Special fixture for high-cycle fatigue testing of composite fan blades

Abstract

This invention discloses a dedicated fixture for high-cycle fatigue testing of composite fan blades. The fixture includes a fixture body and a protective plate. The fixture body has a limiting groove corresponding to the shape of the tenon of the composite blade test piece, with at least a portion of each of the two sides of the limiting groove serving as a working surface. The protective plate is pressed between the composite blade test piece and the working surface, covering at least the entire working surface. By placing the protective plate between the composite blade test piece and the working surface of the limiting groove on the fixture body, the interaction between the composite blade, the protective plate, and the fixture body effectively simulates the actual service state of the composite blade, thereby obtaining high-cycle fatigue data of the blade that most closely approximates the overall engine condition. This provides strong experimental data support for engine testing, crosswind testing, and airworthiness certification.

Description

Technical Field

[0001] This invention relates to the field of aero-engines, and in particular to a special fixture for high-cycle fatigue testing of composite fan blades. Background Technology

[0002] High-bypass turbofan engines have been widely used in civil aircraft and large military transport aircraft due to their low fuel consumption and low noise. With the increase in bypass ratio, fan blades are developing towards larger diameters and lower pressure ratios, which inevitably increases the weight of the fan blades, and consequently, the weight of the fan section. Data shows that for every 1kg increase in fan blade mass, the fan casing and transmission system each increase by 1kg, and the engine mounting structure and wing or fuselage each increase by 0.5kg, resulting in a significant increase in the total engine weight. Resin-based composite fan blades are widely used in modern advanced high-bypass turbofan engines because of their lightweight, high specific strength, and strong resistance to foreign object damage. Advanced companies have achieved 100 million flight hours with their composite engine blades, and composite fan blades have reached the fourth generation. However, domestic research in this area is still in its early stages, with many related fields lacking significant research.

[0003] Like metal blades, composite fan blades also suffer from high-cycle fatigue. High-cycle fatigue is mainly caused by blade vibration, which in turn is primarily induced by crosswinds. Unlike bird strike testing, blade fatigue testing requires sufficient evidence to demonstrate the blade's safety throughout its service life, while minimizing bench testing. Therefore, high-cycle fatigue testing at the material, component, and blade levels is crucial. Due to significant differences between composite and metal blades—such as the tenon joint being hot-pressed from the composite body, transition layer, and sacrificial layer, and the stiffness matching between the composite and metal contact points—traditional metal blade fatigue testing fixtures are unsuitable for composite blades. Therefore, specialized high-cycle fatigue testing fixtures designed specifically for composite fan blades are necessary. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the defect that the metal blade fatigue test fixtures in the prior art are not suitable for composite blades, and to provide a special fixture for high-cycle fatigue testing of composite fan blades.

[0005] The present invention solves the above-mentioned technical problems through the following technical solution:

[0006] A special fixture for high-cycle fatigue testing of composite fan blades, characterized in that it includes:

[0007] The fixture body has a limiting groove that corresponds to the shape of the tenon of the composite blade test piece, and at least a portion of the two sides of the limiting groove are working surfaces.

[0008] A protective sheet is pressed between the composite blade test piece and the working surface, and the protective sheet covers at least the entire working surface.

[0009] In this scheme, a protective plate is placed between the working surface of the limiting groove on the composite blade test piece and the fixture body. Since the interaction between the composite blade, the protective plate and the fixture body effectively simulates the real service state of the composite blade, high-cycle fatigue data of the blade that is closest to the whole engine state can be obtained, providing strong test data support for engine whole test, crosswind test and airworthiness certification.

[0010] Preferably, the protective sheet is elastic and has a rebound force toward the working surface, under the action of the rebound force, the protective sheet adheres to the working surface.

[0011] In this solution, the above structural form allows the protective plate to fit tightly with the fixture body, thereby simulating the actual service state of the composite blade and ensuring the reliability of the high-cycle fatigue data of the composite blade.

[0012] Preferably, the protective plate extends upward from the bottom of the working surface to the top surface of the clamp body, and extends along the top surface of the clamp body in a direction away from the limiting groove, with the side of the protective plate facing the working surface conforming to the side and top surface of the limiting groove.

[0013] In this design, the above structural form makes the bond between the protective plate and the working surface more secure, thereby ensuring that the protective plate always simulates the real service condition during the test, so as to obtain accurate and reliable test data.

[0014] Preferably, the material of the protective plate is the same as that of the fan disc protective sleeve. The protective plate is designed with reference to the corresponding fan disc protective sleeve to ensure that the surface roughness and tolerances of the working surface are consistent with those of the corresponding position on the fan disc protective sleeve, and that the material is the same as that of the fan disc protective sleeve, using a high-temperature alloy with the grade GH4169. This approach ensures that the protective plate consistently simulates real service conditions during testing, thereby obtaining accurate and reliable test data.

[0015] Preferably, a first groove is provided below the limiting groove, which extends in the same direction as the limiting groove. The limiting groove is connected to the first groove, and the top width of the first groove is greater than the bottom width of the limiting groove.

[0016] The special fixture for high-cycle fatigue testing of the composite material fan blades also includes a pressure plate. The pressure plate is disposed in the first groove and abuts against the tenon of the composite blade test piece and the top wall of the first groove. The pressure plate applies a clamping force to the tenon to restrict the downward movement of the blade test piece.

[0017] In this scheme, the clamping force is transmitted from bottom to top through the pressure plate, which effectively simulates the force transmission path of the composite blade under centrifugal force, thereby ensuring the reliability of the test data.

[0018] Preferably, the pressure plate includes a pressure plate body and a composite material layer, the composite material layer being fixed to the side of the pressure plate body facing the tenon, and the material of the composite material layer being the same as the material of the composite material pad.

[0019] In this design, the composite layer is adhered to the working surface of the pressure plate body, specifically the side of the pressure plate body facing the tenon. The composite material backing plate is the component that abuts against the bottom of the tenon in actual service conditions of the composite blade. Therefore, by ensuring that the material of the composite layer is consistent with the material of the composite material backing plate, the fatigue testing process of the composite blade prototype effectively simulates the actual service conditions of the composite fan blade. This allows for the acquisition of high-cycle fatigue data for the blade that most closely approximates the overall engine condition, providing strong experimental data support for engine testing, crosswind testing, and airworthiness certification.

[0020] Preferably, the pressure plate is provided with a second groove, and the bottom of the tenon fits against the bottom surface and two sides of the second groove.

[0021] In this solution, the above mechanism can, on the one hand, increase the contact area between the pressure plate and the tenon, thereby improving the reliability of the pressure plate in limiting the tenon; on the other hand, it can make the pressure plate not only apply an upward force to the bottom surface of the tenon to restrict the vertical movement of the tenon, but also apply a force to the two sides of the tenon to restrict the movement of the tenon in the width direction.

[0022] Preferably, a plurality of first connecting holes are provided on both sides of the limiting groove on the pressure plate, and a second connecting hole is provided on the fixture body, wherein the first connecting holes correspond to the second connecting holes;

[0023] The first bolt passes through the first connecting hole and the second connecting hole in sequence and is connected to the nut.

[0024] In this design, the first bolt connects the pressure plate to the fixture body. The combination of the first bolt, nut, and tightening torque ensures that the pressure plate presses the composite blade test piece against the fixture body. The second connecting holes at both ends of the fixture body are designed as reamed bolt holes. The first and second connecting holes cooperate to provide positioning and guidance, ensuring accurate and unbiased alignment between the pressure plate and the composite blade test piece.

[0025] Preferably, the preload torque of the first bolt generates a preload force that is not less than the centrifugal force borne by the composite blade test specimen. The formula for calculating the preload torque of a single first bolt is as follows:

[0026] M = K * P * D * 10 -3

[0027] Where M is the tightening torque of a single first bolt, in Nm; K is the torque coefficient; D is the nominal diameter of the first bolt, in mm; P is the preload generated by a single first bolt under the tightening torque M, in N; the formula for calculating the preload is as follows:

[0028] P = (m*r*(n*2*π / 60)) 2 ) / N

[0029] In the formula, m is the total weight of the composite blade test piece in kg; r is the radial distance from the center of mass of the composite blade test piece to the central axis of the engine meridional plane in m; n is the engine speed; and N is the number of the first bolts.

[0030] In this scheme, the preload torque and preload force of the first bolt are as required above. In order to more accurately simulate the stress state of the blade during the whole engine test and service, it is beneficial to obtain the blade high-cycle fatigue data that is closest to the whole engine state, and provide strong test data support for the engine whole engine test, crosswind test and airworthiness certification.

[0031] Preferably, when the tightening torque is changed sequentially according to M, M-5, M-10, and M-15, the resonant frequency of the composite blade test piece does not exceed 0.2% with the change in the tightening torque.

[0032] In this scheme, the tightening torque is set as required above, which helps to further ensure the stability of the installation state of the composite blade test piece.

[0033] Preferably, the special fixture for high-cycle fatigue testing of the composite material fan blades further includes a limiting baffle, which abuts against the end of the fixture body and is fixed to the fixture body to restrict the tenon from moving along the length direction of the limiting groove.

[0034] In this design, the above structural form is used to prevent the composite blade test piece from moving along the length direction of the limiting groove, that is, the axial direction. In other words, the function of the limiting baffle is to restrict the axial movement of the composite blade test piece. In actual tests, it needs to be installed on the corresponding side according to the axial movement direction of the blade, so as to restrict the axial movement of the composite blade test piece.

[0035] Preferably, recesses are provided at both ends of the clamp body, and the limiting baffle is detachably fixed in the recesses.

[0036] In this solution, the above-mentioned structural form is adopted, which on the one hand facilitates the positioning of the limiting baffle, thus making installation easier; on the other hand, it also helps to prevent the limiting baffle from protruding from the end face of the fixture body, thereby preventing it from bumping into other materials during installation and improving safety performance.

[0037] Preferably, multiple bolt holes spaced apart are provided on both sides along the length of the clamp body, and the clamp body is fixed to the vibration platform by the second bolt and the bolt holes.

[0038] In this scheme, the above structural form is used to connect the fixture body and the vibration platform, thereby enabling the high-cycle fatigue test to be carried out smoothly.

[0039] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0040] The positive and progressive effects of this invention are as follows: The special fixture for high-cycle fatigue testing of composite fan blades provided by this invention uses a protective plate between the working surface of the limiting groove on the composite blade test piece and the fixture body. Because the interaction between the composite blade, the protective plate, and the fixture body effectively simulates the actual service state of the composite blade, high-cycle fatigue data of the blade can be obtained that most closely approximates the overall engine condition, providing strong experimental data support for engine testing, crosswind testing, and airworthiness certification. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the structure of a special fixture for high-cycle fatigue testing of composite material fan blades according to a preferred embodiment of the present invention.

[0042] Figure 2 for Figure 1 A magnified view of part A in the diagram.

[0043] Figure 3 This is a side view of a special fixture for high-cycle fatigue testing of composite material fan blades according to a preferred embodiment of the present invention.

[0044] Figure 4This is a top view of a special fixture for high-cycle fatigue testing of composite material fan blades according to a preferred embodiment of the present invention.

[0045] Figure 5 For along Figure 4 A schematic diagram of the structure in the BB direction.

[0046] Figure 6 This is a three-dimensional structural diagram of the composite blade test specimen installed in a special fixture for high-cycle fatigue testing of composite fan blades according to a preferred embodiment of the present invention.

[0047] Figure 7 This is a three-dimensional structural diagram of a special fixture for high-cycle fatigue testing of composite fan blades according to a preferred embodiment of the present invention, after the composite blade test piece and the limiting baffle are installed.

[0048] Figure 8 This is a front view of the fixture body in the special fixture for high-cycle fatigue testing of composite material fan blades according to a preferred embodiment of the present invention.

[0049] Figure 9 For along Figure 8 A cross-sectional view of CC in the diagram.

[0050] Figure 10 This is a top view of the fixture body in the special fixture for high-cycle fatigue testing of composite material fan blades according to a preferred embodiment of the present invention.

[0051] Figure 11 For along Figure 10 A cross-sectional view of the FF surface in the diagram.

[0052] Figure 12 For along Figure 10 A cross-sectional schematic diagram of the DD plane.

[0053] Figure 13 For along Figure 10 A cross-sectional schematic diagram of the EE surface.

[0054] Figure 14 This is a three-dimensional structural diagram of the pressure plate in the special fixture for high-cycle fatigue testing of composite material fan blades according to a preferred embodiment of the present invention.

[0055] Figure 15 This is a cross-sectional schematic diagram of the pressure plate in the special fixture for high-cycle fatigue testing of composite material fan blades according to a preferred embodiment of the present invention.

[0056] Figure 16 This is a schematic diagram of the protective sheet in the special fixture for high-cycle fatigue testing of composite fan blades according to a preferred embodiment of the present invention.

[0057] Figure 17This is a schematic diagram of the protective sheet in a special fixture for high-cycle fatigue testing of composite fan blades according to a preferred embodiment of the present invention, from another direction.

[0058] Explanation of reference numerals in the attached figures:

[0059] Clamp body 10

[0060] Limiting groove 101

[0061] Working face 1011

[0062] First groove 102

[0063] Second connecting hole 103

[0064] Bolt hole 104

[0065] Through hole 105

[0066] Protective film 20

[0067] Pressure plate 30

[0068] Second groove 301

[0069] First connecting hole 302

[0070] Limit baffle 40

[0071] First bolt 50

[0072] Second bolt 60

[0073] Limit bolt 70

[0074] Nut 80

[0075] Composite blade test piece 90

[0076] Leaf 901

[0077] Tenon 902 Detailed Implementation

[0078] The present invention will be described more clearly and completely below by way of embodiments and in conjunction with the accompanying drawings, but the present invention is not limited to the scope of the embodiments described herein.

[0079] like Figures 1 to 17 As shown, this embodiment provides a special fixture for high-cycle fatigue testing of composite fan blades. The special fixture includes a fixture body 10 and a protective plate 20. The fixture body 10 is provided with a limiting groove 101 corresponding to the shape of the tenon 902 of the composite blade test piece 90. At least a portion of the two sides of the limiting groove 101 is a working surface 1011. The protective plate 20 is pressed between the composite blade test piece 90 and the working surface 1011, and the protective plate 20 at least covers the entire working surface 1011.

[0080] Specifically, a protective plate 20 is installed between the working surface 1011 of the limiting groove 101 on the composite blade test piece and the fixture body 10. Since the interaction between the composite blade, the protective plate 20 and the fixture body 10 effectively simulates the actual service state of the composite blade, high-cycle fatigue data of the blade that is closest to the overall engine state can be obtained, providing strong test data support for engine testing, crosswind testing and airworthiness certification.

[0081] In this embodiment, the side of the limiting groove 101 is formed by connecting a surface inclined to the vertical direction and a surface parallel to the vertical direction. The surface inclined to the vertical direction is the working surface 1011. The distance between the two working surfaces 1011 of the limiting groove 101 gradually increases from top to bottom, and the surface parallel to the vertical direction is located below the working surface 1011. The distance between the two sides of the tenon 902 at the end facing the blade root also gradually increases from top to bottom, while the distance between the two sides of the tenon 902 at the end away from the blade root gradually decreases from top to bottom. The protective plate 20 is elastic and has a rebound force towards the working surface 1011. Under the action of the rebound force, the protective plate 20 adheres to the working surface 1011. Through the rebound force, the protective plate 20 can tightly adhere to the fixture body 10, thereby simulating the actual service state of the composite blade and ensuring the reliability of the high-cycle fatigue data of the composite blade.

[0082] The tenon 902 of the composite blade test piece 90 is inserted into the limiting groove 101 from one end along the axial direction of the limiting groove 101; the blade body 901 protrudes from the top of the limiting groove 101. The tenon 902 fits against the protective plate 20.

[0083] Furthermore, referring to Figure 2 , Figures 16-17As understood, the protective plate 20 extends upward from the bottom of the working surface 1011 to the top surface of the fixture body 10, and extends along the top surface of the fixture body 10 in a direction away from the limiting groove 101. The side of the protective plate 20 facing the working surface 1011 is in contact with the side and top surface of the limiting groove 101. This structural design ensures a more secure bond between the protective plate 20 and the working surface 1011, thereby guaranteeing that the protective plate 20 always simulates the actual service condition during the test, thus obtaining accurate and reliable test data. The protective plate 20 is installed on the fixture body 10, covering the working surface 1011 of the limiting groove 101 in the fixture body 10, and directly participates in contact with the composite blade test piece 90, simulating the contact situation during the overall machine test and service conditions, ensuring stiffness coordination. The material of the protective plate 20 is the same as the material of the fan disc protective sleeve. When designing the protective plate 20, reference should be made to the corresponding fan disc protective sleeve to ensure that the roughness and tolerance of the working surface 1011 are consistent with the corresponding position of the fan disc protective sleeve, and the material selection is consistent with that of the fan protective sleeve. The material is a high-temperature alloy with the grade GH4169. The fit between the pressure plate 30 and the fixture body 10 is guaranteed by tolerance, and a clearance fit is adopted to ensure that the relative position of the two does not deviate. The clearance between the two is controlled between 0.5-1mm.

[0084] Reference Figures 8-13It is understood that in this embodiment, a first groove 102, extending in the same direction as the limiting groove 101, is provided below the limiting groove 101. The limiting groove 101 and the first groove 102 are connected. The top width of the first groove 102 is greater than the bottom width of the limiting groove 101. The special fixture for high-cycle fatigue testing of composite fan blades also includes a pressure plate 30. The pressure plate 30 is disposed in the first groove 102 and abuts against the tenon 902 of the composite blade test piece and the top wall of the first groove 102. The pressure plate 30 applies a clamping force to the tenon 902 to restrict the downward movement of the blade test piece. By transmitting the clamping force from bottom to top through the pressure plate 30, the force transmission path of the composite blade under centrifugal force is well simulated, thereby ensuring the reliability of the test data. Multiple first connecting holes 302 are respectively provided on both sides of the limiting groove 101 on the pressure plate 30, and a second connecting hole 103 is provided on the fixture body 10. The first connecting holes 302 and the second connecting holes 103 correspond to each other. The first bolt 50 passes through the first connecting holes 302 and the second connecting holes 103 in sequence and is connected to the nut 80. The first bolt 50 is used to connect the pressure plate 30 and the fixture body 10. Through the cooperation of the first bolt 50, the nut 80 and the tightening torque, the pressure plate 30 presses the composite blade test piece 90 and the fixture body 10 tightly. The second connecting holes 103 at both ends of the fixture body 10 are set as reamed bolt holes 104. The first connecting holes 302 and the second connecting holes 103 cooperate with each other to play a positioning and guiding role, ensuring that the pressure plate 30 and the composite blade test piece 90 are accurately matched without deviation. When the fixture is in operation, the first bolt 50 passes through the first connecting hole 302 and the second connecting hole 103 and engages with the nut 80, so that the working surface of the pressure plate 30 contacts and presses against the bottom of the composite blade test piece 90, thereby achieving upward pressing of the composite blade test piece 90. The eye plate is connected to the fixture body 10 by the first bolt 50 and the nut 80. A more significant feature is that the clamping force can be adjusted without disassembling the fixture, avoiding changes in vibration frequency caused by bolt loosening due to prolonged vibration, which could affect the results of the high-cycle fatigue test.

[0085] In this embodiment, two rows of first connecting holes 302 are distributed along the length of the pressure plate 30. Two rows of through holes 105 are provided on the fixture body 10 at positions corresponding to the first connecting holes 302 and the second connecting holes 103 at the bottom of the first groove 102. These through holes 105 allow the clamping bolt to pass through the fixture body, thereby connecting the pressure plate 30 and the fixture body 10, and thus clamping the composite blade test piece 90. It should be noted that the diameter of the through hole 105 is slightly larger than the maximum size of the bolt head of the first bolt 50 to facilitate the passage of the first bolt 50. In this embodiment, the diameter of the through hole 105 is 14 mm, and the first bolt 50 is an M12 bolt. The first bolt 50 cooperates with the nut 80, and the composite blade test piece 90 is clamped by applying a tightening torque. The through hole 105, the first connecting hole 302 and the second connecting hole 103 at the bottom of the first groove 102 are arranged in two rows, with 6 holes in each row. The second connecting hole 103 is a countersunk bolt hole 104. The countersunk bolt holes 104 are located at both ends of the fixture body 10 and are set as hinge bolt holes 104 to play a positioning and guiding role, ensuring that the pressure plate 30 and the composite blade test piece 90 fit accurately without deviation.

[0086] Furthermore, the pressure plate 30 includes a pressure plate body and a composite material layer. The composite material layer is fixed to the side of the pressure plate body facing the tenon 902, and the material of the composite material layer is the same as that of the composite material pad. The composite material layer is adhered to the working surface of the pressure plate body, that is, the side of the pressure plate body facing the tenon 902. The composite material pad is the component that abuts against the bottom of the tenon 902 in actual service conditions of the composite material blade. Therefore, by ensuring that the material of the composite material layer is consistent with the material of the composite material pad, the fatigue test process of the composite blade test piece 90 effectively simulates the actual service conditions of the composite material fan blade, thereby obtaining high-cycle fatigue data of the blade that is closest to the overall engine condition. This provides strong test data support for engine testing, crosswind testing, and airworthiness certification. Moreover, the working surface design must refer to the composite material pad to ensure that the roughness, dimensions, and geometric tolerances of the composite material layer, after being adhered to the pressure plate body, are consistent with the working surface of the composite material pad in actual service conditions. Meanwhile, the sharp corners on the fixture body 10 and the pressure plate 30 should be rounded to avoid damaging the composite blade test piece 90.

[0087] Reference Figure 14 and Figure 15It is understood that in this embodiment, the pressure plate 30 is provided with a second groove 301, and the bottom of the tenon 902 is attached to the bottom surface and two sides of the second groove 301. Through this mechanism, on the one hand, the contact area between the pressure plate 30 and the tenon 902 can be increased, thereby improving the reliability of the pressure plate 30 in limiting the tenon 902; on the other hand, the pressure plate 30 not only applies an upward force to the bottom surface of the tenon 902 to restrict the vertical movement of the tenon 902, but also applies a force to the two sides of the tenon 902 to restrict the width movement of the tenon 902.

[0088] Typically, the composite blade test specimen 90 has a low resonant frequency and undergoes a long high-cycle fatigue test. During prolonged vibration, the lack of axial displacement can cause axial movement in the composite blade test specimen 90. To prevent axial movement of the composite blade test specimen 90, in this embodiment, the special fixture for the high-cycle fatigue test of the composite fan blade also includes a limiting baffle 40. The limiting baffle 40 abuts against the end of the fixture body 10 and is fixed to the fixture body 10 to restrict the tenon 902 from moving along the length direction of the limiting groove 101. Through the above structural form, the axial movement of the composite blade test specimen 90 along the length direction of the limiting groove 101 is prevented. In other words, the function of the limiting baffle 40 is to restrict the axial movement of the composite blade test specimen 90. In actual testing, it needs to be installed on the corresponding side according to the axial movement direction of the blade to restrict the axial movement of the composite blade test specimen 90.

[0089] Furthermore, recesses are provided at both ends of the fixture body 10, and the limiting baffle 40 is detachably fixed within the recesses. This structural design facilitates positioning of the limiting baffle 40, thus simplifying installation; it also prevents the limiting baffle 40 from protruding from the end face of the fixture body 10, preventing it from bumping into other materials during installation and improving safety. Multiple spaced through holes are provided on the limiting baffle 40, and multiple threaded holes are provided at corresponding positions on the recesses of the fixture body 10, with the threaded holes corresponding to the through holes on the limiting baffle 40. The limiting bolt 70 passes through the through holes on the limiting baffle 40 and is threadedly connected to the fixture body 10. The limiting bolt 70 is an M5 bolt, and the limiting baffle 40 is fixed to the end of the furniture body by the limiting bolt 70 to restrict the axial movement of the composite blade test piece 90.

[0090] In this embodiment, multiple spaced bolt holes 104 are provided on both sides along the length of the fixture body 10. The fixture body 10 is fixed to the vibration platform by second bolts 60 and bolt holes 104. This structural design achieves the connection between the fixture body 10 and the vibration platform, thus enabling the high-cycle fatigue test to proceed smoothly. The fixture body 10 is machined into a ribbed shape along both sides along its length, maintaining rigidity while reducing the overall weight of the special fixture. Six bolt holes 104 are provided on each side of the fixture body 10, and a stable and reliable connection to the vibration table is achieved through the second bolts 60. The material of the fixture body 10 is the same as that of the fan disc, and its serial number is TC4.

[0091] In this embodiment, the preload torque of the first bolt 50 is not less than the centrifugal force borne by the composite blade test piece 90. The formula for calculating the preload torque of a single first bolt 50 is as follows:

[0092] M = K * P * D * 10 -3

[0093] Where M is the tightening torque of a single first bolt 50, in Nm; K is the torque coefficient; D is the nominal diameter of the first bolt 50, in mm; P is the preload generated by a single first bolt 50 under the tightening torque M, in N; the formula for calculating the preload is as follows:

[0094] P = (m*r*(n*2*π / 60)) 2 ) / N

[0095] In the formula, m is the total weight of the composite blade test piece 90, in kg; r is the radial distance from the center of mass of the composite blade test piece 90 to the central axis of the engine's meridional plane, in meters; n is the engine speed; and N is the number of first bolts 50. The preload torque and preload force of the first bolts 50 are as required above. In order to more accurately simulate the stress state of the blade during engine testing and service, and thus facilitate obtaining high-cycle fatigue data of the blade that is closest to the engine's condition, this provides strong test data support for engine testing, crosswind testing, and airworthiness certification.

[0096] To further ensure the stability of the composite blade test specimen 90 during installation, before the test, tightening torques of M, M-5, M-10, and M-15 were used. Frequency sweeping was performed on the vibration table to plot the correlation between the tightening torque and the resonant frequency of the composite blade test specimen 90, ensuring that the change in resonant frequency of the composite blade test specimen 90 with the tightening torque did not exceed 0.2%. If the tightening torque M could not guarantee that the resonant frequency change did not exceed 0.2%, the tightening torque was increased in increments of 5 N·m until the frequency change requirement was met. Since the axial load on the composite blade test specimen 90 was relatively small, the tightening torque of the limit bolt 70 was set to 15 N·m.

[0097] The specialized fixture for high-cycle fatigue testing of composite fan blades provided in this embodiment is suitable for full-size composite fan blades, non-full-size composite fan blades, and component-level test pieces with tenons (902). Its usage method is as follows:

[0098] An elastic protective plate 20 is installed in the limiting groove 101 on the fixture body 10, covering the working surface 1011 of the limiting groove 101. Under the action of the rebound force of the protective plate 20, the protective plate 20 is tightly connected to the fixture body 10. A limiting baffle 40 is installed on the fixture body 10 and fixed by a limiting bolt 70, thereby limiting the axial movement of the blade during long-term vibration. A pressure plate 30 is installed axially into the fixture body 10 and contacts the limiting baffle 40. A first bolt 50 enters the first connecting hole 302 through the through hole 105 at the bottom of the first groove 102 and connects the pressure plate 30 and the fixture body 10. A nut 80 connected to the first bolt 50 is installed, but not tightened. The fixture body 10 is connected to the vibration table by a second bolt 60 passing through the bolt hole 104 on the fixture body 10. A composite blade test piece 90 is installed axially into the fixture body 10 and placed above the pressure plate 30, keeping them aligned. Tighten the nut 80 connected to the first bolt 50 to the corresponding tightening torque, and determine the final tightening torque through a vibration pre-test to ensure that the blade frequency no longer changes. By pressing the composite blade test piece 90 from bottom to top with the pressure plate 30, and by matching the contact and stiffness relationship between the composite blade test piece 90, the protective plate, and the fixture body 10, the special fixture provided in this embodiment can fully simulate the high-cycle fatigue boundary of the conformal material fan blade in the overall engine installation state. This allows for the acquisition of blade high-cycle fatigue data that most closely approximates the overall engine state, providing strong test data support for engine testing, crosswind testing, and airworthiness certification.

[0099] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of the present invention is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but all such changes and modifications fall within the scope of protection of the present invention.

Claims

1. A special fixture for high-cycle fatigue testing of composite material fan blades, characterized in that, It includes: The fixture body is provided with a limiting groove that corresponds to the shape of the tenon of the composite blade test piece, and at least a portion of the two sides of the limiting groove are working surfaces. A protective sheet is pressed between the composite blade test piece and the working surface, the protective sheet at least covers the entire working surface, and the composite blade test piece, the protective sheet and the fixture body are stiffness-matched.

2. The special fixture for high-cycle fatigue testing of composite fan blades as described in claim 1, characterized in that, The protective sheet is elastic and has a rebound force toward the working surface. Under the action of the rebound force, the protective sheet adheres to the working surface.

3. The special fixture for high-cycle fatigue testing of composite material fan blades as described in claim 1, characterized in that, The protective plate extends upward from the bottom of the working surface to the top surface of the clamp body, and extends along the top surface of the clamp body in a direction away from the limiting groove. The side of the protective plate facing the working surface is in contact with the side and top surface of the limiting groove.

4. The special fixture for high-cycle fatigue testing of composite fan blades as described in any one of claims 1-3, characterized in that, The material of the protective sheet is the same as that of the fan disc protective sleeve.

5. The special fixture for high-cycle fatigue testing of composite material fan blades as described in any one of claims 1-3, characterized in that, Below the limiting groove, there is also a first groove that extends in the same direction as the limiting groove. The limiting groove is connected to the first groove, and the top width of the first groove is greater than the bottom width of the limiting groove. The special fixture for high-cycle fatigue testing of the composite material fan blades also includes a pressure plate. The pressure plate is disposed in the first groove and abuts against the tenon of the composite blade test piece and the top wall of the first groove. The pressure plate applies a clamping force to the tenon to restrict the downward movement of the blade test piece.

6. The special fixture for high-cycle fatigue testing of composite material fan blades as described in claim 5, characterized in that, The pressure plate includes a pressure plate body and a composite material layer. The composite material layer is fixed to the side of the pressure plate body facing the tenon. The material of the composite material layer is the same as that of the composite material pad.

7. The special fixture for high-cycle fatigue testing of composite material fan blades as described in claim 5, characterized in that, The pressure plate is provided with a second groove, and the bottom of the tenon fits into the bottom surface and two sides of the second groove.

8. The special fixture for high-cycle fatigue testing of composite material fan blades as described in claim 5, characterized in that, Multiple first connecting holes are provided on both sides of the limiting groove on the pressure plate, and a second connecting hole is provided on the fixture body, with the first connecting holes corresponding to the second connecting holes; The first bolt passes through the first connecting hole and the second connecting hole in sequence and is connected to the nut.

9. The special fixture for high-cycle fatigue testing of composite material fan blades as described in claim 8, characterized in that, The preload torque of the first bolt shall not be less than the centrifugal force borne by the composite blade test piece. The formula for calculating the preload torque of a single first bolt is as follows: M=K*P*D*10 -3 Where M is the tightening torque of a single first bolt, in Nm; K is the torque coefficient; D is the nominal diameter of the first bolt, in mm; P is the preload generated by a single first bolt under the tightening torque M, in N; the formula for calculating the preload is as follows: P=(m*r*(n*2*π / 60) 2 ) / N In the formula, m is the total weight of the composite blade test piece in kg; r is the radial distance from the center of mass of the composite blade test piece to the central axis of the engine meridional plane in m; n is the engine speed; and N is the number of the first bolts.

10. The special fixture for high-cycle fatigue testing of composite material fan blades as described in claim 9, characterized in that, When the tightening torque is changed sequentially according to M, M-5, M-10, and M-15, the resonant frequency of the composite blade test piece does not exceed 0.2% with the change in tightening torque.

11. The special fixture for high-cycle fatigue testing of composite material fan blades as described in any one of claims 1-3, characterized in that, The special fixture for high-cycle fatigue testing of the composite material fan blades also includes a limiting baffle. The limiting baffle abuts against the end of the fixture body and is fixed to the fixture body to restrict the tenon from moving along the length direction of the limiting groove.

12. The special fixture for high-cycle fatigue testing of composite material fan blades as described in claim 11, characterized in that, The clamp body has recesses at both ends, and the limiting baffle is detachably fixed in the recesses.

13. The special fixture for high-cycle fatigue testing of composite material fan blades as described in any one of claims 1-3, characterized in that, Multiple bolt holes spaced apart are provided on both sides along the length of the clamp body, and the clamp body is fixed to the vibration platform by the second bolt and the bolt holes.

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