A large-size fan rotor blade vibration fatigue test piece design method

Abstract

The application provides a large-size fan rotor blade vibration fatigue test piece design method, comprising: carrying out modal analysis of a large-size fan rotor blade under test and working conditions to obtain vibration characteristics of the large-size fan rotor blade; determining resonance dangerous positions of the fan rotor blade according to static strength calculation results of the fan rotor blade, the vibration characteristics and whole machine dynamic stress test results; obtaining a truncated blade test piece containing the resonance dangerous positions by truncating the fan rotor blade, the truncated blade test piece having the same or similar stress distribution as the fan rotor blade; determining vibration fatigue test parameters of the truncated blade test piece; carrying out vibration fatigue test of the truncated blade test piece to verify whether a crack position is located at the examined resonance dangerous position, if the crack is located at the examined resonance dangerous position, the truncated test piece is truncated and designed; if the crack is located at a non-examined resonance dangerous position, the truncation position is adjusted until the requirement is met.

Description

Technical Field

[0001] This application belongs to the field of aero-engine technology, and specifically relates to a design method for a vibration fatigue test specimen of a large-size fan rotor blade. Background Technology

[0002] The large-size fan rotor blade with a shoulder is currently the largest, most demanding, and technically challenging titanium alloy rotor blade for aerospace applications in my country. It is primarily used in high-bypass turbofan engines, and high-cycle fatigue resistance is a key factor in its design. Simultaneously, to meet the engine's design requirements for long lifespan and high reliability, vibration fatigue tests on the large-size fan blade are necessary. This allows for understanding and assessing the difference in fatigue strength between the fan rotor component and the test piece, verifying the stability of the manufacturing process, obtaining the fatigue performance of the fan blade, and confirming whether the large-size fan blade can meet the high-cycle fatigue design requirements.

[0003] Conventional blade vibration fatigue tests typically use full-size blades. However, since large-size fan blades are much larger than conventional blades, the excitation energy of conventional test benches cannot meet the requirements, necessitating the purchase of large-thrust test benches. Furthermore, vibration fatigue tests on large-size fan blades can easily cause premature failure of non-tested parts, resulting in insufficient verification of the tested parts and a longer test cycle. Summary of the Invention

[0004] The purpose of this application is to provide a design method for vibration fatigue test specimens of large-size fan rotor blades. By reasonably cutting large-size fan blades to form test specimens, the effectiveness of the test can be guaranteed while saving test costs.

[0005] The technical solution of this application is: a design method for a vibration fatigue test specimen of a large-size fan rotor blade, the design method comprising:

[0006] Modal analysis was conducted on the large-size fan rotor blades under experimental and operational conditions to obtain the vibration characteristics of the large-size fan rotor blades;

[0007] Based on the static strength calculation results, vibration characteristics, and whole-machine dynamic stress test results of the large-size fan rotor blades, the resonance danger locations of the large-size fan rotor blades are determined.

[0008] The large-size fan rotor blades are truncated to obtain truncated blade test specimens containing the resonance hazard areas. The truncated blade test specimens have the same or similar stress distribution as the large-size fan rotor blades.

[0009] Determine the vibration fatigue test parameters of the truncated blade specimen, including the initial vibration load and the bonding position of the strain gauge;

[0010] The vibration fatigue test of the truncated blade test piece is carried out to verify whether the crack position is located at the resonance dangerous position, if the crack is located at the resonance dangerous position, the truncated test piece is truncated and designed; if the crack is located at the non-resonance dangerous position, the truncated position is adjusted until the requirement is met.

[0011] Further, the resonance dangerous position includes a blade root.

[0012] Further, the blade lower half test piece containing the blade root resonance dangerous position is obtained by cutting along the blade profile direction or the horizontal direction.

[0013] Further, when the large-size fan rotor blade has a shoulder, the resonance dangerous position further includes a shoulder root.

[0014] Further, the shoulder upper half test piece containing the shoulder root resonance dangerous position is obtained by cutting along the horizontal direction at the lower side of the shoulder.

[0015] Further, the test initial load is determined by the following formula:

[0016] σ a = A·σ b

[0017] In the formula, σ a is the test initial load, σ b is the material ultimate strength of the large-size fan rotor blade, and A is a load coefficient.

[0018] Further, the load coefficient A is between 0.5 and 0.8.

[0019] Further, the strain gauge bonding position is obtained by conversion of the maximum vibration stress position, wherein the strain gauge vibration stress at the bonding position and the maximum vibration stress satisfy:

[0020] σ= B·σ max

[0021] In the formula, σ is the vibration stress at the strain gauge bonding position, σ max is the maximum vibration stress of the blade, and B is the vibration stress ratio of σ and σ max .

[0022] Further, the vibration stress ratio B is between 0.1 and 0.5.

[0023] The large-size fan rotor blade vibration fatigue test piece design method provided by the application can ensure the effectiveness of the test, greatly shorten the test period, and is not limited by the test equipment, has strong operability, and reduces the test cost. BRIEF DESCRIPTION OF DRAWINGS

[0024] To more clearly illustrate the technical solutions provided in this application, the accompanying drawings will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application.

[0025] Figure 1 The flowchart shows the design method for the vibration fatigue test specimen of the large-size fan rotor blade in this application.

[0026] Figure 2a This is a schematic diagram showing the positions of the first and second short lines according to an embodiment of this application.

[0027] Figure 2b This is a schematic diagram showing the positions of the first and second short lines according to another embodiment of this application. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be described in more detail below with reference to the accompanying drawings.

[0029] To enable vibration fatigue testing of large-sized fan rotor blades on conventional test benches, this application provides a design method for vibration fatigue test specimens of large-sized fan rotor blades. By appropriately shortening the blades, the fatigue performance of key components can be assessed. This method ensures that cracks appear first at the test sites and simultaneously obtains fatigue performance data from multiple test sites. It shortens the test cycle and reduces test costs, providing effective support for the high-cycle fatigue resistance design of large-sized fan rotor blades.

[0030] like Figure 1 The diagram shown is a flowchart of the design method for a large-size fan rotor blade vibration fatigue test specimen provided in this application. The design method includes the following steps:

[0031] S1. Vibration Characteristics Analysis of Large-Size Fan Rotor Blades

[0032] Modal analysis of full-size fan rotor blades under test and operating conditions was conducted to obtain the vibration characteristics of the blades, including vibration frequency and relative vibration stress distribution, providing a basis for determining the test parts in vibration fatigue testing.

[0033] S2. Determine the test areas for vibration fatigue testing.

[0034] Based on the blade static strength calculation results, vibration characteristic results, and whole-body dynamic stress test results, and based on the dynamic strength reserve results, the resonance-prone areas of the blade are obtained by drawing a Goodman diagram.

[0035] Generally, for large-size fan rotor blades with shoulders, in addition to the concerned blade root part, the shoulder root part is also a resonance dangerous part, and thus the examination part of the large-size fan rotor blade with the shoulder is the blade root part and the shoulder root part.

[0036] S3, truncating the fatigue test piece of the large-size fan rotor blade

[0037] The core of the blade truncation is to change the vibration characteristics of the blade by truncating the blade to ensure that the examination part first cracks within the test period. In the truncation process, numerical simulation analysis is required to be repeated and iterated, and finally the truncation scheme of the test piece is determined:

[0038] S31, as shown in Figure 2a and Figure 2b To ensure that the examination parts of the shoulder root part and the blade root part can obtain fatigue strength examination, in the present application, the shoulder J1 and the tenon J2 are respectively taken as test clamping parts, and the first truncation line X1 is used to truncate the lower part of the shoulder J1, so as to divide the large-size fan rotor blade into the upper part 11 of the shoulder and the lower half part 12 of the blade.

[0039] S32, for the size L of the upper part 11 of the shoulder, after truncation, the shoulder J1 can be regarded as a fixed support, and through finite element simulation analysis, it is ensured that the stress distribution of the upper part 11 of the shoulder after truncation can simulate the resonance condition of the shoulder part in the working state of the large-size fan rotor blade, and the two have the same or similar resonance frequency.

[0040] S33, for the size of the lower half part 12 of the blade, the lower half part 12 of the blade can be further truncated by the second truncation line X2. When truncating, the stress distribution and frequency characteristics of the blade root part need to be considered comprehensively, the first is to ensure that the maximum stress point position is located at the blade root part to be examined, and the second is to ensure that the vibration frequency and the maximum amplitude of the truncated blade are increased to the shortest test period.

[0041] In the present application, the second truncation line X2 can be truncated along the blade profile direction or truncated in the horizontal direction. As shown in Figure 2a the second truncation line X2 can be truncated along the blade profile direction, which is basically parallel to the blade root part; as shown in Figure 2b the second truncation line X2 is truncated in the horizontal direction, which is parallel to the first truncation line X1.

[0042] S34, to improve the test efficiency, the lower half part 12 of the blade can be truncated for multiple times by repeating step c until the optimal lower half part 12 of the blade is obtained.

[0043] S4, determining the vibration fatigue test parameters

[0044] For the vibration fatigue test parameters of the large-size fan rotor blade after being truncated, the initial test load and the strain gauge sticking position need to be determined.

[0045] For the initial test load, the large-size fan rotor blade is made of titanium alloy, and the fatigue performance of the blade component is not clear. Meanwhile, there is a big difference between the fatigue strengths of the blade component and the test pressure piece. Therefore, a reasonable initial load must be given to ensure the effectiveness of the test.

[0046] In the present application, the initial test load is determined by the following formula:

[0047] σ a = A·σ b

[0048] In the formula, σ a is the initial test load, σ b is the ultimate strength of the blade material, and A is the load coefficient. The load coefficient A is usually between 0.5 and 0.8, and needs to be determined according to the material performance and the size of the blade component.

[0049] For the strain gauge sticking position, generally, the strain gauge can be stuck on any part of the blade body during the vibration fatigue test, and is preferably stuck at the maximum vibration stress position. However, due to the complex shape of the large-size fan rotor blade, the strain gauge cannot be stuck on some parts of the blade.

[0050] Therefore, the following method is used to determine the sticking position of the strain gauge in the present application:

[0051] σ = B·σ max

[0052] In the formula, σ is the vibration stress at the position where the strain gauge is stuck, σ max is the maximum vibration stress of the blade, and B is the ratio of σ to σ max . By controlling the proportional relationship between the sticking position and the maximum vibration stress, the vibration stress conversion is more accurate. The ratio B needs to be controlled within a certain range, usually between 0.1 and 0.5, and needs to be determined according to the dynamic test results of the whole machine and the fatigue results of similar structures.

[0053] S5, vibration stress test and vibration fatigue test verification of the truncated blade

[0054] In order to ensure that the test achieves the expected effect, firstly, the vibration stress distribution test of the test piece above the shoulder and the test piece below the half blade is carried out, and the maximum stress position of each part is determined and verified. On this basis, the vibration fatigue test of the test piece is carried out, and whether the crack position is located at the examination position of the root of the shoulder and the root of the blade is verified. If the vibration fatigue test of the upper half test piece of the truncated shoulder and the lower half test piece of the blade breaks at the corresponding examination position, respectively, the test piece truncation design is completed; if the vibration fatigue test breaks at a non-examination position, the truncation scheme design is carried out again, the positions of the first truncation line and the second truncation line are adjusted, until the requirements are met.

[0055] The large-size fan rotor blade vibration fatigue test piece design method provided by the application can ensure the effectiveness of the test, greatly shorten the test period, and the test is not limited by the test equipment, has strong operability, and reduces the test cost.

[0056] The above is only a specific embodiment of the application, but the protection scope of the application is not limited thereto, any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the application, which should be covered within the protection scope of the application. Therefore, the protection scope of the application should be subject to the protection scope of the claims.

Claims

1. A method for designing a vibration fatigue test specimen for large-size fan rotor blades, characterized in that, The design method includes: Modal analysis was conducted on the large-size fan rotor blades under experimental and operational conditions to obtain the vibration characteristics of the large-size fan rotor blades. Based on the static strength calculation results, vibration characteristics, and whole-machine dynamic stress test results of the large-size fan rotor blades, the resonance danger locations of the large-size fan rotor blades are determined. The large-size fan rotor blades are truncated to obtain truncated blade test specimens containing the resonance hazard areas. The truncated blade test specimens have the same or similar stress distribution as the large-size fan rotor blades. The vibration fatigue test parameters for the truncated blade specimen are determined, including the initial vibration load and the strain gauge bonding position. The initial test load satisfies: σ a =A·σ b In the formula, σ a The initial load for the test is σ. b The ultimate strength of the material for large-size fan rotor blades is given by A, which is the load factor. The bonding position of the strain gauge is obtained by converting it to the position of maximum vibration stress. The vibration stress of the strain gauge at the bonding position and the maximum vibration stress satisfy: σ = B·σ max In the formula, σ is the vibration stress at the location of the bonded strain gauge, σ max Let B be the maximum vibration stress of the blade and σ be the stress between σ and σ. max Vibration stress ratio; Vibration fatigue tests were conducted on the truncated blade test specimens to verify whether the cracked area was located in the assessed resonance hazard area. If the crack was located in the assessed resonance hazard area, the truncated design of the test specimen was completed; if the crack was located in a non-assessed resonance hazard area, the truncated position was adjusted until the requirements were met.

2. The design method for large-size fan rotor blade vibration fatigue test specimens as described in claim 1, characterized in that, The resonant-prone areas include the leaf roots.

3. The design method for large-size fan rotor blade vibration fatigue test specimens as described in claim 2, characterized in that, Test specimens of the lower half of the blade, including the dangerous resonance area at the root of the blade, are obtained by cutting along the blade profile or horizontally.

4. The design method for large-size fan rotor blade vibration fatigue test specimens as described in claim 2, characterized in that, When the large-sized fan rotor blades have shoulders, the resonance hazard area also includes the root of the shoulders.

5. The design method for large-size fan rotor blade vibration fatigue test specimens as described in claim 4, characterized in that, The upper half of the shoulder test piece, including the dangerous resonance portion at the root of the shoulder, is obtained by cutting along the horizontal direction on the lower side of the shoulder.

6. The design method for large-size fan rotor blade vibration fatigue test specimens as described in claim 1, characterized in that, The load factor A is between 0.5 and 0.

8.

7. The design method for large-size fan rotor blade vibration fatigue test specimens as described in claim 1, characterized in that, The vibration stress ratio B is between 0.1 and 0.5.

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