Triangular enhanced negative poisson's ratio cells and honeycomb structures thereof

Abstract

The application belongs to the technical field of mechanical metamaterials, and particularly relates to a triangularly enhanced negative Poisson's ratio cell and a honeycomb structure thereof. The negative Poisson's ratio cell comprises an inner concave hexagonal structure, the inner concave hexagonal structure comprises two horizontal cell walls and inclined cell walls, each inclined cell wall is formed by two inclined cell wall inner concave bending, left and right symmetrical bending wall rods are embedded in the inner concave hexagonal structure, the bending points of each bending wall rod are connected with the connection points of the two inclined cell walls of the inclined cell wall, and the two ends of each bending wall rod are connected with the horizontal cell walls. The novel honeycomb structure composed of the negative Poisson's ratio cell utilizes the stability of the triangle to overcome the unstable buckling of the traditional inner concave honeycomb structure, enhances the structural rigidity, and makes the honeycomb structure have obvious negative Poisson's ratio effect and better energy absorption performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of mechanical metamaterials, and particularly relates to a triangularly enhanced negative Poisson's ratio cell and a honeycomb structure thereof. BACKGROUND

[0002] The negative Poisson's ratio honeycomb, also known as the auxetic honeycomb structure, is a kind of porous honeycomb structure, which has a special negative Poisson's ratio effect, i.e. expands when stretched and shrinks when compressed, and thus exhibits excellent physical properties such as light weight, impact resistance, dent resistance, energy absorption, sound absorption, high damping and the like. In addition, the honeycomb structure has other special mechanical properties such as higher relative stiffness, strength and high energy absorption capacity after special configuration optimization, so that it has a wide application prospect in the fields of aerospace, medicine, transportation, building materials and the like.

[0003] With the rapid development of additive manufacturing methods such as 3D printing technology, some new structures are being designed to achieve new deformation modes, enhanced stiffness, more obvious NPR effect or higher platform stress and more optimal energy absorption characteristics. Common negative Poisson's ratio cell concave structures mainly include: concave hexagonal structure, origami structure, star structure, chiral / anti-chiral structure and the like. The concave hexagonal structure as a classic negative Poisson's ratio structure has been studied by many scholars at home and abroad, and it is found that it has many superior mechanical properties and certain application prospect in many engineering fields. However, due to the defects of larger void ratio and poor deformation stability in the compression process, the platform stress is low when it is subjected to external load, the resistance to external load is poor, the bearing capacity is insufficient, and the energy absorption performance is greatly reduced.

[0004] Patent 2020105756148 discloses a negative Poisson's ratio cell and its honeycomb structure, which includes six sides, wherein the left and right sides are arc sides, and there are two internal vertical rods inside the cell, which are connected with the arc sides on the left and right sides respectively, overcoming the defects of traditional negative Poisson's ratio structure, such as large internal gap, deformation instability of two side concave angles and poor bearing capacity. However, when the structure is subjected to external load, although the vertical rods inside the structure connected with the arc sides can resist deformation of the arc sides, achieve higher energy absorption and impact resistance and bearing capacity, but this will weaken the negative Poisson's ratio effect of the structure, to some extent, weaken the application potential of the structure. Patent 2021111530054 discloses a star-diamond negative Poisson's ratio structure, which replaces the horizontal and vertical rib plates of the star-shaped honeycomb structure with four single arrowhead structures, thereby forming a star-diamond negative Poisson's ratio structure, which has multi-step deformation and presents multiple platform stresses. The above structures greatly weaken the negative Poisson's ratio effect. In addition, patent 2021113165924 discloses an inner concave negative Poisson's ratio metamaterial cell and honeycomb structure, which is provided with a supporting cell wall on the left and right sides of the inner concave hexagonal structure, the two ends of the supporting cell wall are connected with two horizontal cell walls respectively, and the end of the supporting cell wall does not coincide with the end of the horizontal cell wall, and the midpoint of the supporting cell wall is connected with the connection point of the two inclined cell walls forming the inner concave bending structure. Since the embedded inner cell wall rod is concave in the same direction as the outer cell wall rod, the supporting effect is weak during deformation. SUMMARY

[0005] In order to solve the above problems, a triangular reinforced negative Poisson's ratio cell and its honeycomb structure are provided. The new honeycomb structure uses the stability of the triangle to overcome the unstable buckling of the traditional inner concave honeycomb structure, enhances the structural stiffness, and at the same time, has obvious negative Poisson's ratio effect and better energy absorption performance, solving the problems existing in the prior art.

[0006] The present application provides one of the following technical solutions:

[0007] A triangular reinforced negative Poisson's ratio cell includes an inner concave hexagonal structure, the inner concave hexagonal structure includes two horizontal cell walls and inclined cell walls arranged between the two ends of the two horizontal cell walls, each inclined cell wall is formed by two inclined cell walls being concave and bent, left and right symmetrical bending wall rods are embedded in the inner concave hexagonal structure, the bending points of each bending wall rod are connected with the connection points of the two inclined cell walls of the inclined cell walls, and the two ends of each bending wall rod are connected with the horizontal cell walls respectively.

[0008] Further, the bending wall rod is a vertical wall rod or an outer convex bending wall rod.

[0009] Further, the bent wall rod is composed of two inner wall rods connected at a certain angle; each inner wall rod is arranged at a θ1 angle with the vertical axis where the two inclined cell wall connecting points are located, and the θ1 satisfies: 0°≤θ1≤30°.

[0010] Further, when θ1=30°, the top end and the bottom end of the two bent wall rods are connected respectively.

[0011] Further, the thickness of the inclined cell wall of the inner recessed hexagonal structure is t0, and the thickness of the bent wall rod is t1; t0 is equal to or not equal to t1.

[0012] Further, the horizontal connecting cell wall rods are connected on both sides of the inner recessed hexagonal structure, and each horizontal connecting cell wall rod is connected with the two inclined cell wall connecting points of the inclined cell wall; the length of the horizontal connecting cell wall rod is equal to the length of the horizontal cell wall of the inner recessed hexagonal structure.

[0013] Further, an external bent wall rod is further connected on each horizontal connecting cell wall rod, each external bent wall rod is parallel to the bent wall rod arranged on the same side in the inner recessed hexagonal structure, and the top end and the bottom end of each external bent wall rod are connected with the end portions of the two horizontal cell walls of the inner recessed hexagonal structure on the same side respectively.

[0014] The present application provides the following technical scheme II:

[0015] The triangular enhanced negative Poisson's ratio cell is connected with a vertical rod between the two inclined cell walls of the inner recessed hexagonal inclined cell wall on the basis of the aforementioned negative Poisson's ratio cell; the bent wall rod comprises upper and lower symmetrically arranged upper and lower inner wall rods, the bottom end of the upper inner wall rod and the top end of the lower inner wall rod form connecting points with the inner side of the vertical rod respectively, and the vertical distance between the connecting point of the upper inner wall rod and the vertical rod and the connecting point of the lower inner wall rod and the vertical rod is less than the height of the vertical rod.

[0016] The present application provides the following technical scheme III:

[0017] A negative Poisson's ratio honeycomb structure composed of the triangular enhanced negative Poisson's ratio cell as described above arranged and combined. The triangular enhanced negative Poisson's ratio cell mentioned here refers to the cell of the aforementioned inner recessed hexagonal structure connected with the horizontal connecting cell wall rod.

[0018] Further, the negative Poisson's ratio honeycomb structure is arranged in several columns in the transverse direction and several rows in the longitudinal direction by the aforementioned triangular enhanced negative Poisson's ratio cell; the triangular enhanced negative Poisson's ratio cells arranged in the longitudinal direction share a horizontal cell wall.

[0019] Further, the triangular enhanced negative Poisson's ratio cell is connected between the adjacent columns of the aforementioned negative Poisson's ratio honeycomb structure; the negative Poisson's ratio honeycomb structure is composed of the triangular enhanced negative Poisson's ratio cells connected in an upper and lower staggered manner in the transverse direction.

[0020] Advantages of the present application:

[0021] The triangular reinforced negative Poisson's ratio honeycomb structure of the present application uses the stability of the triangle to overcome the unstable buckling of the traditional concave honeycomb structure, enhances the structural rigidity, and at the same time has obvious negative Poisson's ratio effect and better energy absorption performance. The following advantages are shown in the energy absorption characteristics: (1) the negative Poisson's ratio effect can be ensured while the energy absorption is enhanced; (2) through reasonable parameterized design, the initial peak force of the structure can be reduced and the impact force efficiency can be increased; (3) the structure is simple and effective, not limited to a single material, more convenient and efficient in structure manufacturing, lower production cost, and higher manufacturing efficiency; (4) it can be expanded to a three-dimensional structure, and has greater design and application potential.

[0022] Specifically, the present application embeds a bent wall rod of the "<>" type in the concave hexagon, so that the deformation mode of the unit in the stable compression stage is obviously different from that of the traditional concave hexagonal structure and other improved negative Poisson's ratio honeycomb structures when subjected to external pressure, and the negative Poisson's ratio characteristics are obvious in the compression process, the deformation mode is more uniform, and the triangular reinforcement effect is outstanding. The negative Poisson's ratio honeycomb structure can realize different deformation effects by changing the size of the inner cell wall angle θ1, and improve the platform stress and specific energy absorption.

[0023] In summary, the negative Poisson's ratio honeycomb structure of the present application has obvious negative Poisson's ratio effect while improving the impact resistance and energy absorption, and has a large parameter control range, which can reduce the initial peak force of the structure when subjected to impact; the structure form is simple and effective, and is convenient for production and manufacturing. BRIEF DESCRIPTION OF DRAWINGS

[0024] The accompanying drawings, which are included to provide a further understanding of the present application and constitute a part of this application, illustrate certain illustrative embodiments of the present application and together with their description serve to explain the present application. In the drawings:

[0025] Figure 1 A unit configuration of the triangular reinforced negative Poisson's ratio honeycomb structure of the present application;

[0026] Figure 2 A triangular reinforced negative Poisson's ratio honeycomb structure of the present application;

[0027] Figure 3 A comparison of the deformation modes of the negative Poisson's ratio honeycomb structure of the present application and the traditional negative Poisson's ratio structure under quasi-static compression;

[0028] Figure 4 A Poisson's ratio-strain curve of the negative Poisson's ratio honeycomb structure of the present application and the traditional negative Poisson's ratio structure under quasi-static compression;

[0029] Figure 5 The platform stress influence diagram of the NARH1 configuration of the present application at different angles θ1;

[0030] Figure 6 The specific energy absorption influence diagram of the NARH1 configuration of the present application at different angles θ1;

[0031] Figure 7 The mechanical response of the negative Poisson's ratio honeycomb structure and the conventional negative Poisson's ratio structure under dynamic impact;

[0032] Figure 8 The specific energy absorption of the negative Poisson's ratio honeycomb structure and the conventional negative Poisson's ratio structure under dynamic impact;

[0033] Figure 9 The cell optimization configuration of the NARH1 configuration of the negative Poisson's ratio honeycomb structure of the present application and the PCF and CFE relationship diagram thereof;

[0034] Figures 10-12 The color view corresponding to Figures 5-7 ;

[0035] Figure 13 The color view corresponding to Figure 9 .

[0036] wherein, Figure 1 (a) in the figure is a configuration of a cell of the triangular reinforced negative Poisson's ratio honeycomb structure of the present application, Figure 1 (b) in the figure is another structural configuration of the cell of the triangular reinforced negative Poisson's ratio honeycomb structure;

[0037] Figure 2 (a) in the figure is a sub-configuration NARH1 of the triangular reinforced negative Poisson's ratio honeycomb structure of the present application; Figure 2 (b) in the figure is another sub-configuration NARH2 of the triangular reinforced negative Poisson's ratio honeycomb structure of the present application;

[0038] Figure 9 (a) in the figure is the optimized configuration of the NARH1 cell of the present application; Figure 9 (b) in the figure is the initial peak force and impact force efficiency relationship diagram of the NARH1. DETAILED DESCRIPTION

[0039] The present application will be further described below in conjunction with specific embodiments, but the protection scope of the present application is not limited to these embodiments.

[0040] In the description of the present application, it needs to be understood that the terms "upper", "lower", "front", "back", "left", "right", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0041] Referring to Figure 1 , a negative Poisson's ratio cell of the present application is shown, Figure 1 9 conventional NARH cell parameters are shown in Table 1, the inclined cell wall length is L0, the horizontal cell wall length is h0, the outer cell wall thickness is t0, the inner cell wall thickness is t1, the outer cell wall angle is θ0, the inner cell wall angle is θ1, and the horizontal connecting cell wall rod is L2.

[0042] Example 1

[0043] As shown in Figure 1 (a), a negative Poisson's ratio cell of the present application is shown, which comprises an inner recessed hexagonal structure, the inner recessed hexagonal structure comprises two horizontal cell walls h0 and inclined cell walls arranged between the two ends of the two horizontal cell walls, each inclined cell wall is recessed and bent by two inclined cell walls L0; left and right symmetrical outer convex bent wall rods are embedded in the inner recessed hexagonal structure; the bending points of each outer convex bent wall rod are connected with the connecting points of the two inclined cell walls of the inclined cell wall, and the two ends of each outer convex bent wall rod are connected with the horizontal cell walls.

[0044] Horizontal connecting cell wall rods L2 are connected to both sides of the inner recessed hexagonal structure, and each horizontal connecting cell wall rod is connected with the connecting points of the two inclined cell walls of the inclined cell wall; the length of the horizontal connecting cell wall rod is equal to the length of the horizontal cell wall of the inner recessed hexagonal structure.

[0045] The outer convex bent wall rod is composed of two inner wall rods connected at a certain angle; each inner wall rod is arranged at an angle θ1 with the vertical axis where the connecting points of the two inclined cell walls are located, and in this embodiment, θ1 = 16°.

[0046] As another embodiment of the present application, when θ1 = 30°, the top end and the bottom end of the two outer convex bent wall rods are connected.

[0047] Example 2

[0048] As shown in Figure 1 (b), another negative Poisson's ratio cell of the present application is shown, which is based on the negative Poisson's ratio cell of example 1, and further comprises outer bent wall rods connected to each horizontal connecting cell wall rod L2, each outer bent wall rod is parallel to the outer convex bent wall rod on the same side arranged in the inner recessed hexagonal structure, and the top end and the bottom end of each outer bent wall rod are connected to the end portions of the two horizontal cell walls of the inner recessed hexagonal structure on the same side.

[0049] Figure 1 The thickness t0 of the inner concave hexagonal structure is equal to or different from the thickness t1 of the outer convex curved wall rod.

[0050] Embodiment 3

[0051] Referring to Figure 7 The conventional NARH cell parameters of another triangular reinforced negative Poisson's ratio cell of the present application are shown in (a), wherein the length of the inclined cell wall is L0, the length of the horizontal cell wall is h0, the thickness of the outer cell wall is t0, the thickness of the inner cell wall is t1, the angle of the outer cell wall is θ0, the angle of the inner cell wall is θ1, the horizontal connecting cell wall rod is L2, the vertical rod is W0, and W1 is the distance between the connecting point of the vertical rod and the upper inner wall rod and the lower inner wall rod of the outer convex curved wall rod.

[0052] The triangular reinforced negative Poisson's ratio cell is based on the configuration of the negative Poisson's ratio cell in Embodiment 1, and further comprises a vertical rod W0 connected between the two inclined cell walls of the inner concave hexagonal inclined cell wall. The outer convex curved wall rod comprises an upper inner wall rod and a lower inner wall rod symmetrically arranged on the upper and lower sides. The bottom end of the upper inner wall rod and the top end of the lower inner wall rod form connecting points with the inner side of the vertical rod, respectively. The vertical distance W1 between the connecting point of the upper inner wall rod and the vertical rod and the connecting point of the lower inner wall rod and the vertical rod is less than the height of the vertical rod.

[0053] Embodiment 4

[0054] As shown in Figure 2 The sub-configuration NARH1 of the triangular reinforced negative Poisson's ratio honeycomb structure NARH of the present application is shown in (a). The NARH1 is arranged in several columns in the transverse direction and several rows in the longitudinal direction by using the negative Poisson's ratio cell in (a) of Embodiment 1. The triangular reinforced negative Poisson's ratio cells arranged in the longitudinal direction share a horizontal cell wall.

[0055] Embodiment 5

[0056] As shown in Figure 2 The sub-configuration NARH2 of the triangular reinforced negative Poisson's ratio honeycomb structure NARH of the present application is shown in (b). The NARH2 is arranged in several columns in the transverse direction and several rows in the longitudinal direction by using the negative Poisson's ratio cell in (b) of Embodiment 1. The triangular reinforced negative Poisson's ratio cells arranged in the longitudinal direction share a horizontal cell wall.

[0057] The NARH2 configuration is based on the NARH1 configuration, and a new triangular enhanced negative Poisson's ratio cell is connected between adjacent columns; the negative Poisson's ratio honeycomb structure formed by the new triangular enhanced negative Poisson's ratio cell is composed of upper and lower staggered triangular enhanced negative Poisson's ratio cells in the transverse direction. The upper and lower staggered triangular enhanced negative Poisson's ratio cell structure is the same in size. The NARH2 configuration is equivalent to forming a new triangular enhanced negative Poisson's ratio cell with the same size between every four adjacent triangular enhanced negative Poisson's ratio cells, and the new triangular enhanced negative Poisson's ratio cell is connected in sequence in the longitudinal direction. The inclined cell wall of the new triangular enhanced negative Poisson's ratio cell coincides with the inclined cell wall of the four adjacent triangular enhanced negative Poisson's ratio cells. The horizontal connection cell wall rod of the new triangular enhanced negative Poisson's ratio cell coincides with the horizontal cell wall rod of the outer side upper and lower connected triangular enhanced negative Poisson's ratio cell.

[0058] I. Mechanical response of the new auxetic structure NARH1 and NARH2 under quasi-static compression

[0059] In order to illustrate that the structure proposed in the present application has better deformation stability and negative Poisson's ratio effect than the traditional negative Poisson's ratio structure, the deformation mode and Poisson's ratio under quasi-static compression are studied, and are compared with the traditional concave hexagonal negative Poisson's ratio structure.

[0060] Referring to Figure 3 , the comparison of the honeycomb crushing deformation mode of ARH, NARH1 and NARH2 under quasi-static compression finds that the deformation modes in the stable compression stage are obviously different. For ARH, the "<" deformation mode can be observed at a strain of 0.2. Subsequently, when the strain is 0.4, the ">" deformation mode is gradually formed in the ARH. NARH1 exhibits the initial stage of the "Y" deformation mode. Subsequently, the "X" and "I" deformation modes are entered. For NARH2, the initial deformation mode looks like an "X" band globally. With the increase of the strain, the "I" band is formed and then enters the densification stage. The results show that the NARH structure of the present application is more stable in deformation after entering the platform stage, and has obvious negative Poisson's ratio effect with symmetrical deformation.

[0061] Referring to Figure 4 , the Poisson's ratio-nominal strain curves of the three honeycomb structures under quasi-static compression are given, and NARH1 and NARH2 both exhibit obvious negative Poisson's ratio characteristics in the compression process. The "necking" phenomenon of the honeycomb structure causes a valley in the curve, and then the curve gradually rises with the compression. It is worth noting that the absolute value of the Poisson's ratio of NARH1 is greater than that of ARH and NARH2 in the range of 0.1<ε y <0.5. The absolute value of the Poisson's ratio of NARH2 is greater than that of ARH in the range of 0.1<ε yThe negative Poisson's ratio characteristic of NARH2 in the range of <0.43 is superior to ARH, which is due to the more uniform deformation mode of NARH structure in quasi-static compression.

[0062] II. Effect of different inner cell wall angles θ1 on the platform stress of the negative Poisson's ratio honeycomb structure

[0063] Table 1

[0064]

[0065] Taking the NARH1 configuration of the present application as an example, the effect of different θ1 on the platform stress of the negative Poisson's ratio honeycomb structure is observed by changing the inner cell wall angle θ1. Table 1 provides the cell configuration of the NARH1 configuration of the present application with θ1 in the range of 0°-30°, which is compared with the conventional negative Poisson's ratio cell.

[0066] As Figure 5 , at an impact speed of 10 m / s, the platform stress increases with the increase of θ1, and when θ1≥8°, the increase is not large, as Figure 6 , the specific energy absorption increases with the increase of θ1. By comparison, it can be seen that the platform stress and the specific energy absorption of the conventional ARH structure are lower than those of the NARH1 configuration of the present application with different θ1.

[0067] III. Mechanical response of the new auxetic structure of the present application under dynamic impact

[0068] In order to illustrate that the structure proposed in the present application has better impact energy absorption capacity than the conventional negative Poisson's ratio structure, the platform stress and specific energy absorption of the structure under dynamic impact speeds of 50 m / s and 100 m / s are studied, and are compared with those of the conventional concave hexagonal negative Poisson's ratio structure.

[0069] Table 2

[0070]

[0071] Referring to Figure 7 , the stresses of NARH1 and NARH2 under impact speeds of 50 m / s and 100 m / s are higher than those of the conventional negative Poisson's ratio structure under global strain.

[0072] As shown in Table 2 above, at an impact speed of 50 m / s, the platform stress of NARH2 and NARH1 is 116.93% and 63.86% higher than that of ARH respectively; at an impact speed of 100 m / s, the platform stress of NARH2 and NARH1 is 74.26% and 53.9% higher than that of ARH respectively.

[0073] As Figure 8 shown, the specific energy absorption of NARH1 and NARH2 under global strain is higher than that of the conventional concave hexagonal auxetic structure ARH.

[0074] To reduce the initial peak force (PCF) and improve impact efficiency (CFE) during structural impact, the configuration of NARH1 was further optimized, specifically as follows: Figure 9 As shown in (a), this optimized configuration contains two key parameters, W0 and W1. Dimensionless parameters D0 = W0 / L0 and D1 = W1 / L0 are defined. Adjusting the values ​​of D0 and D1 changes the PCF and CFE values ​​of NARH1. The relationship between PCF and CFE is shown in Figure (a). Figure 9 In Figure (b), it can be observed that compared to the (red) circle in the figure, the PCF and CFE values ​​of the (orange) triangle are reduced by 31% and increased by 22%, respectively. Therefore, by reasonably optimizing the NARH1 configuration, the initial peak force can be reduced and the impact efficiency can be improved, which has an important impact on improving the impact resistance of the honeycomb structure.

[0075] The above description is merely an embodiment of this application, and the scope of protection of this application is not limited to these specific embodiments, but is determined by the claims of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the technical concept and principles of this application should be included within the scope of protection of this application.

Claims

1. A triangularly enhanced negative Poisson's ratio cell, characterized by, The inner recessed hexagonal structure comprises two horizontal cell walls and two inclined cell walls between the two ends of the two horizontal cell walls, and each inclined cell wall is formed by two inclined cell wall recessed bends; left and right symmetrical bending wall rods are embedded in the inner recessed hexagonal structure; the bending points of each bending wall rod are connected with the connection points of the two inclined cell walls of the inclined cell wall, and the two ends of each bending wall rod are connected with the horizontal cell walls respectively; Horizontal connection cell wall rods are connected on both sides of the inner recessed hexagonal structure, and the connection points of each horizontal connection cell wall rod and the two inclined cell walls of the inclined cell wall are connected; the length of the horizontal connection cell wall rod is equal to the length of the horizontal cell wall of the inner recessed hexagonal structure; An external bending wall rod is further connected on each horizontal connection cell wall rod, each external bending wall rod is parallel to the same side bending wall rod arranged in the inner recessed hexagonal structure, and the top end and the bottom end of each external bending wall rod are connected with the same side end of the two horizontal cell walls of the inner recessed hexagonal structure respectively.

2. The triangular enhanced negative Poisson's ratio cell of claim 1, wherein, The bent wall rod is composed of two inner wall rods connected at a certain angle; the vertical axis of the connection point of each inner wall rod and two inclined cell walls is arranged at an angle 0°≤ 0°≤ 30°.

3. The triangular enhanced negative Poisson's ratio cell of claim 2, wherein, When = 30°, the top end and the bottom end of the two-bend wall rod are connected respectively.

4. The triangular enhanced negative Poisson's ratio cell of any of claims 1-3, wherein, A vertical rod is further connected between the two inclined cell walls of the inclined cell wall of the inner recessed hexagonal structure; the bending wall rod comprises an upper inner wall rod and a lower inner wall rod arranged symmetrically upwards and downwards, the bottom end of the upper inner wall rod and the top end of the lower inner wall rod form connection points with the vertical rod respectively, and the vertical distance between the connection point of the upper inner wall rod and the vertical rod and the connection point of the lower inner wall rod and the vertical rod is less than the height of the vertical rod.

5. A negative Poisson's ratio honeycomb structure characterized by, The negative Poisson's ratio honeycomb structure is composed of the triangular enhanced negative Poisson's ratio cell units of claim 1.

6. The negative Poisson's ratio honeycomb structure according to claim 5, wherein The negative Poisson's ratio honeycomb structure is arranged in several columns in the transverse direction and in several rows in the longitudinal direction by the triangular enhanced negative Poisson's ratio cell units; the triangular enhanced negative Poisson's ratio cell units arranged in the longitudinal direction share a horizontal cell wall.

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