Star-shaped negative Poisson's ratio honeycomb structure with double stress platforms

Abstract

A star-shaped negative Poisson's ratio honeycomb structure with double stress platforms comprises a plurality of star-shaped cell elements which are periodically arranged in the same plane in the transverse direction and the longitudinal direction, and each star-shaped cell element comprises a quadrangular star-shaped structure, a circular structure and two double-arrow-shaped structures; the quadrangular star-shaped structure is formed by connecting eight inclined cell walls end to end, so that a closed hollow structure which is symmetrical in the up-and-down and left-and-right directions is formed; the circular structure is embedded in the quadrangular star-shaped structure and intersects with four concave points of the quadrangular star-shaped structure; the two double-arrow-shaped structures are located on the left side and the right side of the quadrangular star-shaped structure respectively, each double-arrow-shaped structure comprises two long cell walls and two short cell walls, and the intersection point of the two long cell walls coincides with the inward concave point of the quadrangular star-shaped structure. Under the action of longitudinal compression, the double-stress-platform characteristic is shown, the good negative Poisson's ratio effect is achieved, the structural bearing capacity and the energy absorption efficiency can be improved, and the double-stress-platform metamaterial belongs to the technical field of mechanical metamaterials.

Description

Technical Field

[0001] The utility model relates to mechanical metamaterials, in particular to a star-shaped negative Poisson's ratio honeycomb structure with double stress platforms. Background Art

[0002] A negative Poisson's ratio structure refers to a special structure that expands transversely when stretched longitudinally and contracts transversely when compressed longitudinally. Due to its unique deformation mechanism, the negative Poisson's ratio structure has significant advantages in mechanical properties and functional design, and has good effects in aspects such as indentation resistance, shear resistance, surface isotropy, fracture toughness, and energy absorption. In recent years, the research on negative Poisson's ratio structures has been continuously deepened, and related manufacturing technologies have also developed rapidly. Negative Poisson's ratio structures have broad application prospects in multiple fields, such as automotive anti-collision, biomedicine, construction engineering, aerospace, human protection, and packaging and transportation.

[0003] Currently, a large number of studies have designed and proposed various negative Poisson's ratio structures with different deformation mechanisms, such as concave polygon structures, rotating rigid body structures, chiral structures, and other negative Poisson's ratio structures. These structures have good negative Poisson's ratio effects, but most of them have only one deformation mode when compressed, showing the characteristics of a single stress platform, and instability often occurs during the deformation process, resulting in poor overall performance of the structure.

[0004] Correspondingly, the new negative Poisson's ratio structure with multiple deformation modes has better mechanical properties, which can not only improve the overall energy absorption effect of the structure, but also expand the application scenarios, and the deformation process is more stable. In addition, through reasonable design of the cell structure, the situation that the initial peak stress of the traditional structure is much greater than the platform stress when compressed can be improved, which can effectively enhance the buffering effect and reduce the losses caused by collisions. Therefore, it is of great significance to design a new structure with multiple stress platform characteristics. Summary of the Utility Model

[0005] Aiming at the technical problems existing in the prior art, the purpose of the utility model is to provide a star-shaped negative Poisson's ratio honeycomb structure with double stress platforms, which has multiple deformation modes while ensuring the negative Poisson's ratio effect, and improves the deformation stability and overall energy absorption effect of the structure through deformation coordination and double stress platforms.

[0006] In order to achieve the above purpose, the utility model adopts the following technical solutions:

[0007] A star-shaped negative Poisson's ratio honeycomb structure with double stress platforms, comprising a plurality of star-shaped cells arranged periodically both horizontally and vertically in the same plane. Each star-shaped cell includes a four-corner star structure, a circular structure, and two double-arrow-shaped structures. The four-corner star structure is formed by connecting eight inclined cell walls end to end, thus forming a closed hollow structure that is symmetric in both the up-down and left-right directions. The circular structure is embedded inside the four-corner star structure and intersects with the four concave points of the four-corner star structure. The two double-arrow-shaped structures are respectively located on the left and right sides of the four-corner star structure. Each double-arrow-shaped structure includes two longer cell walls and two shorter cell walls, and the intersection point of the two longer cell walls coincides with the concave point of the four-corner star structure. The adjacent star-shaped cells in the up-down direction are connected through the four-corner star structure, and the adjacent star-shaped cells in the left-right direction are connected through the double-arrow-shaped structure.

[0008] As a preference, the single star-shaped cells are arranged periodically. Two adjacent star-shaped cells in the left-right direction are on the same horizontal line, and two adjacent star-shaped cells in the up-down direction are on the same vertical line. Each star-shaped cell forms a rhombic hollow area with the adjacent star-shaped cells.

[0009] As a preference, the eight inclined cell walls are exactly the same, and every two inclined cell walls form a concave arrow. The concave angles α of the four concave arrows are equal and satisfy 90° < α < 180°.

[0010] As a preference, in the double-arrow-shaped structure, the included angle β of the longer cell walls and the included angle θ of the shorter cell walls satisfy θ = 2β.

[0011] As a preference, the concave angle α of the concave arrow and the included angle β of the longer cell walls in the double-arrow-shaped structure satisfy α + β = 180°.

[0012] As a preference, the length L1 of the inclined cell walls of the four-corner star structure is equal to the length L2 of the longer cell walls in the double-arrow-shaped structure.

[0013] As a preference, the four-corner star structure and the embedded circular structure are symmetric in both the up-down and left-right directions, and the two double-arrow-shaped structures are symmetric in the up-down direction.

[0014] As a preference, the thicknesses of all cell walls are equal, and the cross-sections are all rectangles.

[0015] As a preference, the base material is made of aluminum alloy.

[0016] As a preference, one end of the honeycomb structure is connected to a fixed end, and the other end is connected to a compression end. When the compression end approaches the fixed end, the four-corner star structure and the circular structure are deformed. When approaching further, the double-arrow-shaped structure is deformed.

[0017] The utility model has the following advantages:

[0018] When the star-shaped negative Poisson's ratio honeycomb structure with double stress platforms provided by the present utility model is longitudinally compressed, it will undergo multi-step deformation, showing the characteristics of double stress platforms and more stable deformation. In the first platform stage, the concave angles of the upper and lower concave arrows of the four-corner star structure continuously expand, and the concave angles of the left and right concave arrows continuously decrease until the upper and lower concave arrows become horizontal. Under the action of the four-corner star structure, the embedded circular structure gradually becomes an ellipse, while the double-arrow structure remains basically unchanged. In the second platform stage, the concave angles of the left and right concave arrows of the four-corner star structure continue to decrease, the upper and lower cell walls approach each other continuously, the embedded circular structure gradually becomes an "I" shape, and the double-arrow structure also contracts inward continuously until all cell walls become basically horizontal.

[0019] The overall deformation of the present utility model is stable, showing the characteristics of double stress platforms and a good negative Poisson's ratio effect. It can significantly reduce the initial peak stress and improve the energy absorption capacity of the structure. Compared with traditional structures, the present utility model has a better energy absorption effect and can be applied to anti-impact, shock absorption, collision and other aspects.

[0020] The four-corner star structure, circular structure and double-arrow structure of the present utility model have a linkage effect. During the compression process, the four-corner star structure drives the circular structure and the double-arrow structure to deform to absorb energy. The circular structure has a supporting effect on the four-corner star structure, enhancing its deformation coordination. The double-arrow structure ensures the stable deformation of the overall structure in the second platform stage and prevents instability. Description of the Drawings

[0021] Figure 1 is a plan view of the star-shaped negative Poisson's ratio honeycomb structure.

[0022] Figure 2 is a plan view of the star-shaped cell.

[0023] Figure 3 is a structural schematic diagram of the star-shaped cell in the embodiment.

[0024] Figure 4 is a parameter schematic diagram of the star-shaped cell.

[0025] Figure 5 is a schematic diagram of vertical finite element loading of the star-shaped negative Poisson's ratio honeycomb structure.

[0026] Figure 6 is a deformation process diagram of numerical simulation when the star-shaped negative Poisson's ratio honeycomb structure is vertically compressed (sequentially carried out from a→f).

[0027] Figure 7 is a nominal stress-strain curve diagram of the star-shaped negative Poisson's ratio honeycomb structure and the traditional star structure with the same parameters under vertical compression load.

[0028] Figure 8 It is the Poisson's ratio - strain curve of the star - shaped negative Poisson's ratio honeycomb structure under vertical compressive load.

[0029] Figure 9 It is the specific energy absorption - strain curve of the star - shaped negative Poisson's ratio honeycomb structure and the traditional star - shaped structure with the same parameters under vertical compressive load.

[0030] In the figure, 1 - star - shaped cell; 11 - four - corner star - shaped structure; 111 - inclined cell wall; 12 - circular structure; 13 - double - arrow - shaped structure; 131 - longer cell wall; 132 - shorter cell wall; 2 is the compression end, and 3 is the fixed end. Specific Embodiments

[0031] The principles and features of the present utility model will be described below in conjunction with the accompanying drawings. The examples given are only used to explain the present utility model and are not intended to limit the scope of the present utility model.

[0032] As shown in Figure 1 and Figure 2 a star - shaped negative Poisson's ratio honeycomb structure with double stress platforms includes a plurality of star - shaped cells 1 arranged periodically in the horizontal and vertical directions in the same plane. Each star - shaped cell 1 includes a four - corner star - shaped structure 11, a circular structure 12, and two double - arrow - shaped structures 13.

[0033] As shown in Figure 3 the four - corner star - shaped structure 11 is composed of eight inclined cell walls 111 connected end to end, thus forming a closed hollow structure that is symmetric in both the up - down and left - right directions; the circular structure 12 is embedded inside the star - shaped structure 11 and intersects with the four concave points of the star - shaped structure 11; the double - arrow - shaped structure 13 includes two longer cell walls 131 and two shorter cell walls 132. In the two double - arrow - shaped structures 13, the intersection points of the longer cell walls 131 coincide with the left - right concave points of the star - shaped structure 11.

[0034] As shown in Figure 1 as an embodiment, a single star - shaped cell 1 is arranged periodically. Two adjacent star - shaped cells 1 on the left and right are on the same horizontal line, and two adjacent star - shaped cells 1 above and below are on the same vertical line. Each star - shaped cell 1 forms a rhombic hollow area with the adjacent star - shaped cells 1.

[0035] As an embodiment, the eight inclined cell walls 111 are completely the same, and every two inclined cell walls 111 form an inward - concave arrow. The inward - concave angles α of the four inward - concave arrows are equal and satisfy 90° < α < 180°.

[0036] As an implementation manner, the double-arrow-shaped structure 13 includes two longer cell walls 131 and two shorter cell walls 132, and the included angle β of the longer cell walls 131 and the included angle θ of the shorter cell walls 132 satisfy θ = 2β.

[0037] As an implementation manner, the concave angle α of the concave arrow and the included angle β of the longer cell walls 131 in the double-arrow-shaped structure 13 satisfy α + β = 180°.

[0038] As an implementation manner, the length L1 of the inclined cell wall 111 of the four-corner star-shaped structure 11 is equal to the length L2 of the longer cell walls 131 in the double-arrow-shaped structure 13.

[0039] As an implementation manner, the four-corner star-shaped structure 11 and the embedded circular structure 12 are symmetric in both the up-down and left-right directions, and the two double-arrow-shaped structures 13 are symmetric up and down.

[0040] As an implementation manner, the thickness of all cell walls in the star-shaped cell 1 is t, and the cross-section is a rectangle.

[0041] As Figure 4 shown, the height of the star-shaped cell is H, and the length L1 of the inclined cell wall 111, the length L2 of the longer cell walls 131, the length L3 of the shorter cell walls 132, and the radius r of the circular structure 12 are all determined by the height H of the star-shaped cell and the concave angle α of the concave arrow. The included angle β of the longer cell walls and the included angle θ of the shorter cell walls are determined by the concave angle α of the concave arrow. The calculation formulas for L1, L2, L3, and r are: The calculation formulas for β and θ are: β = 180° - α, θ = 360° - 2α.

[0042] In this embodiment, the specific dimensions of the star-shaped cell 1 are: H = 10 mm, t = 0.3 mm, α = 120°, β = 60°, θ = 120°, L1 = L2 = 5.77 mm, L3 = 3.33 mm, r = 2.11 mm.

[0043] As an implementation manner, the base material of the star-shaped negative Poisson's ratio honeycomb structure with double stress platforms is aluminum alloy.

[0044] In order to compare the energy absorption characteristics of the star-shaped negative Poisson's ratio honeycomb structure with double stress platforms of the present invention, a traditional star-shaped structure with the same parameters is selected for comparison. The numerical simulation calculation is carried out using the finite element software ANSYS / LS-DYNA. As Figure 5As shown in the figure, a negative Poisson's ratio honeycomb structure is placed between two rigid walls. The lower rigid wall is completely fixed, and the upper rigid wall only retains the vertical translation degree of freedom. In this embodiment, a constant speed of 1 m / s is applied to the upper rigid wall in the vertical downward direction to compress the honeycomb structure. The material of the negative Poisson's ratio honeycomb structure is aluminum alloy, and an ideal elastoplastic model is adopted. The Shell163 element is used to simulate the honeycomb structure, and 5 integration points are defined along the thickness direction. The out-of-plane thickness of the structure is 2 mm. In the model, the negative Poisson's ratio honeycomb structure adopts automatic single-sided contact, and automatic surface-to-surface contact is adopted between the rigid wall and the honeycomb structure. The static friction coefficient and the dynamic friction coefficient are both set to 0.2. In order to improve the calculation efficiency while ensuring the calculation accuracy, after trial calculation and convergence analysis, a grid size of 0.5 mm is selected for element mesh division.

[0045] As Figure 5 shown, in order to ensure that the star-shaped negative Poisson's ratio honeycomb structure with double stress platforms of the present utility model fully exhibits the overall deformation characteristics during finite element simulation, the number of cells of the structure in the horizontal and vertical directions are 6 and 8 respectively.

[0046] In this embodiment, the star-shaped cells are combined by the method of copying and moving to ensure that each star-shaped cell has the same structure and size. The overall size of the honeycomb structure can be adjusted by the length and height of the star-shaped cells and the number of periodic arrangements to meet the requirements of different engineering applications.

[0047] As Figure 6 shown, the deformation process of the honeycomb structure of the present utility model under vertical compression is mainly divided into two stages, which also correspond to two stress platform stages on the nominal stress-strain curve. The first deformation stage: the cell walls of the star-shaped structure undergo rotational deformation, the concave angles of the two upper and lower concave arrows continuously expand, and the concave angles of the two left and right concave arrows continuously decrease, as Figure 6 shown in (a), (b), and (c) in the figure. During this process, the embedded circular structure gradually becomes an ellipse under the action of the star-shaped structure, while the double-arrow-shaped structure remains basically unchanged. As the compression displacement increases, the two upper and lower concave arrows become horizontal, and the two left and right concave arrows come into contact with the double-arrow-shaped structure, as Figure 6 shown in (d) in the figure. The second deformation stage: the two left and right concave arrows of the star-shaped structure continue to undergo rotational deformation, the concave angles continuously decrease, the upper and lower cell walls continuously approach, the embedded circular structure gradually becomes a "work" shape, and the double-arrow-shaped structure also continuously contracts inward until all the cell walls become basically horizontal, and the structure deformation occurs gradually from the middle layer to the compression end and the fixed end until the cell walls are completely compressed, as Figure 6 shown in (e) and (f) in the figure.

[0048] As Figure 7As shown, the nominal stress-strain curves of the honeycomb structure of the present utility model and the traditional star structure under vertical compression are given. It can be seen that for the structure of the present utility model, the curve can be divided into five parts: the linear elastic stage, the first stress plateau stage, the transition stage, the second stress plateau stage, and the densification stage. The two stress plateau stages are relatively stable. The stress of the second plateau is about 4 times that of the first plateau, and compared with the traditional star structure, the plateau stress is greater, significantly enhancing the energy absorption characteristics of the structure.

[0049] As Figure 8 shown, the Poisson's ratio-strain curve of the honeycomb structure of the present utility model under vertical compression is given. It can be seen that the honeycomb structure of the present utility model has an obvious negative Poisson's ratio effect, and as the compression displacement increases, the Poisson's ratio first decreases and then increases. This is because in the initial stage of compression, due to the deformation characteristics of the star-shaped cell walls rotating in the cells, the structure gradually contracts laterally, the lateral strain continuously increases, and the Poisson's ratio rapidly decreases; while as the compression process progresses, the lateral contraction of the structure becomes slow, the lateral strain increases less, so the Poisson's ratio gradually increases.

[0050] As Figure 9 shown, the specific energy absorption-strain curves of the honeycomb structure of the present utility model and the traditional star structure under vertical compression are given. It can be seen that the specific energy absorption of the structure of the present utility model at the same strain is greater than that of the traditional star structure, which means that the structure of the present utility model can absorb more energy at the same mass and has a better energy absorption effect.

[0051] The above embodiments are the preferred embodiments of the present utility model, but the embodiments of the present utility model are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present utility model shall be equivalent replacement methods and are all included in the protection scope of the present utility model.

Claims

1. A star-shaped negative Poisson's ratio honeycomb structure with a double stress platform, comprising a plurality of star-shaped cells periodically arranged in the horizontal and vertical directions in the same plane, characterized in that: Each star-shaped cell consists of a four-pointed star structure, a circular structure and two double-arrow-shaped structures; The four-pointed star-shaped structure is composed of eight inclined cell walls connected end to end, thus forming a closed hollow structure that is symmetrical in the vertical and horizontal directions; the circular structure is embedded in the four-pointed star-shaped structure and intersects with the four concave points of the four-pointed star-shaped structure; the two double-arrow-shaped structures are respectively located on the left and right sides of the four-pointed star-shaped structure, and each double-arrow-shaped structure includes two longer cell walls and two shorter cell walls, and the intersection of the two longer cell walls coincides with the concave point of the four-pointed star structure; the star-shaped cells adjacent to each other are connected through the four-pointed star structure, and the star-shaped cells adjacent to each other are connected through the double-arrow-shaped structure.

2. A star-shaped negative Poisson's ratio honeycomb structure with double stress platforms according to claim 1, characterized in that: The individual star-shaped cells are arranged periodically, with the two adjacent star-shaped cells on the left and right being located on the same horizontal line, and the two adjacent star-shaped cells on the top and bottom being located on the same vertical line, and each star-shaped cell forms a diamond-shaped hollow area with the adjacent star-shaped cells.

3. A star-shaped negative Poisson's ratio honeycomb structure with double stress platforms according to claim 1, characterized in that: The eight inclined cell walls are completely identical, and every two inclined cell walls form an inward-concave arrow, and the inward-concave angles α of the four inward-concave arrows are all equal and satisfy 90°<α<180°.

4. A star-shaped negative Poisson's ratio honeycomb structure with double stress platforms according to claim 3, characterized in that: In the double-arrow-shaped structure, the angle β of the longer cell wall and the angle θ of the shorter cell wall satisfy θ=2β.

5. A star-shaped negative Poisson's ratio honeycomb structure with double stress platforms according to claim 4, characterized in that: The inward angle α of the inward-concave arrow and the included angle β of the longer cell wall in the double-arrow-shaped structure satisfy α+β=180°.

6. A star-shaped negative Poisson's ratio honeycomb structure with double stress platforms according to claim 4, characterized in that: The length L1 of the inclined cell wall of the four-pointed star structure is equal to the length L2 of the longer cell wall in the double-arrow shaped structure.

7. A star-shaped negative Poisson's ratio honeycomb structure with double stress platforms according to claim 1, characterized in that: The four-pointed star-shaped structure and the embedded circular structure are symmetrical in the vertical and horizontal directions, and the two double-arrow-shaped structures are symmetrical in the vertical direction.

8. A star-shaped negative Poisson's ratio honeycomb structure with double stress platforms according to claim 1, characterized in that: All cell walls are of equal thickness and are rectangular in cross-section.

9. A star-shaped negative Poisson's ratio honeycomb structure with double stress platforms according to claim 1, characterized in that: The base material is aluminum alloy.

10. A star-shaped negative Poisson's ratio honeycomb structure with double stress platforms according to claim 1, characterized in that: One end of the honeycomb structure is connected to the fixed end, and the other end is connected to the compression end; when the compression end approaches the fixed end, the four-pointed star structure and the circular structure are deformed, and when they are further approached, the double-arrow-shaped structure is deformed.

Images