Vibration fatigue test piece and design method thereof

Abstract

The present application aims to provide a kind of vibration fatigue test piece and its design method, vibration fatigue test piece includes free section, fixed section and working section. Wherein, along the length direction of vibration fatigue test piece, working section has top, the thickness of vibration fatigue test piece is maximum at top, and the thickness of working section along length direction is continuously changed;Along the width direction of vibration fatigue test piece, the thickness of working section presents the change trend of big in the middle and small on both sides, the thickness of working section is continuously changed, and working section is axisymmetric in width direction;Working section has inner recess on both sides in width direction, in the orthographic projection of vibration fatigue test piece, the outer contour of inner recess is smooth curve, and the two side walls of working section are respectively smoothly transitioned between the top wall of working section and the bottom wall of working section. Through the present vibration fatigue test piece, the fatigue strength of material obtained by testing can be more accurate.

Description

Technical Field

[0001] This invention relates to the field of structural strength testing, and more particularly to a vibration fatigue test specimen and its design method. Background Technology

[0002] Vibration fatigue testing is an important testing method for studying the fatigue performance of structures and their materials. It simulates the vibration of blades under periodic airflow excitation forces, testing the performance, safety, and reliability of structures and their materials throughout their lifespan. It is widely used in industrial fields, especially in aerospace, to verify the fatigue life of blades and their materials.

[0003] When verifying the fatigue life of structures such as blades, the high cost of directly using blades or manufacturing test pieces with the same shape as blades leads to the current widespread use of "structural-like" test pieces in HB5277-1984 "Methods for Vibration Fatigue Testing of Engine Blades and Materials" in material-level vibration fatigue testing. Furthermore, to meet different research objectives, various test piece shapes have been proposed, such as hourglass, waisted, notched, thin-walled, rhomboid, and trapezoidal shapes.

[0004] However, the inventors discovered that the existing "structural component" test pieces still have unreasonable design, which leads to inaccurate material fatigue strength test results. Summary of the Invention

[0005] The purpose of this invention is to provide a vibration fatigue test specimen that can achieve more accurate testing of material fatigue strength.

[0006] Vibration fatigue test specimens for achieving the aforementioned objectives include:

[0007] Free paragraph;

[0008] The fixed section, through which the vibration fatigue test specimen is fixedly connected to the test equipment; and

[0009] The working section is connected between the free section and the fixed section, and there is a smooth transition between the working section and the free section, and a smooth transition between the working section and the fixed section.

[0010] Wherein, along the length direction of the vibration fatigue test specimen, the working section has a top, the thickness of the vibration fatigue test specimen is the greatest at the top, and the thickness of the working section varies continuously along the length direction;

[0011] Along the width direction of the vibration fatigue test specimen, the thickness of the working section shows a trend of being larger in the middle and smaller on both sides. The thickness of the working section is continuously varied, and the working section is axially symmetrical in the width direction.

[0012] The working section has concave portions on both sides in the width direction. In the orthographic projection of the vibration fatigue test piece, the outer contour of the concave portion is a smooth curve. The two side walls of the working section smoothly transition with the top wall and the bottom wall of the working section, respectively.

[0013] In one or more embodiments, the fixed segment has at least two through holes.

[0014] In one or more embodiments, the recessed portion has rounded corners between the upper and lower surfaces in the thickness direction of the working section.

[0015] In one or more embodiments, the cross-sections of the free segments obtained at any position along the length of the vibration fatigue test specimen are identical.

[0016] In one or more embodiments, the ratio of the maximum thickness to the length of the vibration fatigue test specimen is greater than 8 to 1.

[0017] In one or more embodiments, the upper and lower surfaces in the thickness direction of the working section are smooth, continuous curved surfaces.

[0018] On the other hand, according to some embodiments of this application, a method for designing vibration fatigue test specimens is also provided, which includes the following steps:

[0019] The design of the fixing section of the vibration fatigue test piece makes it easy to fix and connect to the test equipment.

[0020] The vibration fatigue test specimen is designed with a free segment that extends along the length of the vibration fatigue test specimen to adjust the resonant frequency of the test specimen.

[0021] Design the working section of the vibration fatigue test specimen, connecting the fixed section and the free section respectively, and ensuring that the working section meets the following conditions:

[0022] The transition between the working segment and the free segment is smooth, and the transition between the working segment and the fixed segment is smooth.

[0023] Along the length direction of the vibration fatigue test specimen, a top is set in the working section, so that the thickness of the vibration fatigue test specimen is maximized at the top, and the thickness of the working section varies continuously along the length direction;

[0024] Along the width direction of the vibration fatigue test specimen, the thickness of the working section is made to vary with a larger thickness in the middle and smaller thickness on both sides, the thickness of the working section is made to vary continuously, and the working section is made to be axially symmetrical in the width direction.

[0025] The working section has recessed portions on both sides in the width direction, with the outer contour of the recessed portions being a smooth curve, and the two side walls of the working section having a smooth transition with the top wall and bottom wall, respectively.

[0026] In one or more embodiments, the method for designing vibration fatigue test specimens further includes the following steps:

[0027] The ratio of the maximum thickness to the length of the vibration fatigue test specimen shall be greater than 8:1.

[0028] In one or more embodiments, the method for designing vibration fatigue test specimens further includes the following steps:

[0029] Adjust the length and thickness of the fixed segment, the radius of the concave portion, and the length and thickness of the free segment according to the frequency of the test object.

[0030] In one or more embodiments, the method for designing vibration fatigue test specimens further includes the following steps:

[0031] Along the length of the vibration fatigue test specimen, the free section is made to have a constant cross-sectional change.

[0032] The beneficial effects of this invention are as follows:

[0033] Verification has shown that by setting up a vibration fatigue test specimen with the aforementioned configuration, the area with a large stress gradient can be constrained to the vicinity of the intersection point T of lines L1 and L2 during vibration fatigue testing. This ensures that the crack initiation location is consistent across different test specimens, and the crack initiation location remains consistent even after the test specimens are strengthened, guaranteeing the comparability of vibration fatigue test data. This test specimen can be used for comparing vibration fatigue tests before and after surface strengthening processes (such as shot peening, laser strengthening, rolling, ultrasonic rolling, water jetting, etc.) or for comparing optimizations of other processing techniques. It ensures that the failure locations of different processes are the same or close, thereby guaranteeing the effectiveness of process improvement, reducing test specimen waste, and improving efficiency.

[0034] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, specific embodiments of this application are given below. Attached Figure Description

[0035] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0036] Figure 1 A top view schematic diagram of a vibration fatigue test specimen according to some embodiments of this application is shown;

[0037] Figure 2 A perspective view of a vibration fatigue test specimen according to some embodiments of this application is shown;

[0038] Figure 3 A front view of a vibration fatigue test specimen according to some embodiments of this application is shown;

[0039] Figure 4 A side view of a vibration fatigue test specimen according to some embodiments of this application is shown;

[0040] Figure 5 It shows Figure 1 A schematic diagram of the AA cross-section. Detailed Implementation

[0041] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0043] During tensile fatigue testing, the inventors discovered that the fatigue strength measured using the standard "hourglass" test specimen was not accurate enough. For example, the standard "hourglass" test specimen yielded a fatigue strength of 10 for TC17 titanium alloy. 7 The fatigue strength is 615 MPa (Wang Jinlong, Study on fatigue failure of TC17 titanium alloy for aero-engines [J]. Journal of Harbin Engineering University); the fatigue strength of TC32 titanium alloy is 10 7 The fatigue strength is 600MPa-550MPa (Wang Zemin, Study on Ultra-High Cycle Fatigue Properties of TC32 Titanium Alloy [J]. Metal Heat Treatment). However, the lifespan obtained using a narrow-waisted flat plate specimen is 10. 7 The fatigue strength is 480 MPa (Xu Wei, Ultra-high cycle fatigue test of TC17 alloy bending vibration [J]. Aero Engine); while the lifespan of a certain type of titanium alloy aero engine blade is 10. 7The fatigue strength was 450 MPa (Zhang Busheng, High-Temperature High-Cycle Vibration Fatigue Experiment of a Certain Type of Titanium-Aluminum Alloy Aero-Engine Blade [J]. Journal of Aeronautical Power). It is clear from the test results recorded in the existing literature that when using existing standard test specimens to verify the fatigue life of blades, the fatigue strength measured in the tests is closer to the fatigue strength of the blade structure, and significantly different from the fatigue strength of the material itself.

[0044] After research, the inventors discovered that, due to the use of the specimen form specified in the standard, the maximum stress zone is distributed across the entire cross-sectional width of the test piece. When the test piece is strengthened, the crack initiation location during the test may be in the middle of the cross-section of the working section of the test piece or at the edge of the working section. This failure mode is similar to the failure mode of blade structural components. Therefore, the obtained fatigue strength is closer to the result of the structural component. However, such a failure mode cannot guarantee the consistency of the failure location of the strengthened test pieces obtained by strengthening with different process parameters. For fatigue performance testing of materials, this will lead to a large error in the material fatigue strength results obtained by using test methods such as the lifting method, group method, and comparison method.

[0045] To address the aforementioned problems, on the one hand, according to some embodiments of this application, a vibration fatigue test specimen is provided.

[0046] like Figure 1 A top view schematic diagram of a vibration fatigue test specimen according to some embodiments of this application is shown. Figure 2 A perspective view of a vibration fatigue test specimen according to some embodiments of this application is shown. Figure 3 A front schematic diagram of a vibration fatigue test specimen according to some embodiments of this application is shown. Figure 4 A side view of a vibration fatigue test specimen according to some embodiments of this application is shown. Figure 5 It shows Figure 1 A schematic diagram of the AA cross-section.

[0047] like Figures 1 to 5 As shown, the vibration fatigue test specimen includes a free section 1, a working section 2, and a fixed section 3. The fixed section 3 is used for fixed connection to the test equipment; therefore, the vibration fatigue test specimen is fixedly connected to the test equipment via the fixed section 3. The free section 1, as shown in the figure, extends along the length direction a of the vibration fatigue test specimen. Since the fixed section 3 is fixedly connected to the test equipment, the free section 1 is a section with a free end and a cantilever beam structure.

[0048] Working section 2 connects to free section 1 and fixed section 3. When using this vibration fatigue test specimen for vibration fatigue testing, it is desirable to determine the crack initiation location within working section 2 during the test. Therefore, the structure of working section 2 must simultaneously meet the following requirements:

[0049] First, there is a smooth transition between working segment 2 and free segment 1. This smooth transition means that in the cross-section of the vibration fatigue test specimen, the connection between working segment 2 and free segment 1 forms a smooth curve without any breaks. The first derivative curve of this curve is smooth and continuous, and the second reciprocal curve is also smooth and continuous. In a specific embodiment, this can be achieved by adding fillets to the connection between working segment 2 and free segment 1. It is understood that in the structure shown in the figure, there are structural lines at the junction of working segment 2 and free segment 1. These structural lines are merely outlines to show the outer contour of the test specimen and do not indicate the presence of a bend at the connection.

[0050] Meanwhile, the transition between working segment 2 and fixed segment 3 is smooth. This smooth transition means that in the cross-section of the vibration fatigue test specimen, the connection between working segment 2 and fixed segment 3 forms a smooth curve without any breaks. The first derivative curve of this curve is smooth and continuous, and the second derivative curve is also smooth and continuous. In a specific embodiment, this can be achieved by adding fillets to the connection between working segment 2 and fixed segment 3. It is understood that in the structure shown in the figure, there are structural lines at the junction of working segment 2 and fixed segment 3. These structural lines are merely outlines to show the outer contour of the test specimen and do not indicate the presence of a bend at the connection.

[0051] Meanwhile, along the length direction a of the vibration fatigue test specimen, working segment 2 has a top, which is schematically marked by line L1 in the figure. It should be understood that line L1 is only for schematic representation of the top structure and does not indicate that working segment 2 has an angle at this point. The thickness of the vibration fatigue test specimen is greatest at this top. The thickness of working segment 2 varies continuously along the length direction a. In any longitudinal section of working segment 2 with this configuration along the length direction a of the vibration fatigue test specimen, the upper and lower outer contours of working segment 2 are smooth curves without discontinuities. The first derivative curve of this curve equation is smooth and continuous, and the second derivative curve is also smooth and continuous. Furthermore, this section has the greatest thickness at line L1.

[0052] Meanwhile, along the width direction b of the vibration fatigue test specimen, the thickness of working section 2 is as follows: Figure 5 As shown, the working segment 2 has a structure that is larger in the middle and smaller on both sides, and the thickness of the working segment 2 varies continuously along the width direction b. In any cross-section along the length direction a of the vibration fatigue test specimen, the outer perimeter of the working segment 2 with this configuration is as follows: Figure 5As shown, the curve is smooth and without breaks. The first and second derivative curves of the curve equation are smooth and continuous. Working segment 2 is axially symmetric in the width direction b. The line L2 in the figure schematically illustrates the axis of symmetry of working segment 2 in the width direction b. It should be understood that line L2 is merely a schematic representation of the top structure and does not indicate that working segment 2 has an angle at this point. At this time, lines L1 and L2 intersect at point T, which is the area with the greatest thickness in working segment 2. The curve from any position in working segment 2 to point T is a smooth curve without breaks. In a specific embodiment, any cross-section of working segment 2 along the length direction a of the vibration fatigue test specimen exhibits a centrally symmetric structure.

[0053] Meanwhile, the working section 2 has concave portions 20 on both sides in the width direction, which, in the orthographic projection of the vibration fatigue test specimen, appear as follows: Figure 1 In the top-view projection shown, the outer contour of the concave portion 20 is a smooth curve. This smooth curve means that the first derivative curve of the curve equation is smooth and continuous, and the second derivative curve is also smooth and continuous. In a specific embodiment, the concave portion 20 is a concave arc-shaped structure extending from the free segment 1 to the fixed segment 3, as shown in the figure.

[0054] At the same time, in such Figure 2 In the structure shown, the working section 2 has a top wall 21 and a bottom wall 22 on both sides in the width direction b, and side walls 23 on both sides in the thickness direction. The side walls 23 have smooth transitions with the top wall 21 and the bottom wall 22. This smooth transition means that in the cross-section of the vibration fatigue test specimen, the connection between the side walls 23 and the top wall 21 and the bottom wall 22 is a smooth curve without any breaks. The first derivative curve of this curve is smooth and continuous, and the second derivative curve is also smooth and continuous. In a specific embodiment, this can be achieved by setting rounded corners at the connection between the side walls 23 and the top wall 21 and the bottom wall 22.

[0055] Verification has shown that by setting up vibration fatigue test specimens with the aforementioned configuration, the range with a large stress gradient can be constrained to the vicinity of the intersection point T of lines L1 and L2 during vibration fatigue testing. This ensures that the crack initiation position of different test specimens is consistent, and even after surface strengthening of the test specimens, the crack initiation position remains consistent, thus guaranteeing the comparability of vibration fatigue test data.

[0056] This test piece can be used for comparison of vibration fatigue tests before and after surface strengthening processes (such as shot peening, laser strengthening, rolling, ultrasonic rolling, water jetting, etc.) or for comparison of other processing optimizations, ensuring that the failure locations of different processes are the same or close, thereby ensuring the effectiveness of process improvement, reducing test piece waste and improving efficiency.

[0057] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0058] According to some embodiments of this application, the fixing segment 3 has at least two through holes 30. It is understood that in the embodiment shown in the figures, the number of through holes 30 is two; in other embodiments different from those shown in the figures, the number of through holes 30 may be greater than two. The fixing segment is connected to the test equipment by passing fasteners through the through holes 30, thereby fixing the vibration fatigue test piece in the test equipment. Since the bolts near the test equipment may experience fretting fatigue during the test after the vibration fatigue test piece is connected to the test equipment using fasteners, using two or more fasteners can reduce connection failure caused by fretting fatigue. In other embodiments different from those shown in the figures, the vibration fatigue test piece may also be connected to the test equipment by, for example, clamping.

[0059] According to some embodiments of this application, the concave portion 20 and the upper and lower surfaces in the thickness direction of the working section 2 have rounded corners, thereby ensuring a smooth transition between the concave portion 20 and the working section 2, so as to alleviate the problem of edge stress concentration.

[0060] According to some embodiments of this application, in conjunction with [see also...] Figure 2 as well as Figure 4 The cross-section of the free segment 1 obtained by cutting at any position along the length direction a of the vibration fatigue test piece is the same, that is, the free segment 1 has a uniform cross-section change along the length direction a of the vibration fatigue test piece, which facilitates processing.

[0061] According to some embodiments of this application, the ratio of the maximum thickness to the length of the vibration fatigue test piece is greater than 8 to 1, so that the vibration fatigue test piece has a thin plate structure as a whole, so that the stress gradient in the thickness direction in the middle of the test piece is smaller and the whole is more uniform during the vibration fatigue test.

[0062] According to some embodiments of this application, as shown in the figure, the upper and lower surfaces in the thickness direction of the working segment 2 are smooth and continuous curved surfaces. For example, in one specific embodiment, the upper and lower surfaces have a centrally convex curved surface structure, and both the upper and lower surfaces in the thickness direction of the working segment 2 are thicker in the middle and thinner at the edges.

[0063] In a specific embodiment, the thickness of the working segment 2 at the intersection T is the same as the maximum thickness of the fixed segment 3, and both can be regarded as the maximum thickness of the vibration fatigue test piece. This setting allows the vibration fatigue test piece to be directly formed by machining from a thin plate with the same thickness as the fixed segment 3, simplifying the forming complexity.

[0064] On the other hand, according to some embodiments of this application, a method for designing vibration fatigue test specimens is also provided, which includes the following steps:

[0065] First, design the fixing section 3 of the vibration fatigue test piece so that the fixing section 3 can be easily fixedly connected to the test equipment. Specifically, this can be achieved by opening through holes in the fixing section 3 that are easy to be connected by fasteners or by setting suitable slots or clamping structures.

[0066] Subsequently, a free segment 1 is designed for the vibration fatigue test specimen, extending along the length direction a of the specimen. This free segment is used to adjust the resonant frequency of the specimen, for example, by changing the length of the free segment 1.

[0067] Subsequently, the working section 2 of the vibration fatigue test specimen was designed, connecting the fixed section 3 and the free section 1 respectively, and ensuring that the working section meets the following conditions:

[0068] First, a smooth transition is required between working segment 2 and free segment 1, and between working segment 2 and fixed segment 3. Here, a smooth transition means that in the cross-section of the vibration fatigue test specimen, the connection points between working segment 2 and free segment 1, and between working segment 2 and fixed segment 3, form smooth curves without discontinuities. The first derivative curve of this curve equation should be smooth and continuous, and the second derivative curve should also be smooth and continuous. This can be achieved, for example, by setting fillets at the connection points between working segment 2 and free segment 1, and between working segment 2 and fixed segment 3.

[0069] Meanwhile, along the length direction a of the vibration fatigue test specimen, a top is set in the working section 2, so that the thickness of the vibration fatigue test specimen is the largest at the top, and the thickness of the working section changes continuously along the length direction; in any longitudinal section of the working section 2 with this configuration along the length direction a of the vibration fatigue test specimen, the upper and lower outer contours of the working section 2 are smooth curves without discontinuities, the first derivative curve of the curve equation is smooth and continuous, and the second derivative curve is smooth and continuous, and the section has the largest thickness at the top.

[0070] Simultaneously, along the width direction b of the vibration fatigue test specimen, the thickness of the working segment 2 is made to vary with a larger thickness in the middle and smaller thickness on both sides, ensuring a continuous variation in thickness, and the working segment 2 is made axially symmetrical along the width direction b; in any cross-section of the working segment 2 with this configuration along the length direction a of the vibration fatigue test specimen, the outer perimeter contour of the working segment 2 is as follows: Figure 5 As shown, it is a smooth curve without discontinuities. The first derivative curve of the curve equation is smooth and continuous, and the second derivative curve is also smooth and continuous.

[0071] In working segment 2, recesses 20 are designed on both sides of the width direction b, with the outer contour of the recesses 20 being a smooth curve, and the two side walls of working segment 2 smoothly transitioning to the top and bottom walls, respectively. This smooth curve refers to the smooth continuity of both the first and second derivative curves of the curve equation.

[0072] The vibration fatigue test specimen designed by the aforementioned method can constrain the range of large stress gradients to the vicinity of the maximum thickness point of working section 2 during vibration fatigue testing. This ensures that the crack initiation position of different test specimens is consistent, and the crack initiation position can still be kept consistent after the test specimen is strengthened, thus ensuring the comparability of vibration fatigue test data.

[0073] According to some embodiments of this application, the method for designing vibration fatigue test specimens further includes the following steps:

[0074] The ratio of the maximum thickness to the length of the vibration fatigue test specimen is made to be greater than 8:1, so that the overall structure of the vibration fatigue test specimen is a thin plate, so that the stress gradient in the thickness direction in the middle of the test specimen is smaller and the whole is more uniform during the vibration fatigue test.

[0075] According to some embodiments of this application, the method for designing vibration fatigue test specimens further includes the following steps:

[0076] By adjusting the length and thickness of the fixed section 3, the radius of the concave part 20, and the length and thickness of the free section 1 according to the frequency of the test object, this vibration fatigue test specimen can be used to test parts with various configurations.

[0077] According to some embodiments of this application, the method for designing vibration fatigue test specimens further includes the following steps:

[0078] Along the length of the vibration fatigue test specimen, the free section is made to have a uniform cross-sectional change, thereby making the free section easier to process.

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A vibration fatigue test specimen, characterized in that, include: Free paragraph; The fixed section, through which the vibration fatigue test specimen is fixedly connected to the test equipment; and The working section is connected between the free section and the fixed section, and there is a smooth transition between the working section and the free section, and a smooth transition between the working section and the fixed section. Wherein, along the length direction of the vibration fatigue test specimen, the working section has a top, the thickness of the vibration fatigue test specimen is the greatest at the top, and the thickness of the working section varies continuously along the length direction; Along the width direction of the vibration fatigue test specimen, the thickness of the working section shows a trend of being larger in the middle and smaller on both sides. The thickness of the working section is continuously varied, and the working section is axially symmetrical in the width direction. The working section has concave portions on both sides in the width direction. In the orthographic projection of the vibration fatigue test piece, the outer contour of the concave portion is a smooth curve. The two side walls of the working section smoothly transition with the top wall and the bottom wall of the working section, respectively.

2. The vibration fatigue test specimen as described in claim 1, characterized in that, The fixed section has at least two through holes.

3. The vibration fatigue test specimen as described in claim 1, characterized in that, The concave portion has rounded corners between its upper and lower surfaces in the thickness direction of the working section.

4. The vibration fatigue test specimen as described in claim 1, characterized in that, The cross-sections of the free segments obtained at any position along the length of the vibration fatigue test specimen are the same.

5. The vibration fatigue test specimen as described in claim 1, characterized in that, The ratio of the maximum thickness to the length of the vibration fatigue test specimen is greater than 8 to 1.

6. The vibration fatigue test specimen as described in claim 1, characterized in that, The upper and lower surfaces in the thickness direction of the working section are smooth and continuous curved surfaces.

7. A method for designing vibration fatigue test specimens, characterized in that, Includes the following steps: The design of the fixing section of the vibration fatigue test piece makes it easy to fix and connect to the test equipment. The vibration fatigue test specimen is designed with a free segment that extends along the length of the vibration fatigue test specimen to adjust the resonant frequency of the test specimen. Design the working section of the vibration fatigue test specimen, connecting the fixed section and the free section respectively, and ensuring that the working section meets the following conditions: The transition between the working segment and the free segment is smooth, and the transition between the working segment and the fixed segment is smooth. Along the length direction of the vibration fatigue test specimen, a top is set in the working section, so that the thickness of the vibration fatigue test specimen is maximized at the top, and the thickness of the working section varies continuously along the length direction; Along the width direction of the vibration fatigue test specimen, the thickness of the working section is made to vary with a larger thickness in the middle and smaller thickness on both sides, the thickness of the working section is made to vary continuously, and the working section is made to be axially symmetrical in the width direction. The working section has recessed portions on both sides in the width direction, with the outer contour of the recessed portions being a smooth curve, and the two side walls of the working section having a smooth transition with the top wall and bottom wall, respectively.

8. The method for designing vibration fatigue test specimens as described in claim 7, characterized in that, It also includes the following steps: The ratio of the maximum thickness to the length of the vibration fatigue test specimen shall be greater than 8:

1.

9. The method for designing vibration fatigue test specimens as described in claim 7, characterized in that, It also includes the following steps: Adjust the length and thickness of the fixed segment, the radius of the concave portion, and the length and thickness of the free segment according to the frequency of the test object.

10. The method for designing vibration fatigue test specimens as described in claim 7, characterized in that, It also includes the following steps: Along the length of the vibration fatigue test specimen, the free section is made to have a constant cross-sectional change.

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