An olive-like zero-poisson's ratio honeycomb unit cell structure and flexible skin sandwich

Abstract

The application belongs to the technical field of flexible skin structure, and particularly relates to an olive-like zero-Poisson's ratio honeycomb cell structure and a flexible skin sandwich. The olive-like zero-Poisson's ratio honeycomb cell structure comprises four inclined cell walls and two horizontal cell walls, the two upper and lower symmetrical inclined cell walls jointly form an olive-like honeycomb unit, two olive-like honeycomb units are left and right symmetrical, one end of the two symmetrical olive-like honeycomb units is connected and closed, the other end is open and not connected, and the two horizontal cell walls are respectively located on the upper and lower sides of the olive-like honeycomb unit; the flexible skin sandwich is composed of an array of the olive-like zero-Poisson's ratio honeycomb cell structures. The olive-like zero-Poisson's ratio honeycomb cell structure has good out-of-plane bearing capacity of the sinusoidal honeycomb cell structure, and can also consider the in-plane tensile and compressive large deformation performance.

Description

Technical Field

[0001] This invention belongs to the field of flexible skin structure technology, specifically relating to an olive-shaped zero Poisson's ratio honeycomb unit cell structure and a flexible skin core. Background Technology

[0002] With increasingly complex flight missions, it is difficult for aircraft with fixed geometry to achieve optimal aerodynamic performance under every design condition. Intelligent morphing technology provides an effective way to solve this problem. The morphing wing is an important component of intelligent morphing aircraft. However, to achieve a smooth and continuous aerodynamic shape during wing deformation, it relies on a flexible skin with large deformation capacity and good load-bearing performance.

[0003] Flexible skins that deform in-plane not only need good in-plane deformation performance, but also need a certain out-of-plane load-bearing capacity. Honeycomb structures, with their characteristics of light weight, high load-bearing capacity, anisotropy, and strong designability, have become an ideal structure for resolving the contradiction between large deformation and high load-bearing capacity in flexible skins. Among them, the zero Poisson's ratio honeycomb structure does not deform in its orthogonal direction when subjected to unidirectional load, which can well meet the in-plane deformation requirements of flexible skins. Moreover, the honeycomb structure itself has the characteristics of high load-bearing capacity and low weight, which can also well meet the out-of-plane load-bearing capacity requirements of flexible skins. Therefore, the zero Poisson's ratio honeycomb structure is an ideal sandwich structure for in-plane deformable flexible skins.

[0004] In hexagonal zero Poisson ratio honeycomb configurations, while honeycomb structures with straight inclined cell walls possess good out-of-plane stiffness, their in-plane deformation capacity is insufficient, making it difficult to meet the requirements of large deformation in flexible skins. However, using curved inclined cell walls can effectively solve the problem of insufficient in-plane deformation capacity in these honeycomb configurations. Prior to this, scholars both domestically and internationally have conducted extensive research on zero Poisson ratio honeycomb configurations with curved inclined cell walls, among which the sinusoidal configuration is a representative example. Figure 1 The diagram shows a sinusoidal zero Poisson's ratio honeycomb unit cell structure, whose equivalent mechanical properties are expressed by the following formula:

[0005]

[0006] In the above formula:

[0007] E is the elastic modulus of the honeycomb material;

[0008] h is the length of the horizontal cell wall of a single cell in a honeycomb.

[0009] l is the length of the inclined cell wall of a single cell in a honeycomb.

[0010] θ is the angle of the tilted cell wall of a honeycomb unit cell;

[0011] t is the thickness of the cell wall;

[0012] A represents the amplitude of the sine curve containing the inclined cell wall;

[0013] D is the length of the region containing the inclined cell wall along the y direction. From the geometric relationship, we can obtain D = 2lsinθ.

[0014] E x and E y These are the equivalent elastic moduli of the unit cell along the x and y directions, respectively.

[0015] v xy and v yx These are the equivalent Poisson's ratios of the unit cell along the x and y directions, respectively.

[0016] G xy It is the in-plane equivalent shear modulus of a single cell.

[0017] In the equivalent mechanical performance formula, the expression characterizing the in-plane deformation capacity of a honeycomb structure is E. y The smaller the angle θ of the tilted cell wall of a honeycomb unit cell, the higher the value of the effective elastic modulus E of the honeycomb unit cell structure. y The smaller the angle, the better the in-plane deformation capability of the honeycomb unit cell structure. Furthermore, in a hexagonal zero Poisson's ratio honeycomb configuration, the optimal design value for the tilted cell wall angle is generally 0°. However, when the design dimensions of the structure are fixed, the tilted cell wall angle of a sinusoidal zero Poisson's ratio honeycomb unit cell cannot achieve its optimal value. For example, when the design dimensions of the honeycomb unit cell are a × b mm and the cell wall thickness is t, the tilted cell wall angle θ in the honeycomb unit cell structure satisfies: θ > arctan(b - 2t / a). Therefore, given a fixed design dimension, the sinusoidal honeycomb configuration limits its in-plane deformation capability.

[0018] Therefore, in view of the shortcomings of existing technologies, we urgently need to propose a solution to address the problem that sinusoidal zero Poisson's ratio honeycomb unit cell structures cannot achieve better in-plane deformation capability under the current design size premise. Summary of the Invention

[0019] To address the problems existing in the prior art, this invention provides an olive-shaped zero Poisson's ratio honeycomb unit cell structure and a flexible skin core by adding accessory cell walls at both ends of the inclined cell wall of the honeycomb unit cell.

[0020] The technical solution provided by this invention is:

[0021] An olive-shaped, zero Poisson's ratio honeycomb single-cell structure, comprising an inclined cell wall 1 and a horizontal cell wall 3;

[0022] There are four inclined cell walls 1, which are divided into two groups. The inclined cell walls 1 in each group are symmetrical from top to bottom, and the two symmetrical inclined cell walls 1 together form an olive-shaped honeycomb unit. The two olive-shaped honeycomb units are symmetrical from left to right, and one end of the two symmetrical olive-shaped honeycomb units is connected and closed while the other end is open and not connected. There are two horizontal cell walls 3, which are located on the upper and lower sides of the olive-shaped honeycomb unit respectively.

[0023] Each inclined cell wall 1 includes a first secondary cell wall 2, a second secondary cell wall 5, and a sinusoidal curved cell wall 4.

[0024] Furthermore, one end of the first subcell wall 2 is connected to the horizontal cell wall 3, and the other end is connected to the sinusoidal curved cell wall 4; one end of the second subcell wall 5 is connected to the sinusoidal curved cell wall 4, and the other end is connected to the second subcell wall 5 of the adjacent inclined cell wall 1.

[0025] Furthermore, the shape of the sinusoidal cell wall 4 is a sine curve, and the shape function of the sine curve is y = Asin(-2π / l), where A is the amplitude of the sine curve and l is the chord length of the sine curve.

[0026] Optionally, h>2(l+t), where h is the length of the horizontal cell wall and t is the thickness of the cell wall.

[0027] Optionally, b1>A, b2>A, D=2(b1+b2), where D is the length of the interval where the inclined cell wall 1 is located, b1 is the length of the first transcellular wall 2, and b2 is the length of the second transcellular wall 4.

[0028] Optionally, the olive-shaped honeycomb unit is integrally formed with the horizontal cell wall 3.

[0029] The present invention also provides a flexible skin sandwich structure, comprising a plurality of olive-shaped zero Poisson's ratio honeycomb unit cells arranged in an array.

[0030] Furthermore,

[0031] In each row, the horizontal cell walls 3 on the same side of the two adjacent olive-shaped honeycomb units are connected to each other;

[0032] In each column, the horizontal cell walls 3 of the two adjacent olive-shaped honeycomb units are stacked and arranged, and the thickness of the horizontal cell walls 3 that are not shared in the flexible skin core is 2t, where t is the cell wall thickness.

[0033] Beneficial effects

[0034] This invention provides an olive-shaped zero Poisson's ratio honeycomb unit cell structure and a flexible skin core. While possessing the good out-of-plane load-bearing capacity of a sinusoidal honeycomb unit cell structure, it introduces a secondary cell wall structure into the sinusoidal honeycomb unit cell structure. The secondary cell wall is designed along the vertical direction, which does not affect the in-plane deformation performance of the honeycomb structure. Furthermore, by adding the secondary cell wall design, the angle of the inclined cell wall of the honeycomb unit cell can be designed to the optimal value, making full use of the design space inside the sinusoidal honeycomb unit cell structure. Under the same design size, it has better in-plane deformation performance compared with the sinusoidal zero Poisson's ratio honeycomb unit cell structure. Attached Figure Description

[0035] Figure 1 The sinusoidal zero Poisson's ratio honeycomb unit cell structure and its structural parameters;

[0036] Figure 2 It has an olive-like, zero Poisson's ratio honeycomb single-cell structure;

[0037] Among them, 1-sloping cell wall, 2-first accessory cell wall, 3-horizontal cell wall, 4-sinusoidal curved cell wall, 5-second accessory cell wall, 6-olive-shaped honeycomb unit;

[0038] Figure 3 The structural parameters of an olive-shaped, zero Poisson's ratio honeycomb unit cell;

[0039] Figure 4 An example of a flexible skin sandwich structure consisting of 6 rows and 3 columns of olive-shaped, zero Poisson's ratio honeycomb units;

[0040] Figure 5 An example of a 12-row, 3-column flexible skin sandwich structure composed of olive-shaped, zero Poisson's ratio honeycomb units;

[0041] Figure 6 An example of a 12-row, 3-column flexible skin sandwich structure composed of sinusoidal zero Poisson's ratio honeycomb unit cells;

[0042] Figure 7 The load-displacement curves of the flexible skin sandwich structure during in-plane tensile deformation are shown.

[0043] Among them, 1-the result corresponding to the sinusoidal configuration, 2-the result corresponding to the olive-shaped configuration;

[0044] Figure 8 The load-displacement curves of the flexible skin sandwich structure during in-plane compression deformation are shown.

[0045] Among them, 1-the result corresponding to the sinusoidal configuration, and 2-the result corresponding to the olive-shaped configuration. Detailed Implementation

[0046] To more concretely demonstrate the large in-plane deformation characteristics of the olive-shaped zero Poisson's ratio honeycomb unit cell structure, this embodiment combines... Figure 5 and Figure 6 The honeycomb structure shown is used to study the deformation capacity of the two structures through finite element numerical simulation. In the accompanying drawings, only a portion of the embodiments with an olive-shaped zero Poisson's ratio honeycomb structure are illustrated. These embodiments are exemplary and primarily intended to demonstrate the large in-plane deformation characteristics of an olive-shaped zero Poisson's ratio honeycomb structure. Based on the embodiments of this invention, any other embodiments obtained without inventive effort are within the scope of protection of this application. The embodiments of this invention will now be described in detail with reference to the accompanying drawings.

[0047] In the description of this embodiment, the orientation and positional relationship are represented based on the orientation or positional relationship shown in the accompanying drawings, where "horizontal" and "vertical", "lateral" and "longitudinal" respectively represent the x-direction and y-direction.

[0048] The following will combine Figures 2 to 8 This embodiment will be described in detail.

[0049] The first aspect of the invention is an olive-shaped, zero Poisson's ratio honeycomb single-cell structure comprising: an inclined cell wall 1 and a horizontal cell wall 3.

[0050] like Figure 2 As shown, there are four inclined cell walls 1, which are formed by sequentially connecting a first secondary cell wall 2, a sinusoidal curved cell wall 4, and a second secondary cell wall 5. The four inclined cell walls 1 are divided into two groups, and the inclined cell walls 1 in each group are symmetrical vertically. The two vertically symmetrical inclined cell walls 1 together form an olive-shaped honeycomb unit. The two olive-shaped honeycomb units are symmetrical horizontally, and one end of the two symmetrical olive-shaped honeycomb units is connected and closed while the other end is open and not connected. There are two horizontal cell walls 3, which are located on the upper and lower sides of the olive-shaped honeycomb unit respectively. The olive-shaped honeycomb unit and the horizontal cell wall 3 are integrally formed.

[0051] like Figure 3 As shown, the olive-shaped zero Poisson's ratio honeycomb single-cell structure includes the following parameters: the length h of the horizontal cell wall 3, the length b1 of the first sub-cell wall 2, the length l of the sinusoidal curved cell wall 4, the amplitude A of the sinusoidal curve, the length b2 of the second sub-cell wall 5, the thickness t of the cell wall, the length D of the interval where the inclined cell wall 1 is located, and the height c of the honeycomb structure (along the z direction).

[0052] The olive-shaped, zero Poisson's ratio honeycomb unit cell structure can be established by the following steps:

[0053] Step 1: Establish a sine curve with a period of -l, a chord length of l, and an amplitude of A along the horizontal direction. Draw line segments of length b1 and b2 upward and downward from the left and right ends of the sine curve, respectively. Then, establish a vertical line at the left end of each line segment at a distance t.

[0054] Step 2: Construct a sine curve with a period of -l, a chord length of 2l, and an amplitude of A below the sine curve. The distance between the two sine curves is t, and the sine curve with a chord length of 2l intersects the two vertical lines mentioned above.

[0055] Step 3: Draw a horizontal line segment of length h / 2-t to the right from the free end of the line segment of length b1. Draw a horizontal line segment of the same length at a distance t above the horizontal line segment and extend it to the left to intersect the vertical line.

[0056] Step 4: Remove the excess line segments. The remaining part should be half a horizontal cell wall and one inclined cell wall. Then, make the remaining part symmetrical vertically and horizontally to obtain an olive-shaped zero Poisson's ratio honeycomb single cell structure.

[0057] Figure 3 The structural parameters of the olive-shaped zero Poisson's ratio honeycomb unit cell structure shown are shown in the table below:

[0058] Table 1. Structural parameters of olive-shaped zero Poisson's ratio honeycomb cells.

[0059]

[0060] A second aspect of the present invention is to provide a flexible skin core structure, wherein the flexible skin core is composed of an olive-shaped zero Poisson's ratio honeycomb unit cell structure.

[0061] The flexible skin core structure includes multiple olive-shaped zero Poisson's ratio honeycomb unit cells arranged in an array, wherein: in each row, the horizontal cell walls 3 on the same side of two adjacent olive-shaped honeycomb units are connected to each other; in each column, the horizontal cell walls 3 of two adjacent olive-shaped honeycomb units are stacked and arranged, and the thickness of the horizontal cell walls 3 that are not shared in the flexible skin core is 2t, where t is the cell wall thickness.

[0062] The olive-shaped, zero Poisson's ratio honeycomb unit cell structure in the flexible skin core can be arranged in any array as needed. For example... Figure 4 In one embodiment shown, the flexible skin core comprises 18 olive-shaped, zero Poisson's ratio honeycomb unit cells arranged in 6 rows and 3 columns. Figure 5 In another embodiment shown, the flexible skin core comprises 36 olive-shaped, zero Poisson's ratio honeycomb unit cells arranged in 12 rows and 3 columns.

[0063] The olive-shaped zero Poisson's ratio honeycomb unit cell structure proposed in this invention exhibits better in-plane deformation performance compared to the sinusoidal zero Poisson's ratio honeycomb unit cell structure under the same design dimensions. To more specifically demonstrate the large in-plane deformation performance of the olive-shaped honeycomb unit cell structure, this embodiment studies its properties through numerical simulation and physical experiments. Figure 5 and 6 The in-plane tensile and compressive properties of the flexible skin sandwich structure shown are given, where the in-plane deformation properties refer to the displacement of the honeycomb structure under the same load conditions.

[0064] In the study of the in-plane large deformation performance of the flexible skin sandwich structure in this embodiment, the honeycomb structure is made of 6061-T6 aluminum alloy. The flexible skin sandwich structure composed of olive-shaped and sinusoidal honeycomb units is as follows: Figure 5 and Figure 6 As shown, both structures have a design size of 141×134mm, and both are composed of 12×3 honeycomb unit cells, with a design size of 11×9mm for each cell. The structural parameters of the sinusoidal honeycomb unit cell are shown in the table below:

[0065] Table 2 Structural parameters of sinusoidal honeycomb unit cells

[0066]

[0067] right Figure 5 and Figure 6 The honeycomb sandwich finite element model shown is subjected to tensile and compressive forces of 50N respectively. The load-displacement curves of the structure in the finite element numerical simulation results under tensile conditions are as follows: Figure 7 As shown, the load-displacement curves of the structure in the finite element numerical simulation results under compression conditions are as follows: Figure 8 As shown.

[0068] Depend on Figure 7 and Figure 8 As can be seen from the load-displacement curves, under a driving force of 50N, the deformation displacement of the flexible skin core corresponding to the olive-shaped configuration under tension and compression conditions is greater than that of the flexible skin core corresponding to the sinusoidal configuration. That is, under the premise of fixed design dimensions, the in-plane deformation performance of the olive-shaped zero Poisson's ratio honeycomb structure is better than that of the sinusoidal zero Poisson's ratio honeycomb structure.

[0069] Note: This patent was supported by the Aeronautical Science Foundation (2023Z073053005).

Claims

1. An olive-shaped, zero Poisson's ratio honeycomb unit cell structure, characterized in that, Including slanted cell walls (1) and horizontal cell walls (3); There are four inclined cell walls (1), and the four inclined cell walls (1) are divided into two groups. The inclined cell walls (1) in each group are symmetrical from top to bottom, and the two symmetrical inclined cell walls (1) together constitute an olive-shaped honeycomb unit. The two olive-shaped honeycomb units are symmetrical from left to right, and one end of the two symmetrical olive-shaped honeycomb units is connected and closed, while the other end is open and not connected. The horizontal cell wall (3) consists of two parts, located on the upper and lower sides of the olive-shaped honeycomb unit, respectively; Each inclined cell wall (1) includes a first subcell wall (2), a second subcell wall (5), and a sinusoidal curved cell wall (4).

2. The olive-shaped, zero Poisson's ratio honeycomb unit cell structure as described in claim 1, characterized in that, One end of the first accessory cell wall (2) is connected to the horizontal cell wall (3), and the other end is connected to the sinusoidal curved cell wall (4); One end of the second accessory cell wall (5) is connected to the sinusoidal curved cell wall (4), and the other end is connected to the second accessory cell wall (5) of the adjacent inclined cell wall (1); The shape of the sinusoidal curved cell wall (4) is a sine curve, and the shape function of the sine curve is y=Asin(-2π / l), where A is the amplitude of the sine curve and l is the chord length of the sine curve; The length of the horizontal cell wall (3) satisfies h>2(l+t), where h is the length of the horizontal cell wall (3) and t is the thickness of the cell wall; The interval where the inclined cell wall (1) is located satisfies b1>A, b2>A, D=2(b1+b2), where D is the length of the interval where the inclined cell wall (1) is located, b1 is the length of the first sub-cell wall (2), and b2 is the length of the second sub-cell wall (5).

3. The olive-shaped, zero Poisson's ratio honeycomb unit cell structure as described in claim 1, characterized in that, The olive-shaped honeycomb unit is integrally formed with the horizontal cell wall (3).

4. A flexible skin sandwich structure, characterized in that, It includes multiple olive-shaped zero Poisson's ratio honeycomb unit cells as described in any one of claims 1-3, and arranged in an array.

5. The flexible skin sandwich structure as described in claim 4, characterized in that, In each row, the horizontal cell walls (3) on the same side of two adjacent olive-shaped cellular units are connected to each other; In each column, the horizontal cell walls (3) of two adjacent olive-shaped honeycomb units are stacked and arranged, and the thickness of the horizontal cell walls (3) that are not shared in the flexible skin core is 2t, where t is the cell wall thickness.

Images