Novel mixed gradient double-arrow negative Poisson's ratio structure and application

Abstract

The invention relates to the technical field of metamaterial design, in particular to a novel mixed-gradient double-arrow negative Poisson's ratio structure and application, the novel mixed-gradient double-arrow negative Poisson's ratio structure comprises a plurality of mutually connected cell elements, and each cell element comprises an arrow part, an arch part and a vertical rib plate; the arrow part is arranged to be a combination of the first concave arrow and the second concave arrow, the arch part is arranged in the arrow part, the vertical rib plates are arranged on the two sides of the arrow part respectively to form complete cell elements, and the negative poisson ratio structure is in a unique deformation mode under in-plane crushing load through mutual connection of the complete cell elements. The cell elements transversely contract and gather towards the core until complete densification is achieved, mixed gradient design is conducted on the thickness of the double-arrow cell walls and the thickness of the arched cell walls, so that the cell walls can present a more reasonable deformation mode in the compression process, the bearing capacity of the structure in the compression process is improved, and it is guaranteed that the comprehensive mechanical property of the whole structure is effectively improved; the problem that in the prior art, a negative Poisson's ratio structure is poor in compression rigidity and energy absorption capacity is solved.

Description

Technical Field

[0001] This invention relates to the field of metamaterial design technology, specifically to a novel double-arrow negative Poisson's ratio structure with hybrid gradients. Background Technology

[0002] In the vast field of materials science, mechanical metamaterials, as a rising star, are attracting the attention of numerous researchers with their unique mechanical properties and broad application prospects. Mechanical metamaterials are a class of artificial composite materials that achieve mechanical properties surpassing those of conventional materials through meticulously designed microstructures. These materials do not rely on the inherent properties of their constituent components, but rather cleverly utilize the arrangement, geometry, and topological configuration of structural units to achieve precise control over their mechanical properties. This unique performance control method provides entirely new ideas and methods for solving the problems faced by traditional materials in many engineering fields, greatly expanding the application boundaries of materials.

[0003] Negative Poisson's ratio honeycomb structures, as an important branch of mechanical metamaterials, have attracted much attention due to their unique mechanical properties and are also known as dilatational structures. Poisson's ratio is an important mechanical parameter describing the ratio of transverse strain to longitudinal strain in a material under uniaxial stress. For most conventional materials, Poisson's ratio is positive, meaning that when the material is stretched in the longitudinal direction, it will contract in the transverse direction; and when it is compressed in the longitudinal direction, it will expand in the transverse direction. However, negative Poisson's ratio materials exhibit the opposite mechanical behavior: under longitudinal tension (compression), they expand (contract) in the transverse direction. This unconventional mechanical property makes negative Poisson's ratio materials potentially valuable in many fields.

[0004] The uniqueness of tensile structures lies not only in their negative Poisson's ratio effect but also in their accompanying superior mechanical properties. Their unique deformation behavior endows them with excellent shear resistance, enabling them to better resist deformation and maintain structural stability under shear forces. Simultaneously, tensile structures possess excellent indentation resistance, effectively dispersing pressure under localized stress, reducing indentation, and protecting the structural surface from damage. Furthermore, their good fracture toughness prevents further crack propagation when cracks are generated under external forces, improving material reliability and service life. Moreover, tensile structures have a strong energy absorption capacity; under dynamic loads such as impact or vibration, they can absorb a large amount of energy through their deformation, thereby mitigating structural damage. These superior mechanical properties make tensile structures a promising candidate for applications in aerospace, automotive, and military fields where material performance requirements are extremely high.

[0005] In engineering applications, an ideal tensile structure needs to possess both excellent compressive stiffness and efficient energy dissipation capabilities. While existing research has enhanced energy absorption performance through structural parameter manipulation, innovative geometric configurations, and the introduction of gradient design, it generally suffers from two key limitations: First, the pursuit of improved negative Poisson's ratio in novel tensile structures often negatively impacts compressive stiffness, leading to insufficient compressive stiffness in mechanical properties. Second, when employing gradient distribution strategies to improve the overall mechanical performance of tensile structures, a uniform gradient pattern is often used for all cell walls. This allows the structure to exhibit different mechanical properties in different locations, better adapting to complex engineering environments. However, current research typically uses a uniform gradient pattern, applying the same gradient variation to all cell walls. While simple and easy to implement, this approach neglects the different roles of different cell wall types within the structure, resulting in insufficient improvement in the overall mechanical performance of the tensile structure.

[0006] Therefore, designing novel negative Poisson's ratio metamaterials that simultaneously possess a certain negative Poisson's ratio effect, enhanced compressive stiffness, and energy absorption capacity, as well as novel gradient design schemes, is of great significance for the development and application of diastatic structures. Summary of the Invention

[0007] To address the problems of poor compressive stiffness and energy absorption capacity of existing negative Poisson's ratio structures, this invention provides a novel bi-arrow negative Poisson's ratio structure with hybrid gradients.

[0008] To achieve the above objectives, the present invention employs the following technical solution: This invention provides a novel double-arrow negative Poisson ratio structure with hybrid gradients, comprising a plurality of interconnected cells, each cell including an arrowhead portion, an arched portion and a vertical rib. The arrow portion includes a first concave arrow and a second concave arrow. The concave directions of the first concave arrow and the second concave arrow are consistent, and the two side wings of the first concave arrow are correspondingly connected to the two side wings of the second concave arrow. The arched portion is located inside the arrowhead portion, and one end of the arched cell wall is connected to the inner wall of the wing on one side of the first concave arrowhead, and the other end is connected to the inner wall of the wing on the other side of the first concave arrowhead. The arched end of the arched portion is connected to the tip of the second concave arrowhead. The vertical ribs are located on both sides of the arrowhead and are connected to the side wings of the first concave arrowhead on the corresponding side. With the arrowhead tip pointing longitudinally, the tip of the first concave arrowhead of the previous cell is connected to the tip of the second concave arrowhead of the next cell in the next longitudinal direction, and the vertical ribs are connected accordingly; the arrowhead side wings of the transversely adjacent cells are connected to each other and share the vertical ribs. The thickness of the first and second concave arrowheads decreases gradually from both ends along the longitudinal direction of the negative Poisson's ratio structure toward the middle; the thickness of the arched portion increases gradually along the longitudinal direction.

[0009] Optionally, the center lines drawn from the tips of the first and second concave arrows are on the same straight line.

[0010] Optionally, the cell is mirror-symmetrical along the midline drawn from the tips of the first and second concave arrows.

[0011] Optionally, the arrowhead portion satisfies: 1=2 2 in, 1 is half the angle between the two wings of the second concave arrow; 2 is half of the angle between the two wings of the first concave arrow.

[0012] Optionally, the radius of the arch is equal to the distance between the two apex points of the first and second concave arrows.

[0013] Optionally, the central angle corresponding to the arched portion α satisfy: α =2 2 in, 2 is half of the angle between the two wings of the first concave arrow.

[0014] Optionally, the vertical ribs have the greatest thickness throughout the cell.

[0015] Optionally, the cell relative density of the novel bi-arrow negative Poisson's ratio structure with hybrid gradients satisfy:

[0016] in, 1 is half the angle between the two wings of the second concave arrow; 2 is half the angle between the two wings of the first concave arrowhead; The distance from the lateral endpoint of the first or second concave arrow to the longitudinal midline of the cell; The thickness of the first or second concave arrowhead; The thickness of the arched part; The thickness of the vertical rib.

[0017] Optionally, the arrowhead, arched portion, and vertical rib are made of metal or carbon fiber composite material.

[0018] The above-mentioned novel double-arrow negative Poisson's ratio structure with hybrid gradients has applications in the engineering field.

[0019] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a novel double-arrow negative Poisson's ratio structure with hybrid gradients, comprising several interconnected cells. Each cell includes an arrowhead portion, an arched portion, and vertical ribs. By setting the arrowhead portion as a combination of a first concave arrowhead and a second concave arrowhead, placing the arched portion inside the arrowhead portion, and placing the vertical ribs on both sides of the arrowhead portion to form a complete cell, the interconnection of the complete cells enables this negative Poisson's ratio structure to exhibit a unique deformation mode under in-plane crushing loads. The cells laterally shrink and converge towards the core until they become completely compacted. In this structure, the combined concave arrowheads of the first and second concave arrowheads in the double-arrow section and the vertical arrowheads of the vertical ribs undergo plastic buckling to form plastic hinges. Furthermore, the arched section's arrowheads undergo plastic deformation under axial loads, forming near-horizontal walls. This allows the structure to absorb a significant amount of energy through plastic deformation when subjected to impact or compressive loads. Compared to classic double-arrowhead honeycomb structures, this structure, with more types of arrowheads participating in plastic deformation, can more effectively convert the work done by external forces into its own plastic deformation energy, thus significantly improving the structure's energy absorption capacity and demonstrating greater application potential in impact resistance and energy absorption. Further, the different types of arrowheads undergo plastic buckling and converge towards the core, gradually entering a densification deformation stage. This deformation method allows the structure to more orderly disperse and transfer loads during stress, avoiding localized stress concentration and improving the overall stability and reliability of the structure. Compared to classic double-arrowhead honeycomb structures, this structure significantly improves its compressive stiffness and energy absorption capacity while maintaining an excellent negative Poisson's ratio effect. Gradient design of the thickness of the double-arrow and arched cell walls enables the structure to exhibit a more reasonable deformation mode during compression, guiding stress redistribution and gradually transferring stress to the thicker cell walls. This improves the load-bearing capacity of the structure during compression, further enhancing its compression and energy absorption capabilities while maintaining an excellent negative Poisson's ratio effect. This ensures an effective improvement in the overall mechanical properties of the structure, promoting the development of tensile structures and their application in specialized fields such as smart materials, aerospace, and biomedical engineering.

[0020] The centerlines of the first and second concave arrows, drawn from their tips, are on the same straight line, enabling them to work together better under stress. When the structure is subjected to in-plane crushing loads, the load can be transmitted more directly and evenly to the entire cell structure along this common centerline, thereby improving the overall load-bearing capacity of the structure.

[0021] Furthermore, considering the excellent load-bearing capacity of the vertical cell walls of the vertical ribs, the thickness of the vertical cell walls is kept at a relatively large constant value in the mixed thickness gradient design. This allows the honeycomb structure to quickly establish a strong supporting effect when subjected to initial compressive load, providing stable initial stiffness for the entire structure and laying a good foundation for the subsequent compression process.

[0022] The aforementioned novel hybrid gradient double-arrow negative Poisson's ratio structure has applications in engineering fields. With its unique negative Poisson's ratio effect and excellent mechanical properties, the hybrid gradient double-arrow negative Poisson's ratio structure exhibits significant application advantages in engineering, meeting the application needs of specialized fields such as aerospace, automotive engineering, biomedicine, and defense technology, and possesses broad application prospects. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of a novel double-arrow negative Poisson's ratio structure with mixed gradients according to the present invention.

[0024] Figure 2 This is a schematic diagram of a single cell structure of a novel double-arrow negative Poisson's ratio structure with mixed gradients according to the present invention.

[0025] Figure 3 This is a schematic diagram of the novel double-arrow negative Poisson's ratio structure with uniform thickness in Comparative Example 1 of the present invention.

[0026] Figure 4 This is a schematic diagram of a novel double-arrow negative Poisson's ratio structure with mixed gradients in Comparative Example 2 of the present invention.

[0027] Figure 5 This is a schematic diagram of the conventional double-arrow negative Poisson's ratio structure in Comparative Example 3 of the present invention.

[0028] Figure 6 This is a schematic diagram of the novel double-arrow negative Poisson's ratio structure of the conventional gradient in Comparative Example 4 of the present invention.

[0029] Figure 7 This is a schematic diagram of the deformation process of the novel double-arrow negative Poisson's ratio structure with mixed gradient in Comparative Example 1 of the present invention under quasi-static compressive load.

[0030] Figure 8 This is a schematic diagram comparing the stress-strain curves and mechanical properties of the novel double-arrow negative Poisson's ratio structure with mixed gradient in Comparative Example 1 and the traditional double-arrow structure in Comparative Example 3 under quasi-static compressive load; wherein, a is a comparison diagram of stress-strain curves with the traditional double-arrow structure, and b is a comparison diagram of mechanical properties with the double-arrow structure in Comparative Example 3.

[0031] Figure 9This is a schematic diagram of the energy absorption mechanism of different types of cell walls in the novel double-arrow negative Poisson's ratio structure with mixed gradient in Comparative Example 1 of the present invention. In this diagram, a is a schematic diagram of the energy absorption mechanism curves of different types of cell walls, b is a pie chart of energy absorption in the energy absorption mechanism of different types of cell walls, and c is a pie chart of specific energy absorption in the energy absorption mechanism of different types of cell walls.

[0032] Figure 10 This is a schematic diagram comparing the stress-strain curves and mechanical properties of the novel double-arrow negative Poisson's ratio structure with mixed thickness gradient in Embodiment 1 and the comparative example of the present invention under quasi-static compressive load. In the diagram, a is the deformation mode diagram under compression in the quasi-static plane, b is the stress-strain curve diagram, c is the dynamic Poisson's ratio curve comparison diagram, and d is the mechanical property comparison diagram.

[0033] Among them, 1-arrowhead, 2-arched part, 3-vertical rib, 4-first concave arrowhead, 5-second concave arrowhead. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0035] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0036] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0037] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper," "lower," "horizontal," or "inner" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of the invention is in use, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. Furthermore, terms such as "first" and "second" are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0038] Furthermore, the use of the term "horizontal" does not imply that the component must be absolutely horizontal, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0039] In the description of the embodiments of the present invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0040] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0041] See Figure 1 and Figure 2 The present invention discloses a novel double-arrow negative Poisson ratio structure with mixed gradients, comprising a plurality of interconnected cells, each cell comprising an arrowhead portion 1, an arched portion 2 and a vertical rib 3; The arrow portion 1 includes a first concave arrow 4 and a second concave arrow 5. The concave direction of the first concave arrow 4 and the second concave arrow 5 is consistent, and the two side wings of the first concave arrow 4 are correspondingly connected to the two side wings of the second concave arrow 5. Preferably, the center lines drawn from the tips of the first concave arrow 4 and the second concave arrow 5 are on the same straight line, and the cell is mirror-symmetrical along the center lines drawn from the tips of the first concave arrow 4 and the second concave arrow 5. Preferably, the arrow portion 1 satisfies: 1=2 2 in, 1 is half the angle between the two wings of the second concave arrow 5; 2 is half of the angle between the two wings of the first concave arrow 4.

[0042] The arched portion 2 is located inside the arrow portion 1, with one end connected to the inner wall of one side wing of the first concave arrow 4, and the other end connected to the inner wall of the other side wing of the first concave arrow 4. The arched end of the arched portion 2 is connected to the tip of the second concave arrow 5. Preferably, the arch radius of the arched portion 2 is equal to the distance between the two apexes of the first and second concave arrows 4 and 5. Preferably, the central angle corresponding to the arched portion 2 is... α satisfy: α =2 2 in, 2 is half of the angle between the two wings of the first concave arrow 4.

[0043] The vertical ribs 3 are disposed on both sides of the arrow part 1 and are connected to the side wings of the first concave arrow 4 on the corresponding side; preferably, in the entire cell, the thickness of the vertical ribs 3 remains unchanged in the entire negative Poisson ratio structure, and the vertical ribs 3 are arranged parallel to each other in the longitudinal direction.

[0044] With the tip of the arrow 1 pointing longitudinally, the tip of the first concave arrow 4 of the previous cell is connected to the tip of the second concave arrow 5 of the next cell in the longitudinal direction, and the vertical rib 3 is connected accordingly; the side wing connection nodes of the arrow 1 of the adjacent cells in the lateral direction are connected and share the vertical rib 3.

[0045] Preferably, the cell relative density of the novel bi-arrow negative Poisson's ratio structure with mixed gradients satisfy:

[0046] in, 1 is half the angle between the two wings of the second concave arrow 5; 2 is half the angle between the two wings of the first concave arrow 4; The distance from the lateral endpoint of the first concave arrow 4 or the second concave arrow 5 to the longitudinal midline of the cell; The thickness of the first concave arrow 4 or the second concave arrow 5; The thickness of arched part 2; The thickness of vertical rib 3.

[0047] Preferably, the arrowhead 1, the arched part 2, and the vertical rib 3 are made of metal or carbon fiber composite material.

[0048] The aforementioned novel hybrid gradient double-arrow negative Poisson's ratio structure has applications in engineering fields. With its unique negative Poisson's ratio effect and excellent mechanical properties, the hybrid gradient double-arrow negative Poisson's ratio structure exhibits significant application advantages in engineering, meeting the application needs of specialized fields such as aerospace, automotive engineering, biomedicine, and defense technology, and possesses broad application prospects.

[0049] To further illustrate the beneficial effects of the present invention, the following description provides a performance comparison of specific embodiments and comparative examples.

[0050] Example 1 See Figure 1 and Figure 2The present invention discloses a novel double-arrow negative Poisson ratio structure with mixed gradients, comprising a plurality of interconnected cells, each cell comprising an arrowhead portion 1, an arched portion 2 and a vertical rib 3; The arrow portion 1 includes a first concave arrow 4 and a second concave arrow 5. The concave direction of the first concave arrow 4 and the second concave arrow 5 is consistent, and the two side wings of the first concave arrow 4 are correspondingly connected to the two side wings of the second concave arrow 5. The midlines drawn from the tips of the first concave arrow 4 and the second concave arrow 5 are on the same straight line, and the cell is mirror-symmetrical along the midlines drawn from the tips of the first concave arrow 4 and the second concave arrow 5. The arrow portion 1 satisfies: 1=2 2 in, 1 is half the angle between the two wings of the second concave arrow 5; 2 is half of the angle between the two wings of the first concave arrow 4.

[0051] The arched portion 2 is located inside the arrow portion 1, with one end connected to the inner wall of one side wing of the first concave arrow 4, and the other end connected to the inner wall of the other side wing of the first concave arrow 4. The arched end of the arched portion 2 is connected to the tip of the second concave arrow 5. The arched radius of the arched portion 2 is equal to the distance between the two apexes of the first and second concave arrows 4 and 5. The central angle corresponding to the arched portion 2 is... α satisfy: α =2 2 in, 2 is half of the angle between the two wings of the first concave arrow 4.

[0052] The vertical ribs 3 are disposed on both sides of the arrow part 1 and are connected to the side wings of the first concave arrow 4 on the corresponding side; preferably, the thickness of the vertical ribs 3 remains unchanged throughout the entire cell in the entire negative Poisson's ratio structure.

[0053] With the tip of the arrow 1 pointing longitudinally, the tip of the first concave arrow 4 of the previous cell is connected to the tip of the second concave arrow 5 of the next cell in the longitudinal direction, and the vertical rib 3 is connected accordingly; the side wing connection nodes of the arrow 1 of the adjacent cells in the lateral direction are connected and share the vertical rib 3.

[0054] Cellular relative density of the novel bi-arrow negative Poisson's ratio structure with hybrid gradients satisfy:

[0055] in, 1 is half the angle between the two wings of the second concave arrow 5; 2 is half the angle between the two wings of the first concave arrow 4; The distance from the lateral endpoint of the first concave arrow 4 or the second concave arrow 5 to the longitudinal midline of the cell; The thickness of the first concave arrow 4 or the second concave arrow 5; The thickness of arched part 2; The thickness of vertical rib 3.

[0056] The arrowhead portion 1, the arched portion 2, and the vertical rib 3 are made of carbon fiber composite material. The thickness of the vertical rib 3 is 0.863 mm. The thickness of the arrowhead portion 1 increases uniformly from 0.31 mm to 0.46 mm from the first and seventh cell layers to the fourth cell layer. The thickness of the arched portion 2 increases uniformly from 0.31 mm to 0.45 mm from the first to the seventh cell layer.

[0057] Comparative Example 1 See Figure 3 Unlike Embodiment 1, the arrowhead portion 1, the arched portion 2, and the vertical rib 3 have the same thickness, which is 0.45 mm.

[0058] Comparative Example 2 See Figure 4 Unlike Example 1, from the first to the seventh cell layer, the thickness of the arrow portion 1 increases uniformly from 0.3 mm to 0.45 mm, and the arched portion decreases uniformly from 0.45 mm to 0.3 mm.

[0059] Comparative Example 3 See Figure 5 Unlike Comparative Example 1, it only includes the arrowhead part 1 and does not include the arched part 2 and the vertical rib 3.

[0060] Comparative Example 4 See Figure 6 Unlike Example 1, the thickness of the arrow part 1, the arched part 2 and the vertical rib 3 are uniformly increased from 0.3 mm to 0.6 mm from the first layer of cells to the seventh layer of cells.

[0061] See Figure 7Figure 1 shows the deformation pattern of the negative Poisson's ratio structure in Comparative Example 1 under in-plane compression. It can be seen that during compression, the novel double-arrow negative Poisson's ratio structure of this application exhibits a unique deformation mode, with the cell shrinking laterally and converging towards the core until it becomes completely compacted. Specifically, at the initial stage of deformation, the vertical rib 3 and the arrowhead 1 rotate inwards, undergoing plastic buckling and exhibiting a typical lateral shrinkage deformation mode. The rotational buckling of the arrowhead 1 transfers the load to the arched section 2, causing the arched structure 2 to undergo plastic buckling and gradually become an approximately horizontal cell wall. It is noteworthy that the arched section 2 and the arrowhead 1 exhibit a synergistic deformation mechanism through mutual constraint: on the one hand, the arched section 2 provides effective support to the arrowhead 1 through its two ends and center, significantly improving the arrowhead 1's resistance to plastic buckling; on the other hand, the arrowhead 1 restricts the radial expansion tendency of the arched section 2 under compression. This unique interaction mechanism effectively enhances the load-bearing capacity of the structure. As compressive strain increases, more vertical ribs 3 and arrowhead sections 1 within the cells undergo plastic buckling, and the arched section 2 is compressed into an approximately horizontal cell wall. Cells aggregate towards the core, and the structure exhibits a typical negative Poisson's ratio effect. As compressive strain increases, different types of cell walls completely plastically collapse and come into contact with each other, and the structural deformation gradually enters the densification stage.

[0062] See Figure 8 Figure a shows the compressive stress-strain curves of Comparative Examples 1 and 3. Under in-plane crushing load, the stress-strain curves of the novel double-arrow negative Poisson's ratio structure exhibit three typical stages: the linear elastic stage, the plateau stress stage, and the compaction stage. In the initial stage, the stress-strain curve shows a linear elastic increase, and the cell wall exhibits a linear elastic deformation mode. When the stress reaches the initial peak, the arrowhead 1 and vertical rib 3 undergo plastic buckling and form plastic hinges, while the arched part 2 undergoes plastic deformation under axial load, forming an approximately horizontal wall. As the strain increases, the arrowhead 1, vertical rib 3, and arched part 2 of different cell layers undergo plastic buckling. The stress-strain curves of this novel double-arrow negative Poisson's ratio structure fluctuate around a constant value, exhibiting a plateau stress stage. As the strain continues to increase, the compression between different types of cell walls causes bending-tension coupling deformation between the cell walls, and more plastic hinges are formed during plastic buckling. Therefore, the load-bearing capacity of the structure gradually increases, and the stress-strain curve shows a gradually increasing trend. As different types of cell walls undergo plastic collapse and aggregate towards the core, the novel double-arrow negative Poisson's ratio structure gradually enters the compaction deformation stage, and the stress-strain curve of the structure rapidly increases. Compared with the traditional double-arrow structure, this novel double-arrow negative Poisson's ratio structure has a larger initial stress peak, a more stable plateau stress stage, and superior load-bearing characteristics.

[0063] See Figure 8Figure b shows the compressive stiffness and specific energy absorption of Comparative Examples 1 and 3. It can be seen that the specific energy absorption of this novel double-arrow negative Poisson's ratio structure is 9.34 kJ / kg, and the stiffness reaches 8351 MPa. Compared with the traditional double-arrow structure, it exhibits superior energy absorption capacity and compressive stiffness, solving the defect of insufficient compressive stiffness in the mechanical properties of novel tensile structures.

[0064] See Figure 9 a) shows the energy-bearing capacity of different cell wall types in Comparative Example 1. Revealing the energy absorption mechanism of different cell wall types is fundamental to effectively developing novel double-arrow hybrid thickness gradient designs. From the magnified view, it can be observed that the energy absorption of the vertical rib 3 is higher than that of the arrowhead 1 and the arched portion 2 at the initial moment. This is because the vertical rib 3 undergoes plastic buckling and consumes the compressive load during the initial deformation stage, while the arrowhead 1 only experiences localized plastic buckling. Furthermore, the arched portion 2 hardly participates in energy absorption, so the energy absorption of the arrowhead 1 is lower than that of the vertical rib 3 but higher than that of the arched portion 2. As the compressive strain increases, the energy absorption of the arrowhead 1 gradually surpasses that of the vertical rib 3. This is attributed to the fact that the arrowhead 1 accounts for 71% of the overall structural mass, and the increase in strain leads to more of the arrowhead 1 forming plastic hinges and participating in energy absorption. However, the arched portion 2 accounts for the least total mass and forms fewer plastic hinges, so its energy absorption remains at the lowest level. Therefore, it can be seen that the energy absorption of the arrowhead 1 and the vertical rib 3 plays a dominant role in the deformation process of the novel double-arrow negative Poisson's ratio structure. (See also...) Figure 9 Figures c and d illustrate the energy absorption and specific energy absorption performance of different types of cell walls. It is noteworthy that the mass percentages of different cell wall types vary significantly; therefore, energy absorption alone cannot effectively characterize the energy absorption properties of the cell walls. Arrowhead 1, arched 2, and vertical rib 3 consume 67.2%, 8.8%, and 24% of the total energy, respectively, but due to differences in cell wall mass, the specific energy absorption of different cell wall types varies significantly. Specifically, vertical rib 3 exhibits the best load-bearing performance, with its specific energy absorption being approximately 60% and 123% higher than that of arrowhead 1 and arched 2, respectively. Therefore, vertical rib 3 has the most significant impact on the energy absorption performance of the structure.

[0065] See Figure 10Figure a shows the deformation pattern of the negative Poisson's ratio structure under in-plane compression in the embodiments and comparative examples of the present invention. For Embodiment 1 and Comparative Example 2 of the hybrid gradient design, although their overall deformation patterns still maintain similar hierarchical characteristics, their deformation mechanisms exhibit more complex mechanical properties. In the hybrid thickness gradient design structure, the cell layer with the smallest cell wall thickness (arrow part 1) undergoes plastic collapse first, and then the deformation gradually extends to adjacent layers. This phenomenon can be explained from the perspective of energy dissipation. According to the principle of plasticity, the plastic collapse process of the cell tends to choose the path with the least energy dissipation, and the thin-walled layer, due to the lower plastic buckling energy required, undergoes plastic collapse first. It is worth noting that after the thinnest layer undergoes plastic buckling, the load-bearing capacity of the novel double-arrow structure decreases sharply, causing the load to be redistributed to the next thinnest layer, thus forming a chain-like progressive failure mode. In particular, for Embodiment 1 of the bidirectional hybrid thickness gradient design, although the top and bottom arrow parts 1 have the same cell wall thickness, the deformation starts from the bottom layer and extends upwards. This deformation characteristic is closely related to the influence of boundary conditions. The vertical rib 3 weakens the lateral contraction of the bottom cell, leading to strain concentration and shear stress in the cell wall of this region, thus promoting preferential plastic buckling of the bottom cell wall. This boundary effect needs special attention in gradient structure design, as it can significantly alter the expected deformation mode.

[0066] See Figure 10 Figure b shows the stress-strain curves of the embodiments and comparative examples of the present invention. Compared with Comparative Example 1, the double-arrow structures using mixed thickness gradients all achieved an increase in initial peak stress. Embodiment 1 and Comparative Example 2, with their mixed thickness gradient designs, both exhibit a gradual increase in plateau stress, and the compaction strain point is delayed to approximately 0.6, which is related to the layer-by-layer crushing deformation mode exhibited by the gradient structure. Specifically, the structure with the mixed thickness gradient design exhibits a typical gradient response during compression. The weakest layer undergoes plastic buckling first, and as the strain increases, the structural cells with the mixed thickness gradient design participate in the load-bearing process sequentially from thin to thick layers, resulting in a stepwise increase in plateau stress. The mixed thickness gradient design induces a delayed compaction strain effect. The layer-by-layer collapse deformation mode of each cell layer fully utilizes the deformation space within the cell. Secondly, this gradual deformation mode effectively avoids locally unstable compaction deformation. The combined effect of these characteristics prolongs the efficient energy absorption stage of the novel double-arrow structure, thereby significantly improving the specific energy absorption.

[0067] See Figure 10c shows a comparison of the dynamic Poisson's ratio curves of Embodiment 1 and the comparative example. Specifically, the hybrid gradient design limits the lateral shrinkage behavior of the structure. The maximum negative Poisson's ratio in Comparative Example 2 is -0.55, a decrease of approximately 31.3% compared to Comparative Example 1. The negative Poisson's ratio effect of Embodiment 1, with its hybrid thickness gradient design, is further reduced, which is a natural consequence of increased stiffness. However, the structure with the hybrid gradient design still maintains a certain negative Poisson's ratio effect.

[0068] See Figure 10 Figure d shows a comparison of the mechanical properties of the embodiments and comparative examples of the present invention. Specifically, the specific energy absorption of the traditional thickness gradient design structure increased by 17.4% compared to the uniform thickness design. The specific energy absorption of the structures with mixed thickness gradient designs was also improved, with the most significant increase of approximately 46.6% observed in Embodiment 1. Regarding compressive stiffness, the compressive stiffness of the traditional thickness gradient design structure remained almost unchanged, while the compressive stiffness of the structure with mixed thickness gradient design in Embodiment 1 increased by 51.4%. This is because the compressive stiffness of the structure is mainly affected by the vertical ribs 3. The reason why the stiffness of the traditional thickness gradient structure remained almost unchanged is that the average thickness of its vertical ribs 3 is consistent with the wall thickness of the uniform thickness vertical ribs 3. However, in the structure with mixed thickness gradient, the thickness of the vertical ribs 3 is a constant value of 0.863 mm, so the compressive stiffness increased in all cases with almost the same increase rate. Overall, the traditional thickness gradient in Comparative Example 4 only slightly improved the specific energy absorption, while the mixed thickness gradient design can comprehensively and effectively improve the mechanical properties of the novel double-arrow structure while maintaining a certain negative Poisson's ratio effect.

[0069] The above description is merely a preferred embodiment of the present invention and is not intended to limit the technical solution of the present invention in any way. Those skilled in the art should understand that, without departing from the spirit and principles of the present invention, the technical solution can be modified and replaced in several simple ways, and these modifications and replacements are all within the scope of protection covered by the claims.

Claims

1. A novel double-arrow negative Poisson's ratio structure with hybrid gradients, characterized in that, It includes several interconnected cells, each cell including an arrowhead (1), an arched part (2) and a vertical rib (3). The arrow part (1) includes a first concave arrow (4) and a second concave arrow (5). The concave directions of the first concave arrow (4) and the second concave arrow (5) are consistent, and the two sides of the first concave arrow (4) are connected to the two sides of the second concave arrow (5). The arched part (2) is located inside the arrow part (1), and one end of the arched cell wall (2) is connected to the inner wall of the side wing of one side of the first concave arrow (4), and the other end is connected to the inner wall of the side wing of the other side of the first concave arrow (4). The arched end of the arched part (2) is connected to the tip of the second concave arrow (5). The vertical ribs (3) are respectively disposed on both sides of the arrow part (1) and connected to the side wings of the first concave arrow (4) on the corresponding side; With the arrowhead (1) pointing in the longitudinal direction, the tip of the first concave arrow (4) of the previous cell is connected to the tip of the second concave arrow (5) of the next cell in the longitudinal direction, and the vertical rib (3) is connected accordingly; the arrowhead (1) side wing connection nodes of the adjacent cells in the lateral direction are connected and share the vertical rib (3). The thickness of the first concave arrow (4) and the second concave arrow (5) decreases gradually from both ends along the longitudinal direction of the negative Poisson's ratio structure toward the middle; the thickness of the arch (2) increases gradually along the longitudinal direction.

2. The novel bi-arrow negative Poisson's ratio structure with hybrid gradients according to claim 1, characterized in that, The midlines of the first concave arrow (4) and the second concave arrow (5) are on the same straight line from the tips of the arrows.

3. The novel double-arrow negative Poisson's ratio structure with hybrid gradients according to claim 2, characterized in that, The cell element is mirror-symmetrical along the midline drawn from the tip of the first concave arrow (4) and the second concave arrow (5).

4. The novel double-arrow negative Poisson's ratio structure with hybrid gradients according to claim 1, characterized in that, The arrowhead (1) satisfies: 1=2 2 in, 1 is half the angle between the two wings of the second concave arrow (5); 2 is half of the angle between the two wings of the first concave arrow (4).

5. The novel double-arrow negative Poisson's ratio structure with hybrid gradients according to claim 1, characterized in that, The radius of the arch (2) is equal to the distance between the two tips of the first concave arrow (4) and the second concave arrow (5).

6. The novel double-arrow negative Poisson's ratio structure with hybrid gradients according to claim 1, characterized in that, The central angle corresponding to the arched part (2) α satisfy: α =2 2 in, 2 is half of the angle between the two wings of the first concave arrow (4).

7. The novel double-arrow negative Poisson's ratio structure with hybrid gradients according to claim 1, characterized in that, The vertical rib (3) has the greatest thickness in the entire cell.

8. The novel double-arrow negative Poisson's ratio structure with hybrid gradients according to claim 1, characterized in that, Cellular relative density of the novel bi-arrow negative Poisson's ratio structure with hybrid gradients satisfy: in, 1 is half the angle between the two wings of the second concave arrow (5); 2 is half the angle between the two wings of the first concave arrow (4); The distance from the lateral endpoint of the first concave arrow (4) or the second concave arrow (5) to the longitudinal midline of the cell; The thickness of the first concave arrow (4) or the second concave arrow (5); The thickness of the arched part (2); The thickness of the vertical rib (3) is given.

9. The novel double-arrow negative Poisson's ratio structure with hybrid gradients according to any one of claims 1-8, characterized in that, The arrowhead (1), arch (2) and vertical rib (3) are made of metal or carbon fiber composite material.

10. The application of the novel bi-arrow negative Poisson's ratio structure with hybrid gradients as described in any one of claims 1-9 in the field of engineering.

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