Fatigue test method for transition section of large-size composite material blade

Abstract

The invention belongs to the field of helicopter structure fatigue design, and relates to a large-size composite material blade transition section fatigue test method. The method comprises the following steps: defining a blade load and a coordinate system; determining test loads of an examination area and an examination section of the blade transition section, wherein the test loads comprise centrifugal force, flapping bending moment and shimmy bending moment; the length of the test piece is determined, and two test loading points are arranged on the two sides of the transition section; transforming the test piece to obtain a paddle transformation piece; the paddle transformation piece comprises a paddle root section, a transition section and a partial airfoil section; according to the structural size of a blade root hole, a blade extension piece connected with the root is designed and manufactured, one end of the extension piece is connected with a blade root section connecting hole through a bolt, and the other end of the extension piece is provided with a connecting joint used for being connected with a test bed constraint mechanism; the section size of the metal extension piece enables the bending rigidity EI of the metal extension piece to be close to the bending rigidity of the paddle; and pasting a strain gauge on the examination profile, and calibrating.

Description

Technical Field

[0001] The invention belongs to the field of helicopter structure fatigue design and relates to a fatigue test method for a transition section of a large-size composite material blade. Background Art

[0002] The transition section of composite blades is a sudden change area of ​​blade structure size and stiffness, and is also a high-incidence area of ​​manufacturing defects. In the past, blades generally used cantilever beam loading or resonance method to perform fatigue test on the transition section. However, for large-sized composite blades, the blade transition section has large structural size and high stiffness, and the resonance method loading is difficult to carry out due to the power limitation of the test equipment; the bending moment distribution of cantilever beam loading is relatively steep, and only a small part of the structural area can meet the loading requirements, and the bending moment in the constraint area is large, which is easy to be damaged prematurely in the constraint area, resulting in the inability to conduct the test. Summary of the invention

[0003] Purpose of the invention: For the test assessment of the transition zone of large-sized composite blades, the loading bending moment distribution needs to be as gentle as possible to meet the load loading of the larger assessment area of ​​the transition section of the large-sized composite blade, and the bending moment of the joint in the constraint area should be reduced to avoid premature damage to the structure.

[0004] Technical solution:

[0005] A fatigue test method for a transition section of a large-size composite blade is provided, comprising:

[0006] Define blade loads and coordinate system;

[0007] Determine the test loads of the blade transition section test area and test section, including centrifugal force, flapping bending moment, and swing bending moment;

[0008] Determine the length of the test piece and set two test loading points on both sides of the transition section;

[0009] Modifying the test piece to obtain a blade modification part; the blade modification part includes a blade root section, a transition section and a part of an airfoil section;

[0010] According to the structural dimensions of the blade root hole, a blade extension connected to the root is designed and manufactured. One end of the extension is connected to the blade root section connection hole by bolts, and the other end is designed with a connecting joint for connection to the test bench constraint mechanism; the cross-sectional dimensions of the metal extension should make its bending stiffness EI close to that of the blade;

[0011] Stick strain gauges on the test section and calibrate them;

[0012] After the calibration is completed, the blade modification part is connected to the metal extension part to form a blade transition section test piece. A constraint is applied to one end of the blade transition section test piece so that the end cannot be displaced and cannot rotate along the x-axis, but can rotate along the y and z-axes. A constraint is also applied to the other end of the blade transition section test piece so that the other end can only slide along the x-axis, cannot rotate along the x-axis, but can rotate along the y and z-axes. The blade centrifugal force is applied to the end that can slide along the x-axis. A splint or an airfoil clamp is used to clamp the platform area between the blade root section and the transition section and the airfoil section after the transition section, and is used to separately apply the flapping force F at two test loading points. 挥舞1 、F 挥舞2 and the oscillating force F 摆振1 、F 摆振2 .

[0013] Furthermore, the method further comprises:

[0014] Carry out test load debugging:

[0015] First, load the centrifugal force Fc to the required centrifugal force, and gradually adjust the four forces at the two loading points. 挥舞1 、F 挥舞2 Make the swing moment of the test section meet the requirements and adjust the swing force F 摆振1 、F 摆振2 Make sure the swing bending moment of the test section meets the requirements.

[0016] Furthermore, the bending moment of the test section of the transition section test piece increases or decreases approximately linearly with the change of the section, and the non-equivalent bending moment distribution of the two test sections is achieved by adjusting the numerical difference of the swing force at the two loading points; the non-equivalent bending moment distribution of the two test sections is achieved by adjusting the numerical difference of the swing force at the two loading points.

[0017] Furthermore, the total length of the test piece is not less than 3 (ba);

[0018] Where a and b are the distances from the start and end positions of the transition section to the center of the propeller root connection hole.

[0019] Furthermore, the length of the metal extension piece is b-2a.

[0020] Furthermore, the coordinate system is defined, including:

[0021] The direction pointing to the blade tip is the x-axis, the direction pointing to the trailing edge is the y-axis, and the z-axis is obtained according to the right-hand rule; the centrifugal force Fc pointing to the blade tip is positive, the flapping bending moment My is positive when the upper surface of the blade is pulled, the swing bending moment Mz is positive when the trailing edge of the blade is compressed, and the torsional bending moment Mx is positive when the leading edge of the blade is bent upward.

[0022] Furthermore, when the centrifugal force Fc is zero, the bending moments generated by the loads at the two test loading points are:

[0023]

[0024] Among them, F1 and M1 are the force loaded at the test loading point 1 and the bending moment generated; F2 and M2 are the force loaded at the test loading point 2 and the bending moment generated; L1 is the distance from the test loading point 1 to the nearest constraint point, L2 is the distance between the two test loading points, and L3 is the distance from the test loading point 2 to the nearest constraint point.

[0025] Beneficial effects:

[0026] The present invention adopts a large-size composite blade transition section fatigue test method by extending the test piece with a dummy and adopting four-point bending loading. This can meet the requirements of variable distributed load loading in a larger assessment area of ​​the transition section of a large-size composite blade, and reduce the bending moment of the joint in the constraint area to avoid premature damage to the joint structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of four-point moment loading;

[0028] Figure 2 This is a schematic diagram of constraint loading in the blade transition section test;

[0029] Figure 3 It is a schematic diagram of the blade transition section structure and patch;

[0030] Figure 4 It is a schematic diagram of the principle of non-equal moment loading at four points of the blade transition section. DETAILED DESCRIPTION

[0031] The present invention proposes a fatigue test method for the transition section of a large-size composite blade by extending the test piece through a dummy and adopting four-point bending loading. The method can effectively meet the loading requirements for fatigue test of the transition section of a large-size composite blade and solve the problem that the transition zone assessment area cannot be fully assessed due to premature damage to the joint constraint zone.

[0032] The present invention provides a fatigue test method for a transition section of a large-size composite blade. The test piece is extended by adding a metal dummy and a four-point bending loading method is adopted. The specific steps of the test method are as follows:

[0033] [1] Definition of blade loads and coordinate system

[0034] The x-axis is pointing to the blade tip, the y-axis is the maximum chord length line of the blade section pointing to the trailing edge, and the z-axis is obtained according to the right-hand rule. The centrifugal force (Fc) is positive when it points to the blade tip, the flapping moment (My) is positive when the upper surface of the blade is pulled, the swing moment (Mz) is positive when the trailing edge of the blade is compressed, and the torsional moment (Mx) is positive when the leading edge of the blade is bent upward.

[0035] [2] Determine the blade transition section test area and the test section load; according to the blade structural dimensions, the area where the chord length changes between the blade root section and the airfoil section is the transition section area, and the entire transition section area is the test area. The starting and ending positions of the transition section are defined as amm and bmm away from the center of the blade root connection hole, respectively. Then a+50mm and b-50mm are defined as the test sections.

[0036] According to the calculated load spectra of the two test sections and the helicopter blade strength design method, the fatigue loads required to be loaded on the two sections are determined respectively. The blade fatigue test loads generally include centrifugal force Fc, flapping bending moment ±My, and swing bending moment ±Mz.

[0037] [3] Specimen length and loading point

[0038] According to Figure 1 The four-point bending moment loading method shown in the figure sets the test loading points on both sides of the transition section. The test loading arm L1 = L3, and it is recommended that it should not be less than the distance L2 between the two loading clamping points. Final loading plan Figure 2 As shown, the total length of the test piece shall not be less than 3(ba)mm.

[0039] Note: The final design length should take into account the dimensions of the wing clamp at the loading clamping point. This length is ignored in steps [3][4][5].

[0040] [4] Test piece modification

[0041] According to the principle of step [3], the length of the blade part of the test piece is determined to be 2b-amm. The blade is cut at this point, and the foam within the specified range of the blade is hollowed out from the cut surface. The short-cut glass fiber mixture is filled and heated to cure; a reinforcing beam belt is laid on the outer surface of the skin, wrapped with cloth and then heat-cured; the assembly holes of the machined modified parts are installed with metal splints.

[0042] [5] Design of metal extensions for propeller blades

[0043] According to the structural dimensions of the blade root hole, a blade extension connected to the root is designed and manufactured. One end of the extension is connected to the blade root connection hole by bolts, and the other end is designed with a connecting joint for connecting to the test bench constraint mechanism. According to the arm requirements of the four-point moment loading method in step [3], the length of the metal extension is determined to be b-2amm. The cross-sectional dimensions of the metal extension should be such that its bending stiffness EI in the flapping and swinging directions is similar to the flapping and swinging bending stiffness of the blade. The preferred flapping stiffness is the average of the actual flapping stiffness of the blade modification; the preferred swing stiffness is the average of the actual swing stiffness of the blade modification.

[0044] [6] Assessment of profile patch calibration

[0045] The bridge strain gauges for swing and shimmy bending moments are attached to the test section of the test piece determined in step [2], and load calibration is performed. The purpose of calibration is to find the corresponding relationship between strain output and bending moment. The calibration of strain gauges is carried out using the overall calibration method, that is, the measurement system and strain gauges are calibrated as a whole. During calibration, the test piece and the root end fixture joint are installed on a special calibration table, and a standard load is applied to the process joint end of the test piece through an actuator. The entire calibration process is carried out strictly in accordance with the requirements of the test outline. Finally, the influence of the blade's deadweight is eliminated by placing the test piece vertically and then clearing the zero point uniformly.

[0046] [7]Test piece installation and loading

[0047] After the blade modification part of step [4] is connected to the metal extension part, a 4-point bending loading method is used for constraint loading. One end is constrained to ux=uy=uz=urx=0 and can rotate along the y and z axes. The other end is constrained to uy=uz=urx=0 and can slide along the x axis and rotate along the y and z axes. The centrifugal force of the blade is applied to the end that can slide along the x axis. The platform area between the root section and the transition section of the blade and the airfoil section after the transition section are clamped with a splint or an airfoil clamp, and the flapping force F is applied separately. 挥舞1 、F 挥舞2 and the oscillating force F 摆振1 、F 摆振2 The loading diagram is as follows Figure 2 shown.

[0048] [8] Test load debugging

[0049] The entire test is loaded and controlled by the control system, and the dynamic signal test and analysis system is used for data acquisition and processing and test load monitoring. First, the centrifugal force Fc is loaded to the required centrifugal force, and the four forces at the two loading points are gradually adjusted. By adjusting the swinging force F 挥舞1 、F 挥舞2 Make the swing moment of the test section meet the requirements and adjust the swing force F 摆振1 、F 摆振2 The bending moment of the test section meets the requirements. The bending moment of the test section of the transition section test piece increases or decreases approximately linearly with the change of the section. The non-uniform bending moment distribution of the swing and swing moment loads of the two test sections is achieved by adjusting the numerical difference between the two loading points of the swing force and the swing force. The schematic diagram of the non-uniform bending moment loading principle is shown in Figure 4 .

Claims

1. A fatigue test method for transition section of large-size composite blades, characterized in that: include: Define blade loads and coordinate system; Determine the test loads of the blade transition section test area and test section, including centrifugal force, flapping bending moment, and swing bending moment; Determine the length of the test piece and set two test loading points on both sides of the transition section; Modifying the test piece to obtain a blade modification part; the blade modification part includes a blade root section, a transition section and a part of an airfoil section; According to the structural dimensions of the blade root hole, a blade extension connected to the root is designed and manufactured. One end of the extension is connected to the blade root section connection hole by bolts, and the other end is designed with a connecting joint for connection to the test bench constraint mechanism; the cross-sectional dimensions of the metal extension should make its bending stiffness EI close to that of the blade; Stick strain gauges on the test section and calibrate them; After the calibration is completed, the blade modification part is connected to the metal extension part to form a blade transition section test piece. A constraint is applied to one end of the blade transition section test piece so that the end cannot be displaced and cannot rotate along the x-axis, but can rotate along the y and z-axes. A constraint is also applied to the other end of the blade transition section test piece so that the other end can only slide along the x-axis, cannot rotate along the x-axis, but can rotate along the y and z-axes. The blade centrifugal force is applied to the end that can slide along the x-axis. A splint or an airfoil clamp is used to clamp the platform area between the blade root section and the transition section and the airfoil section after the transition section, and is used to separately apply the flapping force F at two test loading points. 挥舞1 、F 挥舞2 and the oscillating force F 摆振1 、F 摆振2 .

2. The method according to claim 1, characterized in that The method further comprises: Carry out test load debugging: First, load the centrifugal force Fc to the required centrifugal force, and gradually adjust the four forces at the two loading points. 挥舞1 、F 挥舞2 Make the swing moment of the test section meet the requirements and adjust the swing force F 摆振1 、F 摆振2 Make sure the swing bending moment of the test section meets the requirements.

3. The method according to claim 2, characterized in that The bending moment of the test section of the transition section test piece increases or decreases approximately linearly with the change of the section. The non-equal bending moment distribution of the swinging of the two test sections is achieved by adjusting the numerical difference of the swinging force at the two loading points; the non-equal bending moment distribution of the swinging of the two test sections is achieved by adjusting the numerical difference of the swinging force at the two loading points.

4. The method according to claim 3, characterized in that The total length of the test piece shall not be less than 3 (ba); Where a and b are the distances from the start and end positions of the transition section to the center of the propeller root connection hole.

5. The method according to claim 3, characterized in that: The length of the metal extension is b-2a.

6. The method according to claim 3, characterized in that Define the coordinate system, including: The direction pointing to the blade tip is the x-axis, the direction pointing to the trailing edge is the y-axis, and the z-axis is obtained according to the right-hand rule; the centrifugal force Fc pointing to the blade tip is positive, the flapping bending moment My is positive when the upper surface of the blade is pulled, the swing bending moment Mz is positive when the trailing edge of the blade is compressed, and the torsional bending moment Mx is positive when the leading edge of the blade is bent upward.

7. The method according to claim 6, characterized in that When the centrifugal force Fc is zero, the bending moments generated by the loads at the two test loading points are: Among them, F1 and M1 are the force loaded at the test loading point 1 and the bending moment generated; F2 and M2 are the force loaded at the test loading point 2 and the bending moment generated; L1 is the distance from the test loading point 1 to the nearest constraint point, L2 is the distance between the two test loading points, and L3 is the distance from the test loading point 2 to the nearest constraint point.

8. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the method according to any one of claims 1 to 7 is implemented.

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