Equal biaxial dynamic tensile test device and method
By designing an equibiaxial dynamic tensile testing device and method, the problems of high cost and strain rate limitation of existing equipment are solved, and multi-axial mechanical property testing at high strain rate is realized. It is suitable for impact and collision research and has broad application prospects.
Patent Information
- Application Number
- CN202510878181.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-27
- Publication Date
- 2025-09-12
AI Technical Summary
Existing high-speed tensile equipment and multi-axial testing equipment have high costs, low synchronization and strain rate limitations, and cannot meet the needs of multi-axial mechanical properties testing of materials under high strain rates.
An equibiaxial dynamic tensile testing device was designed, which includes a guide column, a sleeve, a slide, a clamping jaw, and a tensile rod. The uniaxial power of the high-speed tensile machine is converted into a four-directional proportional tensile force through a mechanical transmission mechanism. Combined with DIC digital image testing technology and strain gauge multimodal measurement, biaxial tensile testing at high strain rates can be achieved.
It realizes multi-axial mechanical property testing within a high strain rate range, with high data reliability and low cost. It is suitable for dynamic mechanical property research such as impact and collision, and is suitable for large-scale production and wide application.
Smart Images
Figure CN120628874A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to an equibiaxial dynamic tensile testing device and method, belonging to the technical field of metal material testing. Background Art
[0002] With the rapid development of automobile collision safety, aerospace impact-resistant materials, military protective equipment and other fields, the demand for materials under high strain rate (1-10³s -1 The demand for research into multiaxial mechanical properties under dynamic loads is increasingly urgent. Traditional material testing equipment (such as uniaxial high-speed tensile machines) can only obtain unidirectional mechanical data. However, real-world conditions such as impact and explosion often involve complex bidirectional or even multidirectional stress states, making existing technology unable to meet the testing needs of scientific research and industry. Currently, the global market for dynamic multiaxial testing equipment remains a high-tech market, relying primarily on customized solutions from a few international manufacturers (such as MTS in the United States and Zwick in Germany).
[0003] Deficiencies of existing technology: (1) Current high-speed stretching equipment (such as Hopkinson rods and electromagnetic high-speed stretching machines) can only achieve unidirectional dynamic loading and cannot simulate the mechanical behavior of materials under biaxial or triaxial stress states, resulting in a large deviation between test data and actual applications.
[0004] (2) Quasi-static multiaxial testing equipment (such as biaxial tensile testing machine): only suitable for low strain rates (<10 -1 s -1 ), cannot meet the test requirements of high-speed impact, collision and other working conditions; (3) Hydraulic / electro-hydraulic servo drive system: complex structure (requires 4 sets of independent drive units) and high cost (the price of a single imported equipment exceeds 20 million yuan).
[0005] While the international academic community has proposed a variety of dynamic multiaxial loading schemes in recent years (such as explosive actuation and electromagnetic actuation), these schemes generally suffer from poor repeatability and a narrow test range (limited to specific strain rates). Currently, there is no mature commercial high-strain-rate equiaxial biaxial tensile equipment, resulting in a significant lack of a comprehensive database for dynamic multiaxial mechanical materials. Existing high-speed tensile technology and multiaxial testing equipment suffer from three core drawbacks: high cost, poor synchronization, and strain rate limitations. A dynamic equiaxial biaxial tensile solution with a simplified structure, high precision, and a wide strain rate range is urgently needed. Summary of the Invention
[0006] The technical problem to be solved by the present invention is that existing high-speed stretching technology and multi-axis testing equipment have high cost, low synchronization and strain rate limitations.
[0007] The technical solution adopted by the present invention to solve its technical problems is: an equibiaxial dynamic tensile testing device, including a guide column, a sleeve, a slide, a clamping jaw and a stretching rod, the sleeve being arranged on the guide column, and at least two contact surfaces inclined upward are arranged on the side wall of the sleeve, a through hole is arranged in the middle of the slide, the sleeve is arranged in the through hole at intervals, and a sliding hole is arranged on the side of the slide corresponding to the contact surface along the radial direction of the through hole, one end of the clamping jaw is slidably arranged in the sliding hole, and a transmission surface is provided at the end in the opposite direction of the inclination of the contact surface, the stretching rod is in an inverted concave shape, and the concave end is connected to the lower end of the sleeve, and an industrial camera is provided in the middle of the inner side of the upper end of the stretching rod.
[0008] Wherein, the sliding sleeve in the above device is a quadrangular pyramid structure, and an acceleration block is provided at the lower end, and the concave end of the stretching rod is connected to the lower end of the acceleration block.
[0009] Wherein, the clamping claw in the above device is an L-shaped or U-shaped structure.
[0010] Wherein, the clamping jaw in the above device is detachably provided with a pressure plate at the end away from the sliding sleeve, and an inverted U-shaped support block is provided at the lower end of the sliding seat.
[0011] Wherein, a clamping column is provided at the middle part of the upper end of the stretching rod in the above device.
[0012] Wherein, the guide column in the above device is a T-shaped structure, and a damping block is provided on the lower end surface of the large end.
[0013] Wherein, the sliding hole in the above device is a T-shaped slot or a dovetail slot structure, and the insertion end of the clamping claw is adapted to the shape of the sliding hole.
[0014] Wherein, the contact surface inclination angle of the sliding sleeve and the transmission surface inclination angle of the end of the clamping jaw in the above device are both 45°.
[0015] An equibiaxial dynamic tensile test method, comprising any one of the above-mentioned equibiaxial dynamic tensile test devices, comprises the following steps: a. Prepare a plate-shaped specimen according to the arrangement of the jaws 7, connect the end of the specimen to the end of the jaws away from the sliding sleeve, and apply grease to the sliding part of the device; b. Clamp the upper end of the tensile rod to the clamping end of the high-speed tensile testing machine, and fix the guide column and the lower end of the slide seat on the workbench of the high-speed tensile testing machine; c. Adjust the clamping end position on the high-speed tensile testing machine and clamp it with the upper end of the frame-type tensile rod, and then fine-tune the clamping end position on the tensile machine to pre-tighten the tensile rod and the sliding sleeve; d. Focus the industrial camera on the sample, use DIC digital image testing technology to measure the strain of the sample, and use a strain gauge to measure and calculate the stress of the sample during dynamic biaxial tension; e. Adjust the high-speed tensile testing machine test program, set different dynamic tensile rates, and ensure that the high-speed tensile testing machine signal and the DIC image acquisition signal are collected synchronously; f. Based on the above collected signals, the force-displacement curve and stress-strain curve parameters under different biaxial stretching rates are obtained by post-processing.
[0016] Among them, in the above method, before the experiment, speckle patterns need to be sprayed on the collection area in the middle of the sample. It is required to spray white primer first, then spray black speckle patterns and dry them in the shade; at the same time, strain gauges are pasted on the front and back sides of the sample ends, and the input terminals of the strain gauges are connected to the strain meter for signal processing.
[0017] The present invention has the following beneficial effects: Its unique uniaxial-to-multiaxial conversion technology efficiently converts the uniaxial power of a high-speed tensile tester into four-dimensional proportional tensile forces through a mechanical transmission mechanism, resulting in cost savings compared to conventional multi-drive systems. Furthermore, its high strain rate range (1 / s-1000 / s) fills the gap left by existing biaxial tensile testing equipment, which only supports quasi-static testing, and can be directly applied to dynamic mechanical properties studies such as impact and collision. Furthermore, this technology achieves multimodal measurement fusion, combining strain gauge stress measurement with high-speed DIC full-field strain analysis. The data reliability far exceeds that of single optical or electrical measurement solutions, meeting the needs of high-end scientific research and industrial testing. Furthermore, this technology, based on an optimized modification of an existing high-speed tensile testing machine, has relatively low manufacturing costs and is suitable for large-scale production. The device features a simple design, easy maintenance, low daily maintenance costs, and a long service life, reducing user costs. With the widespread application of new materials in various industries, this device has broad market prospects in a variety of fields, including aerospace, automotive manufacturing, defense industry, and medical devices, and is expected to generate significant economic benefits. This technology possesses significant technical advantages, broad market demand, and good economic benefits, making it highly feasible and promising for widespread application. BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Figure 1 It is a structural schematic diagram of the present invention; Figure 2 It is a schematic diagram of the front view structure of the present invention; Figure 3 It is a schematic diagram of the cross-sectional structure of the present invention; Figure 4 An exploded view of the present invention; Figure 5 Schematic diagram of the sample structure of the present invention.
[0019] The markings in the figure are: 1 is the guide column, 2 is the acceleration block, 3 is the sliding sleeve, 4 is the damping block, 5 is the support block, 6 is the slide, 7 is the clamping jaw, 8 is the specimen, 9 is the pressure plate, 10 is the stretching rod, 11 is the industrial camera, 12 is the acquisition area, and 13 is the strain gauge. DETAILED DESCRIPTION
[0020] The present invention will be further described below with reference to the accompanying drawings and examples.
[0021] like Figures 1 to 5 As shown, an equibiaxial dynamic tensile testing device of the present invention includes a guide column 1, a sleeve 3, a slide 6, a clamp 7 and a stretching rod 10, the sleeve 3 is sleeved on the guide column 1, and at least two contact surfaces inclined upward are provided on the side wall of the sleeve 3, a through hole is provided in the middle of the slide 6, the sleeve 3 is arranged at intervals in the through hole, the slide 6 is provided with a sliding hole along the radial direction of the through hole on the side corresponding to the contact surface, one end of the clamp 7 is slidably arranged in the sliding hole, and a transmission surface is provided at the end in the opposite direction of the inclination of the contact surface, the stretching rod 10 is in an inverted concave shape, and the concave end is connected to the lower end of the sleeve 3, and an industrial camera 11 is provided at the middle inner side of the upper end of the stretching rod 10. Those skilled in the art will appreciate that the structure primarily comprises a guide post 1, a sleeve 3, a slide 6, a clamping jaw 7, and a tensile rod 10. The guide post 1 is a square columnar structure with a sleeve 3 slidingly mounted on its upper portion. Its lower end is fixed to the workbench of the high-speed tensile testing machine, providing a guide for the sliding movement of the sleeve 3. A suitable square hole is preferably provided in the middle of the sleeve 3. The sleeve 3 is mounted on the guide post 1 to convert the upward pulling force into a thrust force applied to the clamping jaw 7 for tensile testing of the specimen 8. The slide 6 is a square structure with a central through-hole. The sleeves 3 are spaced apart within the through-hole. Slide holes are provided radially along the through-hole on the sides of the slide 6 corresponding to the contact surfaces. These holes are located in the middle of each inner wall of the slide 6, and one end of the clamping jaw 7 slides within the holes. Because the side walls of the sleeve 3 are provided with at least two upwardly inclined contact surfaces, and the end of the clamping jaw 7 is provided with a transmission surface in the opposite direction of the contact surface, the sleeve 3 moves upward, and the contact surface and transmission surface contact enable the clamping jaw 7 to move radially along the central through-hole of the slide 6. The lower end of the slide 6 is fixedly mounted on the workbench of the high-speed tensile testing machine. The tensile rod 10 is primarily used to transmit tensile loads. Its upper end is fixed to the upper clamping end of the high-speed tensile testing machine, and its lower end is connected to the lower end of the sleeve 3 at a recess.
[0022] Preferably, the sleeve 3 in the above-mentioned device has a quadrangular pyramidal structure, and an acceleration block 2 is provided at its lower end. The concave end of the stretch rod 10 is connected to the lower end of the acceleration block 2. Those skilled in the art will appreciate that, in this structure, the sleeve 3 preferably has a quadrangular pyramidal structure, so the number of jaws 7 should also be four. The fixed end of the specimen 8 corresponds to the jaws 7, so the specimen 8 should have a cross-shaped structure. To facilitate connection, this structure further provides an acceleration block 2 at the lower end of the sleeve 3, and the concave end of the stretch rod 10 is connected to the lower end of the acceleration block 2 to maintain the stability of the upward tensile force.
[0023] Preferably, the clamping jaw 7 in the above device is L-shaped or U-shaped. Those skilled in the art will appreciate that, in order to maintain the specimen 8 in a horizontal position, the clamping jaw 7 is preferably L-shaped or U-shaped, so that one end of the clamping jaw 7 is inserted into the sliding hole and the other end can be connected and fixed to the end of the specimen 8.
[0024] Preferably, the clamping jaw 7 in the above device is detachably provided with a pressure plate 9 at the end away from the sleeve 3, and an inverted U-shaped support block 5 is provided at the lower end of the slide 6. It will be understood by those skilled in the art that in order to ensure that the sample 8 is firmly connected to the clamping jaw 7, the present device further detachably provides a pressure plate 9 at the end away from the sleeve 3 of the clamping jaw 7. Specifically, threaded holes or through holes can be provided at intervals at the end away from the sleeve 3 of the clamping jaw 7, and through holes are provided on the fixed end of the sample 8 and the pressure plate 9, through which screws or bolts are inserted, so that the sample 8 is fixed between the clamping jaw 7 and the pressure plate 9. In order to facilitate the fixation of the slide 6 to the workbench of the testing machine and to facilitate the connection of the stretching rod 10 to the lower end of the sleeve 3, the present structure is preferably provided with an inverted U-shaped support block 5 at the lower end of the slide 6. The slide 6 is actually fixed to the workbench of the testing machine through the support block 5, and the stretching rod 10 can be inserted along the U-shaped opening of the support block 5 and connected to the lower end of the sleeve 3.
[0025] Preferably, a clamping column 101 is provided in the middle of the upper end of the stretching rod 10 in the above device. Those skilled in the art will understand that, in order to facilitate the clamping of the stretching rod 10 and the testing machine, the present structure preferably provides a clamping column 101 in the middle of the upper end of the stretching rod 10, and the clamping end on the actual testing machine can directly clamp the clamping column.
[0026] Preferably, the guide post 1 in the above device has a T-shaped structure, and a damping block 4 is provided on the lower end surface of the large end. Those skilled in the art will appreciate that in this structure, the guide post 1 is preferably T-shaped, and the upper end of the guide post 1 limits the position of the sliding sleeve 3, while preventing the sliding sleeve 3 from directly colliding with the lower side of the guide main large end. In this structure, the damping block 4 is preferably provided on the lower end surface of the large end of the guide post 1, and the damping block 4 can be a rubber or nylon block.
[0027] Preferably, the sliding hole in the above device is a T-slot or dovetail groove structure, and the insertion end of the clamping jaw 7 is adapted to the shape of the sliding hole. It will be understood by those skilled in the art that in order to ensure that the clamping jaw 7 slides in the inward and outward directions, that is, the radial sliding of the through hole, the sliding hole of this structure is preferably a T-slot or dovetail groove structure, and the insertion end of the clamping jaw 7 is adapted to the shape of the sliding hole, that is, if the sliding hole is a T-slot, the insertion end of the clamping jaw 7 is an inverted T-shaped structure, or if the sliding hole is a dovetail groove structure, the insertion end of the clamping jaw 7 is a dovetail block.
[0028] Preferably, the contact surface inclination angle of the sleeve 3 and the transmission surface inclination angle of the end of the clamping jaw 7 in the above-mentioned device are both 45°. It will be understood by those skilled in the art that in this structure, the contact surface inclination angle of the sleeve 3 and the transmission surface inclination angle of the end of the clamping jaw 7 are preferably both 45°, that is, the tapered angle of the sleeve 3 is 45°, and the clamping jaw 7 cooperates with the four tapered surfaces of the sleeve 3 to achieve a stretching effect in four directions. Preferably, the transmission surface inclination angle of the end of the clamping jaw 7 is 45°, that is, the mating portion is also 45°, so that the upward displacement of the sleeve 3 and the displacement of the clamping jaw 7 in the four directions are in a 1:1 proportional relationship.
[0029] An equibiaxial dynamic tensile test method, comprising any one of the above-mentioned equibiaxial dynamic tensile test devices, comprises the following steps: a. Prepare a plate-shaped specimen 8 according to the arrangement of the jaws 7, connect the end of the specimen 8 to the end of the jaws 7 away from the sleeve 3, and apply grease to the sliding part of the device; b. Clamp the upper end of the stretch rod 10 to the clamping end of the high-speed tensile testing machine, and fix the lower ends of the guide column 1 and the slide 6 on the workbench of the high-speed tensile testing machine; c. Adjust the clamping end position on the high-speed tensile testing machine and clamp it with the upper end of the stretching rod 10, and then fine-tune the clamping end position on the stretching machine to pre-tighten the stretching rod 10 and the sliding sleeve 3; d. Focusing the industrial camera 11 and the sample 8, measuring the strain of the sample 8 using DIC digital image testing technology, and measuring and calculating the stress of the sample 8 during dynamic biaxial tension using a strain gauge; e. Adjust the high-speed tensile testing machine test program, set different dynamic tensile rates, and ensure that the high-speed tensile testing machine signal and the DIC image acquisition signal are collected synchronously; f. Based on the collected signals, post-process the force-displacement curve and stress-strain curve parameters under different biaxial tensile rates. Those skilled in the art will appreciate that in step a, the entire device is assembled, all required connections are fixed, and all relatively sliding parts of the device are coated with grease such as molybdenum disulfide. The prepared sample 8 should correspond to the number and arrangement of the jaws 7. In practice, the sample 8 is preferably cross-shaped, with four jaws 7 and a four-sided sleeve 3. The sample 8 and the jaws 7 are locked together using screws or bolts. In step b, the entire structure is placed on the workbench of a high-speed tensile testing machine, the upper end of the tensile rod 10 is clamped to the upper clamping end of the high-speed tensile testing machine, and the guide column 1 and the lower end of the slide 6 are fixedly mounted on the workbench of the high-speed tensile testing machine. Step c primarily involves adjustment and pre-tightening, which is a conventional operation to ensure data acquisition accuracy. Step d collects a set of data. An industrial camera 11 captures images and processes them using DIC digital image measurement technology to obtain the sample strain. The strain gauge 13 collects and calculates the stress data of the sample during dynamic biaxial tension. Step e is to repeat step d while changing the dynamic stretching rate to collect multiple sets of data. Step f is to process and obtain the force-displacement curve and stress-strain curve parameters under different biaxial stretching rate conditions.
[0030] Preferably, in the above method, before the experiment, it is necessary to spray speckle in the central collection area 12 of the sample 8. It is required to spray white primer first, then spray black speckle and dry it in the shade for use; at the same time, a strain gauge 13 is pasted on the front and back sides of the end of the sample 8, and the input terminal of the strain gauge 13 is connected to the strain gauge for signal processing. It can be understood by those skilled in the art that in order to ensure that the deformation process of the sample 8 is captured for subsequent strain data processing. This method preferably sprays speckle in the central collection area 12 of the sample 8 in advance. It is required to spray white primer first, then spray black speckle and dry it in the shade for use, and the side with the sprayed speckle should be facing up during installation. A strain gauge 13 is pasted on the front and back sides of two adjacent installation points of the sample 8 to ensure accurate collection of strain data.
[0031] Example 1 Sample 8 material: DP590 duplex steel Experimental steps: 1. Preparation of Specimen 8: A 2 mm thick DP590 dual-phase steel plate was used to prepare a cross-shaped specimen 8 by laser cutting. Speckle patterns were sprayed on the effective deformation area, and strain gauges 13 were attached.
[0032] 2. Clamping the specimen 8: Install the specimen 8 in the four-way tapered clamping jaw 7 of the present invention, ensuring a secure fixation and good symmetry.
[0033] 3. System connection: Connect the high-speed tensile testing machine, DIC strain testing system and strain gauge to complete the synchronization of the image system and mechanical signals.
[0034] 4. Set parameters: Set the loading strain rate to 500 s -1 , adjust the focus and calibration of the DIC high-speed camera.
[0035] 5. Start loading: Start the equipment to perform bidirectional synchronous stretching until specimen 8 breaks, while recording stress, strain, and image data.
[0036] 6. Data processing: Collect strain gauge 13 and DIC data, obtain stress-strain curves, and analyze the strain distribution and synchronization during biaxial loading.
[0037] Implementation results: Example 2: Equibiaxial dynamic tensile test of titanium plate Sample 8 material: TA1 sheet Experimental steps: (same as Example 1) Implementation results: Summary of Results: This technology provides an experimental method and system suitable for biaxial dynamic tensile testing of plate materials, enabling simultaneous, high-speed, and uniform loading in four directions. Experiments with DP590 dual-phase steel and TA1 pure titanium plates have demonstrated that this method accurately captures biaxial principal strain data under varying loading rates and materials, ensuring strain synchronization errors of less than 3%. Experimental results demonstrate that this method can effectively reflect the tensile properties of materials under complex stress states and is suitable for research and application evaluation of the forming properties of a variety of engineering materials, including high-strength steel and titanium alloys. It demonstrates broad practicality and potential for widespread application.
Claims
1. An equibiaxial dynamic tensile testing device, characterized by: The invention comprises a guide column (1), a sleeve (3), a slide seat (6), a clamping claw (7) and a stretching rod (10), wherein the sleeve (3) is sleeved on the guide column (1), and at least two contact surfaces inclined upward are provided on the side wall of the sleeve (3), a through hole is provided in the middle of the slide seat (6), the sleeve (3) is arranged in the through hole at intervals, a sliding hole is provided on the side of the slide seat (6) corresponding to the contact surface along the radial direction of the through hole, one end of the clamping claw (7) is slidably provided in the sliding hole, and a transmission surface is provided at the end thereof in the opposite direction to the inclination direction of the contact surface, the stretching rod (10) is in an inverted concave shape, and the inner concave end is connected to the lower end of the sleeve (3), and an industrial camera (11) is provided in the middle of the inner side of the upper end of the stretching rod (10).
2. The equibiaxial dynamic tensile testing device according to claim 1, characterized in that: The sliding sleeve (3) is a quadrangular pyramid structure, and an acceleration block (2) is provided at the lower end. The concave end of the stretching rod (10) is connected to the lower end of the acceleration block (2).
3. The equibiaxial dynamic tensile testing device according to claim 1, characterized in that: The clamping claw (7) is an L-shaped or U-shaped structure.
4. The equibiaxial dynamic tensile testing device according to claim 1, characterized in that: The clamping jaw (7) is detachably provided with a pressing plate (9) at the end away from the sliding sleeve (3), and an inverted U-shaped supporting block (5) is provided at the lower end of the sliding seat (6).
5. The equibiaxial dynamic tensile testing device according to claim 4, characterized in that: A clamping column (101) is provided at the middle portion of the upper end of the stretching rod (10).
6. The equibiaxial dynamic tensile testing device according to claim 1, characterized in that: The guide column (1) is a T-shaped structure, and a damping block (4) is provided on the lower end surface of the large end.
7. The equibiaxial dynamic tensile testing device according to claim 1, characterized in that: The sliding hole is a T-shaped slot or a dovetail slot structure, and the insertion end of the clamping claw (7) is adapted to the shape of the sliding hole.
8. The equibiaxial dynamic tensile testing device according to claim 1, characterized in that: The inclination angle of the contact surface of the sliding sleeve (3) and the inclination angle of the transmission surface at the end of the clamping jaw (7) are both 45°.
9. An equibiaxial dynamic tensile test method, characterized in that: The equibiaxial dynamic tensile testing device comprising any one of claims 1 to 8, wherein the steps are as follows: a. Prepare a plate-shaped specimen (8) according to the arrangement of the clamping jaws (7), connect the end of the specimen (8) to the end of the clamping jaws (7) away from the sliding sleeve (3), and apply grease to the sliding part of the device; b. Clamp the upper end of the stretching rod (10) to the clamping end of the high-speed tensile testing machine, and fix the lower end of the guide column (1) and the slide seat (6) on the workbench of the high-speed tensile testing machine; c. Adjust the clamping end position on the high-speed tensile testing machine and clamp it with the upper end of the frame-type tensile rod (10), and then fine-tune the clamping end position on the tensile machine to pre-tighten the tensile rod (10) and the sliding sleeve (3); d. focusing the industrial camera (11) and the sample (8), using DIC digital image testing technology to test the strain of the sample (8), and using a strain gauge to test and calculate the stress of the sample (8) during dynamic biaxial tension; e. Adjust the high-speed tensile testing machine test program, set different dynamic tensile rates, and ensure that the high-speed tensile testing machine signal and the DIC image acquisition signal are collected synchronously; f. Based on the above collected signals, the force-displacement curve and stress-strain curve parameters under different biaxial stretching rates are obtained by post-processing.
10. The equibiaxial dynamic tensile test method according to claim 9, characterized in that: Before the experiment, the sampling area (12) in the middle of the sample (8) needs to be sprayed with speckles. It is required to spray white primer first, then spray black speckles and dry them in the shade. At the same time, strain gauges (13) are pasted on the front and back sides of the end of the sample (8), and the input terminals of the strain gauges (13) are connected to the strain gauge for signal processing.