A lattice sandwich structure with negative Poisson's ratio characteristics, anti-impact and high energy absorption

Abstract

The present invention discloses a lattice sandwich structure with negative Poisson's ratio characteristics, anti-impact, and high energy absorption. The lattice sandwich structure is based on a high-performance negative Poisson's ratio lattice core material. The negative Poisson's ratio lattice core material is obtained by changing the angle between the struts and the coordinate axes of a three-dimensional cubic structure. When the angle between the struts and the coordinate axes is not equal to zero, a lattice material with negative Poisson's ratio characteristics is obtained. The negative Poisson's ratio lattice material and two thin plates together form a novel negative Poisson's ratio lattice sandwich structure, which will simultaneously possess the characteristics of traditional auxetic lattice structures and traditional lattice sandwich structures, that is, it not only has the characteristics of negative Poisson's ratio and co-directional curvature, but also has excellent mechanical properties such as ultra-lightweight, high specific modulus, high specific strength, anti-impact, and high energy absorption. The sandwich structure described in the present invention also has strong controllability. By adjusting the strut deflection angle and the relative density of the lattice material, the mechanical properties of the lattice sandwich structure described in the present invention can be adjusted within a large range. The lattice sandwich structure has great application prospects in the aerospace field.

Description

Technical Field

[0001] The present invention relates to a lattice sandwich structure, and particularly to a lattice sandwich structure with negative Poisson's ratio characteristics, which has impact resistance and high energy absorption performance. Background Art

[0002] With the continuous development of the aerospace industry, the unique mechanical environments (such as aerodynamic heat, vibration, atmospheric pulsating pressure, etc.) and performance requirements (such as hypersonic speed, high maneuverability, long-range strike, etc.) faced by aircraft pose new problems for structural design: structural lightweighting, structural multi-functionality, and structural optimization design. Among them, structural lightweighting design is the eternal pursuit and key of aerospace structural design. Due to its excellent mechanical properties such as light weight, high specific stiffness, high specific strength, high toughness, and high energy absorption, the porous sandwich structure has received extensive attention in the aerospace field.

[0003] The porous sandwich structure generally consists of two relatively thin panels and a lightweight porous material in the middle. Among them, the selection of the core material is crucial for the performance of the sandwich structure. Currently, the commonly used core materials mainly include honeycombs, metal foams, and lattice materials. Research shows that under the condition of the same relative density, the in-plane Young's modulus of general lattice materials can be more than two orders of magnitude higher than that of lightweight materials such as honeycombs, and its out-of-plane strength can be more than one order of magnitude higher than that of materials such as honeycombs. Compared with metal foams, lattice materials are usually formed by microstructural topology, so they have high designability to meet complex actual needs. In addition, in the complex environments of aerospace and other fields, part of the materials of the sandwich structure are used to meet the requirements of mechanical properties such as stiffness and strength, and the other part of the materials need to meet physical requirements such as vibration isolation and heat insulation. However, it is difficult for traditional structural design methods to simultaneously take into account the lightweight requirements and multi-functional requirements of the structure. The lattice sandwich structure based on periodic microstructures integrates the optimization design concepts of material design, structural design, and functional design, providing us with a new solution.

[0004] Currently, in addition to traditional lattice materials (such as tetrahedral, pyramidal, body-centered cubic, and Kagome-type core topological configurations), new lattice materials with negative Poisson's ratio characteristics have attracted the interest of scholars. The Poisson's ratio of a material is also called the transverse deformation coefficient, which is an elastic constant reflecting the transverse deformation of the material. Its calculation formula is: (where ε x is the transverse positive strain of the material, ε y(is the axial normal strain of the material). On the one hand, a negative Poisson's ratio means that the material will undergo transverse contraction when subjected to unidirectional compression, that is, the material will gather towards the loaded area. The material that contracts / gathers inward will help resist the external load and improve the load-bearing capacity and energy absorption efficiency of the entire material. On the other hand, negative Poisson's ratio lattice materials often generate auxetic effects based on the bending deformation or rotational deformation of the struts, and these two deformation mechanisms weaken the load-bearing capacity of the material to a certain extent. These two contradictory conclusions have hindered the application of negative Poisson's ratio lattice sandwich structures.

[0005] The lattice sandwich structure with negative Poisson's ratio characteristics described in the present invention is a sandwich structure based on a negative Poisson's ratio lattice material as the core material. This negative Poisson's ratio lattice material overcomes the weaknesses of low modulus and low strength of negative Poisson's ratio materials, and has the characteristics of high specific modulus, high specific strength, and high energy absorption. The sandwich structure formed by this lattice material and two thin plates will simultaneously possess the characteristics of traditional lattice sandwich structures and auxetic lattice sandwich structures, that is, it has excellent mechanical properties and mechanical behaviors such as ultra-lightweight, high specific strength, high specific stiffness, impact resistance, high energy absorption, and co-directional curvature. At the same time, the sandwich structure described in the present invention has strong controllability. By adjusting the strut deflection angle and the relative density of the lattice material, the mechanical properties of the lattice sandwich structure described in the present invention can be regulated within a large range to meet more demanding and harsh aerospace use environments and application requirements. Summary of the Invention

[0006] The purpose of the present invention is to propose a novel lattice sandwich structure, a novel lattice sandwich structure based on a negative Poisson's ratio lattice core material and integrating the characteristics of traditional lattice sandwich structures and negative Poisson's ratio lattice sandwich structures. The novel lattice sandwich structure described in the present invention has the characteristics of negative Poisson's ratio and co-directional curvature, and at the same time has excellent mechanical properties such as ultra-lightweight, high specific modulus, high specific strength, impact resistance, and high energy absorption. The novel lattice sandwich structure described can be prepared by 3D printing and has strong controllability to meet different application requirements.

[0007] The present invention is mainly achieved through the following technical solutions:

[0008] An impact-resistant and high-energy-absorbing lattice sandwich structure with negative Poisson's ratio characteristics is composed of a negative Poisson's ratio lattice core material and two thin plates. Among them, the thin plates are located on the upper and lower sides, and the negative Poisson's ratio lattice core material is located in the middle.

[0009] The negative Poisson's ratio lattice core material is topologically composed of negative Poisson's ratio periodic unit cells in three-dimensional space. The negative Poisson's ratio periodic unit cell is obtained by mirroring the smallest representative unit of the negative Poisson's ratio unit cell three times.

[0010] The minimum representative unit of the negative Poisson's ratio unit cell can be obtained by changing the angle θ of the representative unit of the cubic structure. The representative unit of the cubic structure is composed of six cross-shaped two-dimensional unit cells (11). The two-dimensional cross-shaped unit cell is fixedly connected by two struts (111 and 112) that are perpendicular bisectors of each other, and the intersection point of the two struts is O 11 . The two-dimensional cross-shaped unit cells (11) are respectively located on the six faces of the cubic structure, and they are connected together by struts to jointly form a periodic three-dimensional cubic structure representative unit.

[0011] When the minimum representative unit of the negative Poisson's ratio unit cell is obtained by changing the angle θ of the representative unit of the cubic structure, the angle θ is the minimum angle between the strut and the main coordinate axes (x, y or z) of the rectangular coordinate system, and its variation range is 0° < θ < 45°. The four cross-shaped unit cells (13) parallel to the x-z plane and parallel to the y-z plane, under the condition of satisfying connectivity and the two internal struts (131 and 132) remaining perpendicular to each other, respectively take the intersection point O of the two struts 13 as the rotation center and rotate clockwise or counterclockwise by θ. In order to ensure connectivity with the other four cross-shaped unit cells, the two internal struts (121 and 122) of the two cross-shaped unit cells parallel to the x-y plane will no longer maintain a perpendicular relationship, and the two struts respectively take their intersection point O 12 as the rotation center and rotate by θ in opposite rotation directions to become a two-dimensional scissor-cross unit cell (12). Finally, through the regulation of the angle θ, the representative unit of the cubic structure becomes the minimum representative unit of the negative Poisson's ratio unit cell. During the transformation process, the connectivity between the struts remains unchanged, and the minimum angle between each strut and the main coordinate axes (x, y or z) of the rectangular coordinate system is the same, all being θ.

[0012] The geometric size of the minimum representative unit of the negative Poisson's ratio unit cell can be a cube or a cuboid. When the geometric size of the periodically arranged negative Poisson's ratio unit cells is a cuboid, the two struts (131 and 132) of the two-dimensional cross-shaped unit cell have different lengths, and the two struts (121 and 122) of the two-dimensional scissor-cross unit cell need to have the same length.

[0013] There are various choices for the cross-section of the struts in the negative Poisson's ratio lattice core material, including trapezoidal cross-section, I-shaped cross-section, channel-shaped cross-section, rectangular cross-section, circular cross-section, rhombic cross-section, and regular polygon cross-section.

[0014] The negative Poisson's ratio lattice core material described above can regulate the Poisson's ratio of the material by changing the angle θ. When θ = 0°, the Poisson's ratio of the lattice core material is zero. When θ ≠ 0°, the Poisson's ratio of the lattice core material is always negative. When the angle θ is regulated within the range of 0° to 45°, the change range of the Poisson's ratio is from 0 to -1. The described lattice sandwich structure can also regulate the specific stiffness, specific strength, energy absorption efficiency, and specific energy absorption of the structure through the strut angle θ of the core material and the relative density of the core material.

[0015] The negative Poisson's ratio lattice core material described above has an extremely low relative density, and an extremely low relative density below 1% can be achieved. The maximum relative density of the negative Poisson's ratio lattice core material should not exceed 20%.

[0016] The described negative Poisson's ratio lattice sandwich structure can be integrally formed by advanced additive manufacturing technology, or the core material and thin plates can be independently prepared first, and then assembled through bonding or welding processes. The described negative Poisson's ratio lattice core material can be prepared by 3D printing through FDM fused deposition modeling technology, SLA stereolithography technology, DLP selective laser melting technology, SLS selective laser sintering, EBM electron beam melting forming, SLM selective laser melting technology, SHS selective thermal sintering, and 3DP three-dimensional spraying and bonding forming technology.

[0017] The described negative Poisson's ratio lattice sandwich structure can be arranged in multiple layers in the out-of-plane direction to form a multi-level lattice sandwich structure. The described multi-level lattice sandwich structure can be gradient-designed, including relative density gradient design and angle θ gradient design.

[0018] The present invention has the following advantages and effects compared with the prior art:

[0019] (1) The present invention proposes a lattice sandwich structure with negative Poisson's ratio characteristics, anti-impact, and high energy absorption. This lattice sandwich structure adopts a negative Poisson's ratio lattice core material. When this sandwich structure is axially compressed, the internal negative Poisson's ratio sandwich material will shrink inward, and the sandwich material will become denser and denser, so that it can effectively resist the compression load. Therefore, it has broad application prospects in the fields of load-bearing and energy absorption, etc.;

[0020] (2) Compared with the existing porous sandwich structure, this negative Poisson's ratio lattice sandwich structure is lighter, and at the same time has the same-direction curvature property, high fracture toughness of the negative Poisson's ratio material, and high specific modulus, high specific strength, high specific energy absorption, high energy absorption efficiency, anti-impact and other mechanical properties of the traditional lattice material;

[0021] (3) The elastic properties, compressive strength, and impact energy absorption characteristics of the negative Poisson's ratio sandwich structure are controllable. By adjusting the geometric parameters of the struts (length and cross-section), the deflection angle θ, and the relative density, the mechanical properties of the structure can be regulated within a wide range. Among them, the angle θ and the relative density have the greatest influence on its modulus, strength, energy absorption efficiency, and specific energy absorption. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the lattice sandwich structure with negative Poisson's ratio characteristics, which is impact-resistant and highly energy-absorbing, according to the present invention.

[0023] Figure 2 (a) Schematic diagram of a two-dimensional cross-shaped unit cell;

[0024] Figure 2 (b) Schematic diagram of a representative unit of the cubic structure;

[0025] Figure 2 (c) Schematic diagram of a periodic unit cell of the cubic structure;

[0026] Figure 3 (a) Schematic diagram of a two-dimensional scissor-cross unit cell and a two-dimensional cross-shaped unit cell after counterclockwise rotation by θ;

[0027] Figure 3 (b) Schematic diagram of the smallest representative unit of the negative Poisson's ratio unit cell;

[0028] Figure 3 (c) Schematic diagram of a periodic unit cell of the negative Poisson's ratio;

[0029] Figure 4 (a) Schematic diagram of a representative unit of the cuboid structure;

[0030] Figure 4 (b) Schematic diagram of the smallest representative unit of the negative Poisson's ratio unit cell with the geometric dimensions of a cuboid;

[0031] Figure 5(a) Schematic diagram of a three-level lattice sandwich structure designed with relative density as the gradient;

[0032] Figure 5(b) Schematic diagram of a three-level lattice sandwich structure designed with the angle θ as the gradient. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] The present invention will be further described in detail below in combination with specific implementation cases.

[0034] As Figure 1 shown, the present invention is a lattice sandwich structure with negative Poisson's ratio characteristics, which is impact-resistant and highly energy-absorbing. The structure is composed of a negative Poisson's ratio lattice core material and two thin plates. The thin plates are located on the upper and lower sides, and the negative Poisson's ratio lattice core material is located in the middle. Figure 3As shown, the basic building block of the negative Poisson's ratio lattice core material is a negative Poisson's ratio periodic unit cell ( Figure 3 (c)), and the smallest building block is the smallest representative unit of the negative Poisson's ratio unit cell ( Figure 3 (b)). The smallest representative unit of the negative Poisson's ratio unit cell is mirrored three times to obtain the negative Poisson's ratio periodic unit cell, and the negative Poisson's ratio periodic unit cell topologically constitutes the negative Poisson's ratio lattice core material in three-dimensional space.

[0035] As Figure 2 、 Figure 3 shown, the smallest representative unit of the negative Poisson's ratio unit cell can be obtained by changing the angle θ of the representative unit of the cubic structure. As Figure 2 (b) shows, the representative unit of the cubic structure is composed of six two-dimensional cross-shaped unit cells 11. As Figure 2 (a) shows, the two-dimensional cross-shaped unit cell is fixedly connected by two struts 111 and 112 that are perpendicular and bisect each other, and the intersection point of the two struts is O 11 . The two-dimensional cross-shaped unit cells 11 are respectively located on the six faces of the cubic structure, and they are connected together by struts to jointly form a periodic three-dimensional cubic structure representative unit. When the smallest representative unit of the negative Poisson's ratio unit cell is obtained by changing the angle θ of the representative unit of the cubic structure, the angle θ is the smallest angle between the strut and the main coordinate axes (x, y or z) of the rectangular coordinate system, and its range of change is 0° < θ < 45°. In the representative unit of the cubic structure, the four cross-shaped unit cells 11 parallel to the x-z plane and parallel to the y-z plane are respectively rotated clockwise or counterclockwise by θ around the intersection point O 13 of the two struts, satisfying connectivity and keeping the two internal struts 131 and 132 perpendicular, to obtain the rotated cross-shaped unit cell 13. In order to ensure connectivity with the other four cross-shaped unit cells, the two internal struts 121 and 122 of the two cross-shaped unit cells parallel to the x-y plane will no longer maintain a perpendicular relationship, and the two struts are respectively rotated by θ in opposite rotation directions around their intersection point O 12 to become a two-dimensional scissor-crossed unit cell 12. Finally, through the regulation of the angle θ, the representative unit of the cubic structure ( Figure 2 (b)) becomes the smallest representative unit of the negative Poisson's ratio unit cell ( Figure 3 (b)). During the transformation process, the connectivity between the struts remains unchanged, and the smallest angle between each strut and the main coordinate axes (x, y or z) of the rectangular coordinate system is the same, all being θ.

[0036] As Figure 4 shown, the lengths of the struts in the smallest representative unit of the negative Poisson's ratio unit cell can be different. As Figure 4As shown in (a), for the representative unit of the cuboid structure, the relationship among the length (a), width (b), and height (c) is a = b ≠ c. By rotating the cross-shaped structure on the four faces parallel to the z-axis by θ and rotating the struts on the face perpendicular to the z-axis by θ accordingly, the smallest representative unit of the negative Poisson's ratio unit cell is obtained. The smallest representative unit of this negative Poisson's ratio unit cell has the same length and width, and different heights.

[0037] For the core material in the negative Poisson's ratio lattice sandwich structure described above, there are various choices for the cross-section of the struts, including trapezoidal cross-section, I-shaped cross-section, channel-shaped cross-section, rectangular cross-section, circular cross-section, rhombic cross-section, and regular polygon cross-section. The Poisson's ratio of the material can be adjusted by changing the angle θ of the struts. When θ = 0°, the Poisson's ratio of the lattice core material is zero. When θ ≠ 0°, the Poisson's ratio of the lattice core material is always negative. When the angle θ is adjusted within the range of 0° to 45°, the change range of the Poisson's ratio is 0 to -1. The specific stiffness, specific strength, energy absorption efficiency, and specific energy absorption of the structure can also be adjusted by changing the angle θ and relative density. The negative Poisson's ratio lattice core material has an extremely low relative density. As Figure 1 shown in the negative Poisson's ratio lattice sandwich structure, when the cross-section of the strut is a square with a side length of 0.5 mm, the angle between the strut and the coordinate axis is θ = 20°, and the size of the core material is 95.5 mm × 38.5 mm × 38.5 mm, the Poisson's ratio of this core material is approximately -0.8, and the relative density is only 2%.

[0038] The negative Poisson's ratio lattice sandwich structure described above can be integrally formed by advanced additive manufacturing technology, or the core material and thin plates can be prepared independently first, and then assembled through bonding or welding processes. The negative Poisson's ratio lattice core material can be prepared by 3D printing through FDM fused deposition modeling technology, SLA stereolithography technology, DLP digital light processing selective laser melting technology, SLS selective laser sintering, EBM electron beam melting forming, SLM selective laser melting technology, SHS self-propagating high-temperature synthesis, and 3DP three-dimensional printing and bonding forming technology.

[0039] As shown in Fig. 5, the negative Poisson's ratio lattice sandwich structure can be arranged in multiple layers in the out-of-plane direction to form a multi-level lattice sandwich structure. As shown in Fig. 5(a), negative Poisson's ratio lattice sandwich structures with different densities are arranged in a gradient in the z-axis direction. The angles of the three-level lattice structure are all θ = 20°. From top to bottom, the relative density of the core material in the first layer is 0.85%, the relative density of the core material in the second layer is 1.96%, and the relative density of the core material in the third layer is 4.58%. As shown in Fig. 5(b), three-level negative Poisson's ratio lattice sandwich structures with different angles θ are arranged in a gradient in the z-axis direction. The cross-sectional dimensions of the struts of the three-level lattice structure are the same, all being square cross-sections with a side length of 0.5 mm. Among them, the angle parameter of the core material in the first layer is θ = 10°, the angle parameter of the core material in the second layer is θ = 20°, and the angle parameter of the core material in the third layer is θ = 30°.

[0040] The implementation modes of the present invention are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. An anti-impact and high energy-absorbing lattice sandwich structure with negative Poisson's ratio characteristics, characterized in that: The described lattice sandwich structure is composed of a negative Poisson's ratio lattice core material and two thin plates. Among them, the thin plates are located on the upper and lower sides, and the negative Poisson's ratio lattice core material is located in the middle; The described negative Poisson's ratio lattice core material is topologically formed by negative Poisson's ratio periodic unit cells in three-dimensional space. The described negative Poisson's ratio periodic unit cell is obtained by mirroring the smallest representative unit of the negative Poisson's ratio unit cell three times; The smallest representative unit of the described negative Poisson's ratio unit cell is obtained by changing the angle θ of the representative unit of the cubic structure. The described representative unit of the cubic structure is composed of six two-dimensional cross-shaped unit cells. The described two-dimensional cross-shaped unit cell is fixedly connected by two struts that bisect each other perpendicularly. The described two-dimensional cross-shaped unit cells are respectively located on the six faces of the cubic structure, and they are connected together by struts to jointly form a periodic three-dimensional cubic structure representative unit; The angle θ is the minimum angle between the strut and the main coordinate axis of the rectangular coordinate system, and its range of variation is 0° < θ < 45°. The four two-dimensional cross-shaped unit cells parallel to the x-z plane and parallel to the y-z plane rotate clockwise or counterclockwise by θ around the intersection point of the two struts respectively under the condition of satisfying connectivity and the two struts inside remaining perpendicular. In order to ensure connectivity with the other four two-dimensional cross-shaped unit cells, the two struts inside the two two-dimensional cross-shaped unit cells parallel to the x-y plane will no longer maintain a perpendicular relationship. The two struts rotate by θ around their intersection points in opposite rotation directions respectively and become two-dimensional scissor-crossed unit cells. Finally, through the regulation of the angle θ, the representative unit of the cubic structure becomes the smallest representative unit of the negative Poisson's ratio unit cell. During the transformation process, the connectivity between the struts remains unchanged, and the minimum angle between each strut and the main coordinate axis of the rectangular coordinate system is the same, all being θ.

2. The anti-impact and high energy-absorbing lattice sandwich structure with negative Poisson's ratio characteristics according to claim 1, characterized in that: The cross-section of the struts in the described negative Poisson's ratio lattice core material can have various choices, including trapezoidal cross-section, I-shaped cross-section, channel-shaped cross-section, rectangular cross-section, circular cross-section, rhombic cross-section, and regular polygon cross-section.

3. The anti-impact and high energy-absorbing lattice sandwich structure with negative Poisson's ratio characteristics according to claim 2, characterized in that: The described negative Poisson's ratio lattice core material can regulate the Poisson's ratio of the material by changing the angle θ. When the angle θ is regulated within the range of 0° to 45°, the range of variation of the Poisson's ratio is 0 to -1.

4. The anti-impact and high energy-absorbing lattice sandwich structure with negative Poisson's ratio characteristics according to claim 3, characterized in that: The described negative Poisson's ratio lattice core material has an extremely low relative density of less than 1%, and the maximum relative density of the described negative Poisson's ratio lattice core material should not exceed 20%.

5. The anti-impact and high energy-absorbing lattice sandwich structure with negative Poisson's ratio characteristics according to claim 4, characterized in that: The described lattice sandwich structure can regulate the specific stiffness, specific strength, energy absorption efficiency, and specific energy absorption of the structure by changing the angle θ and the relative density.

6. The anti-impact and high energy-absorbing lattice sandwich structure with negative Poisson's ratio characteristics according to claim 5, characterized in that: The negative Poisson's ratio lattice core material of the described lattice sandwich structure can be prepared by 3D printing through FDM fused deposition modeling technology, SLA stereolithography technology, DLP digital light processing selective laser melting technology, SLS selective laser sintering, EBM electron beam melting forming, SLM selective laser melting technology, SHS selective thermal sintering, and 3DP three-dimensional spray bonding forming technology.

7. The anti-impact and high energy-absorbing lattice sandwich structure with negative Poisson's ratio characteristics according to claim 6, characterized in that: The described lattice sandwich structure is integrally formed by advanced additive manufacturing technology, or the core material and the thin plates are independently prepared first, and then assembled through pasting or welding processes.

8. The anti-impact and high energy-absorbing lattice sandwich structure with negative Poisson's ratio characteristics according to claim 7, characterized in that: The described lattice sandwich structure can be arranged in multiple layers in the out-of-plane direction to form a multi-level lattice sandwich structure.

9. The anti-impact and high energy-absorbing lattice sandwich structure with negative Poisson's ratio characteristics according to claim 8, characterized in that: The described multi-level lattice sandwich structure can be gradient-designed, including relative density gradient design and angle θ gradient design.

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