CN110849315A - Dynamic strain tracing calibration method - Google Patents
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- CN110849315A CN110849315A CN201911189068.8A CN201911189068A CN110849315A CN 110849315 A CN110849315 A CN 110849315A CN 201911189068 A CN201911189068 A CN 201911189068A CN 110849315 A CN110849315 A CN 110849315A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B21/00—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant
- G01B21/32—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant for measuring the deformation in a solid
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B21/00—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant
- G01B21/02—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant for measuring length, width, or thickness
- G01B21/04—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant for measuring length, width, or thickness by measuring coordinates of points
- G01B21/042—Calibration or calibration artifacts
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Abstract
The invention discloses a dynamic strain traceability calibration method, and belongs to the field of metering tests. The invention takes the laser vibration meter as the measuring means, and the measuring precision is high; from the definition of the strain, solving the analytic solution of the first-order vibration mode of the rectangular constant-section resonant beam, and establishing a resonant beam dynamic strain calibration tracing method; the standard dynamic strain data of the surface of the resonance beam are obtained through single-point measurement, the measurement process is simple, and the calibration accuracy is high. The method is realized based on the dynamic strain tracing calibration device, and the calibration device comprises a vibration exciter, a resonance beam, a differential laser vibration meter, a data acquisition system, a data processing system, reflective beads, a strain gauge and a strain demodulator. The method measures the surface vibration displacement of the resonance beam, and then obtains the dynamic strain distribution of the surface of the resonance beam through data processing. The invention is not limited by the structure and the installation form of the resonance beam, can obtain the real-time strain data of the surface of the beam and realizes the dynamic strain tracing calibration.
Description
Technical Field
The invention relates to a dynamic strain tracing method, which is used for dynamically calibrating a strain gauge and belongs to the field of measurement and testing.
Background
With the development of scientific technology, strain monitoring is increasingly applied to the industrial field. Compared with static strain, dynamic strain has abundant frequency spectrum information, can completely reflect the running state of a mechanical structure, and has wide application requirements in the fields of health monitoring and detection of aircrafts and high-speed rails, design and manufacture of power machines, damage identification of wind power blades and the like. Because there is the glue film between strainometer and the structure that is surveyed, the strain can't transmit on the strainometer completely, leads to the strainometer to measure the difference of meeting an emergency and the structure that is surveyed and meets an emergency, brings measuring error. Therefore, it is a problem to be solved urgently to perform the strain gauge calibration and reduce the measurement error of the strain gauge. At this stage, some calibration devices for strain gauges are already available. However, the strain gauge is mainly calibrated for static strain, and a dynamic calibration method is not available.
In the dynamic strain calibration method based on the resonant beam, in the calibration process, the accurate value of the strain field on the dynamic resonant beam needs to be measured and used as the standard strain value. The strain field can be measured by adopting a laser speckle method, but the measurement resolution and the real-time property of the strain field are difficult to meet the requirement of dynamic strain calibration.
Disclosure of Invention
The invention discloses a dynamic strain traceability calibration method, which aims to solve the technical problems that: and measuring the surface vibration displacement of the resonance beam, and then processing data to obtain the dynamic strain distribution of the surface of the resonance beam. The invention is not limited by the structure and the installation form of the resonance beam and can obtain the real-time strain data of the surface of the beam.
The invention is realized by the following technical scheme.
The invention discloses a dynamic strain tracing calibration method, which comprises the following steps:
the method comprises the following steps of firstly, determining the first-order natural frequency of the rectangular constant-section resonant beam. Calculating the first-order natural frequency f of the resonant beam according to the material and the structural size of the resonant beam0. Randomly selecting a measuring point at the end point close to the surface of the resonance beam, wherein the transverse coordinate of the measuring point is x; the amplitude of this point is measured by a laser interferometer. With f0Adjusting the vibration frequency f of the vibration exciter to observe the first-order natural frequency of the resonant beam when the peak value of the output peak of the laser interferometer is maximum, wherein the vibration frequency f is the first-order natural frequency f of the resonant beam1。
Step two, adjusting the vibration frequency f and amplitude of the vibration exciter; enabling the resonance beam to be in a stable vibration state through the vibration exciter; the vibration frequency f is at f1(1 ± 0.5%) at a certain point in the frequency range.
Taking a certain position close to the end point of the surface of the resonance beam as a measuring point, wherein the transverse coordinate of the measuring point is x; and measuring the differential dynamic displacement between the free end measuring point and the fixed end in the vertical direction by using a laser interferometer to obtain a relation curve W (t) of the displacement of the point beam in the vertical direction and time. The measurement requirements are as follows: sampling frequency is more than 100 times of vibration frequency, measuring time is more than 10 vibration cycles, M displacement data are continuously acquired, and a displacement and time relation curve W (t) ═ ASin (2 pi ft + theta) is obtained by performing sine fitting on the M displacement data. Wherein, w (t) is the differential displacement of the measuring point relative to the fixed end in the vertical direction at the time t, a is the vibration displacement amplitude, t is the time, f is the vibration frequency, and theta is the vibration phase.
And fourthly, aiming at the rectangular beam with the equal section, the central inertia main shaft of the structure is in the same plane, the external load also acts on the plane, the resonant beam vibrates in the plane in the vertical direction, and the resonant beam mainly deforms into bending deformation.
In the first-order resonance frequency state, the first-order mode curve is as follows:
Y(x)＝A[cosβx-chβx-0.734(sinβx-shβx)](1)
where a is the amplitude coefficient, L is the length of the resonant beam, x is the abscissa of the surface of the resonant beam, β -1.875/L.
Step five, setting the laser vibration meter at x1The measured value y (x) at the point is substituted into (1) to determine the amplitude coefficient a.
Step six, converting the vibration mode curve (1) into a strain curve:
where h is half the thickness of the beam and d2Y(x)/dx2Denotes the second derivative of y (x) with respect to x.
Step seven, standard strain of the mounting point of the resonance beam strain gauge is:
ε(t)＝εmax(Xs)sin(2πft+θ) (3)
wherein XsIs the abscissa, epsilon, of the center point of the strain gauge mounting areamax(Xs) Is XsAnd theta is the initial phase of the resonance beam vibration.
And step eight, the strain gauge to be calibrated is arranged at a calibration point of the resonant beam, the strain demodulator demodulates the strain gauge signal, the data acquisition system synchronously acquires the output signals of the laser vibrometer and the strain demodulator, and the data processing system compares the standard strain value with the output of the strain measurement system to be calibrated, so that the dynamic calibration of the strain gauge is realized.
The invention discloses a dynamic strain tracing calibration method which is realized based on a dynamic strain tracing calibration device, wherein the dynamic strain tracing calibration device comprises a vibration exciter, a resonance beam, a differential laser vibration meter, a data acquisition system, a data processing system, reflective beads, a strain gauge and a strain demodulator;
the resonance beam is arranged on the vibration exciter, the installation point is arranged at the center of the resonance beam to form a dynamic strain generating system, and the laser vibrometer, the data acquisition system and the data processing system are used as a standard dynamic strain measuring system; the reflective micro-beads are adhered to the end part of the upper surface of the resonant beam; two beams of measuring laser emitted by the differential laser vibration meter irradiate the reflective micro-beads, and the reflected light is received by the laser vibration meter, so that the displacement of the measuring point (2) relative to the measuring point (1) is measured; the calibrated strain gauge is arranged on the upper surface of the resonance beam, and the standard strain of the area where the calibrated strain gauge is positioned is compared with the strain measured by the calibrated strain gauge, so that the dynamic strain calibration is realized.
The measuring points (2) and the measuring points (1) are the reflective micro beads (1) and the reflective micro beads (2).
Advantageous effects
The dynamic strain calibration method based on the resonance beam can realize real-time strain measurement on the surface of the resonance beam; the laser vibration meter is used as a measuring means, so that the measuring precision is high; and (3) solving an analytic solution of the first-order vibration mode of the rectangular constant-section resonant beam from the definition of the strain, and establishing a resonant beam dynamic strain calibration tracing method. The standard dynamic strain data of the surface of the resonance beam are obtained through single-point measurement, the measurement process is simple, and the calibration accuracy is high.
Drawings
FIG. 1 is a schematic diagram of a dynamic strain traceability system of the present invention;
the device comprises a vibration exciter 1, a resonance beam 2, a laser vibrometer 3, a data acquisition system 4, a data processing system 5, a reflective microbead 6, a calibrated strain gauge 7 and a strain demodulator 8.
Fig. 2 is a schematic view of a resonant beam structure, in which fig. 2(a) is a front view and fig. 2(b) is a sectional view a-a.
Detailed Description
The invention is further described with reference to the following figures and examples.
Example 1:
the dynamic strain tracing calibration method disclosed in this embodiment is implemented based on the dynamic strain tracing calibration device shown in fig. 1, and the dynamic strain tracing calibration device includes a vibration exciter 1, a resonance beam 2, a laser vibration meter 3, a data acquisition system 4, a data processing system 5, reflective beads 6, a strain gauge 7, and a strain demodulator 8.
The resonance beam is arranged on the vibration exciter 1, the installation point is arranged at the center of the resonance beam 2 to form a dynamic strain generating system, and the laser vibration meter 3, the data acquisition system 4 and the data processing system 5 are used as a standard dynamic strain measuring system; the reflective micro-beads 6 are adhered to the end part of the upper surface of the resonant beam; two beams of measuring laser emitted by the differential laser vibration meter 3 irradiate the reflective micro-bead 6, and the reflected light is received by the laser vibration meter 3, so that the displacement of the point (2) relative to the point (1) is measured; the strain gauge to be calibrated is installed on the upper surface of the resonant beam 2, and the standard strain of the area where the strain gauge to be calibrated is compared with the strain measured by the strain gauge to realize dynamic strain calibration.
The dynamic strain tracing calibration method disclosed by the embodiment specifically comprises the following implementation steps:
the method comprises the following steps of firstly, determining the first-order natural frequency of the rectangular constant-section resonant beam. As shown in FIG. 2, firstly, a resonance beam 2 with a uniform cross section, a length of 110mm, a thickness of 12mm and a natural frequency of 800Hz is selected, the resonance beam 2 is fixed on a vibration exciter 1, reflective micro-beads 6 are arranged at a fixed point and a free end of the upper surface of the resonance beam, and reflective micro-beads x at a free section1The coordinates are 108 mm. Mounting the calibrated strain gauge 7 on the upper surface x of the resonant beam2The coordinate is at 20 mm.
And step two, starting the vibration exciter to enable the constant-section resonant beam 2 to be in a stable resonance state, wherein the vibration frequency is 800 Hz.
Taking a certain position close to the end point of the surface of the resonance beam as a measuring point, wherein the transverse coordinate of the measuring point is x; and measuring the differential dynamic displacement between the free end measuring point and the fixed end in the vertical direction by using a laser interferometer to obtain a relation curve W (t) of the displacement of the point beam in the vertical direction and time. And starting the laser vibration meter, adjusting a light path, measuring the differential vibration state of the glass beads in the direction vertical to the upper surface of the constant-section resonant beam 2, setting the measurement frequency to be 2MHz, and performing continuous measurement. The data acquisition system synchronously acquires output signals of the laser vibration meter and the strain demodulator and performs data analysis through the data processing system.
And fourthly, aiming at the rectangular beam with the equal section, the central inertia main shaft of the structure is in the same plane, the external load also acts on the plane, the resonant beam vibrates in the plane in the vertical direction, and the resonant beam mainly deforms into bending deformation. In the first-order resonance frequency state, the first-order mode curve is as follows: the maximum value Y of the vibration of the measuring point is recorded.
The resonance coefficient β is 1.875/0.11, and the resonance mode curve of the surface of the resonance beam is substituted:
Y＝A{[cos(17.0455·x)-ch(17.0455·x)-0.734·[sin(17.0455·x)-sh(17.0455·x)]} (4)
and step five, substituting the obtained measurement point coordinates (0.108, Y) into the step (1) to obtain the amplitude coefficient A.
Step six, converting the vibration mode curve into a strain curve:
step seven, standard strain of the mounting point of the resonance beam strain gauge is:
ε(t)＝εmax(0.02)sin(1600πt+θ) (6)
therefore, the standard strain is a function of the ordinate Y of the measuring point, the value of the ordinate Y reflects the excitation intensity of the vibration excitation source, and when the Y takes different values, the expression of the amplitude coefficient A and the standard strain epsilon (t) (0.02) is shown in the table 1:
TABLE 1 vibration excitation source different excitation intensity Y corresponding x2Standard strain at 20mm
| Y/μm | A/10-4 | ε(t)(0.02) |
| 373 | -1.9129 | ε(t)＝-0.0005sin(1600πt) |
| 447 | -2.2924 | ε(t)＝-0.0006sin(1600πt) |
| 522 | -2.6770 | ε(t)＝-0.0007sin(1600πt) |
| 596 | -3.0565 | ε(t)＝-0.0008sin(1600πt) |
| 671 | -3.4411 | ε(t)＝-0.0009sin(1600πt) |
| 745 | -3.8232 | ε(t)＝-0.0010sin(1600πt) |
| … | … | … |
And step eight, the strain gauge to be calibrated is arranged at a calibration point of the resonant beam, the strain demodulator demodulates the strain gauge signal, the data acquisition system synchronously acquires the output signals of the laser vibrometer and the strain demodulator, and the data processing system compares the standard strain value with the output of the strain measurement system to be calibrated, so that the dynamic calibration of the strain gauge is realized.
The above detailed description is intended to illustrate the objects, aspects and advantages of the present invention, and it should be understood that the above detailed description is only exemplary of the present invention and is not intended to limit the scope of the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (2)
1. A dynamic strain tracing calibration method is characterized in that: comprises the following steps of (a) carrying out,
the method comprises the following steps of firstly, determining the first-order natural frequency of the rectangular constant-section resonant beam. Calculating the first-order natural frequency f of the resonant beam according to the material and the structural size of the resonant beam0. Randomly selecting a measuring point at the end point close to the surface of the resonance beam, wherein the transverse coordinate of the measuring point is x; the amplitude of this point is measured by a laser interferometer. With f0Adjusting the vibration frequency f of the vibration exciter to observe the first-order natural frequency of the resonant beam when the peak value of the output peak of the laser interferometer is maximum, wherein the vibration frequency f is the first-order natural frequency f of the resonant beam1。
Step two, adjusting the vibration frequency f and amplitude of the vibration exciter; enabling the resonance beam to be in a stable vibration state through the vibration exciter; the vibration frequency f is at f1(1 ± 0.5%) at a certain point in the frequency range.
Taking a certain position close to the end point of the surface of the resonance beam as a measuring point, wherein the transverse coordinate of the measuring point is x; and measuring the differential dynamic displacement between the free end measuring point and the fixed end in the vertical direction by using a laser interferometer to obtain a relation curve W (t) of the displacement of the point beam in the vertical direction and time. The measurement requirements are as follows: sampling frequency is more than 100 times of vibration frequency, measuring time is more than 10 vibration cycles, M displacement data are continuously acquired, and a displacement and time relation curve W (t) ═ ASin (2 pi ft + theta) is obtained by performing sine fitting on the M displacement data. Wherein, w (t) is the differential displacement of the measuring point relative to the fixed end in the vertical direction at the time t, a is the vibration displacement amplitude, t is the time, f is the vibration frequency, and theta is the vibration phase.
And fourthly, aiming at the rectangular beam with the equal section, the central inertia main shaft of the structure is in the same plane, the external load also acts on the plane, the resonant beam vibrates in the plane in the vertical direction, and the resonant beam mainly deforms into bending deformation.
In the first-order resonance frequency state, the first-order mode curve is as follows:
Y(x)＝A[cosβx-chβx-0.734(sinβx-shβx)](1)
where a is the amplitude coefficient, L is the length of the resonant beam, x is the abscissa of the surface of the resonant beam, β -1.875/L.
Step five, setting the laser vibration meter at x1The measured value y (x) at the point is substituted into (1) to determine the amplitude coefficient a.
Step six, converting the vibration mode curve (1) into a strain curve:
where h is half the thickness of the beam and d2Y(x)/dx2Denotes the second derivative of y (x) with respect to x.
Step seven, standard strain of the mounting point of the resonance beam strain gauge is:
ε(t)＝εmax(Xs)sin(2πft+θ) (3)
wherein XsIs the abscissa, epsilon, of the center point of the strain gauge mounting areamax(Xs) Is XsAnd theta is the initial phase of the resonance beam vibration.
And step eight, the strain gauge to be calibrated is arranged at a calibration point of the resonant beam, the strain demodulator demodulates the strain gauge signal, the data acquisition system synchronously acquires the output signals of the laser vibrometer and the strain demodulator, and the data processing system compares the standard strain value with the output of the strain measurement system to be calibrated, so that the dynamic calibration of the strain gauge is realized.
2. The dynamic strain traceability calibration method of claim 1, wherein: the dynamic strain tracing calibration device is realized based on the dynamic strain tracing calibration device, and comprises a vibration exciter, a resonance beam, a differential laser vibration meter, a data acquisition system, a data processing system, reflective micro-beads, a strain gauge and a strain demodulator;
the resonance beam is arranged on the vibration exciter, the installation point is arranged at the center of the resonance beam to form a dynamic strain generating system, and the laser vibrometer, the data acquisition system and the data processing system are used as a standard dynamic strain measuring system; the reflective micro-beads are adhered to the end part of the upper surface of the resonant beam; two beams of measuring laser emitted by the differential laser vibration meter irradiate the reflective micro-beads, and the reflected light is received by the laser vibration meter, so that the displacement of the point (2) relative to the point (1) is measured; the calibrated strain gauge is arranged on the upper surface of the resonance beam, and the standard strain of the area where the calibrated strain gauge is positioned is compared with the strain measured by the calibrated strain gauge, so that the dynamic strain calibration is realized.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114216396A (en) * | 2021-12-16 | 2022-03-22 | 哈尔滨工业大学 | Compound eye unit motion error measuring device based on laser interferometer |
| CN114295097A (en) * | 2021-12-08 | 2022-04-08 | 中国航空工业集团公司北京长城计量测试技术研究所 | High-temperature dynamic strain calibration device based on resonant beam |
| CN114370845A (en) * | 2021-12-08 | 2022-04-19 | 中国航空工业集团公司北京长城计量测试技术研究所 | Resonance type high-temperature dynamic strain calibration method |
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114295097A (en) * | 2021-12-08 | 2022-04-08 | 中国航空工业集团公司北京长城计量测试技术研究所 | High-temperature dynamic strain calibration device based on resonant beam |
| CN114370845A (en) * | 2021-12-08 | 2022-04-19 | 中国航空工业集团公司北京长城计量测试技术研究所 | Resonance type high-temperature dynamic strain calibration method |
| CN114370845B (en) * | 2021-12-08 | 2023-11-24 | 中国航空工业集团公司北京长城计量测试技术研究所 | Resonant high-temperature dynamic strain calibration method |
| CN114295097B (en) * | 2021-12-08 | 2024-01-19 | 中国航空工业集团公司北京长城计量测试技术研究所 | High-temperature dynamic strain calibration device based on resonance beam |
| CN114216396A (en) * | 2021-12-16 | 2022-03-22 | 哈尔滨工业大学 | Compound eye unit motion error measuring device based on laser interferometer |
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