A composite porous structure with a Poisson's ratio close to zero

Abstract

The application provides a composite porous structure with a Poisson's ratio close to zero, and belongs to the technical field of metamaterials. The composite porous structure comprises a plurality of simple cubic unit cells and regular octahedral unit cells, the simple cubic unit cells and the regular octahedral unit cells are arranged alternately in perpendicular X, Y and Z directions, so that each of the simple cubic unit cells is connected to one of the regular octahedral unit cells in six directions; wherein the six surface centers of the simple cubic unit cells and the regular octahedral unit cells are provided with rod end points, so that the simple cubic unit cells and the regular octahedral unit cells are connected through the rod end points. The simple cubic unit cells and the regular octahedral unit cells are arranged alternately to form a composite porous structure, the connection of the unit cells is realized in the three-axis direction by sharing the rod end points at the surface centers, the continuity and stability of the structure are ensured, and the effect of the Poisson's ratio close to zero is realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metamaterials, and more particularly relates to a composite porous structure with a Poisson's ratio close to zero. BACKGROUND

[0002] The Poisson's ratio is the negative ratio of the lateral strain to the longitudinal strain, which is used to describe the relationship between the lateral deformation and the longitudinal deformation of a material when it is stretched or compressed. For most common materials, the lateral deformation is positive and the longitudinal deformation is negative, and vice versa, for example, metals, plastics, etc., and the Poisson's ratio of these materials is usually between 0 and 0.5. The higher the Poisson's ratio of a material, the more obvious the lateral deformation; the lower the Poisson's ratio of a material, the smaller the lateral deformation.

[0003] A material with a Poisson's ratio of 0 does not have any lateral deformation when it is stretched or compressed, and this characteristic makes it valuable in some special application scenarios, such as precision mechanical parts and flexible electronic devices. However, in reality, the Poisson's ratio of natural materials is rarely close to 0, because almost all materials will produce some degree of lateral deformation when subjected to force. In addition, the artificial materials or structures with a Poisson's ratio of 0 designed in the prior art often have problems such as high manufacturing complexity, high cost, or insufficient mechanical properties. SUMMARY

[0004] The main purpose of the present application is to provide a composite porous structure with a Poisson's ratio close to zero, which can ensure the continuity and functionality of the internal structure through the design of the alternately arranged unit cells.

[0005] In order to achieve the above-mentioned purpose, the present application provides a composite porous structure with a Poisson's ratio close to zero, which comprises a plurality of simple cubic unit cells and regular octahedral unit cells. The simple cubic unit cells and the regular octahedral unit cells are arranged alternately in the X-axis, Y-axis and Z-axis directions, respectively, so that each of the six directions of the simple cubic unit cells is connected to a regular octahedral unit cell. The six surface centers of the simple cubic unit cells and the regular octahedral unit cells are provided with rod end points, so that the simple cubic unit cells and the regular octahedral unit cells are connected through the rod end points.

[0006] Further, the six surfaces of the simple cubic unit cells are provided with first connecting rods extending from the center of the unit cell to the surface center, and the rod end points are formed at the ends of the first connecting rods to connect the regular octahedral unit cells.

[0007] Further, the six surfaces of the regular octahedral unit cells are provided with second connecting rods extending from the adjacent surface center to the surface center, and the rod end points are formed at the ends of the second connecting rods to connect the simple cubic unit cells.

[0008] Further, the second connecting rods are connected at the rod end points with smooth transition structures.

[0009] Further, the simple cubic unit cells and the regular octahedral unit cells are connected at the rod end points with smooth transition structures.

[0010] Further, the material of the composite porous structure comprises thermoplastic polyurethane.

[0011] Further, the composite porous structure is printed by using a selective laser sintering 3D printing technology.

[0012] Compared with the prior art, the composite porous structure has the advantages that: by using simple cubic unit cells and regular octahedral unit cells arranged alternately to form a composite porous structure, the connection of the unit cells is realized in a face center sharing rod end point manner in the three-axis direction, the continuity and stability of the structure are ensured, and the effect of the Poisson's ratio being approximately 0 is realized; compared with traditional materials, the structure can significantly reduce the transverse deformation when stretched or compressed, and meets the application scenarios with high precision and special mechanical performance requirements. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 A structure schematic diagram of the composite porous structure with a Poisson's ratio close to 0 is provided for the embodiments of the present application.

[0014] Figure 2 A front view of the composite porous structure with a Poisson's ratio close to 0 is provided for the embodiments of the present application.

[0015] Figure 3 A plan view of the composite porous structure with a Poisson's ratio close to 0 is provided for the embodiments of the present application.

[0016] Figure 4 A structure schematic diagram of the regular octahedral unit cell is provided for the embodiments of the present application.

[0017] Figure 5 A structure schematic diagram of the simple cubic unit cell is provided for the embodiments of the present application.

[0018] Figure 6 A composite structure parameter information table is provided for the embodiments of the present application.

[0019] Figure 7 A composite structure simulation test diagram is provided for the embodiments of the present application.

[0020] Figure 8 A composite structure compression test diagram is provided for the embodiments of the present application.

[0021] In the drawings, the reference signs are as follows: 10, simple cubic unit cell; 11, first connecting rod; 20, regular octahedral unit cell; 21, second connecting rod. DETAILED DESCRIPTION

[0022] The embodiments of the present disclosure will be described in detail below with reference to the drawings.

[0023] The embodiments of the present disclosure will be described in detail below with reference to the drawings.

[0024] Poisson's ratio is the negative ratio of lateral strain to longitudinal strain, which is used to describe the relationship between lateral deformation and longitudinal deformation of a material when it is stretched or compressed. For most common materials, the lateral deformation is positive and the longitudinal deformation is negative, and vice versa, such as metals, plastics, etc., and the Poisson's ratio is usually between 0 and 0.5. The higher the Poisson's ratio of a material, the more obvious the lateral deformation; the lower the Poisson's ratio of a material, the smaller the lateral deformation.

[0025] Materials with a Poisson's ratio of 0 do not deform laterally when stretched or compressed, which makes them valuable in some special applications, such as precision mechanical parts and flexible electronic devices. However, in reality, the Poisson's ratio of natural materials is rarely close to 0, because almost all materials will deform laterally to some extent when subjected to stress. In addition, the existing artificial materials or structures with a Poisson's ratio of 0 often have high manufacturing complexity, high cost, or insufficient mechanical properties.

[0026] To solve this problem, the present embodiment provides a composite porous structure with a Poisson's ratio close to 0.

[0027] As shown in FIG. 1, the composite porous structure of the present embodiment includes a plurality of simple cubic (Simple Cubic) unit cells and octahedral (Octahedron) unit cells, which are arranged alternately in the X, Y and Z directions perpendicular to each other, so that each simple cubic unit cell is connected to an octahedral unit cell in each of the six directions. That is, in the x-axis direction, one simple cubic unit cell is arranged at each position, and an octahedral unit cell is placed adjacent to it; similarly, the arrangement in the y-axis and z-axis directions is the same, ensuring that unit cells of the same type are not adjacent in space. Figures 1-5 ​

[0028] Further, the six surface centers of the simple cubic unit cell and the regular octahedron unit cell are each provided with a rod end point, so that the simple cubic unit cell and the regular octahedron unit cell are connected through the rod end points. The simple cubic unit cell and the regular octahedron unit cell each constitute a cubic structure within a unit range, and at the surface center of each cubic unit, there are rod end points extended from the two kinds of unit cells, which makes the two kinds of unit cells connectable in any direction through the shared rod end points. The entire composite structure does not have independent, unconnected rod end points except for the outer surface, thereby ensuring the continuity and integrity of the overall structure, achieving a Poisson's ratio close to 0, and making the structure significantly reduce transverse deformation when stretched or compressed, thereby meeting the application scenarios with high precision and special mechanical properties.

[0029] Since the composite porous structure of the embodiment is formed by alternately arranging the two kinds of unit cells in the three-axis direction, the six surfaces of each simple cubic unit cell are each connected to one surface of a regular octahedron unit cell, and the six surfaces of the two kinds of unit cells are the same, and the rod end points are the same, while the six surfaces of the simple cubic unit cell each have a first connecting rod (as shown in Figure 5 ) extended from the center of the unit cell to the surface center, and the rod end points are formed at the end of the first connecting rod to connect the regular octahedron unit cell; the six surfaces of the regular octahedron each have a second connecting rod (as shown in Figure 4 ) extended from the center of the adjacent surface to the surface center, and the rod end points are formed at the end of the second connecting rod to connect the simple cubic unit cell, so they can be connected at the surface center of the contact surface of the two kinds of unit cells.

[0030] Further, the rod end points of each contact surface of the two kinds of unit cells can be connected. Compared with the Boolean operation of the two kinds of unit cells with a rod diameter not equal to 0, the rods of the composite porous structure of the embodiment can be integrally formed according to the set rod diameter, and the second connecting rod at the rod end point connection, the first connecting rod, and the second connecting rod at the rod end point each form a smooth transition structure, so that the structure has continuity, avoids powder accumulation at the rod turning point during printing, ensures the beauty of the structure, and enhances the printability.

[0031] Except for the outer surface of the porous structure or except for the outermost ring of unit cells without a contact surface, there are no independent, unconnected rod end points inside the porous structure, which avoids the random movement of the rod with only one end connected inside the overall structure, which is not affected by the overall structure, causing waste of the material for making, reducing the lightweight efficiency, affecting the mechanical properties of the structure, and destroying the stability.

[0032] In one possible embodiment, the selective laser sintering (SLS) printing method in 3D printing can accurately manufacture the composite porous structure in this embodiment, and the alternating arrangement of the unit cell design can be realized without support material, ensuring the continuity and functionality of the internal structure. The thermoplastic polyurethane (TPU) has excellent elasticity, flexibility and durability, can effectively absorb impact energy and avoid brittle failure, and its unique mechanical properties make the relationship between transverse and longitudinal deformation more intuitive, which helps to optimize the performance of the Poisson's ratio. Therefore, we use SLS technology to print the TPU composite porous structure, and perform mechanical tests on the structure in subsequent simulation tests and compression tests to determine whether the Poisson's ratio meets the expected requirements.

[0033] Among them, the selected material is 95A TPU, and the main performance parameters are: the density of the printed part is 0.00115 g / mm³, the tensile strength is 21 MPa, the tensile modulus is 61 MPa, the elongation at break is 310%, the bending strength is 3.3 MPa, the bending modulus is 74 MPa, and the tear strength is 101 N / mm.

[0034] Among them, the SLS process parameters are: laser power 20 W, laser scanning speed 2500 mm / s, laser scanning interval 0.1 mm, powder deposition thickness 0.15 mm, and powder bed temperature 125℃.

[0035] The test conditions can refer to Figure 6 、 Figure 7 and Figure 8 .

[0036] Figure 7 The simulation test stress distribution information of the composite porous structure with different volume fractions is shown, including the stress distribution diagram, the deformation diagram of longitudinal compression of 10 mm, and the deformation diagram of longitudinal compression of 15 mm, which correspond to Figure 6 ① Simulation test structure 29.91%, ② Simulation test structure 40.12%, ③ Simulation test structure 49.90% respectively. According to the pictures, under the conditions of longitudinal compression of 10 mm and 15 mm, the composite porous structure with different volume fractions has no significant deformation in the transverse direction except the longitudinal deformation, and the transverse size after deformation is basically the same as that before deformation, which meets the basic performance of zero Poisson's ratio structure.

[0037] Figure 8The compression test diagram of the composite structure with a volume fraction of 40.00% (±0.10%) is shown in the figure. In the test, the loading rate is set to 5 mm / min, and the loading is continued until the height of the sample is compressed to 10 mm (the sample basically reaches the yield stage) and 18 mm (the sample basically reaches the compaction stage). According to the figure, under the conditions of longitudinal compression of 10 mm and 15 mm, the composite porous structure with different volume fractions does not have significant deformation in the transverse direction in addition to the longitudinal deformation, which meets the basic performance of the structure with a nearly zero Poisson's ratio.

[0038] It can be seen that the composite porous structure of the embodiment realizes the effect of a Poisson's ratio close to zero through the optimization of the unit cell design and arrangement, so that the transverse deformation is extremely small, and the needs of high-precision measurement, structural stability and simplified engineering design are met. Since the transverse deformation is extremely small, the composite porous structure can be used to manufacture high-precision measurement tools or reference parts. In these occasions, the structure needs to maintain dimensional stability under stress to ensure the accuracy of measurement and operation. In architectural or engineering design, the deformation caused by the Poisson effect can be ignored to some extent by using the structure, thereby simplifying the structural design and calculation, improving the design efficiency and reducing the complexity.

[0039] In the description of the present application, it should be understood that the orientations or positional relationships indicated by the terms "intermediate", "length", "upper", "lower", "front", "rear", "vertical", "horizontal", "inner", "outer", "radial", "circumferential" and the like are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0040] In the present application, unless specifically defined and limited otherwise, the first feature "on" the second feature can be direct contact of the first and second features, or indirect contact of the first and second features through an intermediate medium. The meaning of "a plurality of" is at least two, for example, two, three, etc., unless specifically limited.

[0041] In the present application, unless specifically defined and limited otherwise, the terms "mounting", "connection", "connection", "fixing" and the like should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or it can be integrated; it can be mechanically connected, or it can be electrically connected or in communication with each other; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the internal communication of two elements or the interaction relationship between two elements, unless otherwise specifically limited. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0042] The above merely illustrates the embodiments of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made by those skilled in the art within the spirit and principle of the present application without creative labor shall be included in the protection scope of the present application.

Claims

1. A composite porous structure having a Poisson's ratio close to zero, characterized in that, The simple cubic unit cell and the regular octahedral unit cell are arranged alternately in perpendicular X, Y and Z directions, so that each simple cubic unit cell is connected to a regular octahedral unit cell in six directions; The simple cubic unit cell comprises first connecting rods extending from the center of the unit cell to the ±X, ±Y and ±Z directions, and first rod end points are formed at the ends of the first connecting rods to connect the regular octahedral unit cell; The regular octahedral unit cell is a hollow skeleton structure composed of beams, and the regular octahedral unit cell is provided with second rod end points at the six vertices of the ±X, ±Y and ±Z directions to connect the simple cubic unit cell; The simple cubic unit cell and the regular octahedral unit cell are connected through the first rod end points and the second rod end points.

2. The composite porous structure with a Poisson's ratio close to zero according to claim 1, characterized in that, The simple cubic unit cell and the regular octahedral unit cell have a smooth transition structure at the connection of the first rod end points and the second rod end points.

3. The composite porous structure with a Poisson's ratio close to zero according to claim 1, characterized in that, The material of the composite porous structure comprises thermoplastic polyurethane.

4. The composite porous structure with a Poisson's ratio close to zero according to claim 1, characterized in that, The composite porous structure is printed by selective laser sintering 3D printing technology.

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