A multi-tooth mechanical metamaterial with adjustable stiffness, preparation method thereof, and application thereof

Abstract

A multi-tooth mechanical metamaterial with adjustable stiffness, and its preparation method and application. The present invention belongs to the field of mechanical metamaterials. In order to overcome the shortcomings of existing fixed stiffness structures. The metamaterial unit cell of the present invention is assembled from an inner and outer barrel. The variable stiffness shell is the main load-bearing structure of the inner and outer barrels. In order to facilitate the assembly between the unit cells, a first limiting ring, a second limiting ring and a limiting block are designed on the inner and outer barrels respectively. The function of the first limiting ring and the second limiting ring is to "clamp" when adjacent unit cells are connected to prevent different unit cells from detaching. The limiting block plays the role of transferring the load between adjacent unit cells. By making the inner and outer barrels of the unit cell rotate relative to each other, the fan-shaped teeth of different sizes are brought into contact with each other, thereby realizing the stiffness adjustment of the metamaterial. The multi-tooth mechanical metamaterial proposed by the present invention can be used in the joint transmission of flexible robots, adaptive adjustment of mechanical arms and the manufacture of aircraft landing gear.

Description

Technical Field

[0001] The present invention belongs to the field of mechanical metamaterials, and in particular relates to a multi-tooth mechanical metamaterial with adjustable stiffness, a preparation method thereof, and an application thereof. Background Art

[0002] In modern engineering, traditional fixed-stiffness structures struggle to meet the demands of high performance, multifunctionality, and dynamic adaptability. Variable-stiffness structures, as an innovative structural design concept, are becoming a research hotspot, demonstrating unique advantages and enormous application potential in numerous fields. In practical engineering applications, the loads borne by a structure are often not uniform and constant. For example, in aerospace, the magnitude and direction of loads such as aerodynamic forces, gravity, and inertia experienced by an aircraft during takeoff, flight, and landing vary significantly. Variable-stiffness structures can adjust their stiffness in real time based on varying load conditions. They increase stiffness under high loads to ensure structural strength and stability, while appropriately reducing stiffness under low loads to avoid stress concentration or other adverse effects caused by excessive rigidity, thereby improving the reliability and durability of the structure throughout its service life. Furthermore, variable-stiffness structures can play a key role in energy transmission and conversion systems, such as the joint transmission of flexible robots. By adjusting stiffness, the path and method of force transmission can be optimized, reducing energy loss and waste during transmission. For example, a variable stiffness structure is used at the joints of a flexible robot. When performing different action tasks, the joint stiffness is adjusted according to the required force and motion characteristics. This can not only ensure the accuracy and flexibility of the action, but also reduce the consumption of driving energy and improve the overall energy utilization efficiency of the robot. Summary of the Invention

[0003] In order to overcome the shortcomings of existing fixed stiffness structures, the present invention provides a multi-tooth mechanical metamaterial with adjustable stiffness, a preparation method thereof, and an application thereof.

[0004] One of the objectives of the present invention is to provide a multi-tooth mechanical metamaterial with adjustable stiffness, wherein the metamaterial comprises a plurality of unit cells, each unit cell being formed by nesting two inner and outer barrel-shaped members, wherein the inner barrel and the outer barrel are both integral structures;

[0005] The inner barrel includes a first barrel body, a first variable stiffness shell, a plurality of limiting posts and a first limiting ring. The first variable stiffness shell is located at the bottom of the inner barrel. The limiting posts are evenly distributed on the outer wall of the first barrel body and are limited around the outer wall of the barrel top of the first barrel body.

[0006] The outer barrel includes a second barrel body, a second variable stiffness shell, a plurality of limiting grooves, a second limiting ring and a limiting block. The second variable stiffness shell is provided at the lower part of the outer barrel. The limiting grooves are evenly distributed on the inner wall of the second barrel body and are adapted to the limiting posts. The second limiting member is arranged around the inner wall of the second barrel body and is arranged between the second variable stiffness shell and the bottom end of the second barrel body. The limiting block is arranged around the inner wall of the second barrel body and is arranged between the second limiting ring and the second variable stiffness shell.

[0007] The first variable stiffness shell is composed of an outer circular ring, a central circular hole, and an even number of sector teeth between the circular ring and the circular hole. Every two sector teeth are symmetrically arranged. The sector teeth form a preset angle α with the horizontal plane where the outer circumference of the first variable stiffness shell is located, so that the sector teeth are warped toward the outside of the inner barrel. At least one group of adjacent sector teeth has different dimensions, and the different dimensions refer to at least one of the central angle θ and the tooth thickness t of the sector teeth.

[0008] The second variable stiffness shell in the unit cell has the same structure as the first variable stiffness shell, and the sector teeth are warped in opposite directions. Specifically, the second variable stiffness shell is composed of an outer circular ring, a central circular hole, and an even number of sector teeth between the circular ring and the circular hole. Every two sector teeth are symmetrically arranged. The sector teeth and the horizontal plane where the outer circumference of the second variable stiffness shell is located are preset at an angle α, so that the sector teeth warp inward of the outer barrel. At least one group of adjacent sector teeth has different size specifications, and the different size refers to at least one of the central angle θ and the tooth thickness t of the sector teeth.

[0009] Further limit, the number of pairs of sector teeth N p ≥2 pairs.

[0010] It is further defined that α=10-30°.

[0011] Further definition: the tooth thickness t of the sector tooth is less than the ring thickness t B .

[0012] It is further defined that the central angle θ of the sector tooth satisfies 0<θ≤120° / N p .

[0013] Further limit, when N p When the number of pairs is greater than 2, at most one set of sector teeth thickness t of the first variable stiffness shell and the second variable stiffness shell is the same, and the difference in thickness between the inner and outer sector teeth is between 0.1-0.5 mm.

[0014] It is further defined that several unit cells are connected in series and stacked axially, wherein the first limiting ring of one unit cell is adapted to the gap formed between the second limiting ring and the limiting block of another unit cell, and the end face of the barrel wall of the first barrel body abuts against the side wall of the limiting block.

[0015] It is further defined that a number of unit cells are connected in parallel, the unit cells are tiled, and are fixed by an external mechanism.

[0016] It is further defined that the metamaterial is made of photosensitive resin.

[0017] Furthermore, the photosensitive resin includes tough resin, biocompatible resin and flexible resin.

[0018] A second object of the present invention is to provide a method for preparing a multi-tooth mechanical metamaterial with adjustable stiffness, wherein:

[0019] Using the stereolithography method, three-dimensional modeling is first performed, then slicing is performed, and finally 3D printing is performed. After printing is completed, secondary curing is performed.

[0020] A third object of the present invention is to provide a method for adjusting the stiffness of the above-mentioned multi-tooth mechanical metamaterial with adjustable stiffness, wherein the method adjusts the stiffness of the metamaterial by causing the inner and outer barrels of the unit cell to rotate relative to each other so that the fan-shaped teeth of different sizes come into contact with each other.

[0021] Further defined, each rotation angle φ is 180° / N p An integer multiple of .

[0022] A fourth object of the present invention is to provide a multi-tooth mechanical metamaterial with adjustable stiffness for use in aerospace vehicles.

[0023] A fifth object of the present invention is to provide a multi-tooth mechanical metamaterial with adjustable stiffness for use in joint transmission and adaptive adjustment of a flexible robot's robotic arm.

[0024] Compared with the prior art, the present invention has the following significant effects:

[0025] The present invention provides a multi-tooth mechanical metamaterial based on rotational drive, which realizes a wide range of adjustment of structural stiffness. The multi-tooth structural unit cell is assembled from an inner and outer barrel. Since the contact between different teeth is small during compression, in order to limit the displacement of the structure, limit posts 1-3 are set on the inner barrel, and limit grooves 2-3 are designed to match the outer barrel. In particular, the limit posts 1-3 and the limit grooves 2-3 can also play a role in precise positioning when rotating to adjust the structural stiffness. Among them, the variable stiffness shell is the main load-bearing structure of the inner and outer barrels. In order to facilitate the assembly between the unit cells, the first limit ring, the second limit ring and the limit block are respectively designed on the inner and outer barrels. The function of the first limit ring and the second limit ring is to "clamp" when adjacent unit cells are connected to prevent different unit cells from detaching. The limit block plays the role of transferring the load between adjacent unit cells. By making the inner and outer barrels of the unit cell rotate relative to each other, the fan-shaped teeth of different sizes are brought into contact with each other, thereby realizing the stiffness adjustment of the metamaterial. For a tooth pair number of N p For the variable stiffness shell, the rotation angle φ is 180 / N. pAn integer multiple of .

[0026] The present invention achieves stiffness decoupling of truncated conical shell structures through structural design, breaking the problem that the performance of traditional structures is difficult to change once they are manufactured, improving application potential, and providing a possible way to realize stiffness adaptive structures. The multi-tooth configuration of the present invention has a simple structure and is easy to process, and can be mass-produced through stereolithography molding technology. At the same time, it has excellent adjustable stiffness capabilities, and through reasonable design of geometric dimensions, customized production of structures with specific stiffness changes can be achieved. In addition, the mechanical metamaterial of the present invention has the advantages of small size, simple structure, light weight, easy assembly, and adjustable stiffness, and can well match different working conditions. The multi-tooth mechanical metamaterial proposed in the present invention can be used for joint transmission of flexible robots, adaptive adjustment of robotic arms, and landing gear of aircraft. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of the structure of a unit cell of a multi-tooth mechanical metamaterial with adjustable stiffness according to the present invention;

[0028] Figure 2 for Figure 1 Schematic diagram of the inverted structure of the barrel within a single cell;

[0029] Figure 3 This is a schematic diagram of the internal structure of the inner and outer barrels of a unit cell of a multi-tooth mechanical metamaterial with adjustable stiffness according to the present invention;

[0030] Figure 4 A top view of the first variable stiffness shell in the unit cell of the multi-tooth mechanical metamaterial with adjustable stiffness according to the present invention;

[0031] Figure 5 This is a front view of the first variable stiffness shell in the unit cell of the multi-tooth mechanical metamaterial with adjustable stiffness of the present invention;

[0032] Figure 6 A schematic diagram of the structure of two unit cells of the multi-tooth mechanical metamaterial with adjustable stiffness connected in series according to the present invention;

[0033] Figure 7 for Figure 6 A local magnified view of the marked area;

[0034] Figure 8 N in Example 1 p =2 for the quasi-static compression response curves of the inner and outer barrels of a single unit cell at different relative rotation angles;

[0035] Figure 9 The two N in series in Example 1 p =2 when the inner and outer barrels of the unit cell have different relative rotation angles;

[0036] Figure 10 The two N in parallel in Example 1 p =2 when the inner and outer barrels of the unit cell have different relative rotation angles;

[0037] Figure 11 In Example 1, N p =3 for the quasi-static compression response curves of the inner and outer barrels of a single unit cell at different relative rotation angles;

[0038] In the figure, 1-1 is the first barrel body, 1-2 is the first variable stiffness shell, 1-3 is the limiting column, 1-4 is the first limiting ring, 2-1 is the second barrel body, 2-2 is the second variable stiffness shell, 2-3 is the limiting groove, 2-4 is the second limiting ring, 2-5 is the limiting block, 1-2-1 is the outer peripheral ring of the first variable stiffness shell, and 1-2-2 is the sector tooth of the first variable stiffness shell;

[0039] Figure 8 and Figure 11 The midpoint line is the simulation result, and the area is the experimental test result;

[0040] Figure 9 and Figure 10 Here, K0L0 means that the relative rotation angle φ of the inner and outer barrels of the two unit cells is 0°, K0L90 means that the relative rotation angle φ of the inner and outer barrels of one unit cell is 0°, and the relative rotation angle φ of the inner and outer barrels of the other unit cell is 90°, and K90L90 means that the relative rotation angle φ of the inner and outer barrels of the two unit cells is 90°. DETAILED DESCRIPTION

[0041] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0042] In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0043] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0044] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0045] The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, methods, and instruments used are conventional in the art and can be obtained commercially by those skilled in the art unless otherwise specified.

[0046] As used in the following examples, the terms "comprising," "including," "having," "containing," or any other variations thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0047] The indefinite articles "a" and "an" before the elements or components of the present invention do not limit the quantity requirement (i.e. the number of times they appear). Therefore, "a" or "an" should be interpreted as including one or at least one, and elements or components in the singular also include plural forms, unless the quantity clearly refers to only the singular form.

[0048] The term "one embodiment" or "embodiment" of the present invention refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, nor does it necessarily refer to a separate or selective embodiment that is mutually exclusive of other embodiments.

[0049] The endpoints of the ranges and any values ​​disclosed in the present invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed herein.

[0050] Example 1: The multi-tooth mechanical metamaterial with adjustable stiffness in this embodiment includes two unit cells, the unit cell (see Figure 1-3 ) is composed of two barrel-shaped parts, the inner and outer barrels are an integral structure;

[0051] Inner barrel (see Figure 1-3 ) includes a first barrel body 1-1, a first variable stiffness shell 1-2, four limiting posts 1-3 and a first limiting ring 1-4, the first variable stiffness shell 1-2 is located at the bottom of the inner barrel, the limiting posts 1-3 are evenly distributed on the outer wall of the first barrel body 1-1, and the limiting ring 1-4 is arranged around the outer wall of the top of the first barrel body 1-1; wherein the inner diameter of the first barrel body 1-1 is 40mm, the outer diameter is 43mm, and the height is 47mm. The length of the limiting posts 1-3 is L R1 =25mm;

[0052] The outer barrel includes a second barrel body 2-1, a second variable stiffness shell 2-2, four limiting grooves 2-3, a second limiting ring 2-4 and a limiting block 2-5. The second variable stiffness shell 2-2 is arranged at the lower part of the outer barrel. The limiting grooves 2-3 are evenly distributed on the inner wall of the second barrel body 2-1 and are adapted to the limiting columns 1-3. The second limiting ring 2-4 is arranged around the inner wall of the second barrel body 2-1 and is arranged between the second variable stiffness shell 2-2 and the bottom end of the second barrel body 2-1. The limiting block 2-5 is arranged around the inner wall of the second barrel body 2-1 and is arranged between the second limiting ring 2-4 and the second variable stiffness shell 2-2. Among them, the inner diameter of the second barrel body 2-1 is 44mm, the outer diameter is 47mm, and the height is 60mm. The second variable stiffness shell 2-2 is 25mm away from the bottom end of the second barrel body 2-1. The length of the limiting groove 2-3 is L R2 =25mm;

[0053] The first variable stiffness shell 1-2 (see Figure 4-5 ) consists of an outer circular ring 1-2-1, a circular hole in the center, and four (two pairs) sector teeth 1-2-2 between the circular ring and the circular hole. Every two sector teeth are symmetrically arranged. The sector teeth 1-2-2 and the horizontal plane where the outer circumference of the first variable stiffness shell 1-2 are located are preset at an angle α, so that the sector teeth are warped toward the outside of the barrel of the inner barrel. Adjacent sector teeth have different sizes and specifications. The different sizes refer to at least one of the central angle θ and tooth thickness t of the sector teeth. Among them, the radius R of the first variable stiffness shell 1-2 is B1 =40mm, width L of ring 1-2-1 B1 =10mm, thickness t of ring 1-2-1 B1 =3mm, α1=20°, the number of pairs of sector teeth N p =2 pairs, the dimensions of the two pairs of sector teeth are θ1=30°, t1=1mm, θ2=45°, t2=3mm;

[0054] The second variable stiffness shell 2-2 in the unit cell is symmetrical with the first variable stiffness shell 1-2 along the horizontal plane. Specifically, the second variable stiffness shell 2-2 is composed of an outer circular ring 2-2-1, a circular hole in the center, and four (two pairs) sector teeth 2-2-2 between the circular ring and the circular hole. Every two sector teeth are symmetrically arranged. The sector teeth 2-2-2 and the horizontal plane where the outer circumference of the second variable stiffness shell 2-2 is located are preset at an angle α, so that the sector teeth are warped inward of the barrel of the outer barrel. Adjacent sector teeth have different sizes and specifications. The different sizes refer to at least one of the central angle θ and the tooth thickness t of the sector teeth. Among them, the radius R of the second variable stiffness shell 2-2 is 1 / 4 of the center angle θ of the sector teeth and the tooth thickness t. B2 =44mm, width L of ring 2-2-1 B2 =14.2mm, thickness t of ring 2-2-1 B2 =3mm, α2 = 20°, the number of pairs of sector teeth N p =2 pairs, the dimensions of the two pairs of sector teeth are θ1=30°, t1=1mm, θ2=45°, t2=3mm;

[0055] Combine Figure 6-7 The two unit cells are connected in series and stacked along the axial direction. The first limiting ring 1-4 of one unit cell is adapted to the gap formed between the second limiting ring 2-4 and the limiting block 2-5 of the other unit cell, and the end face of the barrel wall of the first barrel body 1-1 abuts against the side wall of the limiting block 2-5.

[0056] In this embodiment, due to minimal contact between the teeth during compression, limiting displacement is achieved by providing stop posts 1-3 on the inner barrel and matching stop slots 2-3 on the outer barrel. In particular, these stop posts 1-3 and stop slots 2-3 provide precise positioning during rotational adjustment of the structural stiffness.

[0057] The variable-rigidity shell is the primary load-bearing structure of the inner and outer barrels. To facilitate assembly between unit cells, first limiting rings 1-4, second limiting rings 2-4, and limiting blocks 2-5 are designed on the inner and outer barrels, respectively. The first limiting rings 1-4 and second limiting rings 2-4 act as a "clamp" when connecting adjacent unit cells, preventing them from detaching. Limiting blocks 2-5 transfer load between adjacent unit cells.

[0058] By making the inner and outer barrels of the unit cell rotate relative to each other, the sector teeth of different sizes come into contact with each other, thus achieving the stiffness adjustment of the metamaterial. p For the variable stiffness shell, the rotation angle φ is 180 / N. p An integer multiple of .

[0059] Preparation method: This embodiment selects green anti-bending photosensitive resin as the base material, and its elastic modulus is 2136MPa (provided by Beijing EasyPure Technology Co., Ltd.). SolidWorks software is used for precise three-dimensional modeling. The model is converted into an STL format file and sliced. The slice thickness is 0.2mm. A G6 light-curing printer (purchased from Shenzhen Aurora Technology Co., Ltd.) is used for printing and curing. After the curing is completed, the removed structure is placed in alcohol for cleaning, and an ultrasonic cleaning device is used to remove the uncured resin remaining on the surface. In order to further improve the performance and stability of the variable stiffness structure, the printed structure is placed in an oven and secondary cured at 50°C for 30 minutes to make the resin more fully cross-linked and cured, thereby improving the strength and stiffness of the structure.

[0060] In Example 1, N p =2, the quasi-static compression response curves of the inner and outer barrels of a single unit cell with a relative rotation angle of φ = 0° and φ = 90° are as follows: Figure 8 shown.

[0061] In Example 1, two N p = 2 unit cells are connected in series, and the relative rotation angle of the inner and outer barrels of the two unit cells is φ = 0° (K0L0); the relative rotation angle of the inner and outer barrels of one unit cell is φ = 0°, and the relative rotation angle of the inner and outer barrels of the other unit cell is φ = 90° (K0L90); the quasi-static compression response curve when the relative rotation angle of the inner and outer barrels of the two unit cells is φ = 90° (K90L90) is as follows Figure 9 shown.

[0062] Example 2:

[0063] The difference between this embodiment and embodiment 1 is that the two unit cells are connected in parallel. Other steps and parameters are the same as those in embodiment 1.

[0064] In Example 2, when two unit cells are tiled in parallel, the relative rotation angle of the inner and outer barrels of the two unit cells is φ = 0° (K0L0); the relative rotation angle of the inner and outer barrels of one unit cell is φ = 0°, and the relative rotation angle of the inner and outer barrels of the other unit cell is φ = 90° (K0L90); the quasi-static compression response curve when the relative rotation angle of the inner and outer barrels of the two unit cells is φ = 90° (K90L90) is as follows Figure 10 As shown, from Figure 9 and Figure 10 As can be seen from the figure, series connection results in a decreasing overall system stiffness. However, when arranged in parallel, the system stiffness equals the sum of the stiffnesses of the individual units, increasing with the number of units. This pattern of change is consistent with the principle of series connection of springs. The multi-toothed mechanical metamaterial with adjustable stiffness proposed in this invention has broad application potential in fields such as vibration control, industrial manufacturing, and intelligent robotics.

[0065] Example 3:

[0066] The difference between this embodiment and embodiment 1 is that the number of pairs of sector teeth N p =3 pairs. In this case, the tooth thickness t of the sector teeth of the first variable stiffness shell and the second variable stiffness shell must meet the requirement that at most one set of thicknesses is the same. The difference in thickness between the inner and outer sector teeth is between 0.1-0.5mm. Specifically, the sector tooth parameters of the inner barrel are: θ1 = 30°, t1 = 1mm, θ2 = 35°, t2 = 2mm, θ3 = 35°, t3 = 3mm. The sector tooth parameters of the outer barrel are: θ1 = 30°, t1 = 1mm, θ2 = 35°, t2 = 1.5mm, θ3 = 35°, t3 = 2.5mm. Other steps and parameters are the same as in Example 1.

[0067] In Example 3, N p =3, the quasi-static compression response curves of the inner and outer barrels of a single unit cell with a relative rotation angle of φ = 0°, φ = 60° and φ = 120° are shown in the figure. Figure 11 As shown, from Figure 8 and Figure 11 It can be seen from the figure that for different rotation angles φ, as the compression displacement increases, the structure can show different load responses, showing the excellent characteristic of adjustable stiffness. At the same time, the number of stiffness changes that the variable stiffness shell structure with different tooth pairs can show is exactly the same as N p equal.

[0068] The foregoing are merely preferred embodiments of the present invention. These embodiments are all different implementations based on the overall concept of the present invention. The scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A multi-tooth mechanical metamaterial with adjustable stiffness, characterized in that: The metamaterial comprises a plurality of unit cells, each unit cell being formed by a nesting of two inner and outer barrel-shaped members, wherein the inner barrel and the outer barrel are both integral structures; The inner barrel comprises a first barrel body (1-1), a first variable stiffness shell (1-2), a plurality of limiting columns (1-3) and a first limiting ring (1-4); the first variable stiffness shell (1-2) is located at the bottom of the inner barrel, the limiting columns (1-3) are evenly distributed on the outer wall of the first barrel body (1-1), and the limiting ring (1-4) is arranged around the outer wall of the barrel top of the first barrel body (1-1); The outer barrel comprises a second barrel body (2-1), a second variable stiffness shell (2-2), a plurality of limiting grooves (2-3), a second limiting ring (2-4) and a limiting block (2-5); the second variable stiffness shell (2-2) is arranged at the lower part of the outer barrel; the limiting grooves (2-3) are evenly distributed on the inner wall of the second barrel body (2-1) and are adapted to the limiting pillars (1-3); the second limiting ring (2-4) is arranged around the inner wall of the second barrel body (2-1) and is arranged between the second variable stiffness shell (2-2) and the bottom end of the second barrel body (2-1); and the limiting block (2-5) is arranged around the inner wall of the second barrel body (2-1) and is arranged between the second limiting ring (2-4) and the second variable stiffness shell (2-2); The first variable stiffness shell (1-2) is composed of an outer circular ring (1-2-1), a circular hole in the center, and an even number of sector teeth (1-2-2) between the circular ring and the circular hole. Every two sector teeth are symmetrically arranged. A preset angle α is formed between the sector teeth (1-2-2) and the horizontal plane where the outer circumference of the first variable stiffness shell (1-2) is located, so that the sector teeth are warped toward the outside of the inner barrel. At least one group of adjacent sector teeth has different size specifications, and the different size refers to at least one of the central angle θ and the tooth thickness t of the sector teeth. In a unit cell, the second variable stiffness shell (2-2) has the same structure as the first variable stiffness shell (1-2), and the sector teeth are warped in opposite directions.

2. The metamaterial according to claim 1, wherein Number of pairs of sector teeth N p ≥2 pairs, α=10-30°, the thickness of the sector tooth (1-2-2) t≤ the thickness of the ring (1-2-1) t B The central angle θ of the sector tooth satisfies 0<θ≤120° / N p .

3. The metamaterial according to claim 1, wherein A plurality of unit cells are connected in series and stacked in an axial direction, wherein a first limiting ring (1-4) of one unit cell is adapted to a gap formed between a second limiting ring (2-4) and a limiting block (2-5) of another unit cell, and an end face of a barrel wall of a first barrel body (1-1) abuts against a side wall of the limiting block (2-5).

4. The metamaterial according to claim 1, wherein Several unit cells are connected in parallel, the unit cells are tiled, and are fixed by an external mechanism.

5. The metamaterial according to claim 1, wherein The metamaterial is made of photosensitive resin.

6. The method for preparing the metamaterial according to any one of claims 1 to 5, characterized in that: The method: Using the stereolithography method, three-dimensional modeling is first performed, then slicing is performed, and finally 3D printing is performed. After printing is completed, secondary curing is performed.

7. The method for adjusting the stiffness of a metamaterial according to any one of claims 1 to 5, characterized in that: The method achieves stiffness adjustment of the metamaterial by causing the inner and outer barrels of the unit cell to rotate relative to each other so that sector-shaped teeth of different sizes come into contact with each other.

8. The method according to claim 7, characterized in that The rotation angle φ of each rotation is 180° / N p An integer multiple of .

9. Use of the metamaterial according to any one of claims 1 to 5 in aerospace vehicles.

10. Application of the metamaterial according to any one of claims 1 to 5 in joint transmission and adaptive adjustment of a flexible robot's manipulator arm.

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