Bolt axial force detection device, calibration equipment, calibration method and detection method

Abstract

The present invention provides a bolt axial force detection device, comprising: a first detection component for being arranged at the first end of the bolt; a second detection component for being arranged at the second end of the bolt; the first detection component having a plurality of first probes arranged in an array embedded therein, the first probes contacting the first end of the bolt, and the plurality of first probes sequentially and periodically transmitting detection signals; and the second detection component having a plurality of second probes arranged in an array embedded therein, the second probes contacting the second end of the bolt, and the plurality of second probes simultaneously receiving the detection signals transmitted by each of the first probes. In the present invention, the plurality of first probes sequentially and periodically transmit detection signals, and the plurality of second probes simultaneously receive the detection signals transmitted by each of the first probes, enabling accurate acquisition of longitudinal acoustic waves and ensuring the accuracy of bolt density distribution calculations.

Description

Technical Field

[0001] The present invention relates to the technical field of engineering component monitoring, and in particular to a bolt axial force detection device, calibration equipment, calibration method and detection method. Background Art

[0002] High wind towers are an inevitable trend of future development, and wind towers are expected to reach a height of 150 to 250 meters.

[0003] However, tall wind towers also pose new challenges to the structural strength of the tower. In particular, the stability of the bolted connections on the tower flanges significantly impacts the service life of the wind turbine tower. Traditional wind turbines typically have six or more flange connections, each requiring over 100 high-strength bolts. During operation, the wind turbine itself experiences significant wind pressure and vibration, which constantly impacts the stability of the bolt connections. In severe cases, this can affect the axial force distribution of the bolts, leading to eccentric tension and ultimately fracture. Therefore, axial force testing of in-service bolts is crucial to the safety and reliability of wind turbine towers.

[0004] Common methods for detecting bolt axial force include resistance strain gauges, piezoelectric impedance testing, and ultrasonic testing. The first two methods have numerous limitations on sensor installation locations and are therefore less applicable. Ultrasonic testing, however, is currently the most widely used method for detecting bolt axial force. Ultrasonic testing essentially uses the acoustoelastic effect to capture changes in the medium's lattice density caused by changes in internal stress, thereby reflecting changes in the acoustic wave velocity within the medium. The captured acoustic wave velocity is typically calculated as the ratio of the acoustic path length to the transit time of the sound wave in the medium.

[0005] However, when a bolt is subjected to stress, the internal lattice density distribution is not uniform, which leads to differences in the internal wave velocity. Traditional ultrasonic testing methods can only infer the bolt's axial stress by calculating the bolt's average wave velocity, but cannot accurately obtain the axial force distribution characteristics within the bolt. As a result, it is impossible to determine the exact stress state of a single bolt, let alone whether the bolt is under eccentric compression. Therefore, the current ultrasonic testing method cannot accurately determine the internal axial force distribution of the bolt and its true stress state in some cases.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] A first aspect of the present invention is to provide a bolt axial force detection device, the detection device comprising:

[0008] The first detection component is arranged on the first end of the bolt,

[0009] The second detection component is arranged on the second end of the bolt,

[0010] The first detection component is embedded with a plurality of first probes arranged in an array, the first probes contact the first end of the bolt, and the plurality of first probes periodically emit detection signals in sequence;

[0011] The second detection component has a plurality of second probes arranged in an array embedded therein, the second probes contact the second end of the bolt, and the plurality of second probes simultaneously receive a detection signal emitted by each of the first probes.

[0012] In a preferred embodiment, the detection signal is a sonic / ultrasonic wave signal;

[0013] The distance between the first probes is greater than twice the wavelength of the sound wave / ultrasonic wave; the distance between the second probes is greater than twice the wavelength of the sound wave / ultrasonic wave.

[0014] In a preferred embodiment, the first detection component and the second detection component are connected in series to the controller.

[0015] The controller controls the first detection component to transmit a detection signal and receives a detection signal returned by the second detection component.

[0016] In a preferred embodiment, the first detection component is filled with a first filling body, and the first filling body causes the first probes to be spaced apart in an array;

[0017] The second detection component is filled with a second filling body, and the second filling body enables the second probes to be spaced apart in an array.

[0018] In a preferred embodiment, the head of the first probe is exposed from the first filling body and is provided with a first spherical protective head;

[0019] The head of the second probe is exposed from the second filling body and is provided with a second spherical protective head.

[0020] In a preferred embodiment, the tail of the first probe is embedded in the first filling body and connected to the first insulating spring.

[0021] The tail of the second probe is embedded in the second filling body and connected to the second insulating spring.

[0022] A second aspect of the present invention is to provide a bolt axial force calibration device, the calibration device comprising:

[0023] A clamping device, used for clamping the bolt and stretching / squeezing the bolt;

[0024] And, a bolt axial force detection device.

[0025] A third aspect of the present invention is to provide a method for calibrating the axial force of a bolt, the method comprising the following steps:

[0026] The controller receives a detection signal, wherein the detection signal is a detection signal emitted by the first detection component and received by the second detection component;

[0027] Wherein, the first detection component is arranged at the first end of the bolt, and the second detection component is arranged at the second end of the bolt;

[0028] The first detection component is embedded with a plurality of first probes arranged in an array, the first probes contact the first end of the bolt, and the plurality of first probes periodically emit detection signals in sequence;

[0029] The second detection component is embedded with a plurality of second probes arranged in an array, the second probes contact the second end of the bolt, and the plurality of second probes simultaneously receive the detection signal emitted by each of the first probes;

[0030] The controller calibrates the bolt axial force through the received detection signal.

[0031] In a preferred embodiment, the detection signal is a sonic / ultrasonic wave signal.

[0032] In a preferred embodiment, the method includes:

[0033] The controller obtains the detection signal;

[0034] Calculate the longitudinal wave velocity of the detection signal in each channel;

[0035] The density of bolts in each channel is calculated using the longitudinal wave velocity of the detection signal in each channel;

[0036] Calculate the density distribution of the entire bolt and fit the nonlinear relationship between the bolt axial stress and the density distribution of the entire bolt;

[0037] The curve of the nonlinear relationship between the bolt axial stress and density distribution is fixed at a certain point and linearly fitted with the bolt clamping length to calibrate the bolt axial force.

[0038] In a preferred embodiment, the longitudinal wave velocity used to calculate the density of the bolts in each passage is:

[0039] In one cycle, the first probes of the first detection component transmit detection signals in sequence, and all the second probes of the second detection component receive the detection signals transmitted by each first probe at the same time;

[0040] Calculate the longitudinal wave velocity of the detection signal in each channel.

[0041] In a preferred embodiment, the longitudinal wave velocity used to calculate the density of the bolts in each passage is:

[0042] The average value of the longitudinal wave velocity of each channel within multiple cycles within a period of time.

[0043] In a preferred embodiment, the density of the bolts in each passage is expressed as follows:

[0044]

[0045] Among them, ρ ij The bolts are in each channel L ij density on the surface, E is the elastic modulus, μ is the Poisson's ratio, v ij It is the longitudinal wave velocity of the detection signal in each channel.

[0046] In a preferred embodiment, the density distribution of the entire bolt is calculated by three-dimensional bilinear interpolation.

[0047] In a preferred embodiment, the nonlinear relationship between the bolt axial stress and density distribution is expressed as follows:

[0048]

[0049] Where σ is the bolt axial stress, ρ x,y,z is the density distribution of the entire bolt, and a, b, and c are unknown parameters.

[0050] In a preferred embodiment, the curve of the nonlinear relationship between the bolt axial stress and density distribution is linearly fitted with the bolt clamping length in the following manner:

[0051]

[0052] in, is the fixed point of the curve of the nonlinear relationship between the bolt axial stress and density distribution, L is the clamping length of the bolt, and α and β are unknown parameters.

[0053] A fourth aspect of the present invention is to provide a method for detecting a bolt axial force, the method comprising:

[0054] Calibrate the bolt axial force according to the bolt axial force calibration method;

[0055] The bolt axial stress detection device is placed on an in-service bolt of the same model as the calibrated bolt to perform axial force detection on the in-service bolt.

[0056] The present invention provides a bolt axial force detection device, in which a first probe is arrayed in a first detection component, and a second probe is arrayed in a second detection component. The multiple first probes periodically transmit detection signals in sequence, and the multiple second probes simultaneously receive the detection signals transmitted by each of the first probes, thereby accurately obtaining the longitudinal sound wave, further ensuring the accuracy of the bolt density distribution calculation.

[0057] The present invention provides a bolt axial force detection device, in which an array of probes is embedded inside a first detection component and a second detection component, and a rubber spherical protective head is provided on the head of the probe. The probe can directly contact the object to be measured without the need for a coupling agent, thereby achieving approximate point contact between the front end of the sonic / ultrasonic probe and the surface of the object to be measured.

[0058] The present invention provides a bolt axial force detection device, in which the probe spacing of the array in the first detection component and the second detection component is reasonable and close to the length of the sound wave, and the contact surface is approximately point contact. In the absence of a coupling agent, the signal transmission connection can be guaranteed, and signal loss due to coupling agent leakage will not occur.

[0059] The present invention provides a bolt axial force detection device, in which an epoxy resin filler is embedded in the first detection component and the second detection component, one end of the probe is embedded in the epoxy resin filler, and an insulating spring is connected to it, which can better fit the surface of objects with various curvatures and has no requirements for the flatness of the surface of the object being measured.

[0060] The present invention provides a bolt axial force detection device that integrates the functions of ultrasonic emission and reception and acoustic emission waveform reception. The ultrasonic probe has an extremely small contact surface and does not require coupling agent during operation. It can directly contact the material being tested and has no requirements for the surface flatness of the object being tested. It is suitable for bolts of different models.

[0061] The present invention provides a bolt axial force detection device that is not affected by the bolt length and is particularly suitable for axial stress detection of wind turbine tower flange bolts. Only one calibration is required to achieve density and axial force detection of all bolts of the same model, effectively saving costs and having a wide range of applications.

[0062] The present invention provides a bolt axial force calibration method and detection method, which realizes the axial force distribution and density detection of the in-service bolts of the wind turbine tower. By constructing a nonlinear relationship between axial force distribution and density and utilizing the relationship between ultrasonic wave velocity and bolt medium lattice density, it is possible to directly judge the degree of damage and stress condition of the in-service bolts.

[0063] The present invention provides a bolt axial force calibration method and detection method, which utilizes the difference in ultrasonic transmission speed in media of different densities to deduce the density distribution of the bolt under different axial stresses, and then constructs a nonlinear fitting relationship between the bolt axial stress and its density distribution, thereby realizing the density distribution and axial stress detection of bolts with different clamping lengths.

[0064] The present invention provides a bolt axial force calibration method and detection method. The method utilizes the principle that the propagation speed of ultrasound in a medium is mainly affected by the density, Poisson's ratio and elastic modulus of the material. Based on the equilibrium equation of elastic vibration, the relationship between ultrasonic longitudinal waves and medium density is derived, and a three-dimensional bilinear interpolation algorithm is used to deduce the global density distribution of the bolt. The method is suitable for density detection of any homogeneous or quasi-homogeneous objects, and is particularly suitable for density detection of small-volume homogeneous metal materials such as bolts.

[0065] The present invention provides a bolt axial force calibration and detection method. The axial stress within a bolt is closely related to its density distribution. The lattice differences in the material itself, caused by uneven stress on the bolt, are reflected in subtle differences in density across space. This method can accurately distinguish differences in material lattice density due to uneven internal stress distribution within the bolt. This allows for density detection of small, homogeneous metal materials such as bolts, as well as calculation of the bolt's axial stress distribution, thereby enabling real-time detection of the bolt's axial stress.

[0066] The present invention provides a bolt axial force detection device, calibration equipment, calibration method and detection method, which are highly operable and repeatable, and only require one preliminary axial force calibration to cope with the axial stress detection of bolts with different clamping lengths. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0068] Figure 1 The schematic diagram of the structure of a bolt axial force detection device in one embodiment of the present invention is shown schematically.

[0069] Figure 2 FIG. 4 is a schematic diagram showing the internal structure of the first detection component in one embodiment of the present invention.

[0070] Figure 3 A schematic diagram of the bottom structure of the first detection component in one embodiment of the present invention is shown.

[0071] Figure 4 FIG. 4 is a schematic diagram showing the internal structure of the second detection component in one embodiment of the present invention.

[0072] Figure 5 A schematic diagram of the bottom structure of the second detection component in one embodiment of the present invention is shown.

[0073] Figure 6A schematic diagram showing the transmission of signals from a bolt axial force detection device inside a bolt in one embodiment of the present invention is shown.

[0074] Figure 7 A schematic structural diagram of a bolt axial force calibration device in one embodiment of the present invention is shown.

[0075] Figure 8 A flowchart of a bolt axial force calibration method according to an embodiment of the present invention is shown.

[0076] Figure 9 A flowchart of a method for detecting bolt axial force in one embodiment of the present invention is shown. DETAILED DESCRIPTION

[0077] In order to make the above and other features and advantages of the present invention more clear, the present invention is further described below with reference to the accompanying drawings. It should be understood that the specific embodiments given herein are for the purpose of explaining to those skilled in the art and are only exemplary and not restrictive.

[0078] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features, and therefore cannot be understood as limiting the present invention.

[0079] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0080] To address the technical problem that existing technologies cannot accurately obtain the axial force distribution characteristics of in-service bolts, resulting in the inability to determine the exact stress state of a single bolt and even the inability to determine whether the bolt is under eccentric compression, the present invention provides a bolt axial force detection device and a calibration method. The calibration device is used to calibrate bolts with the same signal as in-service bolts. After calibration, the detection device is used to detect the axial stress of the in-service bolts.

[0081] like Figure 1 FIG2 is a schematic structural diagram of a bolt axial force detection device according to an embodiment of the present invention. According to an embodiment of the present invention, a bolt axial force detection device includes:

[0082] The first detection component 2 is arranged at the first end of the bolt 4 and transmits a detection signal. The second detection component 3 is arranged at the second end of the bolt 4 and receives the detection signal.

[0083] In some preferred embodiments, when the axial stress of the bolt needs to be calibrated or tested, the first end of the bolt 4 is the nut side of the bolt, and the second end of the bolt 4 is the screw side of the bolt screwed into the nut.

[0084] According to an embodiment of the present invention, the bolt axial force detection device further includes a controller 1, to which the first detection component 2 and the second detection component 3 are connected in series. The controller 1 sends a control instruction to the first detection component 2, controls the first detection component 2 to transmit a detection signal, and receives a detection signal returned by the second detection component 3.

[0085] The controller 1 is connected to the first detection component 2 via a signal output line 103 , and is connected to the second detection component 3 via a signal input line 104 , to receive a detection signal returned by the second detection component 3 .

[0086] The controller 1 has a display panel 101 for displaying the axial stress distribution of the bolt, and an input keyboard 102 for inputting relevant parameters.

[0087] It should be understood that the controller 1 further includes a storage unit, a signal conversion unit, and a data processor. The storage unit is used to store the detection signal returned by the second detection unit 3, as well as the calculated bolt density distribution data and parameter data obtained by bolt calibration.

[0088] The signal conversion unit is used to convert the returned acoustic / ultrasonic detection signal into a digital signal.

[0089] The data processor processes the returned detection signal, outputs bolt calibration parameters and bolt axial stress distribution, and displays them on the display panel 101 .

[0090] like Figure 2The internal structure diagram of the first detection component in one embodiment of the invention is shown. Figure 3 The first detection component 2 is connected to the controller 1 via a signal output line 103 to receive the detection signal output by the controller 1 .

[0091] The first detection component 2 has a plurality of first probes 201 arranged in an array embedded therein. The first probes 201 contact the first end of the bolt 4 , and the plurality of first probes 201 periodically emit detection signals in sequence.

[0092] The first probe 201 is connected to the signal output line 103 via a first connecting line 202. The first detection component 2 is filled with a first filler 203, which spaced the first probes 201 in an array. The head of the first probe 201 is exposed from the first filler 203 and is provided with a first spherical protective head 205. The tail of the first probe 201 is embedded in the first filler 203 and connected to a first insulating spring 204.

[0093] In some preferred embodiments, the detection signal is a sound wave / ultrasonic wave signal, the first probes 201 are arranged in a multi-layer concentric circle array, and the distance between the first probes 201 is greater than twice the wavelength of the sound wave / ultrasonic wave.

[0094] like Figure 4 FIG. 1 is a schematic diagram showing the internal structure of the second detection component in one embodiment of the present invention. Figure 5 The second detection component 3 is connected to the controller 1 via a signal input line 104 to input a detection signal to the controller 1 .

[0095] The second detection component 3 has a plurality of second probes 301 arranged in an array embedded therein. The second probes 301 contact the second end of the bolt. The plurality of second probes 301 simultaneously receive the detection signal emitted by each first probe 201 .

[0096] The second probes 301 are connected to the signal input line 104 via a second connecting line 302. The second detection component 3 is filled with a second filler 303, which spaced the second probes 301 in an array. The heads of the second probes 301 are exposed from the second filler 303 and are provided with a second spherical protective head 305. The tails of the second probes 301 are embedded in the second filler 303 and connected to a second insulating spring 304.

[0097] In some preferred embodiments, the detection signal is a sound wave / ultrasonic wave signal, the second probes 301 are arranged in a multi-layer concentric circle array, and the distance between the second probes 301 is greater than twice the wavelength of the sound wave / ultrasonic wave.

[0098] According to an embodiment of the present invention, both the first probe 201 and the second probe 202 are PZT piezoelectric ceramic microprobes, and the first probe 201 and the second probe 301 have a columnar structure. In some preferred implementations, the diameters of the first probe 201 and the second probe 301 are between 0.3 cm and 1 cm. The first spherical protective head 205 and the second spherical protective head 305 are both rubber spherical protective heads, and the first filler 203 and the second filler 303 are both epoxy resin fillers.

[0099] The first probe 201 and the second probe 301 of the present invention are wrapped with an epoxy resin filler, which serves as a buffering and absorbing material for the acoustic wave signal between the probes, thereby reducing acoustic wave interference between the probes.

[0100] When the second probe 301 receives a signal (sound wave / ultrasound wave), the piezoelectric ceramic probe generates a polarization effect due to the relative displacement of the internal positive and negative charge centers caused by mechanical stress. This causes bound charges of opposite signs to appear on the surfaces of the material at both ends, converting mechanical energy into electrical energy, thereby sensing changes in the elastic wave. This characteristic allows the present invention to accurately capture the arrival time of the elastic wave.

[0101] When the first probe 201 transmits a signal (sound wave / ultrasound wave), the controller 1 connected thereto drives the vibrator through the electrical signal, converting the electrical energy into mechanical energy of the probe, thereby generating an inverse piezoelectric effect.

[0102] It should be understood that in some embodiments, the first probe 201 can be used as a signal receiver or a signal transmitter through functional settings, and the second probe 301 can be used as a signal receiver or a signal transmitter.

[0103] like Figure 6 The figure shows a schematic diagram of the transmission of the signal of the bolt axial force detection device inside the bolt in one embodiment of the present invention. When calibrating or detecting the bolt axial force, the first detection device 2 is arranged at the first end of the bolt 4, and the second detection component 3 is arranged at the second end of the bolt 4.

[0104] The multiple first probes 201 embedded in the first detection component 2 periodically transmit detection signals in sequence, and the multiple second probes 301 embedded in the second detection component 3 simultaneously receive the detection signals transmitted by each first probe 201. For example, the first detection component 2 is embedded with n first probes 201, and the second detection component 3 is embedded with n second probes. The n first probes 201 in the first detection component 2 transmit detection signals in sequence, and the n second probes 301 in the second detection component 3 simultaneously receive the detection signals transmitted by the first probes. When all the n first probes in the first detection component 2 transmit a detection signal once, a cycle is completed. The axial stress of the bolt is calibrated or detected by collecting the acoustic wave velocity of the signal path 401 (described in detail below).

[0105] In some preferred embodiments, within a period of time, the first detection component 2 transmits detection signals for multiple cycles, that is, each first probe 201 transmits detection signals multiple times.

[0106] like Figure 7 The structural diagram of a bolt axial force calibration device in one embodiment of the present invention is as follows. According to an embodiment of the present invention, a bolt axial force calibration device is provided, comprising:

[0107] Frame 5, the upper part of frame 5 can move up and down ( Figure 7 The moving component 8 (arrow a) in FIG. 1 ) and the first and second clamping devices 6 and 7 are used to clamp the bolt 4. The moving component 8 is fixed to the first clamping device 6 and drives the first clamping device 6 to move up and down, stretching / compressing the bolt 4 and adjusting the axial stress of the bolt.

[0108] According to an embodiment of the present invention, a bolt axial force calibration device further includes a bolt axial force detection device having a first detection component 2, a second detection component 3 and a controller 1. The bolt axial force detection device has been described above and will not be repeated here.

[0109] like Figure 8 The flowchart of the bolt axial force calibration method according to one embodiment of the present invention is shown in FIG. 1 . The bolt axial force calibration method provided by the present invention includes the following steps:

[0110] Step S101: Clamp the bolt on the bolt axial force calibration device. Figure 7 As shown, the bolt is fixed between the first clamping device 6 and the second clamping device 7.

[0111] Step S102: Adjust the clamping length of the bolt.

[0112] The clamping length of the bolt is adjusted by adjusting the position of the nut screwed into the bolt.

[0113] Step S103: adjusting the axial stress on the bolt.

[0114] In step S102 and step S103 , the first clamping device 6 is driven to move up and down by the moving component 8 , thereby stretching / pressing the bolt 4 and adjusting the axial stress of the screw.

[0115] Step S104: Arrange bolt axial force detection devices at both ends of the bolt.

[0116] The first detection component 2 is arranged on the first end of the bolt 4 in a manner of interference, and the second detection component 3 is arranged on the second end of the bolt 4 in a manner of interference.

[0117] Step S105: Acquire a detection signal.

[0118] The controller 1 receives a detection signal, wherein the detection signal is a detection signal emitted by the first detection component 2 and received by the second detection component 3 .

[0119] The first detection component 2 includes a plurality of array-arranged first probes 201 embedded therein, which periodically transmit detection signals in sequence.

[0120] The second detection component 3 has multiple array-arranged second probes 301 embedded therein, which simultaneously receive the detection signal emitted by each of the first probes.

[0121] Step S106: Calculate the longitudinal wave velocity of the detection signal in each channel.

[0122] According to an embodiment of the present invention, the detection signal is a sound wave / ultrasonic wave signal. After receiving the detection signal, the controller 1 converts it into a digital signal.

[0123] In some embodiments, the longitudinal wave velocity used to calculate the density of the bolts in each passage is: in one cycle, each first probe F of the first detection component 2 i The detection signals are emitted in sequence, and all the second probes ∑S of the second detection component 3 i At the same time, the detection signal transmitted by each first probe is received.

[0124] The controller collects the detection signal of one cycle and calculates the detection signal in each channel L ij The longitudinal wave velocity v ij , where i is the number of the first probe and j is the number of the second probe.

[0125] In some preferred embodiments, the longitudinal wave velocity used to calculate the density of the bolts in each passage is: the controller collects the average value of the longitudinal wave velocity of each passage in multiple cycles over a period of time.

[0126] The first probe F in each of the first detection components 2 i The acoustic wave signal is continuously and periodically emitted, and all the second probes ∑S of the second detection component 3 i At the same time, each first probe transmits a detection signal and calculates each sound wave path L in each cycle. ij The longitudinal wave velocity v of the sound wave ij , and calculate the mean of the wave speed calculated over multiple cycles over a period of time

[0127] Furthermore, the average of the wave velocities calculated over multiple periods is When the maximum and minimum values ​​are removed to reduce the interference of heterodox values, the L ij Upper wave speed v ij accuracy.

[0128] Step S107: Calculate the density of the bolts in each passage.

[0129] According to an embodiment of the present invention, the density of the bolts in each passage is calculated using the longitudinal wave velocity of the detection signal in each passage.

[0130] The density of bolts in each channel is expressed as follows:

[0131]

[0132] Among them, ρ ij The bolts are in each channel L ij density on the surface, E is the elastic modulus, μ is the Poisson's ratio, and v ij It is the longitudinal wave velocity of the detection signal in each channel.

[0133] In the embodiment, ultrasound is taken as an example. Ultrasonic wave is an elastic wave with a frequency greater than 20kHz. Its propagation speed in a homogeneous medium mainly depends on the density, Poisson's ratio and elastic modulus of the material. Figure 6 As shown, the sizes of the first probe 201 and the second probe 301 of the present invention are much smaller than the diameter of the bolt 4. The process of acoustic wave transmission in the bolt can be regarded as the process of elastic wave transmission in an infinite medium.

[0134] In an infinite elastic medium, the displacement u of the vibrating particle moves along the z axis (vertical axis) and is independent of the displacement of the x and y axes, that is, υ = ω = 0.

[0135] Therefore, the elastic vibration equilibrium equation of sound waves in infinite media can be written as:

[0136]

[0137] In the above formula, λ and γ are the first and second Lame constants respectively, X, Y and Z are the body forces respectively, is the Laplace operator, and ρ is the density of the propagation medium. When the body force is assumed to be zero, only the first equation in the above equations is non-zero, that is:

[0138]

[0139] The velocity in the z-axis direction is obtained by solving:

[0140]

[0141] Will as well as Substituting into the above formula we get:

[0142]

[0143] Square both sides of the above equation to get the bolt length L in each passage ijThe density ρ on ij expression:

[0144]

[0145] Step S108: Calculate the density distribution of the entire bolt.

[0146] According to an embodiment of the present invention, the density distribution of the entire bolt is calculated by three-dimensional bilinear interpolation. The three-dimensional bilinear interpolation calculation formula is:

[0147]

[0148] Step S109: fitting the nonlinear relationship between the axial stress of the bolt and the density distribution of the entire bolt.

[0149] According to an embodiment of the present invention, the nonlinear relationship between the bolt axial stress and density distribution is expressed as follows:

[0150]

[0151] Where σ is the bolt axial stress, ρ x,y,z is the density distribution of the entire bolt, and a, b, and c are unknown parameters.

[0152] After fitting the nonlinear relationship between the bolt axial stress and density distribution, return to step S102 to readjust the clamping length of the screw, and readjust the axial stress in step S103 to obtain multiple sets of bolt axial stress σ and the density distribution ρ of the entire bolt. x,y,z , using the nonlinear relationship between the bolt axial stress and density distribution, the unknown parameters a, b and c are obtained.

[0153] Step S110 , a fixed point of the curve of the nonlinear relationship between the bolt axial stress and the density distribution is linearly fitted with the bolt clamping length to calibrate the bolt axial force.

[0154] According to an embodiment of the present invention, in step S109, a nonlinear relationship between the axial stress and the density distribution of the bolt is obtained, and a linear fit is performed using the fixed points of the curve and the bolt clamping length. The fit is expressed as follows:

[0155]

[0156] in, is the fixed point of the curve of the nonlinear relationship between the bolt axial stress and density distribution, L is the clamping length of the bolt, and α and β are unknown parameters.

[0157] After obtaining the linear fitting relationship between the vertex of the nonlinear fitting curve and the change of the bolt clamping length, the unknown parameters α and β are obtained by adjusting different clamping lengths.

[0158] At this point, the calibration of the bolt is completed.

[0159] Figure 9 A flowchart of a method for detecting a bolt axial force according to an embodiment of the present invention is shown. According to an embodiment of the present invention, a method for detecting a bolt axial force includes:

[0160] Step S201: The bolt axial force calibration device calibrates the bolt axial force.

[0161] According to an embodiment of the present invention, the bolt axial force calibration method of steps S101 to S110 is used to calibrate the bolt axial force.

[0162] Step S202: The bolt axial force detection device is arranged on the in-service bolt.

[0163] The bolt axial force detection device provided by the present invention is placed on an in-service bolt, for example, at both ends of a bolt on a wind turbine tower flange. The controller sends a command to the first detection component 2, which emits a detection signal. The second detection component 3 receives the detection signal and returns it to the controller.

[0164] It should be noted that the bolt axial stress detection device is arranged on an in-service bolt of the same model as the calibrated bolt.

[0165] The bolts in service should be of the same model as the bolts being calibrated. If the models of the bolts in service are different from those of the bolts being calibrated, the bolts of the same model as the bolts in service should be calibrated.

[0166] Step S203: Input the parameters obtained by bolt calibration and perform axial force detection on the in-service bolts.

[0167] The bolt axial force calibration method of steps S101 to S110 is used to calibrate the bolt axial force to obtain parameters a, b and c, as well as unknown parameters α and β, which are input into the controller to perform axial force detection on the in-service bolts.

[0168] It should be understood that the controller executing steps 106 to 110 of the bolt axial force calibration method of the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of the present invention may be implemented using various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0169] The bolt axial force detection process of the present invention is described below through specific embodiments.

[0170] Before testing the strength of in-service bolts, check whether there is data available in the bolt axial force-density fitting database for the same model of bolt to be tested. If not, it is necessary to first use axial force calibration equipment to calibrate the axial force of the same model of bolt to be tested.

[0171] Example 1.

[0172] In this embodiment, the bolt axial force detection device, calibration equipment, calibration method and detection method provided by the present invention are used to detect the axial force distribution of the bolts of the tower flange of a 3MW wind turbine. Each flange of the tower has a total of 136 bolts, and the bolt specifications are shown in Table 1.

[0173] Table 1

[0174]

[0175] When preparing to test the axial force of the tower flange bolts, it was discovered that the same type of bolts used in the flange in this embodiment had not been calibrated for axial force. Therefore, there was no equivalent data in the bolt axial force-density fitting database for direct measurement. Therefore, it was necessary to first find bolts of the same type and perform axial force calibration. The specific steps are as follows:

[0176] 1. Number the bolts of the same model. Since the clamping length of all flange bolts in this embodiment is the same, the clamping length does not need to be changed during the bolt axial force calibration. Therefore, at least 30 bolts need to be numbered to meet the requirements of different axial forces during the bolt axial force calibration process.

[0177] 2. Starting from number 1, gradually increase the axial stress σ of the bolt, ranging from 0kN to 1.5 times the design preload of the bolt. When the service life of the wind turbine tower bolt is more than 3 years, the range needs to be expanded to 2 times the design preload.

[0178] 3. Place the bolts on the bolt axial force calibration device provided by the present invention in sequence according to the numbering order, and adjust the fixed clamping length and the preset axial force.

[0179] 4. The first detection component and the second detection component of the bolt axial force detection device provided by the present invention are arranged at both ends of the bolt and are close to the end face of the bolt to be tested.

[0180] 5. Input the bolt clamping length, tensile axial force, elastic modulus and Poisson's ratio into the controller, use the controller to send instructions to the first detection component to start the bolt axial force calibration test, and obtain the detection signal returned by the second detection component. According to steps S106 to S108 of the above-mentioned bolt axial force calibration method, the density distribution of the bolt is obtained.

[0181] 6. The density distribution results of the bolts are displayed in real time on the controller's display screen. After the controller detects that the bolt density distribution data is stable, it is recorded and stored in a mat format file for subsequent convenient import into MATLAB software processing.

[0182] 7. According to the above bolt axial force calibration method, step S103 is repeatedly performed to adjust different axial stresses, and the controller sequentially obtains and stores the bolt density distribution data under different axial stresses.

[0183] 8. Import the bolt axial force calibration data into MATLAB and use fitting to obtain the nonlinear relationship between the bolt axial stress and density distribution at a specific clamping length, and calculate the unknown parameters a, b, and c. This completes the bolt axial force calibration.

[0184] 9. Start to test the axial force of the in-service bolts. Place the first detection component and the second detection component of the bolt axial force detection device provided by the present invention at both ends of the in-service bolt to be tested and close to the end face of the bolt to be tested.

[0185] 10. Input the values ​​of parameters a, b, and c into the controller, send a command to the first detection component, and start real-time detection of the bolt axial force.

[0186] 11. The bolt axial force test results are displayed in real time on the controller's display screen. When the detected axial force value stabilizes, the controller records and stores the corresponding axial force data and axial force cloud map in a mat format file.

[0187] Example 2.

[0188] In this embodiment, the bolt axial force detection device, calibration equipment, calibration method and detection method provided by the present invention are used to detect the axial force distribution of the tower flange bolts of a 2.5MW wind turbine. Each flange of the tower has a total of 124 bolts, and the bolt specifications are shown in Table 2.

[0189] Table 2

[0190]

[0191] When preparing to test the axial force of the tower flange bolts, it was discovered that the same type of bolts used in the flange in this embodiment had not been calibrated for axial force. Therefore, there was no equivalent data in the bolt axial force-density fitting database for direct measurement. Therefore, it was necessary to first find bolts of the same type and perform axial force calibration. The specific steps are as follows:

[0192] 1. Number bolts of the same model. Because the flange bolts in this case have three different clamping lengths, the clamping length needs to be changed during the bolt axial force calibration. Therefore, at least 90 bolts need to be numbered to meet the requirements of different axial forces during the bolt axial force calibration process.

[0193] 2. Starting from number 1, the calibration bolts are divided into three groups according to the three bolt clamping lengths. The axial stress σ of the bolts is increased step by step in each group, ranging from 0kN to 1.5 times the design preload of the bolts. When the service life of the wind turbine tower bolts is more than 3 years, the range needs to be expanded to 2 times the design preload.

[0194] 3. Place the bolts on the bolt axial force calibration device provided by the present invention in sequence according to the numbering order, and adjust the fixed clamping length and the preset axial force.

[0195] 4. The first detection component and the second detection component of the bolt axial force detection device provided by the present invention are arranged at both ends of the bolt and are close to the end face of the bolt to be tested.

[0196] 5. Input the bolt clamping length, tensile axial force, elastic modulus and Poisson's ratio into the controller, use the controller to send instructions to the first detection component to start the bolt axial force calibration test, and obtain the detection signal returned by the second detection component. According to steps S106 to S108 of the above-mentioned bolt axial force calibration method, the density distribution of the bolt is obtained.

[0197] 6. The density distribution results of the bolts are displayed in real time on the controller's display screen. After the controller detects that the bolt density distribution data is stable, it is recorded and stored in a mat format file for subsequent convenient import into MATLAB software processing.

[0198] 7. According to the above bolt axial force calibration method, step S103 is repeatedly performed to adjust different axial stresses, and the controller sequentially obtains and stores the bolt density distribution data under different axial stresses.

[0199] 8. Import the above bolt axial force calibration data into MATLAB, and use fitting to obtain the nonlinear relationship between the bolt axial stress and density distribution at a specific clamping length, and obtain the unknown parameters a, b and c.

[0200] The unknown parameters α and β are obtained by using the fixed points of the curve of the nonlinear relationship between the bolt axial stress and density distribution and the linear relationship with the bolt clamping length.

[0201] The axial force calibration of the bolt is now completed.

[0202] 9. Start to test the axial force of the in-service bolts. Place the first detection component and the second detection component of the bolt axial force detection device provided by the present invention at both ends of the in-service bolt to be tested and close to the end face of the bolt to be tested.

[0203] 10. Input the values ​​of parameters a, b, c, α, and β into the controller, send a command to the first detection component, and start real-time detection of the bolt axial force.

[0204] 11. The bolt axial force test results are displayed in real time on the controller's display screen. When the detected axial force value stabilizes, the controller records and stores the corresponding axial force data and axial force cloud map in a mat format file.

[0205] Example 3.

[0206] In this embodiment, the bolt axial force detection device, calibration equipment, calibration method and detection method provided by the present invention are used to detect the axial force distribution of the bolts of the tower flange of a 2.5MW wind turbine. Each flange of the tower has a total of 126 bolts, and the bolt specifications are shown in Table 3.

[0207] Table 3

[0208]

[0209] When preparing to test the axial force of the tower flange bolts, it was discovered that the same type of bolts used in the flange in this embodiment had previously been calibrated for axial force. The bolt axial force-density fitting database contained the same data that could be used for direct measurement. Therefore, it was not necessary to conduct a bolt axial force calibration test on the same type of bolts. The specific steps are as follows:

[0210] 1. Start to detect the axial force of the in-service bolts. Place the first detection component and the second detection component of the bolt axial force detection device provided by the present invention at both ends of the in-service bolt to be detected and close to the end face of the bolt to be detected.

[0211] 2. Fill in the values ​​of parameters a, b, c, α, and β of the same type of bolts in the bolt axial force-density fitting database in the controller, send a command to the first detection component, and start real-time detection of the bolt axial force.

[0212] 3. The axial force test results of the bolts are displayed in real time on the display screen of the digital controller. When the detected axial force value stabilizes, the controller records and stores the corresponding axial force data and axial force cloud map in a mat format file.

[0213] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A method for calibrating the axial force of a bolt, characterized in that: The calibration method uses a bolt axial force detection device, which includes: The first detection component is arranged on the first end of the bolt, The second detection component is arranged on the second end of the bolt, The first detection component is embedded with a plurality of first probes arranged in an array, the first probes contact the first end of the bolt, and the plurality of first probes periodically emit detection signals in sequence; The second detection component is embedded with a plurality of second probes arranged in an array, the second probes contact the second end of the bolt, and the plurality of second probes simultaneously receive the detection signal emitted by each of the first probes; The method comprises the following steps: The controller receives a detection signal, wherein the detection signal is a detection signal emitted by the first detection component and received by the second detection component; wherein the first detection component is arranged at the first end of the bolt, and the second detection component is arranged at the second end of the bolt; wherein the first detection component is embedded with a plurality of first probes arranged in an array, the first probes abut against the first end of the bolt, and the plurality of first probes sequentially and periodically emit detection signals; wherein the second detection component is embedded with a plurality of second probes arranged in an array, the second probes abut against the second end of the bolt, and the plurality of second probes simultaneously receive the detection signal emitted by each of the first probes; and the controller calibrates the axial force of the bolt through the received detection signal; The controller acquires the detection signal; calculates the longitudinal wave velocity of the detection signal in each channel; uses the longitudinal wave velocity of the detection signal in each channel to calculate the density of the bolt in each channel; calculates the density distribution of the entire bolt and fits the nonlinear relationship between the axial stress of the bolt and the density distribution of the entire bolt; the curve of the nonlinear relationship between the axial stress and density distribution of the bolt is fixed and linearly fitted with the bolt clamping length to calibrate the axial force of the bolt; The density of bolts in each channel is expressed as follows: ， in, The bolts are in each passage The density on is the elastic modulus, is Poisson's ratio, It is the longitudinal wave velocity of the detection signal in each channel.

2. The bolt axial force calibration method according to claim 1, characterized in that: The detection signal is a sound wave signal; The distance between the first probes is greater than twice the wavelength of the sound wave; the distance between the second probes is greater than twice the wavelength of the sound wave.

3. The method for calibrating the bolt axial force according to claim 1, characterized in that: The first detection component and the second detection component are connected in series to the controller, The controller controls the first detection component to transmit a detection signal and receives a detection signal returned by the second detection component.

4. The method for calibrating the bolt axial force according to claim 1, characterized in that: The longitudinal wave velocity used to calculate the density of bolts in each channel is: In one cycle, the first probes of the first detection component transmit detection signals in sequence, and all the second probes of the second detection component receive the detection signals transmitted by each first probe at the same time; Calculate the longitudinal wave velocity of the detection signal in each channel.

5. The method for calibrating the bolt axial force according to claim 1, characterized in that: The longitudinal wave velocity used to calculate the density of bolts in each channel is: The average value of the longitudinal wave velocity of each channel within multiple cycles within a period of time.

6. A method for detecting bolt axial force, characterized in that: The method comprises: The bolt axial force is calibrated according to the bolt axial force calibration method according to any one of claims 1 to 5.

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