CN112461429A - Ultrasonic pretightening force measurement method for low-elasticity-modulus material bolt - Google Patents
Ultrasonic pretightening force measurement method for low-elasticity-modulus material bolt Download PDFInfo
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- CN112461429A CN112461429A CN202011247059.2A CN202011247059A CN112461429A CN 112461429 A CN112461429 A CN 112461429A CN 202011247059 A CN202011247059 A CN 202011247059A CN 112461429 A CN112461429 A CN 112461429A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L5/00—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
- G01L5/24—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes for determining value of torque or twisting moment for tightening a nut or other member which is similarly stressed
- G01L5/246—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes for determining value of torque or twisting moment for tightening a nut or other member which is similarly stressed using acoustic waves
Abstract
The invention discloses an ultrasonic pre-tightening force measuring method for a bolt made of a low-elasticity-modulus material, and belongs to the technical field of ultrasonic nondestructive testing. The method comprises the following steps: selecting a calibration bolt; under the zero stress state, measuring and calibrating the bolt through ultrasonic waves to obtain a reference waveform; measuring the calibration bolt through ultrasonic waves under different stress states to obtain calibration data; fitting a low elastic modulus bolt pre-tightening force formula by using a least square method and calibration data to obtain a bolt pre-tightening force coefficient; measuring a bolt to be measured through ultrasonic waves to obtain a measured waveform; carrying out noise reduction processing on the measured waveform, and calculating by utilizing a time delay algorithm to obtain ultrasonic time delay between the measured waveform and a reference waveform; and substituting the ultrasonic time delay between the measurement waveform and the reference waveform into calculation by using a low elastic modulus bolt pretightening force formula to obtain the pretightening force of the bolt to be measured. The method is used for measuring the pretightening force of the bolt made of the low-elasticity-modulus material, and the measurement precision can be effectively improved.
Description
Technical Field
The invention relates to an ultrasonic pretightening force measuring method for a bolt made of a low-elasticity-modulus material, and belongs to the technical field of ultrasonic nondestructive testing.
Background
The bolt connection is an important connection mode in engineering production, has the advantages of simple structure, convenience in assembly and disassembly, high efficiency, low cost and the like, and is widely applied to important equipment such as aerospace, traffic bridges, building structures, chemical products and the like.
In actual engineering construction, improper bolt pretightening force can damage the quality of a bolt connecting pair and directly influence the integrity and reliability of equipment. Therefore, the accurate, intuitive and convenient measurement of the bolt pretightening force plays a crucial role in the wide application of the bolt pretightening force in the industrial field. The traditional bolt pretightening force measuring method comprises a torque pulling method, a resistance strain gauge method and the like, but most methods have certain limitations in the aspect of bolt pretightening force monitoring due to the problems of poor control precision, low measuring efficiency and the like. In recent years, an ultrasonic measurement method in a nondestructive testing technology is rapidly developed in bolt pretightening force measurement application, and the theoretical basis of measuring pretightening force based on acoustic elasticity by an ultrasonic method is also perfected through years of research. The ultrasonic longitudinal wave method has extremely high sensitivity to the cylindrical bolt due to transmission along the central axis, and is widely applied to engineering measurement of bolt stress.
In the field of aerospace, with the progress of vehicle weight reduction, bolts made of low-elasticity-modulus materials (such as aluminum bolts and copper bolts) are being used in a large number of vehicle bodies, so that the purpose of reducing the weight of the whole vehicle is achieved. In the existing ultrasonic bolt pretightening force measuring scheme, the measured bolt is mostly a carbon steel or stainless steel bolt, the elasticity modulus of the bolt is large, and the acoustoelastic effect is weak, so that the ultrasonic propagation time and the bolt pretightening force can be approximately considered to be in direct proportion in the measurement. However, for the bolt made of the low elastic modulus material, the elastic modulus is small, the elongation of the bolt under the same pretightening force is much larger than that of a carbon steel or stainless steel bolt, and the acoustic elasticity has an accumulative effect, namely, the change of the ultrasonic propagation time caused by the change of the wave speed caused by the acoustic elasticity effect is increased along with the increase of the elongation of the bolt, so that the influence of the acoustic elasticity effect cannot be ignored when the pretightening force of the bolt is measured by the ultrasonic method for the bolt made of the low elastic modulus material, and the ultrasonic propagation time and the pretightening force of the bolt are not in a simple direct proportion relation. Therefore, the ultrasonic pretightening force measuring method for the low-elasticity-modulus bolt has important application significance in the aspect of pretightening force detection of the key low-elasticity-modulus bolt of the vehicle.
Disclosure of Invention
The invention aims to provide an ultrasonic pre-tightening force measuring method for a bolt made of a low-elasticity-modulus material, which can simply, conveniently and quickly measure the pre-tightening force of the bolt made of the low-elasticity-modulus material at low cost and high precision.
The invention adopts the technical scheme that the invention achieves the aim that: an ultrasonic pretightening force measuring method for a bolt made of a low-elasticity-modulus material comprises the following steps:
s1, selecting any bolts with the same specification and the same batch of bolts to be tested as calibration bolts;
s2, under the zero stress state, measuring the calibration bolt through ultrasonic waves to obtain a reference waveform w0；
S3, under different stress states, measuring the calibration bolt through ultrasonic waves to obtain calibration data sigmaiAnd Δ tiWhere σ isiIndicates the magnitude of the stress, Δ tiRepresenting the ultrasonic time delay under the corresponding stress;
s4, fitting a low elastic modulus bolt pre-tightening force formula by using the calibration data through a least square method to obtain a bolt pre-tightening force coefficient; the low elastic modulus bolt pre-tightening force formula considers nonlinear influence caused by an acoustic elastic effect and is an accurate solving model of bolt pre-tightening force and ultrasonic time delay;
s5, measuring the bolt to be measured through ultrasonic waves to obtain a measured waveform wtest；
S6, measuring the waveform wtestCarrying out noise reduction processing, and calculating by using a time delay algorithm to obtain the measurement waveform wtestAnd the reference waveform w0Ultrasonic time delay Δ t therebetweentest；
S7, the bolt obtained in the step S4Pre-tightening force coefficient, and the measuring waveform w obtained by calculation in the step S6 is obtained by utilizing the low elastic modulus bolt pre-tightening force formulatestAnd the reference waveform w0Ultrasonic time delay Δ t therebetweentestAnd substituting for calculation to obtain the pre-tightening force of the bolt to be detected.
Compared with the prior art, the invention has the beneficial effects that:
the existing ultrasonic bolt pretightening force measurement technology does not consider the nonlinear influence of the acoustic-elastic effect on pretightening force measurement, and approximately considers that the pretightening force magnitude and the ultrasonic time delay are in a linear relationship. However, for the low elastic modulus material, due to the large elongation rate and the aggravation of the acoustic elastic effect, the pretightening force and the ultrasonic time delay are not in a pure linear relation any more, and a large error is generated when the measurement is performed by adopting the prior art scheme. In the technical scheme of the invention, the low elastic modulus bolt pretightening force formula considers the nonlinear influence caused by the acoustic elastic effect and is an accurate solving model of bolt pretightening force and ultrasonic time delay; and solving the bolt pretension coefficient by using a least square method. By adopting the technical scheme of the invention to measure the pretightening force of the bolt made of the low elastic modulus material, the measurement precision of the pretightening force of the bolt made of the low elastic modulus material can be effectively improved.
Further, the expression of the low elastic modulus bolt pretightening force formula is as follows:
in the formula, A, B, C is the bolt pre-tightening force coefficient, σ is the bolt pre-tightening force, and Δ t is the ultrasonic time delay.
The concrete reasoning process of the low elastic modulus bolt pretightening force formula is given as follows:
the length of the bolt to be tested is elongated after the bolt is subjected to the pretightening force, and the change of the ultrasonic propagation time relative to the zero-stress state can be expressed as follows:
wherein L is0The clamping length is in a zero stress state; v. of0The ultrasonic propagation speed is in a zero stress state; delta L is the elongation of the bolt to be tested after being stressed; Δ v is the amount of change in the ultrasound propagation velocity due to the acoustic elastic effect.
According to the Huke's theorem and the acoustic elastic effect:
wherein E is the elastic modulus; k is a radical of2For the acoustic elastic coefficient, this value is only related to the material properties (elastic modulus, poisson's ratio, higher order elastic modulus).
Obtained by combining the formulae (1.1) and (1.2):
due to v0、L0E and k2The method is only related to the material property and the installation mode of the bolt, so that the formula (1.3) can be simplified as follows:
where A, B, C is referred to as the bolt pretension coefficient, which can be expressed as a-v 0,
C＝k2。
further, in step S3, the calibration bolt is measured by ultrasonic waves under different stress states to obtain calibration data σiAnd Δ tiWhere σ isiIndicates the magnitude of the stress, Δ tiThe ultrasonic time delay under the corresponding stress is represented, and the concrete operations comprise:
s3-1, determining the clamping length of the calibration bolt according to the actual fastening condition, and clamping the calibration bolt on a stretcher;
s3-2, atIn the elastic stage of the calibration bolt, a stretcher is utilized to apply different stresses sigma to the calibration boltiAnd collecting ultrasonic signals under corresponding stress to obtain a calibration waveform wiWhere i ═ 1, 2, …, n, denotes the number of different stress states applied by the stretcher; (generally n.gtoreq.5)
S3-3, calibrating waveform wiCarrying out noise reduction treatment, and calculating each calibration waveform w by using a time delay algorithmiAnd a reference waveform w0Ultrasonic time delay Δ t therebetweeni。
Further, in the step S4, fitting the calibration data to a low elastic modulus bolt pretightening force formula by using a least square method to obtain a bolt pretightening force coefficient, where the method includes the steps of: determining a fitting initial value of the bolt pretension coefficient, recording the bolt pretension coefficient as A, B, C, and specifically operating the following steps:
s4-1, calibrating delta t in dataiAs an argument, σiPerforming linear fitting to obtain a linear fitting equation sigma k · Δ t + b as a dependent variable;
s4-2, judging whether the intercept b of the linear fitting equation meets the effective condition of the calibration data, if not, then carrying out calibration data acquisition on the calibration bolt again, and updating the calibration data until the intercept b of the linear fitting equation meets the effective condition of the calibration data;
s4-3, determining that fitting initial values corresponding to the bolt pretension coefficients A, B, C are A respectively according to the linear fitting equation0＝k，B0＝1，C0＝0。
Compared with the prior art, the technical scheme provides a calculation scheme of the fitting initial value of the bolt pretightening force coefficient A, B, C, so that the fitting iteration times are reduced, and the calibration efficiency of the bolt pretightening force is improved.
General procedure for least squares fitting: 1) determining an initial value; 2) carrying out iteration; 3) judging errors and iteration directions by using a least square method; 4) if the error does not reach the minimum value, continuing the steps 2) and 3) until the error reaches the minimum value, and obtaining a fitting value.
Further, between step S1 and step S2, there is further included the step of:
preprocessing the end face of the calibration bolt, and arranging a piezoelectric sensor on the end face of the calibration bolt; the piezoelectric sensor has an ultrasonic self-generating and self-receiving mode and is used for ultrasonic measurement of the calibration bolt.
Further, before step S5, the method further includes the steps of:
preprocessing the end face of the bolt to be detected, and arranging a piezoelectric sensor on the end face of the bolt to be detected; the piezoelectric sensor has an ultrasonic self-transmitting and self-receiving mode and is used for ultrasonic measurement of the bolt to be measured.
Further, the end face of the calibration bolt is preprocessed, a piezoelectric sensor is arranged on the end face of the calibration bolt, and the specific operation comprises the following steps:
polishing the end face of the calibration bolt, and bonding a piezoelectric wafer on the polished end face; the piezoelectric sensor includes a piezoelectric wafer.
Further, it is right the terminal surface of the bolt that awaits measuring carries out the preliminary treatment, and the terminal surface of the bolt that awaits measuring sets up piezoelectric sensor, and concrete operation includes:
polishing the end face of the bolt to be detected, and bonding a piezoelectric wafer on the polished end face; the piezoelectric sensor includes a piezoelectric wafer.
Further, the piezoelectric wafer is a circular piezoelectric wafer, and the circular piezoelectric wafer is concentric with the end face of the calibration bolt or concentric with the end face of the bolt to be detected.
Further, the polished end face satisfies a surface roughness of less than 3.2 μm.
The present invention will be described in further detail with reference to the following detailed description and the accompanying drawings, which are not intended to limit the scope of the invention.
Drawings
FIG. 1 is a flow chart of ultrasonic pre-tightening force measurement of a bolt made of a low elastic modulus material according to an embodiment of the invention.
Fig. 2 is a schematic view of a bonding structure of a piezoelectric wafer and a bolt according to an embodiment of the present invention.
In fig. 2, 1 denotes a bolt, and 2 denotes a piezoelectric wafer.
Detailed Description
The following description of the embodiments of the present invention will be made with reference to the accompanying drawings.
An ultrasonic pretightening force measuring method for a bolt made of a low-elasticity-modulus material comprises the following steps:
s1, selecting any bolts with the same specification and the same batch of bolts to be tested as calibration bolts;
s2, under the zero stress state, measuring the calibration bolt through ultrasonic waves to obtain a reference waveform w0；
S3, under different stress states, measuring the calibration bolt through ultrasonic waves to obtain calibration data sigmaiAnd Δ tiWhere σ isiIndicates the magnitude of the stress, Δ tiRepresenting the ultrasonic time delay under the corresponding stress;
s4, fitting a low elastic modulus bolt pre-tightening force formula by using the calibration data through a least square method to obtain a bolt pre-tightening force coefficient; the low elastic modulus bolt pre-tightening force formula considers nonlinear influence caused by an acoustic elastic effect and is an accurate solving model of bolt pre-tightening force and ultrasonic time delay;
s5, measuring the bolt to be measured through ultrasonic waves to obtain a measured waveform wtest；
S6, measuring the waveform wtestCarrying out noise reduction processing, and calculating by using a time delay algorithm to obtain the measurement waveform wtestAnd the reference waveform w0Ultrasonic time delay Δ t therebetweentest；
S7, according to the bolt pretightening force coefficient obtained in the step S4, the low elastic modulus bolt pretightening force formula is utilized to calculate the measurement waveform w obtained in the step S6testAnd the reference waveform w0Ultrasonic time delay Δ t therebetweentestAnd substituting for calculation to obtain the pre-tightening force of the bolt to be detected.
Further, the expression of the low elastic modulus bolt pretightening force formula is as follows:
in the formula, A, B, C is the bolt pre-tightening force coefficient, σ is the bolt pre-tightening force, and Δ t is the ultrasonic time delay.
Further, in step S3, the calibration bolt is measured by ultrasonic waves under different stress states to obtain calibration data σiAnd Δ tiWhere σ isiIndicates the magnitude of the stress, Δ tiThe ultrasonic time delay under the corresponding stress is represented, and the concrete operations comprise:
s3-1, determining the clamping length of the calibration bolt according to the actual fastening condition, and clamping the calibration bolt on a stretcher;
s3-2, in the elastic stage of the calibration bolt, applying different stresses sigma to the calibration bolt by using a stretcheriAnd collecting ultrasonic signals under corresponding stress to obtain a calibration waveform wiWhere i ═ 1, 2, …, n, denotes the number of different stress states applied by the stretcher; (generally n.gtoreq.5)
S3-3, calibrating waveform wiCarrying out noise reduction treatment, and calculating each calibration waveform w by using a time delay algorithmiAnd a reference waveform w0Ultrasonic time delay Δ t therebetweeni。
Further, in the step S4, fitting the calibration data to a low elastic modulus bolt pretightening force formula by using a least square method to obtain a bolt pretightening force coefficient, where the method includes the steps of: determining a fitting initial value of the bolt pretension coefficient, recording the bolt pretension coefficient as A, B, C, and specifically operating the following steps:
s4-1, calibrating delta t in dataiAs an argument, σiPerforming linear fitting to obtain a linear fitting equation sigma k · Δ t + b as a dependent variable;
s4-2, judging whether the intercept b of the linear fitting equation meets the effective condition of the calibration data, if not, then carrying out calibration data acquisition on the calibration bolt again, and updating the calibration data until the intercept b of the linear fitting equation meets the effective condition of the calibration data;
s4-3, determining that fitting initial values corresponding to the bolt pretension coefficients A, B, C are A respectively according to the linear fitting equation0＝k，B0＝1，C0＝0。
Further, between step S1 and step S2, there is further included the step of:
preprocessing the end face of the calibration bolt, and arranging a piezoelectric sensor on the end face of the calibration bolt; the piezoelectric sensor has an ultrasonic self-generating and self-receiving mode and is used for ultrasonic measurement of the calibration bolt.
Further, before step S5, the method further includes the steps of:
preprocessing the end face of the bolt to be detected, and arranging a piezoelectric sensor on the end face of the bolt to be detected; the piezoelectric sensor has an ultrasonic self-transmitting and self-receiving mode and is used for ultrasonic measurement of the bolt to be measured.
Further, the end face of the calibration bolt is preprocessed, a piezoelectric sensor is arranged on the end face of the calibration bolt, and the specific operation comprises the following steps:
polishing the end face of the calibration bolt, and bonding a piezoelectric wafer on the polished end face; the piezoelectric sensor includes a piezoelectric wafer.
Further, it is right the terminal surface of the bolt that awaits measuring carries out the preliminary treatment, and the terminal surface of the bolt that awaits measuring sets up piezoelectric sensor, and concrete operation includes:
polishing the end face of the bolt to be detected, and bonding a piezoelectric wafer on the polished end face; the piezoelectric sensor includes a piezoelectric wafer.
Further, the piezoelectric wafer is a circular piezoelectric wafer, and the circular piezoelectric wafer is concentric with the end face of the calibration bolt or concentric with the end face of the bolt to be detected.
Further, the polished end face satisfies a surface roughness of less than 3.2 μm.
Examples
The method is used for measuring the pre-tightening force of the aluminum bolt with the diameter of 20mm, and fig. 1 is a flow chart of ultrasonic pre-tightening force measurement of the bolt made of the low-elasticity-modulus material in the embodiment, and comprises a calibration flow and a measurement flow. The following is described in detail in terms of the steps:
s1, selecting any aluminum bolt with the same specification and batch as the bolt to be tested and the diameter of 20mm as a calibration bolt.
Further comprising the steps between step S1 and step S2: the end face of the calibration bolt is polished to meet the requirement that the surface roughness is less than 3.2 mu m, a threaded fastening glue is used for bonding the circular piezoelectric wafer on the polished end face, and meanwhile, the end faces of the circular piezoelectric wafer and the bolt are concentric, and the structure of the calibration bolt is shown in figure 2.
S2, in the zero stress state, the piezoelectric wafer is excited by the self-generating and self-receiving mode to generate ultrasonic waves, and ultrasonic signals are collected to obtain a reference waveform w of the calibration bolt0。
S3, obtaining calibration data sigma through measuring the calibration bolt by ultrasonic wave under different stress statesiAnd Δ tiWhere σ isiIndicates the magnitude of the stress, Δ tiRepresenting the ultrasonic time delay under the corresponding stress. The specific operation comprises the following steps:
s3-1, determining the clamping length of the calibration bolt according to the actual fastening condition, and clamping the calibration bolt on a stretcher;
s3-2, in the elastic stage of the calibration bolt, applying different stresses sigma to the calibration bolt by using a stretcheriAnd collecting ultrasonic signals under corresponding stress to obtain a calibration waveform wiWherein i is 1, 2, 3, 4, 5, which indicates that the number of different stress states applied by the stretcher is 5;
s3-3, calibrating waveform wiCarrying out noise reduction treatment, and calculating each calibration waveform w by using a time delay algorithmiAnd a reference waveform w0Ultrasonic time delay Δ t therebetweeni。
TABLE 1 calibration data
| Ultrasonic time delay (ns) | -0.15625 | 29.2187 | 55 | 74.5312 | 95.7812 | 115 |
| Stress (MPa) | 0 | 29.1 | 61.5 | 90.5 | 121.5 | 150.3 |
S4, fitting a low-elastic-modulus bolt pre-tightening force formula by using a least square method and using calibration data to obtain a bolt pre-tightening force coefficient A, B, C shown in table 2, wherein the low-elastic-modulus bolt pre-tightening force formula considers nonlinear influence caused by an acoustic elastic effect and is an accurate solution model of bolt pre-tightening force and ultrasonic time delay, and the specific expression is
In the formula, sigma is the bolt pretightening force, and delta t is the ultrasonic time delay.
The method for determining the initial fitting value of the bolt pretightening force coefficient A, B, C is as follows:
s4-1, calibrating delta t in dataiAs an argument, σiPerforming linear fitting to obtain a linear fitting equation sigma of 1.3217-delta t-5.8825 as a dependent variable;
s4-2, making the intercept b of a linear fitting equation equal to 5.8825MPa, and performing the next step according with the valid condition of calibration data (namely | b | ≦ 10 MPa);
s4-3, determining fitting initial values corresponding to the bolt pretightening force coefficients A, B, C as A according to a linear fitting equation0＝1.3217，B0＝1，C0＝0。
TABLE 2 bolt pretension factor A, B, C
| Coefficient of bolt pretension | A | B | C |
| Fitting value | 0.086734495 | 0.086730053 | 0.000182629 |
Before step S5, the method further includes the steps of: the end face of the bolt to be tested is polished to meet the requirement that the surface roughness is less than 3.2 mu m, the polished end face is bonded with the circular piezoelectric wafer by using the thread fastening glue, and meanwhile, the end faces of the circular piezoelectric wafer and the bolt are ensured to be concentric, and the structure of the bolt is shown in figure 2.
S5, determining the clamping length of the bolt to be tested according to the actual fastening condition, clamping the bolt to be tested on a stretching machine, respectively stretching the bolt to be tested to 30MPa, 60MPa, 90MPa, 120MPa and 150MPa through the stretching machine, and using the bolt to be testedThe self-receiving mode is sent to excite the piezoelectric chip to generate ultrasonic waves, and ultrasonic signals are collected to obtain a measurement waveform w related to the bolt to be measuredtest。
S6, measuring waveform wtestCarrying out noise reduction processing, and calculating by using a time delay algorithm to obtain a measurement waveform wtestAnd a reference waveform w0Ultrasonic time delay Δ t therebetweentest。
S7, according to the bolt pretightening force coefficient A, B, C obtained in the step S4, the measurement waveform w obtained in the step S6 is calculated by using a low elastic modulus bolt pretightening force formulatestAnd a reference waveform w0Ultrasonic time delay Δ t therebetweentestSubstituting the calculation to obtain the pre-tightening force of the bolt to be measured, wherein the result is shown in the column of 'measuring the pre-tightening force by the technical scheme' in the table 3.
TABLE 3 measurement accuracy COMPARATIVE TABLE
| Axial force applied by stretcher (MPa) | 30.00 | 60.00 | 90.00 | 120.00 | 150.00 | Mean error (%) |
| Prior art measurement Pretightening force (MPa) | 38.62 | 72.69 | 98.51 | 126.59 | 152.00 | 13.23 |
| The technical proposal measures the pretightening force (MPa) | 31.14 | 62.21 | 88.41 | 119.99 | 151.75 | 2.08 |
As can be seen from table 3: the existing ultrasonic bolt pretightening force measurement technology does not consider the nonlinear influence of the acoustic-elastic effect on pretightening force measurement, and for a low elastic modulus material, the elongation is high, and the acoustic-elastic effect is intensified, so that the pretightening force and the ultrasonic time delay are not in a pure linear relation any more, and a large measurement error is generated; in the technical scheme, the low-elastic-modulus bolt pretightening force formula considers the nonlinear influence caused by the acoustic elastic effect, and is an accurate solving model of bolt pretightening force and ultrasonic time delay, and a bolt pretightening force coefficient A, B, C is solved by using a least square method.
Claims (10)
1. The ultrasonic pretightening force measuring method for the bolt made of the low elastic modulus material is characterized by comprising the following steps of:
s1, selecting any bolts with the same specification and the same batch of bolts to be tested as calibration bolts;
s2, under the zero stress state, measuring the calibration bolt through ultrasonic waves to obtain a reference waveform w0；
S3, under different stress states, measuring the mark by ultrasonic wavesFixing the bolt to obtain calibration data sigmaiAnd Δ tiWhere σ isiIndicates the magnitude of the stress, Δ tiRepresenting the ultrasonic time delay under the corresponding stress;
s4, fitting a low elastic modulus bolt pre-tightening force formula by using the calibration data through a least square method to obtain a bolt pre-tightening force coefficient; the low elastic modulus bolt pre-tightening force formula considers nonlinear influence caused by an acoustic elastic effect and is an accurate solving model of bolt pre-tightening force and ultrasonic time delay;
s5, obtaining a measurement waveform w through the ultrasonic vehicle to the bolt to be measuredtest；
S6, measuring the waveform wtestCarrying out noise reduction treatment, and calculating by using a time delay algorithm to obtain the measured splash-shaped wtestAnd the reference waveform w0Ultrasonic time delay Δ t therebetweentest；
S7, according to the bolt pretightening force coefficient obtained in the step S4, the low elastic modulus bolt pretightening force formula is utilized to calculate the measurement waveform w obtained in the step S6testAnd the reference waveform w0Ultrasonic test Δ t therebetweentestAnd substituting for calculation to obtain the pre-tightening force of the bolt to be detected.
2. The ultrasonic pretightening force measurement method for the bolt made of the low elastic modulus material as claimed in claim 1, wherein the pretightening force formula of the bolt made of the low elastic modulus has the following expression:
in the formula, A, B, C is the bolt pre-tightening force coefficient, σ is the bolt pre-tightening force, and Δ t is the ultrasonic time delay.
3. The method for measuring the ultrasonic pre-tightening force of the bolt made of the material with the low elastic modulus as claimed in claim 1, wherein in the step S3, the calibration bolt is measured by ultrasonic waves under different stress states to obtain calibration numbersAccording to sigmaiAnd Δ tiWhere σ isiIndicates the magnitude of the stress, Δ tiThe ultrasonic time delay under the corresponding stress is represented, and the concrete operations comprise:
s3-1, determining the clamping length of the calibration bolt according to the actual fastening condition, and clamping the calibration bolt on a stretcher;
s3-2, in the elastic stage of the calibration bolt, applying different stresses sigma to the calibration bolt by using a stretcheriAnd collecting ultrasonic signals under corresponding stress to obtain a calibration waveform wiWhere i ═ 1, 2, …, n, denotes the number of different stress states applied by the stretcher;
s3-3, calibrating waveform wiCarrying out noise reduction treatment, and calculating each calibration waveform w by using a time delay algorithmiAnd a reference waveform w0Ultrasonic time delay Δ t therebetweeni。
4. The method for measuring the ultrasonic pre-tightening force of the bolt made of the low elastic modulus material as claimed in claim 1, wherein in the step S4, the calibration data is used to fit the low elastic modulus bolt pre-tightening force formula by using a least square method to obtain the bolt pre-tightening force coefficient, and the method comprises the following steps: determining a fitting initial value of the bolt pretension coefficient, recording the bolt pretension coefficient as A, B, C, and specifically operating the following steps:
s4-1, calibrating delta t in dataiAs an argument, σiPerforming linear fitting to obtain a linear fitting equation sigma k · Δ t + b as a dependent variable;
s4-2, judging whether the intercept b of the linear fitting equation meets the effective condition of the calibration data, if not, then carrying out calibration data acquisition on the calibration bolt again, and updating the calibration data until the intercept b of the linear fitting equation meets the effective condition of the calibration data;
s4-3, determining that fitting initial values corresponding to the bolt pretension coefficients A, B, C are A respectively according to the linear fitting equation0＝k，B0＝1，C0＝0。
5. The method for measuring the ultrasonic pre-tightening force of the bolt made of the material with the low elastic modulus as claimed in claim 1, wherein the method further comprises the following steps between the step S1 and the step S2:
preprocessing the end face of the calibration bolt, and arranging a piezoelectric sensor on the end face of the calibration bolt; the piezoelectric sensor has an ultrasonic self-generating and self-receiving mode and is used for ultrasonic measurement of the calibration bolt.
6. The method for measuring the ultrasonic pretightening force of the bolt made of the material with the low elastic modulus as claimed in claim 1, wherein before the step S5, the method further comprises the steps of:
preprocessing the end face of the bolt to be detected, and arranging a piezoelectric sensor on the end face of the bolt to be detected; the piezoelectric sensor has an ultrasonic self-transmitting and self-receiving mode and is used for ultrasonic measurement of the bolt to be measured.
7. The method for measuring the ultrasonic pretightening force of the bolt made of the low elastic modulus material as claimed in claim 5, wherein the end face of the calibration bolt is preprocessed, and a piezoelectric sensor is arranged on the end face of the calibration bolt, and the specific operations include:
polishing the end face of the calibration bolt, and bonding a piezoelectric wafer on the polished end face; the piezoelectric sensor includes a piezoelectric wafer.
8. The method for measuring the ultrasonic pretightening force of the bolt made of the low elastic modulus material as claimed in claim 6, wherein the end surface of the bolt to be measured is preprocessed, and a piezoelectric sensor is arranged on the end surface of the bolt to be measured, and the specific operations include:
polishing the end face of the bolt to be detected, and bonding a piezoelectric wafer on the polished end face; the piezoelectric sensor includes a piezoelectric wafer.
9. The method for measuring the ultrasonic pretightening force of the bolt made of the low elastic modulus material as claimed in claim 7 or 8, wherein the piezoelectric wafer is a circular piezoelectric wafer, and the circular piezoelectric wafer is concentric with the end face of the calibration bolt or concentric with the end face of the bolt to be measured.
10. The method for measuring the ultrasonic pretightening force of the bolt made of the low elastic modulus material according to claim 7 or 8, wherein the polished end face has a surface roughness less than 3.2 μm.
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| CN202011247059.2A Active CN112461429B (en) | 2020-11-10 | 2020-11-10 | Ultrasonic pretightening force measurement method for low-elasticity-modulus material bolt |
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| CN115342955A (en) * | 2022-08-03 | 2022-11-15 | 哈尔滨工业大学 | Stress high-precision measurement method and system based on echo amplitude adaptive weighting compensation |
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