Flexible composite material skin and preparation method thereof

Abstract

The invention provides a flexible composite material skin and a preparation method thereof, and the preparation method comprises the following steps: according to the deformation amount and load required by the skin, simulating, calculating and designing the structure of a zero / negative Poisson's ratio skeleton, preparing the zero / negative Poisson's ratio skeleton, and according to the deformation amount range required by the skin, preparing the flexible composite material skin. Simulating, calculating and designing a preset filling area and a preset total thickness of the flexible base material; the zero / negative Poisson's ratio framework is placed in the filling mold, and the handle is clamped in the first clamping groove and the second clamping groove so that the zero / negative Poisson's ratio framework can be suspended; the forming cavity is filled with the flexible base material according to a preset filling area and a preset total thickness, and the flexible base material and the zero / negative Poisson's ratio framework are connected; and curing to obtain the flexible composite material skin. The filling mold is used for filling the flexible base material, the use amount of the flexible base material can be controlled, the deformation problem of a reinforcing material structure in the compounding process is avoided, the operation process is simple, and the forming quality is good.

Description

Technical Field

[0001] This invention relates to the field of composite materials technology, and more specifically, to a flexible composite material skin and its preparation method. Background Technology

[0002] Variability technology is one of the characteristics of future fighter jets. To improve aircraft maneuverability while ensuring stealth and aerodynamic performance, it is necessary to achieve adaptive continuous variability of the wing, which is a key technology for the high performance of future variable aircraft. Flexible skin can undergo large deformations such as stretching in the in-plane (XY direction) under external driving conditions, and can undergo seamless, continuous, and smooth deformation during aircraft flight. It has high structural stiffness in the out-of-plane (Z direction) to withstand aerodynamic loads during flight, and is a key material for realizing deformable wings.

[0003] To achieve the performance requirements of large in-plane deformation and high out-of-plane load-bearing capacity, flexible skins typically consist of an internal hybrid composite material structure and an external elastic surface layer. The elastic surface layer primarily maintains the continuous, seamless, and smooth tensile / bending deformation of the flexible skin and provides some aerodynamic load-bearing capabilities. There are two main approaches to achieving elastic surfaces: material-based elastic deformation and structure-based elastic surfaces. While elastic surfaces based on the elastic deformation of the flexible material itself offer significant advantages in deformation capacity, they suffer from low stiffness and insufficient aerodynamic load-bearing capacity. Furthermore, precise surface deformation control, structural fatigue, and aeroelasticity issues make them difficult to meet the requirements of engineering applications. Rigid-flexible coupling structures based on flexible matrix materials and internal zero / negative Poisson's degree reinforcement materials can better coordinate the contradiction between deformation and load-bearing capabilities and have become a trend in the design of flexible skin elastic surfaces.

[0004] Currently, flexible skin elastic surfaces composed of reinforcing material skeletons and flexible matrix materials have advantages such as large deformation, fatigue resistance, and zero Poisson's ratio. However, due to the difficulty in ensuring that the reinforcing material skeleton is located in the center of the elastic surface during the molding process, when large deformation occurs, it will bulge or sink to one side, causing the surface to undulate, which has an adverse effect on stealth performance. Summary of the Invention

[0005] (a) Technical problems to be solved The technical problem to be solved by the present invention is that it is difficult to ensure that the reinforcing material skeleton is located in the center of the elastic surface layer in the existing flexible composite material skin molding process.

[0006] (II) Technical Solution To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a method for preparing a flexible composite material skin, which uses a filling mold for molding. The filling mold includes a lower cover plate, a lower pad frame, an upper pad frame, and an upper cover plate stacked sequentially from bottom to top. The lower cover plate, lower pad frame, upper pad frame, and upper cover plate together form a molding cavity. The lower pad frame is provided with a first slot, and the upper pad frame is provided with a second slot. The preparation method includes the following steps: Based on the required deformation and load-bearing capacity of the skin, the structure of the zero / negative Poisson's ratio skeleton is simulated, calculated, and designed, and the zero / negative Poisson's ratio skeleton is fabricated. The zero / negative Poisson's ratio skeleton has handles at both ends. Based on the required deformation range of the skin, the preset filling area and preset total thickness of the flexible matrix material are simulated, calculated, and designed. The zero / negative Poisson's ratio skeleton is placed in the filling mold, and the handle is engaged in the first slot and the second slot, so that the zero / negative Poisson's ratio skeleton is suspended in the air. The flexible matrix material is filled into the molding cavity according to the preset filling area and preset total thickness, and the flexible matrix material and the zero / negative Poisson's ratio skeleton are connected. After curing, a flexible composite material skin is obtained.

[0007] Preferably, the lower cover plate has a first protrusion, which is engaged with the lower pad frame.

[0008] Preferably, the distance between the surface of the first protrusion and the bottom surface of the upper cover plate is equal to the preset total thickness.

[0009] Secondly, the present invention also provides a flexible composite material skin, prepared using the aforementioned preparation method, wherein the flexible composite material skin comprises: Zero / negative Poisson's ratio skeleton with multiple filling regions; A flexible matrix material is disposed within the filling area and encapsulates the zero / negative Poisson's ratio skeleton.

[0010] Preferably, the zero / negative Poisson's ratio skeleton includes multiple support rods and multiple tensile units. The multiple support rods are spaced apart along the X direction, and tensile units are connected between adjacent support rods. The multiple tensile units extend spaced apart along the Y direction.

[0011] Preferably, the tensile unit includes a first tensile plate and a second tensile plate, wherein the first tensile plate and the second tensile plate have the same structure and are mirror images of each other with the X-axis as the axis of symmetry.

[0012] Preferably, the shape of the first tensile plate includes Ω-shaped, V-shaped, cosine curve-shaped, U-shaped, T-shaped, trapezoidal, L-shaped, and rectangular.

[0013] Preferably, the flexible matrix material fills all the space within the filling area, or the flexible matrix material fills a portion of the space within the filling area.

[0014] Preferably, the flexible matrix material includes at least one of polyurethane resin, organic fluorine resin, organic silicone rubber, and hydrogenated nitrile butadiene rubber.

[0015] Preferably, the material of the zero / negative Poisson's ratio skeleton includes at least one of carbon fiber / polyetheretherketone, polyetheretherketone, polyurethane, carbon fiber / polyurethane, superelastic shape memory alloy, and superelastic titanium alloy.

[0016] (III) Beneficial Effects The above-described technical solution of the present invention has at least the following advantages: 1. In this invention, the zero / negative Poisson's ratio skeleton has the characteristics of normal load bearing and large in-plane deformation, so that the skin has the ability to deform. Filling the zero / negative Poisson's ratio skeleton with a flexible matrix material can make the flexible composite material skin maintain the continuity, smoothness and no unevenness of the surface during the deformation process, thereby improving the stealth performance and aerodynamic performance of the corresponding aircraft structure made with the flexible composite material skin.

[0017] 2. In this invention, by designing the molding die, the zero / negative Poisson's ratio skeleton can be ensured to be in the center of the filled flexible matrix material, which effectively solves the problem of surface undulation in the surface layer during the deformation process of the flexible skin. This achieves a continuous and smooth surface of the flexible skin during the deformation process, improves stealth performance, and can meet the specific requirements of variant structures for flexible skin.

[0018] 3. In this invention, by using a filling mold to fill the flexible matrix material, the amount of flexible matrix material can be controlled, avoiding the deformation problem of the reinforcing material structure during the composite process. The operation process is simple and the molding quality is good. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the flexible composite material skin provided in an embodiment of the present invention.

[0021] Figure 2 This is a schematic diagram of the filling mold provided in an embodiment of the present invention.

[0022] Figure 3This is one of the structural schematic diagrams of the zero / negative Poisson's ratio skeleton provided in the embodiments of the present invention.

[0023] Figure 4 This is the second schematic diagram of the zero / negative Poisson's ratio skeleton provided in the embodiment of the present invention.

[0024] Figure 5 This is the third schematic diagram of the zero / negative Poisson's ratio skeleton provided in the embodiments of the present invention.

[0025] Figure 6 This is the fourth structural schematic diagram of the zero / negative Poisson's ratio skeleton provided in the embodiments of the present invention.

[0026] The labels for the attached figures are as follows: 1. Zero / negative Poisson's ratio skeleton; 2. Flexible matrix material; 3. Handle; 11. Filling area; 12. Support rod; 13. Tensile unit; 131. First tensile plate; 132. Second tensile plate; 100. Filling mold; 110. Lower cover plate; 120. Lower pad frame; 130. Upper pad frame; 140. Upper cover plate; 150. First slot; 160. Second slot; 170. First protrusion. Detailed Implementation

[0027] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0028] It should be noted that when a component is referred to as "fixed to" or "set on" another component, it can be located directly on or indirectly on the other component. When a component is referred to as "connected to" another component, it can be directly or indirectly connected to the other component.

[0029] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention, and do not indicate that the device or element must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0030] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating relative importance or the number of technical features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified. The specific implementation of this invention will be described in more detail below with reference to specific embodiments: like Figure 1 and Figure 2 As shown, this embodiment of the invention provides a flexible composite material skin, which is formed using a filling mold 100. The filling mold 100 includes a lower cover plate 110, a lower pad frame 120, an upper pad frame 130, and an upper cover plate 140 stacked sequentially from bottom to top. The lower cover plate 110, lower pad frame 120, upper pad frame 130, and upper cover plate 140 together form a molding cavity. The lower pad frame 120 is provided with a first slot 150, and the upper pad frame 130 is provided with a second slot 160. The preparation method includes the following steps: Based on the required deformation and load-bearing capacity of the skin, the structure of the zero / negative Poisson's ratio skeleton 1 is simulated, calculated, and designed, and the zero / negative Poisson's ratio skeleton 1 is prepared. The zero / negative Poisson's ratio skeleton 1 has handles 3 at both ends. Based on the required deformation range of the skin, the preset filling area and preset total thickness of the flexible matrix material 2 are simulated, calculated, and designed. The zero / negative Poisson's ratio skeleton 1 is placed inside the filling mold 100, and the handle 3 is engaged in the first slot 150 and the second slot 160, so that the zero / negative Poisson's ratio skeleton 1 is suspended in the air; specifically, the zero / negative Poisson's ratio skeleton 1 is placed inside the filling mold 100; specifically, the filling mold can realize the closure of a portion of the space inside the filling area 11, so that the area of ​​the closed area inside the filling area 11 matches the preset filling ratio of the flexible matrix material 2, thereby facilitating the filling of the flexible matrix material 2 and preventing the zero / negative Poisson's ratio skeleton 1 from deforming during the molding process.

[0031] The flexible matrix material 2 is filled into the molding cavity according to the preset filling area and preset total thickness, and the flexible matrix material 2 and the zero / negative Poisson's ratio skeleton 1 are connected; specifically, the flexible matrix material 2 and the inner wall of the zero / negative Poisson's ratio skeleton 1 are connected by a highly flexible adhesive.

[0032] After curing, a flexible composite material skin is obtained.

[0033] Furthermore, the lower cover plate 110 is provided with a first protrusion 170, which is engaged within the lower pad frame 120. The distance between the surface of the first protrusion 170 and the bottom surface of the upper cover plate 140 is equal to the preset total thickness. By setting the first protrusion 170, the position of the lower pad frame 120 can be limited.

[0034] In one embodiment, the zero / negative Poisson's ratio frame 1 includes multiple support rods 12 and multiple tensile units 13. The support rods 12 are spaced apart along the X-direction, and tensile units 13 connect adjacent support rods 12. The tensile units 13 extend spaced apart along the Y-direction. The zero / negative Poisson's ratio frame 1 can achieve load-bearing function in the normal direction and also achieve large in-plane deformation. The zero / negative Poisson's ratio frame 1 has a zero Poisson's ratio structure in the plane, which can ensure that the dimension in the X direction remains unchanged when deformed in the Y-direction. The skin made using this zero / negative Poisson's ratio frame 1 has the characteristics of load-bearing in the normal direction and large in-plane deformation, so that the skin has deformability and the aspect ratio of the wing covering the skin remains unchanged when deformed, ensuring its aerodynamic performance and stealth performance.

[0035] In one embodiment, the tensile unit 13 includes a first tensile plate 131 and a second tensile plate 132. The first tensile plate 131 and the second tensile plate 132 have the same structure and are mirror images of each other with the X-axis as the axis of symmetry. By mirroring the first tensile plate 131 and the second tensile plate 132 with the axis of symmetry, the tensile unit 13 can achieve the function of keeping the X-axis dimension unchanged when deforming in the Y-axis direction in the plane.

[0036] In one embodiment, the shape of the first tensile plate 131 includes Ω-shaped, V-shaped, cosine curve-shaped, U-shaped, T-shaped, trapezoidal, L-shaped, and rectangular. The shape of the first tensile plate 131 is the same as the shape of the second tensile plate 132. Specifically, the specific shapes of the first tensile plate 131 and the second tensile plate 132 can be determined according to the specific design requirements of the skin structure, obtained through topology optimization. Figure 3 As shown, the zero / negative Poisson's ratio skeleton 1 is a skeleton with an Ω-shaped first tensile plate 131; as Figure 4 As shown, the zero / negative Poisson's ratio skeleton 1 is a skeleton with a V-shaped first tensile plate 131; as Figure 5 As shown, the zero / negative Poisson's ratio skeleton 1 is a skeleton with a trapezoidal first tensile plate 131; as Figure 6 As shown, the zero / negative Poisson's ratio skeleton 1 is a skeleton with a rectangular first tensile plate 131.

[0037] In one embodiment, the flexible substrate material 2 fills all the space within the filling region 11, or the flexible substrate material 2 fills a portion of the space within the filling region 11. For example... Figure 1 The image shows a portion of the space within the filled area 11, filled by the flexible matrix material 2. Figure 2The diagram shows the entire space within the filled area 11 filled by the flexible substrate material 2. Specifically, the required filling ratio of the flexible substrate material 2 can be simulated and calculated based on the range of deformation required for the final skin design. The filled area 11 is then filled according to this ratio. By utilizing the tensile effect of the flexible substrate material 2 during deformation, the surface unevenness problem existing in the deformation process of the current flexible skin can be effectively solved.

[0038] In one embodiment, the flexible matrix material 2 comprises at least one of polyurethane resin, fluorine resin, silicone rubber, and hydrogenated nitrile butadiene rubber.

[0039] In one embodiment, the zero / negative Poisson's ratio skeleton 1 is made of a high-performance thermoplastic material and its modifiers and a superelastic lightweight metal material. The high-performance thermoplastic material and its modifiers include at least one of carbon fiber / polyetheretherketone (CF / PEEK), polyetheretherketone (PEEK), polyurethane (PU), and carbon fiber / polyurethane (CF / PU). The superelastic lightweight metal material includes at least one of superelastic shape memory alloys and superelastic titanium alloys.

[0040] The following is a specific implementation method provided in this application: First, a zero / negative Poisson's ratio skeleton 1 with a first tensile plate 131 and a second tensile plate 132 in a cosine curve shape was 3D printed using CF / PEEK material. This skeleton 1 was then placed in a filling mold, and a polyurethane primer was applied to the inner wall of the skeleton 1. A flexible matrix material 2 (specifically silicone rubber) was then filled into the filling area 11 of the skeleton 1. The flexible matrix material 2 was connected to the inner wall of the skeleton 1 using a highly flexible adhesive. After curing, the skeleton was removed to obtain a flexible composite material skin. Testing showed that the in-plane tensile deformation of this flexible composite material skin reached 30%, and the skin could achieve seamless, continuous, and smooth deformation, meeting the aerodynamic and stealth performance requirements of the corresponding structure.

[0041] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method of making a flexible composite material skin, characterized in that, The molding is performed by using a filling mold, the filling mold comprises a lower cover plate, a lower pad frame, an upper pad frame and an upper cover plate which are sequentially stacked from bottom to top, the lower cover plate, the lower pad frame, the upper pad frame and the upper cover plate jointly form a molding cavity, the lower pad frame is provided with a first clamping groove, the upper pad frame is provided with a second clamping groove, and the preparation method comprises the following steps: According to the deformation and load required by the skin, the structure of the zero / negative Poisson's ratio skeleton is simulated and designed, and the zero / negative Poisson's ratio skeleton is prepared, the two ends of the zero / negative Poisson's ratio skeleton are provided with handles, according to the deformation range required by the skin, the preset filling area and the preset total thickness of the flexible matrix material are simulated and designed; The zero / negative Poisson's ratio skeleton is placed in the filling mold, and the handles are clamped in the first clamping groove and the second clamping groove, so that the zero / negative Poisson's ratio skeleton is suspended; The flexible matrix material is filled in the molding cavity according to the preset filling area and the preset total thickness, and the flexible matrix material and the zero / negative Poisson's ratio skeleton are connected. After curing, the flexible composite skin is obtained.

2. The method of making a flexible composite skin of claim 1, wherein, The lower cover plate is provided with a first protrusion, and the first protrusion is clamped in the lower pad frame.

3. The method of making a flexible composite skin of claim 2, wherein, The distance between the surface of the first protrusion and the bottom surface of the upper cover plate is equal to the preset total thickness.

4. A flexible composite material skin characterized by, The flexible composite skin is prepared by using the preparation method of any one of claims 1 to 3, and the flexible composite skin comprises: The zero / negative Poisson's ratio skeleton has a plurality of filling areas. The flexible matrix material is arranged in the filling area and wraps the zero / negative Poisson's ratio skeleton.

5. The flexible composite skin of claim 4, wherein, The zero / negative Poisson's ratio skeleton comprises a plurality of support rods and a plurality of tensile units, the plurality of support rods are arranged at intervals along the X direction, and the tensile unit is connected between the two adjacent support rods, and the plurality of tensile units extend at intervals along the Y direction.

6. The flexible composite skin of claim 5, wherein, The tensile unit comprises a first tensile plate and a second tensile plate, the first tensile plate and the second tensile plate are the same in structure and are mirror image arranged with the X direction as the symmetry axis.

7. The flexible composite skin of claim 6, wherein The shape of the first tensile plate comprises Ω, V, cosine curve, U, T, trapezoid, L and rectangle.

8. The flexible composite skin of claim 4, wherein, The flexible matrix material fills all the space in the filling area, or the flexible matrix material fills part of the space in the filling area.

9. The flexible composite skin of claim 4, wherein, The flexible matrix material comprises at least one of polyurethane resin, organic fluorine resin, silicone rubber and hydrogenated butyronitrile.

10. The flexible composite skin of claim 4, wherein, The material of the zero / negative Poisson's ratio skeleton comprises at least one of carbon fiber / polyether ether ketone, polyether ether ketone, polyurethane, carbon fiber / polyurethane, super-elastic shape memory alloy and super-elastic titanium alloy.

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