A novel metamaterial possessing both multistable and negative Poisson's ratio properties

Abstract

This invention relates to the field of novel materials, specifically a novel metamaterial exhibiting both multi-stable state and negative Poisson's ratio properties. It comprises a concave hexagonal frame, two arc-shaped beams positioned on the upper and lower sides of the frame's inner cavity, and a vertical rod. The two arc-shaped beams are fixedly connected to the upper and lower ends of the vertical rod via their respective central portions. When the structure is subjected to a vertical compressive load, the frame's diagonal bracing rotates inward, contracting and compressing the ends of the arc-shaped beams, generating a significant negative Poisson's ratio effect. This process forces the arc-shaped beams to bend and deform towards the center, accompanied by energy dissipation. When the displacement reaches a critical threshold, the arc-shaped beams buckle and overturn, switching to a steady state. This invention, through specific geometric configurations and differentiated material layouts, achieves morphological self-repair after impact and reuse under low-intensity conditions. This metamaterial can be arranged as a two-dimensional periodic array as a unit cell.

Description

Technical Field

[0001] This invention relates to the field of novel material design technology, specifically to a novel metamaterial that combines multistable and negative Poisson's ratio properties. Background Technology

[0002] In modern industrial fields such as high-end equipment manufacturing, vehicle engineering, aerospace, and precision instrument protection, there is a continuously growing and urgent need for protective structures that can withstand external impact loads and attenuate vibration energy. These shock-absorbing and vibration-resistant structures need to provide reliable energy dissipation pathways under complex operating conditions to protect internal core components from damage. With the continuous improvement of equipment performance, traditional single protective materials are no longer sufficient to meet the current stringent standards for lightweighting, high energy absorption, and adaptability to multiple operating conditions.

[0003] Existing traditional protective structures typically rely on the plastic deformation of metallic materials or the viscoelastic damping of polymers to dissipate energy, which has significant limitations. Traditional metallic energy-absorbing structures become unusable after a single impact due to irreversible plastic deformation. Some metamaterials with negative Poisson's quotient properties exhibit excellent energy absorption potential by resisting volume compression through lateral contraction deformation, but their performance is often limited to a single deformation mechanism. While multistable structures that have emerged in recent years can switch between different stable configurations to achieve energy dissipation, some structures are prone to uncontrollable performance degradation due to fatigue or damage accumulation.

[0004] Existing metamaterial protective structures are highly susceptible to permanent damage such as plastic hinge fracture or cell collapse after being subjected to impacts exceeding their design thresholds, leading to complete and irreversible structural failure. There is a severe lack of integrated solutions that can effectively combine multistable recoverable deformation modes with the superior impact resistance of negative Poisson's ratio structures. Most known structures struggle to simultaneously achieve high energy dissipation, post-impact self-healing mechanisms, and post-damage reusability, failing to provide sufficient technical support for long-life, sustainable protective systems. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a novel metamaterial that combines multistable and negative Poisson's ratio properties, solving the problems of limited buffering efficiency, susceptibility to permanent damage, and difficulty in reusing existing protective structures when facing external forces such as vibration and impact.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: a novel metamaterial with both multistable and negative Poisson's ratio properties, comprising at least one basic unit, wherein the basic unit is provided with a frame, two arc beams and a vertical rod; The outer contour of the frame has a concave hexagonal structure; The two arc-shaped beams are respectively arranged on the upper and lower sides of the inner cavity of the frame, and the opposite ends of each arc-shaped beam are connected to the side wall of the concave hexagonal structure. The vertical rod is vertically installed at the inner center of the frame, and the upper and lower arc-shaped beams are respectively fixedly connected to the upper and lower ends of the vertical rod through their corresponding central parts; The basic unit as a whole is arranged in a biaxially symmetrical manner in both the horizontal and vertical directions.

[0007] Preferably, the frame is composed of two parallel crossbeams and four diagonal braces connected together. The upper and lower diagonal braces on the same side intersect and are recessed into the frame to form the concave hexagonal structure. The end of the arc-shaped beam is directly abutted and fixed to the inner wall of the diagonal brace on the corresponding side.

[0008] Preferably, the cross-sectional thickness of the arc-shaped beam is less than one-tenth of its own length, and the structural thickness of the arc-shaped beam is less than the cross-sectional thickness of the vertical rod.

[0009] Preferably, the main material constituting the basic unit is a high-strength and high-toughness substrate, which is selected from either low-carbon steel or engineering plastics.

[0010] Preferably, the arc-shaped beam, the vertical rod, and the frame are made of a combination of materials with different elastic modulus parameters; The arc-shaped beam is made of a highly elastic deformation material to meet the multi-steady-state overturning conditions; Both the vertical rod and the frame are made of high-rigidity materials for rigid support.

[0011] Preferably, the highly elastic deformable material is a special spring steel or a shape memory polymer, and the highly rigid material is high carbon steel or hard alloy.

[0012] Preferably, the basic unit is configured to exhibit negative Poisson's ratio deformation characteristics when subjected to a vertical compressive load. When the diagonal braces on both sides are compressed, they rotate and contract synchronously inward into the structure, thereby applying radial compressive force to the ends of the upper and lower arc beams. This compressive force forces the two arc beams to bend and deform toward the vertical rod and to press against each other.

[0013] Preferably, the arc-shaped beam has a multi-steady-state deformation reversal mechanism, which is configured such that when the compression displacement reaches a set first critical threshold, the arc-shaped beam buckles and reverses from the initial inward convex bending state to the secondary outward convex bending state, so as to achieve buffer energy absorption through a nonlinear steady-state switching process.

[0014] Preferably, it includes multiple basic units, which are arranged and assembled sequentially along the horizontal X direction and the vertical Y direction; the basic units are spliced ​​and fixed together in a two-dimensional periodic array, thereby forming a composite metamaterial plate or protective filling layer for shock absorption and impact resistance on a macroscopic scale.

[0015] Working principle: When an external vertical compressive load is applied to the end of the structure, the basic unit responds to the external impact through a multi-stage composite physical action mechanism.

[0016] The initial stage of compression triggers a negative Poisson's ratio effect. The diagonal braces on both sides of the concave hexagonal frame rotate and contract inwards under stress, pushing the ends of the two curved beams closer together. This specific geometric movement causes the structure to be compressed vertically while its horizontal span is simultaneously reduced. This process exhibits significant cohesive contraction rather than outward expansion. This typical tensile expansion effect effectively suppresses lateral escape of the material under compression, fundamentally improving the structure's shear resistance and instability resistance.

[0017] As the compression stroke progresses, the structure enters a stage of efficient deformation and energy absorption. The continuous inward movement of the diagonal braces exerts a strong radial compression on both ends of the curved beams, forcing the two curved beams to undergo significant bending deformation towards the central region of the structure. During this process, the upper and lower curved beams support each other and form reverse compression through the vertical rods fixed in the middle. The large-scale elastic bending deformation generated by the curved beams in this stage constitutes the core physical channel for absorbing and dissipating external impact kinetic energy.

[0018] Under continuously increasing external loads, the multi-steady-state characteristics of the structure are fully activated. When the applied compressive displacement reaches the set first critical threshold, the accumulated bending strain energy inside the upper and lower curved beams exceeds the material's bearing capacity. At this moment, the curved beams undergo an instantaneous flip of their buckling mode, with their bending shape rapidly switching from an initial inward convex state to an outward convex state via a nonlinear jump. This mechanical flip process is accompanied by a significant stress drop and the instantaneous release and dissipation of a massive amount of energy. Even if the external load is partially removed, the compressed structure can still stably maintain this new secondary steady-state configuration, providing a large energy absorption capacity.

[0019] After undergoing a low-intensity impact that does not exceed the material's yield strength, the structure exhibits an excellent elastic recovery mechanism. The basic units in the unloaded state can achieve a reverse configuration jump entirely based on their own stored elastic restoring force, autonomously returning to their initial state before compression. This physical mechanism, relying on the synergistic effect of large geometric deformation and highly elastic materials, achieves post-impact self-repair, creating a closed-loop protection system for reusable collision protection structures.

[0020] This invention provides a novel metamaterial that combines multistable state and negative Poisson's ratio properties. It possesses the following beneficial effects: 1. This invention utilizes a synergistic design where a concave hexagonal frame and two curved beams abut against each other at their ends. This design enables the curved beams to undergo efficient and controllable bending deformation under pressure, converting a large amount of the introduced external impact kinetic energy into the elastic strain energy of the material itself and dissipating it. This significantly improves the protective performance and energy absorption rate of the metamaterial structure under dynamic loads such as vibration and impact.

[0021] 2. By relying on the geometric configuration of the central vertical bar connected to the upper and lower curved beams and the selection of highly elastic materials, this invention endows the curved beams with a physical mechanism of buckling mode reversal when subjected to large displacement deformation. This allows the metamaterial to absorb energy in stages and adaptively under different levels of impact intensity, effectively broadening the range of impact energy that the structure can block and greatly enhancing its damage tolerance under complex working conditions.

[0022] 3. This invention utilizes the mechanical transmission path of four inwardly concave braces connected to the ends of the arc-shaped beam. In the initial stage of compression, the braces are forced to rotate and contract inward, thereby causing the basic unit to be compressed in the vertical direction while also undergoing significant contraction and cohesion in the horizontal direction. This negative Poisson's ratio effect effectively suppresses the lateral expansion tendency of the material when impacted, and significantly improves the overall mechanical properties of the structure, including shear resistance, indentation resistance, and resistance to matrix fracture.

[0023] 4. This invention employs a differentiated material distribution method, applying highly elastic materials to the curved beam area to ensure recovery from large deformations, while simultaneously configuring highly rigid materials in the support rods and frame to maintain the overall structural stability. This allows the basic unit to be arranged in a two-dimensional periodic array as a single cell to form a macroscopic protective layer, realizing the self-recovery and reuse of the structure after low-intensity impact damage. It has extremely high engineering application value in the fields of transportation, aerospace, and military protection. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the metamaterial basic unit of the present invention.

[0025] Among them, 1. crossbeam; 2. diagonal brace; 3. curved beam; 4. vertical bar; 5. interior angle. Detailed Implementation

[0026] 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. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example

[0027] like Figure 1 As shown, this embodiment of the invention provides a novel metamaterial possessing both multistable and negative Poisson's ratio properties, comprising at least one basic unit. The main structure of the basic unit consists of a frame, an arc-shaped beam 3, and vertical rods 4. The overall morphology exhibits highly regular horizontal and vertical biaxial symmetry. The frame, serving as the outer load-bearing foundation, has an external contour strictly configured as a concave hexagon 1. The upper and lower boundaries of this hexagon are formed by two parallel horizontal beams 1, which together constitute the main vertical load-bearing surfaces of the structure. The two side boundaries of the frame are formed by four diagonal braces 2 inclined at a specific angle. The angle between the diagonal braces 2 and the horizontal beams 1 is an interior angle 5, and the entire brace is recessed into the internal space of the basic unit.

[0028] Within the frame-defined internal cavity, two symmetrically arranged arc-shaped beams 3 are positioned close to the upper and lower crossbeams 1, respectively. The left and right ends of each arc-shaped beam 3 are rigidly connected and fixed to the inner wall of the corresponding diagonal brace 2. This geometric topological relationship establishes a direct coupling between the motion state of the diagonal brace 2 and the deformation state of the arc-shaped beam 3. To ensure the successful activation of the multi-steady-state overturning characteristics, the cross-sectional thickness of the arc-shaped beam 3 is strictly limited. Its thickness must be less than one-tenth of the extension length of the arc-shaped beam 3 itself, and also less than the cross-sectional dimension of the central support component, thus providing the arc-shaped beam 3 with sufficient flexibility.

[0029] A single vertical rod 4 is installed along the vertical central axis of the structure. The upper end of the vertical rod 4 is connected to the center point of the upper curved beam 3, and the lower end is connected to the center point of the lower curved beam 3. In this way, the two independent curved beams 3 are mechanically linked by the vertical rod 4 in the middle. The intersection and connection points between the horizontal beam 1, the diagonal brace 2, the curved beam 3, and the vertical rod 4 constitute a complete and efficient stress transfer network within the foundation unit.

[0030] In terms of material selection, the overall structure of the basic unit is integrally molded from a high-strength and tough substrate. Suitable materials include low-carbon steel, high-strength engineering plastics (such as polyurethane and nylon), or composite fiber materials. This combination of materials ensures that the structure maintains excellent energy absorption efficiency and outstanding fracture resistance when undergoing large deformations. To seek the optimal solution for mechanical properties, this invention introduces a differentiated material combination design scheme. The curved beam 3 region is prepared using a highly elastic deformable material with a relatively low elastic modulus and a high yield strength. Special spring steel or highly elastic shape memory polymers are ideal choices here. The high elasticity ensures that the curved beam 3 can smoothly undergo large-scale bending, forming the core material basis for generating multi-stable behavior. Correspondingly, the vertical rod 4 and the concave hexagonal frame must be made of materials with higher elastic modulus and yield strength. High-carbon steel or hard alloys are mainly used in this region to provide rigid support and guidance, maintaining the macroscopic stability of the basic unit under complex stress environments.

[0031] When an external vertical (Y-direction) compressive load is applied to the ends of the structure, the basic unit responds to the external force through a specific physical mechanism. In the initial stage of compression, the diagonal braces 2 on both sides of the concave hexagonal frame rotate and contract inward, thereby pushing the ends of the two upper and lower curved beams 3 closer together. This movement directly causes the structure to be compressed vertically while its horizontal (X-direction) span is also reduced. The structure exhibits a significant contraction rather than expansion state, a phenomenon known as the negative Poisson's ratio (tensile expansion) effect. The tensile expansion effect suppresses lateral escape of the material under compression, fundamentally improving the structure's shear resistance and instability resistance.

[0032] As the compression stroke progresses, the efficient deformation energy absorption process begins to emerge. The inward movement of the diagonal brace 2 continuously exerts a huge radial compression force on both ends of the curved beam 3, forcing the two curved beams 3 to bend towards the central region of the structure. In this process, the upper and lower curved beams 3 are mutually compressed and supported by the vertical rod 4 fixed in the middle. The intense elastic bending deformation of the curved beams 3 at this stage constitutes the main channel for absorbing and dissipating the kinetic energy of external impact.

[0033] The external load continues to increase, triggering multi-steady-state characteristics. When the applied compressive displacement reaches a specific first critical threshold, the accumulated bending strain energy inside the two curved beams 3 reaches its limit. At this point, the curved beams 3 undergo an instantaneous flip of their buckling mode, with their bending shape nonlinearly jumping from an initial inward convex state to an outward convex state. This flipping process is accompanied by a significant stress drop and a massive instantaneous dissipation of energy. Even if the external load is partially removed, the structure can still stably maintain this new form (second steady state). This graded energy absorption mechanism, which relies on large geometric deformation, endows the structure with a large energy absorption capacity and impact adaptability. After experiencing a low-intensity impact that does not exceed the material's yield strength, the structure can return to its initial state through its own elastic recovery force, perfectly achieving the design goals of damage self-repair and reuse.

[0034] In practical engineering applications, the aforementioned basic unit is defined as a microscopic unit cell. Unit cells are arranged in a two-dimensional, periodic array along the X and Y axes (such as rectangular orthogonal arrays or honeycomb topological arrays) and ultimately assembled to form macroscopic metamaterial plates, core layers, or filling structures. The assembled composite metamaterials can be directly deployed in automotive bumper energy-absorbing boxes, train anti-climb devices, or aircraft landing gear buffer components, meeting the advanced protection requirements of the transportation industry for occupants and equipment. In the aerospace field, this material can be used in the design of satellite protective shells and spacecraft landing buffer mechanisms. For military and special security scenarios, composite armor layers and blast-resistant wall core materials composed of this array can provide excellent blast resistance and vibration damping performance. For vibration isolation platforms of precision equipment, its negative Poisson's ratio characteristic can better isolate high-frequency micro-vibrations, demonstrating extremely broad prospects for industrial applications.

[0035] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A novel metamaterial possessing both multistable and negative Poisson's ratio properties, characterized in that, It includes at least one basic unit, which is provided with a frame, two curved beams (3) and a vertical bar (4). The outer contour of the frame has a concave hexagonal structure; The two arc-shaped beams (3) are respectively arranged on the upper and lower sides of the inner cavity of the frame, and the opposite ends of each arc-shaped beam (3) are connected to the side wall of the concave hexagonal structure; The vertical rod (4) is vertically set at the inner center of the frame, and the upper and lower arc beams (3) are respectively fixedly connected to the upper and lower ends of the vertical rod (4) through their corresponding central parts; The basic unit as a whole is arranged in a biaxially symmetrical manner in both the horizontal and vertical directions.

2. The novel metamaterial possessing both multistable and negative Poisson's ratio properties according to claim 1, characterized in that, The frame is composed of two parallel crossbeams (1) and four diagonal braces (2) connected together. The upper and lower diagonal braces (2) on the same side intersect and are recessed into the frame to form the concave hexagonal structure. The end of the arc beam (3) is directly abutted and fixed to the inner wall of the diagonal brace (2) on the corresponding side.

3. The novel metamaterial possessing both multistable and negative Poisson's ratio properties according to claim 1, characterized in that, The cross-sectional thickness of the arc beam (3) is less than one-tenth of its own length, and the structural thickness of the arc beam (3) is less than the cross-sectional thickness of the vertical rod (4).

4. A novel metamaterial possessing both multistable and negative Poisson's ratio properties according to claim 1, characterized in that, The main material constituting the basic unit is a high-strength and high-toughness substrate, which is selected from either low-carbon steel or engineering plastics.

5. A novel metamaterial possessing both multistable and negative Poisson's ratio properties according to claim 1, characterized in that, The arc-shaped beam (3), the vertical rod (4), and the frame are made of a combination of materials with different elastic modulus parameters; The arc-shaped beam (3) is made of a highly elastic deformation material to meet the multi-steady-state overturning conditions; Both the vertical rod (4) and the frame are made of high-rigidity materials for rigid support.

6. A novel metamaterial possessing both multistable and negative Poisson's ratio properties according to claim 5, characterized in that, The highly elastic deformable material is a special spring steel or a shape memory polymer, and the highly rigid material is high carbon steel or hard alloy.

7. A novel metamaterial possessing both multistable and negative Poisson's ratio properties according to claim 2, characterized in that, The basic unit is configured to exhibit negative Poisson's ratio deformation characteristics when subjected to a vertical compressive load. When the diagonal braces (2) on both sides are compressed, they rotate and contract synchronously inward into the structure, thereby applying radial compressive force to the ends of the upper and lower arc beams (3). This compressive force forces the two arc beams (3) to bend and deform toward the vertical rod (4) and to press against each other.

8. A novel metamaterial possessing both multistable and negative Poisson's ratio properties according to claim 7, characterized in that, The arc beam (3) has a multi-steady-state deformation reversal mechanism, which is configured such that when the compression displacement reaches the set first critical threshold, the arc beam (3) buckles and reverses from the initial bending state of inward convexity to the secondary bending state of outward convexity, so as to achieve buffer energy absorption through a nonlinear steady-state switching process.

9. A novel metamaterial possessing both multistable and negative Poisson's ratio properties according to claim 1, characterized in that, It includes multiple basic units, which are arranged and assembled sequentially along the horizontal X direction and the vertical Y direction; the basic units are spliced ​​and fixed together in a two-dimensional periodic array, thereby forming a composite metamaterial plate or protective filling layer for shock absorption and impact resistance on a macroscopic scale.

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