Fastener Stress Relaxation Deformation Testing Device and Its Testing Method

Abstract

This application relates to the technical field of mechanical property testing, in particular to a stress relaxation deformation testing device for fasteners and its testing method. The testing device of this application includes a connecting part connected to the fastener to be tested, and also includes a measuring part for testing the deformation of the fastener. The connecting part includes an upper connecting sleeve and a lower connecting sleeve, and the measuring part includes an upper extensometer and a lower extensometer. The measuring device of this application is convenient to use and has high precision. It can be used for conventional fasteners, such as those between specifications M3 - M16, and can be used for measuring the stress relaxation deformation of the whole under normal temperature and high temperature environments, which is close to the actual working conditions and can better meet the life design and safety factor considerations in engineering practice applications. In addition, for aerospace fasteners, testing the whole fastener is more conducive to reducing the testing cost of enterprises, alleviating the economic burden of enterprises, and creating greater value for enterprises.

Description

Technical Field

[0001] This application relates to the technical field of mechanical property testing, in particular to a stress relaxation deformation testing device for fasteners and its testing method. Background Art

[0002] Fasteners are a type of mechanical parts used for fastening connections. With the development of aerospace and industrial gas turbines, etc., superalloys are widely used in these fields, and various superalloy fasteners (bolts, nuts, screws, etc.) are thus put into use in large quantities. During the use of fasteners, the loosening or even detachment of the connection will affect the normal operation of engines and gas turbines, and may even lead to catastrophic accidents. When a fastener fails, it will loosen or even break, and one of the main reasons for its fracture is the detachment of the fastener, resulting in stress relaxation.

[0003] In addition, in many devices in the fields of thermal power generation and nuclear power, the connections of bolts used as fasteners often bear relatively high working temperatures, so stress relaxation will also occur during long-term operation. The occurrence of stress relaxation will cause the residual stress of the bolts in use to continuously decrease. When the residual stress decreases to less than the minimum sealing stress required for fastener connection, it will cause seal failure and result in air leakage, oil leakage, etc., posing major safety hazards. Therefore, it is very necessary to conduct stress relaxation tests on fasteners under normal or high-temperature environments.

[0004] Currently, there is no stress relaxation testing device specifically designed for fasteners, and at present, stress relaxation tests are mainly carried out on samples of raw materials, and there is a gap between the actual data obtained and the actual use conditions. Summary of the Invention

[0005] In view of the technical problems existing in the prior art, for this purpose, this application proposes a stress relaxation deformation testing device specifically designed for fasteners and its testing method.

[0006] On the one hand, the present application proposes a test device for stress relaxation deformation of fasteners. The test device includes a connecting part 2 connected to the fastener 1 to be tested, and further includes a measuring part 3 for measuring the deformation of the fastener; the connecting part 2 includes an upper connecting sleeve 21 and a lower connecting sleeve 22. The top of the upper connecting sleeve 21 is connected to a stud and fixed by threadedly connecting with a first fixed pull rod 23 through the stud. The bottom of the lower connecting sleeve 22 is connected to a stud and fixed by threadedly connecting with a second fixed pull rod 24 through the stud. A first through groove 211 penetrating left and right is opened in the center of the upper connecting sleeve 21, and a first groove 212 is recessed on one side of the lower part of the upper connecting sleeve 21. A second through groove 221 penetrating left and right is opened in the center of the lower connecting sleeve 22, and a second groove 222 is recessed on one side of the upper part of the lower connecting sleeve 22. The first through groove 211, the first groove 212, the second groove 222, and the second through groove 221 of the upper connecting sleeve 21 and the lower connecting sleeve 22 accommodate the fastener 1; the measuring part 3 includes an upper extensometer 31 and a lower extensometer 32 in a gate shape. The upper extensometer 31 passes through the first through groove 211 and is connected to one end of the fastener 1, and the lower extensometer 32 passes through the second through groove 221 and is connected to the other end of the fastener 1. The lower extensometer 32 moves up and down along the second fixed pull rod 24.

[0007] Specifically, the upper extensometer 31 includes a first left rod 312 and a first right rod 314 on the right side. The top of the first left rod 312 is screwed to a first upper cross beam 311 through a first fixing bolt 4, and the top of the first right rod 314 is also screwed to a second upper cross beam 313 through the first fixing bolt 4. The first upper cross beam 311 and the second upper cross beam 313 are fixedly connected with a front-back dislocation, and a first upper screw hole 315 penetrating up and down is opened at the overlapping center of the two.

[0008] Specifically, the lower extensometer 32 includes a second left rod 322 and a second right rod 324. The top of the second left rod 322 is connected to a first lower cross beam 321 through a first fixing bolt 4, and the top of the second right rod 324 is also connected to a second lower cross beam 323 through the first fixing bolt 4. The second lower cross beam 323 and the first lower cross beam 321 are in front-back dislocation fit, and a second lower screw hole 325 penetrating up and down is opened at the overlapping center of the two.

[0009] Specifically, the bottom of the first left rod 312 is screwed to a first upper positioning rod 316 through a second fixing bolt 5, and the bottom of the first right rod 314 is also screwed to a second upper positioning rod 317 through the second fixing bolt 5; the bottom of the second left rod 322 is connected to a first lower positioning rod 326, and the bottom of the second right rod 324 is connected to a second lower positioning rod 327.

[0010] Specifically, the first upper positioning rod 316 and the second upper positioning rod 317 respectively protrude inward from the gable of the upward extensometer 31, and the protruding ends are respectively connected with a first left positioning wheel 318 and a first right positioning wheel 319, and the first left positioning wheel 318 and the first right positioning wheel 319 are displaced front and back; the first lower positioning rod 326 and the second lower positioning rod 327 respectively protrude inward from the gable of the downward extensometer 32, and the protruding ends are respectively connected with a second left positioning wheel 329 and a second right positioning wheel 328, and the second right positioning wheel 328 and the second left positioning wheel 329 are displaced front and back. The first left positioning wheel 318 and the second right positioning wheel 328 are in the front plane and slide along both sides of the second fixed pull rod 24, and the first right positioning wheel 319 and the second left positioning wheel 329 are in the rear plane and slide along both sides of the second fixed pull rod 24.

[0011] Specifically, an elastic first deformation measuring ruler 6 is provided at the other end of the first lower positioning rod 326 relative to the second left positioning wheel 329, and an elastic second deformation measuring ruler 7 is provided at the other end of the second lower positioning rod 327 relative to the second right positioning wheel 328.

[0012] Specifically, the first fixing bolt 4 is a high-temperature bolt resistant to 300°C - 1100°C.

[0013] On the other hand, the present application also proposes a method for testing the stress relaxation deformation of fasteners. Using the testing device as described above, the method includes:

[0014] S1) Preparation of fastener samples and machining at both ends. Positioning holes are first machined at the head and bottom of the fastener (1), and the positioning holes can be fixedly connected by threads with the first upper screw hole (315) and the second lower screw hole (325) through studs.

[0015] S2) Installation of the test tooling and preparation of the test equipment. The upper connecting sleeve (21) is screwed and fixed to the first fixed pull rod (23), the lower connecting sleeve (22) is screwed and fixed to the second fixed pull rod (24), the cross beam of the upper extensometer (31) passes through the first through slot (211), the cross beam of the lower extensometer (32) passes through the second through slot (221), the fastener (1) is placed in the first through slot (211), the first groove (212), the second groove (222), and the second through slot (221), and the cross beam of the upper extensometer (31) is fixed to the head of the fastener (1) through a stud, and the cross beam of the lower extensometer (32) is fixed to the bottom of the fastener (1) through a stud.

[0016] S3) Install the deformation measuring ruler and adjust the overall coaxiality. Install the first deformation measuring ruler (6) at the left end of the first lower positioning rod (326), install the second deformation measuring ruler (7) at the right end of the second lower positioning rod (327), adjust the length of the measuring rulers so that the tops of the two measuring rulers are respectively in contact with the first upper positioning rod (316) and the second upper positioning rod (317), and through force value preloading, observe and adjust the synchronous growth of the left and right deformation measuring rulers during the loading process;

[0017] S4) Set the test plan and conduct the stress relaxation test: After the test starts, as the force value acting on the second fixed pull rod (24) increases, the lower extensometer (32) will slide downward, thereby triggering data changes in the left and right deformation measuring rulers;

[0018] S5) Collect the stress value changes within the specified temperature and time: The measuring ruler will collect the time and force value change data through computer software;

[0019] S6) Calculate the stress relaxation coefficient according to the force value decay: Calculate the stress relaxation coefficient according to the collected force value and time data;

[0020] S7) Fit the stress relaxation coefficient-time curve: Qualitatively judge the stress relaxation resistance performance of the fastener.

[0021] Particularly, when studying the stress relaxation at a certain temperature, in S4), after the sample to be tested, the tooling and the deformation measuring device are fixed as a whole, a certain preload is applied on the testing machine, and the high-temperature furnace is closed; heating is carried out using a high-temperature temperature control system connected to the equipment. The high-temperature temperature control system includes a high-temperature furnace, an S-type thermocouple, and a temperature controller. The heating power can be adjusted at any time during the heating process to achieve precise temperature control. After reaching the heating temperature, keep the temperature for a fixed time

[0022] On the basis of conforming to the common knowledge in the field, the above preferred conditions can be combined arbitrarily to obtain the preferred examples of the present application.

[0023] The above technical solutions have the following advantages or beneficial effects: The measuring device of the present application is convenient to use and has high precision. It can be used for measuring the stress relaxation deformation of the whole conventional fasteners (with specifications between M3 - M16) under normal temperature and high-temperature environments, which is close to the actual working conditions and can better meet the life design and safety factor considerations in engineering practice applications. In addition, for aerospace fasteners, conducting tests on the whole fasteners is more conducive to reducing the testing cost of enterprises, reducing the economic burden on enterprises, and creating greater value for enterprises. Description of the Drawings

[0024] To more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, for those skilled in the art, without creative efforts, other drawings can also be obtained based on the provided drawings.

[0025] Figure 1 It is a schematic structural diagram of a fastener stress relaxation deformation test device according to an embodiment of the present application.

[0026] Figure 2 It is a schematic structural diagram of the connection between the fastener and the connecting part of the fastener stress relaxation deformation test device according to an embodiment of the present application.

[0027] Figure 3 It is a (A) front view schematic diagram, (B) left view schematic diagram, and (C) top view schematic diagram of the upper connecting sleeve of the fastener stress relaxation deformation test device according to an embodiment of the present application.

[0028] Figure 4 It is a left view schematic diagram of the lower connecting sleeve of the fastener stress relaxation deformation test device according to an embodiment of the present application.

[0029] Figure 5 It is a schematic structural diagram of the measuring part of the fastener stress relaxation deformation test device according to an embodiment of the present application.

[0030] Figure 6 It is a schematic structural diagram of the crossbeam of the upper extensometer of the measuring part of the fastener stress relaxation deformation test device according to an embodiment of the present application.

[0031] Figure 7 It is a schematic structural diagram of the crossbeam of the lower extensometer of the measuring part of the fastener stress relaxation deformation test device according to an embodiment of the present application.

[0032] Figure 8 It is a schematic flow diagram of the usage method of the fastener stress relaxation deformation test device according to an embodiment of the present application.

[0033] Figure 9 It is a stress relaxation coefficient - time curve obtained from the fastener stress relaxation deformation test device according to an embodiment of the present application.

[0034] Among them, 1 - fastener; 2 - connecting part; 21 - upper connecting sleeve; 211 - first through groove; 212 - first groove; 22 - lower connecting sleeve; 221 - second through groove; 222 - second groove; 23 - first fixed pull rod; 24 - second fixed pull rod; 3 - measuring part; 31 - upper extensometer; 311 - first upper cross beam; 312 - first left side rod; 313 - second upper cross beam; 314 - first right side rod; 315 - first upper screw hole; 316 - first upper positioning rod; 317 - second upper positioning rod; 318 - first left positioning wheel; 319 - first right positioning wheel; 32 - lower extensometer; 321 - first lower cross beam; 322 - second left side rod; 323 - second lower cross beam; 324 - second right side rod; 325 - second lower screw hole; 326 - first lower positioning rod; 327 - second lower positioning rod; 328 - second right positioning wheel; 329 - second left positioning wheel; 4 - first fixing bolt; 5 - second fixing bolt; 6 - first deformation measuring ruler; 7 - second deformation measuring ruler. Specific embodiments

[0035] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, and are intended to explain the inventive concept. All other embodiments obtained by those skilled in the art based on the embodiments of the present application without creative efforts shall fall within the protection scope of the present application.

[0036] The orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "axial", "radial", "circumferential", etc. used in the description is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the purpose of simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation.

[0037] The terms "first", "second", etc. used in the description are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. The meaning of the term "plurality" is two or more, unless otherwise specifically defined clearly.

[0038] Unless otherwise clearly defined and limited, the terms "connected", "communicated", etc. used in the description should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection, an electrical connection; it can be directly connected, indirectly connected through an intermediate medium; it can be the communication inside two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments can be understood according to specific situations.

[0039] Unless otherwise clearly defined and limited, the first feature being "above", "below", or "on" the second feature can be that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature being "above", "over", or "on" the second feature can be that the first feature is directly above or obliquely above the second feature, or simply means that the first feature has a higher horizontal height than the second feature. The first feature being "below", "beneath", or "under" the second feature can be that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature being "below", "beneath", or "under" the second feature can be that the first feature is directly below or obliquely below the second feature, or simply means that the first feature has a lower horizontal height than the second feature.

[0040] Reference Figure 1 , this application proposes a fastener stress relaxation deformation test device. The test device includes a connection part 2 for connecting and fixing with the fastener 1, and further includes a measurement part 3 for measuring the deformation of the fastener. The connection part 2 includes an upper connection sleeve 21 and a lower connection sleeve 22, and the measurement part 3 includes an upper extensometer 31 and a lower extensometer 32.

[0041] Reference Figure 2 , Figure 3 and Figure 4 , the top of the upper connection sleeve 21 is connected to a stud, and is fixedly connected to the first fixed pull rod 23 through the stud by threading. The bottom of the lower connection sleeve 22 is similarly connected to a stud, and is fixedly connected to the second fixed pull rod 24 through the stud by threading. A first through groove 211 that penetrates left and right is opened in the center of the upper connection sleeve 21, and a first groove 212 is recessed on one side of the lower part of the upper connection sleeve 21. A second through groove 221 that penetrates left and right is opened in the center of the lower connection sleeve 22, and a second groove 222 is recessed on one side of the upper part of the lower connection sleeve 22. The first through groove 211, the first groove 212, the second groove 222, and the second through groove 221 of the upper connection sleeve 21 and the lower connection sleeve 22 can be combined into a space for accommodating the fastener 1 to be tested.

[0042] Reference Figure 5 , Figure 6 and Figure 7, the upper stretching member 31 is in the shape of a door frame, including a first left rod 312 on the left and right sides and a first right rod 314 on the right side. The top of the first left rod 312 is screwed to the first upper cross beam 311 by a first fixing bolt 4 resistant to high temperatures of 300°C - 1100°C, and the bottom of the first left rod 312 is screwed to the first upper positioning rod 316 by a second fixing bolt 5. The top of the first right rod 314 is also screwed to the second upper cross beam 313 by the first fixing bolt 4, and the bottom of the first right rod 314 is also screwed to the second upper positioning rod 317 by the second fixing bolt 5. The first upper cross beam 311 and the second upper cross beam 313 are fixedly connected with a front-back dislocation, and a first upper screw hole 315 penetrating up and down is opened at the center where they overlap. The first upper positioning rod 316 and the second upper positioning rod 317 respectively protrude into the frame of the upper stretching member 31, and the protruding ends are respectively connected with a first left positioning wheel 318 and a first right positioning wheel 319, and the first left positioning wheel 318 and the first right positioning wheel 319 are dislocated front and back.

[0043] Similarly, the lower stretching member 32 is also in the shape of a door frame, including a second left rod 322 on the left side and a second right rod 324 on the right side. The top of the second left rod 322 is connected to the first lower cross beam 321 by a first fixing bolt 4, and the bottom of the second left rod 322 is connected to the first lower positioning rod 326. The top of the second right rod 324 is connected to the second lower cross beam 323 by a first fixing bolt 4, and the bottom of the second right rod 324 is connected to the second lower positioning rod 327. The second lower cross beam 323 and the first lower cross beam 321 are matched with a front-back dislocation, and a second lower screw hole 325 penetrating up and down is opened at the center where they overlap. The first lower positioning rod 326 and the second lower positioning rod 327 respectively protrude into the frame of the lower stretching member 32, and the protruding ends are respectively connected with a second left positioning wheel 329 and a second right positioning wheel 328. Elastic first deformation measuring rulers 6 and second deformation measuring rulers 7 are respectively provided at the opposite ends of the positioning wheels, and the second right positioning wheel 328 and the second left positioning wheel 329 are dislocated front and back. The first left positioning wheel 318 and the second right positioning wheel 328 are in the front plane and slide along both sides of the second fixed pull rod 24, and the first right positioning wheel 319 and the second left positioning wheel 329 are in the rear plane and slide along both sides of the second fixed pull rod 24.

[0044] The assembly and use methods of the fastener stress relaxation deformation testing device of the present application are as follows: (S1) Preparation of the fastener sample and machining of both ends: Positioning holes are first machined into the head and base of the fastener 1. These positioning holes can be threadedly engaged with the first upper screw hole 315 and the second lower screw hole 325 via studs. (S2) Installation of the test fixture and preparation of the test equipment: The upper connecting sleeve 21 is screwed to the first fixing rod 23, and the lower connecting sleeve 22 is screwed to the second fixing rod 24. The crossbeam of the upper extension member 31 is passed through the first through-slot 211, and the crossbeam of the lower extension member 32 is passed through the second through-slot 221. The fastener 1 is placed in the first through-slot 211, the first groove 212, the second groove 222, and the second through-slot 221. The crossbeam of the upper extension member 31 is secured to the head of the fastener 1 via studs, and the crossbeam of the lower extension member 32 is secured to the base of the fastener 1 via studs. (S3) Installing the deformation measuring scales and adjusting overall coaxiality: Install the first deformation measuring scale 6 on the left end of the first lower positioning rod 326, and the second deformation measuring scale 7 on the right end of the second lower positioning rod 327. Adjust the length of the measuring scales so that the top ends of the two measuring scales abut the first upper positioning rod 316 and the second upper positioning rod 317, respectively. (S4) Set up the test plan and conduct a stress relaxation test: After the test begins, as the force acting on the second fixed tie rod 24 increases, the lower extension member 32 will slide downward, triggering changes in the data of the left and right deformation measuring scales. When studying stress relaxation at a certain temperature, first, after the test sample, the fixture, and the deformation measuring device are all fixed, a certain preload is applied to the testing machine, and the high-temperature furnace is closed. Next, heating is performed using a high-temperature temperature control system connected to the equipment (including a high-temperature furnace, S-type thermocouple, temperature controller, etc.). The heating power can be adjusted at any time during the heating process to achieve precise temperature control. Finally, after reaching the heating temperature, the temperature is maintained for a fixed time. (S5) Collecting stress changes over a specified temperature and time: The measuring tape uses computer software to collect time and force change data. (S6) Calculating the stress relaxation coefficient based on force decay: Based on the collected force and time data, the stress relaxation coefficient (relaxation rate) is calculated. (S7) Fitting a stress relaxation coefficient-time curve: Qualitatively assessing the fastener's stress relaxation resistance. Example 1

[0045] This device was used to test the stress relaxation coefficient of an M10 fastener under conditions of a constant temperature of 450°C, a stress of 200 MPa, and a test time of 50 hours. The specific operating process includes (S1) fastener sample preparation and end machining: The fastener to be tested is fixed on a CNC lathe, and the head and bottom of the fastener are first turned flat, followed by machining center locating holes at both ends.

[0046] (S2)Installation of test tooling and preparation of test equipment: Connect and fix the upper connecting sleeve of this application to the upper fixed pull rod, and connect and fix the lower connecting sleeve to the lower fixed pull rod. Fix the cross beam of the upper extensometer to the head of the fastener through a stud, and fix the cross beam of the lower extensometer to the part of the fastener through a stud.

[0047] (S3)Install the deformation measuring ruler and adjust the overall coaxiality: Install the first deformation measuring ruler at the left end of the first lower positioning rod, and install the second deformation measuring ruler at the right end of the second lower positioning rod. Adjust the length of the measuring ruler so that the tops of the two measuring rulers are respectively in contact with the first upper positioning rod and the second upper positioning rod. Perform a preloading of a force value of 500N - 1000N through the manual control box of the existing equipment, and observe whether the left and right deformation measuring rulers increase synchronously. If they do not increase synchronously, check the installed components and make fine adjustments until the left and right deformation measuring rulers increase synchronously during the loading process.

[0048] (S4)Set the test plan and conduct the stress relaxation test: After fixing the sample to be tested, the tooling, and the deformation measuring device as a whole, apply a certain preload on the testing machine, close the high-temperature furnace, and use the high-temperature temperature control system (including the high-temperature furnace, S-type thermocouple, temperature controller, etc.) connected to the equipment for heating. Set the target temperature to 450°C, and the heating power can be adjusted at any time during the heating process to achieve precise temperature control. After reaching the heating temperature, keep it warm for a fixed time of 60 minutes. At the same time, as the force value acting on the second fixed pull rod increases, the lower extensometer will slide downwards, thereby triggering data changes in the left and right deformation measuring rulers.

[0049] (S5)Collect the stress numerical changes within the specified temperature and time: During the test, the test software supporting the existing equipment will collect the data of time and force value changes, and the data collected by the deformation measuring ruler during the process will also be collected through computer software.

[0050] (S6)Calculate the stress relaxation coefficient: After the test, export the test data (force value, time, deformation, etc.), and calculate the stress relaxation coefficient (relaxation rate) according to the force value attenuation and the collected force value and time data.

[0051] (S7)Fit the stress relaxation coefficient - time curve: According to the calculated stress relaxation coefficient, draw the Figure 9 stress relaxation coefficient - time curve shown. The abscissa of this curve is time (h), and the ordinate is the stress relaxation coefficient (%). According to this curve, the anti-stress relaxation performance of the fastener can be qualitatively judged.

[0052] Although the embodiments of the present application have been shown and described above, it is understood that the above embodiments are illustrative and should not be construed as limiting the present application. Various changes and modifications may be made to the present application without departing from the spirit and scope of the present application, and such changes and modifications fall within the scope of the present application for which protection is sought.

Claims

1. A fastener stress relaxation deformation test device, characterized in that: The test device includes a connecting part (2) connected to the fastener to be tested (1), and also includes a measuring part (3) for measuring the deformation of the fastener; the connecting part (2) includes an upper connecting sleeve (21) and a lower connecting sleeve (22). The top of the upper connecting sleeve (21) is connected to a stud, and is fixed by screwing with a first fixed pull rod (23) through the stud. The bottom of the lower connecting sleeve (22) is connected to a stud, and is fixed by screwing with a second fixed pull rod (24) through the stud. A first through groove (211) penetrating left and right is formed in the center of the upper connecting sleeve (21), and a first groove (212) is recessed on one side of the lower part of the upper connecting sleeve (21). A second through groove (221) penetrating left and right is formed in the center of the lower connecting sleeve (22), and a second groove (222) is recessed on one side of the upper part of the lower connecting sleeve (22). The first through groove (211), the first groove (212), the second groove (222), and the second through groove (221) of the upper connecting sleeve (21) and the lower connecting sleeve (22) accommodate the fastener (1); the measuring part (3) includes an upper extensometer (31) and a lower extensometer (32) in a gate shape. The upper extensometer (31) passes through the first through groove (211) and is connected to one end of the fastener (1). The lower extensometer (32) passes through the second through groove (221) and is connected to the other end of the fastener (1). The lower extensometer (32) moves up and down along the second fixed pull rod (24); the upper extensometer (31) includes a first left rod (312) and a first right rod (314) on the right side. The top of the first left rod (312) is screwed to a first upper cross beam (311) through a first fixing bolt (4). The top of the first right rod (314) is also screwed to a second upper cross beam (313) through a first fixing bolt (4). The first upper cross beam (311) and the second upper cross beam (313) are fixedly connected with a front-back dislocation, and a first upper screw hole (315) penetrating up and down is formed at the coincident center of the two; the lower extensometer (32) includes a second left rod (322) and a second right rod (324). The top of the second left rod (322) is connected to a first lower cross beam (321) through a first fixing bolt (4). The top of the second right rod (324) is also connected to a second lower cross beam (323) through a first fixing bolt (4). The second lower cross beam (323) and the first lower cross beam (321) are in front-back dislocation fit, and a second lower screw hole (325) penetrating up and down is formed at the coincident center of the two; the bottom of the first left rod (312) is screwed to a first upper positioning rod (316) through a second fixing bolt (5). The bottom of the first right rod (314) is also screwed to a second upper positioning rod (317) through a second fixing bolt (5); the bottom of the second left rod (322) is connected to a first lower positioning rod (326). The bottom of the second right rod (324) is connected to a second lower positioning rod (327).

2. The fastener stress relaxation deformation test device according to claim 1, wherein: The first upper positioning rod (316) and the second upper positioning rod (317) respectively protrude inward in a U-shape from the upward extension member (31), and the protruding ends are respectively connected with a first left positioning wheel (318) and a first right positioning wheel (319). The first left positioning wheel (318) and the first right positioning wheel (319) are offset front and back; the first lower positioning rod (326) and the second lower positioning rod (327) respectively protrude inward in a U-shape from the downward extension member (32), and the protruding ends are respectively connected with a second left positioning wheel (329) and a second right positioning wheel (328). The second right positioning wheel (328) and the second left positioning wheel (329) are offset front and back. The first left positioning wheel (318) and the second right positioning wheel (328) are in a front plane and slide along both sides of the second fixed pull rod (24), and the first right positioning wheel (319) and the second left positioning wheel (329) are in a rear plane and slide along both sides of the second fixed pull rod (24).

3. The fastener stress relaxation deformation test device according to claim 2, characterized in that: An elastic first deformation measuring ruler (6) is provided at the other end of the first lower positioning rod (326) relative to the second left positioning wheel (329), and an elastic second deformation measuring ruler (7) is provided at the other end of the second lower positioning rod (327) relative to the second right positioning wheel (328).

4. The fastener stress relaxation deformation test device according to claim 1, wherein: The first fixing bolt (4) is a high-temperature bolt resistant to 300°C - 1100°C.

5. A method for testing the stress relaxation deformation of fasteners, characterized in that: Using the test device as described in claim 3, the method includes: S1) Preparation of the fastener sample and machining at both ends. Positioning holes are first machined at the head and bottom of the fastener (1), and the positioning holes can be fixedly connected by threads with the first upper screw hole (315) and the second lower screw hole (325) through studs. S2) Installation of the test tooling and preparation of the test equipment. The upper connecting sleeve (21) is fixedly connected by threads with the first fixed pull rod (23), the lower connecting sleeve (22) is fixedly connected by threads with the second fixed pull rod (24), the cross beam of the upper extension member (31) passes through the first through groove (211), the cross beam of the lower extension member (32) passes through the second through groove (221), the fastener (1) is placed in the first through groove (211), the first groove (212), the second groove (222), and the second through groove (221), and the cross beam of the upper extension member (31) is fixed to the head of the fastener (1) through a stud, and the cross beam of the lower extension member (32) is fixed to the bottom of the fastener (1) through a stud. S3) Installation of the deformation measuring ruler and adjustment of the overall coaxiality. The first deformation measuring ruler (6) is installed at the left end of the first lower positioning rod (326), the second deformation measuring ruler (7) is installed at the right end of the second lower positioning rod (327), the lengths of the measuring rulers are adjusted so that the tops of the two measuring rulers respectively abut against the first upper positioning rod (316) and the second upper positioning rod (317), and through force value preloading, observe and adjust the synchronous growth of the left and right deformation measuring rulers during the loading process. S4) Set the test plan and conduct a stress relaxation test: After the test starts, as the force value acting on the second fixed pull rod (24) increases, the lower extension member (32) will slide downward, thereby triggering data changes in the deformation measuring rulers on both the left and right sides. S5) Collect the change in stress values within the specified temperature and time: The measuring ruler will collect the data of the change in time and force values through computer software; S6) Calculate the stress relaxation coefficient based on the force value decay: Calculate the stress relaxation coefficient according to the collected force value and time data; S7) Fit the stress relaxation coefficient-time curve: Qualitatively judge the stress relaxation resistance performance of the fastener.

6. The fastener stress relaxation deformation test method according to claim 5, characterized in that: When studying the stress relaxation at a certain temperature, in S4), after the sample to be tested, the tooling and the deformation measuring device are fixed as a whole, a certain preload is applied on the testing machine, and the high-temperature furnace is closed; Heating is carried out using a high-temperature temperature control system connected to the equipment. The high-temperature temperature control system includes a high-temperature furnace, an S-type thermocouple, and a temperature controller. The heating power can be adjusted at any time during the heating process to achieve precise temperature control. After reaching the heating temperature, keep the temperature constant for a fixed time.

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