Helicopter composite material propeller hub damage safety test spectrum compilation method

Abstract

The invention belongs to the field of helicopter structure fatigue design, and relates to a helicopter composite material propeller hub damage safety test spectrum compilation method. The method comprises the following steps: selecting a square hole and a flexible arm as a fatigue dangerous part of the composite propeller hub of the helicopter; the square hole is located in the position, close to the rotor shaft, of the flexible arm. The characteristic loads are determined to be the flapping bending moment load of the square hole and the flapping shimmy bending moment load of the flexible arm; in order to monitor the characteristic load of the composite material propeller hub, a strain gauge is attached to the corresponding section, and calibration is carried out; during a damage safety test, loads are applied to all flexible arms of the composite propeller hub of the helicopter at the same time; and according to a damage test result, compiling an actual measurement load spectrum of the helicopter composite material propeller hub.

Description

Technical Field

[0001] The invention belongs to the field of helicopter structural fatigue design and relates to a method for compiling a damage safety test spectrum of a helicopter composite material hub. Background Art

[0002] like Figure 1 As shown in the figure, the composite hub, as the core component of the helicopter rotor system, primarily transfers and balances the centrifugal loads from the blades, transmits lift and control torque, and forms horizontal and vertical hinges. The development of load spectra for composite hub damage safety tests is a key technology for helicopter fatigue life assessment.

[0003] Damage tolerance test spectra developed domestically and internationally primarily for airframe structures are designed for testing. These spectra are primarily designed to withstand low-cycle ground-to-air-ground loads. Composite propeller hubs, on the other hand, are primarily subjected to high-frequency combined ground-to-air-ground fatigue loads, with fatigue failure modes characterized by debonding and delamination. Damage tolerance test spectra for airframe structures, primarily based on low-cycle loads, cannot accurately assess the fatigue failure of composite propeller hubs during flight. Therefore, a method for developing a damage tolerance test spectra tailored to fatigue loads on composite propeller hubs has yet to be proposed. Summary of the Invention

[0004] Purpose of the invention: To provide a method for compiling a damage safety test spectrum for a helicopter composite propeller hub, which is convenient for engineering application and meets the needs of composite propeller hub test verification.

[0005] Technical solution:

[0006] A method for compiling a damage safety test spectrum for a helicopter composite hub is provided, including:

[0007] The square hole and the flexible arm are selected as fatigue risk parts of the helicopter composite rotor hub; the square hole is located at the position of the flexible arm close to the rotor shaft;

[0008] The characteristic loads are determined to be the flapping bending moment load of the square hole and the flapping bending moment load of the flexible arm;

[0009] In order to monitor the characteristic load of the composite hub, strain patches are attached to the corresponding sections and calibrated;

[0010] During the damage safety test, loads are applied simultaneously to all flexible arms of the helicopter composite rotor hub;

[0011] Based on the damage test results, the measured load spectrum of the helicopter composite hub is compiled.

[0012] Furthermore, the cross section includes:

[0013] The section where one end of the square hole rotor shaft is located, which is close to the root of the flexible arm;

[0014] The cross section is selected between the first step and the second step of the flexible arm, and the selected cross section is close to the top of the flexible arm.

[0015] Furthermore, during the damage safety test, loads are applied simultaneously to all flexible arms of the helicopter composite rotor hub, including:

[0016] The flapping excitation is applied to the spherical elastic bearing on one side of the square hole close to the top of the flexible arm, and the flapping excitation and the shimmying excitation are applied to the top of the flexible arm at the same time to achieve simultaneous load application.

[0017] Furthermore, the applied loads include:

[0018] 1) Load F acting on the top of the flexible arm in the swinging direction b1 , determine the flapping bending moment of the composite hub flexible arm BB section, the direction is that the upper surface is under pressure and is positive;

[0019] 2) Load F acting on the flexible arm end in the swing direction T1 , determine the shimmy bending moment of the composite hub flexible arm BB section, the direction is that the leading edge is under pressure and is positive;

[0020] 3) Centrifugal force F, the direction pointing to the end of the flexible arm is positive;

[0021] 4) Load F acting on the spherical elastic bearing in the swinging direction b2 , determine the flapping bending moment of the square hole AA section of the composite hub, with the direction being positive when the upper surface is under pressure;

[0022] 5) Load F acting on the spherical elastic bearing in the shimmying direction T2 , to offset F T1 ;

[0023] Among them, the swing excitation and shimmy excitation applied at the top of the arm are realized by 1) and 2); the swing excitation applied at the spherical elastic bearing is realized by 3)-5).

[0024] Furthermore, based on the damage test results, a measured load spectrum of the helicopter composite hub was compiled, including:

[0025] Preparation of the measured load spectrum of the composite hub: Based on the measured load data of the characteristic loads of the square hole and flexible arm of the composite hub, the measured flight load amplitude and frequency of the characteristic loads of the square hole and flexible arm of the helicopter composite hub are obtained through state division, peak detection, false elimination, filtering, and "rainflow" counting.

[0026] Furthermore, the method further comprises:

[0027] Eliminate the corresponding states that are less than a predetermined proportion of the maximum dynamic load in the measured load spectrum of the composite hub to form the final composite hub damage tolerance test state spectrum;

[0028] During the damage safety test of the composite hub, the static load is superimposed on the dynamic load of each dynamic load spectrum block to compile the damage safety fatigue test load spectrum.

[0029] Furthermore, the predetermined ratio is within a range of 10% to 15%.

[0030] Furthermore, the load spectrum of the damage safety fatigue test includes: spectrum block A and spectrum block B, spectrum block A is a 1-hour spectrum block, and spectrum block B is a 5-hour spectrum block.

[0031] Furthermore, the loading process of a load spectrum block test is applied as follows:

[0032] a) Acting static load;

[0033] b) Flapping bending moment and shimmying bending moment of load spectrum block of damage safety fatigue test;

[0034] c) The swinging bending moment and shimmying bending moment loads return to zero, and then the centrifugal force returns to zero.

[0035] Furthermore, the order of applying the load spectrum blocks of the composite hub damage safety test is: AABAAA arrangement, which constitutes a test dynamic load spectrum corresponding to 5 hours.

[0036] Beneficial effects:

[0037] Based on the load characteristics of helicopter composite hubs, the present invention proposes a method for compiling a damage safety test spectrum for helicopter composite hubs. The method can truly reflect the fatigue damage of the composite hubs in actual flight and can simplify the load to the greatest extent, thereby saving test cycles and economic costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a schematic diagram of the composite propeller hub structure;

[0039] Figure 2 It is a schematic diagram of the damage test patch.

[0040] Figure 3 It is a schematic diagram of dynamic load test loading.

[0041] Figure 4 It is a schematic diagram of the load of the damage test. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solutions and advantages of the implementation of this application clearer, the technical solutions in the implementation of this application will be described in more detail below in conjunction with the drawings in the implementation of this application. In the drawings, the same or similar numbers throughout represent the same or similar elements or elements with the same or similar functions. The described implementation is a part of the implementation of this application, not all of the implementations. The implementation described below with reference to the drawings is exemplary and is intended to be used to explain this application, and should not be understood as a limitation on this application. Based on the implementation in this application, all other implementations obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application. The implementation of this application is described in detail below in conjunction with the drawings.

[0043] In the description of the present invention, it should be understood that the terms "center", "axial", "vertical", "up", "down", "upper end", "bottom end", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship 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 therefore cannot be understood as limiting the scope of protection of the present invention.

[0044] The present invention provides a method for compiling a damage safety test spectrum for a helicopter composite hub, comprising the following steps:

[0045] [1] The method for compiling load spectrum of damage safety test of helicopter composite hub of the present invention selects square hole and flexible arm as fatigue risk parts of helicopter composite hub, such as Figure 1 As shown in Figure 1, the composite hub consists of three centrosymmetric flexible arms and three square holes. The characteristic loads are the flapping bending moment load of the square holes and the flapping bending moment load of the flexible arms.

[0046] [2] Figure 2 As shown in the figure, in order to monitor the characteristic load of the composite hub, strain gauges should be attached to the corresponding sections and calibrated: a) Strain gauges should be attached to section AA to measure the flapping bending moment of the square hole; b) Strain gauges should be attached to section BB to measure the flapping bending moment and shimmying bending moment of the flexible beam arm.

[0047] [3] Figure 3 As shown in the figure, the damage safety test load of the composite hub is applied simultaneously to the three flexible arms of the composite hub during the damage safety test. To facilitate the test loading, the flapping bending moment borne by the square hole of the composite hub and the flapping bending moment and shimmy bending moment borne by the flexible arms can be obtained by applying 5 test loads to each flexible arm:

[0048] 1) Centrifugal force F, the direction pointing to the flexible arm end is positive;

[0049] 2) Static load F acting on the spherical elastic bearing in the oscillation direction T2 ;

[0050] 3) Load F acting on the spherical elastic bearing in the swinging direction b2 ,determine the flapping bending moment of the square hole AA section of the composite hub, the direction is that the upper surface is under pressure and is positive;

[0051] 4) Load F acting on the flexible arm end in the swinging direction b1 , determine the flapping bending moment of the composite hub flexible arm BB section, the direction is that the upper surface is under pressure;

[0052] 5) Load F acting on the flexible arm end in the swing direction T1 , determine the swing bending moment of the flexible arm BB section of the composite hub, with the direction being positive when the leading edge is under pressure.

[0053] [4] The measured load spectrum of the composite propeller hub was compiled. Based on the measured load data of the characteristic loads of the square hole and flexible arm of the composite propeller hub, the flight measured load amplitude and frequency of the characteristic loads of the square hole and flexible arm of the composite propeller hub were obtained through state division, peak detection, false elimination, filtering, and "rain flow" counting.

[0054] [5] Eliminate the corresponding states that are less than a predetermined proportion of the maximum dynamic load in the measured load spectrum of the composite hub to form the final composite hub damage tolerance test state spectrum. The predetermined proportion is generally between 10% and 15%. If the predetermined proportion is too large, the validity of the damage safety test results will be affected. If the predetermined proportion is too small, the simplified state effect cannot be achieved. 10% is preferred.

[0055] [6] During the damage safety test of composite hub, the dynamic load of each dynamic load spectrum block is superimposed on the static load, starting from 0 and finally returning to 0. The dynamic load spectrum is controlled by 5 take-offs and landings per hour, and two test load spectrum blocks are compiled: damage safety fatigue test load spectrum A spectrum block (1 hour spectrum block) and spectrum block B spectrum block (5 hour spectrum block).

[0056] The loading process of a load spectrum block test is applied as follows:

[0057] A) Static loads such as centrifugal force;

[0058] B) Action damage safety fatigue test load spectrum block swinging moment, shimmy bending moment;

[0059] C) The swinging bending moment and shimmying bending moment loads return to zero, and then the centrifugal force returns to zero.

[0060] [7] Figure 4As shown in the figure, the order of applying the load spectrum blocks of the composite hub damage safety test is: AABAAA arrangement, which constitutes the test dynamic load spectrum corresponding to 5 hours.

[0061] [8]:Loading sequence for composite hub damage safety fatigue test:

[0062] 1) 30 hours of the spectrum block;

[0063] 2) 100% limit load test, maintain this load for at least 30 seconds.

[0064] 3) 60 hours of the spectrum block;

[0065] 4) 100% ultimate load test, maintain this load for at least 3 seconds.

[0066] Other embodiments of the present disclosure will readily occur to those skilled in the art after considering the specification and practicing the disclosure 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 common knowledge or customary techniques in the art not disclosed herein. The description and examples are to be considered as exemplary only, with the true scope and spirit of the present disclosure being indicated by the following claims.

[0067] It should be understood that the present disclosure is not limited to the exact structures that have been described above and shown in the drawings, and that various modifications and changes can be made without departing from the scope thereof. The scope of the present disclosure is limited only by the appended claims.

Claims

1. A method for compiling a damage safety test spectrum for a helicopter composite hub, characterized in that: include: The square hole and flexible arm are selected as fatigue risk parts of helicopter composite rotor hub; The square hole is located on the flexible arm near the rotor shaft; The characteristic loads are determined to be the flapping bending moment load of the square hole and the flapping bending moment load of the flexible arm; In order to monitor the characteristic load of the composite hub, strain patches are attached to the corresponding sections and calibrated; During the damage safety test, loads are applied simultaneously to all flexible arms of the helicopter composite rotor hub; Based on the damage test results, the measured load spectrum of the helicopter composite hub is compiled.

2. The method according to claim 1, characterized in that the cross section include: The section where one end of the square hole rotor shaft is located, which is close to the root of the flexible arm; The cross section is selected between the first step and the second step of the flexible arm, and the selected cross section is close to the top of the flexible arm.

3. The method according to claim 2, characterized in that During the damage safety test, loads are applied simultaneously to all flexible arms of the helicopter composite rotor hub, including: The flapping excitation is applied to the spherical elastic bearing on one side of the square hole close to the top of the flexible arm, and the flapping excitation and the shimmying excitation are applied to the top of the flexible arm at the same time to achieve simultaneous load application.

4. The method according to claim 3, characterized in that Applied loads include: 1) Load F acting on the top of the flexible arm in the swinging direction b1 , determine the flapping bending moment of the composite hub flexible arm BB section, the direction is that the upper surface is under pressure and is positive; 2) Load F acting on the flexible arm end in the swing direction T1 , determine the shimmy bending moment of the composite hub flexible arm BB section, the direction is that the leading edge is under pressure and is positive; 3) Centrifugal force F, the direction pointing to the end of the flexible arm is positive; 4) Load F acting on the spherical elastic bearing in the swinging direction b2 , determine the flapping bending moment of the square hole AA section of the composite hub, with the direction being positive when the upper surface is under pressure; 5) Load F acting on the spherical elastic bearing in the shimmying direction T2 , to offset F T1 ; Among them, the swing excitation and shimmy excitation applied at the top of the arm are realized by 1) and 2); the swing excitation applied at the spherical elastic bearing is realized by 3)-5).

5. The method according to claim 4, characterized in that Based on the damage test results, the measured load spectrum of the helicopter composite hub is compiled, including: Compilation of the measured load spectrum of the composite hub: Based on the measured load data of the characteristic loads of the square hole and flexible arm of the composite hub, the measured flight load amplitude and frequency of the characteristic loads of the square hole and flexible arm of the helicopter composite hub are obtained through state classification, peak detection, false positive elimination, filtering, and "rainflow" counting.

6. The method according to claim 5, characterized in that The method further comprises: Eliminate the corresponding states that are less than a predetermined proportion of the maximum dynamic load in the measured load spectrum of the composite hub to form the final composite hub damage tolerance test state spectrum; During the damage safety test of the composite hub, the static load is superimposed on the dynamic load of each dynamic load spectrum block to compile the damage safety fatigue test load spectrum.

7. The method according to claim 6, characterized in that The predetermined ratio ranges from 10% to 15%.

8. The method according to claim 7, characterized in that The load spectrum of the damage safety fatigue test includes: spectrum block A and spectrum block B. Spectrum block A is a 1-hour spectrum block and spectrum block B is a 5-hour spectrum block.

9. The method according to claim 8, characterized in that The loading process of a load spectrum block test is applied as follows: a) Acting static load; b) Flapping bending moment and shimmying bending moment of load spectrum block of damage safety fatigue test; c) The swinging bending moment and shimmying bending moment loads return to zero, and then the centrifugal force returns to zero.

10. The method according to claim 9, characterized in that The order of applying the load spectrum blocks of the composite hub damage safety test is: AABAAA arrangement, which constitutes the test dynamic load spectrum corresponding to 5 hours.

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