A device for preventing instability in a cyclic loading test of steel

Abstract

The application is a kind of steel cyclic loading test anti-instability device, including instrument upper loading head, first pin bolt, first group of nuts, first threaded clamp, extensometer, first nut, test piece, second nut, second threaded clamp, second group of nuts, second pin bolt, instrument lower loading head and pin bolt hole; the device has lower manufacturing cost, simple installation and smaller size; the pre-tightening force of the threaded bolt is used to complete clamping and limit the translation and rotation of the test sample; through strong constraint of the test piece, the steel compression instability is prevented, so as to realize large strain cyclic loading, and the steel cyclic loading test data can be accurately tested before buckling instability, and the material characteristics reflected by the test are more accurate.

Description

Technical Field

[0001] This invention relates to the field of steel loading test technology, and in particular to a device for preventing instability in steel cyclic loading tests. Background Technology

[0002] When an earthquake occurs, structural members typically bear enormous cyclic seismic forces. The main characteristics of cyclic seismic forces are a small number of hysteresis loops, a short load duration, and large plastic deformation of the structure. Structural members resist such loads mainly by structural design and the mechanical properties of the materials themselves. This is reflected at the material level in their ability to withstand ultra-low cycle cyclic loads. As the main material of building structures, the cyclic constitutive relationship of steel is the basis for studying the seismic performance of structures. Therefore, it is particularly important to effectively test the cyclic loading mechanical properties of steel.

[0003] Cyclic loading refers to a deformation process of materials under tensile-compression (or compression-tension) cyclic loading, characterized by complex deformation processes and numerous deformation conditions. During cyclic loading, most metals exhibit the Bauschinger effect, as well as hardening or softening phenomena, and their mechanical properties change at different loading stages. Through tensile-compression (or compression-tension) cyclic loading tests, the stress-strain curves of materials under cyclic stress states can be directly obtained, revealing the changing patterns of the material's mechanical properties.

[0004] With the development of materials science, more and more high-strength steel materials are being used in structural components of buildings. Existing scholars at home and abroad have conducted cyclic loading tests on various steel materials such as ordinary low-carbon steel, low-yield steel, high-strength steel, and stainless steel. However, the clamps used in the existing cyclic loading tests are all ordinary clamps. These clamps are usually large in size, have high manufacturing costs, and are difficult to install. Furthermore, the anti-instability devices in the existing technology have weak constraint capabilities on the specimens, so the specimens will prematurely exhibit buckling instability, which will lead to the inability to conduct large-strain cyclic loading tests. This causes high-strength steel to become unstable prematurely, which greatly reduces the accuracy of the cyclic loading test data of steel and fails to accurately reflect the material properties.

[0005] Therefore, those skilled in the art are dedicated to developing an anti-instability device for cyclic loading tests of steel, aiming to solve the defects existing in the prior art. Summary of the Invention

[0006] In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is that the anti-instability device clamping device in the prior art has a large size, high manufacturing cost, difficult installation, and weak constraint ability on the specimen, which makes it impossible to carry out large strain cyclic loading tests, greatly reducing the accuracy of steel cyclic loading test data and failing to accurately reflect the material properties.

[0007] To achieve the above objectives, the first aspect of the present invention provides a device for preventing instability in a cyclic loading test of steel, comprising: an upper loading head of the instrument, a first pin, a first set of nuts, a first threaded clamp, an extensometer, a first nut, a specimen, a second nut, a second threaded clamp, a second set of nuts, a second pin, a lower loading head of the instrument, and a pin hole;

[0008] The instrument has a loading head and a first threaded clamp with a pin hole. The first pin can be inserted into the loading head of the instrument through the pin hole. After the first pin is inserted, the loading head of the instrument and the first threaded clamp can be locked.

[0009] The instrument's lower loading head and the second threaded clamp have pin holes. The second pin can be inserted into the instrument's lower loading head through the pin holes. After the second pin is inserted, the instrument's lower loading head and the second set of nuts can be locked.

[0010] The first threaded clamp has an external thread on its top. There are 2 to 4 nuts in the first set. The first set of nuts can cooperate with the external thread on the top of the first threaded clamp, so that the first set of nuts can stably fix the first threaded clamp on the loading head of the instrument.

[0011] The second threaded clamp has an external thread on its upper part. There are 2 to 4 nuts in the second set. The second set of nuts can cooperate with the external thread on the upper part of the second threaded clamp, so that the second set of nuts can stably fix the second threaded clamp to the lower loading head of the instrument.

[0012] The test piece is threaded at both ends, and the threads at both ends of the test piece can be matched with the internal threads of the first threaded clamp and the second threaded clamp, respectively.

[0013] The first nut can engage with the thread at the upper end of the specimen, and the first nut can fix the upper end of the specimen together with the first threaded clamp;

[0014] The second nut can engage with the thread at the lower end of the specimen, and the second nut can fix the lower end of the specimen together with the second threaded clamp;

[0015] The extensometer can be fixed with a rubber band. The blades at both ends of the extensometer must be within the gauge length range, and the blades of the extensometer must be perpendicular to the longitudinal axis of the specimen.

[0016] Furthermore, the connection between the first threaded clamp and the loading head on the instrument is designed to match the size and shape of the loading head on the instrument.

[0017] Furthermore, the connection between the second threaded clamp and the instrument's lower loading head is designed to match the size and shape of the instrument's lower loading head;

[0018] Furthermore, the tension of the rubber band fixing the extensometer should not be too tight or too loose; it is only necessary to ensure that the extensometer can work normally during the test.

[0019] A second aspect of the present invention provides a method for using an anti-instability device in a cyclic loading test of steel, comprising the following steps:

[0020] Step 1: Screw the first nut and the second nut into the test piece;

[0021] Step 2: Screw the specimen into the first threaded clamp and the second threaded clamp, and tighten it with the first nut and the second nut;

[0022] Step 3: Screw the first set of nuts onto the first threaded clamp, and screw the second set of nuts onto the second threaded clamp;

[0023] Step 4: The first threaded clamp is installed into the upper loading head of the instrument and the pin is inserted; the second threaded clamp is installed into the lower loading head of the instrument and the pin is inserted.

[0024] Step 5: Tighten the first set of nuts and the second set of nuts to lock the loading head and clamp of the equipment;

[0025] Step 6: Perform a cyclic loading test on the specimen; after the test, the preload needs to be released, and the nut should be manually adjusted to replace the specimen with another one.

[0026] In step 6, the cyclic loading test includes a tensile operation and a compression operation;

[0027] Furthermore, during the stretching operation, it is necessary to continuously tighten the first nut, the second nut, the first set of nuts, and the second set of nuts to eliminate the gap between the threads;

[0028] Furthermore, during the compression operation, the release of tensile strain causes a strong preload to be established in the first set of nuts, the second set of nuts, the upper and lower loading heads of the instrument, the first nut, the second nut, the first threaded clamp, and the second threaded clamp, which plays a role in preventing instability.

[0029] By adopting the above scheme, the anti-instability device for steel cyclic loading test disclosed in this invention has the following advantages:

[0030] (1) The anti-instability device for steel cyclic loading test of the present invention can use a less expensive mechanical pressurization device, which has a lower manufacturing cost; and the anti-instability device of the present invention is easy to install and smaller in size, which is more conducive to its widespread application.

[0031] (2) The anti-instability device for steel cyclic loading test of the present invention completes the clamping by applying the pre-tightening force of the threaded bolt, which restricts the translation and rotation of the test specimen, so that the clamped specimen can only rotate in the normal direction, thereby greatly reducing the possibility of planar instability of the specimen; by strongly constraining the specimen, the steel is prevented from being unstable under compression, thereby realizing large strain cyclic loading, so that the cyclic loading test data of steel can be accurately tested before the steel buckling instability occurs, and the material properties reflected by the test are more accurate.

[0032] In summary, the anti-instability device for steel cyclic loading test disclosed in this invention has low manufacturing cost, simple installation, and smaller size; the clamping is completed by the pre-tightening force applied by the threaded bolts, which restricts the translation and rotation of the test specimen; by strongly constraining the specimen, the steel is prevented from becoming unstable under pressure, thereby realizing large strain cyclic loading, and the material properties reflected in the test are more accurate.

[0033] The following will further explain the concept, specific technical solution and technical effects of the present invention in conjunction with specific embodiments, so as to fully understand the purpose, features and effects of the present invention. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the anti-instability device for steel cyclic loading test of the present invention;

[0035] Figure 2 This is an exploded view of the anti-instability device for cyclic loading test of steel according to the present invention;

[0036] Figure 3 This is a schematic diagram of the anti-instability device for steel cyclic loading test of the present invention after completing installation step 1;

[0037] Figure 4 This is a schematic diagram of the anti-instability device for steel cyclic loading test of the present invention after completing installation step 2;

[0038] Figure 5 This is a schematic diagram of the anti-instability device for steel cyclic loading test of the present invention after completing installation step 3;

[0039] Figure 6 This is a schematic diagram of the anti-instability device for steel cyclic loading test of the present invention after completing installation step 4;

[0040] Figure 7 This is a schematic diagram of the anti-instability device for steel cyclic loading test of the present invention after completing installation step 5;

[0041] Figure 8 This is a plan sectional view of the anti-instability device for steel cyclic loading test of the present invention after installation;

[0042] Figure 9This is an exploded sectional view of the anti-instability device for steel cyclic loading test of the present invention after installation;

[0043] Figure 10 This is a disassembled diagram of the device used in the embodiment of the anti-instability device for steel cyclic loading test of the present invention;

[0044] Figure 11 This is a cyclic loading test curve of Embodiment 1 of the anti-instability device for cyclic loading test of steel of the present invention;

[0045] Figure 12 This is a cyclic loading test curve of Embodiment 2 of the anti-instability device for cyclic loading test of steel of the present invention;

[0046] Figure 13 This is a cyclic loading test curve of the anti-instability device for cyclic loading test of steel of the present invention, as shown in Comparative Example 1;

[0047] In the figure, 1. Loading head on the instrument; 2. First pin; 3. First set of nuts; 4. First threaded clamp; 5. Extensometer; 6. First nut; 7. Specimen; 8. Second nut; 9. Second threaded clamp; 10. Second set of nuts; 11. Second pin; 12. Loading head on the instrument; 13. Pin hole. Detailed Implementation

[0048] The following describes several preferred embodiments of the present invention to make its technical content clearer and easier to understand. The present invention can be embodied in many different forms of embodiments, which are described exemplarily, and the scope of protection of the present invention is not limited to the embodiments mentioned herein.

[0049] like Figure 1 As shown, the anti-instability device for steel cyclic loading test of the present invention includes an upper loading head 1, a first pin 2, a first set of nuts 3, a first threaded clamp 4, an extensometer 5, a first nut 6, a specimen 7, a second nut 8, a second threaded clamp 9, a second set of nuts 10, a second pin 11, a lower loading head 12, and a pin hole 13.

[0050] The loading head 1 and the first threaded clamp 4 on the instrument have pin holes 13. The first pin 2 can be inserted into the loading head 1 through the pin holes 13. After the first pin 2 is inserted, the loading head 1 and the first threaded clamp 4 can be locked.

[0051] The instrument loading head 12 and the second threaded clamp 9 have pin holes 13. The second pin 11 can be inserted into the instrument loading head 12 through the pin holes 13. After the second pin 11 is inserted, the instrument loading head 12 and the second set of nuts 10 can be locked.

[0052] The first threaded clamp 4 has an external thread on its upper part. There are two nuts in the first set 3. The first set of nuts 3 can cooperate with the external thread on the upper part of the first threaded clamp 4, so that the first set of nuts 3 can stably fix the first threaded clamp 4 on the loading head 1 of the instrument.

[0053] The connection between the first threaded clamp 4 and the loading head 1 on the instrument is designed and matched according to the size and shape of the loading head 1 on the instrument;

[0054] The connection between the second threaded clamp 9 and the instrument loading head 12 is designed and matched according to the size and shape of the instrument loading head 12.

[0055] The second threaded clamp 9 has an external thread on its upper part. There are two nuts in the second set 10. The second set of nuts 10 can cooperate with the external thread on the upper part of the second threaded clamp 9, so that the second set of nuts 10 can stably fix the second threaded clamp 9 on the lower loading head 12 of the instrument.

[0056] The two ends of the specimen 7 are provided with threads, and the threads at both ends of the specimen 7 can be matched with the internal threads of the first threaded clamp 4 and the second threaded clamp 9, respectively.

[0057] The first nut 6 can be engaged with the thread at the upper end of the specimen 7, and the first nut 6 can fix the upper end of the specimen 7 together with the first threaded clamp 4;

[0058] The second nut 8 can be engaged with the thread at the lower end of the specimen 7, and the second nut 8 can fix the lower end of the specimen 7 together with the second threaded clamp 9;

[0059] The extensometer 5 can be fixed with a rubber band. The blades at both ends of the extensometer 5 must be within the gauge length range, and the blades of the extensometer 5 must be perpendicular to the longitudinal axis of the specimen 7.

[0060] The tension of the rubber band fixing the extensometer 5 should not be too tight or too loose; it is sufficient to ensure that the extensometer 5 can work normally during the test.

[0061] Example 1: A cyclic loading test was conducted on HRB400E steel using the anti-instability device of the present invention.

[0062] In this specific implementation, the upper loading head, first pin, first set of nuts, first threaded clamp, first nut, second nut, second threaded clamp, second set of nuts, second pin, and lower loading head of the instrument of the present invention all adopt yield strength. f y 785MPa, tensile strength f u The specimen was made of 40Cr mold steel with a strength of 810MPa. Both the monotonic tensile and cyclic loading tests were conducted on an MTS universal testing machine with a maximum range of 600kN. The cyclic loading test used strain-controlled loading with a loading rate of 0.2mm / min. The extensometer was a tension-compression extensometer with a gauge length of 20mm, a tensile range of 25%, and a compressive range of -10%. The extensometer was installed in the middle gauge length section of the specimen and fixed with rubber bands.

[0063] In this Example 1, the cyclic loading specimens for HRB400E steel were designated CE. A total of seven cyclic loading specimens were prepared, numbered CE-1 to CE-7. Both clamping sections of the cyclic loading specimens were threaded. The dimensions of each specimen can be referenced... Figure 10 ;

[0064] In the specific implementation of this embodiment 1, the first group of nuts is selected as M72 nuts, and the second group of nuts is selected as M30 nuts; the second group of nuts is selected as M72 nuts, and the second group of nuts is selected as M30 nuts.

[0065] Next, the anti-instability device is used in the cyclic loading test of the steel. First, perform step 1: screw the first M30 nut and the second M30 nut into the specimen. After completing step 1, ensure that the first and second M30 nuts are tightened until there are no threads left on the specimen. This ensures that the M30 nuts provide sufficient preload to secure the specimen to the nuts. The device diagram after completing step 1 is shown below. Figure 3 As shown;

[0066] Next, proceed to step 2: Screw the specimen into the first and second threaded clamps, and tighten them using the first and second M30 nuts. Screw one end of the specimen into the first threaded clamp, ensuring that all threads are fully engaged to prevent movement. Screw the other end of the specimen into the second threaded clamp, ensuring it is also tightened to provide sufficient preload to secure the clamps. The completed device diagram is shown below. Figure 4 As shown;

[0067] Then proceed to step 3, screwing the first set of M72 nuts onto the first threaded clamp, and the second set of M72 nuts onto the second threaded clamp;

[0068] Screw the first threaded clamp onto the upper thread of the specimen, ensuring that the entire thread of the specimen is screwed into the first threaded clamp; screw the second threaded clamp onto the lower thread of the specimen, ensuring that the entire thread of the specimen is screwed into the second threaded clamp; the device diagram after completing step 3 is as follows. Figure 5 As shown;

[0069] After completing step 3, proceed to step 4: the first threaded clamp is installed on the upper loading head of the instrument and a pin is inserted; the second threaded clamp is installed on the lower loading head of the instrument and a pin is inserted.

[0070] Using the remote control handle of the testing machine, lower the loading head on the instrument to ensure that the pin hole of the second threaded clamp is aligned with the pin hole on the lower loading head of the instrument. Insert the second pin into the pin hole to fix the second threaded clamp. Similarly, insert the first pin into the pin hole to fix the first threaded clamp. The completed device diagram after step 4 is shown below. Figure 6 As shown;

[0071] Finally, proceed to step 5: tighten the first and second sets of M72 nuts to lock the loading head and clamp of the equipment; tighten the first and second sets of M72 nuts to ensure that the first and second threaded clamps are firmly fixed to the upper and lower loading heads of the instrument, respectively, and lock the loading head and clamp of the equipment; the device diagram after completing step 5 is as follows. Figure 7 As shown;

[0072] The Figure 8 This is a plan view of the anti-instability device for the steel cyclic loading test after step 5, showing the completed installation. Figure 9 This is an exploded sectional view of the anti-instability device for steel cyclic loading test of the present invention after installation;

[0073] After completing the installation of the anti-instability device for the cyclic loading test of steel, adjust the angle so that the lower threaded clamp hole is coaxial with the loading head hole below the instrument. After inserting the pin, tighten the lower M72 nut to fix the lower clamp and install the extensometer. In this specific implementation, rubber bands are used to fix the extensometer. The blades at both ends of the extensometer must be within the gauge length range and the blades of the extensometer must be perpendicular to the longitudinal axis of the specimen.

[0074] Then you can proceed to step 6 to complete the cyclic loading test of the steel. During the tensile process, the M72 nut and M30 nut need to be continuously tightened to eliminate the thread gap. When compressed, the release of tensile strain causes a strong preload to be established between the M72 nut and the instrument loading head, the M30 nut and the threaded clamp. Through the strong constraint on the specimen, it plays an extremely good role in preventing instability.

[0075] After the cyclic loading test of each specimen is completed, it is stretched to the historical maximum tensile stress level. At this time, the preload needs to be removed, the nut is manually adjusted and the specimen is replaced. After the specimen is replaced, the cyclic loading test of the steel is carried out again.

[0076] The results of the cyclic loading test on HRB400E steel in Example 1 are as follows: Figure 11 As stated above.

[0077] Example 2: A cyclic loading test was conducted on Q355B steel using the anti-instability device of the present invention.

[0078] Except for the steel material used in the cyclic loading test, the operations in Example 2 are the same as in Example 1.

[0079] In this Example 2, the cyclic loading specimens for Q355B steel were numbered CQ, and there were a total of 5 cyclic loading specimens, numbered CQ-1 to CQ-5 respectively;

[0080] The results of the cyclic loading test on Q355B steel in Example 2 are as follows: Figure 12 As stated above.

[0081] Comparative Example 1: Cyclic loading test of Q355B steel using existing technology.

[0082] In this comparative example 1, the sample used in the cyclic loading test of steel was a hydraulic clamp of the prior art. This hydraulic clamp was fixed with a clamping plate. The strain was also measured by a tension and compression extensometer. The extensometer gauge length was 20 mm, the tensile range was 25%, and the compressive range was -10%. The extensometer was installed in the middle gauge length section of the specimen and fixed with a rubber band.

[0083] In Comparative Example 1, except for the different fixtures used, all other variable conditions, such as the test specimens, were the same as those in Example 2 when the anti-instability device of the present invention was used to complete the cyclic loading test on Q355B steel.

[0084] The results of the cyclic loading test on Q355B steel in Comparative Example 1 are as follows: Figure 13 As stated above.

[0085] Comparative analysis: In Examples 1 and 2, the anti-instability device of the present invention is a mechanical clamp. The manufacturing cost of this mechanical clamp is 5,000 yuan. Both sides of the clamping section of the cyclic loading specimen are provided with threads. The test specimen is disassembled and installed by rotating the threads, which makes the installation simpler and the size smaller.

[0086] The anti-instability device used in Comparative Example 1 is a hydraulic pressurization device, which costs around 100,000 yuan. The test cost in Comparative Example 1 is relatively high. In addition, the hydraulic pressurization device is larger in size, and the installation process of the test piece is more difficult.

[0087] The cyclic loading test curves from Examples 1 and 2 Figure 11 , Figure 12 The cyclic loading test curves of Comparative Example 1 Figure 13 By comparing and analyzing, we can draw conclusions;

[0088] The cyclic loading test curve of Comparative Example 1 Figure 13It can be seen that H-1, H-2, H-3, and H-4 all have extended curves in the upper right of the curve. The reason for this is that the two ends of the hydraulic pressurization are far apart. Existing anti-instability devices are prone to lateral displacement of the cyclically loaded specimen, which leads to instability of the test specimen and makes it impossible to test the value of the area with large compressive strain.

[0089] Specifically Figure 13 In the H-1 diagram, instability occurred at point A when the compressive strain of the test specimen reached 2%; before the compressive strain reached 4%, no further cyclic loading data could be obtained from the specimen; thus, Comparative Example 1 showed the aforementioned H-1 cyclic loading test curve; from Figure 13 Analysis shows that, using existing technology to measure Q355B steel, instability generally occurs at around 2% of the maximum compressive strain, and instability also occurs at less than 4% of the maximum compressive strain. This means that when testing steel with a compressive strain of more than 4%, the steel under test has not yet reached the compressive strain limit, and the anti-instability device using existing technology fails first, causing the tested sample to become unstable; thus, it is impossible to accurately determine the maximum compressive strain limit of the test steel.

[0090] Specifically, regarding the cyclic loading test curve of Comparative Example 1... Figure 13 In H-2, the curve above the horizontal axis in the image is the tensile curve, and the curve below the horizontal axis is the compressive curve. The compressive curve of the test steel in H-2 could not be measured after 2% compression. In the experiment, the test steel could not deform back when compressed. That is, in the H-2 test of Comparative Example 1 using hydraulic clamps, the steel became unstable before the compression reached 2%, and the subsequent related cyclic loading test could not be completed.

[0091] In Example 2, which uses the anti-instability device of the present invention, the test specimens tested were the same type of steel as those in Comparative Example 1. The cyclic loading test curves of Example 2... Figure 12 It can be seen that, Figure 12 The maximum compressive strain of CQ-1 in the test sample exceeded 5% and approached 6%. The sample was able to maintain a stable equilibrium throughout the entire test process. Before reaching the maximum compressive strain of the steel, the test sample steel remained stable and did not become unstable. The maximum compressive strain of the test sample steel Q355B was successfully tested.

[0092] Comparative analysis shows that, comparing the cyclic loading test results of the same type of steel test piece in Example 2 with those in Comparative Example 1, the existing anti-instability device already showed signs of instability when the compressive strain of the test piece reached 2%. However, the anti-instability device for cyclic loading of the steel test piece using the present invention measured a maximum compressive strain close to 6%, and the device maintained the test piece from instability until the maximum compressive strain was reached. Therefore, the device of the present invention has excellent anti-instability performance.

[0093] Cyclic loading test curve of this embodiment 1 Figure 11 Analysis shows that the maximum compressive strain of HRB400E steel reaches 5%. Therefore, the anti-instability device of this invention can maintain the steel until the maximum compressive strain is reached without instability when the maximum compressive strain is 5%. Compared with the existing technology, which generally only has a maximum compressive strain test range of about 2%, the device of this invention has excellent anti-instability performance.

[0094] In summary, this patented technical solution has lower manufacturing costs, is easier to install, and is smaller in size; the pre-tightening force applied by the threaded bolts completes the clamping, restricting the translation and rotation of the test specimen; the strong constraint on the specimen prevents the steel from buckling under pressure, thereby achieving large strain cyclic loading, which allows for accurate testing of the cyclic loading test data of the steel before buckling instability occurs, and the material properties reflected in the test are also more accurate.

[0095] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A device for preventing instability during cyclic loading tests of steel, characterized in that, Includes the instrument loading head (1), first pin (2), first set of nuts (3), first threaded clamp (4), extensometer (5), first nut (6), specimen (7), second nut (8), second threaded clamp (9), second set of nuts (10), second pin (11), instrument loading head (12), and pin hole (13); The loading head (1) on the instrument and the first threaded clamp (4) have pin holes (13). The first pin (2) can be inserted into the loading head (1) on the instrument through the pin holes (13). After the first pin (2) is inserted, the loading head (1) on the instrument and the first threaded clamp (4) can be locked. The instrument loading head (12) and the second threaded clamp (9) have pin holes (13). The second pin (11) can be inserted into the instrument loading head (12) through the pin hole (13). After the second pin (11) is inserted, the instrument loading head (12) and the second set of nuts (10) can be locked. The first threaded clamp (4) has an external thread on its upper part. There are 2 to 4 nuts (3) in the first set. The first set of nuts (3) can cooperate with the external thread on the upper part of the first threaded clamp (4) so ​​that the first set of nuts (3) can stably fix the first threaded clamp (4) on the loading head (1) of the instrument. The second threaded clamp (9) has an external thread on its upper part. There are 2 to 4 nuts (10) in the second set. The second set of nuts (10) can cooperate with the external thread on the upper part of the second threaded clamp (9) so that the second set of nuts (10) can stably fix the second threaded clamp (9) on the lower loading head (12) of the instrument. The test piece (7) has threads at both ends, and the threads at both ends of the test piece (7) can be matched with the internal threads of the first threaded clamp (4) and the second threaded clamp (9), respectively. The first nut (6) can be engaged with the thread on the upper end of the specimen (7), and the first nut (6) can fix the upper end of the specimen (7) together with the first threaded clamp (4); The second nut (8) can be engaged with the thread at the lower end of the specimen (7), and the second nut (8) can fix the lower end of the specimen (7) together with the second threaded clamp (9).

2. The anti-instability device as described in claim 1, characterized in that, The connection between the first threaded clamp (4) and the loading head (1) on the instrument is designed and matched according to the size and shape of the loading head (1) on the instrument; The connection between the second threaded clamp (9) and the instrument loading head (12) is designed and matched according to the size and shape of the instrument loading head (12).

3. The anti-instability device as described in claim 1, characterized in that, The extensometer (5) can be fixed with a rubber band. The blades at both ends of the extensometer (5) must be within the gauge length range, and the blades of the extensometer (5) must be perpendicular to the longitudinal axis of the specimen (7). The tension of the rubber band fixing the extensometer (5) should not be too tight or too loose; it is sufficient to ensure that the extensometer (5) can work normally during the test.

4. A method of using the anti-instability device for cyclic loading tests of steel as described in claim 1, characterized in that, Includes the following steps: Step 1: Screw the first nut (6) and the second nut (8) into the specimen (7); Step 2: Screw the specimen (7) into the first threaded clamp (4) and the second threaded clamp (9), and tighten it with the first nut (6) and the second nut (8); Step 3: Screw the first set of nuts (3) onto the first threaded clamp (4), and screw the second set of nuts (10) onto the second threaded clamp (9); Step 4: The first threaded clamp (4) is installed into the upper loading head (1) of the instrument and a pin is inserted; the second threaded clamp (9) is installed into the lower loading head (12) of the instrument and a pin is inserted. Step 5: Tighten the first set of nuts (3) and the second set of nuts (10) to lock the loading head and clamp of the equipment; Step 6: Perform a cyclic loading test on the specimen (7); after the test, the preload needs to be removed, and the nut should be manually adjusted to replace the specimen (7). In step 6, the cyclic loading test includes a tensile operation and a compression operation.

5. The method of using the anti-instability device for cyclic loading tests as described in claim 4, characterized in that, During the tensile process of the cyclic loading test, the first nut (6), the second nut (8), the first set of nuts (3), and the second set of nuts (10) need to be continuously tightened to eliminate the gap between the threads.

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