Fatigue test device and method for tail reduction platform

Abstract

The invention belongs to the technical field of helicopter fatigue test, and discloses a tail reduction platform fatigue test device and method, and the device comprises a tail reduction platform which is a test piece and is located on a helicopter tail inclined beam; a plurality of holes coaxial with the tail reduction platform are formed in the bottom of the tail reduction false piece, the tail reduction false piece is connected and fixed to the tail reduction platform through a tail reduction bolt assembly, and axial tension and torque are applied to the upper portion of the tail reduction false piece; the vertical constraint supports are fixedly connected to the four vertical side faces of the tail reduction platform, and the bottoms of the four vertical constraint supports are connected through a constraint support fixing bottom plate; the lateral restraining supports are fixedly connected to the three lateral side faces of the tail reduction platform, and the bottoms of the three lateral restraining supports are connected through restraining support fixing side plates. The problem that the fatigue test of the helicopter tail reduction platform is difficult is solved, the strength performance of the helicopter tail reduction platform can be fully verified, and the fatigue life is obtained.

Description

Technical Field

[0001] This invention belongs to the field of helicopter fatigue testing technology, specifically relating to a fatigue testing device and method for a tail suspension platform. Background Technology

[0002] The tail rotor platform is a critical component of helicopters. Located on the tail beam, it provides a mounting platform for the tail gearbox and bears the loads transmitted by the tail gearbox during operation. These loads mainly include axial tension and torque along the tail rotor. Due to its complex structure, heavy loads, and the requirement to keep the weight as light as possible, it is crucial to provide a precise fatigue testing environment to conduct tests and determine fatigue life and weak points. Summary of the Invention

[0003] Purpose of the invention: To address the difficulties in fatigue testing of helicopter tail suspension platforms, this invention provides a fatigue testing device and method for tail suspension platforms. By combining the structural and load characteristics of the helicopter tail suspension platform and designing the test boundary connection conditions and load loading, it is possible to fully verify its strength performance and obtain fatigue life.

[0004] To address the above-mentioned technical issues, the present invention provides the following technical solution: In a first aspect, the present invention provides a fatigue testing device for a tail reduction platform, comprising: The tail reduction platform, which is a prototype, is located on the inclined beam at the tail of the helicopter. The tail reduction dummy has multiple holes at its bottom that are coaxial with the tail reduction platform. It is connected and fixed to the tail reduction platform through the tail reduction bolt assembly, and axial tension and torque are applied to the upper part of the tail reduction dummy. Vertical constraint supports are fixedly connected to the four vertical sides of the tail reduction platform, and the bottoms of the four vertical constraint supports are connected by constraint support fixing base plates. Lateral restraint supports are fixedly connected to the three lateral sides of the tail reduction platform, and the bottoms of the three lateral restraint supports are connected by restraint support fixing side plates.

[0005] As a further technical solution of the present invention: the tail reduction platform is a box structure, the top of which is a tail reducer mounting platform, and the platform is provided with vertical bolt connection holes and side nut fixing holes; The surrounding wall panels are connected to the inclined beam and other structures, and are provided with connection and fixing holes; The platform serves as the assessment area, while the surrounding wall panels act as the clamping area. During the test, the clamping area of ​​the surrounding wall panels of the tail reduction platform was constrained and fixed. The tail reduction dummy was connected and fixed to the tail reduction platform through the tail reduction bolt assembly. Axial tension and torque along the axis of the tail reducer were applied through the tail reduction dummy to realistically simulate the connection, assembly and load transfer relationship between the tail reduction platform, the tail reducer and the tail inclined beam.

[0006] As a further technical solution of the present invention: the tail bolt assembly consists of a tail bolt, a cylindrical nut, and a spring positioning support; The cylindrical nut has a semi-cylindrical structure with an internal thread in the middle that matches the external thread of the tail bolt; The spring positioning support is a thin-walled semi-cylindrical structure, with the thin-walled planes on both sides and the top plane respectively matching the cylindrical side and bottom plane of the cylindrical nut; Assemble the cylindrical nut and spring positioning support together and press them into the lateral nut fixing hole on the tail reduction platform. When pressing them in, the spring positioning support can generate elastic deformation and provide support force to the cylindrical nut, so that the internal thread hole on the cylindrical nut is coaxial with the vertical bolt connection hole on the tail reduction platform. The tail reduction bolts can be tightened from the bolt head to connect and fix the tail reduction platform and tail reduction dummy.

[0007] As a further technical solution of the present invention: the tail reduction dummy is connected and fixed to the tail reduction platform by tail reduction bolts, cylindrical nuts, and spring positioning supports; The upper part of the tail reduction dummy is provided with three "U" forks, one of which has its axis passing through the tail reduction gear axis, and the axial tension is applied through this fork. The other two forks are symmetrically distributed on the axis of the tail reducer, and torque is applied through these two forks.

[0008] As a further technical solution of the present invention, it also includes a loading joint assembly, which is composed of a loading joint, a spherical bearing, and an elastic retaining ring; One end of the loading joint is provided with a hole and a shoulder that are compatible with the spherical plain bearing and a hole that are compatible with the elastic retaining ring. The spherical plain bearing and the elastic retaining ring are assembled onto the loading joint in sequence. Compared with the bearing flange or punch point fixing method, it can effectively prevent the loading joint from slipping off along the axis and breaking during the test. The other end of the loading connector is provided with a threaded rod that connects to the loading actuator; The loading connector assembly consists of three parts, which are respectively connected and fixed to the three "U" fork lugs on the upper part of the tail reduction dummy by bolts.

[0009] As a further technical solution of the present invention: there are 4 vertical constraint supports and 3 lateral constraint supports, and the shape is " ⊥ "shape," ⊥ "The upper surface and holes of the shape are adapted to the surface and holes of the surrounding wall panels of the tail reduction platform, and are fixed by bolt connection." ⊥ The lower end plane and hole of the "shape" are respectively adapted to the base plate and side plate of the constraint support fixing plate, and are fixed by bolt connection; The vertical restraint support has semi-circular holes on both sides of the upper plane to provide space for bolt installation.

[0010] As a further technical solution of the present invention:⊥ The included angle between the upper and lower ends of the "shape" is determined according to the spatial position of the tail reduction platform and the tail reduction dummy, so that the lower end plane of the vertical constraint support is parallel to the upper surface of the tail reduction platform, the lower end plane of the lateral constraint support is perpendicular to the upper surface of the tail reduction dummy, the upper surface of the constraint support fixed base plate is an inclined surface that matches the lower bottom surface of the vertical constraint support, and the lower end plane is parallel to the upper surface of the tail reduction dummy. Vertical restraint supports and lateral restraint supports are designed as " ⊥ The "shaped structure" and the upper surface of the constraint support fixing base plate are designed as bevels, which can place the support fixing base plate and constraint support fixing side plate that are connected and fixed to the test bench in a horizontal or vertical plane, making it convenient to use a general test bench.

[0011] As a further technical solution of the present invention: the constraint support fixing base plate and the constraint support fixing side plate are fixed to the test bench by bolts, thereby realizing the constraint and fixation of the tail reduction platform.

[0012] As a further technical solution of the present invention: the tail reduction platform fatigue testing device is connected to a general test bench, a test hydraulic system and a measurement and control system to conduct tail reduction platform fatigue tests.

[0013] Secondly, the present invention provides a fatigue testing method for a tail reduction platform, which includes the following steps: Step 1: Set the experimental setup status; 1) Fix the base plate and side plate of the constraint support to the test bench with bolts; 2) Fix the vertical restraint support to the restraint support fixing base plate with bolts; 3) Fix the lateral restraint support to the fixed side plate of the restraint support with bolts; 4) Connect and fix the tail reduction platform to the vertical constraint support and the lateral constraint support respectively using bolts; 5) Assemble the cylindrical nut and spring positioning support together and press them into the lateral nut fixing hole on the tail reduction platform; 6) The tail reduction dummy is fixed to the tail reduction platform by tail reduction bolts, and the bolt tightening torque is consistent with the installed state; 7) Connect the assembled test apparatus to the test bench, hydraulic system, and measurement and control system; Step 2: Determine the test load; 1) The average load should be the most representative average value in use; 2) The value of the alternating load should be chosen such that the structure can withstand the changes in load. The value that is corrupted in the next loop; 3) Load adjustment: When the number of test load cycles is greater than 0.5 × 10 6 ~1×10 6If the structure has not yet failed, the test load can be increased by one level; when the number of test load cycles is less than 0.2 × 10⁻⁶. 6 When structural failure occurs, the test load of the next test specimen should be reduced by one level, and so on; the load increase or decrease range should be 10% to 20%. Step 3: Execute the loading and monitor the loading process. During the test, continuously monitor the axial force and torque mentioned above. Step 4: Determine the test stop conditions; The failure criterion for metal structures is the appearance of macroscopic cracks in the main load-bearing structure, and the test is stopped when the test piece shows detectable cracks ≤0.1mm, visually visible cracks ≥0.1mm, or when it fails to bear the load or reaches the expected performance. Step 5: Determine the validity of the test data; After the test, inspect the test piece. If there are no cracks, the number of test cycles completed is valid. If cracks appear in the test piece, recheck the relevant test data. If the load changes significantly, the number of cycles when the load data begins to change significantly shall be the valid number of test cycles.

[0014] In summary, the beneficial effects of the present invention are as follows: 1. During testing, this invention can accurately simulate the boundary conditions of the test piece, ensuring a stable test bench, a good test environment, and minimal load fluctuation.

[0015] 2. By using the device of the present invention for testing, the total test error can be controlled within 3%.

[0016] 3. Life analysis using the test data obtained by the device of the present invention can fully verify its strength performance and obtain fatigue life.

[0017] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of a fatigue testing device for a tail reduction platform according to the present invention.

[0019] Figure 2 This is a top view of a fatigue testing device for a tail reduction platform according to the present invention.

[0020] Figure 3 This is a schematic diagram of the tail reduction platform of the present invention.

[0021] Figure 4 This is a schematic diagram of the tail bolt assembly of the present invention.

[0022] Figure 5 This is a schematic diagram of the structure of the loading connector assembly of the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be described in more detail below with reference to the accompanying drawings.

[0024] In the accompanying drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The described embodiments are some, but not all, of the embodiments of the present invention.

[0025] The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0026] The following is in conjunction with the appendix Figure 1-5 The embodiments of the present invention will be described in detail below.

[0027] Example 1 like Figure 1-5 As shown, the present invention discloses a fatigue testing device for a tail reduction platform, including a tail reduction platform 1, a tail reduction bolt assembly 2, a tail reduction dummy 3, a loading joint assembly 4, a vertical constraint support 5, a constraint support fixing base plate 6, a lateral constraint support 7, and a constraint support fixing side plate 8.

[0028] The tail reduction platform 1 is a test piece located on the tail beam of the helicopter. It has a box-like structure with the tail reducer mounting platform at the top. The platform has vertical bolt connection holes and lateral nut fixing holes. The peripheral wall panels are connected to other structures of the tail beam and have connection and fixing holes. The platform is the test area, and the peripheral wall panels are the clamping area. During the test, the clamping area of ​​the peripheral wall panels of the tail reduction platform 1 is constrained and fixed. The tail reduction dummy 3 is connected and fixed to the tail reduction platform 1 through the tail reduction bolt assembly 2. Axial tension and torque along the tail reducer axis are applied through the tail reduction dummy 3 to realistically simulate the connection, assembly, and load transfer relationship between the tail reduction platform 1, the tail reducer, and the tail beam.

[0029] Furthermore, the tail reducer bolt assembly 2 consists of a tail reducer bolt 2-1, a cylindrical nut 2-2, and a spring positioning support 2-3. The cylindrical nut 2-2 has a large semi-cylindrical structure with an internal thread in the middle that matches the external thread of the tail reducer bolt 2-1. The spring positioning support 2-3 has a thin-walled small semi-cylindrical structure, with its two side thin-walled planes and top plane matching the cylindrical side and bottom planes of the cylindrical nut 2-2, respectively. When the cylindrical nut 2-2 and the spring positioning support 2-3 are assembled together, they are pressed into the lateral nut fixing hole on the tail reducer platform 1. During the pressing, the spring positioning support 2-3 can undergo elastic deformation and provide support force to the cylindrical nut 2-2, making the internal thread hole on the cylindrical nut 2-2 coaxial with the vertical bolt connection hole on the tail reducer platform 1. The tail reducer bolt 2-1 can be tightened from the bolt head to connect and fix the tail reducer platform 1 and the tail reducer dummy 3.

[0030] Furthermore, the bottom of the tail reduction dummy 3 is provided with multiple holes coaxial with the tail reduction platform 1, and is connected and fixed to the tail reduction platform 1 through tail reduction bolts 2-1, cylindrical nuts 2-2, and spring positioning supports 2-3. The upper part of the tail reduction dummy 3 is provided with three "U" fork lugs, one of which has its axis passing through the tail reduction gear axis, and the axial tension is applied through this fork lug; the other two fork lugs are symmetrically distributed on the tail reduction gear axis, and the torque is applied through these two fork lugs.

[0031] Furthermore, the loading connector assembly 4 consists of a loading connector 4-1, a spherical bearing 4-2, and an elastic retaining ring 4-3. One end of the loading connector 4-1 has a hole and a shoulder that mate with the spherical bearing 4-2, and a hole that mates with the elastic retaining ring 4-3. The spherical bearing 4-2 and the elastic retaining ring 4-3 are sequentially assembled onto the loading connector 4-1. Compared to bearing flange or punch point fixing methods, this effectively prevents the loading connector from slipping axially and breaking during the test. The other end of the loading connector 4-1 has a threaded rod that connects to the loading actuator. There are three loading connector assemblies 4, each bolted to one of the three "U"-shaped lugs on the upper part of the tail reduction dummy 3.

[0032] Furthermore, there are 4 vertical restraint supports 5 and 3 lateral restraint supports 7, with a shape of " ⊥ "shape," ⊥ "The upper plane and holes of the shape are adapted to the plane and holes of the peripheral wall panel of the tail reduction platform 1, and are fixed by bolt connection." ⊥ The lower end plane and hole of the "" shape are adapted to the base plate 6 and the side plate 8 of the constraint support fixing plate, respectively, and are fixed by bolt connection. The upper end plane of the vertical constraint support 5 has semi-circular holes on both sides to provide installation space for bolts.

[0033] Furthermore, the aforementioned " ⊥The included angle between the upper and lower ends of the "shape" is determined based on the spatial positions of the tail reduction platform 1 and the tail reduction dummy 3, so that the lower plane of the vertical constraint support 5 is parallel to the upper surface of the tail reduction platform 1, and the lower plane of the lateral constraint support 7 is perpendicular to the upper surface of the tail reduction dummy 3. The upper surface of the constraint support fixing base plate 6 is an inclined surface adapted to the lower bottom surface of the vertical constraint support 5, and its lower plane is parallel to the upper surface of the tail reduction dummy 3. The vertical constraint support 5 and the lateral constraint support 7 are designed as " ⊥ The "shaped structure and the upper surface of the constraint support fixing base plate 6 are designed as inclined surfaces, which can place the support fixing base plate 6 and the constraint support fixing side plate 8, which are connected and fixed to the test bench, in a horizontal or vertical plane, making it convenient to use a general test bench.

[0034] Furthermore, the constraint support fixing base plate 6 and the constraint support fixing side plate 8 are fixed to the test bench by bolts, thereby realizing the constraint and fixation of the tail reduction platform 1.

[0035] Furthermore, the tail reduction platform fatigue testing device is connected to a general-purpose test bench, a test hydraulic system, and a measurement and control system, enabling fatigue testing of the tail reduction platform.

[0036] Example 2 This invention discloses a fatigue testing method for a tail reduction platform, which includes the following steps: Step 1: Set the experimental setup status; 1) Fix the constraint support base plate 6 and the constraint support side plate 8 to the test bench with bolts; 2) Fix the vertical restraint support 5 to the restraint support fixing base plate 6 with bolts; 3) Fix the lateral restraint support 7 to the restraint support fixing side plate 8 with bolts; 4) Connect and fix the tail reduction platform 1 to the vertical constraint support 5 and the lateral constraint support 7 respectively using bolts; 5) Assemble the cylindrical nut 2-2 and the spring positioning support 2-3 together and press them into the lateral nut fixing hole on the tail reduction platform 1; 6) The tail reduction dummy part 3 is fixed to the tail reduction platform 1 by the tail reduction bolt 2-1, and the bolt tightening torque is consistent with the installed state; 7) Connect the assembled test device to the test bench, hydraulic system and measurement and control system.

[0037] Step 2: Determine the test load; 1) The average load should be the most representative average value in use.

[0038] 2) The value of the alternating load should be chosen such that the structure can withstand the load. The value that is corrupted in the next loop.

[0039] 3) Load adjustment: Generally speaking, when the number of test load cycles is greater than 0.5 × 10 6 ~1×10 6 If the structure has not yet failed, the test load can be increased by one level; when the number of test load cycles is less than 0.2 × 10⁻⁶. 6 When structural failure occurs, the test load (for the next test piece) should be reduced by one level, and so on. Generally, the load increase or decrease range is 10% to 20%.

[0040] Step 3: Execute loading and monitor the loading process. During the test, continuously monitor the axial force and torque. If deviations from the preset error value are found, the test should be suspended. The cause should be identified and the fault eliminated before the test can continue. Ensure that the data throughout the test process is true and accurate. The test error control method ensures that the performance error of the force sensor itself is controlled within 0.5%, the performance error of the control system itself is controlled within 0.5%, and the loading error is controlled within 2.5%. The total test error is calculated based on the root mean square of each error, ensuring that the total test error is less than 3%.

[0041] Error analysis is as follows: Sensor error: δ 传 ≤0.5%; Control system error: δ 系 ≤0.5%; Loading error: δ 加 ≤2.5%; Total experimental error: δ 总 ≤ .

[0042] Step 4: Determine the test cessation conditions; The failure criterion for metal structures is the appearance of macroscopic cracks in the main load-bearing structure. Generally, the test is stopped when the test piece shows detectable cracks ≤0.1mm, visually visible cracks ≥0.1mm, or when it is damaged to the point of being unable to bear loads or achieves the expected performance.

[0043] Step 5: Determine the validity of the test data; After the test, inspect the test piece. If there are no cracks, the number of test cycles completed is valid. If cracks appear in the test piece, recheck the relevant test data. If the load changes significantly, the number of cycles when the load data begins to change significantly shall be the valid number of test cycles.

[0044] Thus, the objective of this invention has been achieved.

[0045] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A fatigue testing device for a tail reduction platform, characterized in that, include: The tail reduction platform, which is a prototype, is located on the inclined beam at the tail of the helicopter. The tail reduction dummy has multiple holes at its bottom that are coaxial with the tail reduction platform. It is connected and fixed to the tail reduction platform through the tail reduction bolt assembly, and axial tension and torque are applied to the upper part of the tail reduction dummy. Vertical constraint supports are fixedly connected to the four vertical sides of the tail reduction platform, and the bottoms of the four vertical constraint supports are connected by constraint support fixing base plates. Lateral restraint supports are fixedly connected to the three lateral sides of the tail reduction platform, and the bottoms of the three lateral restraint supports are connected by restraint support fixing side plates.

2. The fatigue testing device for the tail reduction platform according to claim 1, characterized in that, The tail reducer platform is a box structure, with the top being a tail reducer mounting platform. The platform is equipped with vertical bolt connection holes and lateral nut fixing holes. The surrounding wall panels are connected to the inclined beam and other structures, and are provided with connection and fixing holes; The platform serves as the assessment area, while the surrounding wall panels act as the clamping area. During the test, the clamping area of ​​the surrounding wall panels of the tail reduction platform was constrained and fixed. The tail reduction dummy was connected and fixed to the tail reduction platform through the tail reduction bolt assembly. Axial tension and torque along the axis of the tail reducer were applied through the tail reduction dummy to realistically simulate the connection, assembly and load transfer relationship between the tail reduction platform, the tail reducer and the tail inclined beam.

3. The fatigue testing device for the tail reduction platform according to claim 2, characterized in that, The tail bolt assembly consists of a tail bolt, a cylindrical nut, and a spring positioning support. The cylindrical nut has a semi-cylindrical structure with an internal thread in the middle that matches the external thread of the tail bolt; The spring positioning support is a thin-walled semi-cylindrical structure, with the thin-walled planes on both sides and the top plane respectively matching the cylindrical side and bottom plane of the cylindrical nut; Assemble the cylindrical nut and spring positioning support together and press them into the lateral nut fixing hole on the tail reduction platform. When pressing them in, the spring positioning support can generate elastic deformation and provide support force to the cylindrical nut, so that the internal thread hole on the cylindrical nut is coaxial with the vertical bolt connection hole on the tail reduction platform. The tail reduction bolts can be tightened from the bolt head to connect and fix the tail reduction platform and tail reduction dummy.

4. The fatigue testing device for the tail reduction platform according to claim 3, characterized in that, The tail reduction dummy is connected and fixed to the tail reduction platform by tail reduction bolts, cylindrical nuts, and spring positioning supports; The upper part of the tail reduction dummy is provided with three "U" forks, one of which has its axis passing through the tail reduction gear axis, and the axial tension is applied through this fork. The other two forks are symmetrically distributed on the axis of the tail reducer, and torque is applied through these two forks.

5. The fatigue testing device for the tail reduction platform according to claim 4, characterized in that, It also includes a loading joint assembly, which consists of a loading joint, a spherical bearing, and an elastic retaining ring; One end of the loading joint is provided with a hole and a shoulder that are compatible with the spherical plain bearing and a hole that are compatible with the elastic retaining ring. The spherical plain bearing and the elastic retaining ring are assembled onto the loading joint in sequence. Compared with the bearing flange or punch point fixing method, it can effectively prevent the loading joint from slipping off along the axis and breaking during the test. The other end of the loading connector is provided with a threaded rod that connects to the loading actuator; The loading connector assembly consists of three parts, which are respectively connected and fixed to the three "U" fork lugs on the upper part of the tail reduction dummy by bolts.

6. The fatigue testing device for the tail reduction platform according to claim 5, characterized in that, There are 4 vertical constraint supports and 3 lateral constraint supports, shaped like " ⊥ "shape," ⊥ "The upper surface and holes of the shape are adapted to the surface and holes of the peripheral wall panels of the tail reduction platform, and are fixed by bolt connection." ⊥ The lower end plane and hole of the "shape" are respectively adapted to the base plate and side plate of the constraint support fixing plate, and are fixed by bolt connection; The vertical restraint support has semi-circular holes on both sides of the upper plane to provide space for bolt installation.

7. The fatigue testing device for the tail reduction platform according to claim 6, characterized in that, " ⊥ The included angle between the upper and lower ends of the "shape" is determined according to the spatial position of the tail reduction platform and the tail reduction dummy, so that the lower end plane of the vertical constraint support is parallel to the upper surface of the tail reduction platform, the lower end plane of the lateral constraint support is perpendicular to the upper surface of the tail reduction dummy, the upper surface of the constraint support fixed base plate is an inclined surface that matches the lower bottom surface of the vertical constraint support, and the lower end plane is parallel to the upper surface of the tail reduction dummy. Vertical restraint supports and lateral restraint supports are designed as follows: ⊥ The "shaped structure" and the upper surface of the constraint support fixing base plate are designed as bevels, which can place the support fixing base plate and constraint support fixing side plate that are connected and fixed to the test bench in a horizontal or vertical plane, making it convenient to use a general test bench.

8. The fatigue testing device for the tail reduction platform according to claim 7, characterized in that, The constraint support fixing base plate and constraint support fixing side plate are fixed to the test bench by bolts, thereby achieving constraint and fixation of the tail reduction platform.

9. The fatigue testing device for the tail reduction platform according to claim 8, characterized in that, The tail reduction platform fatigue testing device is connected to a general-purpose test bench, a test hydraulic system, and a measurement and control system to conduct tail reduction platform fatigue tests.

10. A fatigue testing method for a tail reduction platform, characterized in that, Includes the following steps: Step 1: Set the experimental setup status; 1) Fix the base plate and side plate of the constraint support to the test bench with bolts; 2) Fix the vertical restraint support to the restraint support fixing base plate with bolts; 3) Fix the lateral restraint support to the fixed side plate of the restraint support with bolts; 4) Connect and fix the tail reduction platform to the vertical constraint support and the lateral constraint support respectively using bolts; 5) Assemble the cylindrical nut and spring positioning support together and press them into the lateral nut fixing hole on the tail reduction platform; 6) The tail reduction dummy is fixed to the tail reduction platform by tail reduction bolts, and the bolt tightening torque is consistent with the installed state; 7) Connect the assembled test apparatus to the test bench, hydraulic system, and measurement and control system; Step 2: Determine the test load; 1) The average load should be the most representative average value in use; 2) The value of the alternating load should be chosen such that the structure can withstand the changes in load. The value that is corrupted in the next loop; 3) Load adjustment: When the number of test load cycles is greater than 0.5 × 10 6 ~1×10 6 If the structure has not yet failed, the test load can be increased by one level; when the number of test load cycles is less than 0.2 × 10⁻⁶. 6 When structural failure occurs, the test load of the next test specimen should be reduced by one level, and so on; the load increase or decrease range should be 10% to 20%. Step 3: Execute the loading and monitor the loading process. During the test, continuously monitor the axial force and torque mentioned above. Step 4: Determine the test stop conditions; The failure criterion for metal structures is the appearance of macroscopic cracks in the main load-bearing structure, and the test is stopped when the test piece shows detectable cracks ≤0.1mm, visually visible cracks ≥0.1mm, or when it fails to bear the load or reaches the expected performance. Step 5: Determine the validity of the test data; After the test, inspect the test piece. If there are no cracks, the number of test cycles completed is valid. If cracks appear in the test piece, recheck the relevant test data. If the load changes significantly, the number of cycles when the load data begins to change significantly shall be the valid number of test cycles.

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