Recoverable bionic spiral metamaterial structure with variable rigidity characteristic

Abstract

The invention relates to the technical field of metamaterials, and particularly discloses a recoverable bionic spiral metamaterial structure with a variable stiffness characteristic, which comprises an upper pressing plate, a lower pressing plate, a plurality of S-shaped spring units and a single-layer frame for fixing the S-shaped spring units, and is characterized in that four S-shaped spring unit structures are connected through the single-layer frame to form a single-layer structure; the single-layer structures are connected layer by layer at a set interlayer spiral angle to form the recoverable bionic metamaterial structure; based on the spiral Bouligand structure and the S-shaped spring, the structure has rigidity transformation of two dimensions, and wide rigidity adjustment can be performed by changing the rotation angle of the unit structure and the interlayer spiral angle between the single-layer structures, so that the engineering application range of the metamaterial junction is expanded, and the metamaterial junction has wide application prospects in impact resistance, energy absorption and stress bearing.

Description

Technical Field

[0001] The present invention relates to the technical field of metamaterials, and in particular to a recoverable bionic spiral metamaterial structure with variable stiffness characteristics. Background Art

[0002] Metamaterials are composite materials or structures constructed through the periodic arrangement and construction of artificial units, with the goal of achieving extraordinary physical properties not possessed by natural materials. Common mechanical properties of metamaterials include negative Poisson's ratio, negative compressibility, multistability, negative stiffness, and negative thermal expansion. Due to their unique mechanical properties, metamaterials are also a hot topic in the field of energy absorption and buffering. Currently, they are categorized into two main types: recoverable and non-recoverable. Non-recoverable metamaterials achieve their buffering effect by consuming energy through material damage or large plastic deformation of their structure when subjected to external loads. Recoverable metamaterials, on the other hand, can recover after deformation by themselves or by relying on external stimulation to return to their initial state.

[0003] Currently, most mechanical metamaterials are made of polymer resin and metal, integrated using 3D printing technology. They rely on plastic deformation or fracture / shattering of the material to offset external impact energy. After a one-time buffering and energy absorption, they cannot return to their original configuration, making these structures suitable only for single-use applications. Discrete resilient metamaterials, on the other hand, rely primarily on elastic deformation to absorb energy and are reusable. If a component is damaged, only the damaged part needs to be repaired, reducing maintenance costs.

[0004] Therefore, the present invention proposes a recoverable bionic spiral metamaterial structure with variable stiffness characteristics. Summary of the Invention

[0005] To address these challenges, the present invention utilizes a helical Bouligand structure and S-shaped springs, employs carbon fiber composite materials, and employs discrete assembly to create a reusable, widely adjustable mechanical metamaterial. The overall structure utilizes detachable bolts and nuts for simple assembly, enabling the metamaterial's stiffness to be adjusted based on actual operating conditions. Combining a unit structure with a single-layer structure allows for two-dimensional stiffness transformation, enabling a wider range of stiffness adjustments based on actual operating conditions. The overall metamaterial structure exhibits excellent resilience.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A recoverable bionic spiral metamaterial structure with variable stiffness characteristics includes an upper pressure plate, a lower pressure plate, multiple S-shaped spring units, and a single-layer frame for fixing the S-shaped spring units. Four S-shaped spring unit structures are connected through the single-layer frame to form a single-layer structure, and the single-layer structures are connected layer by layer with a set inter-layer spiral angle to form a recoverable bionic metamaterial structure.

[0008] Furthermore, the S-shaped spring unit structure includes a unit frame, a carbon fiber shell and bolts and nuts, and the two carbon fiber shells are centrally symmetrically arranged on the unit frame, and one end of one of the carbon fiber shells is fixed to the top of the unit frame by bolts and nuts, and one end of the other carbon fiber shell is fixed to the bottom of the unit frame by bolts and nuts.

[0009] Furthermore, the carbon fiber shell is fixedly connected to the unit frame by three groups of bolts and nuts distributed in a triangular shape.

[0010] Furthermore, the single-layer structure is provided with 4 unit structures in total, which are distributed in parallel in sequence. The unit structures have different stiffness transformations at different unit rotation angles.

[0011] Furthermore, the single-layer frames between different layers are connected by splines and clearance fit to ensure that the rotation angle remains unchanged during the compression displacement process.

[0012] Furthermore, the number and positions of adjacent single-layer carbon fiber shells correspond to each other, ensuring mutual contact during the compression and displacement process.

[0013] Furthermore, the recoverable bionic helical metamaterial structure realizes two-dimensional stiffness transformation under the joint action of different unit rotation angles (60°, 90°, 120°) and different interlayer helical angles (0°, 45°, 60°, 90°) to obtain the stiffness corresponding to the bionic metamaterial in different forms.

[0014] Furthermore, the different unit rotation angles include 60°, 90°, and 120°; the different interlayer helical angles include 0°, 45°, 60°, and 90°.

[0015] Furthermore, the carbon fiber thin shell is prepared by T700 carbon fiber prepreg, with the geometric size of a 70×70mm square, and the laying method is [0° / 90° / 0° / 90° / 0°]. It is laid in a circular tube mold with a radius of 30mm and cured for 3 hours in an autoclave at 180°C and 0.7MPa. After completing the process of high temperature and high pressure curing in the autoclave for 2 hours, the carbon fiber thin shell is furnace cooled and cut to obtain an arc-shaped carbon fiber shell with a radius of 30mm and a central angle of 120°.

[0016] Furthermore, the unit frame, the single-layer frame, the upper and lower pressing plates are all made of white resin material and are manufactured by SLA printing using stereolithography technology.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1) The unit structure of the metamaterial in the present invention is assembled as a whole using bolts and nuts. The unit structure and the single-layer frame, and the single-layer frame and the single-layer frame are fitted with clearances, which makes installation simple and convenient. The unit frame, the single-layer frame, and the pressing plate are made of white resin 3D printing, which has a fast manufacturing speed. The carbon fiber shell is prepared using T700 prepreg, which is light in weight and has high stiffness and strength.

[0019] 2) The present invention is based on a helical Bouligand structure and an S-shaped spring. The structure has two-dimensional stiffness transformation. By changing the rotation angle of the unit structure and the interlayer helical angle between the single-layer structure, a wide range of stiffness adjustments can be performed, which expands the scope of engineering applications of the metamaterial junction and has broad application prospects in impact resistance, energy absorption, and load bearing.

[0020] 3) The carbon fiber shell, which is the main load-bearing component in the present invention, has excellent compression performance, so that the metamaterial structure can return to its original state after being subjected to external pressure, thereby realizing multiple reuse of the structure.

[0021] 4) The present invention mainly relies on elastic deformation to absorb energy and is reusable. If a component is damaged, only the damaged part needs to be repaired, which reduces maintenance costs. Therefore, the present invention has a wide range of application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the preparation process of the recoverable biomimetic spiral metamaterial unit structure in the present invention;

[0023] Figure 2 Schematic diagram of the recoverable biomimetic spiral metamaterial unit structure of the present invention;

[0024] Figure 3 Schematic diagram of the assembly process of the overall structure of the recoverable bionic spiral metamaterial;

[0025] Figure 4 The stiffness data diagram of the recoverable bionic helical metamaterial and the interlayer helical angle under different unit rotation angle conditions;

[0026] Figure 5 Schematic diagram of the overall structure of the recoverable bionic helical metamaterial when the interlayer helical angle is equal to 0 and the unit rotation angles are 60°, 90°, and 120°;

[0027] Figure 6 Schematic diagram of the overall structure of the recoverable biomimetic helical metamaterial with interlayer helical angles of 0°, 45°, 60°, and 90°;

[0028] In the figure: 1. Mold; 2. Carbon fiber prepreg; 3. Bolts and nuts; 4. Unit structure fixing plate; 5. Carbon fiber shell; 6. Unit frame; 7. Single-layer frame; 8. Upper and lower pressure plates. DETAILED DESCRIPTION

[0029] The present invention will be further described below with reference to the accompanying drawings.

[0030] A recoverable bionic spiral metamaterial structure with variable stiffness characteristics belongs to the field of metamaterial technology. The structure consists of four S-shaped spring units through a single-layer frame 7 to form a single-layer structure, which is then arranged and connected by three single-layer structures according to a specific spiral angle, and finally assembled using upper and lower pressure plates 8.

[0031] In this embodiment: the S-shaped spring unit is composed of a unit frame 6, a carbon fiber shell 5, a spiral nut 3 and a unit structure fixing plate 4; two carbon fiber shells 5 are centrally symmetrically arranged on the unit frame 5, and the unit frame 5 has a Japanese-shaped structure, and one end of one of the carbon fiber shells 5 is fixed to the top of the unit frame 5 by a bolt and nut 3 and the unit structure fixing plate 4, and one end of the other carbon fiber shell is fixed to the bottom of the unit frame 5 by a bolt and nut 3 and the unit structure fixing plate 4.

[0032] In this embodiment, the single-layer structure is provided with a plurality of unit structures, which are sequentially distributed in parallel. The unit structures have different stiffness transformations at different unit rotation angles.

[0033] Figure 1 This is a schematic diagram of the preparation process of the unit structure of the recoverable bionic spiral metamaterial in the present invention. The carbon fiber shell is prepared using T700 carbon fiber prepreg with a geometric size of 70×70mm. The number of carbon fiber plies is five, and the ply stacking angle is [0° / 90° / 0° / 90° / 0°].

[0034] According to the designed dimensions of the composite shell, the carbon fiber prepreg was cut using a Cricut automatic paper cutter. Subsequently, a 60mm diameter round tube mold was cleaned with alcohol to remove stains on the mold surface. The carbon fiber prepreg was laid in sequence according to the designed laying angles, and Teflon tape was affixed to the mold surface where the mold contacted the composite shell to facilitate demolding after the composite shell was formed.

[0035] After laying, it is placed in an autoclave and cured for 2 hours at 150°C and 0.7MPa in the autoclave. It is then furnace-cooled, and the thin shell is taken out of the autoclave. After cutting, an arc-shaped carbon fiber shell with a radius of 30mm and a central angle of 120° is obtained.

[0036] The carbon fiber shell of the S-shaped spring unit structure is fixed to one side of the unit frame 5 by three sets of bolts and nuts 3 in a triangle shape, so that the unit structure can be stably stressed. Figure 2 shown.

[0037] Figure 3This is a schematic diagram of the overall structural assembly process of a recoverable bionic spiral metamaterial with variable stiffness characteristics. Four S-shaped spring unit structures are connected through a single-layer frame to obtain a single-layer structure, and then the single-layer structure is connected layer by layer with a specific interlayer spiral angle to obtain the final bionic metamaterial.

[0038] The recoverable bionic spiral metamaterial structure of the present invention adopts clearance fit between the unit structure and the single-layer frame, and between the single-layer frames, so the installation is simple and convenient. The unit frame, the single-layer frame and the pressure plate are made of white resin 3D printing.

[0039] like Figure 3 As shown, an appropriate gap is selected when connecting the S-shaped spring unit structure to the single-layer frame. This ensures that when the recoverable bionic spiral metamaterial structure is compressed, the S-shaped spring unit does not experience changes in rotation angle that would affect its mechanical performance, while also allowing the S-shaped spring unit to easily rotate around the axis of the single-layer frame to adjust its stiffness. The use of a gap fit in the connection between the layers ensures that when the recoverable bionic spiral metamaterial structure is compressed, the friction between the single-layer frame connections will not affect its mechanical performance.

[0040] like Figure 4 、 5 6, the present invention is a recoverable biomimetic spiral metamaterial structure with variable stiffness characteristics, which realizes two-dimensional stiffness transformation under the combined action of different unit rotation angles (60°, 90°, 120°) and different interlayer spiral angles (0°, 45°, 60°, 90°). The data graph shows that the stiffness of the biomimetic metamaterial in different forms ranges from 0.89×10 3 —10.8×10 3’ , showing a wide range of stiffness variations.

[0041] Example: The carbon fiber shell utilizes T700 / epoxy resin prepreg produced by Toray Industries, Japan. This composite material, composed of T700 carbon fiber and epoxy resin prepreg, exhibits excellent strength, stiffness, and corrosion resistance. Preparation process: The T700 composite shell is produced using an autoclave process. The specific steps include: ① cutting the carbon fiber prepreg; ② laying the shell; ③ autoclave high-temperature and high-pressure curing; ④ demolding; and ⑤ assembly.

[0042] Furthermore, according to the designed size of the composite shell, the carbon fiber prepreg was cut using a Cricut automatic paper cutter; then, the circular tube mold with a diameter of 60 mm was cleaned with alcohol to remove stains on the mold surface, and the carbon fiber prepreg was laid in sequence according to the designed laying angle, and Teflon tape was affixed to the mold surface where the mold and the composite shell were in contact to facilitate demolding of the composite shell after molding.

[0043] After the layup is complete, the composite shell is placed in an autoclave and cured at 150°C for 2 hours. The shell is then removed from the autoclave and demolded to form the S-shaped spring element. The unit structural frame is then 3D printed using white resin. Bolts and nuts are used to connect the composite shell and the structural frame to create the final S-shaped spring element.

[0044] The unit structure frame has three holes through which bolts can be connected to nuts to secure the carbon fiber shell, creating a stable S-shaped spring unit. Four S-shaped spring units are connected through a single-layer frame to form a single-layer structure. The single-layer structure is then connected layer by layer at a specific interlayer helical angle to form the final biomimetic metamaterial.

[0045] The unit frame, single-layer frame, and pressure plate are made of white resin and are manufactured using stereolithography (SLA) printing technology. The S-shaped spring unit can achieve stiffness transformation by changing the unit rotation angle (60°, 90°, 120°).

[0046] The recoverable bionic metamaterial realizes two-dimensional stiffness transformation under the joint action of different unit rotation angles (60°, 90°, 120°) and different interlayer helix angles (0°, 45°, 60°, 90°) to obtain the corresponding stiffness of the bionic metamaterial in different forms.

[0047] The above description of the disclosed embodiments is intended to enable those skilled in the art to implement or apply the present invention. Various modifications to these embodiments will be apparent to those skilled in the art. The general principles described herein may be applied to other embodiments without departing from the core spirit or scope of the present invention. Therefore, the scope of application of the present invention is not limited to the embodiments shown herein, but should conform to the broadest scope consistent with the principles and unique features disclosed herein to ensure compliance with the principles of the present invention.

Claims

1. A recoverable biomimetic helical metamaterial structure with variable stiffness characteristics, characterized in that: It includes an upper pressure plate, a lower pressure plate, multiple S-shaped spring units and a single-layer frame for fixing the S-shaped spring units. Four S-shaped spring unit structures are connected through the single-layer frame to form a single-layer structure. Multiple single-layer structures are connected layer by layer with a set inter-layer spiral angle to form a recoverable bionic metamaterial structure.

2. The recoverable biomimetic spiral metamaterial structure with variable stiffness characteristics according to claim 1, characterized in that: The S-shaped spring unit structure includes a unit frame, a carbon fiber shell and bolts and nuts. The two carbon fiber shells are centrally symmetrically arranged on the unit frame, and one end of one carbon fiber shell is fixed to the top of the unit frame by a bolt and nut, and the other end of the carbon fiber shell is fixed to the bottom of the unit frame by a bolt and nut.

3. The recoverable biomimetic spiral metamaterial structure with variable stiffness characteristics according to claim 1, characterized in that: The carbon fiber thin shell is fixedly connected to the unit frame by three groups of bolts and nuts distributed in a triangle.

4. The recoverable biomimetic spiral metamaterial structure with variable stiffness characteristics according to claim 1, characterized in that: The single-layer structure is provided with 4 unit structures in total, which are sequentially distributed in parallel. The unit structures have different stiffness transformations under different unit rotation angles; the rotation angles of the 4 unit structures in the same layer remain consistent.

5. The recoverable biomimetic spiral metamaterial structure with variable stiffness characteristics according to claim 1, characterized in that: The single-layer frames between different layers are connected by splines and clearance fit to ensure that the rotation angle remains unchanged during the compression displacement process.

6. The recoverable biomimetic spiral metamaterial structure with variable stiffness characteristics according to claim 1, characterized in that: The number and positions of adjacent single-layer carbon fiber shells correspond to each other, ensuring that they contact each other during the compression and displacement process.

7. The recoverable biomimetic spiral metamaterial structure with variable stiffness characteristics according to claim 4, characterized in that: The recoverable bionic helical metamaterial structure realizes two-dimensional stiffness transformation under the joint action of different unit rotation angles and different interlayer helical angles to obtain the stiffness corresponding to the bionic metamaterial in different forms.

8. The recoverable biomimetic spiral metamaterial structure with variable stiffness characteristics according to claim 7, characterized in that: The different unit rotation angles include 60°, 90°, and 120°; the different interlayer helical angles include 0°, 45°, 60°, and 90°.

9. The recoverable biomimetic spiral metamaterial structure with variable stiffness characteristics according to claim 1, characterized in that: The carbon fiber thin shell is prepared using T700 carbon fiber prepreg, with geometric dimensions of a 70×70 mm square and a ply pattern of [0° / 90° / 0° / 90° / 0°]. It is laid in a circular tube mold with a radius of 30 mm and cured for 2 hours in an autoclave at 150°C and 0.7 MPa. After completing the autoclave high-temperature and high-pressure curing process for 2 hours, the carbon fiber thin shell is furnace-cooled and cut to obtain an arc-shaped carbon fiber shell with a radius of 30 mm and a central angle of 120°.

10. The recoverable biomimetic spiral metamaterial structure with variable stiffness characteristics according to claim 1, characterized in that: The unit frame, the single-layer frame, the upper and lower pressing plates are all made of white resin material and are manufactured by SLA printing using stereolithography technology.

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