A flexible skin based on a double-layer deformable honeycomb in the shape of a jujube

Abstract

The present invention discloses a flexible skin structure based on a double-layer deformable honeycomb, which belongs to the field of flexible structure design of deformable aircraft and is composed of a deformable support skeleton, a flexible filling and an elastic surface layer. The flexible filling adopts the method of silicone foaming, the elastic surface layer is a silicone panel, and the deformable support skeleton is a jujube-shaped double-layer deformable honeycomb. The double-layer deformable honeycomb is composed of an arrangement of jujube-shaped single cells, and the jujube-shaped single cells are composed of elastic units. The flexible skin structure is formed by filling the pores of the deformable honeycomb with foamed silicone and laying silicone panels on the surface. The out-of-plane stiffness of the flexible skin is provided by the facade of the deformable honeycomb wall panel, and the deformable honeycomb surface can produce telescopic deformation. The flexible skin structure of the present invention has a good in-plane deformation effect and a good out-of-plane load-bearing capacity; the double-layer deformable honeycomb structure is highly designable and easy to process; the pores are filled with silicone foaming to ensure good air tightness of the structure and smoothness of the skin surface.

Description

Technical Field

[0001] The invention belongs to the field of flexible structure design of variant aircraft, and in particular relates to a flexible skin structure based on a double-layer deformable honeycomb. Background Art

[0002] Morphing aircraft can change their structural shape in real time during flight to achieve optimal aerodynamic performance under different flight conditions and maneuvers. Flexible skin technology is one of the key technologies enabling morphing aircraft. Its technical challenges lie in the following aspects: 1. The flexible skin must be able to withstand significant in-plane deformation; 2. It must have sufficient out-of-plane stiffness to withstand aerodynamic loads; and 3. The skin surface must be smooth. Flexible skin design technology has recently garnered considerable attention.

[0003] Conventional skins have a conflicting in-plane deformation capacity and out-of-plane load-bearing capacity, and their deformation capacity is very low. To address this conflict between in-plane deformation and out-of-plane stiffness, researchers have explored various ingenious structural forms, such as "fish-scale laminated" flexible skins and corrugated flexible skins. These structures offer improved deformation and load-bearing capacity, but all suffer from surface smoothness and out-of-plane stiffness issues. Summary of the Invention

[0004] To address the challenges of existing technologies, a deformable honeycomb-supported elastic membrane structure offers the advantages of light weight, large in-plane deformation, and strong out-of-plane load-bearing capacity, making it a relatively ideal structural form. Therefore, the present invention proposes a flexible skin structure that addresses the challenges of in-plane deformation, out-of-plane load-bearing, and surface smoothness. This flexible skin is highly designable and easy to manufacture.

[0005] The present invention is achieved in that:

[0006] A flexible skin based on a jujube-shaped double-layer deformable honeycomb, characterized in that the flexible skin comprises a deformable support frame, a flexible filling, and an elastic surface layer; the flexible filling is made of silicone foam, the elastic surface layer is a silicone panel, and the deformable support frame is a jujube-shaped double-layer deformable honeycomb; the pores of the deformable honeycomb are filled with silicone foam, and the surface is then covered with the silicone panel. The foamed silicone and the silicone panel are connected into one body, resulting in a flexible skin structure with a smooth surface.

[0007] The elastic units are combined and arranged into a jujube-shaped double-layer deformable honeycomb; the elastic units include connecting plates, curved plates connected to the connecting plates, slits on the curved plates, and crack-stop holes at the roots of the curved plates; the curved plates include curved plates at different levels, and the curved plates at different levels are bent in different directions but are perpendicular to the plate surface of the curved plates; the ends of the curved plates on the same level of adjacent elastic units are welded to form a single cell, and after the elastic units are arranged in a row, the curved plates therein generate bending deformation to ensure the in-plane deformation capacity of the skin; when subjected to out-of-plane loads, the vertical surfaces of each curved plate and the connecting plate provide out-of-plane stiffness, so that the flexible skin has out-of-plane load-bearing capacity.

[0008] Furthermore, the elastic unit is a+2b long, h wide, and t thick, where a is the length of the connecting plate, and b is the length of the upper and lower curved plates; a slit with a length of b and a width of d is formed at h / 2 in the width direction of the curved plate, and the curved plate is cut to form two levels of curved plates, namely the upper curved plate and the lower curved plate; or two slits with a length of b and a width of d are formed at 1 / 4h and 3 / 4h in the width direction of the curved plate, and the curved plate is cut to form three levels of curved plates, namely the upper curved plate, the middle curved plate, and the lower curved plate; the diameter D of the crack-stop hole is more than 3 times the slit width d.

[0009] Furthermore, the elastic units are combined and arranged into a double-layer deformable honeycomb structure, including an upper deformable honeycomb and a lower deformable honeycomb; the double-layer deformable honeycomb structure has a length of L = n(a + 2b) and a width of W = (m + 1) c, where n is the number of rows of elastic units, m is the number of columns of elastic units, and c is the spacing between two adjacent columns of elastic units, and c determines the initial bending shape of the bending plate; the upper deformable honeycomb initially bends c / 2 to one side, and the lower deformable honeycomb initially bends c / 2 to the other side.

[0010] Furthermore, the deformation effect and bearing capacity of the jujube-shaped unit cell are changed by adjusting the parameters m, n, a, b, h and t; according to the out-of-plane bearing requirements of the flexible skin, the total width of m columns of elastic units is set to w, and the m columns of elastic units are combined into a beam to calculate the bearing capacity; under the given displacement limit, the width and height of the beam are calculated by the deflection formula of the material mechanics beam; due to the stratification of the deformable honeycomb, there is a conversion coefficient for the out-of-plane bending stiffness, the out-of-plane stiffness of the double-layer deformable honeycomb is 1 / 4 of that in the non-stratified case, and the out-of-plane stiffness of the three-layer deformable honeycomb is 5 / 32 of that in the non-stratified case; then according to the requirements of the pore size of the deformable honeycomb, the value of the column number m is adjusted, thereby determining the distance between adjacent columns, determining the initial bending shape of the elastic unit bending plate, and obtaining the values ​​of the remaining parameters; finally, a deformable honeycomb structure with good out-of-plane bearing capacity and good in-plane deformation effect is obtained.

[0011] The beneficial effects of the present invention compared with the prior art are:

[0012] The present invention utilizes a double-layer deformable honeycomb in the shape of a jujube as the supporting structure, employs a silicone foaming method for flexible filling, and lays silicone panels on the surface to form a flexible skin structure. This flexible skin exhibits out-of-plane bending resistance, allows for significant in-plane expansion and contraction deformation, and has a smooth surface, strong designability, and ease of processing.

[0013] The flexible skin structure of the present invention exhibits excellent in-plane deformation and possesses good out-of-plane load-bearing capacity. The double-layer deformable honeycomb structure offers strong design flexibility and ease of fabrication. The flexible skin structure utilizes silicone foam to fill pores, ensuring excellent airtightness and a smooth surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a schematic diagram of a jujube-shaped double-layer deformable honeycomb structure of the present invention;

[0015] Figure 2 This is a schematic diagram of an elastic unit in a flexible skin based on a jujube-shaped double-layer deformable honeycomb according to the present invention;

[0016] Figure 3 This is a schematic diagram of the flexible skin structure of a flexible skin based on a jujube-shaped double-layer deformable honeycomb according to the present invention;

[0017] Among them, 1- obliquely connected jujube-shaped unit cells, 2-upper deformable honeycomb, 3-lower deformable honeycomb, 4-straight connected jujube-shaped unit cells, 5-middle deformable honeycomb, 6-upper curved plate, 7-middle curved plate, 8-lower curved plate, 9-connecting plate, 10-cut seam, 11-crack stop hole, 12-silicone panel, 13-silicone foaming. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solution and effect of the present invention clearer and more specific, the following examples are given to further illustrate the present invention in detail. It should be noted that the specific implementation described here is only used to explain the present invention and is not intended to limit the present invention.

[0019] like Figures 1 to 3 As shown, the flexible skin structure proposed by the present invention consists of a deformable support skeleton, a flexible filling, and an elastic surface layer. The flexible filling adopts the method of silicone foaming 13, the elastic surface layer is a silicone panel 12, and the deformable support skeleton is a jujube-shaped double-layer deformable honeycomb. The double-layer deformable honeycomb is composed of jujube-shaped single cells arranged in an arrangement, and the jujube-shaped single cells are composed of elastic units. The flexible skin structure is formed by filling the pores of the deformable honeycomb with foamed silicone and laying the silicone panel on the surface. The out-of-plane stiffness of the flexible skin is provided by the facade of the deformable honeycomb wall panel, and the deformable honeycomb can produce telescopic deformation within the surface.

[0020] like Figure 2As shown, the elastic unit has curved plates at different levels, which bend in different directions (perpendicular to the plate surface). The ends of the curved plates at the same level on adjacent elastic units are welded together to form a jujube-shaped unit cell. Depending on the bending direction of the curved plates on the same level, unit cell structures of different shapes can be formed, including directly connected jujube-shaped units and obliquely connected jujube-shaped units. The unit cell structure can be easily replicated and combined to form a double-layer or triple-layer deformable honeycomb structure; directly connected jujube-shaped units form a three-layer deformable honeycomb structure, while obliquely connected jujube-shaped units form a double-layer deformable honeycomb structure.

[0021] Schematic diagram of double-layer deformable honeycomb structure Figure 1 shown. Figure 1 (a) is a deformable honeycomb with obliquely connected jujube-shaped single cells, which is characterized by: the upper honeycomb is a complete plane; the upper right elastic unit of the complete jujube core (bold part) is the lower left elastic unit of the adjacent jujube core (the upper right adjacent jujube core), and the lower right elastic unit of the complete jujube core is the upper left elastic unit of another adjacent jujube core (the lower right adjacent jujube core). Figure 1 (b) is a deformable honeycomb structure with directly connected jujube-shaped cells. The characteristic of direct connection is that there is a height difference between the upper honeycomb structure and the middle honeycomb structure (arranged in a way that one row is high and the other row is low).

[0022] Figure 2 The elastic unit in the deformable honeycomb includes a connecting plate 9, a curved plate connected to the connecting plate 9, a slit 10 on the curved plate, and a crack stop hole 11 at the base of the curved plate. The elastic unit has a length of a+2b, a width of h, and a thickness of t, where a is the length of the connecting plate 9 and b is the length of the upper and lower curved plates. A slit 10 with a length of b and a width of d is formed at h / 2 in the width direction, splitting the curved plate to form two layers of curved plates, namely the upper curved plate 6 and the lower curved plate 8. Figure 2 In (a), the left side is the lower curved plate 8, and the right side is the upper curved plate 6. Alternatively, two slits of length b and width d are formed at 1 / 4h and 3 / 4h, and the curved plate is cut to form three layers of curved plates, namely the upper curved plate 6, the middle curved plate 7, and the lower curved plate 8. Figure 2In (b), the left side is the lower layer bending plate 8, the middle side is the middle layer bending plate 7, and the right side is the upper layer bending plate 6; a crack stop hole 11 is provided at the junction of the bending plate and the connecting plate (i.e., the root of the bending plate), and the diameter D of the crack stop hole is more than 3 times the slit width d. The ends of the bending plates of adjacent elastic units are welded to form a single cell. According to the different bending directions of the bending plates on the same layer of the elastic unit, an obliquely connected jujube-shaped single cell structure and a directly connected jujube-shaped single cell structure can be formed. After the elastic units are arranged in a row, the bending plates therein can produce bending deformation, thereby ensuring the in-plane deformation capacity of the skin. When subjected to out-of-plane loads, the facades of each bending plate and the connecting plate provide out-of-plane stiffness, so that the flexible skin has out-of-plane load-bearing capacity.

[0023] Schematic diagram of double-layer deformable honeycomb structure Figure 1 As shown, the length is L = n(a + 2b), and the width is W = (m + 1)c, where n is the number of rows of elastic units, m is the number of columns of elastic units, and c is the spacing between two adjacent columns of elastic units. c determines the initial bending shape of the bending plate: the upper layer initially bends c / 2 to one side, and the lower layer initially bends c / 2 to the other side. The portion enclosed by the rectangular frame is selected for analysis. This portion of the double-layer deformable honeycomb is 4(a + 2b) long and 4c wide, consisting of four rows and four columns of elastic units. The bending pattern of the bending plate is identical for every other column of elastic units, and so is the bending pattern for every other row of elastic units. Therefore, only the bending pattern of the bending plate for two rows and two columns of elastic units needs to be determined. The remaining bending patterns can be derived based on the above-mentioned rules. The bolded portion of the figure is selected for detailed explanation.

[0024] Figure 1 (a) is a double-layer deformable honeycomb structure with an oblique connection and a jujube-shaped structure. The upper lower layer and lower upper layer of the first row and first column of the thickened portion are tilted to the left, while the upper upper layer and lower lower layer are tilted to the right; the upper upper layer and lower lower layer of the first row and second column of the elastic units are tilted to the left, while the upper lower layer and lower upper layer are tilted to the right; the upper upper layer and lower lower layer of the second row and first column of the elastic units are tilted to the left, while the upper lower layer and lower upper layer are tilted to the right; the upper lower layer and lower upper layer of the second row and second column of the elastic units are tilted to the left, while the upper upper layer and lower lower layer are tilted to the right. The upper curved plate of this portion constitutes the upper deformable honeycomb 2 (shown in solid lines), and the lower curved plate, the elastic units on the left, and the elastic units on the right constitute the lower deformable honeycomb 3 (shown in dashed lines). This allows for continuous replication and expansion as needed.

[0025] Figure 1(b) is a three-layer deformable honeycomb structure formed by directly connecting jujube-shaped cells 4. The first row and first column of the bold part have the upper and lower layers deviated to the left, and the middle layer deviated to the right; the first row and second column of the elastic units have the middle layer deviated to the left, and the upper and lower layers deviated to the right; the second row and first column of the elastic units have the middle layer deviated to the left, and the upper and lower layers deviated to the right; the second row and second column of the elastic units have the upper and lower layers deviated to the left, and the middle layer deviated to the right. The upper curved plates in this part constitute the upper deformable honeycomb 2 represented by the solid line, the lower curved plates constitute the lower deformable honeycomb 3 represented by the short dashed line, and the middle curved plates 7, the elastic units on the left, and the elastic units on the right constitute the middle deformable honeycomb 5 represented by the long dashed line. Every two rows and two columns of elastic units form a jujube-shaped cell. The ends of the elastic unit curved plates of the same layer at the corresponding positions of each adjacent column are welded together to form a deformable honeycomb structure. Honeycombs of different layers are connected together by connecting plates.

[0026] By adjusting the parameters m, n, a, b, h, and t, the deformation effect and load-bearing capacity of the jujube-shaped unit cell can be changed. According to the out-of-plane load-bearing requirements of the flexible skin, the total width of m columns of elastic units is set to w, and the m columns of elastic units are combined into a beam to calculate the load-bearing capacity. Under the given displacement limit, the width and height of the beam are calculated using the material mechanics formula. Due to the stratification of the deformable honeycomb, there is a conversion coefficient for the out-of-plane bending stiffness. The out-of-plane stiffness of the double-layer deformable honeycomb is 1 / 4 of that in the unstratified case, and the out-of-plane stiffness of the three-layer deformable honeycomb is 5 / 32 of that in the unstratified case. Then, according to the requirements of the deformable honeycomb pore size, the value of the number of columns m is adjusted, thereby determining the distance between adjacent columns, the initial bending shape of the elastic unit bending plate, and the values ​​of the remaining parameters. Finally, a deformable honeycomb structure with good out-of-plane load-bearing capacity and good in-plane deformation effect is obtained.

[0027] Silicone foam is used as a flexible filler to fill the pores of the deformable honeycomb in the form of silicone foam, and then the surface is covered with a silicone panel. The foamed silicone and the silicone panel are connected into one, and a flexible skin structure with a smooth surface is obtained, which can also relax the size limit of the honeycomb pores. The flexible skin structure diagram is as follows Figure 3 shown.

[0028] The specific data are listed below to further illustrate the specific embodiments of the present invention.

[0029] In this embodiment, the flexible skin has a length L = 240 mm, a width W = 200 mm, and a height H = 11 mm. The flexible skin is required to achieve an in-plane deformation of 20%, and a uniformly distributed load of 0.02 MPa is applied to the surface of the flexible skin. The deformable honeycomb is made of 7-series aluminum alloy with a height h = 10 mm, an elastic modulus E = 71.7 GPa, a Poisson's ratio μ = 0.33, and a density ρ = 2.81 g / cm. 3 .

[0030] The vertical panels of the deformable honeycomb provide out-of-plane bending stiffness. To ensure that the flexible skin structure can withstand out-of-plane loads, the height deformation of the deformable honeycomb under load must be ω ≤ 1.5 mm. Assuming the total width of m rows of elastic elements is w, the load-bearing capacity of these rows of elements is calculated by combining them into a beam. The beam length is 240 mm, the height of the beam section is h, and the beam width w is also 10 mm. After clamping the beam at both ends and applying a uniformly distributed load of 0.02 MPa to the beam surface, the maximum deformation is 0.592 mm, meeting the deformation requirement. Therefore, the beam width w = 10 mm can be used. Since the deformable honeycomb is divided into two layers in the middle, the height becomes twice h / 2. According to the bending stiffness formula, for the same beam width, the bending stiffness is reduced to 1 / 4 of that in the unlayered case. Therefore, the total thickness of the m rows of elastic elements should be 40 mm. Based on the porosity requirement, m = 20, and a total of 20 rows of elastic elements are arranged, with a thickness of t = 2 mm per elastic element. The deformable honeycomb structure can withstand out-of-plane loads.

[0031] Each column contains n elastic units. An entire row of elastic units in the same column is made from an elastic sheet of length n(a+2b). By cutting slits at corresponding positions on the sheet, a whole row of elastic units is obtained. Then, the ends of the bent sheets of the elastic units at the same level at corresponding positions in adjacent columns are welded together to form a deformable honeycomb structure. Honeycombs at different levels are connected together by connecting plates. According to the above dimensional parameters, the spacing c between two adjacent columns of elastic units is 10mm. Take the length of the bent sheet b = 8mm, the length of the connecting sheet a = 8mm, the width of the slit d = 0.2mm, the diameter of the crack stop hole D = 1mm, the width h = 10mm, and the plate thickness t = 2mm.

[0032] Based on the small deformation assumption, the deformation of each bending plate is 1.2mm, and the deformation of each elastic unit is 2.4mm, resulting in an overall deformation of the deformable honeycomb of 48mm. Therefore, the maximum deformation of the deformable honeycomb structure can reach 24%. Under the action of a uniformly distributed out-of-plane load of 0.02MPa, calculations have verified that the deformable honeycomb can withstand the out-of-plane load of 0.02MPa.

[0033] Fill the pores of the deformable honeycomb with foamed silicone and lay silicone panels on the surface of the deformable honeycomb to make a flexible skin structure. The skin structure cannot be too thick, and the thickness of the silicone panel is selected as t f =1mm. The length and width of the silicone panel are the same as those of the flexible skin.

[0034] By adjusting the parameters m, n, a, b, h, and t according to the desired size of the deformable honeycomb pores, flexible skins with varying deformation and load-bearing properties are achieved to meet a variety of design requirements. This results in a smooth surface, excellent in-plane unidirectional expansion and contraction, and excellent out-of-plane bending resistance.

[0035] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements can be made without departing from the principles of the present invention. These improvements should also be regarded as the scope of protection of the present invention.

Claims

1. A flexible skin based on a double-layer deformable honeycomb in the shape of a jujube, characterized in that: The flexible skin comprises a deformable support frame, a flexible filling and an elastic surface layer; The flexible filling adopts silicone foam (13), the elastic surface layer is a silicone panel (12), and the deformable support skeleton is a jujube-shaped double-layer deformable honeycomb; the pores of the deformable honeycomb are filled in the form of silicone foam, and then the surface is covered with the silicone panel (12), so that the foamed silicone and the silicone panel are connected into one body, thereby obtaining a flexible skin structure with a smooth surface; The elastic units are combined and arranged to form a double-layer deformable honeycomb in the shape of a jujube core; the elastic units include a connecting plate (9), a curved plate connected to the connecting plate (9), a slit (10) on the curved plate, and a crack-stop hole (11) at the root of the curved plate; the curved plate includes curved plates at different levels, and the curved plates at different levels are bent in different directions but are perpendicular to the plate surface of the curved plate; the ends of the curved plates on the same level of adjacent elastic units are welded to form a unit cell, After the elastic units are arranged in a row, the bending plates therein generate bending deformation to ensure the in-plane deformation capacity of the skin; when subjected to out-of-plane loads, the vertical surfaces of each bending plate and the connecting plate provide out-of-plane stiffness, so that the flexible skin has out-of-plane bearing capacity; the elastic unit is a+2b long, h wide, and t thick, wherein a is the length of the connecting plate (9), and b is the length of the upper and lower bending plates; a slit with a length of b and a width of d is formed at h / 2 in the width direction of the bending plate, and the bending plate is cut to form two layers of bending plates, namely the upper bending plate (6) and the lower bending plate (8); or two slits with a length of b and a width of d are formed at 1 / 4h and 3 / 4h in the width direction of the bending plate, and the bending plate is cut to form three layers of bending plates, namely the upper bending plate (6), the middle bending plate (7), and the lower bending plate (8); the diameter D of the crack stop hole is more than 3 times the slit width d.

2. The flexible skin based on a double-layer deformable honeycomb in a jujube-shaped shape according to claim 1, characterized in that: The elastic units are combined and arranged into a double-layer deformable honeycomb structure, including an upper deformable honeycomb (2) and a lower deformable honeycomb (3); the double-layer deformable honeycomb structure has a length of L=n(a+2b) and a width of W=(m+1)c, where n is the number of rows of elastic units, m is the number of columns of elastic units, and c is the spacing between two adjacent columns of elastic units, and c determines the initial bending shape of the bending plate; the upper deformable honeycomb (2) is initially bent to one side by c / 2, and the lower deformable honeycomb (3) is initially bent to the other side by c / 2.

3. The flexible skin based on a jujube-shaped double-layer deformable honeycomb according to claim 2, characterized in that: By adjusting the parameters m, n, a, b, h, and t, the deformation effect and load-bearing capacity of the jujube-shaped unit cell are changed. Based on the out-of-plane load-bearing requirements of the flexible skin, the total width of m rows of elastic units is set to w, and the m rows of elastic units are combined into a beam to calculate the load-bearing capacity. Under a given displacement limit, the deflection formula of the beam in material mechanics is used to calculate the width and height of the beam. Due to the delamination of the deformable honeycomb, the out-of-plane bending stiffness has a conversion factor. The out-of-plane stiffness of the double-layer deformable honeycomb is 1 / 4 of that of the unlayered case, and the out-of-plane stiffness of the triple-layer deformable honeycomb is 5 / 32 of that of the unlayered case. Then, according to the requirements of the deformable honeycomb pore size, the value of the column number m is adjusted to determine the distance between adjacent columns, the initial bending shape of the elastic unit bending plate, and the values ​​of the remaining parameters; finally, a deformable honeycomb structure with good out-of-plane load-bearing capacity and good in-plane deformation effect is obtained.

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