CN115508160A - A Vibration Fatigue Test Specimen with Gradient Cross-section and Its Design Method - Google Patents

Abstract

The invention discloses a vibration fatigue test piece with a gradually-changed section and a design method thereof, and belongs to the technical field of vibration fatigue tests. The test piece comprises a clamping end, a transition part, a working part and a free end which are connected in sequence; 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 in a shape that two sides are wide and the middle is narrow; in the longitudinal direction from front to back, the working part is in a shape that the middle is thick and the two sides are thin; 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 curved surfaces; in the transverse direction from left to right, the free end is rectangular; in the longitudinal direction from front to back, the free end is in a shape of being thick in the middle and thin at two sides. The invention can restrain the crack position of the test piece in the middle part of the working part, thereby eliminating the uncertainty of the crack occurrence position.

Description

A Vibration Fatigue Test Specimen with Gradient Cross-section and Its Design Method

technical field

The invention relates to the technical field of vibration fatigue tests, in particular to a vibration fatigue test piece with a gradually changing section and a design method thereof.

Background technique

Vibration fatigue test is an important test method to study the fatigue performance of structures and materials. The vibration fatigue test can simulate the vibration phenomenon of the blade under the exciting force of the periodic airflow, and test the performance, safety and reliability of the structure and its materials in the life cycle. It is widely used in the industrial field, especially in the aviation field. To verify the fatigue life of blades and their materials, etc.

When conducting material-level vibration fatigue test research, the specimen form in HB5277-1984 "Engine Blade and Material Vibration Fatigue Test Method" is mostly used. At the same time, in order to meet different research purposes and research needs, researchers have proposed various A variety of test pieces, of which the more typical forms are thin-waisted, notched, thin-walled, diamond-shaped, trapezoidal, etc. (Zhang Qin, research progress on vibration fatigue of materials and components [J]. Material development and application).

However, one problem with the above test pieces is that the crack positions of different test pieces are inconsistent, resulting in inaccurate results of material fatigue performance. The test piece is in the form of a flat plate as a whole. According to the finite element simulation results of the flat test piece, 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-section of the working part of the test piece. It may also be at the edge of the working part of the test piece. Due to the different crack positions of different test pieces, the results of material fatigue properties obtained by using the lifting method, group method, comparison method and other test methods are not accurate. For example, the vibration fatigue test is carried out on a thin-waisted flat specimen, and the fatigue limit obtained when the life base is 10 ⁷ is 480MPA (Xu Wei, TC17 alloy bending vibration ultra-high cycle fatigue test [J]. Aeroengine), but using "Hourglass" specimen tensile fatigue test, the fatigue limit of TC17 titanium alloy is ^615MPa (Wang Jinlong, research on fatigue failure of titanium alloy TC17 for aero-engine [J]. Journal of Harbin Engineering University); TC32 titanium alloy The life base is 107 and the fatigue limit is 600MPa-550MPa (Wang Zemin, TC32 titanium alloy ultra-high cycle fatigue performance research [J]. Metal heat treatment). It can be seen that, compared with the results of the tensile fatigue test, the fatigue limit obtained by the flat piece under the same life base is relatively low.

Another problem that exists 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 low, about 260Hz, and the time required to obtain the fatigue limit under the 107 life base is about ¹⁰ hours; at the same time, due to the fatigue performance of the material The test (lifting method, group method, comparison method, etc.) requires a large number of test pieces, so the total test time is very long. Although there are also literatures (Xu Wei, TC17 alloy flexural vibration ultra-high cycle fatigue test [J]. Aeroengine) designed a thin-waisted flat plate test piece to greatly increase the first-order natural frequency, but such test pieces still exist. the first question. Therefore, when studying the fatigue properties of materials, it is necessary to overcome the above problems and design more reasonable test pieces.

Contents of the invention

The purpose of the present invention is to provide a vibration fatigue test piece with a gradual cross section and its design method, 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.

To achieve the above object, the present invention provides the following scheme:

A vibration fatigue test piece with a gradual cross section, the test piece includes a clamping end, a transition part, a working part and a free end connected in sequence; the right end face of the clamping end is connected with the left end face of the transition part; the The right end surface of the transition part is connected to the left end surface of the working part; the right end surface of the working part 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 The shape 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 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 curved surfaces; in the transverse direction from left to right, the free end is rectangular; In the longitudinal direction to the rear, the free end is thick in the middle and thin in both sides.

Optionally, the clamping end has a cuboid structure, and at least two through holes are opened in the thickness direction.

Optionally, the through hole is located on the middle line of the clamping end from left to right.

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

Optionally, 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 circular arc surfaces protruding in the middle.

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

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 circular arc surfaces protruding outward in the middle.

Optionally, the cross section of the working part is symmetrical front and back; the longitudinal section of the working part is symmetrical up and down.

Optionally, the thickness from the left end surface of the working part to the right end surface of the free end decreases gradually, and the shape of the left end surface of the free end is the same as that of the right end surface of the working part.

The present invention also provides a design method of a vibration fatigue test piece with a gradual cross section, the method is used to design the above-mentioned test piece, and the method includes:

Obtain the structural dimension data of multiple groups of test pieces; the structural dimension data includes the shape data of the left end surface of the working part, the shape data of the right end surface of the working part, the shape data of the right end surface of the free end, the length data of the working part and the shape data of the free end. length data;

Constructing test piece models respectively according to the structural size data of each group, and obtaining a plurality of test piece models of different sizes;

Carry out finite element analysis on each test piece model separately, and calculate the corresponding first-order natural frequency and maximum equivalent stress point;

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

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

If the set frequency is satisfied, the corresponding structural size data will be used as the optimal structural size data; if the set frequency is not satisfied, the length of the free end will be adjusted according to the relationship between the set frequency and the first-order natural frequency calculated by finite element analysis , and use the adjusted structural size data as the optimal structural size data; the optimal structural size data is used to make the test piece required for the material-level vibration fatigue test.

According to the specific embodiments provided by the invention, the invention discloses the following technical effects:

The invention provides a vibration fatigue test piece with a gradual cross section and a design method thereof. The test piece includes a clamping end, a transition part, a working part and a free end connected in sequence; the upper end surface of the working part, 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 in a shape with wide sides and a narrow middle; In the longitudinal direction, the working part is thick in the middle and thin on both sides; 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 curved surfaces; In the transverse direction to the right, the free end is rectangular; in the longitudinal direction from front to back, the free end is thick in the middle and thin at both sides. The vibration fatigue test piece with gradual cross-section provided by 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 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 period.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required in the embodiments. Obviously, the accompanying drawings in the following description are only some of the present invention. Embodiments, for those of ordinary skill in the art, other drawings can also be obtained according to these drawings without paying creative labor.

Fig. 1 is the three-dimensional figure of the vibration fatigue test piece of gradual change section provided by the present invention;

Fig. 2 is the top view of the vibration fatigue test piece of gradual cross-section provided by the present invention;

Fig. 3 is the front view of the vibration fatigue test piece of gradual cross-section provided by the present invention;

Fig. 4 is the equal scale enlarged right view of the vibration fatigue test piece with gradual cross-section provided by the present invention;

Fig. 5 is a cross-sectional view of a vibration fatigue test piece with a gradual cross section provided by the present invention.

Explanation of symbols: clamping end—100, transition portion—101, working portion—102, free end—103, through hole—104, right end face of clamping end—105, left end face of working portion—106, right end face of working portion —107, the right end face of the free end—108.

detailed description

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

In describing the present invention, it is to be understood that the terms "central", "longitudinal", "transverse", "front", "rear", "left", "right", "vertical", "horizontal", The orientations or positional relationships indicated by "top", "bottom", "inner", "outer", etc. are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying the Means that a device or element must have a specific orientation, be constructed and operate in a specific orientation, and therefore should not be construed as limiting the scope of the invention.

The purpose of the present invention is to provide a vibration fatigue test piece with a gradual cross section and its design method, 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.

In order to make the above objects, features and advantages of the present invention more comprehensible, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

Fig. 1 is a three-dimensional view of a vibration fatigue test piece with a gradual cross section provided by the present invention. If the test piece is placed horizontally, then Fig. 2 is a top view of the test piece, Fig. 3 is a front view of the test piece, and Fig. 4 is an equal scale enlarged right view of the test piece.

As shown in Figures 1-4, 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 in contact with the transition portion The left end surface of 101 is connected; the right end surface of the transition part 101 is connected with the left end surface of the working part 102; the right end surface of the working part 102 is connected with 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 connected in one piece and formed from the same raw material.

There is only one clamping end 100, which is a cuboid structure, and at least two through holes 104 are provided in the thickness direction (that is, 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 on the fixture of the test bench by bolts during the test. Preferably, the through holes 104 are equal in size and located on the middle line (ie the horizontal line in FIG. 2 ) of the clamping end 100 from left to right.

The transition part 101 is used to connect the clamping end 100 and the working part 102 . In this embodiment, the transition part 101 is a trapezoidal platform structure, and the thickness of the transition part 101 gradually decreases from left to right, so as to prevent excessive changes in cross-sectional dimensions from the clamping end 100 to the working part 102 resulting in stress concentration.

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 curved surfaces; in the transverse direction from left to right, see In Fig. 2, the working part 102 is in the shape of wide sides and narrow in the middle; in the longitudinal direction from front to back, see Fig. 4, the working part 102 is in the shape of thick in the middle and thin in the two sides. Preferably, the width of the working part 102 (ie, the vertical distance from the front end surface of the working part 102 to the rear end surface of the working part 102 ) gradually decreases from the left and right sides to the middle.

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 circular arc surfaces protruding from the middle. Moreover, the size and shape of the upper end surface of the working part 102 and the lower end surface of the working part 102 are the same, and the directions are opposite, so that the longitudinal section of the working part 102 is vertically symmetrical. The size and shape of the front end surface of the working part 102 and the rear end surface of the working part 102 are the same, and the directions are opposite, so that the cross section of the working part 102 is symmetrical front and back.

In this embodiment, the cross-section of the working part is I-shaped, and its upper and lower end faces and front and rear end faces are arc-shaped, that is, the thickness gradually decreases from the middle to both ends, and the cross-sectional shape has a symmetrical shape. Therefore, it can ensure that the middle position of the working part is the position with the maximum equivalent stress, that is, the starting position of crack initiation.

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 transverse direction from left to right, see In FIG. 2 , the free end 103 is rectangular; in the longitudinal direction from front to back, referring to FIG. 4 , the free end 103 is thick in the middle and thin on both sides.

Further, 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 circular arc surfaces protruding from the middle.

Further, 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.

In this embodiment, the free end 103 has a platform-like ellipse structure, and the free ends 103 have the same vertical cross-sectional shape in the direction from left to right, and are all similar to an ellipse.

As a specific implementation manner, referring to FIG. 3 and FIG. 4 , the thickness from the left end surface 106 of the working part to the right end surface 108 of the free end gradually decreases, that is, there is a slightly smaller taper. As shown in Figure 4, the shape of the left end surface of the transition part is the same as that of the right end surface 105 of the clamping end, and both are rectangular; the shape of the right end surface of the transition part is the same as that of the left end surface 106 of the working part , and both are oval-like; the right end surface 107 of the working part is the same shape as the left end surface of the free end, and both are oval-like; the right end surface 108 of the free end is also oval-like. And, the size of each end surface has the following relationship: the area of the right end surface 105 of the clamping end is greater than the area of the left end surface 106 of the working part, the area of the right end surface 107 of the working part is greater than the right end surface 108 of the free end area.

Fig. 5 is the sectional view of test piece, as shown in Fig. 4 and Fig. 5, the shape of surface 106 (being the section A-A in Fig. 5) is a quasi-ellipse shape, and the shape of surface 107 (being the section B-B in Fig. 5) is also A quasi-ellipse shape, the surface 108 is the right end face 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 circular arc segments with different radii, and the total transverse 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 part 102 and the free end 103, the first-order natural frequency and the position of the maximum equivalent stress of the test piece can be controlled.

Constantly adjusting the above-mentioned several variables can obtain a series of sample geometries with different sizes. The finite element analysis is performed on the test pieces of each geometry to obtain the first-order natural frequency and the maximum equivalent stress point. Finally, compare the positions of the maximum equivalent stress points in all schemes, and 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 requirements of the test, the most suitable sample structure size for the material level vibration fatigue test can be found.

The present invention also provides a design method of a vibration fatigue test piece with a gradual cross section, the method is used to design the above-mentioned test piece, and the method includes:

Step 1: Obtain the structural dimension data of multiple groups of test pieces; the structural dimension data includes the shape data of the left end surface of the working part, the shape data of the right end surface of the working part, the shape data of the right end surface of the free end, and the length data of the working part and length data at the free end. The shape data includes 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.

Step 2: Construct test piece models respectively according to the structural size data of each group, and obtain multiple test piece models of different sizes.

Step 3: Carry out finite element analysis on each test piece model, and calculate the corresponding first-order natural frequency and maximum equivalent stress point.

Step 4: Comparing the positions of the maximum equivalent stress points corresponding to each of the test piece models, and determining the test piece model whose position of the maximum equivalent stress point is closest to the middle position of the working part.

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

Step 6: If the set frequency is satisfied, the corresponding structural size data will be used as the optimal structural size data; if the set frequency is not satisfied, then the adjustment will be made according to the size relationship between the set frequency and the first-order natural frequency calculated by finite element analysis The length of the free end, 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.

The invention provides a vibration fatigue test piece with a gradual cross section and its design method, which can increase the natural frequency of the test piece and shorten the test period; at the same time, compared with the traditional test piece, the maximum stress area is limited to the working part of the test piece In the middle position, the range with a large stress gradient is restricted near the center position, so that the crack initiation positions of different specimens are consistent, thereby ensuring the comparability of vibration fatigue test data.

The advantages and positive effects of the vibration fatigue test piece with gradual cross-section provided by the invention and its design method are mainly reflected in:

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

2. In this test piece, 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 also restricted to the center position, so that the starting positions of cracks of different test pieces are consistent, ensuring vibration fatigue Comparability of experimental data.

3. The natural frequency of the test piece is high, and the required test period is short.

Each embodiment in this specification is described in a progressive manner, each embodiment focuses on the difference from other embodiments, and the same and similar parts of each embodiment can be referred to each other.

In this paper, specific examples have been used to illustrate the principle and implementation of the present invention. The description of the above embodiments is only used to help understand the core idea of the present invention; meanwhile, for those of ordinary skill in the art, according to the thought of the present invention, There will be changes in specific implementation methods and application ranges. In summary, the contents of this specification should not be construed as limiting the present invention.

Claims (10)

1. a kind of vibration fatigue test piece of progressive cross-section, it is characterized in that, described test piece comprises clamping end, transition part, working part and free end connected successively; The right end surface of described clamping end and the The left end surface is connected; the right end surface of the transition part is connected with the left end surface of the working part; the right end surface of the working part is connected with 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 The shape 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 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 curved surfaces; in the transverse direction from left to right, the free end is rectangular; In the longitudinal direction to the rear, the free end is thick in the middle and thin in both sides. 2 . The vibration fatigue test piece with gradual cross-section according to claim 1 , wherein the clamping end is a cuboid structure, and at least two through holes are opened in the thickness direction. 3 . 3 . The vibration fatigue test piece with gradual cross section according to claim 2 , wherein the through hole is located on the center line of the clamping end from left to right. 4 . 4. The vibration fatigue test piece with gradual cross-section according to claim 1, characterized in that the thickness of the transition portion decreases gradually from left to right. 5. The vibration fatigue test piece with gradual cross section according to claim 1, characterized in that, 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 The rear end faces are all arc-shaped faces protruding outward from the middle. 6 . The vibration fatigue test piece with gradual cross-section according to claim 1 , wherein the clamping end, the transition portion, the working portion and the free end are integrally formed. 7 . 7. The vibration fatigue test piece with gradual cross-section according to claim 1, characterized in that, 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 The arc surface protrudes outward in the middle. 8. The vibration fatigue test piece with gradual cross section according to claim 5, characterized in that, the cross section of the working part is symmetrical front and back; the longitudinal section of the working part is symmetrical up and down. 9. The vibration fatigue test piece with gradual cross-section according to claim 1, wherein the thickness from the left end surface of the working part to the right end surface of the free end gradually decreases, and the shape of the left end surface of the free end It is the same shape as the right end surface of the working part. 10. A design method of a vibration fatigue test piece with a gradual cross section, characterized in that, the method is used to design the test piece according to any one of claims 1-9, and the method comprises: Obtain the structural dimension data of multiple groups of test pieces; the structural dimension data includes the shape data of the left end surface of the working part, the shape data of the right end surface of the working part, the shape data of the right end surface of the free end, the length data of the working part and the shape data of the free end. length data; Constructing test piece models respectively according to the structural size data of each group, and obtaining a plurality of test piece models of different sizes; Carry out finite element analysis on each test piece model separately, and calculate the corresponding first-order natural frequency and maximum equivalent stress point; Comparing the positions of the maximum equivalent stress points corresponding to each of the test piece models, and determining the test piece model whose position of the maximum equivalent stress point is closest to the middle position of the working part; Judging whether the first-order natural frequency of the test piece model whose position of the maximum equivalent stress point is closest to the middle position of the working part meets the set frequency; If the set frequency is satisfied, the corresponding structural size data will be used as the optimal structural size data; if the set frequency is not satisfied, the length of the free end will be adjusted according to the relationship between the set frequency and the first-order natural frequency calculated by finite element analysis , and use the adjusted structural size data as the optimal structural size data; the optimal structural size data is used to make the test piece required for the material-level vibration fatigue test.

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