Stress-strain measuring device and curve measuring method for metal materials

Abstract

The present invention discloses a stress-strain measuring device and curve measuring method for metal materials, belonging to the technical field of material mechanical property test. The device includes a high-speed tensile testing machine, a clamping rod 1 and a clamping rod 2, a strain gauge fixed on the surface of the clamping rod, a tensile specimen to be tested, a limit nut 1, a limit nut 2 and a sleeve, and a DIC device; wherein the clamping rod 1 and the clamping rod 2 are respectively connected to the high-speed tensile testing machine; the tensile specimen to be tested, the limit nut 1 and the limit nut 2 are respectively connected to the clamping rod 1 and the clamping rod 2 through internal threads; the tensile specimen to be tested, the limit nut 1, the limit nut 2, the clamping rod 1 and the clamping rod 2 can slide in the sleeve; an observation window is provided on the side of the sleeve, and the deformation process of the specimen is photographed by a high-speed camera. The device can accurately measure strain limit and stress-strain curve under continuous strain rate range conditions such as quasi-static, medium state and dynamic.

Description

Technical Field

[0001] The invention relates to the technical field of material mechanical property testing, and in particular to a stress-strain measuring device and a curve measuring method for metal materials. Background Art

[0002] The mechanical behavior and plastic deformation mechanism of metal materials under different strain rate conditions are basic scientific issues of great concern in the field of material mechanics. Related research has very important application value in the fields of military protection and automobile lightweight design. At present, researchers generally use universal material testing machines to obtain the mechanical properties of materials under quasi-static strain rates (strain rate ≤ 10 -3 s -1 ) condition, a split Hopkinson tie rod was used to obtain the mechanical properties of the material under dynamic strain rate (10 2 s -1 <Strain rate≤10 4 s -1 During the tensile test, the sample went through the whole process from loading to final fracture. In order to observe the microstructural evolution of the sample at different deformation stages, the researchers designed an interruption experiment, that is, the deformation of the sample can be controlled, which is of great significance for the study of the mechanical behavior of materials.

[0003] However, the mechanical properties of materials under medium strain rate conditions are often ignored. How to design interruption experiments to achieve controllable deformation of the sample under medium strain rate conditions, thereby comprehensively covering the strain limit and stress-strain curve accurate measurement under continuous strain rate ranges such as quasi-static, medium and dynamic conditions, is a major problem in the field of material mechanics. In the prior art, patent CN109238855A discloses a method and device for obtaining and verifying dynamic failure parameters of constitutive parameters, and patent CN110929438B discloses a constitutive curve coupling epitaxy method considering strain rate effect, but both cannot solve the above problems. Summary of the invention

[0004] The present invention combines a high-speed tensile testing machine and a strain limit device to provide a stress-strain measuring device and a stress-strain curve measuring method for metal materials, which can perform accurate measurement of strain limit and stress-strain under continuous strain rate range conditions such as quasi-static, medium-state and dynamic.

[0005] In a first aspect, an embodiment of the present invention provides a stress-strain measurement device for metal materials, comprising: a high-speed tensile testing machine, a clamping rod 1 and a clamping rod 2 with external threads, a strain gauge fixed on the surface of the clamping rod, a tensile specimen to be tested, a limit nut 1, a limit nut 2 and a sleeve for controlling the deformation of the specimen, and a DIC device for accurately characterizing the deformation of the specimen; wherein,

[0006] One side of the clamping rod 1 and the clamping rod 2 is a clamping section, and the other side is a threaded section, and each clamping section is connected to the high-speed tensile testing machine respectively;

[0007] The tensile specimen to be tested is flat in the middle and cylindrical with internal threads at both ends;

[0008] The tensile specimen to be tested, the first limiting nut and the second limiting nut are respectively connected to the first clamping rod and the second clamping rod through internal threads;

[0009] The tensile specimen to be tested, the first limiting nut and the second limiting nut are all placed in the sleeve; the tensile specimen to be tested, the first limiting nut, the second limiting nut, the first clamping rod and the second clamping rod can slide in the sleeve; the limit nut cooperates with the sleeve to control the deformation of the specimen;

[0010] An observation window is provided on the side of the sleeve, and the deformation process of the sample is photographed by a high-speed camera, and combined with DIC technology, the purpose of accurately measuring the deformation amount of the sample is achieved;

[0011] The strain gauges are attached to the clamping rod 1 and the clamping rod 2 respectively, and are used to measure the load borne by the sample during the experiment.

[0012] In a second aspect, an embodiment of the present invention provides a stress-strain curve measurement method for a metal material, using the device described in the above embodiment to measure the stress-strain curve of the tensile specimen to be measured;

[0013] The method comprises:

[0014] Determine a plurality of deformation thresholds of the tensile specimen to be tested, wherein the thresholds are arranged in numerical order, and the temperature of the tensile specimen to be tested can be maintained within a set range when the tensile specimen to be tested is deformed between two adjacent thresholds;

[0015] Set the first threshold as the current threshold and initialize the previous threshold to 0;

[0016] Adjust the distance between the first limiting nut and the second limiting nut so that the maximum deformation of the sample is controlled within the current threshold value;

[0017] The tensile test specimen to be tested is stretched by the high-speed tensile testing machine, and the change process of the deformation of the specimen from the previous threshold value to the current threshold value is recorded by the high-speed camera, and the load change process borne by the specimen during the same period is measured by each strain gauge;

[0018] The current threshold is used as a new previous threshold, the next threshold is used as a new current threshold, and the distance between the first and second limit nuts is adjusted to control the maximum deformation of the sample within the current threshold until all the multiple thresholds are traversed;

[0019] According to the changes in the deformation and load of the sample recorded in each cycle, a stress-strain curve segment between every two adjacent thresholds is generated, and each curve segment together constitutes a complete stress-strain curve.

[0020] The stress-strain measuring device and stress-strain curve measuring method for metal materials provided by the embodiments of the present invention have the following advantages:

[0021] 1. By using a high-speed tensile testing machine instead of the traditional universal material testing machine + split Hopkinson pull rod, it can be used for strain limiting under continuous strain rate range conditions such as quasi-static, medium state and dynamic, especially the medium state strain rate range;

[0022] 2. In the tensile test, the clamping rod 1 drives the limit nut 1 to move upward and contact with the top surface of the sleeve, thereby driving the sleeve to move upward, so that the bottom surface of the sleeve contacts the limit nut 2, so that the sleeve is limited, and the deformation of the sample can be accurately limited;

[0023] 3. The deformation of the specimen can be adjusted at both ends through two limit nuts, and the adjustment method is more flexible;

[0024] 4. Fix the strain gauge to the clamping rod. The clamping rod will not break or undergo large deformation. The strain gauge measures the elastic strain of the clamping rod, and the load borne by the sample can be calculated. This measurement method is conducive to obtaining the stress-strain curve of the tensile sample under large strain conditions.

[0025] 5. By using DIC technology instead of the traditional stop ring technology, the stress-strain curve of the tensile specimen can be accurately measured, solving the measurement error of the specimen deformation caused by the elastic deformation of the traditional stop ring;

[0026] 6. By adjusting the two limit nuts, the deformation of each tensile test is limited, the adiabatic temperature rise effect of the specimen during continuous deformation is weakened, and the stress-strain curve under limited deformation is measured in sections, so that the entire curve basically meets the constant temperature condition. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A schematic diagram of a stress-strain measurement device for metal materials provided by an embodiment of the present invention;

[0028] Figure 2 A schematic structural diagram of a strain limiting device provided in an embodiment of the present invention;

[0029] Figure 3 A schematic diagram of the structure of a tensile specimen provided by an embodiment of the present invention;

[0030] Figure 4A schematic diagram of the structure of a sleeve provided in an embodiment of the present invention;

[0031] Figure 5 is a flow chart of a stress-strain curve measurement method for metal materials provided by an embodiment of the present invention;

[0032] Figure 6 is a schematic diagram of a stress-strain curve provided by an embodiment of the present invention;

[0033] Figure 7 is a schematic diagram of multiple groups of marking points provided by an embodiment of the present invention;

[0034] Among them, 1-high-speed tensile testing machine clamping rod 1, 2-high-speed tensile testing machine clamping rod 2, 3-tensile specimen to be tested, 30-flat middle section, 31-arc-shaped transition section I, 32-arc-shaped transition section II, 33-cylindrical section I, 34-cylindrical end II, 4-limiting nut 1, 5-limiting nut 2, 6-sleeve, 7-DIC device, 8-strain gauge. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] Combination Figure 1-Figure 4 This embodiment provides a stress-strain measuring device for metal materials, including a high-speed tensile testing machine and a strain limiting device. Figure 1 As shown in the structure, the strain limit device includes a high-speed tensile test machine clamping rod 1, a high-speed tensile test machine clamping rod 2, a tensile specimen to be tested 3, a flat middle section 30, an arc-shaped transition section I 31, an arc-shaped transition section II 32, a cylindrical clamping section I 33, a cylindrical clamping section II 34, a limit nut I 4, a limit nut II 5, a sleeve 6, a DIC device 7, and a strain gauge 8. Optionally, the material of the clamping rod, the limit nut and the sleeve 6 is Cr12MoV die steel, or other high-strength steel.

[0037] Optionally, the middle section of the tensile specimen is in the shape of a plate, the clamping section is in the shape of a cylinder, and an arc-shaped transition section is provided between the flat middle section 30 and the cylindrical clamping section. This special shape of tensile specimen has two advantages: on the one hand, the cylindrical clamping section facilitates connection with the clamping rod of the high-speed tensile testing machine; on the other hand, the flat middle section facilitates the DIC technology to accurately measure the surface deformation of the tensile specimen; thus solving the problem that traditional sheet tensile specimens are difficult to cooperate with high-speed tensile testing machines or that the surface deformation of cylindrical tensile specimens is difficult to accurately measure. Exemplarily, the width of the flat middle section 30 of the tensile specimen to be tested is 20 mm, and the outer diameter of the cylindrical clamping section is 30 mm.

[0038] The tensile specimen 3 to be tested, the limit nut 1 4 and the limit nut 2 5 are respectively connected to the clamping rod 1 and the clamping rod 2 2 of the high-speed tensile testing machine through internal threads. Optionally, the diameter of the clamping rod 1 and the clamping rod 2 is 19 mm.

[0039] The tensile specimen 3 to be tested, the limit nut 1 4 and the limit nut 2 5 are all placed in the sleeve 6, and the tensile specimen 3 to be tested, the limit nut 1 4, the limit nut 2 5, the clamping rod 1 and the clamping rod 2 2 can all slide in the sleeve 6; the limit nut cooperates with the sleeve 6 to control the deformation of the tensile specimen to be tested. Optionally, the outer diameter of the limit nut is 33 mm, which is slightly larger than the diameter of the cylindrical clamping section of the tensile specimen to be tested, and plays a role in supporting the sleeve to prevent friction between the sleeve and the specimen.

[0040] Optionally, the threads of the tensile sample 3 to be tested, the clamping rod of the high-speed tensile testing machine and the limit nut in the device are all precision threads that match each other, and the deformation of the tensile sample to be tested is controlled by controlling the position of the limit nut on the clamping rod.

[0041] Optionally, the sleeve 6 is a split structure, including a left half cylinder and a right half cylinder, which are connected by four bolts distributed at the four corners of the sleeve; the inner cavity of the sleeve is cylindrical, and the deformation of the sample (or sample strain) is controlled by the limiting effect of the limiting sleeve on the movement of the limiting nut; the left half cylinder has a rectangular observation window, which is convenient for a high-speed camera to shoot the deformation process of the sample, and combined with the DIC technology, the deformation of the sample can be accurately measured. Compared with the traditional stop ring technology, the DIC technology can effectively avoid the measurement error of the sample deformation caused by the elastic deformation of the stop ring, and greatly improve the measurement accuracy of the sample deformation.

[0042] The middle part of the clamping rod 1 and the clamping rod 2 of the high-speed tensile testing machine is affixed with a strain gauge, which is connected to the bridge box and is used to accurately test the load during the tensile process of the sample. In the traditional method, the strain gauge is usually fixed in the middle of the sample. When the plastic deformation of the sample is large, the strain gauge will be damaged, so it is impossible to obtain the stress-strain curve of the tensile sample under large strain conditions; while in this embodiment, the strain gauge is fixed to the clamping rod, and the clamping rod will not break or undergo large deformations. The strain gauge measures the elastic strain of the clamping rod, and the load borne by the sample can be calculated. This measurement method is conducive to obtaining the stress-strain curve of the tensile sample under large strain conditions.

[0043] Further, combined with Figure 1 and Figure 2 , the limit nut 1-4 is located above the limit nut 2-5, and the clamping rod 2-5 is fixed to the base of the high-speed tensile testing machine. During the tensile test, the clamping rod 1-1 moves upward at high speed under the action of the high-speed tensile testing machine to stretch the sample 3. When the sample 3 is stretched to the point where the limit nut 1-4 contacts the top surface of the sleeve 6, the sleeve 6 is driven to slide upward. When the sleeve 6 slides to the point where the bottom surface of the sleeve contacts the limit nut 2-5, the sleeve 6 is limited and the sample reaches the maximum deformation.

[0044] Due to the use of a high-speed tensile testing machine in the above device, tensile tests can be carried out under continuous strain rate conditions such as quasi-static, medium and dynamic. At the same time, the strain of the sample is limited by the strain limit device, and accurate measurement of stress and strain can be achieved under quasi-static, medium and dynamic conditions. Among them, quasi-static refers to a strain rate ≤10 -3 s -1 , the medium state refers to 10 -3 s -1 <Strain rate≤10 2 s -1 , dynamic refers to 10 2 s -1 <Strain rate≤10 4 s -1 .

[0045] Based on the above device, Figure 5 1 is a flow chart of a stress-strain curve measurement method for metal materials provided by an embodiment of the present invention. The method uses the device described in any of the above embodiments to measure the stress-strain curve of the tensile specimen 3 to be tested. Figure 5 As shown, the method specifically includes:

[0046] S110, determining a plurality of deformation thresholds of the tensile specimen 3 to be tested, wherein the thresholds are arranged in numerical order, and the temperature of the tensile specimen 3 to be tested can be maintained within a set range when the deformation occurs between two adjacent thresholds.

[0047] This embodiment takes into account the adiabatic temperature rise effect of the sample during continuous deformation, and pre-selects multiple increasing deformation thresholds as the maximum deformation of each tensile test. The increase between adjacent thresholds is not very large, which can ensure that when the sample is deformed between two adjacent thresholds, the insulation temperature rise of the sample is very small, and the temperature can be maintained within the set range, so that the final measured stress-strain curve is a constant temperature state curve. Exemplarily, during the stress-strain curve test, the temperature fluctuates up and down by ≤5°C, which can be considered constant. Optionally, for 304 austenitic stainless steel, the multiple thresholds can be 1%, 2%, 3%, 4%, 6%, 8%, 11%, 13%, and 15.5%.

[0048] S120: Set the first threshold as the current threshold and initialize the previous threshold to 0.

[0049] S130, adjusting the distance between the limit nut 1 4 and the limit nut 2 5 so that the maximum deformation of the sample 3 is controlled within the current threshold value.

[0050] Taking the current threshold of 1% as an example, the distance between the limit nut 1 4 and the limit nut 2 5 is adjusted so that the maximum deformation of the sample is exactly equal to 1%, or is close to 1%.

[0051] S140, stretching the sample 3 using a high-speed tensile testing machine, and recording the change process of the sample deformation from the previous threshold value to the current threshold value through the high-speed camera, and measuring the load change process of the sample during the same period through each strain gauge 8.

[0052] Still taking the current threshold of 1% as an example, the sample is stretched using a high-speed tensile testing machine, and the change process of the sample deformation from 0 to 1% is recorded by the high-speed camera, and the load change process of the sample during the same period is measured by each strain gauge 8. Optionally, the strain and stress at multiple moments during the stretching process can be recorded, and the strain and stress data at the same moment can be used as data points for fitting the stress-strain curve later.

[0053] Furthermore, when measuring strain by a high-speed camera, two points can be marked in advance on the surface of the sample 3; the sample 3 is photographed by the high-speed camera during the stretching process, and the distance between the two points at each moment is calculated based on the photographed image; the distance at each moment is divided by the distance between the two points before the first stretching to obtain the sample deformation (i.e., sample strain) at each moment.

[0054] S150, taking the current threshold as the new previous threshold and the next threshold as the new current threshold, returning to the distance between the adjustment limit nut 1 4 and the limit nut 2 5, so that the maximum deformation of the sample is controlled within the operation of the current threshold until all the multiple thresholds are traversed.

[0055] Still taking the current threshold of 1% as an example, after this stretching is completed, 1% is used as the new previous threshold, and 2% is used as the new current threshold, and the process returns to S130. By adjusting the distance between limit nut 1 4 and limit nut 2 5, the maximum deformation of the sample is equal to the new current threshold of 2%, and S140 is repeated; this cycle is repeated until all thresholds are reached.

[0056] S160, generating a stress-strain curve segment between every two adjacent threshold values ​​according to the deformation and load variation process recorded in each cycle, and each curve segment together constitutes a complete stress-strain curve.

[0057] In this embodiment, multiple tensile tests are performed by controlling the strain in a small range multiple times. The stress-strain data measured in each test can obtain a small stress-strain curve. By splicing each curve, a stress-strain curve in a larger strain range can be obtained. Figure 6 As shown in the figure, the horizontal axis True strain represents the sample strain measured by the high-speed camera, and the vertical axis True stress represents the stress load measured by the strain gauge 8.

[0058] Furthermore, considering that the positions of the two points marked in S140 are different, the measured deformation amounts may also be different. For example, if the deformation in the middle area of ​​the specimen is large and the deformation in the areas on both sides is small, then the strain values ​​measured at the two points in the middle area become larger, and the strain values ​​measured at the two points in the areas on both sides are smaller. Therefore, in another specific embodiment, when marking the positions of two points in S140, multiple groups of marking points are selected with the center of the flat middle section as the midpoint. Specifically, two points are marked at the same distance on both sides of the midpoint along the longitudinal direction of the specimen as a group of marking points; the distance from the marking point to the midpoint is changed in the same manner, and two points are marked at each distance as a group of marking points. The multiple groups of marking points finally obtained are as follows: Figure 7 As shown, the rectangle represents the flat middle section of the sample, the dotted line direction represents the longitudinal direction of the sample, point O represents the center of the flat middle section, A1 and A2 are a group of marking points, and the distance from A1 to point O is equal to the distance from A2 to point O; and so on, B1 and B2, ..., N1 and N2 are respectively a group of marking points.

[0059] Accordingly, when the distance between the two points at each moment in the stretching process is recorded by the high-speed camera, the distance between each group of marking points at each moment in the stretching process can be recorded separately. Optionally, a high-speed camera is used to take photos at each moment, and each group of marking points is identified from the photographed photos based on the positional relationship between each group of marking points and point O (A1 and A2 are closest to point O, and N1 and N2 are farthest from point O), and then the distance between two points in each group of marking points is calculated according to the camera parameters.

[0060] Correspondingly, when the distance at each moment is divided by the distance between the two points before the first stretching to obtain the deformation of the sample at each moment, the distance of a group of marking points at each moment can be divided by the distance of the group of marking points before the first stretching to obtain the deformation of the sample at each moment. The same operation is performed on each group of marking points to obtain the deformation of the sample at each moment for each group of marking points.

[0061] The above operation is performed in each cycle of S150. After the cycle is completed, a complete stress-strain curve can be obtained in S160 by the following steps:

[0062] Step 1: For each moment t, extract the sample deformation measured by each group of marking points at the moment t from all records, and calculate the normalized value of each sample deformation. Exemplarily, for the moment t1 in the first stretching, extract the sample deformation at the moment t1 measured by each group of marking points from the data of the first stretching record, and normalize all sample deformations at the moment t1 so that the normalized deformation remains in the interval [0,1], wherein the group of marking points with the largest sample deformation at the moment t1 corresponds to the normalized value 1, and the group of marking points with the smallest sample deformation at the moment t1 corresponds to the normalized value 0. The same operation is performed for all moments, and each group of marking points corresponds to a normalized value at each moment. Optionally, the maximum and minimum normalization method can be used.

[0063] Step 2: For each group of marking points, calculate the standard deviation of the normalized value of the specimen deformation of the current group of marking points at each moment. For example, for the first group of marking points A1 and A2, calculate the standard deviation of the normalized deformation of A1 and A2 at all moments. Perform the same operation on all marking point groups, and each group of marking points can get a standard deviation.

[0064] Step 3: Select a group of marking points with the smallest standard deviation as the preferred marking points. The above standard deviation can reflect the change in the stress level of a group of marking points in the entire flat middle section of the specimen during the entire stretching process. The smaller the standard deviation, the more stable the stress level, and avoid a group of marking points that are sometimes the points with the largest stress in the entire flat middle section and sometimes the points with the smallest stress in the entire flat middle section. Such large fluctuations in stress levels are not conducive to stable measurement of strain.

[0065] Step 4: Generate a stress-strain curve segment between each two adjacent thresholds according to the change process of the sample deformation and load recorded by the preferred marking points in each cycle, and each curve segment together constitutes a complete stress-strain curve. The stress-strain curve determined according to the preferred marking points can more stably reflect the mechanical properties of the sample and is also more accurate.

[0066] Obviously, those skilled in the art can make various changes and modifications to the embodiments of the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A stress-strain curve measurement method for metal materials, characterized in that: Using a stress-strain measuring device for metal materials, measuring a stress-strain curve of a tensile specimen (3) to be tested; The device comprises: a high-speed tensile testing machine, a clamping rod (1) and a clamping rod (2) with external threads, a strain gauge (8) fixed on the surface of the clamping rod, a tensile specimen to be tested (3), a limit nut (4), a limit nut (5) and a sleeve (6) for controlling the deformation of the specimen, and a DIC device (7) for accurately characterizing the deformation of the specimen; wherein one side of the clamping rod (1) and the clamping rod (2) is a clamping section and the other side is a threaded section, and each clamping section is respectively connected to the high-speed tensile testing machine; the tensile specimen to be tested (3) is in the shape of a plate in the middle and in the shape of a cylinder with internal threads at both ends; the tensile specimen to be tested (3), the limit nut (4) and the limit nut (5) are respectively connected to the high-speed tensile testing machine through the internal threads. The sleeve (6) is connected to the clamping rod 1 (1) and the clamping rod 2 (2); the tensile specimen to be tested (3), the limit nut 1 (4) and the limit nut 2 (5) are all placed in the sleeve; the tensile specimen to be tested (3), the limit nut 1 (4), the limit nut 2 (5), the clamping rod 1 (1) and the clamping rod 2 (2) can slide in the sleeve (6); the limit nut cooperates with the sleeve (6) to control the deformation of the specimen; an observation window is provided on the side of the sleeve (6), and the deformation process of the specimen is photographed by a high-speed camera, and the DIC technology is combined to achieve the purpose of accurately measuring the deformation of the specimen; the strain gauge (8) is respectively attached to the clamping rod 1 (1) and the clamping rod 2 (2) to measure the load borne by the specimen during the experiment; The method comprises: Determining a plurality of deformation thresholds of the tensile specimen (3) to be tested, wherein the thresholds are arranged in numerical order, and the temperature of the tensile specimen (3) to be tested can be maintained within a set range when deforming between two adjacent thresholds; Set the first threshold as the current threshold and initialize the previous threshold to 0; Adjust the distance between the limit nut 1 (4) and the limit nut 2 (5) so that the maximum deformation of the sample is controlled within the current threshold value; The high-speed tensile testing machine is used to stretch the tensile specimen (3) to be tested, and the high-speed camera is used to record the change process of the specimen deformation from the previous threshold value to the current threshold value, and the strain gauges (8) are used to measure the change process of the load borne by the specimen during the same period; The current threshold is used as a new previous threshold, the next threshold is used as a new current threshold, and the distance between the adjustment limit nut 1 (4) and the limit nut 2 (5) is returned so that the maximum deformation of the sample is controlled within the current threshold until all the multiple thresholds are traversed; According to the changes in the deformation and load of the sample recorded in each cycle, a stress-strain curve segment between every two adjacent thresholds is generated, and each curve segment together constitutes a complete stress-strain curve.

2. The method according to claim 1, characterized in that: The limiting nut 1 (4) is located above the limiting nut 2 (5), and the clamping rod 2 (2) is fixed to the base of the high-speed tensile testing machine; In the tensile test, the clamping rod (1) moves upward under the action of the high-speed tensile testing machine to stretch the tensile specimen (3) to be tested; When the tensile test specimen (3) to be tested is stretched to the point where the limiting nut (4) contacts the top surface of the sleeve (6), the sleeve (6) is driven to slide upward; When the sleeve (6) slides to the point where the bottom surface of the sleeve (6) contacts the second limiting nut (5), the sleeve (6) is limited and the tensile specimen (3) to be tested reaches a maximum deformation.

3. The method according to claim 1, characterized in that The device can be used to carry out tensile tests under continuous strain rate conditions including quasi-static, medium and dynamic conditions, and to limit the deformation of the specimen. -3 s -1 , the medium state satisfies 10 -3 s -1 <Strain rate≤10 2 s -1 , dynamically meet 10 2 s -1 <Strain rate≤10 4 s -1 .

4. The method according to claim 1, characterized in that: The tensile test specimen (3) to be tested comprises a flat plate-shaped middle section (30) and a cylindrical clamping section, with an arc transition provided between the two.

5. The method according to claim 1, characterized in that The internal thread of the tensile specimen (3) to be tested, the external thread of the clamping rod, the internal threads of the first limit nut (4) and the second limit nut (5) are all precision threads that match each other. The deformation of the tensile specimen (3) to be tested is controlled by controlling the position of the limit nut on the clamping rod.

6. The method according to claim 1, characterized in that The sleeve (6) is a split structure, comprising a left half-cylinder and a right half-cylinder, which are connected by four bolts distributed at the four corners of the sleeve; The left half cylinder is provided with a rectangular observation window for cooperating with the DIC device to accurately measure the deformation of the tensile specimen.

7. The method according to claim 1, characterized in that The step of recording the change process of the deformation of the sample from the previous threshold value to the current threshold value by the high-speed camera includes: Marking two points on the surface of the tensile specimen (3) to be tested; Recording the distance between the two points at each moment during the stretching process by the high-speed camera; The distance at each moment is divided by the distance between the two points before the first stretching to obtain the deformation of the sample at each moment.

8. The method according to claim 7, characterized in that The marking of two points on the surface of the tensile specimen (3) to be tested comprises: taking the center of the tensile specimen (3) to be tested as the midpoint, marking two points at the same distance on both sides of the midpoint along the longitudinal direction of the tensile specimen (3) to be tested; changing the distance to the midpoint, marking two points at each distance; Accordingly, recording the distance between the two points at each moment during the stretching process by the high-speed camera comprises: taking the two points at each distance as a group of marking points, and recording the distance between each group of marking points at each moment during the stretching process by the high-speed camera; Correspondingly, the distance at each moment is divided by the distance between the two points before the first stretching to obtain the sample deformation at each moment, including: dividing the distance of each group of marking points at each moment by the distance of each group of marking points before the first stretching to obtain the sample deformation of each group of marking points at each moment.

9. The method according to claim 8, characterized in that According to the change process of the deformation and load of the sample recorded in each cycle, a stress-strain curve segment between every two adjacent threshold values ​​is generated, and each curve segment together constitutes a complete stress-strain curve, including: For each moment, the deformation of the specimen measured by each group of marking points at the current moment is extracted from all records, and the normalized value of the deformation of each specimen is calculated; For each group of marking points, the standard deviation of the normalized value of the specimen deformation of the current group of marking points at each moment is calculated respectively; Select a group of marking points with the smallest standard deviation as the preferred marking points; According to the variation process of the deformation and load of the sample recorded by the preferred marking points in each cycle, a stress-strain curve segment between every two adjacent threshold values ​​is generated, and each curve segment together constitutes a complete stress-strain curve.

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