A multifunctional negative Poisson's ratio diamond honeycomb structure

Abstract

The present invention belongs to the technical field of mechanical metamaterials, and specifically relates to a multifunctional negative Poisson's ratio rhombus honeycomb structure. The multifunctional negative Poisson's ratio rhombus honeycomb structure includes a plurality of unit cell structures periodically arranged in the same plane, and each unit cell structure is connected end to end to form a rhombus; the unit cell structure includes four straight beams and four variable cross-section beams, and the side of each variable cross-section beam is set at a certain angle to the straight beam to which it is connected, and the inner sides of the left and right adjacent and symmetrical variable cross-section beams are connected to each other to form an inward concave arrow structure, and the outer sides of the left and right adjacent and symmetrical variable cross-section beams are connected in the vertical direction. The multifunctional negative Poisson's ratio rhombus honeycomb structure has an excellent negative Poisson's ratio effect, and the structural deformation is uniform, and it has a robust platform stage that can be used for structural energy absorption; and the structural form is simple and easy to make, and can be mass-produced by traditional methods such as casting and cutting.

Description

Technical Field

[0001] The present invention belongs to the technical field of mechanical metamaterials, and in particular relates to a multifunctional negative Poisson's ratio rhombus honeycomb structure. Background Art

[0002] Material buckling is generally considered an undesirable structural failure mode because it can cause permanent plastic deformation or even destruction of the structure. However, research on elastic materials has changed this perception. The reversible buckling and post-buckling behavior of elastic porous materials has brought new opportunities for the design of multifunctional structures, such as using the mechanical instability in porous materials to design expansion materials, develop soft actuators, control the propagation of elastic waves, manufacture reusable energy-absorbing materials, design energy capture devices, and design multi-scale materials with switchable functions and morphological changes. A widely studied buckling-based elastic material is the mode conversion mechanical metamaterial, which exhibits the phenomenon that when the material is compressed beyond a threshold, the cells undergo cooperative buckling and the nodes undergo large-scale rotation. This process usually causes the structure to have an adjustable Poisson's ratio, changing the structure's Poisson's ratio from positive to negative. Therefore, the mode conversion characteristics can be used to design porous structures with a negative Poisson's ratio effect.

[0003] While conventional materials contract laterally under tension and expand laterally under compression, negative Poisson's ratio materials expand laterally under tension and contract laterally under compression. The concept of negative Poisson's ratio was first mentioned in the 18th century, and subsequent research on natural materials has revealed materials exhibiting this effect, such as pyrite crystals and load-bearing cancellous bone. Furthermore, a series of artificial structures with this effect have been proposed, including concave-angle honeycombs, chiral structures, interlocking polygonal structures, perforated plate structures, and rotated polygonal structures, all of which exhibit significant negative Poisson's ratio effects. Due to their excellent shear resistance, indentation resistance, surface isotropy, and variable permeability, negative Poisson's ratio materials have found widespread application in defense, military, aerospace, biomedicine, transportation, and other fields. The use of mode conversion to achieve the negative Poisson's ratio effect is primarily seen in elastic perforated plate structures, and this design approach has gradually been applied to honeycomb structures, such as square and hexagonal honeycombs.

[0004] Honeycomb structures have been extensively studied as a type of porous structure. Diamond-shaped honeycomb structures, in particular, are an ideal material for shock absorption and energy absorption. They offer advantages such as strong compression deformation, low relative density, high specific strength, and ease of design and fabrication. They are widely used in a variety of fields, including packaging, vehicle transportation, aerospace, biomedicine, and construction. Conventional diamond-shaped honeycombs exhibit full-wave bending deformation of their cell walls under uniaxial compression and do not exhibit a negative Poisson's ratio. Achieving a negative Poisson's ratio in honeycomb structures typically involves utilizing concave-angle honeycomb designs, such as concave hexagonal honeycombs, arrow-shaped honeycombs, and star-shaped honeycombs. The mechanism for achieving a negative Poisson's ratio is that when a concave-angle honeycomb structure is subjected to tensile / compressive loads, the inclined members simultaneously undergo in-plane rotation while bending. This causes the structure to expand outward in tension and collapse inward in compression. These inclined members primarily bear axial forces and bending moments and typically have a large aspect ratio, resulting in a weak resistance to deformation and limited overall load-bearing capacity. The method of making the diamond honeycomb have a negative Poisson's ratio is usually to combine the diamond honeycomb with a star-shaped / arrow-shaped honeycomb. The structure obtained by this approach has a complex geometric shape, which is not conducive to large-scale production and manufacturing, and the diamond structure in the combined structure mainly plays the role of enhancing and improving the mechanical properties of the structure, rather than directly producing a negative Poisson's ratio. For example, the patent "A Star-shaped-diamond Negative Poisson's Ratio Structure" 2021111530054 discloses a star-shaped-diamond combined honeycomb. When axially compressed, the structure will neck and produce a negative Poisson's ratio effect. Its basic component cells include a star-shaped structure and four single-arrow-shaped structures, two of which are connected to form a diamond structure. This design improves the negative Poisson's ratio effect of the structure and makes the deformation of the structure more stable. It has a wider platform stage, thereby improving the energy absorption effect of the structure, but it also makes the structure complicated, which brings trouble to large-scale production. Similarly, patent "An X-shaped honeycomb structure with a negative Poisson's ratio" 2022108695554 designs an X-shaped honeycomb based on a diamond honeycomb. In terms of the mechanism for achieving a negative Poisson's ratio, the negative Poisson's ratio appears under in-plane axial compression because the longer inclined rods are the first to bend and deform, causing the structure as a whole to shrink laterally; in terms of the strategy for increasing platform stress, the patented X-shaped honeycomb design increases the number of rods to share the load, and the added rods enhance the constraints on the structure, so that the platform stress of the structure can be increased.

[0005] In addition, mode conversion characterized by local buckling will also cause the Poisson's ratio of the porous structure to change from a positive value to a negative value, thereby achieving a negative Poisson's ratio effect. The mechanical properties of the structure are excellent, and the deformation is uniform and stable. For example, the structure has high stiffness, a robust platform stage, and the rotation of the nodes during compression. However, traditional honeycomb structures do not experience mode conversion under uniaxial compression. This is because the stress required to trigger mode conversion characterized by local buckling is always higher than the stress required to trigger bending deformation or overall buckling of the structure. Therefore, in order to achieve mode conversion of the diamond honeycomb, its geometric configuration must be modified to change the preferred deformation mode of the structure.

[0006] In order to obtain a diamond honeycomb structure that directly produces a negative Poisson's ratio effect, this patent modifies the topological configuration of the diamond honeycomb, introduces the mode conversion effect into it, and designs a new multifunctional diamond honeycomb structure with a negative Poisson's ratio effect, and the stiffness, platform stress, etc. of the structure are greatly improved.

[0007] As a method of achieving an adjustable negative Poisson's ratio of a porous structure based on structural mode conversion, Patent No. 201480024260, "Porous Structure with Repeating Elongated Hole Pattern," is designed for the pattern after mode conversion of a porous structure with a square array of circular pores. The geometric configuration is different from that of this patent. It opens holes in a flat plate under a stress-free state according to the deformed pore shape. The pore shape is elliptical pores arranged alternately orthogonally or pores with similar elliptical pore characteristics, thereby obtaining the desired negative Poisson's ratio under macroscopic stress / strain, and adjusting the mechanical properties of the structure by adjusting the porosity and the aspect ratio of the pores. In addition, in terms of the application of mode conversion characteristics, it designs the structure for the geometric configuration after the structural mode conversion, so that it directly produces a negative Poisson's ratio. This is significantly different from the mode conversion in this patent under uniaxial compression, which gives the structure a negative Poisson's ratio effect. Summary of the Invention

[0008] The present invention provides a multifunctional negative Poisson's ratio diamond honeycomb structure, which realizes the transformation of the diamond honeycomb deformation mode by regulating parameters such as the angle and length of the variable-section beam. It has an excellent negative Poisson's ratio effect, and the structure deforms uniformly. It has a robust platform stage that can be used for structural energy absorption. The structure is simple and easy to manufacture. It can be mass-produced by traditional methods such as casting and cutting, thus solving the problems existing in the prior art.

[0009] The present invention provides the following technical solutions:

[0010] A multifunctional negative Poisson's ratio rhombus honeycomb structure comprises a plurality of unit cell structures periodically arranged in the same plane, wherein the unit cell structures are connected end to end to form a rhombus honeycomb;

[0011] The unit cell structure includes four straight beams and four variable-section beams. The side of each variable-section beam is set at a certain angle to the straight beam to which it is connected. The inner sides of the adjacent and symmetrical variable-section beams on the left and right are connected to each other to form an inward-concave arrow structure, and the outer sides of the adjacent and symmetrical variable-section beams on the left and right are connected in the vertical direction.

[0012] Furthermore, the straight beam is composed of two first inclined cell walls and a second inclined cell wall; the variable-section beam is composed of an inner-section beam cell wall and an outer-section beam cell wall, and the inner and outer-section beam cell walls are symmetrically arranged on both sides of the straight beam axis; the upper and lower adjacent outer-section beam cell walls are directly connected or connected by vertical cell walls.

[0013] Furthermore, the two upper and lower adjacent unit cell structures share a second inclined cell wall.

[0014] Furthermore, the thickness of the straight beam is t, and the length of the straight beam is l e / 2; the angle between the side of the variable-section beam and the axis of the straight beam it connects is θ, and the axis length of the variable-section beam is l / 2-l e / 2, the cross-sectional width of the variable cross-section beam is t(x)=t+2tanθ·x,x∈[0,l / 2-l e / 2].

[0015] Furthermore, l is the sum of the axial lengths of the straight beams and the axial lengths of the inclined beams of the upper and lower adjacent unit cell structures forming a single rhombus honeycomb; l e It is the sum of the lengths of the straight beams of the upper and lower adjacent unit cell structures that form a single diamond honeycomb.

[0016] Furthermore, the above parameters satisfy: e / l≤0.6;15°≤θ≤45°;0.08≤t / l≤0.16.

[0017] Furthermore, the application of the multifunctional negative Poisson's ratio rhombus honeycomb structure in a nonlinear elastic damper can be used to manufacture a reusable nonlinear elastic damper for structural vibration reduction.

[0018] Beneficial effects of the present invention:

[0019] 1. Compared with the existing technology, the present invention is an improved design of the diamond honeycomb structure with a simple geometric configuration. By adjusting the topological configuration of the diamond honeycomb, it induces a mode transition under uniaxial compression, thereby giving the structure a negative Poisson's ratio effect. Specifically, the transformation of the diamond honeycomb deformation mode is achieved by regulating parameters such as the angle and length of the variable-section beam. When the structure is compressed beyond a threshold, the Poisson's ratio of the structure rapidly drops from a positive value to a negative value.

[0020] 2. This invention improves structural rigidity and plateau stress by increasing the geometric dimensions of the nodes. The robust plateau phase of the new rhombus honeycomb under axial compression provides excellent energy absorption. This reinforced node design enhances the structure's resistance to deformation, significantly increasing the Young's modulus, specific stiffness, and plateau stress of the rhombus honeycomb, thereby improving the mechanical properties of the structure. Furthermore, the structure is simple and easy to manufacture, allowing for mass production through traditional methods such as casting and cutting.

[0021] 3. The present invention introduces mode conversion into the honeycomb structure by using a node enhancement method. Mode conversion enables the nodes of the diamond honeycomb to have rotational characteristics, which can produce a large range of rotation, and convert the linear motion of the structure into the rotational motion of the nodes. This characteristic can be used to develop torsion actuators, etc. Since similar rotational effects also exist in some bones, this provides valuable insights into the development of biomedical materials.

[0022] In summary, the present invention improves and enriches the mechanical properties of the diamond honeycomb structure and broadens the application range of the diamond honeycomb. The design concept and method are also applicable to square honeycombs and hexagonal honeycombs. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0024] Figure 1 This is a schematic diagram of the unit cell structure of Example 1 of the present invention;

[0025] Figure 2 for Figure 1 Schematic diagram of parameter marking of unit cell structure;

[0026] Figure 3 This is a schematic diagram of the unit cell structure of Example 2 of the present invention;

[0027] Figure 4 This is a schematic diagram of the unit cell structure of Example 3 of the present invention;

[0028] Figure 5 This is a schematic diagram of the unit cell structure of Example 4 of the present invention;

[0029] Figure 6 Schematic diagram of the negative Poisson's ratio rhombus honeycomb structure of the present invention and its deformation mode under compression load (l = 8mm, l e =3mm, t = 0.8mm and θ = 30° as an example);

[0030] Figure 7 Schematic diagram of a traditional diamond honeycomb structure and its deformation mode under compressive load;

[0031] Figure 8 The variation of Poisson's ratio of the negative Poisson's ratio rhombus structure of the present invention and the traditional rhombus honeycomb structure with strain under uniaxial compression;

[0032] Figure 9 are the stress-strain curves of the two structures;

[0033] Figure 10 The graph shows the variation of the rotation angle of the nodes of the negative Poisson's ratio rhombus honeycomb structure of the present invention with strain under uniaxial compression.

[0034] in, Figure 8-10 Here, "Structure 1" refers to the negative Poisson's ratio rhombus honeycomb structure of the present invention, and "Structure 2" refers to the traditional rhombus honeycomb structure.

[0035] In the drawings, 1 is a straight beam, 101 is a first inclined cell wall, 102 is a second inclined cell wall, 2 is a variable-section beam, 201 is an inner-section beam cell wall, 202 is an outer-section beam cell wall, and 203 is a vertical cell wall. DETAILED DESCRIPTION

[0036] The present invention is further described below with reference to specific examples, but the protection scope of this application is not limited to these examples.

[0037] In the description of the present invention, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "top", "bottom", "inside", "outside", etc., indicating directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as limiting the present invention.

[0038] By topologically reconstructing the traditional rhombus honeycomb structure, a new honeycomb structure with a mode conversion effect was designed. This honeycomb structure consists of multiple unit cells periodically arranged in the same plane, connected end-to-end to form a multifunctional negative Poisson's ratio rhombus. The unit cell structure includes four straight beams 1 and four variable-section beams 2. The sides of each variable-section beam are arranged at a specific angle to the straight beam to which it connects. The inner sides of adjacent and symmetrical variable-section beams on the left and right are connected to form a concave arrow structure, while the outer sides of adjacent and symmetrical variable-section beams on the left and right are connected vertically.

[0039] The straight beam is composed of two first inclined cell walls 101 and a second inclined cell wall 102, and the two upper and lower adjacent single cell structures share one second inclined cell wall 102; the variable-section beam 2 is composed of an inner-section beam cell wall 201 and an outer-section beam cell wall 202; the ends of the upper and lower adjacent outer-section beam cell walls are directly connected or are also connected to a vertical cell wall 203.

[0040] The thickness of the straight beam is t and the length of the straight beam is l e / 2; the angle between the side of the variable-section beam and the axis of the straight beam it connects is θ, and the axis length of the variable-section beam is l / 2-l e / 2, the cross-sectional width of the variable cross-section beam is t(x)=t+2tanθ·x,x∈[0,l / 2-l e / 2]. l is the sum of the axial lengths of the straight beams and the axial lengths of the variable slope beams of the upper and lower adjacent unit cell structures that form a single rhombus honeycomb; l e is the sum of the lengths of the straight beams of the upper and lower adjacent unit cells that form a single rhombus honeycomb. e / l≤0.6;15°≤θ≤45°;0.08≤t / l≤0.16.

[0041] The specific method of obtaining the above-mentioned unit cell structure is as follows: on the basis of the traditional rhombus honeycomb structure, at a distance of l from the midpoint of the rhombus honeycomb cell wall, e / 2, the two outer edges of the cell wall are simultaneously deflected outward by an angle θ to form a variable-section beam, which intersects at the node and is cut off at the intersection of the line segments; specifically, among the two sides of the variable-section beam, the inner sides intersect at the node and are cut off at the intersection of the line segments, the outer side and the inner side are equal, and the upper and lower outer sides are connected by a vertical line.

[0042] Example 1

[0043] See also Figure 1 and Figure 2 , showing a structural form composed of a single-cell structure of a multifunctional negative Poisson's ratio rhombus honeycomb according to the present invention. In this structure, the inner sides of two adjacent and symmetrical variable-slope beams intersect at point A. The first inclined cell wall 101 of the straight beam in the upper left corner and the variable-section beam 2 are connected at points B and C. The outer first inclined cell wall of the straight beam in the lower left corner and the outer side of the variable-section beam are connected at point F. The length of line segment AB is equal to that of line segments CD and EF, and a vertical line connects points D and E.

[0044] In this embodiment, the specific dimensions of the unit cell structure are: l is 8 mm, l e is 3mm, t is 0.8mm, and θ is 30°.

[0045] Example 2

[0046] See also Figure 3 , showing another structural form composed of a multifunctional negative Poisson's ratio rhombus honeycomb unit cell structure of the present invention. This structure is similar to the unit cell structure of Example 1, except that the straight beams l are shorter than those obtained from the traditional rhombus honeycomb structure of Example 1. As a result of the improved design concept of the present invention, the outer edges of the upper and lower adjacent variable-section beams of the resulting unit cell structure overlap and are directly connected.

[0047] Example 3

[0048] See also Figure 4 , showing another structural form of the multifunctional negative Poisson's ratio rhombus honeycomb unit cell structure of the present invention. This structure is similar to the unit cell structure of Example 1, except that when the angle θ between the side of the variable-section beam and the axis of the straight beam it connects to is smaller, line segments CD and EF are no longer on the same vertical line, and a vertical line connects points D and E.

[0049] Example 4

[0050] Similarly, as another embodiment, when the angle θ is greater than Figure 1 When the angle θ in the unit cell is larger, line segments CD and EF are tilted outward in the vertical direction. In this case, a vertical line is also used to connect points D and E. Figure 5 .

[0051] Example 4 Multifunctional negative Poisson's ratio diamond honeycomb structure and deformation mode

[0052] Taking the unit cell structure of Example 1 as an example, its deformation mode is examined. Through the above design, when the rhombus honeycomb is subjected to an axial compression load exceeding the threshold, the cell wall will become unstable, forming a local buckling deformation mode, and the cell wall will change from full-wave bending to half-wave bending, and drive the two adjacent rows of nodes to rotate in opposite directions, that is, the structure undergoes a mode conversion, such as Figure 6 The deformation mechanism is that the enlarged nodes strengthen the constraints on the uniform cross-section beam, making the deformation more concentrated in the straight beam, which is more susceptible to slight disturbances and produces a new equilibrium mode, making it more prone to local buckling rather than continuing the original deformation mode until the cell walls contact each other. The rotation of the nodes of the diamond honeycomb caused by the mode conversion causes the structure to fold inward, causing the Poisson's ratio of the structure to quickly drop from a positive value to a negative value, as shown in Figure 8 In addition, the local buckling characteristics of the rhombus honeycomb cell wall during mode conversion make the stress-strain curve of the structure have a continuous and stable platform stage, as shown in Figure 9 As shown in Figure 2, this gives the structure good energy absorption characteristics. This reinforced node design improves the structure's ability to resist deformation, greatly improving the Young's modulus, specific stiffness, and platform stress of the diamond honeycomb.

[0053] See also Figure 7 and Figure 8 , Traditional diamond honeycombs usually experience bending deformation of the cell walls under uniaxial compression, have limited bearing capacity and do not have the negative Poisson's ratio effect.

[0054] See also Figure 10, shows the variation in the rotation angle of the nodes of the negative Poisson's ratio rhombus honeycomb structure of the present invention with strain under uniaxial compression. This converts the linear motion of the structure into rotational motion of the nodes, i.e., mode conversion, giving the rhombus honeycomb nodes rotational properties. This property can be exploited to develop torsional actuators, etc.

[0055] It should be noted that the terms "first," "second," and the like in the specification and claims of this application and the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than that illustrated or described herein.

[0056] The foregoing is merely an embodiment of the present application, and the scope of protection of the present application is not limited by these specific embodiments, but is determined by the claims of the present application. For those skilled in the art, the present application may have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc. made within the technical ideas and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A multifunctional negative Poisson's ratio rhombus honeycomb structure, characterized in that: It includes multiple unit cell structures periodically arranged in the same plane, and each unit cell structure is connected end to end to form a diamond honeycomb; The unit cell structure includes four straight beams and four variable-section beams, the side of each variable-section beam is arranged at a certain angle to the straight beam it is connected to, the inner sides of the left and right adjacent and symmetrical variable-section beams are connected to each other to form an inward-concave arrow structure, and the outer sides of the left and right adjacent and symmetrical variable-section beams are connected in the vertical direction; The straight beam is composed of two first inclined cell walls and a second inclined cell wall, and the two upper and lower adjacent single cell structures share a second inclined cell wall; the variable cross-section beam is composed of an inner cross-section beam cell wall and an outer cross-section beam cell wall, and the inner and outer cross-section beam cell walls are symmetrically arranged on both sides of the straight beam axis; the upper and lower adjacent outer cross-section beam cell walls are directly connected or connected by a vertical cell wall; The thickness of the straight beam is t, and the length of the straight beam is l e / 2; the angle between the side of the variable-section beam and the axis of the straight beam it connects is θ, and the axis length of the variable-section beam is l / 2 -l e / 2, the cross-sectional width of the variable cross-section beam is 。 2. The multifunctional negative Poisson's ratio diamond honeycomb structure according to claim 1, characterized in that: l It is the sum of the axial lengths of the straight beams and the axial lengths of the inclined beams of the upper and lower adjacent unit cells that form a single diamond honeycomb; l e It is the sum of the lengths of the straight beams of the upper and lower adjacent unit cell structures that form a single diamond honeycomb.

3. The multifunctional negative Poisson's ratio diamond honeycomb structure according to claim 1, characterized in that: The above parameters meet: l e / l ≤0.6; 15°≤θ≤45°; 0.08≤ t / l ≤0.16.

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