beam, the ultrasonic transmitter and ultrasonic receiver are located on the same vertical plane, and their connection forms a 45-degree angle with the axis of the beam; the main control device calculates the shear stress according to the following formula: Where τ is the shear stress of the beam section, in MPa, and G is the shear modulus of the beam, in GPa. Δφ is the rate of change of the oblique propagation wave velocity of the beam, in km / s; Δφ is the phase shift of the first wave peak measured under stress, in radians; β and γ are the shear sensitivity coefficients of the beam, dimensionless.

[0034] (III) Beneficial Effects

[0035] This invention proposes a beam stress measurement method based on multi-frequency ultrasound. By applying multi-frequency ultrasound, non-destructive, accurate and real-time stress distribution measurement can be achieved, which is especially suitable for health monitoring of concrete structures such as bridges and buildings.

[0036] This invention, through the combined analysis of multi-frequency ultrasound with wave velocity gradient and phase difference, can effectively overcome the limitations of traditional single-point measurement, and improve the accuracy and application range of measurement. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the beam stress measurement device based on multi-frequency ultrasound according to the first embodiment of the present invention.

[0038] Figure 2 yes Figure 1 In the first embodiment, the oscilloscope displays waveforms of ultrasonic waves at multiple frequencies.

[0039] Figure 3 This is a schematic diagram of the beam stress measurement device based on multi-frequency ultrasound according to the second embodiment of the present invention. Detailed Implementation

[0040] To address the problems existing in the prior art, this invention proposes a beam stress measurement method and corresponding measurement device based on multi-frequency ultrasound.

[0041] This invention arranges pairs of ultrasonic probes on two opposite sides of a beam. Each ultrasonic probe pair includes an ultrasonic transmitter and an ultrasonic receiver, located on opposite sides of the beam. During measurement, the ultrasonic transmitter emits multi-frequency ultrasonic waves, and the ultrasonic receiver receives the multi-frequency ultrasonic waves. The preferred frequency of the multi-frequency ultrasonic waves is 0.1–0.8 MHz.

[0042] This invention calculates the stress borne by the beam based on the received multi-frequency ultrasonic waves. Specifically, this invention uses... This invention converts multi-band ultrasonic data into stress-sensitive indicators, and also incorporates an amplitude attenuation term C. a ·ln(A0 / A) corrects the effect of microcracks in the beam.

[0043] Preferably, the present invention employs a dual-parameter fusion algorithm, which combines the linear weighted sum of the wave velocity change rate (compression zone) and the amplitude logarithmic ratio (tension zone).

[0044] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0045] Figure 1 This is a schematic diagram of the beam stress measurement device based on multi-frequency ultrasound according to the first embodiment of the present invention. Figure 1 As shown, this first embodiment uses a beam stress measurement device based on multi-frequency ultrasound to detect the normal stress of a concrete beam. The normal stress σ of the concrete beam... bThe beam varies in height, with compression at the upper end and tension at the lower end. The device includes an ultrasonic probe pair, a waveform generator, an oscilloscope, and a host computer. The ultrasonic probe pair includes an ultrasonic transmitter and an ultrasonic receiver. The ultrasonic transmitter and receiver are located on opposite sides of the beam. The waveform generator generates multi-frequency ultrasonic waves and transmits them to the ultrasonic transmitter, causing the transmitter to emit multi-frequency ultrasonic waves. The ultrasonic receiver receives the multi-frequency ultrasonic waves and transmits them to the oscilloscope. The host computer, as the main control device, controls the waveform generator to generate ultrasonic waves of multiple frequencies, thereby controlling the ultrasonic transmitter to emit ultrasonic waves. It also controls the operation of the ultrasonic receiver and oscilloscope, enabling the receiver to receive multi-frequency ultrasonic waves and display the ultrasonic waveforms on the oscilloscope. Simultaneously, the host computer also has data processing capabilities, capable of calculating the normal stress on the beam based on the received multi-frequency ultrasonic waves. In other embodiments, the host computer can be replaced by any other device with data processing capabilities, such as a computer with software installed to perform the aforementioned calculations, etc.

[0046] To calculate the normal stress, it is necessary to calibrate the reference wave velocity at each frequency under stress-free conditions and the first wave amplitude at the intermediate frequency (e.g., 0.5 MHz) under stress-free conditions before actual measurement. Furthermore, the wave velocity stress sensitivity coefficient (MPa⁻¹) is calibrated using a three-point bending test, and the amplitude damage coefficient (dimensionless) is calibrated using a crack width-amplitude relationship test.

[0047] Figure 2 yes Figure 1 In the first embodiment, the oscilloscope displays waveforms of ultrasonic waves at multiple frequencies. From Figure 2 As can be seen, the waveforms of ultrasonic waves at four frequencies—0.10MHz, 0.30MHz, 0.50MHz, and 0.70MHz—are displayed, along with a time difference Δt between the time the ultrasonic wave is emitted by the transmitter and the time it is received by the receiver. Furthermore, the location of the first peak amplitude can be observed from the waveforms. Therefore, the host computer can extract the wave velocity by running a corresponding program. and the first peak amplitude A(f mid ), combined with the dynamic elastic modulus E of concrete and the parameter C calibrated through experiments. u C a The normal stress σ of a concrete beam can be inverted. b The calculation formula is as follows:

[0048] in:

[0049] σ b : Normal stress (MPa) of beam section, to be determined and output;

[0050] E: Dynamic elastic modulus of concrete (GPa). In this embodiment, the dynamic elastic modulus E is related to the wave velocity V. p0 Having an experiential relationship (Applicable to C20-C50 concrete).

[0051] V p0 (f): The reference wave velocity (km / s) corresponding to frequency f under stress-free conditions, initial calibration;

[0052] V p (f): Measured wave velocity (km / s) under stress;

[0053] A0(f mid ): The initial amplitude of the first wave at the intermediate frequency (e.g., 0.5MHz) under stress-free conditions, for initial calibration;

[0054] A(f mid ): Measured amplitude of the first wave under stress;

[0055] C u Wave velocity stress sensitivity coefficient (MPa-1), calibrated by three-point bending test;

[0056] C a : Amplitude damage coefficient (dimensionless), crack width-amplitude relationship test calibration.

[0057] In this embodiment, the beam is a C30 concrete beam. The calibration data is as follows:

[0058] E = 30 GPa, C u =0.12MPa -1 C a =0.08;

[0059] Reference wave speed V p0 (0.5MHz) = 4.2km / s;

[0060] The reference amplitude A0 (0.5MHz) = 1.35V.

[0061] The measured data for this embodiment are as follows:

[0062] Pressure zone V p (0.5MHz)=4.25km / s(ΔV p / V p0 =-1.19%);

[0063] The pull-in region A (0.5MHz) = 0.82V (ln(A0 / A) = 0.50);

[0064] Dispersion integral result: ζ(ΔV) p / fV p0 df = 1.05 × 10-3

[0065] The calculation process is as follows:

[0066] σ b =30×10 3 [0.12×1.05×10 -3 +0.08×0.50]=30×(0.126+0.04)=4.98MPa

[0067] It should be noted that this embodiment was carried out at room temperature, so no temperature correction is required.

[0068] The derivation of the above formula is as follows:

[0069] First, the wave velocity-stress relationship, that is, the relationship between the change of wave velocity and stress in the compression zone of concrete, is approximately linear (Ki-IlSong, San-Ha Kim, Jong-Won Lee, Hyunwoo Kim, Tae-Min Oh, 2025. Influence of jointstiffness and roughness on elastic wave propagation in jointed rockmasses. KSCE Journal of Civil Engineering. 29(8), 100-179):

[0070]

[0071] Where k u As a material constant, a dispersion enhancement factor is introduced. To improve low-frequency sensitivity, the integral yields:

[0072]

[0073] Secondly, regarding the amplitude-damage relationship, microcracks in the tensile zone cause amplitude attenuation, and the logarithmic model is more consistent with the energy dissipation law:

[0074]

[0075] (ε crack (for crack strain)

[0076] Finally, the combined wave velocity (macro-elasticity) and amplitude (micro-damage) effects are multiplied by the elastic modulus E to obtain the final normal stress.

[0077] This embodiment also preferably utilizes temperature-stress decoupling to correct stress. Specifically, stress correction is performed using the following formula:

[0078] in,

[0079] σ means For normal stress or shear stress that has been measured;

[0080] η: Coefficient of thermal expansion of concrete (usually 10) -5 / ℃);

[0081] T represents the current measured temperature of the beam;

[0082] T0: Reference temperature (temperature during calibration).

[0083] It should be noted that although the embodiments of the present invention use concrete as an example, the present invention can be extended to fields such as rock and composite materials, but the calibration coefficients (such as E, C) need to be adjusted. u C a To adapt to material properties. In this embodiment, for stress monitoring of concrete beams, it is also preferable to add an aggregate particle size compensation factor:

[0084] σ concrete =σ·[1+γ·(d max -20)],

[0085] Where d max γ is the maximum aggregate particle size (mm), and γ is the material coefficient.

[0086] Figure 3 This is a schematic diagram of the beam stress measurement device based on multi-frequency ultrasound according to the second embodiment of the present invention. Figure 3 As shown, this second embodiment uses a beam stress measurement device based on multi-frequency ultrasound to detect the shear stress of a concrete beam. The device in this embodiment is largely the same as that in the first embodiment, except for the positions of the transmitter and receiver, and the calculation formula used by the host computer.

[0087] Specifically, this embodiment uses a 45° oblique probe pair, positioned near the neutral axis of the beam web (the area of ​​maximum shear stress). At this angle, the propagation direction of the multi-frequency ultrasound is at 45° to the principal stress direction, which is the surface of maximum shear force. That is, the ultrasonic transmitter and receiver are located on the same horizontal plane, and their connection forms a 45-degree angle with the beam's axis. During measurement, the ultrasonic transmitter and receiver can be positioned at multiple locations at the same height on the beam to obtain the shear stress distribution at different locations.

[0088] In this second embodiment, the shear sensitivity coefficients β and γ of the beam need to be calibrated before measuring the shear stress of the beam.

[0089] The formula for calculating the shear stress in the host computer of this embodiment is as follows:

[0090] Where τ is the shear stress of the beam section, in MPa, and G is the shear modulus of the beam, in GPa. Δφ is the rate of change of the oblique propagation wave velocity of the beam, in km / s; Δφ is the phase shift of the first wave peak measured under stress, in radians; β and γ are the shear sensitivity coefficients of the beam, dimensionless.

[0091] The second embodiment uses the same beam as the first embodiment, and measures ΔV. p,τ = -3.1% (0.6MHz), Δφ = 0.12rad, at this time, take β = 25, γ = 8 → τ≈4.7MPa.

[0092] The principle behind the above calculation of shear stress is as follows:

[0093] Shear wave velocity response: Shear stress causes polarization distortion in the oblique P-wave path, with significant changes in wave velocity in the high-frequency band (>0.5MHz).

[0094] Phase difference detection: Shear deformation causes waveform phase shift Δφ = tan -1 (Im(FFT) / Re(FFT)).

[0095] Frequency domain differentiation: Extract the dispersion features specific to shearing.

[0096] Similar to the first embodiment, the shear stress can also be corrected using temperature-stress decoupling technology and compensated using aggregate particle size compensation factors.

[0097] The first and second embodiments described above can be used to measure the normal stress and shear stress of a beam, respectively. In other embodiments, the devices for measuring normal stress and shear stress can be integrated into one device. This only requires that the host computer (main control device) simultaneously calculate the normal stress using multi-frequency ultrasonic waves obtained from the normal stress measurement and calculate the shear stress using multi-frequency ultrasonic waves obtained from the shear stress measurement.

[0098] When the normal stress and shear stress of a beam are measured simultaneously using this invention, the results can be verified to increase their reliability. The verification method is as follows:

[0099] Calculate whether the normal stress and shear stress satisfy the formula. Where I is the moment of inertia, S is the static moment, b is the beam width, and d is the effective height.

[0100] As can be seen from the above embodiments, this invention utilizes dispersion integration to suppress single-frequency noise and temperature compensation to resolve thermal expansion interference, thus exhibiting strong anti-interference capabilities. This invention supports rectangular, T-shaped, and I-shaped cross-section beams; the rock parameter library supports granite, sandstone, etc., and adapts aggregate characteristics through γ, thus demonstrating wide applicability. This invention also combines wave velocity (macro-stress) and amplitude (micro-damage), with the error controllable below 5%, exhibiting high accuracy (in controllable experimental data, wave velocity variation was 2.5-4.1% under 10MPa stress).

[0101] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for measuring beam stress based on multi-frequency ultrasound, used to measure the stress in a beam, characterized in that, Includes the following steps: Step S1: Arrange a pair of ultrasonic probes on two opposite sides of the beam. The ultrasonic probe pair includes an ultrasonic transmitter and an ultrasonic receiver, which are located on opposite sides of the beam respectively. During measurement, the ultrasonic transmitter is used to emit multi-frequency ultrasonic waves, and the ultrasonic receiver is used to receive multi-frequency ultrasonic waves. Step S2: Calculate the stress borne by the beam based on the received multi-frequency ultrasonic waves.

2. The beam stress measurement method based on multi-frequency ultrasound according to claim 1, characterized in that, In step S1, the ultrasonic transmitter and ultrasonic receiver are located on the same horizontal plane, and their connection is perpendicular to the axis of the beam. During measurement, the ultrasonic transmitter and ultrasonic receiver are set at multiple positions at different heights of the beam. In step S2, the wave velocity of the multi-frequency ultrasonic wave is calculated, the amplitude of the multi-frequency ultrasonic wave is detected, and the normal stress distribution of the beam section is calculated based on the normal stress calculation formula.

3. The beam stress measurement method based on multi-frequency ultrasound according to claim 2, characterized in that, The formula for calculating normal stress is: in, σ b V is the normal stress of the beam section, in MPa; E is the dynamic elastic modulus of the beam, in GPa; V p0 (f) is the reference wave velocity corresponding to frequency f of the beam under stress-free conditions, in km / s and V. p (f) represents the measured wave velocity under stress, in km / s, A0(f) mid A(f) represents the amplitude of the first peak of the beam at the intermediate frequency when the beam is stress-free. mid C represents the amplitude of the first wave peak measured when the beam is under stress. u The wave velocity stress sensitivity coefficient of the beam is expressed in MPa⁻¹, C. a Let be the amplitude damage coefficient of the beam, which is dimensionless.

4. The beam stress measurement method based on multi-frequency ultrasound according to claim 3, characterized in that, It also includes step S0: determining the reference wave velocity V corresponding to the frequency f of the beam under stress-free conditions. p0 (f) Calibrate the amplitude A0(f) of the first peak of the beam at the intermediate frequency when the beam is under no stress. mid The beam's wave velocity stress sensitivity coefficient C is calibrated. u Calibration is performed on the beam's amplitude damage coefficient C. a Perform calibration.

5. The beam stress measurement method based on multi-frequency ultrasound according to claim 1, characterized in that, In step S1, the ultrasonic transmitter and ultrasonic receiver are located on the same vertical plane, and their connection is at a 45-degree angle to the axis of the beam. During measurement, the ultrasonic transmitter and ultrasonic receiver are set at multiple positions at the same height of the beam. In step S2, the wave velocity of the multi-frequency ultrasonic wave is calculated, the amplitude of the multi-frequency ultrasonic wave is detected, and the shear stress distribution of the beam section is calculated based on the shear stress calculation formula.

6. The beam stress measurement method based on multi-frequency ultrasound according to claim 5, characterized in that, The formula for calculating shear stress is: Where τ is the shear stress of the beam section, in MPa, and G is the shear modulus of the beam, in GPa. Δφ is the rate of change of the oblique propagation wave velocity of the beam, in km / s; Δφ is the phase shift of the first wave peak measured under stress, in radians; β and γ are the shear sensitivity coefficients of the beam, dimensionless.

7. The beam stress measurement method based on multi-frequency ultrasound according to claim 6, characterized in that, It also includes step S0: calibrating the shear sensitivity coefficients β and γ of the beam.

8. The beam stress measurement method based on multi-frequency ultrasound according to any one of claims 1 to 7, characterized in that, The process also includes step S3: measuring the current temperature of the beam and correcting the calculated stress distribution of the beam section according to the following formula: Where, σ means The measured normal or shear stress is η, the thermal expansion coefficient of the beam is T, the current temperature of the beam is T0, and the reference temperature is T0.

9. A beam stress measurement device based on multi-frequency ultrasound, characterized in that, include: An ultrasonic probe pair, including an ultrasonic transmitter and an ultrasonic receiver, is located on two opposite sides of a beam. The ultrasonic transmitter is used to emit multi-frequency ultrasonic waves, and the ultrasonic receiver is used to receive multi-frequency ultrasonic waves. The main control device is used to control the operation of the ultrasonic transmitter and ultrasonic receiver, and at the same time, calculate the stress borne by the beam based on the received multi-frequency ultrasonic waves.

10. The beam stress measurement device based on multi-frequency ultrasound according to claim 9, characterized in that, When the beam stress measuring device is used to measure the normal stress of a beam, the ultrasonic transmitter and ultrasonic receiver are located on the same horizontal plane, and their connection is perpendicular to the axis of the beam; the main control device calculates the normal stress according to the following formula: in, σ b V is the normal stress of the beam section, in MPa; E is the dynamic elastic modulus of the beam, in GPa; V p0 (f) is the reference wave velocity corresponding to frequency f of the beam under stress-free conditions, in km / s and V. p (f) represents the measured wave velocity under stress, in km / s, A0(f) mid A(f) represents the amplitude of the first wave at the intermediate frequency of the beam when it is stress-free. mid C represents the amplitude of the first wave measured under stress on the beam. u The wave velocity stress sensitivity coefficient of the beam is expressed in MPa⁻¹, C. a Let be the amplitude damage coefficient of the beam, which is dimensionless; When the beam stress measuring device is used to measure the shear stress of a beam, the ultrasonic transmitter and ultrasonic receiver are located on the same vertical plane, and their connection forms a 45-degree angle with the axis of the beam; the main control device calculates the shear stress according to the following formula: Where τ is the shear stress of the beam section, in MPa, and G is the shear modulus of the beam, in GPa. Δφ is the rate of change of the oblique propagation wave velocity of the beam, in km / s; Δφ is the phase shift of the first wave peak measured under stress, in radians; β and γ are the shear sensitivity coefficients of the beam, dimensionless.

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