Novel zero-Poisson-ratio honeycomb sandwich type flexible skin

Abstract

The invention discloses a novel zero-Poisson-ratio honeycomb sandwich type flexible skin, and relates to the fields of airplanes, mechanics and materials. The requirement for large in-plane deformation and high out-of-plane bearing can be met at the hinge position of the wing of the foldable morphing aircraft, and good wing surface smoothness and pneumatic sealing performance are achieved. The zero-Poisson-ratio flexible skin comprises a zero-Poisson-ratio honeycomb sandwich structure, fixers fixedly arranged on the two sides of the zero-Poisson-ratio honeycomb sandwich structure, and an outer-layer rubber skin wrapping the zero-Poisson-ratio honeycomb sandwich structure. Practical engineering application finds that the skin solves the skin design problems of in-plane large deformation and out-plane high bearing, the weight of an aircraft body can be greatly reduced, and the flight performance is improved.

Description

Technical Field

[0001] The present invention relates to the fields of aircraft, mechanics and materials, and in particular to the technical field of large deformation skin of a foldable aircraft, specifically a flexible skin that can meet the requirements of large in-plane deformation and high out-of-plane load required at the hinge of a foldable foldable aircraft, and can better maintain the aerodynamic shape of the foldable foldable aircraft, reduce the weight of the fuselage, and improve the flight efficiency. Background Art

[0002] Since the Wright brothers first achieved powered flight, people have always dreamed of designing an aircraft that can freely deform like a bird's wing, adjust the wing shape according to different flight conditions, and optimize the aerodynamic characteristics and maneuverability under various flight conditions. However, the current fixed-wing aircraft wing can only guarantee that one design point is optimal. The geometric shape of the wing is not optimal in most cases. The flight parameters change continuously during the flight. For example, it requires a high lift-to-drag ratio and a large wing area during cruising, a high lift coefficient and a large wing area during takeoff and landing, and a large sweep angle and a small aspect ratio during high-speed flight. The emergence of variant aircraft has solved the above problems well.

[0003] Since the 1950s, scientists led by the United States have conducted in-depth research on variant aircraft. From the initial variable-sweep aircraft to the span-folding aircraft, and then to the adaptive verification aircraft, variant aircraft has become an industry development trend. The supersonic full tailless layout has become the key direction of future air combat platform development with its omnidirectional stealth capability and long-distance flight capability brought by the high lift-to-drag ratio, but the supersonic full tailless layout aircraft is difficult to control at supersonic speed. Based on this, scholars use folding wing technology to change the lateral stability and control the focus movement to achieve the control effect. One of the important technical features of the variant aircraft is that the wing surface must always remain smooth, continuous and seamless during the large changes in the wing geometric parameters such as chord length, span, sweep angle and area. Therefore, the skin needs a large deformation amount to ensure the realization of the above technical features, and it must have sufficient rigidity to maintain the aerodynamic shape of the wing during the deformation process, while reducing the requirements for the energy consumption of the drive.

[0004] Among traditional skins, silicone rubber skins can meet large deformation requirements, but it is difficult to withstand high aerodynamic loads; shape memory polymers, they transform the original high modulus material into a low modulus material by heating the resistance wire, but the resistance wire and the shape memory polymer are prone to separation during the deformation process; composite deformable skins, this type of skin has an obvious Poisson effect, that is, when tensile deformation occurs in one direction, there is obvious contraction deformation in the other direction; fish scale laminations, its biggest feature is that it meets high load and deformation requirements, but during the deformation process, the steps and gaps between the laminations cannot meet the airtightness and wing surface smoothness. The research on deformable skins is extremely difficult and challenging. Summary of the invention

[0005] In view of the above problems, the present invention proposes a novel zero Poisson's ratio honeycomb sandwich flexible skin, which can meet the requirements of large in-plane deformation and high out-of-plane load-bearing at the hinge of the wing of a foldable variant aircraft, and has good wing surface smoothness and aerodynamic sealing.

[0006] The technical solution of the present invention is as follows: the zero Poisson's ratio flexible skin comprises a zero Poisson's ratio honeycomb sandwich structure 2, a fixture 1 fixed on both sides of the zero Poisson's ratio honeycomb sandwich structure 2, and an outer rubber skin 3 covering the zero Poisson's ratio honeycomb sandwich structure 2;

[0007] The fixture 1 is divided into two parts, one part is used for fixed connection at the position to be installed, and the other part is connected to the zero Poisson's ratio honeycomb sandwich structure 2 as a whole, and the two parts are detachably connected through a mortise and tenon structure;

[0008] The zero Poisson's ratio honeycomb sandwich structure 2 includes a plurality of unit cells distributed in an array, the unit cells are distributed in a plurality of columns, and two adjacent columns of unit cells are connected as a whole by purlins and kept separated; the unit cell includes a secondary cell body, the secondary cell body includes two first-level cell bodies in the shape of an Ω with openings arranged opposite to each other, and the two ends of the first-level cell body are connected as a whole with the purlin or a part of the fixture 1; a plurality of first-level cell bodies on the same column are distributed at equal intervals;

[0009] The outer rubber skin 3 is made of a flexible material and is fixedly connected to the fixer 1 . The zero Poisson's ratio honeycomb sandwich structure 2 is encapsulated and fixed on the inner side of the outer rubber skin 3 .

[0010] The overall honeycomb sandwich structure 2 is not limited to a single unit cell size, and can be unevenly distributed according to needs to achieve the best deformation effect of the foldable variant aircraft. Its large and small arcs are smoothly connected to the connecting rods, and the straight lines where the inner and outer sides of the connecting rods are located are tangent to the arcs to ensure that stress concentration does not occur.

[0011] The thickness of the outer rubber skin 3 is selected according to different requirements, and is bonded to the internal honeycomb sandwich structure 2 by glue to ensure that its surface is smooth and wrinkle-free.

[0012] The first-level cell body includes a large arc, two small arcs and two horizontal straight rods, and the width of any cross section of the first-level cell body is t, wherein the radius of the large arc is R, and the radius of the small arc is r;

[0013] The distance between two primary cell bodies in a secondary cell body, that is, the interval m within the cell structure, the distance between the large arc and the purlin n, X1 represents the length of the secondary cell body in the X direction, and Y1 represents the length of the secondary cell body in the Y direction, where: X1 = (√2+2)r+(√2+4)t+2R+2m, Y1 = 2(R+t+n).

[0014] The deformation law of the overall honeycomb sandwich structure 2 at different widths t under the same stress is relatively consistent. Under a smaller tensile stress, the deformation of the honeycomb sandwich structure is relatively uniform, and a stress concentration area appears at the maximum turning point of the honeycomb sandwich structure. Under a smaller tensile strain, as the width t increases, the displacement at the free end of the structure gradually decreases and the stress concentration area becomes smaller. The larger the width of the structure, the weaker the in-plane deformation capacity.

[0015] The in-plane tensile deformation law of the overall honeycomb sandwich structure 2 is relatively consistent when the small arc radius r takes different values ​​under the same stress. Under a smaller tensile strain, the deformation of the honeycomb sandwich structure is relatively uniform, and a stress concentration area appears at the maximum turning point of the honeycomb sandwich structure, which is opposite to the effect of the width t on the honeycomb sandwich structure: as the small arc radius r increases, the area of ​​the stress concentration area becomes larger and larger.

[0016] When the large arc radius R takes different values ​​under the same stress, the in-plane tensile deformation law of the honeycomb sandwich structure 2 is relatively consistent, and the effect of the small arc radius r on the in-plane tensile deformation of the honeycomb sandwich structure is similar: the stress concentration occurs at the maximum turning point of the structure and the structural deformation is uniform.

[0017] The variation law of the tensile loading curve of the integral honeycomb sandwich structure 2 with different thicknesses h under the same stress is basically the same, and no obvious strengthening stage and yield stage appear. As the thickness h of the structure increases, the curve position where the material enters plastic deformation is advanced. Under the same load, the deformation generated by the structure decreases as the thickness h of the structure increases, and the large in-plane deformation capacity of the structure decreases, but the deformation rate within its elastic limit reaches more than 80%.

[0018] A part of the fixture 1 is provided with a slot 4 and is fixed to the fuselage or wing by screws 5, and another part of the fixture 1 is provided with a key 6 corresponding to the slot 4, and the two parts are tightly connected by the key 6 and the slot 4.

[0019] The flexible skin is installed at the hinge of the foldable variant aircraft and is wrapped around the hinge. The fixer 1 and the purlin in the flexible skin are parallel to the rotation axis of the hinge.

[0020] The present invention has the following beneficial effects:

[0021] 1. Since the skin itself needs to have good structural strength, the elastic modulus of the material itself is usually large and does not have good tensile properties. In this case, the equivalent elastic modulus of the entire skin is much smaller than the elastic modulus of the material itself through structural improvement and optimization, thereby ensuring that after the skin is installed at the hinge of the foldable variant aircraft, it can cope with the rotation of the hinge well.

[0022] Second, through further simulation and calculation, we can obtain the influence of width t, small arc radius r, large arc radius R, and thickness h on the equivalent elastic modulus of the structure, so as to select the optimal structural parameters according to different needs.

[0023] 3. Through actual engineering applications, it was found that the skin solved the design problems of skin with large in-plane deformation and high out-of-plane load, and it can greatly reduce the weight of the fuselage and improve flight performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of an implementation mode of the present invention.

[0025] Figure 2 is a schematic diagram of the overall structure of the skin of the present invention,

[0026] Figure 3 is a schematic diagram of the first-level cell hierarchy structure of the present invention,

[0027] Figure 4 is a schematic diagram of the secondary cell hierarchy structure of the present invention,

[0028] Figure 5 is a schematic diagram of a multi-level cell structure of an array distribution of the present invention,

[0029] Figure 6 A schematic diagram of a non-uniformly distributed multi-level cell structure of the present invention;

[0030] Figure 7 It is a simulation effect diagram of the present invention. DETAILED DESCRIPTION

[0031] In order to clearly illustrate the technical features of this patent, this patent is elaborated in detail below through a specific implementation method and in combination with its accompanying drawings.

[0032] like Figure 1 Shown is a schematic diagram of an implementation of the present invention, which is used to be installed at the hinge of a foldable variant aircraft, such as the hinge of a wing and a fuselage. The flexible skin can be arranged at the gap position of the folding mechanism, wrapped around the hinge, and fixedly connected to the wing and the fuselage on both sides.

[0033] like Figure 2The figure shows a novel zero Poisson's ratio honeycomb sandwich flexible skin, including a fixture 1, a zero Poisson's ratio honeycomb sandwich structure 2, and an outer rubber skin 3. The fixture 1 is detachably connected by a mortise and tenon structure, which is convenient for replacing the skin structure. The zero Poisson's ratio honeycomb sandwich structure 2 is obtained by a unit cell array, and the structure is a deformed core structure. The zero Poisson's ratio honeycomb sandwich structure 2 and the skin connection end of the fixture 1 are integrally printed by 3D printing technology, and the outer rubber skin 3 is made of thermoplastic polyurethane material TPU. By adopting a novel zero Poisson's ratio honeycomb sandwich flexible skin of the present invention, the requirements of large in-plane deformation and high out-of-plane load required at the hinge of a foldable variant aircraft can be met, and the aerodynamic shape of the foldable variant aircraft can be better maintained, the weight of the fuselage can be reduced, and the flight efficiency can be improved. At the same time, it also lays a good foundation for applications in high-tech fields such as aerospace, vehicles, and ships.

[0034] like Figure 3 The figure shows a primary cell body structure, wherein the primary cell body comprises a large arc, two small arcs and two horizontal straight rods, and the openings of all primary cell elements are opposite to each other.

[0035] like Figure 4 As shown, the first-level cell body is obtained by symmetry to obtain a second-level cell body, wherein the width of any cross section of the cell body is t, wherein the radius of the large arc is R, the radius of the small arc is r, the spacing within the cell structure is m, the distance between the large arc and the horizontal straight plate is n, and the thickness of the interlayer is h. X1 represents the horizontal length of the unit, and Y1 represents the vertical height of the structure. Where: X1 = (√2+2)r + (√2+4)t + 2R + 2m, Y1 = 2(R + t + n).

[0036] like Figure 5 As shown, the secondary cell bodies can obtain a uniformly distributed multi-level cell body structure through an array, and the structure consists of 4*6 secondary cell bodies with equal parameters and two sections of fixers. The fixers corresponding to the outer sides of each row of cell bodies are provided with a key and a slot, and a screw hole is provided between every two slots for installing the fixer.

[0037] like Figure 6 As shown in the figure, a non-uniformly distributed multi-level cell structure is obtained by structural optimization and arrangement and combination of secondary cell bodies with different parameters. The structure consists of 4 parameters, 6 secondary cell bodies of each type, and two sections of fixtures. The fixtures corresponding to the outer side of each row of cell bodies are provided with a key and a slot, and a screw hole is provided between every two slots for installing the fixture. The cell body of this structure is thickened in the middle part of the large arc to improve the service life of the structure.

[0038] like Figure 7As shown, after simulation verification, a fixed constraint was applied to one end of the structure and a 10N uniformly distributed load was applied to the other end. The structure was stretched from the original 160mm to 280mm, the deformation reached 80%, and the structure was not damaged, indicating that the in-plane deformation effect of this case is good and the in-plane large deformation capacity is strong.

[0039] There are many specific implementation ways of the present invention. The above is only the preferred implementation mode 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 principle of the present invention. These improvements should also be regarded as the protection scope of the present invention.

Claims

1. A new type of zero Poisson's ratio honeycomb sandwich flexible skin, characterized in that: The zero Poisson's ratio flexible skin comprises a zero Poisson's ratio honeycomb sandwich structure (2), a fixture (1) fixed on both sides of the zero Poisson's ratio honeycomb sandwich structure (2), and an outer rubber skin (3) covering the zero Poisson's ratio honeycomb sandwich structure (2); The fixture (1) is divided into two parts, one part is used for fixed connection at the position to be installed, and the other part is connected to the zero Poisson's ratio honeycomb sandwich structure (2) as a whole, and the two parts are detachably connected via a mortise and tenon structure; The zero Poisson's ratio honeycomb sandwich structure (2) comprises a plurality of crystal unit cells distributed in an array, wherein the crystal unit cells are distributed in a plurality of columns, and two adjacent columns of crystal unit cells are connected as a whole by purlins and are kept separated; the crystal unit cells comprise a secondary cell body, wherein the secondary cell body comprises two first-level cell bodies in the shape of an Ω with openings arranged opposite to each other, and the two ends of the first-level cell body are connected as a whole with the purlins or a part of the fixer (1); and the plurality of first-level cell bodies in the same column are distributed at equal intervals; The outer rubber skin (3) is made of a flexible material and is fixedly connected to the fixer (1); the zero Poisson's ratio honeycomb sandwich structure (2) is encapsulated and fixed on the inner side of the outer rubber skin (3).

2. A novel zero Poisson's ratio honeycomb sandwich flexible skin according to claim 1, characterized in that: The first-level cell body includes a large arc, two small arcs and two horizontal straight rods, and the width of any cross section of the first-level cell body is t, wherein the radius of the large arc is R, and the radius of the small arc is r; The distance between two primary cell bodies in a secondary cell body, that is, the interval m within the cell structure, the distance between the large arc and the purlin n, X1 represents the length of the secondary cell body in the X direction, and Y1 represents the length of the secondary cell body in the Y direction, where: X1 = (√2+2)r+(√2+4)t+2R+2m, Y1 = 2(R+t+n).

3. The novel zero Poisson's ratio honeycomb sandwich flexible skin according to claim 1, characterized in that: A part of the fixture (1) is provided with a slot (4) and is fixed to the fuselage or wing by means of screws (5); another part of the fixture (1) is provided with a key (6) corresponding to the slot (4); the two parts are tightly connected via the key (6) and the slot (4).

4. The novel zero Poisson's ratio honeycomb sandwich flexible skin according to claim 1, characterized in that: The flexible skin is installed at the hinge of the foldable variant aircraft and is wrapped around the hinge. The fixer (1) and the purlin in the flexible skin are parallel to the rotation axis of the hinge.

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