Single and biaxial extensometer automatic calibration device and method

Abstract

This invention belongs to the field of strain measurement technology and discloses an automatic calibration device and method for single-axis and dual-axis extensometers. The device includes a cross-shaped guide rail mounted on a base plate. The two straight tracks of the cross-shaped guide rail are divided into a first section and a second section by their perpendicular intersection. The first section is equipped with a closed-loop stepper motor, a motor connecting shaft, a moving slider, and a moving extensometer connecting shaft. The second section is equipped with a fixed slider, a locking bolt, and the extensometer connecting shaft. The fixed extensometer connecting shaft cooperates with the moving extensometer connecting shaft to fix the extensometer. The closed-loop stepper motor is connected to a host computer for signal transmission. When working synchronously, it can calibrate dual-axis extensometers; when working independently, it can calibrate single-axis extensometers. The two closed-loop stepper motors can work together in both phases and opposite phases, and can also calibrate dual-axis extensometers in proportional or non-proportional conditions. Therefore, this invention has the characteristics of high accuracy, strong adaptability, simple operation, and flexible application.

Description

Technical Field

[0001] This invention belongs to the field of strain measurement technology, specifically, it relates to an automatic calibration device and method for single-axis and biaxial extensometers. Background Technology

[0002] Extensometers are generally used in the mechanical property testing of materials and are considered precision measuring instruments. To ensure the reliability of extensometer measurement results, it is essential to calibrate the extensometer using a calibration device before it leaves the factory, after a period of use, and after it has been unused for a long time, in accordance with the "JJG762-2007 Extensometer Verification Procedure".

[0003] Currently, widely used extensometer calibration devices have two shortcomings. Firstly, they are all uniaxial extensometer calibration devices. However, with increasing attention to the biaxial mechanical properties of materials, more and more in-plane biaxial tests are being conducted. In biaxial experiments, the calibration of biaxial extensometers using uniaxial extensometer calibration devices requires calibrating the two measuring axes of the biaxial extensometer twice. Due to the Poisson effect, deformation in one direction of the biaxial extensometer will inevitably cause corresponding deformation in the other direction. Therefore, using a uniaxial extensometer calibrator to calibrate a biaxial extensometer is not only time-consuming and labor-intensive, but also fails to identify the coupling effect between the two axes, making accurate calibration impossible. Secondly, most are manually operated, involving manually rotating a micrometer, manually reading and recording the measurements. This method inevitably introduces additional errors. Therefore, there is an urgent need for an automated extensometer calibration technology applicable to various pin types, with multiple ranges, and simultaneously capable of uniaxial and biaxial calibration. Summary of the Invention

[0004] This invention aims to solve the technical problems related to existing extensometer calibration devices and provides an automatic calibration device and method for single-axis and dual-axis extensometers. By setting the calibration scheme through a host computer, it can automatically calibrate single-axis or dual-axis extensometers. It features high accuracy, strong adaptability, simple operation, reliable structure, and flexible application.

[0005] To solve the above-mentioned technical problems, the present invention is implemented through the following technical solution:

[0006] According to one aspect of the present invention, an automatic calibration device for a single- or dual-axis extensometer is provided, comprising a cross-shaped guide rail disposed on the surface of a base plate, the cross-shaped guide rail being composed of two mutually perpendicular straight tracks, both of the two straight tracks being divided into a first segment and a second segment by a perpendicular intersection point, and the length of the first segment being greater than the length of the second segment.

[0007] Closed-loop stepper motors are respectively installed at the ends of the first sections of the two linear tracks, and the closed-loop stepper motors are fixed to the base plate; the closed-loop stepper motors are connected to the host computer and can execute the calibration scheme set in the host computer;

[0008] Each of the closed-loop stepper motors is connected to a movable slider via a motor connecting shaft. The movable slider slides in engagement with the linear track. The motor connecting shaft converts the rotational motion of the closed-loop stepper motor into linear motion and pushes the movable slider to move linearly along the linear track. The movable slider is fixedly connected to a movable extensometer connecting shaft.

[0009] The second section of each of the two linear tracks is provided with a fixed slider. The fixed slider is fixedly connected to the linear track by a locking bolt. The locking bolt, in conjunction with the fixed slider, allows the fixed slider to be changed in its fixed position on the linear track to meet the calibration requirements of extensometers with different ranges. The fixed slider is fixedly connected to a fixed extensometer connecting shaft.

[0010] The fixed extensometer connecting shaft and the movable extensometer connecting shaft are used to fix the extensometer.

[0011] Furthermore, the front end face of the movable extensometer connecting shaft is provided with a V-shaped groove and the front periphery is provided with a circumferential groove for fixing extensometers of different pin types.

[0012] Furthermore, the front end face of the fixed extensometer connecting shaft is provided with a V-shaped groove and the front periphery is provided with a circumferential groove for fixing extensometers of different pin types.

[0013] According to another aspect of the present invention, an automatic calibration method for single-axis and bi-axis extensometers based on the above-described apparatus is provided, applied to the calibration of single-axis extensometers, comprising the following steps:

[0014] (1) Determine the relative positions of the movable extensometer connecting shaft and the fixed extensometer connecting shaft according to the range of the single-axis extensometer to be calibrated; fix the single-axis extensometer between the movable extensometer connecting shaft and the fixed extensometer connecting shaft, where the movable extensometer connecting shaft and the fixed extensometer connecting shaft correspond to the same straight track of the cross-shaped guide rail.

[0015] (2) The host computer controls the closed-loop stepper motor to apply a given displacement to the single-axis extensometer point by point, and records the total displacement value applied by the closed-loop stepper motor and the measured value of the single-axis extensometer.

[0016] (3) Continue to control the closed-loop stepper motor to apply a given displacement relative to the total displacement value already applied along the original direction through the host computer, and record the current total displacement value applied by the closed-loop stepper motor and the measured value of the single-axis extensometer; repeat this operation until the maximum range of the single-axis extensometer is reached;

[0017] (4) The strain obtained by converting the total displacement value applied by the closed-loop stepper motor controlled by the host computer to the single-axis extensometer to be calibrated is taken as the true strain, and the measured value of the single-axis extensometer to be calibrated at the same time is taken as the strain to be calibrated, and the single-axis extensometer is calibrated.

[0018] (5) Remove the uniaxial extensometer and repeat steps (1) to (4) three times to complete the final calibration of the uniaxial extensometer.

[0019] Furthermore, in step (3), the given displacement applied each time is the same and does not exceed one-tenth of the range of the uniaxial extrusion measurement.

[0020] According to another aspect of the present invention, an automatic calibration method for a single-axis and biaxial extensometer based on the above-described device is provided, applicable to the calibration of a biaxial extensometer, comprising the following steps:

[0021] (1) Determine the relative positions of the moving extensometer connecting shaft and the fixed extensometer connecting shaft according to the range of the biaxial extensometer to be calibrated, and fix the biaxial extensometer between the moving extensometer connecting shaft and the fixed extensometer connecting shaft; wherein, the 1st shaft and the 2nd shaft of the biaxial extensometer are respectively installed between the moving extensometer connecting shaft and the fixed extensometer connecting shaft corresponding to the two straight tracks of the cross-shaped guide rail;

[0022] (2) The host computer controls two closed-loop stepper motors to apply a given displacement to axis 1 and axis 2 of the biaxial extensometer point by point, and records the total displacement value applied by the two closed-loop stepper motors and the corresponding measurement values ​​of axis 1 and axis 2 of the biaxial extensometer.

[0023] (3) Continue to control the two closed-loop stepper motors through the host computer to apply a given displacement along the original direction relative to the total displacement value already applied, and record the total displacement value applied by the two closed-loop stepper motors and the corresponding 1-axis measurement value and 2-axis measurement value of the biaxial extensometer respectively; repeat this operation until the maximum range of the 1-axis and 2-axis measurement range of the biaxial extensometer is reached;

[0024] Step four: Convert the total displacement values ​​applied by the two closed-loop stepper motors controlled by the host computer to the 1st and 2nd axes of the biaxial extensometer to be calibrated into strain display values. and Due to the Poisson effect, the strain readings are not accurate and require coupling compensation according to equation (3) to obtain the true strain. and The measured values ​​of axes 1 and 2 of the biaxial extensometer 12, corresponding to the two closed-loop stepper motors 3 at the same time, are used as the strains to be calibrated, and the actual strains are then used as the values. and Calibrate the biaxial extensometer 12;

[0025] Step 5: Remove the biaxial extensometer and repeat steps (1) to (4) three times to complete the final calibration of the biaxial extensometer.

[0026] Furthermore, in step (3), the given displacement applied each time is the same and does not exceed one-tenth of the range of the 1st or 2nd axis of the biaxial extensometer.

[0027] The beneficial effects of this invention are:

[0028] The device of this invention adopts a horizontal design, which can eliminate the influence of the extensometer's own weight on the calibration results. It has a compact and reliable structure and excellent stability. It is equipped with two closed-loop stepper motors, which can perform dual-axis extensometer calibration when working synchronously and single-axis extensometer calibration when working alone. The two closed-loop stepper motors can work together in the same phase and opposite phase, and can also perform proportional or non-proportional calibration of dual-axis extensometers. The main body of the device and the host computer adopt a separate design, which can place the calibration device in various environmental chambers, such as high-temperature furnaces, vacuum chambers, and liquid environment chambers, and the host computer controls the accurate calibration of extensometers used in special environments.

[0029] Based on the device of the present invention, the method of the present invention can automatically calibrate a single-axis or biaxial extensometer, which is simple to operate and flexible in application; in particular, considering the biaxial coupling effect caused by the Poisson effect, it can accurately calibrate a biaxial extensometer. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the structure of the automatic calibration device for single and dual-axis extensometers provided by the present invention;

[0031] Figure 2 This is a schematic diagram of the automatic calibration method for a single-axis extensometer provided by the present invention;

[0032] Figure 3 This is a schematic diagram of the automatic calibration method for a biaxial extensometer provided by the present invention.

[0033] In the above diagram: 1. Base plate; 2. Cross-shaped guide rail; 3. Closed-loop stepper motor; 4. Motor connecting shaft; 5. Moving slider; 6. Moving extensometer connecting shaft; 7. Fixed extensometer connecting shaft; 8. Fixed slider; 9. Locking bolt; 10. Signal transmission line; 11. Host computer; 12. Dual-axis extensometer; 13. Single-axis extensometer. Detailed Implementation

[0034] To further understand the content, features, and effects of this invention, the following embodiments are provided, and detailed descriptions are given below in conjunction with the accompanying drawings:

[0035] like Figure 1 As shown, this embodiment provides an automatic calibration device for single and dual-axis extensometers, including a base plate 1, a cross-shaped guide rail 2, a closed-loop stepper motor 3, a motor connecting shaft 4, a moving slider 5, a moving extensometer connecting shaft 6, a fixed extensometer connecting shaft 7, a fixed slider 8, a locking bolt 9, a signal transmission line 10, and a host computer 11.

[0036] A cross-shaped guide rail 2 is mounted on the surface of the base plate 1 and consists of two mutually perpendicular straight tracks. Each track is divided into a first section and a second section at its perpendicular intersection, with the first section being longer than the second section. The second section serves as a fixed area, while the first section serves as a movable area, to accommodate the calibration of extensometers of various gauge lengths.

[0037] The closed-loop stepper motor 3 is located at the end of the first section of the two-wire guide rail and is fixed to the surface of the base plate 1. The closed-loop stepper motor 3 is connected to the host computer 11 via the signal transmission line 10 and can automatically execute the calibration scheme set in the host computer 11.

[0038] The closed-loop stepper motor 3 is connected to the movable slider 5 via the motor connecting shaft 4. The bottom of the movable slider 5 is connected to the cross-shaped guide rail 2 and can slide relative to the first section. The motor connecting shaft 4 is used to convert the rotational motion of the closed-loop stepper motor 3 into linear motion and push the movable slider 5 to make absolutely linear motion along the first section of the linear track.

[0039] The movable slider 5 is fixedly connected to the movable extensometer connecting shaft 6, which is coaxially arranged with the motor connecting shaft 4, enabling synchronous movement between the movable extensometer connecting shaft 6 and the movable slider 5. The front end face of the movable extensometer connecting shaft 6 is provided with a V-shaped slot, and the front periphery is provided with an circumferential groove, which can be used to fix extensometers of different pin types.

[0040] The fixed slider 8 is located in the second section of the cross-shaped guide rail 2, and its bottom is connected to the cross-shaped guide rail 2. The fixed slider 8 is fixedly connected to the cross-shaped guide rail 2 by locking bolts 9. By changing the fixed position of the fixed slider 8 in the second section of the cross-shaped guide rail 2, the calibration requirements of extensometers with different ranges can be met.

[0041] The fixed slider 8 is fixedly connected to the fixed extensometer connecting shaft 7. The front end face of the fixed extensometer connecting shaft 7 is provided with a V-shaped groove, and the front periphery is provided with a circumferential groove, which can cooperate with the movable extensometer connecting shaft 6 to fix extensometers of different pin types.

[0042] The closed-loop stepper motor 3, motor connecting shaft 4, moving slider 5, moving extensometer connecting shaft 6, fixed extensometer connecting shaft 7, fixed slider 8, and locking bolt 9 are all identically configured for the two linear tracks of the cross-shaped guide rail 2. The two closed-loop stepper motors 3 can work synchronously or independently to calibrate dual-axis or single-axis extensometers.

[0043] Based on the above-mentioned automatic calibration method for single- and biaxial extensometers, the coupling effect of the two axes of the biaxial extensometer is first calibrated. According to the "JJG762-2007 Verification Procedure for Extensometers," the calibration point is linearly selected to calibrate axis 1 of the biaxial extensometer, while axis 2 remains fixed during the process. Due to the Poisson effect, although axis 2 of the biaxial extensometer has no strain, it will still display a strain value ε2. Based on the fact that Poisson's ratio is constant, the strain display value ε2 of axis 2 and the calibration strain ε1 of axis 1 satisfy the following relationship:

[0044]

[0045] Equation (1) can express the effect of deformation of axis 1 on axis 2 of the biaxial extensometer. Similarly, the relationship between the effect of deformation of axis 2 on axis 1 can be obtained:

[0046]

[0047] In equation (2), υ1 and υ2 are the 1-axis Poisson's ratio and 2-axis Poisson's ratio of the strain gauge in the biaxial extensometer, respectively.

[0048] In actual use of a biaxial extensometer, without coupling compensation, the strain readings for axes 1 and 2 of the extensometer are as follows: and With real response and Differences exist:

[0049]

[0050] Therefore, during the biaxial calibration of the biaxial extensometer, the coupling effect between the two axes needs to be compensated in the control software according to formula (3).

[0051] like Figure 2 As shown, the automatic calibration device for single and dual-axis extensometers of the present invention is applied to the calibration of a single-axis extensometer 13, and includes the following steps:

[0052] Step 1: Determine the relative positions of the moving extensometer connecting shaft 6 and the fixed extensometer connecting shaft 7 according to the range of the single-axis extensometer 13 to be calibrated. Then, fix the single-axis extensometer 13 to be calibrated in the corresponding grooves of the moving extensometer connecting shaft 6 and the fixed extensometer connecting shaft 7 using a pin. Specifically, the single-axis extensometer 13 is installed between the moving extensometer connecting shaft 6 and the fixed extensometer connecting shaft 7 corresponding to one of the straight tracks of the cross-shaped guide rail 2.

[0053] Step 2: In accordance with the "JJG762-2007 Verification Procedure for Extensometers", the host computer 11 controls the closed-loop stepper motor 3 to apply a given displacement point by point to the single-axis extensometer 13 to be calibrated, and records the total displacement value applied by the closed-loop stepper motor 3 and the measured value of the single-axis extensometer 13.

[0054] Step 3: Continue to control the closed-loop stepper motor 3 to apply the given displacement relative to the total displacement value already applied along the original direction through the host computer 11, and record the current total displacement value applied by the closed-loop stepper motor 3 and the measurement value of the single-axis extensometer 13; repeat this operation until the maximum range of the single-axis extensometer 13 is reached.

[0055] The given displacement applied each time should be the same and not exceed one-tenth of the range of the uniaxial extensometer 13, so as to ensure that each group of measurements has no less than 10 measurement points (excluding the zero point).

[0056] Step 4: The strain obtained by converting the total displacement value applied by the host computer 11 to the closed-loop stepper motor 3 to the single-axis extensometer 13 to be calibrated is taken as the true strain. At the same time, the measured value of the single-axis extensometer 13 to be calibrated is taken as the strain to be calibrated, and the single-axis extensometer 13 is calibrated.

[0057] Step 5: Remove the uniaxial extensometer 13 and repeat steps 1 to 4 three times to complete the final calibration of the uniaxial extensometer 13.

[0058] It should be noted that the host computer 11 described in this invention supports pre-setting a calibration scheme and automatically completes steps one to four to achieve automatic calibration.

[0059] like Figure 3 As shown, the automatic calibration device for single and dual-axis extensometers of the present invention is applied to the calibration of dual-axis extensometer 12, and includes the following steps:

[0060] Step 1: Determine the relative positions of the moving extensometer connecting shaft 6 and the fixed extensometer connecting shaft 7 according to the range of the biaxial extensometer 12 to be calibrated. Then, fix the biaxial extensometer 12 to be calibrated in the corresponding grooves of the moving extensometer connecting shaft 6 and the fixed extensometer connecting shaft 7 using a pin mechanism. Specifically, shafts 1 and 2 of the biaxial extensometer 12 are respectively installed between the moving extensometer connecting shaft 6 and the fixed extensometer connecting shaft 7 on the two linear tracks of the cross-shaped guide rail 2.

[0061] Step 2: In accordance with the "JJG762-2007 Verification Procedure for Extensometers", the host computer 11 controls two closed-loop stepper motors 3 to apply a given displacement point by point to the 1st and 2nd axes of the biaxial extensometer 12 to be calibrated. The total displacement value applied by the two closed-loop stepper motors 3 and the corresponding measured values ​​of the 1st and 2nd axes of the biaxial extensometer 12 are recorded.

[0062] Step 3: Continue to control the two closed-loop stepper motors 3 to apply the given displacement along the original direction relative to the total displacement value already applied, and record the total displacement value applied by the two closed-loop stepper motors 3 and the corresponding 1-axis and 2-axis measurement values ​​of the biaxial extensometer 12. Repeat this operation until the maximum range of the 1-axis and 2-axis measurement range of the biaxial extensometer 12 is reached.

[0063] The given displacement applied each time should be the same and not exceed one-tenth of the range of the 1-axis or 2-axis biaxial extensometer 12, so as to ensure that each group of measurements has no less than 10 measurement points (excluding the zero point).

[0064] Step four: Convert the total displacement values ​​applied to the 1st and 2nd axes of the biaxial extensometer 12 by the two closed-loop stepper motors 3 controlled by the host computer 11 to obtain the strain display values. and Due to the Poisson effect, the strain readings are not accurate and require coupling compensation according to equation (3) to obtain the true strain. and The measured values ​​of axes 1 and 2 of the biaxial extensometer 12, corresponding to the two closed-loop stepper motors 3 at the same time, are used as the strains to be calibrated, and the actual strains are then used as the values. and The biaxial extensometer 12 was calibrated.

[0065] Step 5: Remove the biaxial extensometer 12 and repeat steps 1 to 4 three times to complete the final calibration of the biaxial extensometer 12.

[0066] It should be noted that the host computer 11 described in this invention supports pre-setting a calibration scheme and automatically completes steps one to four to achieve automatic calibration.

[0067] Although the preferred embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many specific modifications under the guidance of the present invention without departing from the spirit of the invention and the scope of protection of the claims, and these modifications all fall within the scope of protection of the present invention.

Claims

1. A single or biaxial extensometer auto-calibration device, characterized by, It includes a cross-shaped guide rail set on the surface of the base plate. The cross-shaped guide rail is composed of two mutually perpendicular straight rails. The two straight rails are divided into a first section and a second section by a perpendicular intersection point, and the length of the first section is greater than the length of the second section. Closed-loop stepper motors are respectively installed at the ends of the first sections of the two linear tracks, and the closed-loop stepper motors are fixed to the base plate; the closed-loop stepper motors are connected to the host computer and can execute the calibration scheme set in the host computer; Each of the closed-loop stepper motors is connected to a movable slider via a motor connecting shaft. The movable slider slides in engagement with the linear track. The motor connecting shaft can convert the rotational motion of the closed-loop stepper motor into linear motion and push the movable slider to move linearly along the linear track. The movable slider is fixedly connected to a movable extensometer connecting shaft. The second section of each of the two linear tracks is provided with a fixed slider. The fixed slider is fixedly connected to the linear track by a locking bolt. The locking bolt, in conjunction with the fixed slider, allows the fixed slider to be changed in its fixed position on the linear track to meet the calibration requirements of extensometers with different ranges. The fixed slider is fixedly connected to a fixed extensometer connecting shaft. The fixed extensometer connecting shaft and the movable extensometer connecting shaft are used to fix the extensometer; The calibration scheme set in the host computer is applied to the calibration of the single-axis extensometer, including: using the strain obtained by converting the total displacement value applied by the host computer to the closed-loop stepper motor to the single-axis extensometer to be calibrated as the true strain, and using the measured value of the single-axis extensometer to be calibrated at the same time as the strain to be calibrated. The calibration scheme set in the host computer is applied to the calibration of the biaxial extensometer, including: converting the total displacement values ​​applied by the two closed-loop stepper motors controlled by the host computer to the 1st and 2nd axes of the biaxial extensometer to be calibrated into strain display values. and Due to the Poisson effect, the strain readings are not accurate and require coupling compensation according to equation (3) to obtain the true strain. and The measured values ​​of axes 1 and 2 of the biaxial extensometers corresponding to the two closed-loop stepper motors at the same time are used as the strains to be calibrated, and the actual strains are then used as the values. and Calibrate the biaxial extensometer 12; （3）； in, and Display the strain values ​​for axes 1 and 2 of the extensometer; and To respond realistically, , These are the 1-axis Poisson's ratio and 2-axis Poisson's ratio of the strain gauge in the biaxial extensometer, respectively.

2. The automatic calibration device for a single or biaxial extensometer according to claim 1, characterized in that, The front end face of the movable extensometer connecting shaft is provided with a V-shaped groove and the front periphery is provided with a circumferential groove for fixing extensometers of different pin types.

3. The automatic calibration device for a single or biaxial extensometer according to claim 1, characterized in that, The front end face of the fixed extensometer connecting shaft is provided with a V-shaped groove and the front periphery is provided with a circumferential groove for fixing extensometers of different pin types.

4. An automatic calibration method for single-axis and biaxial extensometers based on the device described in any one of claims 1-3, characterized in that, The calibration of a uniaxial extensometer includes the following steps: (1) Determine the relative positions of the moving extensometer connecting shaft and the fixed extensometer connecting shaft according to the range of the single-axis extensometer to be calibrated; fix the single-axis extensometer between the moving extensometer connecting shaft and the fixed extensometer connecting shaft, where the moving extensometer connecting shaft and the fixed extensometer connecting shaft correspond to the same straight track of the cross-shaped guide rail. (2) The host computer controls the closed-loop stepper motor to apply a given displacement to the single-axis extensometer point by point, and records the total displacement value applied by the closed-loop stepper motor and the measured value of the single-axis extensometer. (3) Continue to control the closed-loop stepper motor to apply a given displacement relative to the total displacement value already applied along the original direction through the host computer, and record the current total displacement value applied by the closed-loop stepper motor and the measured value of the single-axis extensometer; repeat this operation until the maximum range of the single-axis extensometer is reached; (4) The strain obtained by converting the total displacement value applied by the closed-loop stepper motor controlled by the host computer to the single-axis extensometer to be calibrated is taken as the true strain, and the measured value of the single-axis extensometer to be calibrated at the same time is taken as the strain to be calibrated, and the single-axis extensometer is calibrated. (5) Remove the uniaxial extensometer and repeat steps (1) to (4) three times to complete the final calibration of the uniaxial extensometer.

5. The automatic calibration method of mono- or biaxial extensometer according to claim 4, characterized in that, In step (3), the given displacement applied each time is the same and does not exceed one-tenth of the range of the uniaxial extrusion measurement.

6. A method for automatic calibration of a single or biaxial extensometer based on the apparatus of any one of claims 1-3, characterized in that, The calibration of a biaxial extensometer includes the following steps: (1) Determine the relative positions of the moving extensometer connecting shaft and the fixed extensometer connecting shaft according to the range of the biaxial extensometer to be calibrated, and fix the biaxial extensometer between the moving extensometer connecting shaft and the fixed extensometer connecting shaft; wherein, the 1st shaft and the 2nd shaft of the biaxial extensometer are respectively installed between the moving extensometer connecting shaft and the fixed extensometer connecting shaft corresponding to the two straight tracks of the cross-shaped guide rail; (2) The host computer controls two closed-loop stepper motors to apply a given displacement to axis 1 and axis 2 of the biaxial extensometer point by point, and records the total displacement value applied by the two closed-loop stepper motors and the corresponding measurement values ​​of axis 1 and axis 2 of the biaxial extensometer. (3) Continue to control the two closed-loop stepper motors to apply a given displacement relative to the total displacement value applied in the original direction through the host computer, and record the total displacement value applied by the two closed-loop stepper motors and the corresponding 1-axis measurement value and 2-axis measurement value of the biaxial extensometer respectively; repeat this operation until the maximum range of the 1-axis and 2-axis measurement range of the biaxial extensometer is reached; (4) The total displacement values ​​applied by the two closed-loop stepper motors controlled by the host computer to the 1st and 2nd axes of the biaxial extensometer to be calibrated are converted into strain display values. and Due to the Poisson effect, the strain readings are not accurate and require coupling compensation according to equation (3) to obtain the true strain. and The measured values ​​of axes 1 and 2 of the biaxial extensometer corresponding to the two closed-loop stepper motors at the same time are used as the strain to be calibrated, and the actual strain is then used as the reference strain. and Calibrate the biaxial extensometer; (5) Remove the biaxial extensometer and repeat steps (1) to (4) three times to complete the final calibration of the biaxial extensometer.

7. The automatic calibration method for single-axis and biaxial extensometers according to claim 6, characterized in that, In step (3), the given displacement applied each time is the same and does not exceed one-tenth of the range of the 1-axis or 2-axis of the biaxial extensometer.

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