A vibration fatigue test piece with a gradual cross section and its design method

Abstract

The present invention discloses a vibration fatigue test piece with a gradual cross-section and a design method thereof, and belongs to the field of vibration fatigue test technology. The test piece includes a clamping end, a transition part, a working part and a free end connected in sequence; the upper end face of the working part, the lower end face of the working part, the front end face of the working part and the rear end face of the working part are all curved surfaces; in the lateral direction from left to right, the working part is wide on both sides and narrow in the middle; in the longitudinal direction from front to back, the working part is thick in the middle and thin on both sides; the upper end face of the free end, the lower end face of the free end, the front end face of the free end and the rear end face of the free end are all curved surfaces; in the lateral direction from left to right, the free end is rectangular; in the longitudinal direction from front to back, the free end is thick in the middle and thin on both sides. The present invention can constrain the crack position of the test piece to the middle part of the working part, thereby eliminating the uncertainty of the crack position.

Description

Technical Field

[0001] The invention relates to the technical field of vibration fatigue testing, and in particular to a vibration fatigue testing piece with a gradual cross-section and a design method thereof. Background Art

[0002] Vibration fatigue test is an important test method for studying the fatigue performance of structures and their materials. Vibration fatigue test can simulate the vibration phenomenon of blades under periodic airflow excitation force, test the performance, safety and reliability of structures and their materials during their life cycle, and is widely used in the industrial field, especially in the aviation field, to verify the fatigue life of blades and their materials.

[0003] When conducting material-level vibration fatigue test research, the specimen form in HB5277-1984 "Engine Blade and Material Vibration Fatigue Test Method" is often used. At the same time, in order to meet different research purposes and research needs, researchers have proposed a variety of specimens with different shapes, among which the more typical forms include thin waist shape, notch shape, thin wall shape, diamond shape, trapezoid shape, etc. (Zhang Qin, Progress in Research on Vibration Fatigue of Materials and Components [J]. Materials Development and Application).

[0004] However, one problem with the above test pieces is that the crack positions of different test pieces are inconsistent, resulting in inaccurate material fatigue performance results. The test piece is in the form of a flat plate as a whole. From the finite element simulation results of the flat plate test piece, it can be seen that the maximum stress area of ​​the test piece is distributed on the cross-sectional width of the working part. During the test, the crack may be in the middle of the cross-sectional area of ​​the working part of the test piece, or it may be at the edge of the working part of the test piece. Due to the different crack positions of different test pieces, the material fatigue performance results obtained by test methods such as the lifting method, the grouping method, and the comparison method are not accurate. For example, a thin waist-shaped flat plate specimen was used for vibration fatigue testing. When the life base was 10 7 The fatigue limit obtained when the TC17 alloy is 480MPA (Xu Wei, TC17 alloy bending vibration ultra-high cycle fatigue test [J]. Aero Engine), but the tensile fatigue test of the "hourglass" specimen obtained that the life base of TC17 titanium alloy is 10 7 The fatigue limit of TC17 titanium alloy for aeroengines is 615MPa (Wang Jinlong, Research on Fatigue Failure of TC17 Titanium Alloy for Aeroengines [J]. Journal of Harbin Engineering University); the fatigue limit of TC32 titanium alloy with a life base of 107 is 600MPa-550MPa (Wang Zemin, Research on Ultra-High Cycle Fatigue Performance of TC32 Titanium Alloy [J]. Metal Heat Treatment). It can be seen that compared with the results of tensile fatigue tests, the fatigue limit of flat parts under the same life base is lower.

[0005] Another problem is that the test time of the test piece is too long. This is because the first-order natural frequency of the test piece specified in HB5277-1984 is relatively low, about 260Hz, and the 10 7 The time required for the fatigue limit under the life base is about 10 hours; at the same time, due to the large number of test pieces required for the material fatigue performance test (lifting method, grouping method, comparison method, etc.), the total test time is very long. Although there are also literatures (Xu Wei, TC17 alloy bending vibration ultra-high cycle fatigue test [J]. Aero Engine) that designed a thin waist-shaped flat plate test piece to greatly increase its first-order natural frequency, such a test piece still has the first problem mentioned above. Therefore, when conducting fatigue performance research on materials, it is necessary to overcome the above problems and design more reasonable test pieces. Summary of the invention

[0006] The purpose of the present invention is to provide a vibration fatigue test piece with a gradually changing cross section and a design method thereof, which can constrain the crack position of the test piece to the middle part of the working part and eliminate the uncertainty of the crack occurrence position.

[0007] To achieve the above object, the present invention provides the following solutions:

[0008] A vibration fatigue test piece with a gradual cross-section, the test piece comprising a clamping end, a transition portion, a working portion and a free end connected in sequence; the right end surface of the clamping end is connected to the left end surface of the transition portion; the right end surface of the transition portion is connected to the left end surface of the working portion; the right end surface of the working portion is connected to the left end surface of the free end;

[0009] The upper end surface of the working part, the lower end surface of the working part, the front end surface of the working part and the rear end surface of the working part are all curved surfaces; in the transverse direction from left to right, the working part is wide at both sides and narrow in the middle; in the longitudinal direction from front to back, the working part is thick in the middle and thin at both sides;

[0010] The upper end face of the free end, the lower end face of the free end, the front end face of the free end and the rear end face of the free end are all curved surfaces; in the horizontal direction from left to right, the free end is rectangular; in the longitudinal direction from front to back, the free end is thick in the middle and thin on both sides.

[0011] Optionally, the clamping end is a rectangular parallelepiped structure and is provided with at least two through holes in the thickness direction.

[0012] Optionally, the through hole is located on a midline of the clamping end from left to right.

[0013] Optionally, the thickness of the transition portion gradually decreases from left to right.

[0014] Optionally, the upper end surface of the working portion, the lower end surface of the working portion, the front end surface of the working portion and the rear end surface of the working portion are all arc surfaces that bulge outward in the middle.

[0015] Optionally, the clamping end, the transition portion, the working portion and the free end are integrally formed.

[0016] Optionally, the upper end surface of the free end, the lower end surface of the free end, the front end surface of the free end and the rear end surface of the free end are all arc surfaces that bulge outward in the middle.

[0017] Optionally, the cross section of the working portion is symmetrical front to back; and the longitudinal section of the working portion is symmetrical top to bottom.

[0018] Optionally, the thickness from the left end surface of the working portion to the right end surface of the free end gradually decreases, and the shape of the left end surface of the free end is the same as the shape of the right end surface of the working portion.

[0019] The present invention also provides a method for designing a vibration fatigue test piece with a gradual cross-section, the method being used to design the above test piece, the method comprising:

[0020] Acquire structural dimension data of multiple groups of test pieces; the structural dimension data includes shape data of the left end face of the working part, shape data of the right end face of the working part, shape data of the right end face of the free end, length data of the working part and length data of the free end;

[0021] Constructing test piece models respectively according to the structural dimension data of each group to obtain a plurality of test piece models with different dimensions;

[0022] Finite element analysis was performed on each test piece model to calculate the corresponding first-order natural frequency and maximum equivalent stress point;

[0023] Comparing the positions of the maximum equivalent stress points corresponding to the test piece models, and determining the test piece model whose maximum equivalent stress point is closest to the middle position of the working part;

[0024] Determine whether the first-order natural frequency of the test piece model whose maximum equivalent stress point is closest to the middle position of the working part meets the set frequency;

[0025] If the set frequency is met, the corresponding structural dimension data is used as the optimal structural dimension data; if the set frequency is not met, the length of the free end is adjusted according to the relationship between the set frequency and the first-order natural frequency calculated by finite element analysis, and the adjusted structural dimension data is used as the optimal structural dimension data; the optimal structural dimension data is used to produce the test piece required for the material-level vibration fatigue test.

[0026] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0027] The present invention provides a vibration fatigue test piece with a gradual cross section and a design method thereof, wherein the test piece comprises a clamping end, a transition portion, a working portion and a free end connected in sequence; the upper end face of the working portion, the lower end face of the working portion, the front end face of the working portion and the rear end face of the working portion are all curved surfaces; in the lateral direction from left to right, the working portion is wide on both sides and narrow in the middle; in the longitudinal direction from front to back, the working portion is thick in the middle and thin on both sides; the upper end face of the free end, the lower end face of the free end, the front end face of the free end and the rear end face of the free end are all curved surfaces; in the lateral direction from left to right, the free end is rectangular; in the longitudinal direction from front to back, the free end is thick in the middle and thin on both sides. The vibration fatigue test piece with a gradual cross section provided by the present invention can constrain the crack position of the test piece to the middle part of the working portion, thereby eliminating the uncertainty of the crack occurrence position. In addition, the present invention can also increase the first-order natural frequency of the test piece by shortening the length of the free end, thereby shortening the test cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0029] Figure 1 A three-dimensional diagram of a vibration fatigue test piece with a gradual cross section provided by the present invention;

[0030] Figure 2 A top view of a vibration fatigue test piece with a gradual cross section provided by the present invention;

[0031] Figure 3 A front view of a vibration fatigue test piece with a gradual cross section provided by the present invention;

[0032] Figure 4 It is an isometric enlarged right view of the vibration fatigue test piece with a gradual cross section provided by the present invention;

[0033] Figure 5 This is a cross-sectional view of a vibration fatigue test piece with a gradual cross-section provided by the present invention.

[0034] Explanation of symbols: clamping end—100, transition portion—101, working portion—102, free end—103, through hole—104, right end surface of the clamping end—105, left end surface of the working portion—106, right end surface of the working portion—107, right end surface of the free end—108. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the scope of protection of the present invention.

[0037] The purpose of the present invention is to provide a vibration fatigue test piece with a gradually changing cross section and a design method thereof, which can constrain the crack position of the test piece to the middle part of the working part and eliminate the uncertainty of the crack occurrence position.

[0038] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0039] Figure 1 The three-dimensional diagram of the vibration fatigue test piece with a gradual cross section provided by the present invention. If the test piece is placed horizontally, Figure 2 is the top view of the test piece. Figure 3 is the main view of the test piece. Figure 4 This is an isometric enlarged right view of the test piece.

[0040] like Figure 1-Figure 4As shown, the test piece includes a clamping end 100, a transition portion 101, a working portion 102 and a free end 103 connected in sequence; wherein the right end surface of the clamping end 100 is connected to the left end surface of the transition portion 101; the right end surface of the transition portion 101 is connected to the left end surface of the working portion 102; the right end surface of the working portion 102 is connected to the left end surface of the free end 103. The clamping end 100, the transition portion 101, the working portion 102 and the free end 103 are all connected in an integral form and are formed from the same piece of raw material.

[0041] The clamping end 100 is provided with only one and is a rectangular parallelepiped structure, and is provided with at least two through holes 104 in the thickness direction (i.e., the vertical direction from the upper end surface of the clamping end 100 to the lower end surface of the clamping end 100). The through holes 104 are used to fix the test piece to the fixture of the test bench by bolts during the test. Preferably, the through holes 104 are equal in size and are all located at the midline of the clamping end 100 from left to right (i.e., Figure 2 ).

[0042] The transition portion 101 is used to connect the clamping end 100 and the working portion 102. In this embodiment, the transition portion 101 is a trapezoidal structure, and the thickness of the transition portion 101 gradually decreases from left to right, thereby preventing stress concentration caused by excessive change in the cross-sectional size from the clamping end 100 to the working portion 102.

[0043] The upper end surface of the working portion 102, the lower end surface of the working portion 102, the front end surface of the working portion 102 and the rear end surface of the working portion 102 are all curved surfaces; in the lateral direction from left to right, see Figure 2 , the working portion 102 is wide on both sides and narrow in the middle; in the longitudinal direction from front to back, see Figure 4 The working portion 102 is thick in the middle and thin at both sides. Preferably, the width of the working portion 102 (i.e., the vertical distance from the front end surface of the working portion 102 to the rear end surface of the working portion 102) gradually decreases from the left and right sides to the middle.

[0044] Further, the upper end surface of the working part 102, the lower end surface of the working part 102, the front end surface of the working part 102 and the rear end surface of the working part 102 are all arc surfaces that bulge outward in the middle. In addition, the upper end surface of the working part 102 and the lower end surface of the working part 102 are of the same size and shape, and are in opposite directions, so that the longitudinal section of the working part 102 is symmetrical from top to bottom. The front end surface of the working part 102 and the rear end surface of the working part 102 are of the same size and shape, and are in opposite directions, so that the cross section of the working part 102 is symmetrical from front to back.

[0045] In this embodiment, the cross-section of the working part is an I-shaped part, and its upper and lower end faces and front and rear end faces are all arc surfaces, that is, the thickness gradually decreases from the middle to the two ends, and the cross-sectional shape is symmetrical, thereby ensuring that the middle position of the working part is the position of maximum equivalent stress, that is, the starting position of crack initiation.

[0046] The upper end surface of the free end 103, the lower end surface of the free end 103, the front end surface of the free end 103 and the rear end surface of the free end 103 are all curved surfaces; in the lateral direction from left to right, see Figure 2 , the free end 103 is rectangular; in the longitudinal direction from front to back, see Figure 4 The free end 103 is thick in the middle and thin at both sides.

[0047] Furthermore, the upper end surface of the free end 103 , the lower end surface of the free end 103 , the front end surface of the free end 103 , and the rear end surface of the free end 103 are all arc surfaces that bulge outward in the middle.

[0048] Furthermore, the first-order natural frequency of the test piece can be increased by shortening the length of the free end 103. The length of the free end 103 can also be adjusted according to the first-order natural frequency calculated by finite element analysis.

[0049] In this embodiment, the free end 103 is an elliptical cone-like structure. From left to right, the longitudinal cross-sections of the free end 103 have the same shape, which is elliptical.

[0050] As a specific implementation method, see Figure 3 and Figure 4 The thickness from the left end face 106 of the working portion to the right end face 108 of the free end gradually decreases, that is, there is a slightly smaller taper. Figure 4 As shown, the left end face of the transition portion is in the same shape as the right end face 105 of the clamping end, and both are rectangular; the right end face of the transition portion is in the same shape as the left end face 106 of the working portion, and both are elliptical; the right end face 107 of the working portion is in the same shape as the left end face of the free end, and both are elliptical; the right end face 108 of the free end is also elliptical. In addition, the area of ​​each end face has the following relationship: the area of ​​the right end face 105 of the clamping end is larger than the area of ​​the left end face 106 of the working portion, which is larger than the area of ​​the right end face 107 of the working portion, which is larger than the area of ​​the right end face 108 of the free end.

[0051] Figure 5 is a cross-sectional view of the test piece, such as Figure 4 and Figure 5 As shown, surface 106 (i.e. Figure 5 The shape of the cross section AA in FIG. 1 is elliptical, and the surface 107 (i.e. Figure 5 The shape of the cross section BB in the figure is also a quasi-ellipse shape, and the surface 108 is the right end surface of the free end 103, and its shape is also a quasi-ellipse shape. The outer contours of these three surfaces are all composed of arc segments with different radii, and the total lateral length is the same. By adjusting the radius of the arc segments constituting the outer contours of the surfaces 106, 107, and 108 and the lengths of the working portion 102 and the free end 103, the first-order natural frequency of the test piece and the position of the maximum equivalent stress can be controlled.

[0052] By continuously adjusting the variables mentioned above, a series of specimen geometries with different sizes can be obtained. Finite element analysis is performed on each specimen with a certain geometry to obtain the first-order natural frequency and the maximum equivalent stress point. Finally, the positions of the maximum equivalent stress points in all schemes are compared to observe which one is closest to the middle position of the working part and whether it has a suitable first-order natural frequency. Through the above methods and different test requirements, the most suitable specimen structure size for material-level vibration fatigue testing can be found.

[0053] The present invention also provides a method for designing a vibration fatigue test piece with a gradual cross-section, the method being used to design the above test piece, the method comprising:

[0054] Step 1: Obtain structural dimension data of multiple groups of test pieces; the structural dimension data include shape data of the left end face of the working part, shape data of the right end face of the working part, shape data of the right end face of the free end, length data of the working part and length data of the free end. The shape data include the area of ​​the end face, the length of the arc constituting the contour line of the end face and the radius of the arc constituting the contour line of the end face.

[0055] Step 2: Construct test piece models respectively according to the structural dimension data of each group to obtain multiple test piece models of different sizes.

[0056] Step 3: Perform finite element analysis on each test piece model and calculate the corresponding first-order natural frequency and maximum equivalent stress point.

[0057] Step 4: Compare the positions of the maximum equivalent stress points corresponding to the test piece models, and determine the test piece model whose maximum equivalent stress point is closest to the middle position of the working part.

[0058] Step 5: Determine whether the first-order natural frequency of the test piece model whose maximum equivalent stress point is closest to the middle position of the working part meets the set frequency.

[0059] Step 6: If the set frequency is met, the corresponding structural dimension data is used as the optimal structural dimension data; if the set frequency is not met, the length of the free end is adjusted according to the relationship between the set frequency and the first-order natural frequency calculated by finite element analysis, and the adjusted structural dimension data is used as the optimal structural dimension data; the optimal structural dimension data is used to make the test piece required for the material-level vibration fatigue test.

[0060] A vibration fatigue test piece with a gradual cross-section and a design method thereof provided by the present invention can improve the natural frequency of the test piece and shorten the test cycle; at the same time, compared with traditional test pieces, the maximum stress area is limited to the middle position of the working part of the test piece, and the range with a large stress gradient is constrained near the center position, so that the crack initiation positions of different test pieces are consistent, thereby ensuring the comparability of vibration fatigue test data.

[0061] The advantages and positive effects of the vibration fatigue test piece with a gradual cross-section and the design method thereof provided by the present invention are mainly reflected in:

[0062] 1. This test piece can meet the requirements of material-level vibration fatigue test, and the test results obtained are closer to the tensile fatigue test results of the standard "hourglass-shaped" test piece.

[0063] 2. This test piece limits the maximum stress area to the middle position of the working part of the test piece, and also constrains the range with larger stress gradient to the center position, so that the crack starting positions of different test pieces are consistent, ensuring the comparability of vibration fatigue test data.

[0064] 3. The natural frequency of this test piece is high and the required test cycle is short.

[0065] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0066] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A vibration fatigue test piece with a gradual cross section, characterized in that: The test piece comprises a clamping end, a transition portion, a working portion and a free end connected in sequence; the right end surface of the clamping end is connected to the left end surface of the transition portion; the right end surface of the transition portion is connected to the left end surface of the working portion; the right end surface of the working portion is connected to the left end surface of the free end; The upper end surface of the working part, the lower end surface of the working part, the front end surface of the working part and the rear end surface of the working part are all curved surfaces; in the transverse direction from left to right, the working part is wide at both sides and narrow in the middle; in the longitudinal direction from front to back, the working part is thick in the middle and thin at both sides; The upper end face of the free end, the lower end face of the free end, the front end face of the free end and the rear end face of the free end are all curved surfaces; in the horizontal direction from left to right, the free end is rectangular; in the longitudinal direction from front to back, the free end is thick in the middle and thin on both sides.

2. The vibration fatigue test piece with a gradual cross section according to claim 1, characterized in that: The clamping end is a rectangular parallelepiped structure and is provided with at least two through holes in the thickness direction.

3. The vibration fatigue test piece with a gradual cross section according to claim 2, characterized in that: The through hole is located on the center line of the clamping end from left to right.

4. The vibration fatigue test piece with a gradual cross section according to claim 1, characterized in that: The thickness of the transition portion gradually decreases from left to right.

5. The vibration fatigue test piece with a gradual cross section according to claim 1, characterized in that: The upper end surface of the working part, the lower end surface of the working part, the front end surface of the working part and the rear end surface of the working part are all arc surfaces convex outward in the middle.

6. The vibration fatigue test piece with a gradual cross section according to claim 1, characterized in that: The clamping end, the transition portion, the working portion and the free end are integrally formed.

7. The vibration fatigue test piece with a gradual cross section according to claim 1, characterized in that: The upper end surface of the free end, the lower end surface of the free end, the front end surface of the free end and the rear end surface of the free end are all arc surfaces that bulge outward in the middle.

8. The vibration fatigue test piece with a gradual cross section according to claim 5, characterized in that: The cross section of the working part is symmetrical front to back; the longitudinal section of the working part is symmetrical up and down.

9. The vibration fatigue test piece with a gradual cross section according to claim 1, characterized in that: The thickness from the left end surface of the working portion to the right end surface of the free end gradually decreases, and the shape of the left end surface of the free end is the same as the shape of the right end surface of the working portion.

10. A method for designing a vibration fatigue test piece with a gradual cross section, characterized in that: The method is used to design a test piece as claimed in any one of claims 1 to 9, and the method comprises: Acquire structural dimension data of multiple groups of test pieces; the structural dimension data includes shape data of the left end face of the working part, shape data of the right end face of the working part, shape data of the right end face of the free end, length data of the working part and length data of the free end; Constructing test piece models respectively according to the structural dimension data of each group to obtain a plurality of test piece models with different dimensions; Finite element analysis was performed on each test piece model to calculate the corresponding first-order natural frequency and maximum equivalent stress point; Comparing the positions of the maximum equivalent stress points corresponding to the test piece models, and determining the test piece model whose maximum equivalent stress point is closest to the middle position of the working part; Determine whether the first-order natural frequency of the test piece model whose maximum equivalent stress point is closest to the middle position of the working part meets the set frequency; If the set frequency is met, the corresponding structural dimension data is used as the optimal structural dimension data; if the set frequency is not met, the length of the free end is adjusted according to the relationship between the set frequency and the first-order natural frequency calculated by finite element analysis, and the adjusted structural dimension data is used as the optimal structural dimension data; the optimal structural dimension data is used to produce the test piece required for the material-level vibration fatigue test.

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