Method and system for verifying residual strength of helicopter body composite material structure after lightning stroke

Abstract

The invention belongs to the technical field of helicopter structure strength design, and relates to a method and system for verifying residual strength of a helicopter body composite material structure after lightning stroke. The method comprises the following steps: determining a test piece and a laying layer and size thereof; performing a lightning current impact test on the selected lightning stroke test piece; respectively carrying out residual strength test on the damaged test piece and the comparison piece after lightning stroke; and comparing and analyzing to obtain the residual strength of the composite material structure after lightning stroke, and judging whether the residual strength meets requirements.

Description

Technical Field

[0001] The present invention belongs to the technical field of helicopter structural strength design, and relates to a method and system for verifying the residual strength of a helicopter airframe composite structure after lightning strike. Background Art

[0002] With the development of composite materials, the proportion of composite structures in helicopter airframe structures is increasing. The fuselage skin, fairing, etc. are usually composite structures. In recent years, helicopters have been increasingly widely used, and helicopters are at risk of being struck by lightning during missions. Lightning strikes will cause damage to the composite structure parts of the helicopter airframe to a certain extent, thus affecting the safe flight of the helicopter.

[0003] In order to ensure that the helicopter can land safely after a lightning strike, the skin of key parts should not cause structural damage that endangers flight safety due to lightning strikes. It is necessary to analyze the residual strength of the composite structure of the airframe after a lightning strike. Since it is difficult to accurately simulate the damage degree of the composite structure after a lightning strike through a theoretical model, it is currently very difficult to accurately analyze the residual strength of the composite structure of the airframe after a lightning strike by calculation methods. Summary of the Invention

[0004] Object of the Invention: To solve the problem that the residual strength of the composite structure of the airframe after a lightning strike cannot be accurately analyzed theoretically in the related art, the present invention proposes a test verification method and system for the residual strength of a helicopter airframe composite structure after a lightning strike, which can accurately and effectively verify the residual strength of the helicopter airframe composite structure after being struck by lightning.

[0005] Technical Solution:

[0006] In the first aspect, a method for verifying the residual strength of a helicopter airframe composite structure after a lightning strike is provided, including:

[0007] Determine the test piece, its ply and size;

[0008] Conduct a lightning current impulse test on the selected lightning strike test piece;

[0009] Conduct residual strength tests on the damaged test piece after the lightning strike and the comparison piece respectively;

[0010] Obtain the residual strength of the composite structure after the lightning strike through comparative analysis, and judge whether it meets the requirements.

[0011] Further, determining the test piece, its ply and size includes:

[0012] According to the lightning zone of the helicopter and the stress characteristics of the airframe structure, determine the airframe structure part where the test piece is selected;

[0013] Determine the layup and dimensions of the test piece according to the position of the selected test piece in the airframe structure.

[0014] Furthermore, conduct a lightning current impulse test on the selected lightning strike test piece, including:

[0015] Determine the number of test pieces;

[0016] Conduct a lightning current impulse test on the test pieces respectively according to the lightning zones of the helicopter where the airframe composite material structure of the test pieces is located, so as to cause lightning strike damage to the body of the composite material lightning strike test piece;

[0017] Analyze the damage positions and damage degrees of each test piece.

[0018] Furthermore, determine the airframe structure parts for test piece selection according to the lightning zones of the helicopter and the force characteristics of the airframe structure, including:

[0019] Select typical structural parts in typical lightning areas as the parts for selecting the test pieces for the post-lightning strike residual strength test. These structural parts are the airframe composite skin structures, including the laminate load-bearing structures and honeycomb load-bearing structures with different composite material layups.

[0020] Furthermore, determine the layup and dimensions of the test piece according to the position of the selected test piece in the airframe structure, including:

[0021] According to the airframe structure parts for the post-lightning strike residual strength test, respectively select the shear skin structures in the typical sections of the helicopter, namely the front fuselage, middle fuselage, transition section, tail section, and horizontal tail structure, as the layup input of the test piece, determine the layup types of the test piece, and the size of each test piece is determined to be 500mm×500mm.

[0022] Furthermore, conduct a residual strength test on the post-lightning strike test piece and the comparison test piece, including:

[0023] Before the test, adjust the press so that the load on the test piece in the initial state is 0, adopt the displacement control mode for loading, and the press automatically loads at a set speed according to the control program until the test piece becomes unstable and then fails;

[0024] Record the load-displacement curve, record the load and instability form at the time of instability, and the maximum load and failure form at the time of failure;

[0025] Among them, the composite skin structures of each section of the helicopter airframe are shear skins, and the typical load they bear is shear load; verify the residual strength of the post-lightning strike test piece by conducting a shear load-bearing capacity test on the test piece; the test support method is: support by using a four-link mechanism fixture, and apply loads through two diagonals of the four-link mechanism. The four-link mechanism is connected to the four sides of the test piece with rivets.

[0026] Further, analyze the damage locations and degrees of damage of each test piece, including:

[0027] Perform statistical analysis on the recorded test loads and failure modes, compare the shear bearing capacities of the damaged test pieces after different lightning strikes for each ply with the corresponding comparison test pieces of the ply, and according to the determined criteria, determine whether the remaining bearing capacity of the damaged test pieces after lightning strikes can meet the criteria requirements, and finally give a conclusion on whether the helicopter can land safely after being struck by lightning.

[0028] In a second aspect, a verification system for the remaining strength of a helicopter airframe composite structure after lightning strikes is provided, including: a test piece, a loading mechanism, and a processor;

[0029] Among them, the test piece refers to a structural member of a specific ply determined for the remaining strength test of the helicopter airframe composite structure after lightning strikes;

[0030] The loading mechanism is used to hold, fix, and load the test piece, and includes a press platform and a four-link mechanism;

[0031] The processor is used to record the test applied load and determine the test failure load.

[0032] Beneficial effects: The verification method and system for the remaining strength of the helicopter airframe composite structure after lightning strikes proposed in this application can play a guiding and reference role in the process of the remaining strength test of the helicopter airframe composite structure after lightning strikes. By experimentally verifying the remaining strength of the airframe composite structure after lightning strikes, testing the damage degree of the composite structure, and obtaining its remaining strength, the safe flight of the helicopter after being struck by lightning is ensured. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic flow chart of a verification method for the remaining strength of a helicopter airframe composite structure after lightning strikes provided by this application.

[0034] Figure 2 It is a schematic diagram of the typical dimensions of a test piece for the remaining strength of a helicopter airframe composite structure after lightning strikes (honeycomb sandwich structure on the left, laminate structure on the right).

[0035] Figure 3 It is a schematic diagram of the support and loading of a test piece for the remaining strength of a helicopter airframe composite structure after lightning strikes provided by this application.

[0036] Figure 4 It is a schematic diagram of the loading mechanism of a system for the remaining strength of a helicopter airframe composite structure after lightning strikes provided by this application.

[0037] Figure 5Schematic diagram of lightning strike zones for the remaining strength test of a helicopter airframe composite structure provided by this application. Specific implementation mode

[0038] To make the purpose, technical solutions and advantages of the implementation of this application clearer, the technical solutions in the implementation modes of this application will be described in more detail below in conjunction with the accompanying drawings in the implementation modes of this application. In the drawings, the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions from beginning to end. The described implementation modes are part of the implementation modes of this application, not all of them. The implementation modes described below by referring to the accompanying drawings are exemplary and are intended to explain this application and should not be construed as limiting this application. Based on the implementation modes in this application, all other implementation modes obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of this application. The implementation modes of this application will be described in detail below in conjunction with the accompanying drawings.

[0039] In the description of the present invention, it should be understood that the orientation or positional relationships indicated by the terms "center", "axial direction", "vertical", "upper", "lower", "upper end", "bottom end", "inner", "outer", etc. are based on the orientation or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the scope of protection of the present invention.

[0040] The present invention provides a method for verifying the remaining strength of a composite airframe structure after lightning strike. First, determine the test piece, its layup and dimensions, then conduct a lightning current impact test on the selected lightning strike test piece, and then conduct remaining strength tests on the damaged test piece after lightning strike and the comparison piece respectively. Finally, obtain the remaining strength of the composite structure after lightning strike through comparative analysis and judge whether it meets the requirements.

[0041] Among them, the specific method includes:

[0042] [1] According to the lightning strike zones of the helicopter ( Figure 5 ), and the force characteristics of the airframe structure, determine the parts of the airframe structure where the test pieces are selected.

[0043] For the composite structure components in the typical lightning initial attachment area and sweeping area of the helicopter airframe structure, after being impacted by the direct effect environment and indirect effect environment of lightning strike, the helicopter should be able to land safely, and the skin structure at key parts should not cause structural damage endangering the flight safety of the helicopter due to lightning strike. Therefore, select typical structural parts in the typical lightning areas as the parts where the test pieces for the remaining strength test after lightning strike are selected. These structural parts are mainly the composite skin structures of the airframe, including the laminated plate load-bearing structures and honeycomb load-bearing structures with different composite layups.

[0044] [2] Determine the layup and dimensions of the test specimens according to the location of the selected test specimens in the airframe structure.

[0045] According to the airframe structural parts for the post-lightning residual strength test determined in [1], shear skin structures are respectively selected from the front fuselage, middle fuselage, transition section, tail section, and horizontal tail structure of each typical section of the helicopter as the layup input of the test specimens, determine the types of layup of the test specimens, and the size of each test specimen is determined to be 500 mm × 500 mm.

[0046] In order to be able to cooperate with the installation of the test fixture, cut off the four right angles of the test specimen, as shown in the appendix Figure 1 as shown.

[0047] [3] Determine the number of test specimens

[0048] The total number of test specimens corresponding to each type of layup determined in [2] is 6 pieces each, among which 3 pieces are lightning strike test specimens and 3 pieces are comparison test specimens. Among them, the lightning strike test specimens are used to conduct lightning strikes first and then residual strength tests, and the comparison test specimens do not undergo lightning strikes and directly conduct strength tests. Their test results are compared with the residual strength test results of the lightning strike test specimens to evaluate whether the composite material structural parts can meet the residual strength requirements after lightning strikes, and to ensure the safe landing of the helicopter after lightning strikes.

[0049] [4] Conduct lightning current impulse tests

[0050] According to the lightning zone where the selected airframe composite material structure of the test specimen is located, conduct lightning current impulse tests on the lightning strike test specimens respectively to cause lightning strike damage to the body of the composite material lightning strike test specimens.

[0051] [5] Analyze the damage location and damage degree of the airframe composite material lightning strike test specimens.

[0052] After lightning strikes, tap the damaged test specimens after lightning strikes and conduct ultrasonic non-destructive testing to preliminarily determine the area and damage degree of the damaged area of the test specimens.

[0053] [6] Conduct residual strength tests on the test specimens after lightning strikes and comparison test specimens;

[0054] The composite skin structures of each section of the helicopter airframe are mainly shear skins, and the typical loads they mainly bear are shear loads. Therefore, the residual strength of the test specimens after lightning strikes is verified by conducting shear bearing capacity tests on the test specimens.

[0055] Conduct shear bearing capacity tests on 3 damaged test specimens after lightning strikes and comparison test specimens respectively.

[0056] The test support method is as follows: use a four-bar mechanism fixture for support and apply loads through two diagonals of the four-bar mechanism. The four-bar mechanism is connected to the four sides of the test piece with rivets. For details, see the appendix Figure 2 .

[0057] Test process: Before the test, adjust the press so that the load on the test piece in the initial state is 0. Adopt the displacement control mode for loading. The press automatically loads at a set speed (1 mm / min) according to the control program until the test piece becomes unstable and then fails; record the load-displacement curve, record the load and instability form at the time of instability, and the maximum load and failure form at the time of failure.

[0058] [7] Analyze the test results and their effectiveness.

[0059] Conduct statistical analysis on the test loads and failure modes recorded in [6]. Compare the shear bearing capacity of three damaged test pieces after lightning strike of each ply with that of three corresponding comparison test pieces of the same ply. According to the determined criterion, determine whether the remaining bearing capacity of the damaged test pieces after lightning strike can meet the criterion requirements, and finally give a conclusion on whether the helicopter can land safely after being struck by lightning.

[0060] The present invention also provides a verification system for the remaining strength of a helicopter airframe composite structure after lightning strike, which is used for the method for verifying the remaining strength of a helicopter airframe composite structure after lightning strike described in the first aspect. The system includes: a test piece, a loading mechanism, and a processor.

[0061] Among them, the test piece refers to a structural member of a specific ply determined for the test of the remaining strength of a helicopter airframe composite structure after lightning strike;

[0062] The loading mechanism is used to hold, fix, and load the test piece, and includes a press platform and a four-bar mechanism;

[0063] The processor is used to record the test applied load and determine the test failure load.

[0064] The system is as Figure 3 shown.

[0065] A specific implementation example is further described as follows:

[0066] (1) According to the lightning protection zones of a certain type of helicopter, as Figure 4 shown, determine the composite structure components located in the areas with relatively severe lightning current impacts. Select the skin structure parts of the front fuselage, middle fuselage, tail section, and horizontal tail of the airframe as typical lightning strike test pieces, and the selected structures are shown in Table 1. Among them, there are two typical composite structures, namely, composite laminate structure and composite honeycomb sandwich structure.

[0067] Table 1 Test pieces

[0068] Serial number Position Layup Number of specimens 1 Front fuselage skin (honeycomb sandwich structure) Layup 1 3 lightning strike specimens + 3 comparison specimens 2 Middle fuselage skin (laminate structure) Layup 2 3 lightning strike specimens + 3 comparison specimens 3 Tail section skin (honeycomb sandwich structure) Layup 3 3 lightning strike specimens + 3 comparison specimens 4 Horizontal tail skin (honeycomb sandwich structure) Layup 4 3 lightning strike specimens + 3 comparison specimens

[0069] (2) Based on the structural parts of the airframe determined in (1) for the post-lightning strike residual strength test, shear skin structures are respectively selected in the front fuselage, middle fuselage, transition section, tail section, and horizontal tail structure of each typical section of the helicopter as the ply input of the test specimens. It is determined that the types of plies for the test specimens are 4, namely Ply 1 to Ply 4, and the size of each test specimen is determined to be 500 mm × 500 mm.

[0070] (3) The number of test specimens is 6 for each ply, including 3 lightning strike specimens and 3 comparison specimens.

[0071] (4) According to the lightning zones where the selected composite material structures of the airframe of the test specimens are located, lightning current impact tests are respectively carried out on the lightning strike test specimens to cause lightning strike damage to the bodies of the composite material lightning strike test specimens.

[0072] (5) Knock and ultrasonic non-destructive testing are carried out on the lightning strike damage generated in (4) to determine the degree and scope of the damage after lightning strike.

[0073] (6) Residual strength tests are carried out on the test specimens after lightning strike and the comparison test specimens.

[0074] Shear bearing capacity tests are carried out on the test specimens. First, the test specimens are bolted to the inner connecting rods as required, and then the outer connecting rods are fixed to the inner connecting rods with bolts. The two diagonals of the test specimens with the fixtures installed are connected to the pressure platform of the testing machine, and loading is carried out on the two diagonals of the four-link mechanism. The installation diagram is attached Figure 3 as shown.

[0075] Before the test, adjust the press so that the load received by the test specimens in the initial state is 0. According to the requirements of the test task book, the displacement control mode is adopted for loading. The press automatically loads at a set speed (1 mm / min) according to the control program until the test specimens become unstable and then fail; record the load-displacement curve, record the load and instability form at the time of instability, and the maximum load and failure form at the time of failure.

[0076] [7] Analyze the test results

[0077] Based on the test results recorded in (6), taking Ply 1 as an example, as shown in Table 1.

[0078] Table 2 Test Results (Ply 1)

[0079]

[0080] From the perspective of the test failure mode, the test specimens all become unstable and finally fail along the force direction, and the failure mode is reasonable.

[0081] From the statistical data of the failure load of the test piece, comparing the failure load of the shear test of the test piece before and after lightning strike, the percentage of the remaining strength of the test piece after lightning strike is 91.6%.

[0082] According to the development requirements of a certain type of aircraft, it is necessary to ensure safe landing under the service load condition after lightning strike damage. The percentage of the service load of the structural member is 67%. Therefore, the remaining strength of the structural member after lightning strike is greater than its service load (limit load), meeting the requirements.

[0083] In the embodiment of the present invention, a verification system for the remaining strength of a helicopter airframe composite structure after lightning strike is also provided, which is used for the method for verifying the remaining strength of a helicopter airframe composite structure after lightning strike described in the above embodiment. The system includes: a test piece, a loading mechanism, and a processor.

[0084] Among them, the test piece refers to a structural member of a specific ply determined for the test of the remaining strength of a helicopter airframe composite structure after lightning strike; the loading mechanism is used to hold, fix, and load the test piece, including a press platform and a four-bar mechanism; the processor is used to record the test applied load and determine the test failure load.

[0085] Those skilled in the art will readily conceive of other embodiments of the present disclosure after considering the specification and the practice disclosed herein. This application is intended to cover any variations, uses, or adaptations of the present disclosure that follow the general principles of the present disclosure and include known common knowledge or conventional technical means in the technical field not disclosed in the present disclosure. The specification and examples are only regarded as exemplary, and the true scope and spirit of the present disclosure are pointed out by the following claims.

[0086] It should be understood that the present disclosure is not limited to the exact structure already described and shown in the drawings, and various modifications and changes can be made without departing from its scope. The scope of the present disclosure is only limited by the appended claims.

Claims

1. A method for verifying the remaining strength of a helicopter airframe composite material structure after lightning strike, characterized in that, including: Determine the test piece, its ply layup and dimensions; Conduct lightning current impulse tests on the selected lightning strike test pieces; Conduct residual strength tests on the damaged test pieces after lightning strike and the comparison pieces respectively; Obtain the residual strength of the composite material structure after lightning strike through comparative analysis, and judge whether it meets the requirements.

2. The method according to claim 1, wherein Determine the test piece, its ply layup and dimensions, including: According to the lightning protection zones of the helicopter and the stress characteristics of the airframe structure, determine the airframe structure parts where the test pieces are selected; According to the position of the selected test piece in the airframe structure, determine the ply layup and dimensions of the test piece.

3. The method according to claim 2, wherein Conduct lightning current impulse tests on the selected lightning strike test pieces, including: Determine the number of test pieces; According to the lightning protection zones of the helicopter where the selected airframe composite material structures of the test pieces are located, conduct lightning current impulse tests on the test pieces respectively, so as to cause lightning strike damage to the body of the composite material lightning strike test pieces; Analyze the damage positions and damage degrees of each test piece.

4. The method according to claim 3, wherein According to the lightning protection zones of the helicopter and the stress characteristics of the airframe structure, determine the airframe structure parts where the test pieces are selected, including: Select typical structural parts in typical lightning areas as the parts where the test pieces for residual strength tests after lightning strike are selected. These structural parts are the composite material skin structures of the airframe, including the laminate load-bearing structures and honeycomb load-bearing structures with different composite material ply layups.

5. The method according to claim 4, wherein According to the position of the selected test piece in the airframe structure, determine the ply layup and dimensions of the test piece, including: According to the airframe structure parts used for the residual strength test after lightning strike, select the shear skin structures in the front fuselage, middle fuselage, transition section, tail section, and horizontal tail structures of each typical section of the helicopter respectively as the ply layup input of the test piece, determine the ply layup types of the test piece, and the size of each test piece is determined to be 500mm×500mm.

6. The method according to claim 5, wherein Conduct residual strength tests on the test pieces after lightning strike and the comparison test pieces, including: Before the test, adjust the press so that the load received by the test piece in the initial state is 0, adopt the displacement control mode for loading, and the press automatically loads at a set speed according to the control program until the test piece becomes unstable and then fails; Record the load-displacement curve, record the load and instability form at the time of instability, and the maximum load and failure form at the time of failure; Among them, the composite material skin structures of each section of the helicopter airframe are shear skins, and the typical load they bear is shear load; verify the residual strength of the test pieces after lightning strike by conducting shear bearing capacity tests on the test pieces; the test support method is: support with a four-link mechanism fixture, and apply load through two diagonals of the four-link mechanism; the four-link mechanism is connected to the four sides of the test piece with rivets.

7. The method according to claim 6, wherein Analyze the damage positions and damage degrees of each test piece, including: Conduct statistical analysis on the recorded test loads and failure modes, compare the shear bearing capacity of the damaged test pieces after lightning strike with different ply layups of each ply with the comparison test pieces of the corresponding ply, and according to the determined criteria, judge whether the remaining bearing capacity of the damaged test pieces after lightning strike can meet the requirements of the criteria, and finally give the conclusion on whether the helicopter can land safely after being struck by lightning.

8. A verification system for the residual strength of a composite structure of an airframe after lightning strike, characterized in that, including: Test pieces, loading mechanism and processor; Among them, the test piece refers to the structural part with a specific ply layup determined for conducting the residual strength test of the composite material structure of the helicopter airframe after lightning strike; The loading mechanism is used to hold, fix and load the test piece, and includes a press platform and a four-bar linkage mechanism; The processor is used to record the test applied load and determine the test failure load.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, the method described in any one of claims 1-7 is implemented.

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