CN216482795U - Strainometer calibrating device - Google Patents
Strainometer calibrating device Download PDFInfo
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- CN216482795U CN216482795U CN202123152748.8U CN202123152748U CN216482795U CN 216482795 U CN216482795 U CN 216482795U CN 202123152748 U CN202123152748 U CN 202123152748U CN 216482795 U CN216482795 U CN 216482795U
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Abstract
The utility model discloses a strainometer calibrating device, which is characterized by comprising a force standard machine, a tested sample for fixedly sticking a strainometer to be tested and a strain measuring system, wherein the tested sample is connected between an upper chuck and a lower chuck of the force standard machine; the strain measurement system comprises a laser interferometer, a steering mirror, an interference mirror and a measurement mirror; the interference mirror and the measuring mirror are vertically distributed on the tested sample; the emergent laser of the laser interferometer faces the steering mirror, and the emergent light of the steering mirror can sequentially reach the interference mirror and the measuring mirror along the vertical direction; the strain gauge further comprises a measuring instrument for detecting the relative resistance variation on the strain gauge to be measured. The utility model has the advantages of can trace to the measurement benchmark completely to the measurement standard utensil, can calibrate surface strain gauge.
Description
Technical Field
The utility model relates to a measure measurement technical field, very much relate to a strainometer calibrating device.
Background
The strain testing technology is widely applied to the aspects of aerospace, chemistry, metallurgical industry, civil engineering, material engineering and the like, and is a common means for testing, analyzing and evaluating the reliability and safety of structural design, manufacture and assembly. In engineering, especially in mechanical engineering, strain, stress measurements are of great importance. Through strain and stress measurement, engineering design and construction quality can be verified, and data is provided for safe operation; the stress state and the engineering state of a part, a mechanism or a structure can be analyzed and researched, the correctness of design calculation is verified, and the load spectrum and the mechanism of a physical phenomenon in the whole engineering process are determined. Therefore, the method plays an important role in developing the design theory of structures and machines, ensuring safe operation, and realizing automatic detection and automatic control. The strain and stress measuring system (strain electrical measurement method) is a common experimental stress analysis method, in which a strain gauge is adhered to a measured piece to form a testing system with a resistance strain gauge and related instruments, the surface strain of a member is measured, and then the stress state of the surface of the member is determined according to a relation between the strain and the stress. The strain gauge generates relative resistance variation due to the surface strain of the member, and the strain gauge is connected to the strain gauge and finally obtains a strain measurement value through a measurement circuit and an amplification circuit of the strain gauge.
Whether the strain measurement result is accurate or not is closely related to indication error, repeatability and the like of the resistance strain gauge and working characteristics (sensitivity coefficient and the like) of the strain gauge. In order to ensure the accuracy of the strain measurement result, the dynamic strain gauge and the static strain gauge need to be verified and calibrated according to JJG623-2005 resistance strain gauge metrological verification regulation, and meanwhile, the working characteristics of the resistance strain gauge (sheet) need to be calibrated and calibrated according to the relevant requirements in JJF1046-1994 metal resistance strain gauge working characteristic technical specification. However, the accuracy and traceability of the obtained strain measurement result cannot be guaranteed only by calibrating the resistance strain gauge without performing third-party calibration on the working characteristics (sensitivity coefficient) of the strain gauge (sheet). However, the conventional isostrain (isointensity) calibration beam method has the problems that the measurement standard cannot be completely traced to the measurement reference, and the surface strain gauge cannot be calibrated.
SUMMERY OF THE UTILITY MODEL
To the not enough of above-mentioned prior art, the utility model aims to solve the technical problem that: provided is a strain gauge calibration device capable of completely tracing a measurement standard instrument to a measurement standard and calibrating a surface type strain gauge.
In order to solve the technical problem, the utility model discloses a following technical scheme:
the strain gauge calibration device is characterized by comprising a force standard machine, a tested sample and a strain measurement system, wherein the tested sample is fixedly adhered to a strain gauge to be tested; the strain measurement system comprises a laser interferometer, a steering mirror, an interference mirror and a measurement mirror; the interference mirror and the measuring mirror are vertically distributed on the tested sample; the emergent laser of the laser interferometer faces the steering mirror, and the emergent light of the steering mirror can sequentially reach the interference mirror and the measuring mirror along the vertical direction; the strain gauge further comprises a measuring instrument for detecting the relative resistance variation on the strain gauge to be measured.
By adopting the structure, the force standard machine is utilized to carry out tensile loading on the tested sample, span deformation values corresponding to different micro-strains can be read through the laser interferometer, and meanwhile, the relative resistance variation output by the strain gauge to be tested can be recorded by the measuring instrument, so that the strain value can be converted into the deformation value measured by the laser interferometer. Because the laser interferometer and the force standard machine can be respectively traced to the national length and the mechanical standard, the surface strain quantity actually generated by the tested sample can be traced to the national length and the mechanical standard by an indirect verification mode through the strain gauge calibration device.
Furthermore, two gauge blocks which are vertically arranged are fixed on the sample to be measured, and a distance for setting a nominal gauge block in a parallel lapping way is formed between the two gauge blocks; the interference mirror and the measuring mirror are respectively arranged on the measuring blocks at the bottom and the top.
The distance between the two gauge blocks is provided with a distance which can be used for setting a nominal gauge block in a grinding way, namely, the distance between the two gauge blocks is the nominal value of the nominal gauge block, so that the distance between the interference mirror and the measuring mirror is more accurate, and the calibration precision is ensured.
Furthermore, two universal joints are respectively arranged at two ends of the tested sample and are respectively connected to the upper chuck and the lower chuck of the force standard machine.
Thus, the pulling force axis is ensured to be a connecting line of the central points of the upper chuck and the lower chuck.
Furthermore, two temperature measuring sensors are stuck on the side surface of the sample to be tested.
Furthermore, the device also comprises a wind-proof heat-insulating cover which covers the tested sample and the strain measurement system.
Furthermore, the force standard machine comprises an upper cross beam and a lower cross beam which are fixedly arranged, and two ends of the upper cross beam and the lower cross beam are respectively connected with a screw rod which can be rotatably arranged; a middle cross beam is arranged between the upper cross beam and the lower cross beam in parallel, and two ends of the middle cross beam are respectively matched with the lead screw through lead screw nuts; the end parts of the two lead screws are connected with a lead screw driving mechanism.
Further, the screw driving mechanism comprises a servo motor and a planetary gear speed reducer, the input end of the planetary gear speed reducer is connected with the output end of the servo motor, the output end of the planetary gear speed reducer is provided with a driving synchronous belt wheel, the input end of the screw is provided with a driven synchronous belt wheel, and the driving synchronous belt wheel and the driven synchronous belt wheel are connected with a synchronous belt.
Further, the tested sample is a metal flat plate or a ruler strip.
Further, the test sample is in H-type.
To sum up, the utility model has the advantages of can trace to the measurement benchmark completely to the measurement standard utensil, can calibrate surface strain gauge.
Drawings
Fig. 1 is a schematic structural diagram of an embodiment of the present invention.
Fig. 2 is a schematic diagram of the optical path principle of the strain measurement system.
Detailed Description
The present invention will be described in further detail with reference to examples.
In specific implementation, as shown in fig. 1, a strain gauge calibration device includes a force standard machine 1, a sample 2 to be tested and a strain measurement system 3, wherein the sample 2 to be tested and the strain measurement system 3 are fixedly attached to a strain gauge to be tested, the force standard machine 1 includes an upper beam 11 and a lower beam 12 which are fixedly arranged, and two ends of the upper beam 11 and the lower beam 12 are respectively connected with a screw 13 which can be rotatably arranged; a middle cross beam 14 arranged in parallel is further arranged between the upper cross beam 11 and the lower cross beam 12, and two ends of the middle cross beam 14 are respectively matched with the screw 13 through screw nuts; the end parts of the two lead screws 13 are connected with a lead screw driving mechanism. The screw driving mechanism comprises a servo motor 15 and a planetary gear speed reducer 16, the input end of the planetary gear speed reducer 16 is connected with the output end of the servo motor 15, the output end of the planetary gear speed reducer 16 is provided with a driving synchronous belt pulley 17, the input end of the screw 13 is provided with a driven synchronous belt pulley 18, and the driving synchronous belt pulley 17 and the driven synchronous belt pulley 18 are connected with a synchronous belt.
The tested sample 2 is an H-shaped metal flat plate or a ruler strip, and the upper end and the lower end of the tested sample are respectively provided with a universal joint which is respectively connected to the upper chuck and the lower chuck of the force standard machine 1. The strain measurement system 3 comprises a laser interferometer 31, a steering mirror 32, an interference mirror 33 and a measurement mirror 34; the interference mirror 33 and the measuring mirror 34 are vertically distributed on the sample 2 to be tested; the outgoing laser of the laser interferometer 31 faces the turning mirror 32, and the outgoing light of the turning mirror 32 can sequentially reach the interference mirror 33 and the measuring mirror 34 along the vertical direction; the strain gauge further comprises a measuring instrument for detecting the relative resistance variation on the strain gauge to be measured.
Specifically, two gauge blocks which are vertically arranged are fixed on the sample to be tested 2, and a distance for setting a nominal gauge block in parallel is formed between the two gauge blocks; the interference mirror 33 and the measuring mirror 34 are respectively installed on the lowermost and uppermost gauge blocks. During assembly, three parallel measuring blocks are firstly attached to the surface of a sample to be tested, the uppermost measuring block and the lowermost measuring block are fixedly bonded on the sample to be tested 2 by glue (502 and other strong glue), and then the middle measuring block is taken down.
The side of the tested sample 2 is pasted with two temperature measuring sensors and is provided with a wind-proof heat-insulating cover, and the wind-proof heat-insulating cover covers the tested sample 2 and the strain measuring system 3.
To further illustrate the present invention, the following description is made of the principle of the strain gauge calibration apparatus:
the strain gauge calibration device mainly comprises: closed-loop control force source, metal plate (sample) -elastic deformation body and strain (micro-displacement) measuring system (laser interference displacement measuring system). This calibrating device accessible is indirect the mode of examining and determine, and according to the chain of tracing to the source of length, power value to the national standard, this dependent variable value can regard as standard dependent variable to use.
The strain gauge calibration apparatus is based on the principle of strain gauge definition, and performs a tensile and compressive test on a standard metal flat plate (sample) by a standard force source in a closed-loop force control manner. The displacement measurement (linear measurement) of metal plate (sample) is carried out in real time and with high precision by laser interference method, and the formula is defined by the dependent variable
Calculating to obtain the standard strain value in the measuring section of the metal flat plate (sample) -elastic deformation body. By effectively controlling the uncertainty of the surface strain measurement of the elastic body, the device finally realizes that the uncertainty in the micro-strain measurement range of the surface strain measurement of the deformable body (500-3000) reaches 2 mu m/m or 0.2% (k is 2).
The closed-loop control force source of the strain gauge calibration device adopts a force standard machine, the accuracy grade of the force standard machine is 0.1 grade, and the strain gauge calibration device has higher integral rigidity relative to a tested sample and is not easy to deform. The force standard machine is integrally installed on a stable foundation, a standard force measuring instrument and a tested sample are connected in series through a corresponding clamp, a connecting piece or a reverse frame, and a set force value is mechanically applied to a metal flat plate (test sample) to generate elastic deformation (tiny displacement). The rotation of the screw rod is controlled by a servo motor. In the axial direction of stretching and compressing, when the stop knob of the screw rod pair is controlled, the screw rod pair is meshed with the screw rod, and the screw rod stops rotating, the automatic locking of the cross beam can be realized. (because the amount of deformation of the metal plate is small, the lead screw changes in the vertical and horizontal directions in a low rotation speed state)
Principle of strain (micro-displacement) measurement
The device adopts an absolute measurement method for a corresponding variable (micro-displacement), namely, the deformation of a metal flat plate in the installation range of a strain gauge (strain gauge) is compared with the wavelength of light waves to determine the actual measurement value of the relative deformation.
As shown in fig. 2, a frequency-stabilized laser beam (circularly polarized light) is emitted by a he-ne laser, becomes parallel light through a light pipe, and tilts horizontal light rays by an angle of 90 degrees through an adjustable steering mirror, and the horizontal light rays are divided into two paths (two linearly polarized light beams) by a beam splitter in an interference mirror; one path is reflected back to the spectroscope by the pyramid reference mirror in the interference mirror and returns to the laser head through the original path, and reaches a signal receiving device of the laser head, and the signal receiving device has a fixed optical path; one path is refracted to the pyramid measuring mirror fixed on the moving axis and then reflected back to the spectroscope, and the optical path changes along with the movement of the moving axis, so that the two paths of light are converged on the spectroscope to generate the light interference phenomenon. Since the laser interferometer length measurement system is not provided with an absolute zero position, the position of the measurement mirror on the motion axis can be regarded as an initial position, and the interference counter is set to zero. When the moving axis measuring mirror generates displacement along the light path, bright stripes appear when the difference of the two paths of optical paths is even times of half wavelength of the laser; dark streaks appear at odd multiples. Interference fringes with alternating bright and dark appear with the continuous movement of the motion axis. The changed optical signal is refracted back to the photosensitive element in the laser by the spectroscope and converted into an alternately changed electric signal, and the pulse number is recorded by a counter after the electric signal is processed by a circuit.
And calibrating the initial span between the interference mirror and the measuring mirror by using a gauge block. The interference mirror and the measuring mirror are respectively erected on the two measuring blocks, and the distance between the linear measuring optical mirror groups is determined by using the grinding performance between the measuring surfaces of the measuring blocks in a material measuring tool mode.
From the saint wien principle, it can be seen that the specific distribution pattern of the boundary conditions at a position slightly distant from the load acting region only affects the stress distribution in the vicinity of the load acting region. The range thereof is not larger than the range of the transverse dimension of the rod member, and therefore, the stress state of the displacement measuring section in axial tension can be regarded as a uniaxial stress state conforming to the assumption of a flat section.
Therefore, the method comprises the following steps:
L1before axial stretching, a laser interferometer measures a displacement value of a measuring optical path between a reference mirror and a measuring mirror;
L2after the axial stretching, the laser interferometer measures the displacement value of the measuring optical path between the reference mirror and the measuring mirror;
L3for the strain gauge span, the displacement between the reference mirror to the measurement mirror (the sum of the calibration displacement and the measurement optical path) is determined by the gauge block before axial stretching.
Device commissioning
1. Adjusting laser measuring beam to be parallel to motion axis of force source lead screw
The laser interferometer is firstly placed on the ground stably and adjusted horizontally, an adjustable steering mirror is installed, and horizontal laser emitted by a laser head of the laser interferometer is steered to the vertical direction. And then linear measurement optical lens groups (an interference lens and a measurement lens) are respectively arranged on a base and a middle cross beam of the force source, and the measurement axis is considered to be close to the surface of the metal sample as much as possible during installation so as to reduce Abbe errors.
The translation of the optical head is adjusted when the movable optical element approaches the laser head by repeatedly adjusting the movable optical element both when the movable optical element approaches and when the movable optical element moves away from the laser head; the yaw or pitch of the head is adjusted when the movable optical element is moved away from the head. At the starting end of the stroke, the laser head aims at the target center of the movable optical piece; moving the movable optical part to the tail end of the stroke, enabling the incident light spot to deviate from the target center, enabling the optical position to be fixed, and adjusting the deflection angle of the laser head to enable the light spot to move to the target center; the movable optical piece moves back to the starting end of the stroke, the light spot deviates from the target center again, and the laser head is translated to move the light spot to the position of the target center; the adjustment is carried out in a repeated and continuous iterative mode until the position of the incident light spot is not changed in the whole travel range, which indicates that the laser beam is adjusted to be in good enough conformity with the direction of the measured axis, so that the cosine error is within an acceptable range.
2. Mounting strain generators-metal plates or rulers
Proper pull-direction tools are arranged on an upper chuck and a lower chuck of a force source, universal joints are respectively arranged between a strain generator-a metal flat plate or a ruler strip and the pull-direction tools, the pull-direction stress axis is ensured to be a connecting line of central points of the upper chuck and the lower chuck, and when a middle cross beam moves along the direction of a lead screw, uniaxial strain of the lead screw (the motion axial direction) is generated on the metal flat plate or the ruler strip.
3. Linear optical lens set mounted and adjusted on metal plate or rule strip
And determining the displacement between the other two measuring blocks by utilizing the lapping property between the measuring blocks and the parallel lapping of the three groups of measuring blocks according to the nominal value of the middle measuring block. The other two gauge blocks are glued to the metal plate or the tape with 502 glue. And then the interference mirror and the measuring mirror are respectively erected on the two gauge blocks. Vibration and looseness of the optical part are reduced to the minimum through correct installation, all supports are guaranteed to be absolutely stable and unchanged, and positive errors are avoided.
The position of the interference mirror and the measuring mirror is adjusted so that the light beam is conformed sufficiently well to make the light intensity indicator in the green region throughout the entire stroke and to emphasize the measuring light to the maximum value as much as possible.
A windproof heat-preservation cover is arranged in the measurement area, and a thermometer is attached to the metal sample. Two temperature measuring sensors are attached to the side surface of the metal sample and distributed near two Bessel points of the metal sample.
The measuring laser beam should avoid the temperature gradient area, and the wind-proof heat preservation cover is arranged to reduce the influence of air flow disturbance and air temperature gradient on the measuring result. Atmospheric pressure, air temperature, air humidity measuring instrument all put outside preventing wind heat preservation cover, arrange environmental parameter measuring device like this and be favorable to improving measurement accuracy, can not influence the instrument surrounding environment because of equipment generates heat simultaneously again.
The strain generator (metal sample) is designed as a metal ruler strip with an H-shaped section, and transverse stiffening plates are arranged at intervals, particularly at the chuck parts at two ends. The designed length of the metal sample is 1m, and the material design is made of nickel steel containing Ni 58% or 2Cr13 material.
The H-shaped cross section has a good rigidity, and the measurement region of the standard strain amount can be designed on the neutral plane of the sample (the neutral plane region of the metal sample can be provided with the interference mirror, the measurement mirror, and the device to be calibrated (strain gauge, surface strain gauge)), so the metal sample is considered to be an open cross section. Meanwhile, in order to reduce the influence of torsion and bending on the deformation of the metal sample in the actual stretching process as much as possible, the metal sample is designed into an opening thin-wall section with an H-shaped section. The H-shaped cross-section has a comparable polar moment of inertia and moment of inertia to the neutral axis superior to the L-shaped, channel section, T-shaped. The stiffening plates are arranged on the open thin-walled rod (non-measuring area) at intervals, so that the projection shape of the contour line of the cross section on the plane before the deformation of the rod piece is kept unchanged when the rod piece is twisted, and the distortion of the cross section is reduced when the rod piece is bent, so that the test better conforms to a theoretical calculation model.
Adopt the utility model discloses when the scheme is measured, install laser interferometer, interference mirror, measuring mirror according to the picture. And (3) installing a metal sample in a standard force source test space, installing a strain gauge or a surface type strain gauge, and connecting a digital multimeter (or a resistance strain gauge) to acquire the relative resistance variation output by the strain gauge or the surface type strain gauge.
The measuring mirror, the interference mirror and the laser interferometer are adjusted to be on the same straight line, and when the middle cross beam moves in the measuring range to stretch the metal sample, the laser interferometer can read continuously.
After the adjustment is finished, the temperature is kept constant for at least 2 hours. The temperature fluctuation of the air in the windproof heat-preservation cover in the one-time measurement process is less than or equal to 0.08 ℃.
Before a load is applied, parameters such as air temperature, air pressure, humidity and the like are input into a laser interferometer, and digital display is cleared.
The moving beam is loaded, deformation values of spans corresponding to 200 micro-strain, 400 micro-strain, 600 micro-strain, 1000 micro-strain, 1500 micro-strain, 2000 micro-strain, 2500 micro-strain and 3000 micro-strain are read on a laser interferometer respectively, and meanwhile, relative resistance change values output by the strain gauge are recorded on a digital multimeter (or a resistance strain gauge).
During the measurement, three measurements should be taken, and the average of the three measurements is taken as the measurement result.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the present invention, and any modifications, equivalents and improvements made within the spirit and principles of the present invention are intended to be included within the scope of the present invention.
Claims (9)
1. The strain gauge calibration device is characterized by comprising a force standard machine (1), a tested sample (2) and a strain measurement system (3), wherein the tested sample (2) is fixedly adhered to a strain gauge to be tested, and the tested sample (2) is connected between an upper chuck and a lower chuck of the force standard machine (1); the strain measurement system (3) comprises a laser interferometer (31), a steering mirror (32), an interference mirror (33) and a measurement mirror (34); the interference mirror (33) and the measuring mirror (34) are vertically distributed on the sample to be tested (2); the outgoing laser of the laser interferometer (31) faces the steering mirror (32), and the outgoing light of the steering mirror (32) can sequentially reach the interference mirror (33) and the measuring mirror (34) along the vertical direction; the strain gauge further comprises a measuring instrument for detecting the relative resistance variation on the strain gauge to be measured.
2. The strain gauge calibration device according to claim 1, characterized in that two gauge blocks arranged vertically are fixed on the sample to be tested (2), and a distance for setting a nominal gauge block is arranged between the two gauge blocks in a parallel lapping way; the interference mirror (33) and the measuring mirror (34) are respectively arranged on the measuring blocks at the lowest part and the highest part.
3. The strain gauge calibration device according to claim 1, characterized in that the sample under test (2) is provided with a universal joint at each end and is connected to the upper and lower clamps of the force gauge machine (1), respectively.
4. The strain gauge calibration device according to claim 1, wherein two temperature sensors are attached to the side of the sample (2) to be tested.
5. The strain gauge calibration device according to claim 1, further comprising a wind shield insulation cover, which is provided outside the sample under test (2) and the strain measurement system (3).
6. The strain gauge calibration device according to claim 1, wherein the force standard machine (1) comprises an upper beam (11) and a lower beam (12) which are fixedly arranged, and two ends of the upper beam (11) and the lower beam (12) are respectively connected with a screw (13) which can be rotatably arranged; a middle cross beam (14) arranged in parallel is further arranged between the upper cross beam (11) and the lower cross beam (12), and two ends of the middle cross beam (14) are respectively matched with the screw rod (13) through screw rod nuts; the end parts of the two lead screws (13) are connected with a lead screw driving mechanism.
7. The strain gauge calibration device according to claim 6, wherein the lead screw driving mechanism comprises a servo motor (15) and a planetary gear reducer (16), an input end of the planetary gear reducer (16) is connected with an output end of the servo motor (15), an output end of the planetary gear reducer (16) is provided with a driving synchronous pulley (17), an input end of the lead screw (13) is provided with a driven synchronous pulley (18), and a synchronous belt is connected on the driving synchronous pulley (17) and the driven synchronous pulley (18).
8. The strain gauge calibration device according to claim 1, wherein the sample (2) to be tested is a metal plate or a ruler strip.
9. The strain gauge calibration device as claimed in claim 8, characterized in that the sample (2) under test is H-shaped.
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| CN202123152748.8U CN216482795U (en) | 2021-12-06 | 2021-12-06 | Strainometer calibrating device |
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| CN202123152748.8U CN216482795U (en) | 2021-12-06 | 2021-12-06 | Strainometer calibrating device |
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