A method for compiling the swing fatigue test load spectrum of an elastic ball-and-bowl element

Abstract

This application provides a method for compiling the swing fatigue test load spectrum of an elastic ball-and-socket element, belonging to the field of aircraft component fatigue testing technology. The method includes: determining the overall load spectrum of a UAV rotor system; determining the flight load spectrum of the elastic upper and lower ball-and-socket elements based on the overall load spectrum of the UAV rotor system and the main loads borne by the elastic upper and lower ball-and-socket elements; determining the test loading method based on the flight load spectrum of the elastic upper and lower ball-and-socket elements; determining the flight test load spectrum of the elastic upper and lower ball-and-socket elements based on the flight load spectrum and the test loading method; determining the tensile load in the flight test constant amplitude load spectrum based on the principle of equal damage and the dimensions of the test piece; determining the swing angle of the elastic lower ball-and-socket element based on the stiffness of the test piece and the swing load in the flight test load spectrum, ultimately obtaining the swing fatigue test constant amplitude load spectrum of the elastic upper and lower ball-and-socket elements.

Description

Technical Field

[0001] This application belongs to the field of fatigue testing technology for aircraft components, and specifically relates to a method for compiling a swing fatigue test load spectrum for an elastic ball cup element. Background Technology

[0002] In the strength design of the rotor hub components of an unmanned aerial vehicle (UAV) rotor system, the elastic upper and lower ball bearings are key components. These elastic upper and lower ball bearing elements are important parts of the rotor hub, characterized by high axial stiffness (in the direction of rotor thrust) and low flapping stiffness. The flapping fatigue test of the elastic upper and lower ball bearings is an experiment to verify the ability of these elements in the UAV rotor system to withstand complex load conditions. The load on the elastic upper and lower ball bearings is related to factors such as flight speed, altitude, flight attitude, time, load frequency, and flapping angle. The load history of the elastic upper and lower ball bearing elements is complex, which is not conducive to conducting experiments. Therefore, it is necessary to simplify the load spectrum of the flapping fatigue test for the elastic upper and lower ball bearings. Summary of the Invention

[0003] The purpose of this application is to provide a method for compiling the load spectrum of a swing fatigue test for an elastic ball cup element, so as to solve or alleviate at least one of the problems in the background art.

[0004] The technical solution of this application is: a method for compiling the swing fatigue test load spectrum of an elastic ball-and-socket element, comprising:

[0005] Determine the overall load spectrum of the UAV rotor system, and based on the overall load spectrum of the UAV rotor system and the main loads borne by the elastic upper and lower ball cup elements, determine the flight load spectrum of the elastic upper and lower ball cup elements;

[0006] The test loading method is determined based on the flight load spectrum of the elastic upper and lower ball cup components;

[0007] Based on the flight load spectrum and the test loading method, the flight test load spectrum of the elastic upper and lower ball cup elements is determined;

[0008] Based on the principle of equal damage and in combination with the size of the test specimen, the tensile load in the constant amplitude load spectrum of the flight test is determined;

[0009] The swing angle of the elastic lower ball cup is determined based on the stiffness of the test piece and the swing load in the flight test load spectrum, and finally the constant amplitude load spectrum of the swing fatigue test of the elastic upper and lower ball cup components is obtained.

[0010] Preferably, the overall load spectrum of the UAV rotor system includes triaxial overloads Fx, Fy, Fz and torques Mx, My, Mz under multiple flight states, wherein the subscripts x, y, and z are the X-axis, Y-axis and Z-axis directions in the body coordinate system, respectively.

[0011] The flight load spectrum of the elastic upper and lower ball bowl elements includes axial lift and flapping moment. The axial lift Fzi is the overload Fz under multiple flight conditions in the overall load spectrum, and the flapping moment Mi is the larger value between the moment Mxi and the moment Myi under multiple flight conditions in the overall load spectrum.

[0012] Preferably, the loading method is as follows:

[0013] The axial lift Fzi of the elastic upper and lower ball bowl elements is achieved by applying a static lift load to the elastic upper ball bowl, and the flapping moment Mi is achieved by applying a flapping load Fhi to the loading points on both sides of the flapping disk fixture of the elastic lower ball bowl.

[0014] Preferably, the flight test load spectrum of the elastic upper and lower ball bowl elements includes the axial lift Fzi under multiple flight conditions, the load Fwi at the connecting bolts of the small joint of the elastic lower ball bowl, and the flapping load Fhi at the loading points on both sides of the flapping disk fixture, where:

[0015]

[0016]

[0017] In the formula, Lw is the distance from the axis of the connecting bolt of the small joint of the ball bowl to the central axis of the ball bowl, and Lh is the distance from the loading point of the flapping disk fixture to the central axis of the ball bowl.

[0018] Preferably, the process of determining the tensile load in the equal-amplitude load spectrum of the flight test is as follows: [[ID=2)]]

[0019] Calculate the total damage of the flight test load spectrum , where ti is the time of each flight condition;

[0020] Calculate the total damage of the equal-amplitude load spectrum of the flight test , where the equal-amplitude load Fwd in the equal-amplitude load spectrum of the flight test takes the maximum value of the load Fwi in the flight test load spectrum, and the tensile load Fzd in the equal-amplitude load spectrum of the flight test takes the axial lift Fzi in the flight condition corresponding to the maximum value of the load Fwi;

[0021] Obtain the ratio N based on the total damage S of the flight test load spectrum and the total damage Sf of the equal-amplitude load spectrum of the flight test. When 5 < N < 15, the value of the tensile load Fzd is reasonable; otherwise, adjust the value of the tensile load Fzd to make 5 < N < 15, so as to obtain the tensile load Fzd.

[0022] Preferably, the calculation method of the flapping angle is as follows:

[0023]

[0024]

[0025] In the formula, X is the stiffness of the elastic upper and lower ball bowl components, and the load Fh is the maximum value of the load Fhi at the loading point of the waving disc fixture in the flight test load spectrum.

[0026] The fatigue test load spectrum compilation method for elastic ball cup elements provided in this application can realize the compilation of fatigue test load spectrum for elastic ball cup elements, and the compiled fatigue test load spectrum is relatively accurate. Attached Figure Description

[0027] To more clearly illustrate the technical solutions provided in this application, the accompanying drawings will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application.

[0028] Figure 1 This is a schematic diagram illustrating the method for compiling the fatigue load spectrum of the elastic ball-and-bowl element in this application. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be described in more detail below with reference to the accompanying drawings.

[0030] The purpose of this application is to propose a method for compiling the swing fatigue test load spectrum of the elastic upper and lower ball cup components used in UAV rotor systems. The elastic upper and lower ball cup components in UAV rotor systems need to transmit centrifugal force, torsional bending moment, and swinging moment, while also realizing the swinging, oscillation, and pitch-changing motion of the blades. The complex deformation of the structural components mainly relies on the deformation of the rubber components. This application simplifies the complex load on the elastic upper and lower ball cup components through the fatigue damage equivalence principle, which facilitates the conduct of fatigue tests and provides a basis for life assessment.

[0031] like Figure 1 As shown, the method for compiling the swing fatigue test load spectrum of the elastic ball-and-socket element of the rotor system of an unmanned aerial vehicle (UAV) provided in this application includes the following steps:

[0032] Step S1: Determine the overall load spectrum of the UAV rotor system. Based on the overall load spectrum of the UAV rotor system and the main loads borne by the elastic upper and lower ball cup components, determine the flight load spectrum of the elastic upper and lower ball cup components.

[0033] The overall load spectrum of a UAV rotor system typically includes three-dimensional overloads Fx, Fy, Fz and torques Mx, My, Mz under multiple flight conditions, where subscripts x, y, and z represent the X-axis, Y-axis, and Z-axis directions in the body coordinate system, respectively.

[0034] The main loads borne by the elastic upper and lower ball-and-socket components include axial lift and flapping moment. Therefore, the flight load spectrum of the elastic upper and lower ball-and-socket components includes both axial lift and flapping moment. Specifically, the axial lift Fzi in the flight load spectrum of the elastic upper and lower ball-and-socket components represents the overload Fz (i.e., lift) under various flight states in the overall load spectrum of the UAV rotor system. The flapping moment Mi in the flight load spectrum of the elastic upper and lower ball-and-socket components is the larger of the moments Mxi and Myi in the overall load spectrum, i.e.: , where i represents the flight state (i.e., the operating condition).

[0035] Step S2: Determine the test loading method based on the flight load spectrum of the elastic upper and lower ball cup elements.

[0036] In this application, the elastic upper and lower ball cup components mainly bear the continuous axial lift force Fzi and the swinging torque Mi. The axial lift force Fzi is achieved by applying a static lift load to the elastic upper ball cup, and the swinging torque Mi is achieved by applying a swinging load Fhi to the loading points on both sides of the swinging disc clamp of the elastic lower ball cup.

[0037] Step S3: Determine the flight test load spectrum of the elastic upper and lower ball cup elements based on the flight load spectrum and the test loading method.

[0038] In this application, the flight test load spectrum of the elastic upper and lower ball cup components includes the axial lift Fzi under various flight conditions, the load Fwi at the connecting bolt of the elastic lower ball cup small joint, and the swing load Fhi at the loading points on both sides of the swinging disc clamp, wherein:

[0039]

[0040]

[0041] In the formula, Lw is the distance from the axis of the ball cup small connector connecting bolt to the central axis of the ball cup, and Lh is the distance from the loading point of the swinging disc clamp to the central axis of the ball cup.

[0042] Step S4: Based on the principle of equal damage and the size of the test piece, determine the tensile load in the constant amplitude load spectrum of the flight test.

[0043] In this application, the tensile load in the constant amplitude load spectrum of the flight test is determined based on the axial lift Fzi and the load Fwi at the ball joint bolt in the flight test load spectrum, using the principle of equal damage. The process is as follows:

[0044] First, calculate the total damage of the flight test load spectrum:

[0045]

[0046] In the formula, ti represents the time for each flight state.

[0047] After that, calculate the total damage of the constant amplitude load spectrum of the flight test:

[0048]

[0049] In the formula, the constant amplitude load Fwd in the constant amplitude load spectrum of the flight test takes the maximum value of the load Fwi in the flight test load spectrum, and the tensile load Fzd in the constant amplitude load spectrum of the flight test takes the axial lift Fzi in the flight state corresponding to the maximum value of the load Fwi.

[0050] Through the above formula, the ratio N of the total damage S of the flight test load spectrum to the total damage Sf of the constant amplitude load spectrum of the flight test can be obtained. When 5 < N < 15, the value of the tensile load Fzd is reasonable; otherwise, adjust the value of the tensile load Fzd to make 5 < N < 15, so as to obtain the tensile load Fzd.

[0051] Step S5: Determine the flapping angle of the elastic lower ball bowl according to the stiffness of the test piece and the flapping load in the flight test load spectrum, and finally obtain the constant amplitude load spectrum of the flapping fatigue test of the elastic upper and lower ball bowl elements.

[0052] The stiffness of the elastic upper and lower ball bowl elements is X (N / °), and the load Fh takes the maximum value of the load Fhi at the loading point of the flapping disk fixture in the flight test load spectrum. The flapping angle is calculated according to the following formula:

[0053]

[0054] .

[0055] According to the tensile load Fzd and the flapping angle determined in the constant amplitude load spectrum of the flight test, the constant amplitude load spectrum of the flapping fatigue test of the elastic upper and lower ball bowl elements is finally obtained, as shown in Table 1.

[0056] Table 1 Constant amplitude load spectrum of flapping fatigue test of elastic upper and lower ball bowl elements

[0057]

[0058] The method for compiling the fatigue test load spectrum of the elastic ball bowl element provided by this application can realize the compilation of the fatigue test load spectrum of the elastic ball bowl element, and the compiled fatigue test load spectrum is relatively accurate.

[0059] The above is only the specific implementation manner of this application, but the protection scope of this application is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by this application should be covered within the protection scope of this application. Therefore, the protection scope of this application should be subject to the protection scope of the claimed rights.

Claims

1. A method for compiling the load spectrum of a swing fatigue test for an elastic ball-and-socket element, characterized in that, Comprising: Determine the overall load spectrum of the UAV rotor system, and determine the flight load spectrum of the elastic upper and lower ball bowl elements according to the overall load spectrum of the UAV rotor system and the main loads borne by the elastic upper and lower ball bowl elements; Determine the test loading method according to the flight load spectrum of the elastic upper and lower ball bowl elements; Determine the flight test load spectrum of the elastic upper and lower ball bowl elements according to the flight load spectrum and in combination with the test loading method; Determine the tensile load in the flight test constant amplitude load spectrum according to the equal damage principle and in combination with the test piece size; Determine the flapping angle of the elastic lower ball bowl according to the stiffness of the test piece and the flapping load in the flight test load spectrum, and finally obtain the constant amplitude load spectrum for the flapping fatigue test of the elastic upper and lower ball bowl elements.

2. The method for compiling the swing fatigue test load spectrum of the elastic ball-and-socket element as described in claim 1, characterized in that, The overall load spectrum of the UAV rotor system includes three-directional overloads Fx, Fy, Fz and torques Mx, My, Mz in multiple flight states, where the subscripts x, y, z are the X-axis, Y-axis and Z-axis directions in the body coordinate system respectively; The flight load spectrum of the elastic upper and lower ball bowl elements includes axial lift and flapping torque. The axial lift Fzi is the overload Fz in multiple flight states in the overall load spectrum, and the flapping torque Mi is the larger of the torques Mxi and Myi in multiple flight states in the overall load spectrum.

3. The method for compiling the swing fatigue test load spectrum of the elastic ball-and-socket element as described in claim 2, characterized in that, The loading method is as follows: The axial lift Fzi of the elastic upper and lower ball bowl elements is achieved by applying a static lift load on the elastic upper ball bowl, and the flapping torque Mi is achieved by applying a flapping load Fhi at the loading points on both sides of the flapping disk fixture of the elastic lower ball bowl.

4. The method for compiling the swing fatigue test load spectrum of the elastic ball-and-socket element as described in claim 3, characterized in that, The flight test load spectrum of the elastic upper and lower ball bowl elements includes axial lift Fzi, load Fwi at the connecting bolts of the small joints of the elastic lower ball bowl, and flapping load Fhi at the loading points on both sides of the flapping disk fixture in multiple flight states, where: In the formula, Lw is the distance from the axis of the connecting bolt of the small joint of the ball bowl to the axis of the center of the ball bowl, and Lh is the distance from the loading point of the flapping disk fixture to the axis of the center of the ball bowl.

5. The method for compiling the swing fatigue test load spectrum of the elastic ball-and-cup element as described in claim 4, characterized in that, The process of determining the tensile load in the flight test constant amplitude load spectrum is as follows: Calculate the total damage of the flight test load spectrum In the formula, ti represents the time for each flight state; Calculate the total damage of the constant amplitude load spectrum in flight tests. In the formula, the constant amplitude load Fwd in the constant amplitude load spectrum of the flight test takes the maximum value of the load Fwi in the load spectrum of the flight test, and the tensile load Fzd in the constant amplitude load spectrum of the flight test takes the axial lift Fzi in the flight state corresponding to the maximum value of the load Fwi. Obtain the ratio N from the total damage S of the flight test load spectrum and the total damage Sf of the flight test constant amplitude load spectrum. When 5 < N < 15, the value of the tensile load Fzd is reasonable; otherwise, adjust the value of the tensile load Fzd to make 5 < N < 15, so as to obtain the tensile load Fzd.

6. The method for compiling the swing fatigue test load spectrum of the elastic ball-and-cup element as described in claim 5, characterized in that, The calculation method of the flapping angle is as follows: In the formula, X is the stiffness of the elastic upper and lower ball bowl elements, and the load Fh takes the maximum value of the load Fhi at the loading point of the flapping disk fixture in the flight test load spectrum.

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