A Biaxial Fatigue Testing Device and Testing Method for Wind Turbine Blades

Abstract

The present invention relates to the technical field of shaft fatigue testing, and specifically discloses a biaxial fatigue testing device and testing method for a wind turbine blade, including a base and a blade body. The root of the blade body is installed on the test bench base, and a fixture is arranged on the side wall of the blade body. A traction assembly for adjusting the vibration frequency of the fixture is arranged at the top of the base. The fixture includes two cross plates, the two cross plates are respectively located on both sides of the blade body, second clamping blocks are arranged on the opposite sides of the two cross plates, and four second double-headed studs are arranged through between the two cross plates. The present invention loads the blade in the form of resonance through a cable, avoids the power loss added by the inertial mass block, reduces the requirement for the motor capacity, has the function of evenly winding the cable, effectively avoids the knotting and wear of the cable, prolongs the service life of the cable, and has a structure capable of switching between single-axis and biaxial fatigue testing.

Description

Technical Field

[0001] The present invention relates to the technical field of shaft fatigue testing, and particularly relates to a biaxial fatigue testing device and testing method for wind turbine blades. Background Art

[0002] Among the components of a wind turbine, the wind turbine blade is an important component for converting wind energy into mechanical energy and is one of the core components of the wind turbine. Its structure, strength, and stability play an important role in the reliability of the unit. Fatigue testing is an effective way to conduct quality inspection and certification of wind turbine blades, and can verify the ability of wind turbine blades to withstand loads under given working conditions. With the development trend of larger blades, resonance-type fatigue testing technology has received extensive attention, and higher requirements are put forward for test cycles, energy consumption, system performance, etc.

[0003] Chinese Patent (CN106840928B) discloses a fatigue loading test device for wind turbine blades, including a servo motor installed on the machine body, a lead screw connected to the output shaft of the servo motor through a coupling, and a protection box with a counterweight firmly connected to the slider. The characteristics are as follows: circular holes with different diameters are provided at the centers of the front and rear side walls of the box body of the slider, a nut is installed in the circular hole with a larger diameter, a guide wheel I and a guide wheel II are respectively installed on the left and right side walls of the box body through a pin shaft III and a pin shaft IV, the slider is sleeved on the lead screw through the nut, and the guide wheel I and the guide wheel II are in contact with the guide rail to provide guiding support for the slider. The transmission of the fatigue loading device uses a hollow ball screw.

[0004] However, there are some drawbacks in the above related technologies. For example, during the use of the fatigue loading test device for wind turbine blades, due to the use of a mass block to apply inertial excitation force, it consumes additional power, requires a servo motor with a high cost, and when performing biaxial testing, multiple groups of fatigue loading test devices need to be installed on the blade, which not only increases the weight, reduces the natural frequency of the blade, extends the test cycle, but also consumes additional power and is not energy-saving enough. Summary of the Invention

[0005] To solve the above problems existing in the prior art, the present invention provides a biaxial fatigue testing device and testing method for wind turbine blades, which can overcome technical defects.

[0006] The object of the present invention can be achieved by the following technical solutions:

[0007] A biaxial fatigue testing device for wind turbine blades includes a base and a blade body. The root of the blade body is installed on a test bench base, and a fixture is provided on the side wall of the blade body. A traction assembly for adjusting the vibration frequency of the fixture is provided at the top of the base;

[0008] The clamp comprises two horizontal plates, the two horizontal plates are respectively located on both sides of the blade body, a second clamping block is arranged on the opposite sides of the two horizontal plates, four second studs are arranged between the two horizontal plates, nuts are connected to both ends of the second studs, and a rope connecting piece is arranged at the bottom end of the horizontal plate located at the bottom;

[0009] The traction assembly includes a winding roller, two U-shaped plates are provided at the top of the base, the winding roller passes through and is rotatably installed between the two U-shaped plates, two support rods are fixedly installed between the two U-shaped plates, a slider is slidably installed between the two support rods, a support frame is fixedly installed at one end of the slider, a changing wheel is rotatably installed between the opposite sides of the support frame, a cable is wound between the winding roller, the changing wheel and the rope connecting member in sequence, and the two ends of the cable are respectively connected to the winding roller and the rope connecting member, wherein a driving assembly for driving the winding roller to rotate is provided on one side of the U-shaped plate, a driving mechanism for adjusting the position of the slider is provided between the two U-shaped plates, a reciprocating mechanism for uniformly winding the winding roller is provided between the two U-shaped plates, and a transmission assembly is provided between the reciprocating mechanism and the winding roller.

[0010] Preferably, the rope connecting member comprises a circular plate, a support column and a circular ring which are integrally arranged, and the rope connecting member is made of metal.

[0011] Preferably, the drive assembly includes an L-shaped plate, which is fixedly mounted on the side wall of one of the U-shaped plates, a clutch is provided at the top of the horizontal section of the L-shaped plate, and a first motor is provided on the side wall of the vertical section of the L-shaped plate, the clutch is used to separate or combine the winding roller shaft and the output shaft of the first motor, the output shaft of the first motor is arranged to penetrate the L-shaped plate, and a coupling is provided between the output shaft of the first motor and the input shaft of the clutch.

[0012] Preferably, the driving mechanism includes a second motor, a screw rod is passed through and rotatably installed between the two U-shaped plates, the slider is threadedly connected to the screw rod, the second motor is fixedly installed on the side wall of one of the U-shaped plates, and the output shaft of the second motor is fixedly connected to the screw rod through a coupling mechanism.

[0013] Preferably, the reciprocating mechanism includes a reciprocating screw rod, which passes through and is rotatably installed between the two U-shaped plates, a guide rod is fixedly installed between the two U-shaped plates, a support block is slidably installed on the guide rod, a limiting column is provided at the bottom end of the support block, the limiting column matches the reciprocating screw rod, a limiting wheel is rotatably installed between the opposite sides of the support block, and the cable passes around the limiting wheel.

[0014] Preferably, the transmission assembly includes a first pulley and a second pulley. The first pulley is fixedly installed on the shaft body of the winding roller, and the second pulley is fixedly installed on the shaft body of the reciprocating lead screw. A synchronous belt is wound between the first pulley and the second pulley.

[0015] Preferably, the diameter of the second pulley is larger than that of the first pulley.

[0016] A biaxial fatigue test method for a wind turbine blade includes the following steps:

[0017] S1. According to the frequency to be applied to the blade body, install the blade body on the test bench base. The second motor drives the screw to rotate, and the slider slides between the two support rods to adjust the relative positions of the two traction points on the blade body, and perform a biaxial fatigue test with simultaneous loading in the flap and pitch directions on the blade. Then fix the fixture at the position to be detected on the blade body;

[0018] S2. Connect one end of the cable to the winding roller, and after passing the other end of the cable through the limit wheel and the deflection wheel in sequence, connect it to the rope connecting piece;

[0019] S3. When the first motor pulls the blade body through the winding roller, the main and slave parts of the clutch are in the engaged state. The torque of the output shaft of the first motor is transmitted to the winding roller through the coupling and the clutch. The winding roller retracts the cable, and the blade body moves downward under the traction of the cable. At this time, the rotation directions of the first motor and the winding roller are the same. When the blade body vibrates to the lowest point, the main and slave parts of the clutch are separated. At this time, the elastic potential energy of the blade body needs to be converted into kinetic energy, and the blade body begins to rebound. During the rebound process, due to the separation of the main and slave parts of the clutch, the torque of the first motor cannot be transmitted, and the winding roller will release the cable as the blade body rebounds, and the winding roller starts to rotate in the opposite direction, while the first motor maintains its original rotation direction. At this time, the rotation directions of the first motor and the winding roller are opposite;

[0020] S4. When the blade body reaches the highest point again, the clutch is engaged again, and the output shaft of the first motor transmits torque to the winding roller to apply a downward traction excitation to the blade body, close to the natural frequency of the vibration of the blade body, so as to achieve applying a half-wave form of excitation to the blade body without reversing the clutch. The cable pulls the blade with a composite frequency obtained by superimposing the natural frequency of the blade flap and the natural frequency of the blade pitch, so that the blade performs a Lissajous motion in the flap and pitch directions;

[0021] S5. During the rotation of the winding roller, it drives the first pulley to rotate, and together with the synchronous belt and the second pulley, drives the reciprocating lead screw to rotate, driving the limit post, the limit wheel and the support block to slide back and forth synchronously on the guide rod, and the cable winding and unwinding process is evenly distributed.

[0022] Preferably, in S1, the second motor drives the screw rod to rotate, and the slider slides between the two support rods. When the slider is directly below the rope connecting member, the two traction points of the slider and the rope connecting member are located in the same vertical plane, and a single-axis fatigue test in the flapping direction of the blade body is performed.

[0023] The beneficial effects of the present invention are as follows:

[0024] 1. By setting the fixture and the traction assembly, the beneficial effect that can be obtained is that when the first motor pulls the blade body through the wire winding roller, the main and slave parts of the clutch are in a combined state. The torque of the output shaft of the first motor is transmitted to the wire winding roller through the coupling and the clutch. The wire winding roller recovers the cable, and the blade body moves downward under the traction of the cable. At this time, the rotation directions of the first motor and the wire winding roller are the same. When the blade body vibrates to the lowest point, the main and slave parts of the clutch are separated. At this time, the elastic potential energy of the blade body needs to be converted into kinetic energy, and the blade body begins to rebound. During the rebound process, since the main and slave parts of the clutch are separated and cannot transmit the torque of the first motor, the wire winding roller will release the cable as the blade body rebounds, and the wire winding roller starts to move in the opposite direction, while the first motor maintains its original rotation direction. At this time, the rotation directions of the first motor and the wire winding roller are opposite. When the blade body reaches the highest point again, the clutch is combined again, and the output shaft of the first motor transmits torque to the wire winding roller to apply a downward traction excitation to the blade body to approach the natural frequency of the vibration of the blade body. It is possible to apply a half-wave form of excitation to the blade body without reversing the clutch. According to the frequency to be applied to the blade body, the first motor is used as the power source to apply the frequency, and the blade is loaded in the form of resonance through the cable, avoiding the power loss caused by the additional inertial mass block and reducing the requirement for the motor capacity.

[0025] 2. By setting the reciprocating mechanism, the beneficial effect that can be obtained is that the reciprocating screw rod penetrates and is rotatably installed between the two U-shaped plates. A guide rod is fixedly installed between the two U-shaped plates. A support block is slidably installed on the guide rod. A limiting column is arranged at the bottom end of the support block, and the limiting column is matched with the reciprocating screw rod. Limiting wheels are rotatably installed between the opposite sides of the support block. The cable bypasses the limiting wheels. A transmission assembly is arranged between the reciprocating screw rod and the wire winding roller. The transmission assembly includes a first belt pulley and a second belt pulley. The first belt pulley is fixedly installed on the shaft body of the wire winding roller, and the second belt pulley is fixedly installed on the shaft body of the reciprocating screw rod. A synchronous belt is wound between the first belt pulley and the second belt pulley;

[0026] During the rotation of the wire winding roller, the first belt pulley is driven to rotate. In cooperation with the synchronous belt and the second belt pulley, the reciprocating screw rod is driven to rotate, driving the limiting column, the limiting wheel and the support block to slide back and forth synchronously on the guide rod. The cable is evenly wound and unwound during the winding and unwinding process, having the function of evenly winding and unwinding the cable, effectively avoiding the knotting and wear of the cable, and prolonging the service life of the cable.

[0027] 3. By setting up the driving mechanism, the beneficial effects that can be obtained are as follows: The driving mechanism includes a second motor. A screw rod is penetrated and rotatably installed between two U-shaped plates. The slider is threadedly connected to the screw rod. The second motor is fixedly installed on the side wall of one of the U-shaped plates, and the output shaft of the second motor is fixedly connected to the screw rod through a coupling mechanism.

[0028] Install the blade body on the test bench base. The second motor drives the screw rod to rotate, and the slider slides between the two support rods to adjust the relative positions of the two traction points on the blade body, and conduct a biaxial fatigue test with simultaneous loading in the flapping and pitching directions of the blade. The single cable uses a composite frequency obtained by superimposing the two frequencies of the blade flapping natural frequency and the blade pitching natural frequency to traction the blade, so that the blade performs a Lissajous motion in the flapping and pitching directions. When the slider is directly below the rope connecting piece, the two traction points of the slider and the rope connecting piece are located in the same vertical plane, and a uniaxial fatigue test in the pitching direction of the blade body is carried out, which has a structure capable of switching between uniaxial and biaxial fatigue tests. Brief Description of the Drawings

[0029] For the convenience of those skilled in the art to understand, the present invention will be further described below with reference to the accompanying drawings.

[0030] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0031] Figure 2 It is a mounting structure diagram of the fixture in the present invention;

[0032] Figure 3 It is a mounting structure diagram of the transmission component in the present invention;

[0033] Figure 4 It is a mounting structure diagram of the slider and the U-shaped frame in the present invention;

[0034] Figure 5 It is a mounting structure diagram of the reciprocating mechanism in the present invention;

[0035] Figure 6 It is a mounting structure diagram of the support block in the present invention.

[0036] Explanation of the Reference Numerals in the Drawings:

[0037] In the figure: 1. Base; 2. Blade body; 31. Cross plate; 32. Second clamping block; 33. Second double-headed stud; 34. Rope connecting piece; 41. U-shaped plate; 42. Winding roller; 43. Support rod; 44. Slider; 45. Support frame; 46. Direction-changing wheel; 47. Cable; 51. L-shaped plate; 52. Clutch; 53. First motor; 54. Coupling; 61. Screw rod; 62. Second motor; 71. Reciprocating lead screw; 72. Guide rod; 73. Support block; 74. Limit post; 75. Limit wheel; 81. First pulley; 82. Second pulley; 83. Timing belt. Detailed implementation manners

[0038] To further illustrate the technical means and effects adopted by the present invention to achieve the intended invention purpose, the following describes in detail the specific implementation manners, structures, features and their effects of the present invention in combination with the accompanying drawings and preferred embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0039] In the description of the present application, it should be understood that the orientation or positional relationship indicated by terms such as "inside", "outside", etc. is based on the orientation or position shown in the drawings. It is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, a specific orientation structure and operation. Therefore, it should not be construed as a limitation to the present application.

[0040] Refer to Figures 1-6 , a biaxial fatigue test device for a wind turbine blade disclosed by the present invention, which includes a base 1 and a blade body 2, and the root of the blade body 2 is installed on the test bench base.

[0041] A fixture is provided on the side wall of the blade body 2. The fixture includes two cross plates 31 which are respectively located on both sides of the blade body 2. Second clamping blocks 32 are provided on the opposite sides of the two cross plates 31. Four second double-headed studs 33 penetrate between the two cross plates 31. Nuts are connected to both ends of the second double-headed studs 33. A rope connecting member 34 is provided at the bottom end of the lower cross plate 31. The rope connecting member 34 includes a circular plate, a support column and a circular ring which are integrally arranged. The rope connecting member 34 is made of metal.

[0042] At the top of the base 1, there is a traction component for adjusting the vibration frequency of the fixture. The traction component includes a wire winding roller 42. At the top of the base 1, there are two U-shaped plates 41. The wire winding roller 42 passes through and is rotatably installed between the two U-shaped plates 41. Between the two U-shaped plates 41, two support rods 43 are fixedly installed. A slider 44 is slidably installed between the two support rods 43. One end of the slider 44 is fixedly installed with a support frame 45. A deflecting wheel 46 is rotatably installed between the opposite sides of the support frame 45. A cable 47 is sequentially wound between the wire winding roller 42, the deflecting wheel 46 and the rope connecting piece 34. The two ends of the cable 47 are respectively connected to the wire winding roller 42 and the rope connecting piece 34. On one side of the U-shaped plate 41, there is a driving component for driving the wire winding roller 42 to rotate. The driving component includes an L-shaped plate 51. The L-shaped plate 51 is fixedly installed on the side wall of one of the U-shaped plates 41. At the top of the horizontal section of the L-shaped plate 51, there is a clutch 52. On the side wall of the vertical section of the L-shaped plate 51, there is a first motor 53. The clutch 52 is used to separate or combine the shaft body of the wire winding roller 42 and the output shaft of the first motor 53. The output shaft of the first motor 53 penetrates through the L-shaped plate 51. A coupling 54 is arranged between the output shaft of the first motor 53 and the input shaft of the clutch 52. Between the two U-shaped plates 41, there is a driving mechanism for adjusting the position of the slider 44. The driving mechanism includes a second motor 62. A screw rod 61 passes through and is rotatably installed between the two U-shaped plates 41. The slider 44 is threadedly connected to the screw rod 61. The second motor 62 is fixedly installed on the side wall of one of the U-shaped plates 41. The output shaft of the second motor 62 is fixedly connected to the screw rod 61 through a coupling mechanism. The blade body 2 is fixed on the test bench base. When the first motor 53 pulls the blade body 2 through the wire winding roller 42, the main and slave parts of the clutch 52 are in a combined state. The torque of the output shaft of the first motor 53 is transmitted to the wire winding roller 42 through the coupling 54 and the clutch 52. The wire winding roller 42 winds and unwinds the cable 47. The angle between the cable 47 and the vertical direction is 30° - 70°. When the frequency at which the first motor 53 pulls the blade body 2 through the wire winding roller 42 is close to or equal to the natural frequency of the blade body 2, the blade body 2 can effectively absorb energy, resulting in the largest amplitude and the lowest energy consumption of the blade body 2. The cable 47 superimposes the two natural frequencies of the flapping and pitching of the blade body 2, and at the same time superimposes the loading forces at these two natural frequencies. The angle of the cable 47 and the two loading forces on the cable 47 need to be optimized and adjusted according to the natural frequencies of the two directions of different blade bodies. These optimizations and adjustments are all controlled and realized by a computer.

[0043] A reciprocating mechanism for evenly winding the cable on the winding roller 42 is arranged between the two U-shaped plates 41. The reciprocating mechanism includes a reciprocating lead screw 71 which penetrates and is rotatably installed between the two U-shaped plates 41. A guide rod 72 is fixedly installed between the two U-shaped plates 41. A support block 73 is slidably installed on the guide rod 72. A limit post 74 is arranged at the bottom end of the support block 73, and the limit post 74 is matched with the reciprocating lead screw 71. A limit wheel 75 is rotatably installed between the opposite sides of the support block 73. The cable 47 bypasses the limit wheel 75. A transmission assembly is arranged between the reciprocating mechanism and the winding roller 42. The transmission assembly includes a first belt pulley 81 and a second belt pulley 82. The first belt pulley 81 is fixedly installed on the shaft body of the winding roller 42, and the second belt pulley 82 is fixedly installed on the shaft body of the reciprocating lead screw 71. A synchronous belt 83 is wound between the first belt pulley 81 and the second belt pulley 82.

[0044] The present invention also discloses a biaxial fatigue test method for a wind turbine blade, including the following steps:

[0045] S1. According to the frequency to be applied to the blade body 2, the blade body 2 is installed on the test bench base. The second motor 62 drives the screw 61 to rotate, and the slider 44 slides between the two support rods 43 to adjust the relative positions of the two traction points of the blade body 2, and a biaxial fatigue test of simultaneous loading in the flap and pitch directions of the blade is carried out. Then, the fixture is fixed at the position to be detected on the blade body 2;

[0046] S2. One end of the cable 47 is connected to the winding roller 42, and the other end of the cable 47 passes through the limit wheel 75 and the deflecting wheel 46 in sequence and then is connected to the rope connecting member 34;

[0047] S3. When the first motor 53 pulls the blade body 2 through the winding roller 42, the main and slave parts of the clutch 52 are in a combined state. The torque of the output shaft of the first motor 53 is transmitted to the winding roller 42 through the coupling 54 and the clutch 52. The winding roller 42 retracts the cable 47, and the blade body 2 moves downward under the traction of the cable 47. At this time, the rotation directions of the first motor 53 and the winding roller 42 are the same. When the blade body 2 vibrates to the lowest point, the main and slave parts of the clutch 52 are separated. At this time, the elastic potential energy of the blade body 2 needs to be converted into kinetic energy, and the blade body 2 begins to rebound. During the rebound process, due to the separation of the main and slave parts of the clutch 52, the torque of the first motor 53 cannot be transmitted, and the winding roller 42 will release the cable 47 as the blade body 2 rebounds, and the winding roller 42 starts to move in the opposite direction, while the first motor 53 maintains the original rotation direction. At this time, the rotation directions of the first motor 53 and the winding roller 42 are opposite;

[0048] S4. When the blade body 2 reaches the highest point again, the clutch 52 engages again, and the output shaft of the first motor 53 transmits torque to the wire winding roller 42, applying a downward traction excitation to the blade body 2 to approach the natural frequency of the vibration of the blade body 2. It is possible to apply a half-wave form of excitation to the blade body 2 without reversing the clutch 52. The cable 47 pulls the blade with a composite frequency obtained by superimposing the two frequencies of the natural frequency of the blade flapping and the natural frequency of the blade pitching, causing the blade to perform a Lissajous motion in the flapping direction and the pitching direction. The angle between the cable 47 and the flapping direction of the blade and the magnitude of the loading force at the two frequencies are the key parameters of the present invention, and must be optimized according to the natural frequencies of the two directions of the measured blade and the target load to obtain the best parameters;

[0049] S5. During the rotation of the wire winding roller 42, the first pulley 81 is driven to rotate, and the reciprocating lead screw 71 is driven to rotate in cooperation with the synchronous belt 83 and the second pulley 82, driving the limit post 74, the limit wheel 75 and the support block 73 to slide reciprocally on the guide rod 72 synchronously, and the winding and unwinding process of the cable 47 is evenly distributed;

[0050] In S1, the second motor 62 drives the screw 61 to rotate, and the slider 44 slides between the two support rods 43. When the slider 44 is directly below the rope connecting member 34, the two traction points of the slider 44 and the rope connecting member 34 are located in the same vertical plane, and a single-axis fatigue test in the pitching direction of the blade body 2 is performed.

[0051] The above is only a preferred embodiment of the present invention, and does not impose any form of limitation on the present invention. Although the present invention has been disclosed above with a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to the above-disclosed technical content to make equivalent embodiments with equivalent changes within the scope of the technical solution of the present invention. However, as long as it does not depart from the content of the technical solution of the present invention, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention still belong to the scope of the technical solution of the present invention.

Claims

1. A biaxial fatigue testing device for a wind turbine blade, characterized in that It includes a base (1) and a blade body (2). The root of the blade body (2) is installed on the test bench base, and a fixture is provided on the side wall of the blade body (2). A traction component for adjusting the vibration frequency of the fixture is provided at the top of the base (1). The fixture includes two cross plates (31). The two cross plates (31) are respectively located on both sides of the blade body (2). Second clamping blocks (32) are provided on the opposite sides of the two cross plates (31). Four second double-headed bolts (33) are penetratingly arranged between the two cross plates (31). Nuts are connected to both ends of the second double-headed bolt (33). A rope connecting member (34) is provided at the bottom end of the lower cross plate (31). The traction component includes a wire winding roller (42). Two U-shaped plates (41) are provided at the top of the base (1). The wire winding roller (42) is penetratingly and rotatably installed between the two U-shaped plates (41). Two support rods (43) are fixedly installed between the two U-shaped plates (41). A slider (44) is slidably installed between the two support rods (43). One end of the slider (44) is fixedly installed with a support frame (45). A deflecting wheel (46) is rotatably installed between the opposite sides of the support frame (45). A cable (47) is sequentially wound between the wire winding roller (42), the deflecting wheel (46) and the rope connecting member (34). The two ends of the cable (47) are respectively connected to the wire winding roller (42) and the rope connecting member (34). A driving component for driving the wire winding roller (42) to rotate is provided on one side of the U-shaped plate (41). A driving mechanism for adjusting the position of the slider (44) is provided between the two U-shaped plates (41). A reciprocating mechanism for evenly winding the wire winding roller (42) is provided between the two U-shaped plates (41). A transmission component is provided between the reciprocating mechanism and the wire winding roller (42). The driving component includes an L-shaped plate (51). The L-shaped plate (51) is fixedly installed on the side wall of one of the U-shaped plates (41). A clutch (52) is provided at the top of the horizontal section of the L-shaped plate (51). A first motor (53) is provided on the side wall of the vertical section of the L-shaped plate (51). The clutch (52) is used to separate or combine the shaft body of the wire winding roller (42) and the output shaft of the first motor (53). The output shaft of the first motor (53) penetrates through the L-shaped plate (51). A coupling (54) is provided between the output shaft of the first motor (53) and the input shaft of the clutch (52).

2. The biaxial fatigue testing device for a wind turbine blade according to claim 1, wherein The rope connecting member (34) includes a circular plate, a pillar and a ring which are integrally arranged. The rope connecting member (34) is made of metal.

3. The biaxial fatigue test device for a wind turbine blade according to claim 1, characterized in that, The driving mechanism includes a second motor (62). A screw rod (61) is penetratingly and rotatably installed between the two U-shaped plates (41). The slider (44) is threadedly connected to the screw rod (61). The second motor (62) is fixedly installed on the side wall of one of the U-shaped plates (41). The output shaft of the second motor (62) is fixedly connected to the screw rod (61) through a coupling mechanism.

4. The biaxial fatigue testing device for a wind turbine blade according to claim 3, wherein, The reciprocating mechanism includes a reciprocating lead screw (71) which passes through and is rotatably installed between the two U-shaped plates (41). A guide rod (72) is fixedly installed between the two U-shaped plates (41). A support block (73) is slidably installed on the guide rod (72). A limit post (74) is provided at the bottom end of the support block (73), and the limit post (74) is matched with the reciprocating lead screw (71). A limit wheel (75) is rotatably installed between the opposite sides of the support block (73), and the cable (47) bypasses the limit wheel (75).

5. A biaxial fatigue testing device for a wind turbine blade according to claim 4, characterized in that, The transmission assembly includes a first pulley (81) and a second pulley (82). The first pulley (81) is fixedly installed on the shaft body of the winding roller (42), and the second pulley (82) is fixedly installed on the shaft body of the reciprocating lead screw (71). A synchronous belt (83) is wound between the first pulley (81) and the second pulley (82).

6. The biaxial fatigue testing device for a wind turbine blade according to claim 5, wherein, The diameter of the second pulley (82) is larger than that of the first pulley (81).

7. A biaxial fatigue test method for wind turbine blades, applied to the biaxial fatigue test device for wind turbine blades described in claim 5, characterized in that, It includes the following steps: S1. According to the frequency to be applied to the blade body (2), the blade body (2) is installed on the test bench base. The second motor (62) drives the screw (61) to rotate, and the slider (44) slides between the two support rods (43) to adjust the relative positions of the two traction points of the blade body (2), and a biaxial fatigue test of simultaneous loading in the flapping and pitching directions of the blade is carried out. Then, the fixture is fixed at the position of the blade body (2) to be detected; S2. One end of the cable (47) is connected to the winding roller (42). After the other end of the cable (47) passes through the limit wheel (75) and the deflecting wheel (46) in sequence, it is connected to the rope connecting piece (34); S3. When the first motor (53) pulls the blade body (2) through the winding roller (42), the main and slave parts of the clutch (52) are in a combined state. The torque of the output shaft of the first motor (53) is transmitted to the winding roller (42) through the coupling (54) and the clutch (52). The winding roller (42) winds up the cable (47), and the blade body (2) moves downward under the traction of the cable (47). At this time, the rotation directions of the first motor (53) and the winding roller (42) are the same. When the blade body (2) vibrates to the lowest point, the main and slave parts of the clutch (52) are separated. At this time, the elastic potential energy of the blade body (2) needs to be converted into kinetic energy, and the blade body (2) begins to rebound. During the rebound process, since the main and slave parts of the clutch (52) are separated and cannot transmit the torque of the first motor (53), the winding roller (42) will release the cable (47) as the blade body (2) rebounds, and the winding roller (42) starts to move in the opposite direction, while the first motor (53) maintains its original rotation direction. At this time, the rotation directions of the first motor (53) and the winding roller (42) are opposite; S4. When the blade body (2) reaches the highest point again, the clutch (52) engages again, and the output shaft of the first motor (53) transmits torque to the wire winding roller (42), applying a downward traction excitation to the blade body (2) to approach the natural frequency of the vibration of the blade body (2). It is possible to apply an excitation in the form of a half-wave to the blade body (2) without reversing the clutch (52). The cable (47) pulls the blade with a composite frequency obtained by superimposing the two frequencies of the natural frequency of the blade flapping and the natural frequency of the blade pitching, causing the blade to perform a Lissajous motion in the flapping direction and the pitching direction; S5. During the rotation of the wire winding roller (42), it drives the first pulley (81) to rotate, and cooperates with the synchronous belt (83) and the second pulley (82) to drive the reciprocating lead screw (71) to rotate, driving the limit post (74), the limit wheel (75) and the support block (73) to slide back and forth synchronously on the guide rod (72), and the winding and unwinding process of the cable (47) is evenly distributed.

8. A method for biaxial fatigue testing of a wind turbine blade according to claim 7, characterized in that, In S1, the second motor (62) drives the screw (61) to rotate, and the slider (44) slides between the two support rods (43). When the slider (44) is directly below the rope connecting member (34), the two traction points of the slider (44) and the rope connecting member (34) are located in the same vertical plane, and a single-axis fatigue test in the pitching direction of the blade body (2) is carried out.

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