A flexible morphing wing based on three-dimensional star-shaped negative poisson's ratio lattice and method

Abstract

The application discloses a flexible deformable wing based on a three-dimensional star-shaped negative Poisson's ratio lattice and a method, the flexible deformable wing comprises a supercritical wing box, the supercritical wing box is mainly composed of a leading edge, a trailing edge, an upper skin and a lower skin, the supercritical wing box is filled with a three-dimensional star-shaped negative Poisson's ratio lattice structure, the three-dimensional star-shaped negative Poisson's ratio lattice structure is combined by three layers of star-shaped frames and two layers of inclined rods, the offset angle of a unit cell in each layer of star-shaped frames changes in a gradient from the leading edge to the trailing edge, and the offset angle of the unit cell at the leading edge is smaller than that of the unit cell at the trailing edge. The 3D-SAU lattice filling structure obtained through conformal design can be seamlessly attached to the wing skin and effectively reduce stress concentration; the lattice filling structure has the characteristics of quasi-zero bending stiffness, can realize deformation of the wing with lower driving energy, has stronger self-adapting deformation capacity, and can realize lightweight, impact resistance and flexible deformation design of the unmanned aerial vehicle wing.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of wing design, and particularly relates to a flexible deformable wing based on a three-dimensional star-shaped negative Poisson's ratio lattice and a method. BACKGROUND

[0002] Super material refers to a special material artificially designed with special structure and super physical properties. The structure and material of the super material need to be designed according to specific requirements to meet the specified use requirements. At present, the flexible deformable wing is filled with super materials such as honeycomb core sandwich structure, corrugated core structure and lattice structure.

[0003] With the development of unmanned aerial vehicle technology, the performance requirements for structural materials are higher and higher. In the design process of the flexible deformable wing, a suitable filling material needs to be selected to ensure that the wing produces stable deformation. The flexible deformable wing made of the existing filling material has poor impact resistance and insufficient deformation capacity. In addition, since the unmanned aerial vehicle has different requirements for the shape of the wing during cruising and high-speed flight, a high aspect ratio is required during cruising, and a low aspect ratio is required during high-speed flight, so the wing needs to have self-adaptive adjustment capability. In view of the complex working conditions of the wing, it is urgent to design a way to enable the wing to adaptively adjust according to the actual flight conditions to produce stable deformation to improve the flight efficiency. SUMMARY

[0004] To solve the above problems, an embodiment of the application provides a flexible deformable wing based on a three-dimensional star-shaped negative Poisson's ratio lattice and a method.

[0005] The three-dimensional star-shaped negative Poisson's ratio (3D-SAU) lattice structure has stable negative Poisson's ratio effect in three directions, and has good bending deformation capacity in the out-of-plane direction, so that the lightweight, impact resistance and flexible deformation design of the unmanned aerial vehicle wing can be realized.

[0006] The flexible deformable wing based on the three-dimensional star-shaped negative Poisson's ratio lattice of the application comprises a supercritical wing box, and the supercritical wing box is mainly composed of a leading edge, a trailing edge, an upper skin and a lower skin. The three-dimensional star-shaped negative Poisson's ratio lattice structure is filled in the supercritical wing box, and the three-dimensional star-shaped negative Poisson's ratio lattice structure is composed of three layers of star-shaped frames and two layers of inclined rods. The offset angle of the unit cell in each layer of star-shaped frame changes in a gradient from the leading edge to the trailing edge, and the offset angle of the unit cell at the leading edge of the wing is smaller than that of the unit cell at the trailing edge of the wing.

[0007] The offset angle of the unit cell at the leading edge of the wing is 40°, and the offset angle of the unit cell at the trailing edge of the wing is 50°.

[0008] The star-shaped frame comprises three columns of unit cells, and the two outer columns of the star-shaped frame comprise one more unit cell than the middle column of the star-shaped frame.

[0009] The two outer columns of the star-shaped frame are sequentially connected by 12 unit cells, and the middle column of the star-shaped frame is sequentially connected by 11 unit cells.

[0010] The unit cell is alternately and spacedly arranged by three outer convex corners and three inner concave corners, two inner concave corners are arranged on both sides of each outer convex corner, two outer convex corners are arranged on both sides of each inner concave corner, and the outer convex corner and the inner concave corner between the adjacent two unit cells are connected.

[0011] In the three-dimensional star-shaped negative Poisson's ratio lattice structure, from the upper skin to the lower skin, the sequence is a star-shaped frame, a diagonal rod, a star-shaped frame, a diagonal rod and a star-shaped frame, wherein the outer convex corner of the unit cell in each star-shaped frame is connected with the inner concave corner of the corresponding unit cell in the adjacent layer star-shaped frame, and the inner concave corner in each star-shaped frame is connected with the outer convex corner of the corresponding unit cell in the adjacent star-shaped frame.

[0012] The variation amount of the bias angle in the star-shaped frame is Δθ:

[0013]

[0014] In the formula, θ α and θ β are the sizes of the bias angles at both ends of the star-shaped frame, and a is the array number of the lattice unit cell in the direction I.

[0015] The preparation method of the flexible deformable wing based on the three-dimensional star-shaped negative Poisson's ratio lattice of the application comprises the following steps:

[0016] (1) selecting a wing profile, selecting a supercritical wing NASA SC(2)-0706 as a filling object;

[0017] (2) establishing a three-dimensional model of a wing box, the leading edge and the trailing edge of the wing box are manufactured by printing with photosensitive resin, and the upper skin and the lower skin are made of shape memory alloy;

[0018] (3) determining the overall structure size of the filling structure, i.e. the three-dimensional star-shaped negative Poisson's ratio lattice structure, according to the size parameters of the wing, and determining reasonable unit cell parameters and array directions;

[0019] (4) the filling structure is composed of a three-dimensional star-shaped negative Poisson's ratio lattice structure, and the design of the structural part mainly comprises two steps: modeling and processing and forming by using an additive manufacturing technology;

[0020] (5) Modeling: The lattice model design consists of two steps of building star-shaped frame on the skin and connecting diagonal rods, star-shaped frame building: three reference surfaces are established above the wing box corresponding to the upper skin, middle surface and lower skin of the wing box area, and the star-shaped frame is drawn on the reference surface, and the star-shaped frame with gradient change is obtained by adjusting the size of the unit cell offset angle;

[0021] (6) The star-shaped frame on the reference surface is mapped to the corresponding area inside the wing box to obtain the star-shaped frame curve consistent with the curvature change of the skin, and the unit cell of the star-shaped frame consists of three outer convex angles and three inner concave angles;

[0022] (7) Diagonal rod connection: the star-shaped frame structure between the upper skin, middle surface and lower skin is connected by diagonal rods, that is, the outer convex angle and the inner concave angle of one surface are connected with the inner concave angle and the outer convex angle of the adjacent surface, and the complete lattice filling structure model is obtained;

[0023] (8) The lattice filling structure is processed by using additive manufacturing technology;

[0024] (9) The leading edge, trailing edge and filling structure of the wing are glued to the upper skin and lower skin by epoxy resin adhesive (AWG 97033).

[0025] In the process of converting the three-dimensional star-shaped negative Poisson's ratio lattice structure into the lattice filling structure fitted to the upper skin and lower skin of the wing, the distance h between the adjacent two layers of star-shaped frames changes, which is denoted as Δh, resulting in the change of the size l1 and the inclination angle β of the diagonal rod, which are denoted as l1' and β',

[0026]

[0027] Wherein, θ is the offset angle, and l is the side length of the unit cell.

[0028] The offset angle refers to 1 / 2 of the supplementary angle of the outer convex angle, and the gradient change of the offset angle refers to that a linear gradient value is preset, so that the size of the lattice filling structure offset angle changes equally from the leading edge to the trailing edge, that is, the offset angle change value of the corresponding positions of any two adjacent unit cells is the same.

[0029] The beneficial effects of the present application are,

[0030] 1. The 3D-SAU lattice filling structure obtained by the conformal design can be seamlessly fitted to the wing skin, and can effectively reduce stress concentration; the lattice filling structure has the characteristics of quasi-zero bending stiffness, can realize the deformation of the wing with lower driving energy, has stronger self-adaptive deformation ability, and can realize the lightweight, impact resistance and flexible deformation design of the unmanned aerial vehicle wing.

[0031] 2. The lattice structure has a negative Poisson's ratio effect, under the action of bending load, the lattice structure in the loading area will shrink, thereby increasing the density of the loaded area, improving the bending stiffness, inhibiting the excessive bending of the wing, and maintaining stable deformation. Thus, the bending degree of the wing increases when flying at high speed, the lattice gathers to the bending part, the density of the part increases, thereby reducing the aspect ratio of the wing and reducing the resistance; when the aircraft is in a cruising state, the loading decreases, the gathering degree of the lattice decreases, the aspect ratio of the wing increases, the lift is improved, and the endurance of the aircraft is improved.

[0032] 3. Inspired by the gradual change of the cattail leaf gas cavity wall inclination angle, the lattice filling structure designed has the characteristics of gradient change of the bias angle, the deformation ability of the local area of the wing can be adjusted by changing the gradient size, the transmission of the flutter wave is effectively inhibited, and the anti-flutter ability of the wing is improved.

[0033] 4. The wing airfoil designed in the application is a supercritical wing, which has the advantages of small wave resistance, good lift performance and high fuel efficiency, and is widely used in aircraft design. DETAILED DESCRIPTION

[0034] Figure 1 is a frame diagram of the aircraft wing of the application;

[0035] Figure 2 is a 3D-SAU lattice structure mapping diagram of the application;

[0036] Figure 3 is a cattail blade gas cavity section view and a star-shaped frame diagram;

[0037] Figure 4 is a test piece schematic diagram of the 3D-SAU lattice for three-point bending experiment;

[0038] Figure 5 is a test piece schematic diagram of the 3D-RE lattice for three-point bending experiment;

[0039] Figure 6 is a test piece schematic diagram of the BCC lattice for three-point bending experiment;

[0040] Figure 7 is a force-displacement curve diagram of the BCC lattice, the 3D-SAU lattice and the 3D-RE lattice in the three-point bending experiment;

[0041] Figure 8 is a gradient change 3D-SAU lattice filling wing structure schematic diagram of the application;

[0042] Figure 9 is a 40° 3D-SAU lattice filling wing structure schematic diagram;

[0043] Figure 10This is a schematic diagram of a 50° 3D-SAU dot matrix filled wing structure;

[0044] Figure 11 These are displacement diagrams of three offset lattice-filled wing structures at different nodes. Detailed Implementation

[0045] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0046] like Figures 1-11 As shown, the flexible deformable wing based on a three-dimensional star-shaped negative Poisson's ratio lattice of the present invention includes a supercritical wing box, which is mainly composed of a leading edge, a trailing edge, an upper skin, and a lower skin. Relevant design parameters include the wing chord length c and the leading edge length l. L Trailing edge length l T Leading edge thickness t L trailing edge thickness t T and skin thickness t S wing frame, like Figure 1 As shown.

[0047] The supercritical wing box is filled with a three-dimensional star-shaped negative Poisson's ratio lattice structure. This structure consists of three star-shaped frames and two layers of diagonal braces, with the two diagonal braces positioned between the three star-shaped frames. Specifically, in the three-dimensional star-shaped negative Poisson's ratio lattice structure, from the upper skin to the lower skin, the sequence is: star-shaped frame, diagonal brace, star-shaped frame, diagonal brace, and star-shaped frame again.

[0048] Each star-shaped frame consists of three rows of cells arranged sequentially and connected to each other. The two outer rows of star-shaped frames contain one more cell than the middle row of star-shaped frames.

[0049] Specifically, the two outer star-shaped frames are composed of 12 units connected in sequence, while the middle star-shaped frames are composed of 11 units connected in sequence.

[0050] The unit cell is composed of three convex angles and three concave angles arranged alternately. Each convex angle has two concave angles on both sides, and each concave angle has two convex angles on both sides. The convex angles and concave angles between two adjacent unit cells are connected.

[0051] The convex angle of the unit cell in each layer of the star frame is connected to the concave angle of the corresponding unit cell in the adjacent layer of the star frame by a diagonal bar.

[0052] In each star-shaped frame, the offset angle of the unit cell changes gradually from the leading edge to the trailing edge, with the offset angle of the unit cell at the leading edge of the wing being smaller than that of the unit cell at the trailing edge. The offset angle of the unit cell at the leading edge of the wing is 40°, and the offset angle of the unit cell at the trailing edge of the wing is 50°.

[0053] The variation in the offset angle of the unit cells within each layer of the star-shaped framework incorporates biomimetic principles, derived from cattail leaves. The cross-section of a cattail leaf reveals a sophisticated honeycomb-like air cavity structure, such as... Figure 3 As shown in (a), the thin-walled angles separating the air chambers exhibit a significant gradient change. In the middle region of the cross-section, the air chamber walls are approximately perpendicular to the blade surface, with an inclination angle b2 close to 90°, providing high local stiffness and support. As the section transitions towards the tip, the inclination angle b1 of the air chamber walls gradually decreases, giving this region greater local flexibility. The cattail blade cross-section has a symmetrical structure, and the change in inclination angle from the middle to the tip gradually increases its flexibility.

[0054] This invention, based on the variation law of the tilt angle of the inner wall of the air cavity in cattail leaves, designs a lattice-filled structure with a gradient change in offset angle. Unlike the symmetrical structure of cattail leaves, the lattice-filled structure of this invention adopts a gradient design where the offset angle changes monotonically from one end to the other. For example... Figure 3 As shown in (b), different offset angles θ are set at both ends of the lattice star-shaped frame. a and θ β The gradient of the lattice offset angle in the middle section varies. The offset angle varies uniformly along direction one, and the change in the offset angle of adjacent star-shaped frames is Δθ.

[0055]

[0056] In the formula, θ α and θ β denoted by the offset angles at both ends of the star-shaped frame, and 'a' represents the number of times the lattice unit cell array is arranged in direction one.

[0057] The offset angle is half of the supplementary angle of the convex angle of a unit cell. The gradient change of the offset angle means that a linear gradient value is set in advance so that the size of the offset angle of the lattice filling structure changes equally from the leading edge to the trailing edge. That is, the offset angle change value is the same for any two adjacent unit cells.

[0058] Offset angle θ of the leading edge of the wing box α It must be smaller than the offset angle θ at the trailing edge. βThe reason is that a smaller offset angle results in greater stiffness in the corresponding area. Since the leading edge of the wing bears a greater load than the trailing edge, a smaller offset angle is needed to provide greater stiffness. The size of the offset angle significantly affects the deformability of the wing box. A smaller offset angle at the front results in weaker deformability, ensuring reliable wing deformation; while a larger offset angle at the rear results in stronger deformability, enabling aerodynamic adaptive deformation. Furthermore, thanks to the gradient design of the offset angle, the density of the lattice filling structure changes from the front to the rear, effectively suppressing flutter wave transmission and improving the wing's flutter resistance.

[0059] This invention presents a flexible deformable wing filled with a 3D-SAU lattice structure, exhibiting excellent bending deformation performance and capable of controlling local wing bending performance by utilizing gradient changes in the offset angle. Benefiting from the superior bending deformation capability and negative Poisson's ratio effect of the 3D-SAU lattice, the wing displays different morphologies during high-speed flight and cruise, enabling adaptive adjustment.

[0060] Existing 3D-SAU lattice structures have a traditional parallel configuration with parallel upper and lower surfaces. However, the upper and lower surfaces of wing skin are curved structures. Therefore, existing 3D-SAU lattices cannot be directly used for filling flexible deformable wings. This invention proposes a design scheme utilizing skin mapping, which ensures that the curvature change of the lattice filling structure is consistent with the wing skin. This effectively completes the conformal design of the 3D-SAU filling lattice structure, resulting in a conformal structure that fully conforms to the curved surface of the wing skin. The conversion process is as follows: Figure 2 As shown.

[0061] The present invention provides a method for fabricating a flexible deformable airfoil based on a three-dimensional star-shaped negative Poisson's ratio lattice, comprising the following steps:

[0062] (1) Select the airfoil and use the supercritical airfoil NASA SC(2)-0706 as the filling object;

[0063] (2) Establish a three-dimensional model of the wing box. The leading and trailing edges of the wing box are manufactured by photosensitive resin printing, and the upper and lower skins are made of shape memory alloy.

[0064] (3) Determine the overall structural dimensions of the filling structure, i.e., the three-dimensional star-shaped negative Poisson's ratio lattice structure, based on the wing's size parameters, and determine reasonable unit cell parameters and array direction;

[0065] (4) The filling structure is composed of a three-dimensional star-shaped negative Poisson's ratio lattice structure. The design of the structural components is mainly divided into two steps: modeling and processing into shape using additive manufacturing technology.

[0066] (5) Modeling: The design of the lattice model consists of two steps: building a star-shaped frame on the skin and connecting the diagonal rods. Star-shaped frame building: three reference planes are established above the wing box, corresponding to the upper skin, middle surface and lower skin of the wing box area respectively. The star-shaped frame is drawn on the reference plane. The star-shaped frame with gradient changes is obtained by adjusting the size of the unit cell offset angle.

[0067] (6) Map the star-shaped frame on the reference plane to the corresponding area inside the wing box to obtain the star-shaped frame curve that is consistent with the change of skin curvature. The unit cell of the star-shaped frame consists of three convex corners and three concave corners.

[0068] (7) Diagonal bracing: The star-shaped frame structure between the upper skin, middle surface and lower skin is connected by diagonal bracing, that is, the convex corner and concave corner of one surface are connected to the concave corner and convex corner of the adjacent surface respectively, thus obtaining a complete lattice-filled structure model.

[0069] (8) Use additive manufacturing technology to process lattice-filled structural parts;

[0070] (9) The leading edge, trailing edge and filling structure of the wing are bonded to the upper skin and lower skin by epoxy resin adhesive (AWG 97033).

[0071] During the conversion of the three-dimensional star-shaped negative Poisson's ratio lattice structure, i.e., the 3D-SAU lattice structure, into a lattice-filled structure that fits the upper and lower skin of the wing, the distance h between two adjacent star-shaped frames changes, denoted as Δh. This causes changes in the dimensions l1 of the diagonal struts and the tilt angle β, denoted as l1' and β', respectively.

[0072]

[0073] Where θ is the offset angle and l is the side length of the unit cell.

[0074] The 3D-SAU lattice-filled structure prepared by the method of the present invention can perfectly fit the wing skin, so that the external load is continuously transferred to the internal lattice-filled structure, effectively reducing stress concentration.

[0075] Control experiment

[0076] To highlight the advantages of the 3D-SAU lattice structure in terms of bending performance, a three-point bending experiment was conducted on a body-centered cubic (BCC) lattice structure and a 3D re-entrant (3D-RE) lattice structure for comparison.

[0077] The lattice structures used in the three-point bend experiment were all manufactured using 3D printing. The printing material selected was CUV9400A photosensitive resin, with a density of 1.11-1.15 g / cm³. 3The parameters of the 3D-SAU unit cell are: rod diameter d = 1.3 mm, side length l = 5.5 mm, and offset angle θ = 45°; the overall dimensions of all lattice specimens are length A = 200 mm, width B = 75 mm, and height C = 11 mm. The specific structures of the 3D-SAU, 3D-RE, and BCC lattice specimens are as follows... Figures 4-6 As shown. The three-point bend test was conducted in accordance with ASTM C393 / C393M-16 standards, and the final force-displacement curve is shown below. Figure 7 As shown in the figure, the curve corresponding to the 3D-SAU lattice is relatively flat, demonstrating its quasi-zero bending stiffness.

[0078] Based on data obtained from the three-point bending test, the bending stiffness K of different lattice structures can be calculated using the following formula. b :

[0079]

[0080] Where L represents the support span of the specimen in the experiment, and γ is the slope corresponding to the linear elastic stage of the specimen. Based on the calculated bending stiffness, the bending compliance S of different lattice structures can be calculated using the following formula. b Used to evaluate the deformation capacity of different lattice structures:

[0081]

[0082] Comparative analysis reveals the following conclusions: Under three-point bending loads, the bending stiffness of the 3D-SAU lattice structure is lower than that of the BCC and 3D-RE lattice structures. Since stiffness and flexibility are inversely related, the lattice structure with lower bending stiffness exhibits better deformation capability; therefore, the 3D-SAU lattice is adopted in the design of flexible deformable wings.

[0083] Selection of offset angle

[0084] To investigate the effect of the offset angle on the deformability of a flexible airfoil, lattice-filled structural specimens with offset angles of 40°, 50°, and an offset angle varying with the airfoil gradient were fabricated. The specific structures of the lattice-filled structural specimens with offset angles of 40° and 50° are shown below. Figure 9 and Figure 10 As shown, the lattice-filled structure specimen with an offset angle varying according to the gradient of the wing is as follows. Figure 8 As shown, in the lattice-filled structure specimen with a random wing gradient, the offset angle is 40° at the front end of the wing box, 50° at the rear end, and uniformly varies with the array direction in the middle, with a variation of 1°. The lattice structures with different offset angles all consist of three columns. The outer two columns contain 12 unit cells, while the middle column consists of 11 unit cells. The overall size of the lattice structure is approximately 115mm × 30mm.

[0085] In the wing deformation performance test, temperature changes were used to control the wing deformation. Due to limitations in the experimental conditions, it was difficult to ensure that the upper and lower shape memory alloy skins deformed synchronously. Therefore, in this experiment, shape memory alloy was only added to the lower skin of the wing.

[0086] The parameters of the prepared wing box specimen are as follows: wing chord length c = 200 mm, leading edge length l L =35mm, trailing edge length l T =48mm, leading edge thickness t L =1.6mm, trailing edge thickness t T =1.6mm, skin thickness t of the upper and lower skin S =0.8mm. The leading edge, trailing edge, and infill lattice of the specimen were all 3D printed from photosensitive resin, and the type of resin was the same as that used for the three-point bend specimen. The lower skin was prepared using a nickel (Ni)-titanium (Ti) based shape memory alloy, and the dimensions of the shape memory alloy lower skin were 135mm × 30mm × 0.8mm. The deformation of the shape memory alloy is mainly affected by temperature. At the low temperature phase of 20℃, its shape is consistent with the lower skin of the wing. As the temperature increases, the skin gradually bends downward, and at 50℃ it transforms into a high temperature phase, at which time it reaches the maximum degree of bending.

[0087] In the experiment, a DH-HG2 industrial digital display hot air gun was used as the heating device to heat the shape memory alloy lower skin. Simultaneously, a TM-902C thermocouple thermometer was used to monitor the skin temperature in real time, maintaining it at 50℃ to ensure maximum bending deformation of the specimen. Furthermore, the morphology of the specimen before and after deformation was recorded using grid coordinate paper. To quantitatively evaluate the deformability of the specimen, six nodes were evenly selected on the shape memory alloy lower skin, with the wing box end selected as the seventh node. The deformability of different specimens was evaluated by measuring the displacement changes at these nodes. The displacements at each node for the three filling methods are shown below. Figure 11 As shown.

[0088] The results show that among the wings filled with 3D-SAU lattice structures, the wing box with an offset angle of 50° exhibits the largest deformation. Compared to the wing boxes with an offset angle of 40° and gradient lattice filling, the displacement at node P7 increases by 20.19% and 12.04%, respectively, indicating that lattice filling with a larger offset angle can provide the wing with stronger deformation capability. Furthermore, comparing the wing boxes with an offset angle of 40° and those with an offset angle varying according to the wing gradient, it was found that the displacement difference at the first three nodes is small, with a maximum of only 0.2 mm, while the displacement difference at the last four nodes is larger, reaching a maximum of 2.2 mm at node P7. This is mainly because the offset angle of the gradient lattice increases sequentially from 40° at the leading edge, resulting in deformation at the first three nodes similar to the 40° offset lattice; as the offset angle increases, the deformation capability of the gradient lattice gradually strengthens, leading to larger displacements at the last four nodes. In addition, after the wing box deforms under load, the internal lattice filling structure converges, and the degree of convergence is positively correlated with the magnitude of the load. When the load is small, the displacement of each node is small, corresponding to cruise mode, with low lattice convergence, high aspect ratio, and strong lift. When the load is large, the displacement of each node is large, corresponding to high-speed flight, with high load, high lattice convergence, low aspect ratio, and low drag. Experimental results show that increasing the offset angle of the 3D-SAU lattice filling structure can enhance the wing's deformability, and this lattice filling structure can be used to achieve adaptive adjustment of the wing. Furthermore, through gradient design, the offset angle gradient can be varied to improve the deformability of a specified area, effectively suppressing flutter wave transmission and meeting more demanding usage requirements.

[0089] Although the above embodiments have been shown and described, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions and variations made to the above embodiments by those skilled in the art are within the protection scope of the present invention.

Claims

1. A flexible deformable airfoil based on a three-dimensional star-shaped negative Poisson's ratio lattice, comprising a supercritical airfoil box, the supercritical airfoil box mainly composed of a leading edge, a trailing edge, an upper skin, and a lower skin, characterized in that, The supercritical wing box is filled with a three-dimensional star-shaped negative Poisson's ratio lattice structure. The three-dimensional star-shaped negative Poisson's ratio lattice structure is composed of three layers of star-shaped frames and two layers of diagonal rods. The offset angle of the unit cell in each star-shaped frame changes in a gradient from the leading edge to the trailing edge. The offset angle of the unit cell located at the leading edge of the wing is smaller than that of the unit cell located at the trailing edge of the wing.

2. The flexible deformable wing based on a three-dimensional star-shaped negative Poisson's ratio lattice as described in claim 1, characterized in that, The offset angle of the unit cell at the leading edge of the wing is 40°, and the offset angle of the unit cell at the trailing edge of the wing is 50°.

3. The flexible deformable wing based on a three-dimensional star-shaped negative Poisson's ratio lattice according to claim 1, characterized in that, The star-shaped frame comprises three columns of cells, with the outer two columns containing one more cell than the middle column.

4. The flexible deformable wing based on a three-dimensional star-shaped negative Poisson's ratio lattice according to claim 3, characterized in that, The two outer star-shaped frames are composed of 12 units connected in sequence, while the middle star-shaped frame is composed of 11 units connected in sequence.

5. The flexible deformable wing based on a three-dimensional star-shaped negative Poisson's ratio lattice according to claim 1, characterized in that, The unit cell is formed by alternating three convex angles and three concave angles. Each convex angle has two concave angles on both sides, and each concave angle has two convex angles on both sides. The convex angles and concave angles between two adjacent unit cells are connected.

6. The flexible deformable wing based on a three-dimensional star-shaped negative Poisson's ratio lattice according to claim 1, characterized in that, In the three-dimensional star-shaped negative Poisson's ratio lattice structure, from the upper skin to the lower skin, there are star-shaped frames, diagonal bars, star-shaped frames, diagonal bars, and star-shaped frames in sequence. The convex angle of the unit cell in each star-shaped frame is connected to the concave angle of the corresponding unit cell in the adjacent star-shaped frame, and the concave angle in each star-shaped frame is connected to the convex angle of the corresponding unit cell in the adjacent star-shaped frame.

7. The flexible deformable wing based on a three-dimensional star-shaped negative Poisson's ratio lattice according to claim 1, characterized in that, The change in the offset angle in the star-shaped frame is Δθ: In the formula, θ α and θ β denoted by the offset angles at both ends of the star-shaped frame, and 'a' represents the number of times the lattice unit cell array is arranged in direction one.

8. A method for fabricating a flexible deformable airfoil based on a three-dimensional star-shaped negative Poisson's ratio lattice according to any one of claims 1-7, characterized in that, Includes the following steps: (1) Select the airfoil and use the supercritical airfoil NASA SC(2)-0706 as the filling object; (2) Establish a three-dimensional model of the wing box. The leading and trailing edges of the wing box are manufactured by photosensitive resin printing, and the upper and lower skins are made of shape memory alloy. (3) Determine the overall structural dimensions of the filling structure, i.e., the three-dimensional star-shaped negative Poisson's ratio lattice structure, based on the wing's size parameters, and determine reasonable unit cell parameters and array direction; (4) The filling structure is composed of a three-dimensional star-shaped negative Poisson's ratio lattice structure. The design of the structural components is mainly divided into two steps: modeling and processing into shape using additive manufacturing technology. (5) Modeling: The design of the lattice model consists of two steps: building a star-shaped frame on the skin and connecting the diagonal rods. Star-shaped frame building: three reference planes are established above the wing box, corresponding to the upper skin, middle surface and lower skin of the wing box area respectively. The star-shaped frame is drawn on the reference plane. The star-shaped frame with gradient changes is obtained by adjusting the size of the unit cell offset angle. (6) Map the star-shaped frame on the reference plane to the corresponding area inside the wing box to obtain the star-shaped frame curve that is consistent with the change of skin curvature. The unit cell of the star-shaped frame consists of three convex corners and three concave corners. (7) Diagonal bracing: Connect the star-shaped frame structure between the upper skin, middle surface and lower skin with diagonal bracing, that is, connect the convex and concave corners of one surface with the concave and convex corners of the adjacent surface to obtain a complete lattice-filled structure model. (8) Use additive manufacturing technology to process lattice-filled structural parts; (9) The leading edge, trailing edge and filling structure of the wing are bonded to the upper skin and lower skin by epoxy resin adhesive (AWG 97033).

9. The method for fabricating a flexible deformable airfoil based on a three-dimensional star-shaped negative Poisson's ratio lattice according to claim 8, characterized in that, During the conversion of the three-dimensional star-shaped negative Poisson's ratio lattice structure into a lattice-filled structure that fits the upper and lower skins of the wing, the distance h between two adjacent star-shaped frames changes, denoted as Δh. This causes changes in the dimensions l1 and tilt angle β of the diagonal struts, denoted as l1' and β'. Where θ is the offset angle and l is the side length of the unit cell.

10. The method for fabricating a flexible deformable airfoil based on a three-dimensional star-shaped negative Poisson's ratio lattice according to claim 8, characterized in that, The offset angle refers to 1 / 2 of the supplementary angle of the convex angle. The gradient change of the offset angle means that a linear gradient value is preset so that the size of the offset angle of the lattice filling structure changes equally from the leading edge to the trailing edge, that is, the offset angle change value is the same for any two adjacent unit cells.

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