A set of fixtures for measuring the stiffness of metal bellows expansion joints and their assembly structures

Abstract

A set of fixtures for measuring the stiffness of metal bellows expansion joints and their assembly structures relates to the field of fixture technology. It includes a fixed end fixture and a movable end fixture. The movable end fixture includes a fixture body, a connecting column, a nozzle elbow, and a fixed clamp. The fixture body has a first workpiece flange connection hole. The connecting column has a first connection hole and first planes on both sides. The exposed end of the nozzle elbow is internally threaded. The middle section in the thickness direction of the fixed clamp is in the same plane as the middle section in the thickness direction of the fixture body. The fixed end fixture includes a fixture body and a connecting column. The fixture body has a second workpiece flange connection hole. The connecting column has a second connection hole and second planes on both sides. The present invention achieves the use of only one set of fixtures to simultaneously meet the stiffness measurement test conditions of the metal bellows expansion joint and its assembly structure with or without axial and lateral pressure, thereby reducing costs.

Description

Technical Field

[0001] The invention belongs to the technical field of fixtures, and in particular relates to a fixture used for a universal testing machine to measure the axial and lateral stiffness of a metal bellows expansion joint and its assembly structure with or without pressure. Background Art

[0002] The axial and lateral stiffness measurement experiment of metal bellows expansion joints and their assembly structures with or without pressure is to measure the axial tension / compression stiffness and lateral stiffness of the metal bellows expansion joints and their assembly structures under specific internal pressure conditions. It is required to maintain a specific air pressure in the workpiece during the measurement process, and to perform axial tension, compression or lateral movement at the same time, and measure the load-displacement curve.

[0003] The axial stiffness K of the metal bellows expansion joint and its assembly structure is defined as shown in formula (1):

[0004] K=F / δ (1)

[0005] Where F is the applied load and δ is the displacement of the metal bellows expansion joint and its assembly structure under the action of axial load.

[0006] Transverse stiffness K of metal bellows expansion joint and its assembly structure y The definition is shown in formula (2):

[0007] K y =F y / y (2)

[0008] where F y is the load applied in the y direction perpendicular to the axial direction, and y is the displacement of the metal bellows expansion joint and its assembly structure under the action of the y direction load.

[0009] The universal force testing machine is a testing machine commonly used for mechanical property tests such as tension, compression, bending, shearing, tearing, and peeling of materials. The operation method is to assemble the workpiece with a specific fixture, and then assemble it as a whole with the universal force testing machine. By controlling the crossbeam of the universal force testing machine, the workpiece is stretched and compressed to obtain the corresponding load-displacement curve.

[0010] At present, the axial tensile and compressive stiffness of general metal standard size bars and other workpieces are usually measured using a universal testing machine. The stiffness of the workpiece is obtained through the interaction between the workpiece and the crossbeam of the universal testing machine. However, due to the lack of matching fixtures and the fact that the universal testing machine only moves in the longitudinal reciprocating direction, it is difficult to measure the lateral stiffness using a universal testing machine.

[0011] There is currently no suitable fixture for measuring the axial and lateral stiffness of metal bellows expansion joints and their assembly structures with or without pressure. The existing fixtures have the following main disadvantages:

[0012] 1. Conventional fixtures used for tensile testing are often used to clamp general metal standard size bars, pipes, and plates, such as Φ10mm*55mm round bars. The size range of the workpiece being clamped (such as diameter, thickness, etc.) is usually 0-14mm. The metal bellows expansion joint and its assembled structure specimens can be approximately regarded as hollow cylinders with a diameter usually above 30mm, which cannot be clamped by general fixtures.

[0013] 2. Conventional fixtures used for tension / compression experiments do not have reserved air inlet holes and sealing designs, making it impossible to inflate and pressurize the interior of the workpiece, and unable to measure the axial and lateral pressure stiffness of the metal bellows expansion joint and its assembly structure.

[0014] 3. If there is no suitable fixture, the universal testing machine can be used to measure the lateral stiffness of the metal bellows expansion joint and its assembly structure.

[0015] 4. Since the connection between the universal testing machine and the fixture requires high precision and tight assembly, the existing commonly used fixture connection column designs are all complete and uniform cylinders, the processing accuracy of the matching surface is high, and the assembly is often not smooth. Summary of the invention

[0016] The purpose of the present invention is to provide a set of fixtures for measuring the axial and lateral stiffness of metal bellows expansion joints and their assembly structures with or without pressure by a universal force testing machine, so as to solve the problems existing in the fixtures of the universal force testing machine in the above-mentioned background technology. Only one set of fixtures is used, and the test conditions for measuring the axial and lateral stiffness of metal bellows expansion joints and their assembly structures with or without pressure can be met at the same time, thereby reducing costs.

[0017] To achieve the above-mentioned purpose, the technical solution provided by the present invention is: a set of tooling fixtures for measuring the axial and lateral stiffness of metal bellows expansion joints and their assembly structures with or without pressure using a universal testing machine, characterized in that the fixtures include two independent parts, namely a fixed end fixture and a movable end fixture.

[0018] The mobile end fixture comprises a mobile end fixture body (1), a mobile end fixture connecting column (3), a gas nozzle elbow (6), and a fixed clamp (7);

[0019] The movable end fixture body (1) is a disc structure, a plurality of first workpiece flange connection holes (2) are provided on the movable end fixture body (1), and the bottom roughness of the movable end fixture body (1) is required to be no greater than 3.2.

[0020] The mobile end fixture connection column (3) is coaxially located at the center of the upper surface of the mobile end fixture body (1), and two first planes (5) are provided on the upper part of both sides of the mobile end fixture connection column (3). A first connection hole (4) is provided on the side of the mobile end fixture connection column (3). The first connection hole (4) is a through hole, and the length direction or the center axis is perpendicular to the axial direction of the mobile end fixture connection column (3); the side surfaces of the mobile end fixture connection column (3) corresponding to the two sides of the first connection hole (4) are the first planes (5), and the two first planes (5) are parallel. The first plane (5) is a cross-sectional plane formed by removing the arc surface from the side surface of the mobile end fixture connection column (3), and the first plane (5) is parallel to the center axis of the mobile end fixture connection column (3) and the center axis of the first connection hole (4);

[0021] The movable end clamp body (1) is provided with an air nozzle elbow (6), which is a curved hollow tube structure; one end of the air nozzle elbow (6) is unthreaded, and the other end is internally threaded; a through hole is opened on the movable end clamp body (1), and the unthreaded end is inserted to form a tight connection with the movable end clamp body (1).

[0022] A fixed clamp (7) is provided on the side of the mobile clamp body (1), the thickness direction of the fixed clamp (7) is consistent with the axial direction of the mobile clamp body (1), and the axial direction of the mobile clamp body (1) is also the thickness direction of the mobile clamp body (1). The central section of the mobile clamp body (1) perpendicular to the thickness direction is coplanar with the central section of the fixed clamp (7) perpendicular to the thickness direction.

[0023] The fixed end clamp comprises a fixed end clamp body (8) and a fixed end clamp connecting column (10).

[0024] The fixed end clamp body (8) is a disc structure, and a plurality of second workpiece flange connection holes (9) are arranged on the fixed end clamp body (8), and the bottom roughness requirement is not greater than 3.2.

[0025] The fixed end clamp connection column (10) is coaxially located at the center position of the upper surface of the clamp body (8), and a second plane (12) is provided on the upper part of both sides of the fixed end clamp connection column (10). A second connection hole (11) is provided on the fixed end clamp connection column (10), and the second connection hole (11) is a through hole, and the length direction or the center axis is perpendicular to the axial direction of the fixed end clamp connection column (10); the side surfaces of the fixed end clamp connection column (10) corresponding to the two sides of the second connection hole (11) correspond to the second plane (12), and the two second planes (12) are parallel. The second plane (12) is a cross-sectional plane formed by removing the arc surface from the side surface of the fixed end clamp connection column (10), and the second plane (12) is parallel to the center axis of the fixed end clamp connection column (10) and the center axis of the second connection hole (11).

[0026] The present invention provides a set of fixtures for measuring the axial and lateral stiffness of metal bellows expansion joints and their assembly structures with or without pressure using a universal testing machine, which has the following beneficial effects:

[0027] (1) This set of fixtures can be used to clamp the conventional tensile fixture and fixed clamp of the universal testing machine, realizing the measurement experiment of lateral stiffness with or without pressure, and the test process is simple.

[0028] (2) In the axial and lateral stiffness measurement test of metal bellows expansion joints and their assembly structures with or without pressure, the same set of fixtures can be used for tension, compression and lateral tests, reducing the number of fixtures and reducing costs.

[0029] (3) This fixture can be used to inflate and pressurize the workpiece (air pressure range: 0-1.5MPa) to ensure the test conditions. The upper end of the air nozzle elbow is pre-threaded, which can be easily connected to the air nozzle quick connector to inflate and pressurize the workpiece.

[0030] (4) This set of fixtures can simultaneously meet the requirements of tests for pressurizing or not pressurizing the metal bellows expansion joint and its assembly structure. If the nozzle elbow on the mobile end fixture is not connected to the air pipe quick connector or other equipment for air intake, the internal and external air pressures can be connected, meeting the requirements of the axial and lateral zero internal pressure stiffness measurement test of the metal bellows expansion joint and its assembly structure.

[0031] (5) Flat surfaces are provided on both sides of the connecting column of this set of clamps, which can allow air to be discharged smoothly during the clamping process, making the clamping smooth. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a three-dimensional view of the clamp structure of the present invention;

[0033] Figure 2 It is an assembly schematic diagram of the fixture of the present invention used to measure the axial compressive stiffness of the metal bellows expansion joint-net sleeve assembly structure;

[0034] Figure 3 It is a schematic diagram of the measurement process of the clamp of the present invention being used to measure the axial compressive stiffness of the metal bellows expansion joint-net sleeve assembly structure;

[0035] Figure 4 It is a schematic diagram of the process of using the fixture of the present invention to measure the transverse compression stiffness of the metal bellows expansion joint-net sleeve assembly structure;

[0036] Figure 5 It is a schematic diagram of the measurement process of the clamp of the present invention being used to measure the transverse compressive stiffness of the metal bellows expansion joint-net sleeve assembly structure;

[0037] In the figure: 1. The main body of the movable end fixture; 2. The first workpiece flange connection hole; 3. The connecting column of the movable end fixture; 4. The first connection hole; 5. The first plane; 6. The nozzle elbow; 7. The fixed clamp; 8. The main body of the fixed end fixture; 9. The second workpiece flange connection hole; 10. The connecting column of the fixed end fixture; 11. The second connection hole; 12. The second plane; 13. The metal bellows expansion joint-net sleeve assembly structure workpiece; 14. The upper end flange of the metal bellows expansion joint-net sleeve assembly structure workpiece; 15. The lower end flange of the metal bellows expansion joint-net sleeve assembly structure workpiece; 16. The sealing gasket; 17. The bolt; 18. The air pipe quick connector; 19. The air pipe; 20. The bottom fixing column of the universal capacity testing machine; 21. The universal capacity 1. Connecting hole at the fixed end of the testing machine; 2. Connecting pin at the fixed end of the universal testing machine; 2. Movable crossbeam of the universal testing machine; 2. Fixed column at the mobile end of the universal testing machine; 2. Fixed connecting hole at the mobile end of the universal testing machine; 2. Connecting pin at the mobile end of the universal testing machine; 2. Special fixture for lateral stiffness test; 2. Fixed column for special fixture for lateral stiffness test; 2. Connecting hole of special fixture for lateral stiffness test; 3. Connecting pin for special fixture for lateral stiffness test; 3. Conventional tensile fixture of universal testing machine; 3. Connecting column for conventional tensile fixture of universal testing machine; 3. Connecting hole of conventional tensile fixture of universal testing machine; 3. Fastening handle of conventional tensile fixture of universal testing machine. DETAILED DESCRIPTION

[0038] The technical scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings in the patent embodiment of the present invention.

[0039] like Figure 1 As shown, a set of fixtures for measuring the axial and lateral stiffness of metal bellows expansion joints and their assembly structures with or without pressure using a universal testing machine is mainly characterized in that it includes two separate parts, namely a fixed end fixture and a movable end fixture.

[0040] The mobile end fixture comprises a mobile end fixture body 1 , a mobile end fixture connecting column 3 , an air nozzle elbow 6 , and a fixed clamp 7 .

[0041] The mobile end fixture body 1 is evenly provided with first workpiece flange connection holes 2, which can be reliably assembled with the flange holes on the metal bellows expansion joint and its assembly structure through bolts. The bottom roughness of the mobile end fixture body 1 is required to be no more than 3.2, and it can be better combined with the sealing gasket during use, with good air tightness.

[0042] The mobile end clamp connecting column 3 is located in the middle of the clamp body, perpendicular to the mobile end clamp body 1, and a first connecting hole 4 is provided on the mobile end clamp connecting column 3, which is convenient for assembly with the universal testing machine. There are first planes 5 on the upper parts of both sides of the mobile end clamp connecting column 3, which can make the air discharged smoothly during the clamping process, and the clamping is smooth, thereby improving work efficiency.

[0043] The air nozzle elbow 6 is hollow inside, and meets the demand for internal inflation and pressurization during the test of the metal bellows expansion joint and its assembly structure. One end of the air nozzle elbow 6 is unthreaded, and the other end is internally threaded. The internal thread facilitates its connection with the trachea quick-connect connector, optimizing the air path assembly time. A hole is opened on the mobile end fixture body 1, and the unthreaded end is inserted to form a tight connection with the fixture. The exposed threaded end of the air nozzle elbow 6 faces outward to avoid the influence of the assembly of the trachea and the components of the universal testing machine.

[0044] The middle section of the fixed clamp plate 7 along the thickness direction is in the same plane as the middle section of the movable end clamp body 1 along the thickness direction. During the lateral stiffness test, the fixed clamp plate is clamped with a conventional tensile clamp of a universal testing machine to change the moving direction of the top clamp and complete the lateral compression stiffness test.

[0045] The fixed end clamp comprises a fixed end clamp body 8 and a fixed end clamp connecting column 10 .

[0046] The fixed end clamp body 8 is evenly provided with second workpiece flange connection holes 9, which can be reliably assembled with the flange holes on the metal bellows expansion joint and its assembly structure through bolts. The bottom roughness of the fixed end clamp body 8 is required to be no more than 3.2, so it can be better combined with the sealing gasket during use and has good air tightness.

[0047] The fixed end clamp connecting column 10 is located in the middle of the clamp body, perpendicular to the fixed end clamp body 8, and a second connecting hole 11 is provided on the fixed end clamp connecting column 10, which is convenient for assembly with the universal testing machine. There are second planes 12 on the upper parts of both sides of the fixed end clamp connecting column 10, which can allow the air to be discharged smoothly during the clamping process, making the clamping smooth and improving work efficiency.

[0048] Figure 2 It is a schematic diagram of the assembly of the fixture of the present invention when measuring the axial compressive stiffness of the metal bellows expansion joint-mesh sleeve assembly structure.

[0049] First, place the sealing gasket 16 between the lower end flange 15 of the metal bellows expansion joint-mesh assembly structure workpiece and the fixed end fixture body 8, and use the bolt 17 to form a fastening connection with the corresponding workpiece flange connection hole left on the lower end flange 15 of the metal bellows expansion joint-mesh assembly structure workpiece through the second workpiece flange connection hole 9; insert the assembled whole downward into the bottom fixing column 20 of the universal capacity testing machine, align the second connection hole 11 with the fixed end connection hole 21 of the universal capacity testing machine, and insert the fixed end connection pin 22 of the universal capacity testing machine into the aligned hole to connect one end of the metal bellows expansion joint-mesh assembly structure workpiece 13 with the universal capacity testing machine.

[0050] Then, place the sealing gasket 16 between the upper end flange 14 of the metal bellows expansion joint-mesh assembly structure workpiece and the movable end fixture fixture body 1, and use the bolt 17 to form a fastening connection with the corresponding workpiece flange connection hole left on the upper end flange 14 of the metal bellows expansion joint-mesh assembly structure workpiece through the first workpiece flange connection hole 2; form a fastening connection between the air pipe quick connector 18 and the internal threaded end of the air nozzle elbow 6; adjust the movable crossbeam 23 of the universal capacity testing machine, so that the mobile end fixture connecting column 3 is inserted into the mobile end fixed column 24 of the universal capacity testing machine, align the mobile end fixed connection hole 25 of the universal capacity testing machine with the first connection hole 4, and insert the mobile end connecting pin 26 of the universal capacity testing machine to connect the other end of the metal bellows expansion joint-mesh assembly structure workpiece 13 with the universal capacity testing machine.

[0051] Finally, the pressure required for the experiment is charged into the metal bellows expansion joint-net sleeve assembly structure workpiece 13 through the air pipe 19 to complete the assembly.

[0052] Figure 3 The figure is a schematic diagram of the measuring process of the clamp of the present invention in measuring the axial compressive stiffness of the metal bellows expansion joint-mesh sleeve assembly structure.

[0053] The movable crossbeam 23 of the universal testing machine is controlled by a program to move upward or downward at a constant speed, and the workpiece is stretched or compressed, and the load-displacement curve is recorded, so as to obtain the axial stiffness of the metal bellows expansion joint-net sleeve assembly structure under pressure.

[0054] Figure 4 The present invention is a schematic diagram of the process of using the fixture of the present invention to measure the transverse compressive stiffness of a metal bellows expansion joint-mesh sleeve assembly structure.

[0055] First, place the sealing gasket 16 between the lower end flange 15 of the metal bellows expansion joint-mesh assembly structure workpiece and the fixed end fixture body 8, and use bolts 17 to form a fastening connection with the corresponding workpiece flange connection holes left on the lower end flange 15 of the metal bellows expansion joint-mesh assembly structure workpiece through the second workpiece flange connection hole 9; place the sealing gasket 16 between the upper end flange 14 of the metal bellows expansion joint-mesh assembly structure workpiece and the movable end fixture fixture body 1, and use bolts 17 to form a fastening connection with the upper end flange 14 of the metal bellows expansion joint-mesh assembly structure workpiece through the first workpiece flange connection hole 2 The corresponding workpiece flange connection holes left on it form a fastening connection; the air pipe quick-connect connector 18 is fastened to the internal threaded end of the air nozzle elbow 6; the assembled metal bellows expansion joint-mesh sleeve assembly structure workpiece fixed end fixture connecting column 10 is inserted into the fixed column 28 of the special fixture for transverse stiffness test, the second connecting hole 11 is aligned with the connecting hole 29 of the special fixture for transverse stiffness test, and the connecting pin 30 of the special fixture for transverse stiffness test is inserted into the aligned hole, so that one end of the metal bellows expansion joint-mesh sleeve assembly structure workpiece 13 is connected to the special fixture for transverse stiffness test.

[0056] Then, insert the universal capacity testing machine conventional tensile clamp connecting column 32 of the universal capacity testing machine conventional tensile clamp 31 into the universal capacity testing machine movable end fixed column 24, align the universal capacity testing machine movable end fixed connecting hole 25 with the universal capacity testing machine conventional tensile clamp connecting hole 33, insert the universal capacity testing machine movable end connecting pin 26 into the aligned connecting holes, so that the universal capacity testing machine conventional tensile clamp 31 is connected to the universal tensile machine movable beam 23.

[0057] Then adjust the position of the special fixing device for the lateral stiffness test so that the mobile end fixture fixing plate 7 is directly below the conventional tensile fixture 31 of the universal capacity testing machine, adjust the position of the movable beam 23 of the universal tensile machine so that the conventional tensile fixture 31 of the universal capacity testing machine clamps the mobile end fixture fixing plate 7, and turn the tightening handle 34 of the universal capacity testing machine so that the conventional tensile fixture 31 of the universal capacity testing machine forms a tightening connection with the mobile end fixture fixing plate 7.

[0058] Finally, the pressure required for the experiment is charged into the metal bellows expansion joint-net sleeve assembly structure workpiece 13 through the air pipe 19 to complete the assembly.

[0059] Figure 5 It is a schematic diagram of the measurement process of the clamp of the present invention being used to measure the transverse compressive stiffness of the metal bellows expansion joint-net sleeve assembly structure;

[0060] The movable crossbeam 23 of the universal capacity testing machine is controlled by a program to move downward at a constant speed, and the load-displacement curve is recorded, thereby obtaining the transverse stiffness (axial displacement x=0) of the metal bellows expansion joint-net sleeve assembly structure under pressure.

Claims

1. A set of fixtures for measuring the axial and lateral stiffness of metal bellows expansion joints and their assembly structures with or without pressure using a universal testing machine, characterized in that: It includes two independent parts, namely a fixed end fixture and a movable end fixture; The mobile end fixture comprises a mobile end fixture body (1), a mobile end fixture connecting column (3), a gas nozzle elbow (6), and a fixed clamp (7); The movable end fixture body (1) is a disc structure, and a plurality of first workpiece flange connection holes (2) are provided on the movable end fixture body (1); The mobile end fixture connecting column (3) is coaxially located at the center of the upper surface of the mobile end fixture fixture body (1), and two first planes (5) are provided on the upper part of both sides of the mobile end fixture connecting column (3). A first connecting hole (4) is provided on the side of the mobile end fixture connecting column (3). The first connecting hole (4) is a through hole, and the length direction or the center axis is perpendicular to the axial direction of the mobile end fixture connecting column (3); the side surfaces of the mobile end fixture connecting column (3) corresponding to the first connecting hole (4) on both sides correspond to the first planes (5), and the two first planes (5) are parallel. The first plane (5) is a cross-sectional plane formed by removing the arc surface from the side surface of the mobile end fixture connecting column (3), and the first plane (5) is parallel to the center axis of the mobile end fixture connecting column (3) and the center axis of the first connecting hole (4); The movable end clamp body (1) is provided with a nozzle elbow (6), which is a curved hollow tube structure; one end of the nozzle elbow (6) is unthreaded, and the other end is internally threaded; a through hole is opened on the movable end clamp body (1), and the unthreaded end is inserted to form a tight connection with the movable end clamp body (1); A fixed clamp (7) is provided on the side of the mobile end clamp body (1), the thickness direction of the fixed clamp (7) is consistent with the axial direction of the mobile end clamp body (1), and the axial direction of the mobile end clamp body (1) is also the thickness direction of the mobile end clamp body (1); the central section of the mobile end clamp body (1) in the vertical thickness direction is coplanar with the central section of the fixed clamp (7) in the vertical thickness direction; The fixed end clamp comprises a fixed end clamp body (8) and a fixed end clamp connecting column (10); The fixed end clamp body (8) is a disc structure, and a plurality of second workpiece flange connection holes (9) are provided on the fixed end clamp body (8); The fixed end clamp connecting column (10) is coaxially located at the center position of the upper surface of the fixed end clamp main body (8), and a second plane (12) is provided on the upper part of both sides of the fixed end clamp connecting column (10). A second connecting hole (11) is provided on the fixed end clamp connecting column (10), and the second connecting hole (11) is a through hole, and the length direction or the center axis is perpendicular to the axial direction of the fixed end clamp connecting column (10); the side surfaces of the fixed end clamp connecting column (10) corresponding to the two sides of the second connecting hole (11) correspond to the second plane (12), and the two second planes (12) are parallel. The second plane (12) is a cross-sectional plane formed by removing the arc surface from the side surface of the fixed end clamp connecting column (10), and the second plane (12) is parallel to the center axis of the fixed end clamp connecting column (10) and the center axis of the second connecting hole (11).

2. A set of fixtures for measuring the axial and lateral stiffness of metal bellows expansion joints and their assembly structures with or without pressure using a universal testing machine according to claim 1, characterized in that: The bottom roughness of the movable end fixture body (1) and the bottom roughness of the fixed end fixture body (8) are both required to be no greater than 3.

2.

3. A set of fixtures for measuring the axial and lateral stiffness of metal bellows expansion joints and their assembly structures with or without pressure by a universal testing machine according to claim 1, characterized in that: When used to measure the axial pressure stiffness of the metal bellows expansion joint-net sleeve assembly structure, firstly, a sealing gasket (16) is placed between the lower end flange (15) of the metal bellows expansion joint-net sleeve assembly structure workpiece and the fixed end fixture fixture body (8), and a bolt (17) is used to form a fastening connection with the corresponding workpiece flange connection hole left on the lower end flange (15) of the metal bellows expansion joint-net sleeve assembly structure workpiece through the second workpiece flange connection hole (9); the assembled whole is inserted downward into the bottom fixing column (20) of the universal capacity testing machine, the second connection hole (11) is aligned with the fixed end connection hole (21) of the universal capacity testing machine, and the fixed end connection pin (22) of the universal capacity testing machine is inserted into the aligned hole, so that one end of the metal bellows expansion joint-net sleeve assembly structure workpiece (13) is connected to the universal capacity testing machine; Then, the sealing gasket (16) is placed between the upper end flange (14) of the metal bellows expansion joint-net sleeve assembly structure workpiece and the movable end clamp fixture body (1), and a bolt (17) is used to form a fastening connection with the corresponding workpiece flange connection hole left on the upper end flange (14) of the metal bellows expansion joint-net sleeve assembly structure workpiece through the first workpiece flange connection hole (2); the air pipe quick connector (18) is fastened to the internal thread end of the air nozzle elbow (6); the movable crossbeam (23) of the universal capacity testing machine is adjusted so that the movable end clamp connection column (3) is inserted into the movable end fixed column (24) of the universal capacity testing machine, the universal end fixed connection hole (25) of the universal capacity testing machine is aligned with the first connection hole (4), and the universal end connection pin (26) of the universal capacity testing machine is inserted to connect the other end of the metal bellows expansion joint-net sleeve assembly structure workpiece (13) to the universal capacity testing machine; Finally, the pressure required for the experiment is charged into the metal bellows expansion joint-net sleeve assembly structure workpiece (13) through the air pipe (19) to complete the assembly; The movable crossbeam (23) of the universal testing machine is controlled by a program to move upward or downward at a constant speed, and the workpiece is stretched or compressed, and the load-displacement curve is recorded, thereby obtaining the axial rigidity of the metal bellows expansion joint-net sleeve assembly structure under pressure.

4. A set of fixtures for measuring the axial and lateral stiffness of metal bellows expansion joints and their assembly structures with or without pressure by a universal testing machine according to claim 1, characterized in that: When used to measure the transverse pressure stiffness of the metal bellows expansion joint-net sleeve assembly structure: First, a sealing gasket (16) is placed between the lower end flange (15) of the metal bellows expansion joint-net sleeve assembly structure workpiece and the fixed end fixture fixture body (8), and a bolt (17) is used to pass through the second workpiece flange connection hole (9) and the corresponding workpiece flange connection hole left on the lower end flange (15) of the metal bellows expansion joint-net sleeve assembly structure workpiece to form a fastening connection; a sealing gasket (16) is placed between the upper end flange (14) of the metal bellows expansion joint-net sleeve assembly structure workpiece and the movable end fixture fixture body (1), and a bolt (17) is used to pass through the first workpiece flange connection hole (2) and the upper end flange (14) of the metal bellows expansion joint-net sleeve assembly structure workpiece to form a fastening connection. The corresponding workpiece flange connection holes left on the flange (14) are fastened together; the air pipe quick-connect joint (18) is fastened together with the internal threaded end of the air nozzle elbow (6); the assembled metal bellows expansion joint-net sleeve assembly structure workpiece fixed end fixture connection column (10) is inserted into the fixed column (28) of the special fixture for transverse stiffness test, the second connection hole (11) is aligned with the connection hole (29) of the special fixture for transverse stiffness test, and the connection pin (30) of the special fixture for transverse stiffness test is inserted into the aligned hole, so that one end of the metal bellows expansion joint-net sleeve assembly structure workpiece (13) is connected to the special fixture for transverse stiffness test; Then, the universal capacity testing machine conventional tensile fixture connection column (32) of the universal capacity testing machine conventional tensile fixture (31) is inserted into the universal capacity testing machine movable end fixed column (24), so that the universal capacity testing machine movable end fixed connection hole (25) is aligned with the universal capacity testing machine conventional tensile fixture connection hole (33), and the universal capacity testing machine movable end connection pin (26) is inserted into the aligned connection holes, so that the universal capacity testing machine conventional tensile fixture (31) is connected to the universal capacity testing machine movable crossbeam (23); Then, the position of the special fixture for the transverse stiffness test is adjusted so that the mobile end fixture fixing plate (7) is located directly below the conventional tensile fixture (31) of the universal capacity testing machine, the position of the movable crossbeam (23) of the universal capacity testing machine is adjusted so that the conventional tensile fixture (31) of the universal capacity testing machine clamps the mobile end fixture fixing plate (7), and the tightening handle (34) of the conventional tensile fixture of the universal capacity testing machine is rotated so that the conventional tensile fixture (31) of the universal capacity testing machine forms a tightened connection with the mobile end fixture fixing plate (7); Finally, the pressure required for the experiment is charged into the metal bellows expansion joint-net sleeve assembly structure workpiece (13) through the air pipe (19) to complete the assembly; The movable crossbeam (23) of the universal capacity testing machine is controlled by a program to move downward at a constant speed, and a load-displacement curve is recorded, thereby obtaining the transverse rigidity of the metal bellows expansion joint-net sleeve assembly structure under pressure.

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