A new type of zero-poisson-ratio honeycomb sandwich flexible skin

Abstract

The application discloses a novel zero-Poisson-ratio honeycomb sandwich flexible skin, and relates to the fields of aircrafts, mechanics and materials. The zero-Poisson-ratio honeycomb sandwich flexible skin can meet the requirements of large in-plane deformation and high out-of-plane load bearing at a foldable variable aircraft wing hinge, and has good wing surface smoothness and aerodynamic sealing performance. The zero-Poisson-ratio honeycomb sandwich flexible skin comprises a zero-Poisson-ratio honeycomb sandwich structure, a fixer fixed on both sides of the zero-Poisson-ratio honeycomb sandwich structure, and an outer rubber skin wrapped outside the zero-Poisson-ratio honeycomb sandwich structure. It is found through actual engineering application that the skin solves the skin design problems of large in-plane deformation and high out-of-plane load bearing, and greatly reduces the weight of the aircraft body and improves the flight performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of aircraft, mechanics, materials, in particular to the technical field of morphing aircraft large deformation skin. Specifically, it is a flexible skin that can meet the requirements of large in-plane deformation and high out-of-plane load at the hinge of the foldable morphing aircraft, and can better maintain the aerodynamic shape of the foldable morphing aircraft, reduce the weight of the fuselage, and improve the flight efficiency. BACKGROUND

[0002] Since the Wright brothers first achieved powered flight, people have always dreamed of designing a flying machine that can freely deform like a bird's wing, adjusting the wing shape in real time according to different flight states, and optimizing the aerodynamic characteristics and maneuvering performance in various flight states. However, the wings of current fixed-wing aircraft can only guarantee that one design point is optimal, and the geometric shape of the wing is not optimal in most cases. During flight, flight parameters change continuously, such as requiring high lift-drag ratio and large wing area during cruising, high lift coefficient and large wing area during takeoff and landing, and large sweep angle and small aspect ratio during high-speed flight. The emergence of morphing aircraft has solved the above problems.

[0003] Since the 1950s, scientists led by the United States have conducted in-depth research on morphing aircraft, from the initial variable sweep aircraft to the spanwise folding aircraft, and then to the adaptive verification machine. Morphing aircraft has become a development trend in the industry. The supersonic all-tailless layout has become a key direction for the development of future air combat platforms due to its all-around stealth capability and long-range endurance capability brought by high lift-drag ratio, but it is difficult to control the supersonic all-tailless layout aircraft at supersonic speed. Accordingly, scholars have changed the lateral stability through folding wing technology to control the focus movement to achieve control effect. One of the important technical features of morphing aircraft is that the wing geometric parameters such as chord length, span length, sweep angle, and area need to change significantly while the wing surface remains smooth, continuous, and seamless. Therefore, the skin needs to have a large deformation to ensure the realization of the above technical features, and has enough stiffness to maintain the aerodynamic shape of the wing during deformation, while reducing the energy consumption requirements of the drive.

[0004] In traditional skin, silicone rubber skin can meet the requirement of large deformation, but it is difficult to withstand high aerodynamic load; shape memory polymer changes from high modulus to low modulus by heating the resistance wire to complete deformation, but separation between the resistance wire and the shape memory polymer is prone to occur during deformation; composite deformation skin has obvious Poisson effect, that is, when one direction is stretched, the other direction is obviously contracted; the fish scale has the characteristics of meeting the requirements of high load and deformation, but the steps and gaps between the scales during deformation cannot meet the air tightness and smoothness of the wing surface. The research on deformation skin is extremely difficult and challenging work. SUMMARY

[0005] The present application aims at the above problems, and provides a new type of zero Poisson's ratio honeycomb sandwich flexible skin, which can meet the requirements of large in-plane deformation and high out-of-plane load at the wing hinge of a foldable morphing aircraft, and has good wing surface smoothness and aerodynamic sealing.

[0006] The technical scheme of the present application is as follows: the zero Poisson's ratio flexible skin comprises a zero Poisson's ratio honeycomb sandwich structure 2, a fixer 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 fixer 1 is divided into two parts, one part is used for fixed connection at the installation position, and the other part is integrated with the zero Poisson's ratio honeycomb sandwich structure 2, and the two parts are detachably connected through a mortise and tenon structure.

[0008] The zero Poisson's ratio honeycomb sandwich structure 2 comprises a plurality of unit cells arranged in an array, the unit cells are arranged in a plurality of columns, and adjacent two columns of unit cells are integrated through a purlin and are kept separated; the unit cell comprises a secondary cell body, the secondary cell body comprises two first cell bodies in the shape of omega with open opposite arrangement, and the two ends of the first cell body are integrated with the purlin or a part of the fixer 1; a plurality of first cell bodies in the same column are arranged at equal intervals.

[0009] The outer rubber skin 3 is made of flexible material and is fixedly connected with the fixer 1, and 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 non-uniformly distributed according to requirements to achieve the best deformation effect of the foldable morphing aircraft, and the size arc and connecting rod are smooth links, and the straight lines where the inner and outer sides of the connecting rod 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 the inner honeycomb sandwich structure 2 is bonded by glue to ensure that the surface is smooth and wrinkle-free.

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

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

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

[0015] The in-plane tensile deformation rules of the integral honeycomb sandwich structure 2 under the same stress and different values of the small circular arc radius r are relatively consistent, the deformation of the honeycomb sandwich structure is relatively uniform under a small tensile strain, and a stress concentration area appears at the maximum turning point of the honeycomb sandwich structure, which is contrary to the influence of the width t on the honeycomb sandwich structure: the larger the small circular arc radius r, the larger the area of the stress concentration area.

[0016] The in-plane tensile deformation rules of the integral honeycomb sandwich structure 2 under the same stress and different values of the large circular arc radius R are relatively consistent, which is similar to the influence of the small circular arc radius r on the in-plane tensile deformation of the honeycomb sandwich structure: the stress concentration area appears at the maximum turning point of the structure and the deformation of the structure is uniform.

[0017] The tensile loading curve change rules of the integral honeycomb sandwich structure 2 under the same stress and different thicknesses h are basically consistent, and there is no obvious strengthening stage and yield stage, the plastic deformation curve position of the material is advanced with the increase of the thickness h of the structure, under the same load, the deformation of the structure decreases with the increase of the thickness h of the structure, and the in-plane large deformation capacity of the structure decreases, but the deformation rate of the structure within the elastic limit reaches more than 80%.

[0018] A part of the fixer 1 is provided with a clamping groove 4 and is fixed to the fuselage or wing through a screw 5, and the other part of the fixer 1 has a key 6 corresponding to the clamping groove 4, and the two parts are tightly connected through the key 6 and the clamping groove 4.

[0019] The flexible skin is installed at the hinge of the foldable variable aircraft and covers the hinge, the fixer 1 and the purlin in the flexible skin are parallel to the rotating shaft of the hinge.

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

[0021] I. Since the skin itself needs to have good structural strength, the elastic modulus of the material itself is usually large, and it cannot have good tensile properties. The application optimizes the structure to make the equivalent elastic modulus of the whole skin much smaller than the elastic modulus of the material itself, so that after the skin is installed at the hinge of the foldable variable aircraft, it can well cope with the rotation of the hinge.

[0022] II. Through further simulation and calculation, the influence of width t, small arc radius r, large arc radius R and thickness h on the equivalent elastic modulus of the structure can be obtained, so as to select the optimal structural parameters according to different requirements.

[0023] III. Through actual engineering application, it is found that the skin solves the design problem of large in-plane deformation and high out-of-plane load bearing, and greatly reduces the weight of the aircraft and improves the flight performance. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a schematic diagram of an embodiment of the application.

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

[0026] Figure 3 is a schematic diagram of the hierarchical structure of the primary cell of the application,

[0027] Figure 4 is a schematic diagram of the hierarchical structure of the secondary cell of the application,

[0028] Figure 5 is a schematic diagram of the multi-level cell structure of the application with array distribution,

[0029] Figure 6 is a schematic diagram of the multi-level cell structure of the application with non-uniform distribution;

[0030] Figure 7 is a simulation effect diagram of the application. DETAILED DESCRIPTION

[0031] In order to clearly illustrate the technical features of the patent, the patent will be described in detail below with reference to the specific embodiments and the accompanying drawings.

[0032] As Figure 1 shown is a schematic diagram of an embodiment of the application, which is used to be installed at the hinge of the foldable variable aircraft, such as the hinge of the wing and the fuselage. The flexible skin can be arranged at the gap position of the folding mechanism, wrapped outside the hinge, and fixedly connected to the wing and the fuselage on both sides.

[0033] As Figure 2A new type of zero poisson's ratio honeycomb sandwich flexible skin is shown, including fixer 1, zero poisson's ratio honeycomb sandwich structure 2, outer rubber skin 3, the fixer 1 is detachably connected through mortise and tenon structure, the skin structure is convenient to replace. The zero poisson's ratio honeycomb sandwich structure 2 is obtained by cell unit array, and the structure is a deformed core structure. The skin connecting end of the zero poisson's ratio honeycomb sandwich structure 2 and the fixer 1 is integrally printed by 3D printing technology, and the outer rubber skin 3 is made of thermoplastic polyurethane material TPU. By adopting the new type of zero poisson's ratio honeycomb sandwich flexible skin, the requirements of in-plane large deformation and out-of-plane high bearing of the hinge of the foldable variable aircraft can be met, the aerodynamic shape of the foldable variable aircraft can be better maintained, the weight of the fuselage can be reduced, and the flight efficiency can be improved. Meanwhile, it lays a good foundation for the application of high-tech fields such as aerospace, vehicles and ships.

[0034] As shown in Figure 3 The primary cell body structure is shown, which includes a large circular arc, two small circular arcs and two horizontal straight rods, and the openings of all primary cell elements are opposite.

[0035] As shown in Figure 4 The primary cell body is obtained by symmetry to obtain a secondary cell body, wherein the arbitrary cross-sectional width of the cell body is t, the radius of the large circular arc is R, the radius of the small circular arc is r, the interval in the cell structure is m, the distance between the large circular arc and the horizontal straight plate is n, and the interlayer thickness is h. X1 represents the horizontal length of the unit, and Y1 represents the vertical height of the structure. Wherein: X1=(sqrt(2)+2)r+(sqrt(2)+4)t+2R+2m, Y1=2(R+t+n).

[0036] As shown in Figure 5 The secondary cell body can obtain a uniformly distributed multi-level cell body structure by array, which is composed of 4*6 secondary cell bodies with equal parameters, two fixers, a key and a clamping groove are arranged on each corresponding fixer outside the cell body in each row, and a screw hole is arranged between every two clamping grooves for installing the fixer.

[0037] As shown in Figure 6 A non-uniform multi-level cell body structure is obtained by structure optimization and arrangement and combination of different parameters of the secondary cell body, which is composed of 4 kinds of secondary cell bodies with 6 parameters each and two fixers, a key and a clamping groove are arranged on each corresponding fixer outside the cell body in each row, and a screw hole is arranged between every two clamping grooves for installing the fixer. The cell body in the middle part of the large circular arc is thickened to improve the service life of the structure.

[0038] As shown in Figure 7As shown, through simulation verification, a fixed constraint is applied to one end of the structure, and a 10N uniform load is applied to the other end, the structure is stretched from the original 160mm to 280mm, the deformation reaches 80%, and the structure does not break, indicating that the in-plane deformation effect is good, and the in-plane large deformation capacity is strong.

[0039] The present application has many specific implementation approaches, and the above description is only the preferred embodiment of the present application. It should be pointed out that for ordinary skilled persons in the art, without departing from the principles of the present application, a number of improvements can be made, and these improvements should also be considered as the protection scope of the present application.

Claims

1. A novel zero Poisson's ratio honeycomb sandwich flexible skin, characterized in that, The zero Poisson's ratio honeycomb sandwich flexible skin includes 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 fastener (1) is divided into two parts. One part is used to fix it to the position to be installed, and the other part is integrated with the zero Poisson's ratio honeycomb sandwich structure (2). The two parts are detachably connected by a tenon and mortise structure. The zero Poisson's ratio honeycomb sandwich structure (2) includes an array of several unit cells distributed in several columns. Adjacent columns of unit cells are connected by purlins and kept separate. Each unit cell includes a secondary cell, which includes two primary cells with openings facing each other in an Ω shape. The two ends of the primary cells are connected to a part of the purlins or the fixture (1). Several primary cells in the same column are evenly spaced. The outer rubber skin (3) is made of flexible material and is fixedly connected to the fixture (1). The zero Poisson's ratio honeycomb sandwich structure (2) is encapsulated and fixed inside the outer rubber skin (3). The primary cell comprises a large circular arc, two small circular arcs, and two horizontal straight rods. The width of any cross section of the primary cell is t, where the radius of the large circular arc is R and the radius of the small circular arc is r. The distance between two primary cells in a secondary cell is m, the intracellular spacing m, the distance n between the great circle and the purlin, X1 represents the X-axis length of the secondary cell, and Y1 represents the Y-axis length of the secondary cell, where: Y1 = 2(R + t + n).

2. The novel zero Poisson's ratio honeycomb sandwich flexible skin according to claim 1, characterized in that, One part of the fixture (1) is fitted with a slot (4) and fixed to the fuselage or wing by screws (5). The other part of the fixture (1) has a key (6) corresponding to the slot (4), and the two parts are tightly connected by the key (6) and the slot (4).

3. A 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 covers the outside of the hinge. The retainer (1) and purlin in the flexible skin are parallel to the pivot of the hinge.

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