Fatigue test method for rotor swing type vibration absorber

Abstract

The invention belongs to the field of helicopter fatigue design, and relates to a fatigue test method for a rotor swing type vibration absorber. The method comprises the following steps: transforming a test piece to obtain a test transformed piece; installing a test transformation piece; applying a characteristic load, wherein the characteristic load comprises a centrifugal force, a waving bending moment and a shimmy bending moment; according to fatigue test requirements and termination conditions, fatigue tests are carried out on the test transformation part, and different fatigue tests are adopted according to the loading characteristics of different structural parts of the pendulum type vibration absorber.

Description

Technical Field

[0001] The invention belongs to the field of helicopter fatigue design and relates to a fatigue test method for a rotor swing type vibration absorber. Background Art

[0002] During the flight of a helicopter, the rotor rotates in a very complex aerodynamic environment, and the alternating vibration loads on each blade converge on the hub, forming the main vibration source of the helicopter. The pendulum vibration absorber is a hub vibration absorbing device. As the rotor rotates, the force form is very complex, mainly subject to dynamic loads such as centrifugal force, flapping moment, and swing moment. During the fatigue design process, it is necessary to conduct fatigue tests on the pendulum vibration absorber to determine its dangerous parts and assess its fatigue performance, providing a basis for the final life assessment. Summary of the invention

[0003] The purpose of the present invention is to provide a rotor swing type vibration absorber fatigue test method, which can relatively simply carry out the vibration absorber fatigue test.

[0004] Technical solution:

[0005] A method for fatigue testing a rotor swing absorber is provided, comprising:

[0006] Transforming the test piece to obtain a test transformed piece;

[0007] Install test modifications;

[0008] Apply characteristic loads, which include centrifugal force, flapping bending moment, and shimmying bending moment;

[0009] Fatigue tests are carried out on the test modified parts according to fatigue test requirements and termination conditions, wherein different fatigue tests are adopted according to the load characteristics of different structural parts of the pendulum vibration absorber.

[0010] Further, the test piece is modified, including:

[0011] Select a molded blade, bore it and install the gasket, cut it at the Z400 section, keep the root section, and then lay a mat between the Z200 and Z300 sections; the mat material is dry glass cloth.

[0012] Install the pendulum vibration absorber to the specified position, apply primer and adhesive between the vibration absorber and the pad cloth, tighten the upper and lower shells with bolts according to the specified tightening torque, and cure them at room temperature to obtain the test modified part.

[0013] Furthermore, the glass cloth is pre-impregnated with adhesive, and before laying, the space between the cloth and the blade body is cleaned.

[0014] Further, the test modification parts are installed, including:

[0015] The test modification part is connected to the fixture and fixed on the test bench by connecting bolts according to actual use conditions; the test load is applied by the actuator according to the loading position requirements; the test control system adopts a multi-point coordinated loading system for loading control; the main blade pendulum vibration absorber is fixed at the blade bushing position, and the rotating shaft, rocker arm and rocker arm mounting bolt structure are dummy parts.

[0016] Furthermore, characteristic loads are applied, including:

[0017] For low-cycle fatigue tests, the characteristic load that causes damage to the shell is applied, namely the centrifugal force generated by the pendulum ball;

[0018] For high cycle fatigue testing, characteristic loads of the shaft, rocker arm and rocker arm mounting bolt structure, namely the centrifugal force and lateral force of the swing ball, are applied.

[0019] Further, low cycle fatigue testing, including:

[0020] The shell is subjected to low-cycle fatigue test, in which the shaft, rocker arm and rocker arm mounting bolt structure are dummy parts.

[0021] Further, high cycle fatigue testing, including:

[0022] After completing the low-cycle fatigue test assessment of the shell, the shaft, rocker arm and rocker arm mounting bolt structure are replaced with real parts, assembled according to actual installation conditions, and high-cycle fatigue tests are carried out on the shaft, rocker arm and rocker arm mounting bolt structure.

[0023] Furthermore, all loads are loaded in phase.

[0024] Beneficial effects: Due to the current lack of research on pendulum vibration absorbers in China, there is no fatigue test verification method for pendulum vibration absorbers, and the safety of helicopter pendulum vibration absorbers cannot be guaranteed. The present invention provides a fatigue test verification method for a pendulum vibration absorber, which performs fatigue test verification on the pendulum vibration absorber, determines its dangerous parts, assesses its fatigue performance, and provides a basis for the final life assessment. The present invention provides pendulum vibration absorber test piece modification, test plan formulation, test loading method and test operation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the blade root structure.

[0026] Figure 2 This is a schematic diagram of the structure of the modified test piece.

[0027] Figure 3 Schematic diagram of the test constraints.

[0028] Figure 4 Schematic diagram of loading for low cycle fatigue test of shell.

[0029] Figure 5 Schematic diagram of high cycle fatigue test loading. Figure 6 Schematic diagram of high cycle fatigue test loading. DETAILED DESCRIPTION

[0030] The present invention provides

[0031] The specific steps include:

[0032] Step 1: Test piece modification;

[0033] Step 2: Test piece installation and loading;

[0034] Step 3: characteristic load application;

[0035] Step 4: Fatigue test requirements and termination conditions;

[0036] The present invention will be further described in detail below with reference to the accompanying drawings:

[0037] Step 1: Select a molded blade, bore it and install the gasket, cut it at the Z400 section, keep the root section, and then lay the pad between the Z200 and Z300 sections. The schematic diagram of the blade root structure is as follows: Figure 1 The mat material is dry glass cloth, which is pre-impregnated with adhesive. Before laying, the mat and the blade body should be clean. Install the pendulum vibration absorber to the specified position, apply primer and adhesive between the vibration absorber and the mat, tighten the upper and lower shells with bolts according to the specified tightening torque, and cure at room temperature. The structural diagram of the modified test piece is shown in Figure 2 .

[0038] Step 2: Test piece installation and loading

[0039] Use connecting bolts to connect the pendulum vibration absorber fatigue test piece with the fixture and fix it on the test bench according to the actual use conditions. The test constraint diagram is shown in Figure 3 As shown, the test load is applied by the actuator according to the loading position requirements. The test control system uses a multi-point coordinated loading system for loading control. The main blade pendulum vibration absorber is fixed at the blade bushing position, and the shaft, rocker arm and rocker arm mounting bolt structure are dummy parts.

[0040] Step 3: Test content

[0041] Different fatigue test methods are used according to the load characteristics of different structural parts of the pendulum vibration absorber.

[0042] 1 Low cycle fatigue test

[0043] According to finite element analysis, the structural stress under high-cycle load is very small and will not affect the structural life, so the test is simplified and only the ground-air-ground cycle load, that is, the low-cycle load, is considered. The pendulum absorber shell is mainly subjected to the low-cycle load caused by the ground-air-ground cycle and the change of the helicopter's flight state, and the characteristic load that causes damage to the shell is the centrifugal force generated by the pendulum ball. Therefore, the shell is subjected to low-cycle fatigue test, in which the shaft, rocker arm and rocker arm mounting bolt structure are dummy parts. The schematic diagram of the shell fatigue test loading is shown in Figure 4 As shown, the direction of the rocker arm is parallel to the direction of the blade.

[0044] According to the ground-air-ground cycle frequency specified in the helicopter flight spectrum, a low-cycle fatigue test load spectrum block is formulated. Each load spectrum block corresponds to 500 flight hours and contains 2 states:

[0045] a) State 1: 1000 cycles of supertorque centrifugal force

[0046] b) State 2: 100 cycles of ultracentrifugation

[0047] Low cycle fatigue test load:

[0048] State 1:

[0049] F1 loading load: 0N-1000N-0N

[0050] F2 loading load: 0N-1000N-0N

[0051] State 2:

[0052] F1 loading load: 0N-2000N-0N

[0053] F2 loading load: 0N-2000N-0N

[0054] Along the direction of the rocker arm, the direction indicated by the arrow in the figure is positive, that is, the rocker arm is pulled positively.

[0055] All loads are applied in phase.

[0056] 2 High cycle fatigue test

[0057] According to finite element analysis, the main characteristic loads of the shaft, rocker arm and rocker arm mounting bolt structure are the centrifugal force and lateral force of the swing ball, which are high-cycle fatigue loads. Therefore, after the low-cycle fatigue test assessment of the shell is completed, the shaft, rocker arm and rocker arm mounting bolt structure will be replaced with real parts and assembled according to actual installation conditions. The high-cycle fatigue test loading diagram is shown in Figure 6 , the direction of the rocker arm is parallel to the direction of the blade.

[0058] The force on the swing ball in the hub rotating coordinate system is as follows: Figure 5 shown.

[0059] According to the D'Alembert principle of classical mechanics, the pendulum ball is in a state of equilibrium under the action of centrifugal force, Coriolis force, inertial force, and constraint reaction force. The vector expression is as follows:

[0060]

[0061] Among them, FC: pendulum ball centrifugal force, along the axis of the rocker arm, FI: pendulum ball inertia force and Fcor: pendulum ball Coriolis force, FN: pendulum ball constraint reaction force.

[0062] The pendulum ball constraint reaction force is the structural load on the single pendulum vibration absorber that needs to be calculated.

[0063] Fθ_Z:=-FN_X·β-FN_Y·θ+FN_Z

[0064] The vector expression of the force balance equation is projected into the hub rotating coordinate system XYZ, and we get:

[0065] FC_X+Fcor_X+FI_X+FN_X=0

[0066] FC_Y+Fcor_Y+FI_Y+FN_Y=0

[0067] FC_Z+Fcor_Z+FI_Z+FN_Z=0

[0068] The final load form is:

[0069]

[0070] The load in the X direction is the test load F3 and F4;

[0071] The loads in the Y and Z directions are combined into F5 and F6 loads.

[0072] The high cycle fatigue test load is:

[0073] F3=F4=2000±1000N

[0074] Along the direction of the rocker arm, the direction indicated by the arrow in the figure is positive, that is, the rocker arm is pulled positively.

[0075] F5=F6=200±300N

[0076] The direction of the vertical rocker arm is indicated by the arrow in the figure.

[0077] All loads are applied in phase.

[0078] Step 4:

[0079] The low-cycle fatigue test of the shell needs to complete 100 load spectrum blocks. That is, after meeting the low-cycle fatigue life index requirements, high-cycle fatigue test assessments are carried out on structural parts such as the shaft, rocker arm and rocker arm mounting bolts. During the test, it is necessary to record and check the test load and cracks of the test piece every 50,000 cycles of loading. If cracks appear in the shell during the test, the test is terminated. If other structural parts are damaged, spare parts can be replaced and the test is continued until the life index requirements are met.

Claims

1. A fatigue test method for a rotor swing absorber, characterized in that: include: Transforming the test piece to obtain a test transformed piece; Install test modifications; Apply characteristic loads , characteristic loads include: centrifugal force, flapping bending moment, and shimmying bending moment; Fatigue tests are carried out on the test modified parts according to fatigue test requirements and termination conditions, wherein different fatigue tests are adopted according to the load characteristics of different structural parts of the pendulum vibration absorber.

2. The method according to claim 1, characterized in that Modification test piece, including: Select a molded blade, bore it and install the gasket, cut it at the Z400 section, keep the root section, and then lay a mat between the Z200 and Z300 sections; the mat material is dry glass cloth. Install the pendulum vibration absorber to the specified position, apply primer and adhesive between the vibration absorber and the pad cloth, tighten the upper and lower shells with bolts according to the specified tightening torque, and cure them at room temperature to obtain the test modified part.

3. The method according to claim 2, characterized in that The glass cloth is pre-soaked with adhesive, and before laying, the space between the cloth and the blade body should be clean.

4. The method according to claim 3, characterized in that Install the test modification, including: The test modification part is connected to the fixture and fixed on the test bench by connecting bolts according to actual use conditions; the test load is applied by the actuator according to the loading position requirements; the test control system adopts a multi-point coordinated loading system for loading control; the main blade pendulum vibration absorber is fixed at the blade bushing position, and the rotating shaft, rocker arm and rocker arm mounting bolt structure are dummy parts.

5. The method according to claim 4, characterized in that Apply characteristic loads, including: For low-cycle fatigue tests, the characteristic load that causes damage to the shell is applied, namely the centrifugal force generated by the pendulum ball; For high cycle fatigue testing, characteristic loads of the shaft, rocker arm and rocker arm mounting bolt structure, namely the centrifugal force and lateral force of the swing ball, are applied.

6. The method according to claim 5, characterized in that Low cycle fatigue testing, including: The shell is subjected to low-cycle fatigue test, in which the shaft, rocker arm and rocker arm mounting bolt structure are dummy parts.

7. The method according to claim 5, characterized in that High cycle fatigue testing, including: After completing the low-cycle fatigue test assessment of the shell, the shaft, rocker arm and rocker arm mounting bolt structure are replaced with real parts, assembled according to actual installation conditions, and high-cycle fatigue tests are carried out on the shaft, rocker arm and rocker arm mounting bolt structure.

8. The method according to claim 6 or 7, characterized in that: All loads are applied in phase.

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