A structure design method of a tail-raising rocker joint fatigue test piece

Abstract

The present application belongs to the field of helicopter important joint fatigue test design, and relates to a tail lifting rocker joint fatigue test piece structure design method, which comprises the following steps: 1, connecting the tail lifting gear rocker with the fuselage structure through two joints on the left and right sides, and selecting the left or right joint and the fuselage connecting structure as the tail lifting rocker joint fatigue test piece; 2, determining the technical state of the tail lifting rocker joint fatigue test piece; 3, determining the installation mode of the tail lifting rocker joint fatigue test piece; 4, creating a finite element model of the tail lifting rocker joint fatigue test piece; 5, determining the thickness of the connecting area between the tail lifting rocker joint fatigue test piece and the test fixture, the number and diameter of the connecting bolts between the tail lifting rocker joint fatigue test piece and the fixture; 6, optimizing the finite element model in step 4 according to step 5, performing damage calculation, and ensuring that the fuselage connecting structure and the connecting part with the test fixture will not be damaged by fatigue before the tail lifting rocker joint reaches the examination life.

Description

Technical Field

[0001] This invention belongs to the field of fatigue test design for important helicopter joints, and relates to a structural design method for a fatigue test specimen of a tail boom rocker arm joint. Background Technology

[0002] Traditionally, fatigue life tests on critical joints on helicopters involve treating the joint as a standalone test piece, securing it to the test bench with bolts, while the connected airframe structure is not tested alongside it. Directly connecting the joint to the test fixture fails to simulate a realistic installation, and the stiffness of the connected airframe structure directly affects the load distribution on the joint. Without designing its stiffness, the accuracy of the entire fatigue test is compromised, compromising the accuracy and reliability of the joint fatigue life test results.

[0003] To accurately simulate the actual stress state, load transfer, and diffusion of the taillift rocker arm joint during actual installation, the fuselage structure connected to the joint was used as a test specimen for fatigue life testing together with the taillift rocker arm joint. Considering the production cycle and cost of the test specimen, as well as the load diffusion area of ​​the joint, a portion of the fuselage structure connected to the rocker arm joint was selected as the test specimen. With the stress distribution level in the connection area between the rocker arm joint and the fuselage structure as the target, the stiffness of the test specimen was designed and the installation scheme of the test specimen was determined through multiple rounds of numerical simulation iterations. Summary of the Invention

[0004] The purpose of this invention is to realistically simulate the actual stress state of the tail boom rocker arm joint on the aircraft, and to propose a structural design method for a fatigue test piece of the tail boom rocker arm joint. Fatigue life tests are conducted on the tail boom rocker arm joint and the fuselage connection structure to determine the fatigue characteristics and fatigue stress spectrum of the tail boom rocker arm joint and the fuselage connection structure, thereby improving the fatigue test design of the helicopter landing gear connection joint.

[0005] The technical solution of the present invention:

[0006] A method for designing a fatigue test specimen for a tail boom rocker joint includes the following steps:

[0007] Step 1: Connect the tail landing gear rocker arm to the fuselage structure through two connectors on the left and right sides, and select the connection structure between the left or right connector and the fuselage as the fatigue test specimen for the tail landing gear rocker arm connector;

[0008] Step 2: Determine the technical condition of the tail boom rocker joint fatigue test specimen;

[0009] Step 3: Determine the installation method of the tail boom rocker arm joint fatigue test specimen;

[0010] Step 4: Create a finite element model of the tail boom joint fatigue test specimen;

[0011] Step 5: Determine the thickness of the connection area between the tail boom rocker joint fatigue test specimen and the test fixture, as well as the number and diameter of the bolts connecting the tail boom rocker joint fatigue test specimen and the fixture;

[0012] Step 6: Based on Step 5, optimize the finite element model in Step 4, perform damage calculations, and ensure that the tail boom rocker joint will not suffer fatigue damage to the fuselage connection structure and the connection part with the test fixture before reaching the test life.

[0013] Furthermore, step 2 specifically involves cutting off a portion of the machine body structure connected to the tail rocker arm connector as a test specimen.

[0014] Furthermore, the method for using a portion of the machine body structure connected to the tail boom rocker arm joint as a test specimen is as follows:

[0015] The frame and longitudinal beams of the body structure connected to the tail boom joint were cut off at the locations where the original integral structure of the body structure had stiffeners.

[0016] Determine the front and rear boundaries of the skin section. The front boundary of the skin section is determined based on the load transfer path and diffusion area of ​​the tail boom joint, while the rear boundary of the skin section is located at the longitudinal beam section position.

[0017] Furthermore, step 3 determines the installation method of the tail boom rocker joint fatigue test specimen, including:

[0018] The frame reinforcement bars and the end vertical reinforcement bars of the longitudinal beam of the tail-start rocker arm joint fatigue test specimen are connected to the test fixture by bolts;

[0019] The skin is connected to the test fixture via connecting angle brackets. The connecting angle brackets are connected to the skin by rivets, and the connecting angle brackets are connected to the test fixture by bolts.

[0020] Furthermore, step 4 specifically involves creating a finite element model of the tail boom joint fatigue test specimen based on the finite element platform Patran / Nastran.

[0021] Furthermore, the finite element model of the tail boom joint fatigue test specimen was created based on the finite element platform Patran / Nastran, including:

[0022] Solid elements in the finite element platform Patran / Nastran were used to simulate the tail boom rocker joint, frame, and longitudinal beam.

[0023] Shell elements in the finite element platform Patran / Nastran were used to simulate the skin, strip, and angle metal connected to the skin.

[0024] Beam elements and connectors are created between solid elements and shell elements to simulate bolts and rivets connecting them; connectors are created between shell elements to simulate rivets connecting them.

[0025] Create boundary constraints based on the actual situation, constraining the translational degrees of freedom in three directions of the center point of the bolt hole connecting the frame ribs, longitudinal beams and test fixtures, and constraining the translational degrees of freedom in three directions of the center point of the bolt hole connecting the angle member and test fixtures.

[0026] The test load is manually distributed to the center point A of the lug bolt hole of the tail boom rocker arm joint, with forces in three directions.

[0027] Further, step 5 specifically involves: setting the initial thickness of the connection area between the tail boom rocker joint fatigue test specimen and the test fixture, and the installation scheme of the test specimen. Using the finite element model created in step 4, the stress distribution level of the connection area between the tail boom rocker joint and the fuselage structure is obtained and compared with the stress distribution of the tail boom rocker joint static strength analysis finite element model under the same working condition. The finite element model created in step 4 is defined as FEM1, and the tail boom rocker joint static strength analysis finite element model is defined as FEM2. Through comparative analysis of the numerical simulation results of finite element models FEM1 and FEM2, repeated modifications and iterations are made until the stress distribution state of FEM1 and FEM2 is the same under the same load condition. Finally, the thickness of the connection area between the test specimen and the test fixture, and the number and diameter of the bolts connecting the test specimen and the fixture are determined.

[0028] Furthermore, step 6 specifically involves determining the final thickness of the connection area between the test piece and the test fixture, the number and diameter of the bolts connecting the test piece and the fixture, based on step 5; optimizing the finite element model FEM1 in step 4; and using the safe fatigue life method to calculate damage, ensuring that the fuselage connection structure and the connection part with the test fixture will not suffer fatigue damage before the tail boom rocker joint reaches its test life.

[0029] The beneficial effects of this invention are:

[0030] This paper provides a structural design method for fatigue test specimens of tail boom rocker arm joints, ensuring that the influence of the stiffness of the fuselage structure on the accuracy of fatigue tests is within an acceptable range, and that the fatigue test results are reliable and reasonable; it also more accurately verifies whether the joint and fuselage connection structure meet the fatigue strength design requirements. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the fatigue test specimen for the tail boom rocker joint;

[0032] Figure 2 This is a schematic diagram showing the installation position of the fatigue test specimen for the tail boom rocker arm joint. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0034] A method for designing a fatigue test specimen for a tail boom rocker joint includes the following steps:

[0035] Step 1: Connect the tail landing gear rocker arm to the fuselage structure through two connectors on the left and right sides, and select the connection structure between the left or right connector and the fuselage as the fatigue test specimen for the tail landing gear rocker arm connector;

[0036] Step 1 specifically involves selecting half of the structure as the test specimen because the left and right side joints and the fuselage connection structure are completely symmetrical. Step 1 achieves the following: initially selecting a single-sided joint and fuselage connection structure as the test specimen during fatigue test specimen design simplifies the finite element analysis model and improves the efficiency of strength analysis and design; simultaneously, it shortens the test specimen production cycle, reduces manufacturing costs, reduces the workload of the testing department, and accelerates the fatigue life test progress.

[0037] Step 2: Determine the technical condition of the tail boom rocker joint fatigue test specimen;

[0038] Step 2 specifically involves cutting off a portion of the machine body structure connected to the tail rocker arm connector as a test specimen.

[0039] The method for using a section of the machine body structure connected to the tail boom rocker arm joint as a test specimen is as follows:

[0040] The frame and longitudinal beams of the body structure connected to the tail boom joint were cut off at the locations where the original integral structure of the body structure had stiffeners.

[0041] Determine the front and rear boundaries of the skin section. The front boundary of the skin section is determined based on the load transfer path and diffusion area of ​​the tail boom joint, while the rear boundary of the skin section is located at the longitudinal beam section position.

[0042] Step 3: Determine the installation method of the tail boom rocker joint fatigue test specimen; including:

[0043] The frame reinforcement bars and the end vertical reinforcement bars of the longitudinal beam of the tail-start rocker arm joint fatigue test specimen are connected to the test fixture by bolts;

[0044] The skin is connected to the test fixture via connecting angle brackets. The connecting angle brackets are connected to the skin by rivets, and the connecting angle brackets are connected to the test fixture by bolts.

[0045] Step 4: Create a finite element model of the tail boom joint fatigue test specimen;

[0046] Step 4 specifically involves creating a finite element model of the tail boom joint fatigue test specimen based on the finite element platform Patran / Nastran.

[0047] Furthermore, the finite element model of the tail boom joint fatigue test specimen was created based on the finite element platform Patran / Nastran, including:

[0048] Solid elements in the finite element platform Patran / Nastran were used to simulate the tail boom rocker joint, frame, and longitudinal beam.

[0049] Shell elements in the finite element platform Patran / Nastran were used to simulate the skin, strip, and angle metal connected to the skin.

[0050] Beam elements and connectors are created between solid elements and shell elements to simulate bolts and rivets connecting them; connectors are created between shell elements to simulate rivets connecting them.

[0051] Create boundary constraints based on the actual situation, constraining the translational degrees of freedom in three directions of the center point of the bolt hole connecting the frame ribs, longitudinal beams and test fixtures, and constraining the translational degrees of freedom in three directions of the center point of the bolt hole connecting the angle member and test fixtures.

[0052] The test load is manually distributed to the center point A of the lug bolt hole of the tail boom rocker arm joint, with forces in three directions.

[0053] Step 5: Determine the thickness of the connection area between the tail boom rocker joint fatigue test specimen and the test fixture, as well as the number and diameter of the bolts connecting the tail boom rocker joint fatigue test specimen and the fixture. Specifically, set the initial thickness of the connection area between the tail boom rocker joint fatigue test specimen and the test fixture, and the test specimen installation scheme. Apply the finite element model created in Step 4 to obtain the stress distribution level of the connection area between the tail boom rocker joint and the fuselage structure, and compare it with the stress distribution of the tail boom rocker joint static strength analysis finite element model under the same working condition. The finite element model created in Step 4 is defined as FEM1, and the tail boom rocker joint static strength analysis finite element model is defined as FEM2. Through comparative analysis of the numerical simulation results of finite element models FEM1 and FEM2, it is repeatedly modified and iterated until the stress distribution state of FEM1 and FEM2 is the same under the same load condition. Finally, determine the thickness of the connection area between the test specimen and the test fixture, and the number and diameter of the bolts connecting the test specimen and the fixture.

[0054] Step 6: Based on Step 5, optimize the finite element model in Step 4, perform damage calculations, and ensure that the tail boom rocker joint will not suffer fatigue damage to the fuselage connection structure and the connection part with the test fixture before reaching the test life.

[0055] Specifically, based on step 5, the final thickness of the connection area between the test piece and the test fixture, the number and diameter of the bolts connecting the test piece and the fixture are determined. The finite element model FEM1 in step 4 is optimized, and the damage calculation is performed using the safe fatigue life method to ensure that the fuselage connection structure and the connection part with the test fixture will not suffer fatigue damage before the tail boom rocker joint reaches the test life.

[0056] The above description is merely a specific embodiment of the present invention, providing a detailed description of the invention. Parts not covered herein are conventional techniques. However, the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. The scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A structural design method for a fatigue test specimen of a tail boom rocker arm joint, characterized in that, Includes the following steps: Step 1: Connect the tail landing gear rocker arm to the fuselage structure through two connectors on the left and right sides, and select the connection structure between the left or right connector and the fuselage as the fatigue test specimen for the tail landing gear rocker arm connector; Step 2: Determine the technical condition of the fatigue test specimen for the tail boom rocker arm joint. Specifically, a section of the machine body structure connected to the tail boom rocker arm joint is taken as the test specimen. The method for taking the section of the machine body structure connected to the tail boom rocker arm joint as the test specimen is as follows: The frame and longitudinal beams of the body structure connected to the tail boom joint were cut off at the locations where the original integral structure of the body structure had stiffeners. Determine the front and rear boundaries of the skin section. The front boundary of the skin section is determined based on the load transfer path and diffusion area of ​​the tail boom joint, and the rear boundary of the skin section is at the longitudinal beam section position. Step 3: Determine the installation method of the tail boom rocker arm joint fatigue test specimen; Step 4: Create a finite element model of the tail boom joint fatigue test specimen; Step 5: Determine the thickness of the connection area between the tail boom rocker joint fatigue test specimen and the test fixture, as well as the number and diameter of the bolts connecting the tail boom rocker joint fatigue test specimen and the fixture; Step 6: Based on Step 5, optimize the finite element model in Step 4, perform damage calculations, and ensure that the tail boom rocker joint will not suffer fatigue damage to the fuselage connection structure and the connection with the test fixture before reaching the test life.

2. The structural design method for a tail boom rocker joint fatigue test specimen according to claim 1, characterized in that, Step 3 determines the installation method of the tail boom rocker joint fatigue test specimen, including: The frame reinforcement bars and the end vertical reinforcement bars of the longitudinal beam of the tail-start rocker arm joint fatigue test specimen are connected to the test fixture by bolts; The skin is connected to the test fixture via connecting angle brackets. The connecting angle brackets are connected to the skin by rivets, and the connecting angle brackets are connected to the test fixture by bolts.

3. The structural design method for a tail-start rocker arm joint fatigue test specimen according to claim 2, characterized in that, Step 4 specifically involves creating a finite element model of the tail boom joint fatigue test specimen based on the finite element platform Patran / Nastran.

4. The structural design method for a tail-start rocker arm joint fatigue test specimen according to claim 3, characterized in that, The finite element model of the tail boom joint fatigue test specimen created based on the finite element platform Patran / Nastran includes: Solid elements in the finite element platform Patran / Nastran were used to simulate the tail boom rocker joint, frame, and longitudinal beam. Shell elements in the finite element platform Patran / Nastran were used to simulate the skin, strip, and angle metal connected to the skin. Beam elements and connectors are created between solid elements and shell elements to simulate bolts and rivets connecting them; connectors are created between shell elements to simulate rivets connecting them. Create boundary constraints based on the actual situation, constraining the translational degrees of freedom in three directions of the center point of the bolt hole connecting the frame ribs, longitudinal beams and test fixtures, and constraining the translational degrees of freedom in three directions of the center point of the bolt hole connecting the angle member and test fixtures. The test load is manually distributed to the center point A of the lug bolt hole of the tail boom rocker arm joint, with forces in three directions.

5. The structural design method for a tail-start rocker arm joint fatigue test specimen according to claim 4, characterized in that, Step 5 specifically involves: setting the initial thickness of the connection area between the tail boom rocker joint fatigue test specimen and the test fixture, and the specimen installation scheme. Using the finite element model created in step 4, the stress distribution level of the connection area between the tail boom rocker joint and the fuselage structure is obtained and compared with the stress distribution of the tail boom rocker joint static strength analysis finite element model under the same working condition. The finite element model created in step 4 is defined as FEM1, and the tail boom rocker joint static strength analysis finite element model is defined as FEM2. Through comparative analysis of the numerical simulation results of finite element models FEM1 and FEM2, repeated modifications and iterations are made until the stress distribution state of FEM1 and FEM2 is the same under the same load condition. Finally, the thickness of the connection area between the test specimen and the test fixture, and the number and diameter of the bolts connecting the test specimen and the fixture are determined.

6. The structural design method for a tail-start rocker arm joint fatigue test specimen according to claim 5, characterized in that, Step 6 specifically involves determining the final thickness of the connection area between the test piece and the test fixture, the number and diameter of the bolts connecting the test piece and the fixture, based on step 5. The finite element model FEM1 in step 4 is optimized, and the damage calculation is performed using the safe fatigue life method to ensure that the fuselage connection structure and the connection part with the test fixture will not suffer fatigue damage before the tail boom rocker joint reaches the test life.

Images