Design method of blades for fly-off test, blades and blade fly-off test method

Abstract

The present invention discloses a design method for a fly-off test blade, a blade, and a blade fly-off test method. The design method for the fly-off test blade includes determining a fly-off speed between a minimum fly-off speed and a maximum fly-off speed; based on statics, determining a first width and a first thickness of a residual area according to the centrifugal force generated by the fly-off speed and the material strength limit of the blade; based on dynamics, obtaining a second width and a second thickness according to the determined expected first-order critical speed; based on the second width and the second thickness, performing finite element analysis on the blade to obtain a third width and a third thickness; and opening a weakening groove on the fly-off test blade according to the third width and the third thickness. The method combines multiple means such as statics, dynamics, and finite element analysis, and continuously optimizes the size of the residual area, so that the actual fly-off speed of the blade is close to the previously determined fly-off speed, thereby ensuring the smooth progress of the fly-off test.

Description

Technical Field

[0001] The present application relates to the field of aero-engine testing, and in particular to a design method for a blade for a fly-off test, a blade, and a blade fly-off test method. Background Art

[0002] The "Blade Containment and Rotor Imbalance Test" clause of the "Aircraft Engine Airworthiness Regulations" CCAR33.94 stipulates that aircraft engines need to undergo blade shedding tests. Blade shedding technology mainly includes the control of shedding speed, the control of shedding quality, and the stability of shedding control technology.

[0003] There are currently two common fan blade flying techniques. One is to pre-set cracks at specified positions on the fan blades to keep them partially connected. As the fan rotates, the centrifugal force becomes greater and greater as the speed increases, causing the fan blades to fly off at a certain speed. The other technique is to bury explosives. When the fan rotor reaches a specified speed, the explosives are detonated to cause the fan blades to fly off.

[0004] Both of these flying-off technologies have their own shortcomings. For the preset crack technology, its principle is the flying-off caused by centrifugal force. This technology can accurately control the flying-off quality, but the flying-off speed control accuracy is often insufficient, and premature flying-off often occurs. The reason is that in the prior art, if only the effect of centrifugal force is considered when pre-setting cracks, that is, only the static analysis results are considered, it is easy for the reserved connection part to be insufficiently strong, resulting in fracture and flying-off before the expected speed is reached; if too many reserved parts are reserved, it may lead to the situation that the blade does not fly off at the expected speed, making it difficult to make the blade fly off within the expected speed range, and it is difficult to meet the requirements of the flying-off test.

[0005] For the method of pre-setting explosives, although it can be detonated at a specified rotation speed, the quality control accuracy of the fly-off is relatively poor. More importantly, the impact generated by the explosion greatly interferes with the load measurement after the fly-off. In addition, explosives also have certain risks. Summary of the invention

[0006] The technical problem to be solved by the present invention is to overcome the defect in the prior art that the design of a fly-off test blade is difficult to meet the requirements of the fly-off test, and to provide a design method for a fly-off test blade, a blade and a blade fly-off test method.

[0007] The present invention solves the above technical problems through the following technical solutions:

[0008] A method for designing a blade for a fly-off test, the method comprising:

[0009] Determine the take-off speed between the minimum take-off speed and the maximum take-off speed;

[0010] Based on statics, according to the centrifugal force generated by the fly-off speed and the material strength limit of the blade, the total cross-sectional area of ​​the two residual regions is obtained, and the first width and the first thickness of the residual region are determined according to the cross-sectional area;

[0011] determining an expected first critical speed of the blade;

[0012] Based on dynamics, according to the expected first-order critical speed, the first width and the first thickness are corrected to obtain a second width and a second thickness;

[0013] Based on the second width and the second thickness, a finite element analysis is performed on the blade, and the second width and the second thickness are corrected so that the first-order critical speed of the blade obtained by the finite element analysis is equal to the expected first-order critical speed, and a third width and a third thickness are obtained;

[0014] A weakening groove is provided on the fly-off test blade according to the third width and the third thickness.

[0015] In this scheme, the size of the residual area (first width and first thickness) is estimated based on statics, and then based on dynamics, the size of the residual area is corrected according to the expected first-order critical speed to obtain the second width and second thickness. Finally, according to the results of finite element analysis, the size of the residual area is corrected again to obtain the third width and third thickness. This method combines the three means of statics, dynamics and finite element analysis to continuously optimize the size of the residual area, so that the actual blade fly-off speed is close to the predetermined fly-off speed, ensuring the smooth progress of the fly-off test.

[0016] Preferably, based on statics, the first width and the first thickness of the residual area are obtained according to the centrifugal force generated by the fly-off speed and the material strength limit of the blade, using the following formula:

[0017]

[0018] Where S is the total cross-sectional area of ​​the two residual regions, a 1 is the first width, b 1 is the first thickness, m is the mass of the blade flying part, r is the distance from the center of mass of the blade flying part to the blade rotation center, ω 0 is the flyaway speed, σ b is the tensile stress strength limit of the blade.

[0019] Preferably, based on the dynamics, according to the expected first-order critical speed, the first width and the first thickness are corrected to obtain the second width and the second thickness, using the following formula:

[0020]

[0021] Among them, a 2 is the second width, b 2 is the second thickness, ω C1 is the expected first-order critical speed, ω 0 is the flying speed, R is the hole radius of the weakening groove end, E is the elastic modulus of the blade material, L is the distance from the center of mass of the flying blade to the weakening groove, m is the mass of the flying blade, r is the distance from the center of mass of the flying blade to the blade rotation center, σ b is the blade tensile stress strength limit, k is the correction factor, and 2 <k<4。

[0022] Preferably, the expected first-order critical speed is greater than the take-off speed and less than or equal to the maximum take-off speed.

[0023] Preferably, if the third thickness is inconsistent with the thickness of the blade, a rounded transition structure is provided between the residual area and an area of ​​the blade excluding the residual area.

[0024] Preferably, the edges of the weakening groove are polished to reduce stress concentration at the edges of the weakening groove.

[0025] Preferably, the two residual regions have equal cross-sectional areas and the same cross-sectional shapes.

[0026] A blade is used for a blade fly-off test, wherein the blade is obtained by the design method of the blade for the fly-off test as described above.

[0027] A blade flying off test method, the method comprising:

[0028] Providing a blade manufactured by using the design method of the fly-off test blade as described above;

[0029] Disposing a strain gauge at the residual area of ​​the blade;

[0030] Rotating the blades and gradually increasing the rotation speed of the blades;

[0031] Compare the real-time strain measured by the strain gauge with the elastic limit strain, and the blade rotation speed with the minimum elastic strain limit rotation speed and the maximum elastic strain limit rotation speed,

[0032] Wherein, the elastic limit strain corresponds to the strain when the blade material reaches the elastic limit of tensile stress;

[0033] The minimum elastic strain limit speed is: the blade speed corresponding to the blade at the tensile stress elastic limit when the blade having the residual area cross-sectional area calculated by statics with the minimum fly-off speed as the fly-off speed;

[0034] The maximum elastic strain limit speed is: the blade speed corresponding to the blade at the tensile stress elastic limit when the blade having a residual area cross-sectional area calculated by using statics with the maximum fly-off speed as the fly-off speed.

[0035] In this scheme, since a blade manufactured by the design method of the fly-off test blade as described above is used, the actual fly-off speed of the blade is close to the predetermined fly-off speed, which is conducive to the fly-off test. Moreover, the relationship between the speed and the strain can be obtained according to the real-time strain measured by the strain gauge, and then the actual speed of the blade when it flies off can be determined. In addition, during the test, the blade speed can be changed by judging whether the real-time strain reaches the elastic limit strain, so that the blade flies off as much as possible between the minimum fly-off speed and the maximum fly-off speed.

[0036] Preferably, the comparison between the real-time strain measured by the strain gauge and the elastic limit strain, and between the blade rotation speed and the minimum elastic strain limit rotation speed and the maximum elastic strain limit rotation speed is:

[0037] When the real-time strain reaches 80-100% of the elastic limit strain, if the blade rotation speed is less than the minimum elastic strain limit rotation speed, the test is stopped.

[0038] Preferably, the comparison between the real-time strain measured by the strain gauge and the elastic limit strain, and between the blade rotation speed and the minimum elastic strain limit rotation speed and the maximum elastic strain limit rotation speed is:

[0039] When the real-time strain reaches the elastic limit strain, if the blade rotation speed is between the minimum elastic strain limit rotation speed and the maximum elastic strain limit rotation speed, the blade continues to rotate at an accelerated speed until the blade flies off.

[0040] Preferably, the comparison between the real-time strain measured by the strain gauge and the elastic limit strain, and between the blade rotation speed and the minimum elastic strain limit rotation speed and the maximum elastic strain limit rotation speed is:

[0041] If the real-time strain does not reach the decision strain threshold when the blade speed reaches the minimum fly-off speed, the blade speed is adjusted to the first-order critical speed;

[0042] If the real-time strain increases to exceed the limit strain, the blade speed is maintained at the first-order critical speed until the blade flies off;

[0043] If the blade speed remains at the first-order critical speed and the real-time strain has not reached the limit strain, the test is stopped;

[0044] The decision strain threshold is: a theoretical strain value of the residual area when the blade having a cross-sectional area of ​​the residual area calculated by using statics with a maximum fly-off speed as the fly-off speed is at a minimum fly-off speed.

[0045] The positive and progressive effects of the present invention are as follows: the design method of the blade for the fly-off test of the present invention estimates the size of the residual area based on statics, and then based on dynamics, corrects the size of the residual area according to the expected first-order critical speed to obtain the second width and the second thickness, and finally corrects the size of the residual area again according to the finite element analysis results to obtain the third width and the third thickness. The method combines multiple means such as statics, dynamics and finite element analysis, and continuously optimizes the size of the residual area, so that the actual fly-off speed of the blade is close to the predetermined fly-off speed, ensuring the smooth progress of the fly-off test; the blade fly-off test method of the present invention uses a blade manufactured by the design method of the fly-off test blade as described above, so the actual fly-off speed of the blade is close to the predetermined fly-off speed, which is conducive to the fly-off test, and the relationship between the speed and the strain can be obtained according to the real-time strain measured by the strain gauge, and then the actual speed of the blade when it flies off can be judged. And during the test, by judging whether the real-time strain reaches the elastic limit strain, the blade speed can be changed so that the blade flies off as much as possible between the minimum fly-off speed and the maximum fly-off speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 The present invention is a flowchart of a method for designing a blade for a flyaway test according to an embodiment of the present invention.

[0047] Figure 2 It is a schematic structural diagram of a blade according to an embodiment of the present invention.

[0048] Figure 3 for Figure 2 Schematic cross-section of the residual area of ​​the blade.

[0049] Figure 4 This is the stress-strain curve of general parts during tensile test.

[0050] Figure 5 This is the first-order natural frequency vibration mode of the blade according to an embodiment of the present invention.

[0051] Fig. 6A and Figure 6B They are schematic diagrams of the partial structures of blades according to two preferred embodiments of the present invention.

[0052] Figure 7 The present invention provides a blade shedding test method according to an embodiment of the present invention.

[0053] Figure 8 It is a schematic structural diagram of a blade according to an embodiment of the present invention, wherein a strain gauge is provided on the residual area.

[0054] Fig. 9 This is a diagram (I) showing the relationship between the real-time strain measured by the strain gauge and the rotational speed when the blade according to one embodiment of the present invention is subjected to a fly-off test.

[0055] Fig.10 This is a diagram (II) showing the relationship between the real-time strain measured by the strain gauge and the rotational speed when the blade according to an embodiment of the present invention is subjected to a fly-off test.

[0056] Fig.11 This is a diagram (III) showing the relationship between the real-time strain measured by the strain gauge and the rotational speed when the blade according to an embodiment of the present invention is subjected to a fly-off test.

[0057] Fig.12 This is a graph (IV) showing the relationship between the real-time strain measured by the strain gauge and the rotational speed when the blade according to an embodiment of the present invention is subjected to a fly-off test.

[0058] Fig.13 FIG5 is a graph showing the relationship between the real-time strain measured by the strain gauge and the rotational speed when the blade of one embodiment of the present invention is subjected to a fly-off test.

[0059] Fig.14 FIG. 4 is an influence of the damping ratio of a blade on strain according to an embodiment of the present invention. DETAILED DESCRIPTION

[0060] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples.

[0061] like Figure 1 As shown, this embodiment provides a design method for a fly-off test blade. This embodiment also provides a blade 10, which is manufactured according to the design method for a fly-off test blade of this embodiment, such as Figure 2 As shown, the middle part of the blade has a weakening groove 1, and the two ends of the weakening groove 1 in the extension direction are respectively two residual areas 2 of the blade. When the blade flies off, it breaks at the residual area 2, especially at the position with the smallest cross-sectional area of ​​the residual area 2. A circular hole 3 is provided at each end of the weakening groove 1 to reduce stress concentration.

[0062] According to the design requirements of the flyaway test, the minimum flyaway speed of the blade can be obtained: 1 With the maximum take-off speed ω 2 , at the minimum take-off speed ω 1 With the maximum take-off speed ω 2 Select the take-off speed between 0 , and based on the take-off speed ω 0 Design the size of the blade. Preferably, ω 0 =(ω 1 +ω 2) / 2.

[0063] During the blade flying test, the residual area 2 is broken under the centrifugal force (the blade material reaches the strength limit σ b ).like Figure 3 As shown, the cross section of the residual area of ​​the blade is rectangular or approximately rectangular, the width of the cross section is a, and the thickness is b, wherein the width direction of the cross section is the same as the extension direction of the weakening groove, and the thickness direction of the cross section is the same as the thickness direction of the blade. In this embodiment, the cross-sectional areas of the two residual areas are equal in size and shape, so the total cross-sectional area S of the two residual areas satisfies the formula S=2ab. According to the tensile properties of the material, after the material enters the yield stage, the tension increases slightly, and the strain will increase significantly, such as Figure 4 As shown, ε e Indicates the stress σ when the part is stretched to its elastic limit e The corresponding elastic limit strain, ε b Expressed as the ultimate stress of the tensile strength of the part σ b The corresponding strength limit strain, ω e Indicates that the elastic limit strain ε is reached e The speed at which b Indicates that the ultimate strength strain ε is reached b The elastic modulus E and the ultimate strength σ of the material b As known conditions, it can be deduced based on the centrifugal force formula and the average stress of the tensile section Figure 3 The calculation formula for the total cross-sectional area of ​​the residual area is:

[0064]

[0065] Where S is the total cross-sectional area of ​​the two residual regions, a 1 is the first width, b 1 is the first thickness, m is the mass of the blade flying part, r is the distance from the center of mass 20 of the blade flying part to the blade rotation center 30, ω 0 is the flyaway speed, σ b is the blade tensile stress strength limit. Therefore, based on statics, at the flyaway speed ω 0 When the total cross-sectional area S of the two residual regions is determined, the first width a of the residual region can be determined according to the cross-sectional area. 1 and the first thickness b 1 .

[0066] It is understandable that statics can only determine the total cross-sectional area S of the two residual regions, but cannot uniquely determine the first width a. 1 and the first thickness b 1 , the first thickness b can be determined by referring to the blade thickness 1, and then use the area relationship to determine the first width a 1 .

[0067] The vibration mode of the first-order natural frequency of the blade (corresponding to the first-order critical speed of the blade) is as follows: Figure 5 As shown in Figure 2, when the blade speed increases, if the first-order resonance occurs, then Figure 4 The strain-speed curve shown will change, such as Fig.14 As shown, ω c Represents the resonant speed. At the resonant speed, the strain peak value depends on the blade structure damping. The smaller the damping ratio ζ, the greater the response. Fig.14 The damping ratio relationship shown in is ζ 1 <ζ 2 <ζ 3 However, it is difficult to accurately obtain the damping ratio ζ of the blade structure during design. In addition, the response peak at the resonance is also affected by factors such as the rise rate, which increases the uncertainty of the flyaway speed design. In order to enhance the reliability of the flyaway speed design, it is necessary to adjust the first-order critical speed of the blade to the minimum value ω of the required flyaway speed range. 1 Above, and it is best to leave a certain margin; the first-order critical speed of the blade depends on the bending stiffness of the remaining connection part after cutting, which is related to ab 3 into a certain proportional relationship, so according to the selected first-order critical speed ω C1 And S = ab estimates the value of the cross-sectional thickness b. In the estimation formula for the thickness b, there is a correction factor k, preferably, 2 <k<4。

[0068] Specifically in this embodiment, the expected first-order critical speed ω of the blade is determined C1 , and the expected first-order critical speed ω C1 At the take-off speed ω 0 With the maximum take-off speed ω 2 Based on dynamics, according to the expected first-order critical speed, the first width a is corrected 1 and the first thickness b 1 , get the second width a 2 and the second thickness b 2 , the specific formula is as follows:

[0069]

[0070] Among them, a 2 is the second width, b 2 is the second thickness, ω C1 is the expected first-order critical speed, ω 0is the flying speed, R is the radius of the circular hole 3 at the end of the weakening groove, E is the elastic modulus of the blade material, L is the distance from the center of mass 20 of the blade flying part to the weakening groove, m is the mass of the blade flying part, r is the distance from the center of mass of the blade flying part to the blade rotation center 30, σ b is the blade tensile stress strength limit, k is the correction factor, and 2 <k<4。

[0071] Based on the second width a 2 and the second thickness b 2 , three-dimensional modeling of the blade is performed, and finite element analysis is performed on the three-dimensional model of the blade. The finite element analysis obtains the first-order critical speed of the blade (corresponding to the first-order vibration mode) and corrects the second width a 2 and the second thickness b 2 , so that the first critical speed of the blade obtained by finite element analysis is equal to the expected first critical speed, and the third width a is obtained 3 and the third thickness b 3 .

[0072] In correcting the second width a 2 and the second thickness b 2 Generally speaking, the first-order critical speed mainly depends on the thickness b of the residual area. The first-order critical speed increases when the thickness increases, and decreases when the thickness decreases. The thickness of the residual area can be adjusted according to the structure calculated by the finite element under the premise that the package cross-sectional area S remains unchanged, so that the first-order critical speed of the blade is as close to the design target as possible. C1 .like Fig. 6A and Figure 6B As shown, the final third thickness b 3 May not correspond to the thickness of the blade, e.g. Fig. 6A Middle, third thickness b 3 is greater than the thickness of the blade, then the thickness of the residual area and the area around the weakening groove is increased so that the thickness of the above-mentioned area is greater than the thickness of other areas of the blade, or, for example, Figure 6B Middle, third thickness b 3 If the thickness of the residual area and the area around the weakening groove is smaller than the thickness of the blade, the thickness of the residual area and the area around the weakening groove is reduced so that the thickness of the above area is smaller than the thickness of other areas of the blade. In order to avoid the appearance of steps and stress concentration, a rounded transition structure 5 can be provided between the residual area and the area around the weakening groove and the area of ​​the blade other than the residual area and the area around the weakening groove.

[0073] Finally, according to the third width a 3 and the third thickness b 3, manufacture the flyaway test blade. Preferably, the weakening groove of the blade is polished to reduce stress concentration, and the cap beam where large initial cracks occur is reduced as much as possible, reducing the impact of large cracks on the design results, and preventing the blade from flying off and breaking before reaching the flyaway speed.

[0074] The design method of the blade for the flyaway test of this embodiment estimates the size of the residual area based on statics, and then corrects the size of the residual area based on dynamics according to the expected first-order critical speed to obtain the second width and the second thickness, and finally corrects the size of the residual area again according to the finite element analysis results to obtain the third width and the third thickness. This method combines statics, dynamics, finite element analysis, fracture mechanics and other means to continuously optimize the size of the residual area, especially the size of the cross section of the residual area, so that the actual flyaway speed of the blade obtained according to this method is close to the previously determined flyaway speed, ensuring the smooth progress of the flyaway test.

[0075] In addition, the expected first-order critical speed ω C1 Under the premise of unchanged, it can also be based on the minimum take-off speed ω 1 With the maximum take-off speed ω 2 Design spare fly-off blades for actual fly-off tests.

[0076] like Figure 7 As shown, this embodiment also provides a blade flying test method, which uses the blade as before, sets a strain gauge 6 at the residual area of ​​the blade, then rotates the blade 10, and gradually increases the rotation speed of the blade. The state of the blade can be judged according to the real-time strain measured by the strain gauge 6, and the rotation speed is adjusted accordingly according to the state, so that the blade flying test is successfully completed. Specifically, by comparing the size between the real-time strain and the elastic limit strain, and between the blade rotation speed and the minimum elastic strain limit rotation speed and the maximum elastic strain limit rotation speed, wherein the elastic limit strain corresponds to the strain when the blade material reaches the elastic limit of the tensile stress.

[0077] The minimum elastic strain limit speed is defined as: the blade speed corresponding to the residual area cross-sectional area of ​​the blade calculated by using statics with the minimum fly-off speed as the fly-off speed when it is at the tensile stress elastic limit, that is, using the minimum fly-off speed as the fly-off speed, the residual area cross-sectional area of ​​the blade is calculated by statics, so that the blade with the residual area cross-sectional area rotates, and the blade speed continuously accelerates. When the blade reaches the tensile stress elastic limit, the corresponding blade speed at this time is the minimum elastic strain limit speed.

[0078] Similarly, the maximum elastic strain limit speed is defined as the blade speed corresponding to the tensile stress elastic limit of the blade having a residual area cross-sectional area calculated using statics with the maximum fly-off speed as the fly-off speed.

[0079] Since the blades manufactured by the design method of the fly-off test blades are used, the actual fly-off speed of the blades is close to the predetermined fly-off speed, which is conducive to the fly-off test. Moreover, the actual speed of the blades when they fly off can be determined based on the real-time strain measured by the strain gauge 6. In addition, during the test, the blade speed can be changed by judging whether the real-time strain reaches the elastic limit strain, so that the blades can be as close to the minimum fly-off speed ω as possible. 1 With the maximum take-off speed ω 2 The flight will be within the flight interval. Figure 8 As shown, the position of the strain gauge 6 covers the minimum cross-sectional area of ​​the residual area to monitor the strain of the weakest area. If the residual area is small, only one strain gauge 6 can be set, which can also meet the monitoring requirements and save costs. Multiple strain gauges 6 can also be set to improve monitoring accuracy.

[0080] Through the strain gauge 6, the speed-strain curve (such as Figure 9-12 As shown in the figure, point B represents the minimum elastic strain limit speed, and point D represents the maximum elastic strain limit speed. The curve between point O and point B represents the centrifugal force The strain curve corresponding to the stress curve obtained by dividing the cross-sectional area of ​​the residual area. The curve between points O and D represents the centrifugal force. The strain curve corresponding to the stress curve obtained by dividing the cross-sectional area of ​​the residual area, that is, the OB curve and the OD curve are respectively obtained by using statics according to the minimum fly-off speed ω 1 With the maximum take-off speed ω 2 The calculated strain-speed curve of the blade is predicted by the theoretical calculation. Similarly, the OC curve is calculated by statics according to the flyaway speed ω 0 The calculated strain-speed curve of the blade predicted by theory.

[0081] Below Figure 9-12 Taking the flyaway test method as an example, the application of the flyaway test method in different situations is discussed in detail.

[0082] See also Fig. 9 As shown in Figure 1, in this test, the speed-strain curve falls into the OAB interval. When the real-time strain reaches a certain threshold (in actual tests, the threshold can be 80%, 85%, 90%, 95% or 100% of the elastic limit strain), if the blade speed is less than the minimum elastic strain limit speed, the strain in the residual area has approached or reached the elastic limit strain, which means that the blade may fly off prematurely. The main possible reasons include design, manufacturing, and the actual mechanical properties of the material. For example, the strength limit σ of the material used for the blade bThe residual cross-sectional area of ​​the designed and processed blade is smaller than the residual area required in reality because the residual modulus E is greater than the real strength limit of the material, or the elastic modulus E of the material used in the design is different from the real material elastic modulus, etc. In order to avoid plastic deformation of the blade or even premature flying off, the test can be stopped. Furthermore, a spare blade with a larger residual area cross-sectional area S can be replaced and tested again.

[0083] See also Fig.10 As shown in the figure, in this test, the speed-strain curve falls into the OBD interval, indicating that when the real-time strain reaches the elastic limit strain, the blade speed falls between the minimum elastic strain limit speed and the maximum elastic strain limit speed, which means that the design, manufacturing, and the actual mechanical properties of the material are basically in line with expectations. Then, the blade can continue to accelerate until the blade flies off. If the blade can be accelerated at the designed fly-off speed ω 0 The nearby part flew off and the fracture was basically a tensile fracture.

[0084] See also Fig.11 As shown, in this test, the speed-strain curve falls into the ODE interval. In this test, the speed approaches or reaches the minimum take-off speed ω 1 , the real-time strain has not reached the decision strain threshold, where the decision strain threshold is: the theoretical strain value of the residual area when the blade with the residual area cross-sectional area calculated by statics with the maximum fly-off speed as the fly-off speed is at the minimum fly-off speed, that is, Fig.11 In the figure, the OD curve is at the minimum fly-off speed ω 1 In this case, the test is quite different from the prediction, which means that the blade may not fly off within the flying interval. The main possible reasons also include design, manufacturing, and the actual mechanical properties of the material. For example, the strength limit σ of the material used in the design b Less than the actual strength limit of the material, etc., resulting in the designed and processed blade cutting residual cross-sectional area being larger than the actual required residual area. In this case, the speed can be further increased to the expected first-order critical speed ω C1 and stay at this speed to observe the change of strain amplitude. If the strain increases and exceeds the elastic limit strain ε e ,like Fig.12 As shown in the figure, the flying off can be achieved with the help of resonance at the critical speed. If the flying off occurs at the critical speed, the fracture surface may still have certain fatigue characteristics.

[0085] If the expected first-order critical speed ω C1 When the real-time strain increases insufficiently, it still does not exceed the elastic limit strain ε e , then continue to accelerate to the maximum elastic strain limit speed. If the real-time strain still does not exceed the elastic limit strain ε e ,like Fig.13As shown, it means that the remaining cross-sectional area of ​​the designed and processed blade is larger than the actually required remaining area, so the test needs to be stopped. Furthermore, a spare blade with a smaller cross-sectional area of ​​the residual area can be replaced and tested again.

[0086] Although the specific embodiments of the present invention are described above, it should be understood by those skilled in the art that this is only for illustration and the protection scope of the present invention is defined by the appended claims. Those skilled in the art may make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but these changes and modifications all fall within the protection scope of the present invention.

Claims

1. A method for designing a blade for a fly-off test, characterized in that: The method comprises: Determine the take-off speed between the minimum take-off speed and the maximum take-off speed; Based on statics, according to the centrifugal force generated by the fly-off speed and the material strength limit of the blade, the total cross-sectional area of ​​the two residual regions is obtained, and the first width and the first thickness of the residual region are determined according to the cross-sectional area; determining an expected first critical speed of the blade; Based on dynamics, according to the expected first-order critical speed, the first width and the first thickness are corrected to obtain a second width and a second thickness; Based on the second width and the second thickness, a finite element analysis is performed on the blade, and the second width and the second thickness are corrected so that the first-order critical speed of the blade obtained by the finite element analysis is equal to the expected first-order critical speed, and a third width and a third thickness are obtained; A weakening groove is provided on the fly-off test blade according to the third width and the third thickness.

2. The method for designing a blade for a fly-off test according to claim 1, characterized in that: Based on statics, the first width and the first thickness of the residual area are obtained according to the centrifugal force generated by the fly-off speed and the material strength limit of the blade, using the following formula: Where S is the total cross-sectional area of ​​the two residual regions, a1 is the first width, b1 is the first thickness, m is the mass of the blade flying part, r is the distance from the center of mass of the blade flying part to the blade rotation center, ω0 is the flying speed, σ b is the tensile stress strength limit of the blade.

3. The method for designing a blade for a fly-off test according to claim 1, characterized in that: Based on the dynamics, according to the expected first-order critical speed, the first width and the first thickness are corrected to obtain the second width and the second thickness, using the following formula: Where a2 is the second width, b2 is the second thickness, ω C1 is the expected first-order critical speed, ω0 is the flying speed, R is the radius of the circular hole at the end of the weakening groove, E is the elastic modulus of the blade material, L is the distance from the center of mass of the flying part of the blade to the weakening groove, m is the mass of the flying part of the blade, r is the distance from the center of mass of the flying part of the blade to the rotation center of the blade, σ b is the blade tensile stress strength limit, k is the correction factor, and 2 <k<4。 4. The method for designing a blade for a fly-off test according to claim 1, characterized in that: The expected first-order critical speed is greater than the take-off speed and less than or equal to the maximum take-off speed.

5. The method for designing a blade for a fly-off test according to claim 1, characterized in that: If the third thickness is inconsistent with the thickness of the blade, a rounded transition structure is provided between the residual region and a region of the blade excluding the residual region.

6. The method for designing a blade for a fly-off test according to claim 1, characterized in that: The edges of the weakening grooves are polished to reduce stress concentration at the edges of the weakening grooves.

7. The method for designing a blade for a fly-off test according to claim 1, characterized in that: The two residual regions have equal cross-sectional areas and the same cross-sectional shapes.

8. A blade for blade flying test, characterized in that: The blade is obtained by the design method of the fly-off test blade as described in any one of claims 1-7.

9. A blade flying test method, characterized in that: The method comprises: Providing a blade as claimed in claim 8; Disposing a strain gauge at a residual area of ​​the blade; Rotating the blades and gradually increasing the blade rotation speed; Compare the real-time strain measured by the strain gauge with the elastic limit strain, and the blade rotation speed with the minimum elastic strain limit rotation speed and the maximum elastic strain limit rotation speed, Wherein, the elastic limit strain corresponds to the strain when the blade material reaches the elastic limit of tensile stress; The minimum elastic strain limit speed is: the blade speed corresponding to the blade at the tensile stress elastic limit when the blade having the residual area cross-sectional area calculated by statics with the minimum fly-off speed as the fly-off speed; The maximum elastic strain limit speed is: the blade speed corresponding to the blade at the tensile stress elastic limit when the blade having a residual area cross-sectional area calculated by using statics with the maximum fly-off speed as the fly-off speed.

10. The blade flying test method according to claim 9, characterized in that: The comparison between the real-time strain measured by the strain gauge and the elastic limit strain, and between the blade rotation speed and the minimum elastic strain limit rotation speed and the maximum elastic strain limit rotation speed comprises: When the real-time strain reaches 80-100% of the elastic limit strain, if the blade rotation speed is less than the minimum elastic strain limit rotation speed, the test is stopped.

11. The blade flying off test method according to claim 9, characterized in that: The comparison between the real-time strain measured by the strain gauge and the elastic limit strain, and between the blade rotation speed and the minimum elastic strain limit rotation speed and the maximum elastic strain limit rotation speed comprises: When the real-time strain reaches the elastic limit strain, if the blade rotation speed is between the minimum elastic strain limit rotation speed and the maximum elastic strain limit rotation speed, the blade continues to rotate at an accelerated speed until the blade flies off.

12. The blade flying test method according to claim 9, characterized in that: The comparison between the real-time strain measured by the strain gauge and the elastic limit strain, and between the blade rotation speed and the minimum elastic strain limit rotation speed and the maximum elastic strain limit rotation speed comprises: If the real-time strain does not reach the decision strain threshold when the blade speed reaches the minimum fly-off speed, the blade speed is adjusted to the first-order critical speed; If the real-time strain increases to exceed the limit strain, the blade speed is maintained at the first-order critical speed until the blade flies off; If the blade speed remains at the first-order critical speed and the real-time strain still does not reach the elastic limit strain, the test is stopped; The decision strain threshold is: a theoretical strain value of the residual area when the blade having a cross-sectional area of ​​the residual area calculated by using statics with a maximum fly-off speed as the fly-off speed is at a minimum fly-off speed.

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