Star-shaped hyperbolic negative Poisson's ratio honeycomb structure based on auxetic metamaterial

Abstract

The invention discloses a star-shaped hyperbolic negative Poisson's ratio honeycomb structure based on auxetic metamaterials, which comprises structural shapes, the structural shapes comprise curve shapes and linear shapes, the curve shapes are positioned on the left and right sides of the structural shapes, the linear shapes are positioned on the upper and lower sides of the structural shapes, and main curve spaces are arranged in the curve shapes; a concave hyperbolic curve is arranged between the main curved spaces and located in the middle of the structural appearance, triangular spaces are arranged in the linear appearance and located on the upper side and the lower side of the structural appearance, a rhombic four-curve is arranged in each main curved space, and four auxiliary curved spaces are arranged at the upper position and the lower position of each rhombic four-curve. The auxiliary curved spaces are located on the left side and the right side of the inwards-concave hyperbolic curve. The star-shaped hyperbolic negative Poisson's ratio honeycomb structure based on the auxetic metamaterial has a guiding effect on negative Poisson's ratio structure research and practical application, and is beneficial for designing a most coincident structural form according to specific performance required by practical engineering.

Description

Technical Field

[0001] The present invention relates to the technical field of metamaterials, and in particular to a star-shaped hyperbolic negative Poisson's ratio honeycomb structure based on auxetic metamaterials. Background Art

[0002] As new types of artificial functional materials, these materials do not exist in nature. They have some special properties, such as allowing light and electromagnetic waves to change their usual properties, which is an effect that traditional materials cannot achieve. There is nothing special about the composition of metamaterials. Their unique properties come from their precise geometric structure and size. The microstructure in them is smaller than the wavelength of its action, so it can exert an influence on the wave. The preliminary research on metamaterials is negative refractive index metamaterials. When subjected to axial tension or compression, axial expansion metamaterials can produce lateral expansion or contraction deformation different from conventional materials, so they have a negative Poisson's ratio effect. Their mechanical properties are controlled by changing their geometric structure design, thereby realizing conventional forward design from structure to performance.

[0003] The negative Poisson's ratio effect means that when a material is stretched, it expands laterally within its elastic range, while when it is compressed, it contracts laterally. This phenomenon is thermodynamically possible, but it is not generally observed in materials. In recent years, some materials with special structures have been discovered to have a negative Poisson's ratio effect, and due to their unique properties, they have attracted much attention from materials scientists and physicists.

[0004] Among existing auxetic metamaterial structures, one example is a three-dimensional auxetic metamaterial with a negative Poisson's ratio, documented in publication number CN110014641A. Its technical solution comprises multiple mesostructures, including a four-pointed star-shaped concave structure and two concave hexagonal structures of identical size and structure. The four-pointed star-shaped concave structure is arranged horizontally, with the four-pointed star-shaped concave knot and the two concave hexagonal structures perpendicular to each other. The four-pointed star-shaped concave structure includes curved struts and connecting struts located at the bends of the curved struts. The concave hexagonal structure includes two parallel horizontal crossbars and an inclined vertical bar connecting the horizontal crossbars. The mesostructures in the technical solution of the present invention are three-dimensional and simple. Therefore, this metamaterial has wider applicability and can be more flexibly applied to different locations.

[0005] However, in practical engineering, reverse design from performance to structure is often more pressing than conventional forward design from structure to performance. Compared to conventional forward design, which maps structure to performance in a one-to-one fashion, reverse design often involves a one-to-many mapping process, meaning that a given target performance corresponds to multiple sets of structural parameters, making it more challenging to achieve. Currently, the most mature and effective reverse design methods for auxetic metamaterials are primarily topology optimization methods, but these methods are theoretically complex, involve tedious processes, and require high mathematical and physics expertise from the designer.

[0006] In view of this, we conducted in-depth research on the above issues, which led to the emergence of this case. Summary of the Invention

[0007] The purpose of the present invention is to provide a star-shaped hyperbolic negative Poisson's ratio honeycomb structure based on an auxetic metamaterial to solve the problem mentioned in the background art that when materials are actually used in engineering, the influence of some factors such as the external environment, processing conditions and the impurity content of the test piece is often not negligible, and it is unrealistic to provide specific guidance for actual engineering applications only through theoretical analysis.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] A star-shaped hyperbolic negative Poisson's ratio honeycomb structure based on an auxetic metamaterial includes a structural shape, wherein the structural shape includes a curved shape and a straight shape, wherein the curved shape is located on the left and right sides of the structural shape, and the straight shape is located on the upper and lower sides of the structural shape, main curved spaces are provided inside the curved shapes, and concave hyperbolas are provided between the main curved spaces, and the concave hyperbolas are located in the middle of the structural shape, triangular spaces are provided inside the straight shape, and the triangular spaces are located on the upper and lower sides of the structural shape, and a diamond-shaped quadrilateral is provided inside the main curved space, and four auxiliary curved spaces are provided above and below the diamond-shaped quadrilateral, and the auxiliary curved spaces are all located on the left and right sides of the concave hyperbola.

[0010] Preferably, the curved shape is an outer convex surface, and the curved shape is located on the left and right sides of the structural shape in the horizontal direction.

[0011] Preferably, a main curved space is provided inside the curved outer shape, and the main curved space is shuttle-shaped, and the edge where the curved outer shape and the main curved space meet has a negative Poisson's ratio effect.

[0012] Preferably, the left and right sides of the concave hyperbola are concave curve structures, and the upper and lower sides of the concave hyperbola are concave straight line structures with included angles, and the concave hyperbola is located in the middle of the structural shape and has a negative Poisson's ratio effect.

[0013] Preferably, the concave hyperbola is analyzed using the finite element software COMSOL to analyze the parameters a and b of the control curve portion, with the value of a set to 5 mm and the value of b set to 15 mm. The two parameter formulas for the control hyperbola equation are:

[0014] y2 / a 2 -x 2 / b 2 =1.

[0015] Preferably, the space between the left and right sides of the concave hyperbola and the main curve is set to t, and the t value is set to 4.4 mm. The heights of the upper and lower sides of the concave hyperbola are set to l, and the l value is set to 50 mm. When a, b, t, and l are combined, the Poisson's ratio reaches a minimum value of -4.6.

[0016] Preferably, the straight outer shape is located at the upper and lower sides of the structural outer shape, and a triangular space is provided inside the straight outer shape, and the edge of the triangular space is a straight structure.

[0017] Preferably, diamond-shaped four-curves are provided inside the left and right sides of the main curved space, and the edges of the diamond-shaped four-curves are all concave curve structures. Four auxiliary curved spaces are provided around the diamond-shaped four-curves, and the auxiliary curved spaces are all shuttle-shaped.

[0018] Preferably, the vertical hyperbola movement distance of the auxiliary curved space is set to h, and the horizontal hyperbola movement distance of the auxiliary curved space is set to d, and the width of the auxiliary curved space and the curved shape is set to t. The deformation mechanism of the orthogonal hyperbola anti-chirality structure of the structural shape takes a set of representative units with geometric parameters of a=6mm, b=8mm, t=2mm, d=3.5mm, and k=6.5mm. At this time, the porosity is 0.416.

[0019] Preferably, the structural shape is analyzed by COMSOL parametric modeling to obtain specific models under models with different parameters, and the point calculation function of the software is used to calculate the equivalent Poisson's ratio and elastic modulus of each model, where the elastic modulus E = 1.114 GPa, the density p = 1.179×103 kg / m3, and the Poisson's ratio v = 0.413.

[0020] Compared with the prior art, the beneficial effects of the present invention are: the star-shaped hyperbolic negative Poisson's ratio honeycomb structure based on auxetic metamaterial,

[0021] 1. A concave hyperbola is provided, and the left and right sides of the concave hyperbola are concave curve structures, and the upper and lower sides of the concave hyperbola form a concave straight line structure with an included angle. The concave hyperbola is located in the middle of the structure shape, which has a negative Poisson's ratio effect. As a new type of honeycomb structure that has developed rapidly in recent years, the chiral honeycomb structure has the advantages of traditional honeycomb structures while having more superior mechanical properties and can complete the dual effects of out-of-plane load and in-plane deformation. These obvious advantages will continuously enhance the use value and development potential of the honeycomb structure, and will also make the research topic of honeycomb structure materials a hot topic in the global scientific research community;

[0022] 2. A honeycomb structured auxiliary curved space is provided. The left and right sides of the main curved space are each internally provided with a diamond-shaped quadrilateral, and the edges of the diamond-shaped quadrilateral are all concave curved structures. Four auxiliary curved spaces are provided around the diamond-shaped quadrilateral, and the auxiliary curved spaces are all shuttle-shaped. By studying the mechanical properties of the negative Poisson's ratio honeycomb structure in practical applications, especially studying the effects of different tensile expansion structures on the overall mechanical properties, it has a guiding role in the research and practical application of negative Poisson's ratio structures, and is conducive to designing the most suitable structural form according to the specific performance required by the actual project;

[0023] 3. A diamond-shaped quadrilateral is arranged in the middle of the auxiliary curved space. The edges of the quadrilateral are all concave curve structures. When stretched in the vertical direction, the structure undergoes significant lateral expansion deformation, that is, the structure has tensile deformation capability. After being subjected to tensile load, high stress areas exist in the connecting ligaments between the four windmill-shaped rotating units inside the model. This means that these ligaments undergo bending deformation during the stretching process, causing the windmill-shaped units to rotate. This is also the reason why this type of tensile metamaterial can produce a tensile effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of the front main structure of the present invention;

[0025] Figure 2 This is a schematic diagram of the front detailed structure of the present invention;

[0026] Figure 3 Schematic diagram of the deformation mechanism of the anti-chirality and chiral structure of a specific embodiment;

[0027] Figure 4 Schematic diagram of the design steps of the orthogonal hyperbolic reverse handedness structure in a specific embodiment;

[0028] Figure 5 Schematic diagram of the effect of a and b on Poisson's ratio of the concave hyperbolic structure in a specific embodiment;

[0029] Figure 6Schematic diagram of a unit deformation mode of an orthogonal hyperbolic anti-chirality structure according to a specific embodiment;

[0030] Figure 7 Schematic diagrams of different shapes of the new structure with different geometric parameters in a specific embodiment;

[0031] Figure 8 Schematic diagram of the influence of Poisson's ratio of the new backhanded structure under changes in a and b in a specific implementation method.

[0032] In the figure: 1. Structural shape; 2. Curved shape; 3. Main curved space; 4. Concave hyperbola; 5. Straight shape; 6. Triangular space; 7. Rhombus quadrilateral; 8. Auxiliary curved space. DETAILED DESCRIPTION

[0033] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0034] See also Figure 3-8 , the present invention provides a technical solution:

[0035] Chiral honeycomb structures, a new type of honeycomb structure that has rapidly developed in recent years, possess the advantages of traditional honeycomb structures while offering superior mechanical properties. They can also handle both out-of-plane loads and in-plane deformation. These significant advantages will continuously enhance the value and development potential of honeycomb structures, and will also make the research of honeycomb structural materials a hot topic in the global scientific community.

[0036] Compared with ordinary honeycomb structures, the deformation mechanism and structural form of chiral honeycomb structures are very different. Studies have shown that the main reasons for the honeycomb structure to have a negative Poisson's ratio of the tensile effect are two deformation mechanisms: one is the concave deformation mechanism, and the other is the rotational deformation mechanism. Figure 3 The chiral honeycomb structure studied in .

[0037] Figure 4 The figure shows a new chiral structure formed by rotating a unit cut by an orthogonal hyperbola. It not only has a chiral rotation mechanism, but also has a concave deformation mechanism on all sides. This honeycomb structure is composed of five geometric parameters: t is the width of the curved rod; due to the characteristics of the hyperbola, the hyperbola is rotated at the far point to Figure 1In the orange part, h is the vertical hyperbola moving distance, and then folded; d is the horizontal hyperbola moving distance; in addition, a and b are the hyperbola formulas (y2 / a 2 -x 2 / b 2 =1). By combining the intersection of the two pairs of hyperbolas after translation, we can get Figure 1 The nine units on the right side of the middle are combined, and the complete structure of the representative unit in the middle is left, thus forming Figure 5 Schematic diagram of the structural model in the lower left corner of the center. This modeling method ensures that these five geometric parameters control the size and shape of the chiral structure. By varying the values of these five parameters, various forms of the model can be obtained.

[0038] In order to study the deformation mechanism of the new orthogonal hyperbolic anti-chirality structure, a set of representative units with geometric parameters of a = 6mm, b = 8mm, t = 2mm, d = 3.5mm, k = 6.5mm is taken, and the porosity is 0.416. Figure 6 As shown in the figure, a vertical displacement of 5mm is applied to the upper and lower boundaries respectively to make the model produce uniform tensile deformation. At the same time, the displacement in the x and y directions is constrained at the positions of its longitudinal and transverse symmetry lines respectively to prevent the structure from undergoing rigid body displacement under tensile load, which would cause the calculation to not converge. It can be found that when the structure is stretched in the vertical direction, it undergoes obvious expansion deformation in the transverse direction, that is, the structure has the ability to deform in tension. At the same time, it can be seen from the figure that after being subjected to tensile load, there are high stress areas in the connecting ligaments between the four windmill-shaped rotating units inside the model. This means that these ligaments undergo bending deformation during the stretching process, causing the windmill-shaped units to rotate. This is also the reason why this type of auxetic metamaterial can produce auxetic effect.

[0039] This model uses COMSOL parametric modeling analysis, which can obtain specific models under different parameters, and then use the software's point calculation function to calculate the equivalent Poisson's ratio and elastic modulus of each model. The material parameters are: elastic modulus E = 1.114Gpa, density p = 1.179×103kg / m3, Poisson's ratio v = 0.413. Since the change of parameters has a great influence on the shape of the model, I have selected several representative structural shapes obtained by parameter changes, such as Figure 7As shown. Similarly, by parametrically scanning the model strain under various parameter combinations, it can be calculated that this model presents a negative Poisson's ratio effect in all forms, but the degree of negative Poisson's ratio is not as obvious as the concave hyperbola designed above. However, since this model is composed entirely of curves, the stress concentration phenomenon on the entire surface will be lower than the above-mentioned concave hyperbola structure and the traditional concave hexagonal structure in Chapter 3. Since this model is mainly obtained by rotating the ligaments of the hyperbola, the a and b parameters that mainly control the degree of bending of the hyperbola will be analyzed. In the COMSOL model, only a and b are parametrically scanned, and t, d, and k are fixed at 1.5mm, 5mm, and 9mm, respectively. The Poisson's ratio results obtained by extracting strain are plotted on Figure 8 As shown in the figure, it is clear that the negative Poisson's ratio effect is most pronounced when the value of b is approximately twice that of a. Changing only the values of a and b allows the structure to reach a maximum Poisson's ratio of -0.9, and can contain regions with negative, positive, and zero Poisson's ratios. Because this structure is composed entirely of curved bars, stress concentration is largely avoided.

[0040] The contents not described in detail in this specification belong to the prior art known to those skilled in the art.

[0041] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A star-shaped hyperbolic negative Poisson's ratio honeycomb structure based on auxetic metamaterial, comprising a structural shape (1), characterized in that: The structural outer shape (1) comprises a curved outer shape (2) and a straight outer shape (5), wherein the curved outer shape (2) is located on the left and right sides of the structural outer shape (1), and the straight outer shape (5) is located on the upper and lower sides of the structural outer shape (1), a main curved space (3) is provided inside the curved outer shape (2), and an inward concave hyperbola (4) is provided between the main curved spaces (3), and the inward concave hyperbola (4) is located in the middle of the structural outer shape (1), a triangular space (6) is provided inside the straight outer shape (5), and the triangular space (6) is located on the upper and lower sides of the structural outer shape (1), a rhombus quadrilateral (7) is provided inside the main curved space (3), and four auxiliary curved spaces (8) are provided at the upper and lower positions of the rhombus quadrilateral (7), and the auxiliary curved spaces (8) are all located on the left and right sides of the inward concave hyperbola (4).

2. The star-shaped hyperbolic negative Poisson's ratio honeycomb structure based on auxetic metamaterial according to claim 1, characterized in that: The curved outer shape (2) is an outer convex curved surface, and the curved outer shape (2) is located on the left and right sides of the structural outer shape (1) in the horizontal direction.

3. The star-shaped hyperbolic negative Poisson's ratio honeycomb structure based on auxetic metamaterial according to claim 2, characterized in that: A main curved space (3) is provided inside the curved outer shape (2), and the main curved space (3) is in a shuttle shape. The edge where the curved outer shape (2) and the main curved space (3) meet has a negative Poisson's ratio effect.

4. The star-shaped hyperbolic negative Poisson's ratio honeycomb structure based on auxetic metamaterial according to claim 1, characterized in that: The left and right sides of the indented hyperbola (4) are indented curve structures, and the upper and lower sides of the indented hyperbola (4) are indented straight line structures with angles, and the indented hyperbola (4) is located in the middle of the structural outer shape (1) and has a negative Poisson's ratio effect.

5. The star-shaped hyperbolic negative Poisson's ratio honeycomb structure based on auxetic metamaterial according to claim 4, characterized in that: The concave hyperbola (4) is analyzed using the finite element software COMSOL to analyze the parameters a and b of the control curve part, with the value of a set to 5 mm and the value of b set to 15 mm. The two parameter formulas of the control hyperbola equation are: y2 / a 2 -x 2 / b 2 =1.

6. The star-shaped hyperbolic negative Poisson's ratio honeycomb structure based on auxetic metamaterial according to claim 5, characterized in that: The left and right sides of the concave hyperbola (4) are connected to the main curved space (3) at a distance set to t, and the t value is set to 4.4 mm. The upper and lower sides of the concave hyperbola (4) have a height set to l, and the l value is set to 50 mm. When a, b, t, and l are combined, the Poisson's ratio reaches a minimum value of -4.

6.

7. The star-shaped hyperbolic negative Poisson's ratio honeycomb structure based on auxetic metamaterial according to claim 1, characterized in that: The straight outer shape (5) is located at the upper and lower sides of the structural outer shape (1), and a triangular space (6) is provided inside the straight outer shape (5), and the edge of the triangular space (6) is a straight structure.

8. The star-shaped hyperbolic negative Poisson's ratio honeycomb structure based on auxetic metamaterial according to claim 1, characterized in that: The left and right sides of the main curved space (3) are each internally provided with a diamond-shaped quadrilateral (7), and the edges of the diamond-shaped quadrilateral (7) are each in a concave curved structure. Four auxiliary curved spaces (8) are each provided around the diamond-shaped quadrilateral (7), and the auxiliary curved spaces (8) are each in a shuttle shape.

9. The star-shaped hyperbolic negative Poisson's ratio honeycomb structure based on auxetic metamaterial according to claim 8, characterized in that: The vertical hyperbolic movement distance of the auxiliary curved space (8) is set to h, and the horizontal hyperbolic movement distance of the auxiliary curved space (8) is set to d, and the width of the auxiliary curved space (8) and the curved profile (2) is set to t. The deformation mechanism of the orthogonal hyperbolic anti-chirality structure of the structural profile (1) is taken as a representative unit with a set of geometric parameters of a=6mm, b=8mm, t=2mm, d=3.5mm, and k=6.5mm. At this time, the porosity is 0.

416.

10. The star-shaped hyperbolic negative Poisson's ratio honeycomb structure based on auxetic metamaterial according to claim 1, characterized in that: The structural shape (1) is analyzed by COMSOL parametric modeling to obtain specific models under models with different parameters, and the point calculation function of the software is used to calculate the equivalent Poisson's ratio and elastic modulus of each model, wherein the elastic modulus E=1.114GPa, the density p=1.179×103kg / m3, and the Poisson's ratio v=0.413.

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