A bolt axial stress measurement device and method based on ultrasonic wave

Abstract

The present invention discloses a bolt axial stress measuring device based on ultrasonic wave, comprising a microprocessor, an ultrasonic measuring device, a temperature measuring module and a coefficient calibration module, wherein the ultrasonic measuring device measures the acoustic time difference of ultrasonic wave in the bolt; the temperature measuring module measures the temperature of the bolt; the coefficient calibration module measures the acoustic time difference of ultrasonic wave at least three times through the ultrasonic measuring device and the temperature measuring module, and determines the coefficient according to the matrix formula; the microprocessor determines the functional relationship between the bolt temperature, axial stress and acoustic time difference according to the coefficient, and determines the current axial stress of the bolt based on the functional relationship. The invention can measure the bolt axial stress at any temperature.

Description

Technical Field

[0001] The present invention relates to the technical field of bolt preload force detection, and in particular to an ultrasonic-based bolt axial stress measurement device and method. Background Art

[0002] Bolts are products that generate stress through threads to tighten the clamped parts and are widely used in various mechanical equipment. Bolt flange connection is a detachable static sealing connection structure that is widely used in wind power generation, pressure vessels, petrochemical equipment and pipelines. In bolted connections, the bolts must be tightened during installation, that is, before the connection is subjected to the working load, it is pre-loaded. This pre-loaded force is called pre-tightening force. The purpose of pre-tightening is to enhance the reliability and tightness of the connection to prevent gaps or relative slippage between the connected parts after loading. Therefore, in flange bolt connections, accurate pre-tightening force values ​​and good control accuracy play an important role in controlling leakage on the joint surface.

[0003] The main failure mode of flange bolt connection system is leakage, and bolt pre-tightening is one of the important links to ensure that the connection surface does not leak. Most bolt force detection technologies in engineering are not suitable for bolt flange joints or damage the bolt force. Therefore, a non-destructive online bolt force detection method is needed to monitor the bolts in real time to obtain accurate pre-tightening force values. The temperature effect will cause thermal stress in the bolt rod and affect the safety of the bolt connection. Therefore, monitoring the thermal stress and pre-tightening force of the bolt rod under the temperature effect is more effective in judging its working state, and it also has guiding significance for the application of bolt pre-tightening force.

[0004] So far, domestic and foreign research on the use of ultrasonic non-destructive detection technology to measure the preload of bolts has achieved certain results. The common basic principle is based on the phenomenon that the ultrasonic wave velocity changes with the stress state of the propagation medium, that is, the acoustic elastic phenomenon, which exists in both the elastic range and the nonlinear stress-strain range. In the existing ultrasonic stress measurement technology, the ultrasonic bolt stress measurement method that does not consider the temperature effect will cause the thermal stress generated by the bolt rod to be ignored, which means that the calibration results at room temperature will no longer be applicable to high or low temperature working environments, affecting the safety judgment of the monitoring results of the bolt connection parts and affecting the application of bolt preload during production, installation and maintenance. The patent application publication number is CN109883664A, a wind power bolt real-time monitoring and diagnosis system. The patent mentions the influence of temperature on ultrasonic stress measurement and also provides a temperature sensor for temperature compensation, but does not provide how to use temperature to compensate for the ultrasonic stress measurement results. The bolt axial stress testing device based on ultrasonic measurement with patent application publication number CN111208207A provides a test method and test equipment. Based on experience and experiments, the ultrasonic monitoring of pre-tightened bolts is compensated. However, the test equipment needs to combine a high and low temperature test chamber with a tensile testing machine, and requires multiple sets of calibration, which is complex and costly. Summary of the invention

[0005] In view of this, the present invention provides an ultrasonic-based bolt axial stress measurement device and method, which can measure the bolt axial stress at any temperature.

[0006] To achieve the above object, the present invention provides an ultrasonic-based bolt axial stress measurement device, comprising a microprocessor, an ultrasonic measuring device, a temperature measurement module and a coefficient calibration module, wherein:

[0007] The ultrasonic measuring device measures the acoustic time difference of the ultrasonic wave in the bolt;

[0008] The temperature measurement module measures the temperature of the bolt;

[0009] The coefficient calibration module measures the ultrasonic time difference at least three times through the ultrasonic measuring device and the temperature measuring module, respectively at the first bolt temperature T 0 and the first prestress F 0 The first sound time difference t obtained by the first measurement under the condition of 0 , at the first bolt temperature T 0 and the first prestress F 1 The second sound time difference t obtained by the second measurement under the condition of a , and the second bolt temperature T 1 and the first prestress F 0The third sound time difference t obtained by the third measurement under the condition of b , determine the coefficients A, B, C and D according to the following matrix formula:

[0010]

[0011] Among them, δt a =t a -t 0 ,δt b =t b -t 0 ;

[0012] The microprocessor determines a functional relationship between the bolt temperature, the axial stress and the acoustic time difference according to the coefficient, and determines the current axial stress of the bolt based on the functional relationship, wherein the functional relationship is:

[0013] A·T+B·F+C·δt+D=0;

[0014] Among them, δt is the acoustic time difference of the current ultrasonic wave in the bolt, T is the current bolt temperature, and F is the current axial stress.

[0015] Preferably, the bolt preload force measuring device includes a detection head, the ultrasonic measuring device includes a first piezoelectric chip and a second piezoelectric chip, the temperature measuring module includes a thermistor, and the first piezoelectric chip, the second piezoelectric chip and the thermistor are packaged together at the top of the detection head.

[0016] Preferably, the microprocessor generates a pulse electric signal, applies the pulse electric signal to the first piezoelectric chip, and records the sending time of the pulse electric signal; the first piezoelectric chip generates ultrasonic waves to propagate in the bolt; the second piezoelectric chip receives the signal returned by the ultrasonic waves in the bolt and converts it into a pulse electric signal, which is sent to the microprocessor; the microprocessor records the receiving time of the received pulse electric signal, performs a difference operation between the receiving time and the sending time, and obtains the acoustic time difference of the ultrasonic waves in the bolt; the thermistor measures the temperature of the bolt, and sends the temperature to the microprocessor.

[0017] Preferably, the coefficient calibration module is specifically used for:

[0018] The material structural properties defined based on Young's modulus E and Poisson's ratio ν are converted into properties defined by the Lame coefficient, that is, the first Lame coefficient parameter λ:

[0019]

[0020] The second Lame coefficient parameter μ:

[0021]

[0022] On the basis of the first Lame coefficient parameter and the second Lame coefficient parameter, a third-order superelastic coefficient correction l, m, n is added. The superelastic coefficient correction is obtained through experimental measurement, and the correction relationship between the preload force and the sound velocity and the sound velocity relationship are obtained:

[0023]

[0024] c σ =c 0 (1+CLσ;

[0025] Among them, c σ is the speed of sound under the influence of preload, c 0 is the speed of sound without the influence of preload, C L To calculate c σ is the correction parameter of the bolt, and σ is the deformation per unit length of the bolt caused by the preload.

[0026] Preferably, the coefficient calibration module is further specifically used for:

[0027] The first measurement condition is set as the first bolt temperature T 0 300K and the first prestress F 0 0kN;

[0028] The second measurement condition is set as the first bolt temperature T 0 300K and the second prestress F 1 is 1000kN; the third measurement condition is set to the second bolt temperature T 1 350K and the first prestress F 0 is 0kN.

[0029] Preferably, the δt is calculated by using the corrected relational expression of the speed of sound and the relational expression of the speed of sound.

[0030] Preferably, the microprocessor generates an analysis graph corresponding to the relationship among the bolt temperature, axial stress and acoustic time difference according to the functional relationship among the bolt temperature, axial stress and acoustic time difference;

[0031] Based on the analysis spectrum, when the bolt working temperature and the acoustic time difference of the ultrasonic wave are measured, a unique bolt axial stress is determined in the analysis spectrum.

[0032] Preferably, the microprocessor determines a unique bolt working temperature in the analysis spectrum when the axial stress of the bolt and the acoustic time difference of the ultrasonic wave are measured based on the analysis spectrum.

[0033] Preferably, the microprocessor includes a burning module for burning the functional relationship between the bolt temperature, axial stress and acoustic time difference into the microprocessor, and the microprocessor calculates the corresponding axial stress based on the acquired current bolt temperature and ultrasonic acoustic time difference.

[0034] To achieve the above object, the present invention provides a method for measuring the axial stress of a bolt based on ultrasound, the method comprising:

[0035] The ultrasonic measuring device and the temperature measuring module are used to measure at least three times, respectively, at the first bolt temperature T 0 and the first prestress F 0 The first sound time difference t obtained by the first measurement under the condition of 0 , at the first bolt temperature T 0 and the first prestress F 1 The second sound time difference t obtained by the second measurement under the condition of a , and the second bolt temperature T 1 and the first prestress F 0 The third sound time difference t obtained by the third measurement under the condition of b , determine the coefficients A, B, C and D according to the following matrix formula:

[0036]

[0037] Among them, δt a =t a -t 0 ,δt b =t b -t 0 ;

[0038] A functional relationship between the bolt temperature, the axial stress and the acoustic time difference is determined according to the coefficient, and the current axial stress of the bolt is determined based on the functional relationship, wherein the functional relationship is:

[0039] A·T+B·F+C·δt+D=0;

[0040] Among them, δt is the acoustic time difference of the current ultrasonic wave in the bolt, T is the current bolt temperature, and F is the current axial stress.

[0041] Compared with the prior art, the ultrasonic-based bolt axial stress measurement device and method provided by the present invention have the following beneficial effects: the present invention only requires three measurements to obtain the ultrasonic measurement law of the bolt under any temperature and any prestress, and can determine the combined effect of the bolt prestress and the temperature compensation effect, and is applied to the preload force measurement at any temperature without repeated calibration at different temperatures; the technical solution is simpler, more effective, and has a wider coverage; the bolt stress measurement part and the temperature measurement part are integrated into a unified probe, and no additional additional equipment such as a constant temperature box is required; the characteristic curve of the ultrasonic measurement of the bolt axial stress and the characteristic curve of the temperature and prestress are combined to provide a characteristic map of comprehensive stress and temperature, which can be more conveniently used in ultrasonic detectors for on-site bolt detection; and an effective technical solution for ultrasonic measurement of the bolt axial stress that changes with temperature is provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 4 is a system schematic diagram of a bolt axial stress measuring device based on ultrasound according to an embodiment of the present invention.

[0043] Figure 2 is a schematic diagram of a detection head according to an embodiment of the present invention.

[0044] Figure 3 It is an analysis graph corresponding to the relationship among bolt temperature, preload force and acoustic time difference according to an embodiment of the present invention.

[0045] Figure numbers: 201 - first piezoelectric chip; 202 - second piezoelectric chip; 203 - thermistor; 13 - microprocessor. DETAILED DESCRIPTION

[0046] The present invention will be described in detail below in conjunction with the specific embodiments shown in the accompanying drawings, but these embodiments do not limit the present invention. Structural, methodological, or functional changes made by ordinary technicians in the field based on these embodiments are all included in the protection scope of the present invention.

[0047] like Figure 1 An embodiment of the present invention is shown, the present invention provides an ultrasonic-based bolt axial stress measurement device, the device comprising an ultrasonic measuring device 10, a temperature measuring module 11, a coefficient calibration module 12 and a microprocessor 13, wherein:

[0048] The ultrasonic measuring device 10 measures the acoustic time difference of the ultrasonic wave in the bolt;

[0049] The temperature measuring module 11 measures the temperature of the bolt;

[0050] The coefficient calibration module 12 measures the ultrasonic sound time difference at least three times through the ultrasonic measuring device and the temperature measuring module, respectively at the first bolt temperature T 0 and the first prestress F 0 The first sound time difference t obtained by the first measurement under the condition of 0 , at the first bolt temperature T 0 and the first prestress F 1 The second sound time difference t obtained by the second measurement under the condition of a , and the second bolt temperature T 1 and the first prestress F 0 The third sound time difference t obtained by the third measurement under the condition of b , determine the coefficients A, B, C and D according to the following matrix formula,

[0051]

[0052] Among them, δt a =t a -t 0 ,δt b =t b -t 0 ;

[0053] The microprocessor 13 determines a functional relationship between the bolt temperature, the axial stress and the acoustic time difference according to the coefficient, and determines the current axial stress of the bolt based on the functional relationship, wherein the functional relationship is:

[0054] A·T+B·F+C·δt+D=0;

[0055] Among them, δt is the acoustic time difference of the current ultrasonic wave in the bolt, T is the current bolt temperature, and F is the current axial stress.

[0056] like Figure 2As shown, the bolt preload force measuring device includes a probe, the ultrasonic measuring device includes the first piezoelectric chip 201 and the second piezoelectric chip 202, the temperature measuring module includes a thermistor 203, the first piezoelectric chip 201, the second piezoelectric chip 202 and the thermistor 203 are packaged together and installed on the top of the probe, and are installed on the top of the bolt. When installing, it is necessary to apply an affinity agent on the surface of the probe, and then install it on the top of the bolt for weighing. The microprocessor generates a pulse electrical signal, applies the pulse electrical signal to the first piezoelectric chip, and records the sending time of the pulse electrical signal. By applying a pulse voltage to the first piezoelectric chip, instantaneous expansion and contraction can be generated, thereby giving a pulse pressure signal to the bolt that is close to it. The first piezoelectric chip generates an ultrasonic wave, which propagates in the bolt. The second piezoelectric chip receives the signal returned by the ultrasonic wave propagating in the bolt and converts it into a pulse electrical signal, which is sent to the microprocessor. The microprocessor receives the pulse electrical signal and records the receiving time, and performs a difference operation between the receiving time and the sending time to obtain the acoustic time difference of the ultrasonic wave in the bolt. The thermistor measures the temperature of the bolt and sends the temperature to the microprocessor. In this embodiment, a piezoelectric chip is used to collect ultrasonic signals, which can also be replaced by an electromagnetic ultrasonic circulator to collect ultrasonic signals.

[0057] In general, the structural properties of a material can be defined by Young's modulus E and Poisson's ratio v, and both can be defined by a temperature-dependent piecewise function T and measured experimentally. Currently, there is a detailed database available for various steel materials used in industry.

[0058] The material structural properties defined based on Young's modulus E and Poisson's ratio v can be translated into properties defined by the Lamé coefficient, i.e., the first Lamé coefficient parameter λ:

[0059]

[0060] The second Lame coefficient parameter μ:

[0061]

[0062] On the basis of the first Lame coefficient parameter and the second Lame coefficient parameter, a third-order superelastic coefficient correction l, m, n is added. The superelastic coefficient correction is obtained through experimental measurement, and the correction relationship between the preload force and the sound velocity and the sound velocity relationship are obtained:

[0063]

[0064] c σ =c 0 (1+C L σ);

[0065] Among them, c σ is the speed of sound under the influence of preload, c 0 is the speed of sound without the influence of preload, C L To calculate c σ The correction parameter is σ, which is the deformation per unit length of the bolt caused by the preload. Through the pulsed electrical signal converted by the second piezoelectric chip, the microprocessor obtains the acoustic time difference of the ultrasonic wave in the bolt. The acoustic time difference is affected by the size of the sound velocity, that is, the change in the sound velocity of the ultrasonic wave caused by the preload and temperature, the length of the sound path, and the deformation of the bolt caused by the preload and the deformation caused by the thermal expansion effect. Studies have shown that when the daily temperature changes are not large (-50K~100K) and the preload does not cause plastic deformation of the material, these effects can be approximately regarded as linear relationships. The coefficient calibration is based on the above principle.

[0066] The coefficient calibration module measures the propagation time of the ultrasonic wave at least three times through the ultrasonic measuring device and the temperature measuring module, respectively at the first bolt temperature T 0 and the first prestress F 0 The first sound time difference t measured under the condition of 0 , at the first bolt temperature T 0 and the first prestress F 1 The second sound time difference t measured under the condition of a , and the second bolt temperature T 1 and the first prestress F 0 The third sound time difference t measured under the condition of b , determine the coefficients A, B, C and D according to the following matrix formula;

[0067]

[0068] Among them, δt a =t a -t 0 ,δt b =t b -t 0 Specifically, the first measurement: the bolt temperature T is measured by the thermistor. 0 The first prestress F is applied to the bolt by an external stress stretching device. 0 Under the condition of 0kN, the microprocessor generates a pulse electrical signal and applies it to the first piezoelectric chip. The first piezoelectric chip excites the ultrasonic signal and propagates in the bolt. The second piezoelectric chip receives the echo signal and converts it into a pulse electrical signal and sends it to the microprocessor. The microprocessor obtains the first sound time difference t of the ultrasonic wave. 0 Similarly, the second measurement: at the first bolt temperature T 0 300K and the second prestress F1 The second sound time difference t measured under the condition of 1000kN a ; The third measurement: at the second bolt temperature T 1 350K and the first prestress F 0 The third sound time difference t measured under the condition of 0kN b Based on the three sets of measured data, coefficients A, B, C and D are calculated according to the above matrix formula. In this embodiment, three sets of measured data are used to achieve coefficient calibration. However, using more sets of measured data for coefficient calibration to achieve higher accuracy also belongs to the scope of the present invention.

[0069] The microprocessor determines a functional relationship between the bolt temperature, the axial stress and the acoustic time difference based on the coefficients obtained above, and determines the current axial stress of the bolt based on the functional relationship, wherein the functional relationship is:

[0070] A·T+B·F+C·δt+D=0;

[0071] Among them, δt is the acoustic time difference of the current ultrasonic wave in the bolt, T is the current bolt temperature, and F is the current axial stress. The δt is calculated by the corrected relationship of the speed of sound and the speed of sound relationship. Based on the above-mentioned plane formula, under the condition of a given temperature T, the bolt preload F and the acoustic time difference have a one-to-one correspondence, thereby obtaining the relationship between the acoustic time difference of the ultrasonic wave and the axial stress at different temperatures. The current bolt temperature is measured by a thermistor, and the acoustic time difference of the current ultrasonic wave in the bolt is measured by an ultrasonic measuring device. Then, according to the plane formula, the corresponding preload of the current bolt can be obtained. According to a specific embodiment of the present invention, the microprocessor generates an analysis graph corresponding to the relationship among the bolt temperature, axial stress and acoustic time difference based on the functional relationship among the bolt temperature, axial stress and acoustic time difference, such as Figure 3 As shown in the figure, F represents axial stress and T represents acoustic time difference. Based on the analysis spectrum, the microprocessor determines the only bolt axial stress in the analysis spectrum when the bolt working temperature and the ultrasonic acoustic time difference are measured; or based on the analysis spectrum, determines the only bolt working temperature in the analysis spectrum when the bolt axial stress and the ultrasonic acoustic time difference are measured.

[0072] According to a specific embodiment of the present invention, the microprocessor includes a burning module for burning the functional relationship between the bolt temperature, axial stress and acoustic time difference into the microprocessor. During the bolt preload measurement process, the microprocessor calculates the corresponding axial stress based on the current bolt temperature and the ultrasonic acoustic time difference. In another embodiment of the present invention, the microprocessor sends the current bolt temperature and ultrasonic acoustic time difference to a cloud server, and the cloud server calculates the corresponding axial stress based on the functional relationship between the bolt temperature, axial stress and acoustic time difference.

[0073] The present invention provides a method for measuring the axial stress of a bolt based on ultrasound, the method comprising:

[0074] The ultrasonic measuring device and the temperature measuring module are used to measure at least three times, respectively, at the first bolt temperature T 0 and the first prestress F 0 The first sound time difference t obtained by the first measurement under the condition of 0 , at the first bolt temperature T 0 and the first prestress F 1 The second sound time difference t obtained by the second measurement under the condition of a , and the second bolt temperature T 1 and the first prestress F 0 The third sound time difference t obtained by the third measurement under the condition of b , determine the coefficients A, B, C and D according to the following matrix formula:

[0075]

[0076] Among them, δt a =t a -t 0 ,δt b =t b -t 0 ;

[0077] A functional relationship between the bolt temperature, the axial stress and the acoustic time difference is determined according to the coefficient, and the current axial stress of the bolt is determined based on the functional relationship, wherein the functional relationship is:

[0078] A·T+B·F+C·δt+D=0;

[0079] Wherein, δt is the acoustic time difference of the current ultrasonic wave in the bolt, T is the current bolt temperature, and F is the current axial stress. The δt is calculated by the correction relation of the velocity of sound and the velocity of sound relation. Based on the above plane formula, under the condition of a given temperature T, the bolt preload F and the acoustic time difference have a one-to-one correspondence, thereby obtaining the relationship between the acoustic time difference of the ultrasonic wave and the axial stress at different temperatures.

[0080] Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

1. An ultrasonic-based bolt axial stress measuring device, characterized in that: It includes a microprocessor, an ultrasonic measuring device, a temperature measuring module and a coefficient calibration module, wherein: The ultrasonic measuring device measures the acoustic time difference of the ultrasonic wave in the bolt; The temperature measurement module measures the temperature of the bolt; The coefficient calibration module measures the ultrasonic time difference at least three times through the ultrasonic measuring device and the temperature measuring module, respectively at the first bolt temperature and the first prestress The first sound time difference obtained by the first measurement under the condition of , at the first bolt temperature and the second prestress The second sound time difference obtained by the second measurement under the condition of , and the second bolt temperature and the first prestress The third sound time difference obtained by the third measurement under the condition of , determine the coefficients A, B, C and D according to the following matrix formula: ； in, , ; The microprocessor determines a functional relationship between the bolt temperature, the axial stress and the acoustic time difference according to the coefficient, and determines the current axial stress of the bolt based on the functional relationship, wherein the functional relationship is: ； in, is the acoustic time difference of the current ultrasonic wave in the bolt, T is the current bolt temperature, and F is the current axial stress.

2. The ultrasonic-based bolt axial stress measuring device according to claim 1, characterized in that: The bolt axial stress measuring device includes a detection head, the ultrasonic measuring device includes a first piezoelectric chip and a second piezoelectric chip, the temperature measuring module includes a thermistor, and the first piezoelectric chip, the second piezoelectric chip and the thermistor are packaged together at the top of the detection head.

3. The ultrasonic-based bolt axial stress measuring device according to claim 2, characterized in that: The microprocessor generates a pulse electrical signal, applies the pulse electrical signal to the first piezoelectric wafer, and records the sending time of the pulse electrical signal; The first piezoelectric chip generates ultrasonic waves to propagate in the bolt; The second piezoelectric chip receives the signal returned by the ultrasonic wave propagating through the bolt and converts it into a pulse electrical signal, and sends it to the microprocessor; The microprocessor records the receiving time of the received pulse electrical signal, and performs a difference operation between the receiving time and the sending time to obtain the acoustic time difference of the ultrasonic wave in the bolt; The thermistor measures the bolt temperature and sends the bolt temperature to a microprocessor.

4. The ultrasonic-based bolt axial stress measuring device according to claim 3, characterized in that: The coefficient calibration module is specifically used for: Based on Young's modulus Poisson's ratio The material structure properties defined by the Lame coefficients are converted into the properties defined by the Lame coefficients, i.e. the first Lame coefficient parameters : ； Second Lame coefficient parameter : ； Add the third-order hyperelastic coefficient correction based on the first and second Lame coefficient parameters The superelastic coefficient correction is obtained through experimental measurement, and the correction relationship between the preload force and the speed of sound and the speed of sound relationship are obtained: ； ； in, is the speed of sound under the influence of preload, is the speed of sound without the influence of preload, For calculation The correction parameters of It is the deformation per unit length of the bolt caused by the preload force.

5. The ultrasonic-based bolt axial stress measuring device according to claim 4, characterized in that: The coefficient calibration module is also specifically used for: The first measurement condition is set to the first bolt temperature 300K and the first prestress 0kN; The second measurement condition is set to the first bolt temperature 300K and the second prestress 1000kN; The third measurement condition is set to the second bolt temperature 350K and the first prestress is 0kN.

6. The ultrasonic-based bolt axial stress measuring device according to claim 4, characterized in that: Said It is calculated by using the corrected relational expression of the speed of sound and the relational expression of the speed of sound.

7. The ultrasonic-based bolt axial stress measuring device according to claim 6, characterized in that: The microprocessor also generates an analysis spectrum corresponding to the relationship among the bolt temperature, axial stress and acoustic time difference according to the functional relationship among the bolt temperature, axial stress and acoustic time difference. Based on the analysis spectrum, when the bolt working temperature and the acoustic time difference of the ultrasonic wave are measured, a unique bolt axial stress is determined in the analysis spectrum.

8. The ultrasonic-based bolt axial stress measuring device according to claim 7, characterized in that: The microprocessor is also used to determine a unique bolt working temperature in the analysis spectrum based on the analysis spectrum when the axial stress of the bolt and the acoustic time difference of the ultrasonic wave are measured.

9. The ultrasonic-based bolt axial stress measuring device according to claim 7, characterized in that: The microprocessor includes a burning module for burning the functional relationship between the bolt temperature, axial stress and acoustic time difference into the microprocessor. The microprocessor calculates the corresponding axial stress based on the acquired current bolt temperature and ultrasonic acoustic time difference.

10. A method for measuring the bolt axial stress based on ultrasonic wave according to any one of claims 1 to 9, characterized in that: The method comprises: The ultrasonic measuring device and the temperature measuring module are used to measure at least three times, respectively, at the first bolt temperature and the first prestress The first sound time difference obtained by the first measurement under the condition of , at the first bolt temperature and the second prestress The second sound time difference obtained by the second measurement under the condition of , and the second bolt temperature and the first prestress The third sound time difference obtained by the third measurement under the condition of , determine the coefficients A, B, C and D according to the following matrix formula: ； in, , ; A functional relationship between the bolt temperature, the axial stress and the acoustic time difference is determined according to the coefficient, and the current axial stress of the bolt is determined based on the functional relationship, wherein the functional relationship is: ； in, is the acoustic time difference of the current ultrasonic wave in the bolt, T is the current bolt temperature, and F is the current axial stress.

Images