CN116176056A

CN116176056A - Composite material with density gradient and negative poisson ratio honeycomb structure

Info

Publication number: CN116176056A
Application number: CN202310117185.3A
Authority: CN
Inventors: 刘雪强; 张长琦; 沈灿铎; 刘毅; 孟佳
Original assignee: Institute of Systems Engineering of PLA Academy of Military Sciences
Current assignee: Institute of Systems Engineering of PLA Academy of Military Sciences
Priority date: 2023-02-15
Filing date: 2023-02-15
Publication date: 2023-05-30
Anticipated expiration: 2043-02-15
Also published as: CN116176056B

Abstract

The invention provides a composite material with a density gradient and a negative poisson ratio honeycomb structure and a preparation method thereof, relates to the field of composite materials, and aims to solve the technical problem that a plate cannot be light in weight, high in performance and low in cost. The composite material comprises two substrates and a core body arranged between the two substrates, wherein the substrates are fiber reinforced resin substrates, and the core body is a honeycomb member formed by splicing a plurality of pipe bodies and a plurality of plate bodies; the cross section of body is indent hexagon, along first direction, and a plurality of body splice in proper order, along the second direction, adjacent body passes through the plate body coupling in a plurality of bodies, and the tip of plate body is connected with the depressed part that corresponding second wallboard had respectively, and along first direction, the angle of the indent angle of a plurality of body is progressively decreased in proper order, along the second direction, and the indent angle of a plurality of body is the same, and wherein, the indent angle is: the included angle between the wallboard segment and the corresponding first wallboard.

Description

Composite material with density gradient and negative poisson ratio honeycomb structure

Technical Field

The invention relates to the field of composite materials, in particular to a composite material with a density gradient and a negative poisson ratio honeycomb structure and a preparation method thereof.

Background

With the gradual popularization of the light weight of automobiles, the anti-impact performance of automobile plates becomes an important point of attention, but the traditional metal plates can bring about the increase of the weight of the plates due to the improvement of the anti-impact performance, and the cost is also continuously increased. The fiber composite material is a lightweight material used as a substitute for metal, and a composite board having excellent properties can be produced by bonding fibers and a resin, but the interlayer bonding ability is weak, resulting in weak impact resistance.

At present, the microstructure material is one of effective means for realizing both light weight and high strength as a mechanical metamaterial, but cannot realize both high performance and low cost.

Disclosure of Invention

The invention aims to provide a composite material with a density gradient and a negative poisson ratio honeycomb structure and a preparation method thereof, so as to solve the technical problem that the plate cannot be light in weight, high in performance and low in cost.

In order to achieve the above object, the present invention provides the following technical solutions:

the composite material with the density gradient and the negative poisson ratio honeycomb structure provided by the embodiment of the invention comprises two substrates and a core body arranged between the two substrates, wherein the substrates are fiber reinforced resin substrates, and the core body is a honeycomb member formed by splicing a plurality of pipe bodies and a plurality of plate bodies;

the cross section of the pipe body is of a concave hexagon, and the pipe body comprises two first wall plates arranged in parallel and two second wall plates arranged oppositely and arranged between the two first wall plates;

each second wall plate comprises two wall plate sections, each wall plate section inclines towards the inside of a cavity of the pipe body along the direction away from the first wall plate, two wall plate sections in each second wall plate are connected with a concave part, the concave part is positioned at the middle part between the two first wall plates, and the distance between the two first wall plates is the same as the width of the first wall plate;

along the first direction, a plurality of the body splices in proper order, along the second direction, a plurality of adjacent in the body passes through the plate body is connected, the tip of plate body respectively with corresponding the depressed part that the second wallboard had is connected, wherein, the first direction is: the distribution directions of the two first wall plates of the pipe body are the same; the second direction is: the distribution directions of the two second wall plates of the pipe body are the same;

along the first direction, the angle of the concave angles of the plurality of pipe bodies is gradually decreased, and along the second direction, the concave angles of the plurality of pipe bodies are the same, wherein the concave angles are as follows: and an included angle between the wall plate segment and the corresponding first wall plate.

According to at least one embodiment of the present disclosure, along a first direction, central axes of a plurality of the tubes spliced in sequence are on the same plane; and/or the number of the groups of groups,

along the second direction, the central axes of the pipe bodies with the same concave angle are positioned on the same plane.

According to at least one embodiment of the present disclosure, each of the pipe bodies has the same thickness as the first wall plate, the second wall plate, and each of the plate bodies.

According to at least one embodiment of the present disclosure, the width of the plate body between two adjacent pipe bodies having the largest concave angle is the same as the width of the first wall plate, and the width direction of the plate body, the width direction of the first wall plate, and the second direction are the same.

According to at least one embodiment of the present disclosure, the concave angle is α, wherein α is 50 ° or less and 85 °.

According to at least one embodiment of the present disclosure, the number of the pipes spliced to each other along the first direction is n, and the difference between the internal concave angles of two adjacent pipes is less than 35 °/n, and the difference between the internal concave angles of each adjacent pipe is the same.

According to at least one embodiment of the present disclosure, the material of the core is aluminum alloy or aramid fiber.

According to at least one embodiment of the present disclosure, the composite material further includes a hot melt adhesive film disposed between the core and the corresponding substrate, the hot melt adhesive film being used for bonding between the core and the corresponding substrate, and the hot melt adhesive film material includes one of polyethersulfone and thermoplastic polyurethane elastomer rubber.

According to at least one embodiment of the present disclosure, the fibers of the fiber reinforced resin substrate are one or more of hemp fibers, cotton fibers, bamboo fibers, carbon fibers, glass fibers, and aramid fibers;

the fiber in the fiber reinforced resin substrate is one or more of fiber cloth, fiber felt, unidirectional fiber and short fiber;

the resin is one or more of polypropylene, polyether-ether-ketone, nylon 6, nylon 66, ABS, polyether-imide, polyphenylene sulfide and polylactic acid.

Compared with the prior art, the composite material with the density gradient and the negative poisson ratio honeycomb structure has the following advantages:

according to the composite material with the density gradient and the negative poisson ratio honeycomb structure, the core body is arranged between the two fiber reinforced resin substrates, and the core body adopts the negative poisson ratio honeycomb structure and is used as one of microstructure materials, so that the composite material has strong impact resistance and compression resistance, can be light in weight and high in strength, and overcomes the defect that a high-performance plate for an automobile in the prior art is impact-resistant by depending on pile quality. The honeycomb-shaped member is formed by splicing a plurality of pipe bodies and a plurality of plate bodies, the cross section of each pipe body is of a concave hexagon, each pipe body comprises two first wall plates which are arranged in parallel and two second wall plates which are arranged oppositely, the pipe bodies are spliced in sequence along a first direction, adjacent pipe bodies in the pipe bodies are connected through the plate bodies along a second direction, the end parts of the plate bodies are respectively connected with concave parts of the corresponding second wall plates, and the concave angles of the pipe bodies are the same along the second direction; that is, the concave angle in the tube body of each layer decreases along the first direction, so that the mass of each layer increases while the volume is substantially unchanged, and the density increases layer by layer, forming a density gradient. The concave hexagonal negative poisson ratio structure has the characteristics of stretching and transverse expansion and compressing and transverse shrinkage, and has better shock resistance. The core body with the density gradient negative poisson ratio honeycomb structure is arranged between the two fiber reinforced resin substrates, and compared with a negative poisson ratio material with a single structure, the core body has higher shock resistance and energy absorption performance. Further, the mechanical properties are better than those of the conventional interlayer material.

Compared with a honeycomb structure without a density gradient, the negative poisson ratio honeycomb structure with the density gradient is more material-saving and lower in cost. Meanwhile, the composite material obtained by clamping the negative poisson ratio honeycomb structure with the density gradient by using the substrate has good integrity, and the impact resistance is obviously improved and the comprehensive mechanical properties are excellent on the premise of ensuring good bending strength, tensile property and other mechanical properties.

Another object of the present invention is to provide a method for preparing a composite material having a negative poisson's ratio honeycomb structure with a density gradient, the method comprising:

mixing the fiber and the resin, and heating under pressure to form a fiber reinforced resin substrate;

manufacturing the core body through 3D printing;

in the first direction, the top and the bottom of the core body are respectively paved with a hot melt adhesive film and a base plate in sequence and then integrally formed.

Compared with the prior art, the preparation method of the composite material with the negative poisson ratio honeycomb structure with the density gradient has the advantages which are the same as those of the composite material with the negative poisson ratio honeycomb structure with the density gradient, and the description is omitted.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.

Fig. 1 is a schematic perspective view of a core according to an embodiment of the present invention.

Fig. 2 is a schematic elevational structural view of a core according to an embodiment of the present invention.

Fig. 3 is a schematic plan view of a core according to an embodiment of the invention.

Reference numerals: 10. a tube body; 11. a first wall plate; 12. a second wall plate; 121. a wall panel section; 122. a recessed portion; 20. a plate body.

Detailed Description

The present invention will be described in further detail with reference to the drawings and embodiments. It is to be understood that the specific embodiments described herein are merely illustrative of the substances, and not restrictive of the invention. It should be further noted that, for convenience of description, only the portions related to the present invention are shown in the drawings.

In addition, the embodiments of the present invention and the features of the embodiments may be combined with each other without collision. The present invention will be described in detail below with reference to the accompanying drawings in conjunction with embodiments.

With the gradual popularization of the light weight of automobiles, the anti-impact performance of automobile plates becomes an important point of attention, but the traditional metal plates can bring about the increase of the weight of the plates due to the improvement of the anti-impact performance, and the cost is also continuously increased. The fiber composite material is a lightweight material used for replacing metal, and has weak impact resistance due to weak interlayer bonding capability, so that the lightweight material is difficult to achieve both lightweight and high performance.

It should be noted that, in the embodiment of the present invention, the first direction is a direction from top to bottom of the viewing surface in fig. 2, and the second direction is a left-right direction of the viewing surface in fig. 2.

Referring to fig. 1-3, an exemplary embodiment of the present invention provides a composite material having a density gradient and a honeycomb structure with a negative poisson ratio, which includes two substrates and a core disposed between the two substrates, wherein the substrates are fiber reinforced resin substrates, and the core is a honeycomb member formed by splicing a plurality of tubes 10 and a plurality of plates 20; the cross section of the pipe body 10 is of a concave hexagon, and the pipe body 10 comprises two first wall plates 11 which are arranged in parallel and two second wall plates 12 which are arranged oppositely and are arranged between the two first wall plates 11; each second wall plate 12 comprises two wall plate sections 121, each wall plate section 121 inclines towards the inside of a cavity of the pipe body 10 along the direction away from the first wall plate 11, the two wall plate sections 121 in each second wall plate 12 are connected with a concave part 122, the concave part 122 is positioned at the middle part between the two first wall plates 11, and the space between the two first wall plates 11 is the same as the width of the first wall plates 11; along the first direction, a plurality of body 10 splice in proper order, along the second direction, adjacent body 10 passes through plate body 20 connection in a plurality of body 10, and the tip of plate body 20 is connected with the depressed part 122 that corresponding second wallboard 12 had respectively, and wherein, first direction is: the distribution direction of the two first wall plates 11 of the pipe body 10; the second direction is: the distribution direction of the two second wall plates 12 of the pipe body 10; along the first direction, the angles of the concave angles of the plurality of pipe bodies 10 decrease in sequence, and along the second direction, the concave angles of the plurality of pipe bodies 10 are the same, wherein the concave angles are as follows: the angle between the wall segments 121 and the respective first wall 11.

The above-mentioned multiple tubes 10 are spliced in turn, that is, along the first direction, the tubes 10 in a row are spliced with each other, and the adjacent first wall plates 11 between two adjacent tubes 10 may be shared by two tubes, which is the first wall plate 11 at the bottom of the upper tube 10 and the first wall plate 11 at the top of the lower tube 10. The adjacent tubes 10 of the plurality of tubes 10 are connected by the plate 20 along the second direction, that is, the plurality of tubes 10 of one row are connected by the plate 20 along the second direction. So that the tube forms a core with a negative poisson's ratio honeycomb in a plurality of rows and columns.

Each of the second wall plates 12 includes two wall plate sections 121, each wall plate section 121 is inclined toward the inside of the cavity of the pipe body 10 in a direction away from the first wall plate 11, the two wall plate sections 121 in each second wall plate 12 are connected to a recess 122, the recess 122 is located at a middle portion between the two first wall plates 11, and a space between the two first wall plates 11 is the same as a width of the first wall plate 11. The pipe body forms a concave hexagonal section, and the concave portion 122 is a concave structure formed at the joint because both wall plate segments 121 incline toward the inside of the pipe body. The recess 122 is located in the middle, i.e. the two wall segments 121 are symmetrically arranged and the width and height of the entire tube 10 are uniform. And the ends of the plate body 20 are respectively connected with the concave portions 122 of the corresponding second wall plates 12, that is, the plate body 20 is in parallel relation with the two first wall plates 11.

In some embodiments, referring to fig. 3, the concave angle is: the angles between the wall plate segments 121 and the corresponding first wall plates 11 are the same in the same pipe body due to the arrangement of the structures. In the first direction, the angles of the inner concave angles of the plurality of tubes 10 decrease in sequence, that is, the inner concave angles of the tubes of each layer decrease, so that the mass of each layer increases while the volume is substantially unchanged, and thus the density increases layer by layer, forming a density gradient. Compared with a negative poisson ratio material with a single structure, the multi-structure negative poisson ratio material with the density gradient has more excellent shock resistance and energy absorption performance, saves more materials, has more designability, and has better mechanical property compared with other interlayer materials when being used as an interlayer of a sandwich structure.

In some embodiments, referring to fig. 1, in a column of tubes 10 along a first direction, central axes of a plurality of tubes 10 spliced in sequence are in the same plane; the impact resistance is better ensured, and it can be understood that in a row of pipe bodies 10, the central axes of a plurality of pipe bodies 10 spliced in sequence are not in the same plane, but are staggered from each other, and certain impact resistance can be realized. In the second direction, the central axes of the respective tubes 10 having the same concave angle are in the same plane in one row of the tubes 10. This arrangement results in better impact resistance.

In some embodiments, referring to fig. 1-2, each tube 10 has a first wall 11, a second wall 12, and a thickness of each plate 20 that are the same. The plate structures with the same thickness ensure that the honeycomb structure has more balanced performance and simpler manufacturing process. In a specific implementation, the thickness of the first wall plate 11, the second wall plate 12 and each plate body 20 is 1mm, and the width and the height of each pipe body 10 are 20mm.

For example, referring to fig. 3, in the core, the width of the plate 20 between two adjacent pipes 10 having the largest concave angle is the same as the width of the first wall 11, and the width direction of the plate 20 and the width direction of the first wall 11 are the same as the second direction. That is, the width of the plate 20 between the tube bodies 10 in one row at the top of the core is the same as the width of the first wall plate 11, and accordingly, the width of the plate 20 between the tube bodies 10 in each row below the top increases due to the decrease of the concave angle, so as to adapt to the constant width of the whole core in the second direction.

The above-mentioned internal concave angle is α in consideration of the influence of the internal concave angle on the whole composite material, wherein 50.ltoreq.α.ltoreq.85 °. This is because when the angle is 90 ° or more than 85 °, the concave angle is too large, and the negative poisson's ratio effect of the core is not obvious; when the angle is smaller than 45 degrees, the concave angle is too small, the support force of the inner wall of the honeycomb is insufficient, and the honeycomb is easy to damage.

In some embodiments, the number of tubes 10 spliced to each other along the first direction is n, i.e. with n layers of tubes, the difference in the decreasing concave angle of each adjacent tube 10 may be the same or different, depending on the number of layers of tubes, and when the decreasing angles should be less than 35 °/n, the decreasing angles may be 1 °,2 °,3 °,4 ° … … or 1.5 °, 2.5 °, 3.5 ° … …, for example, when the decreasing angles are the same.

For easy workability of the core while having good properties, the material of the core is exemplified by aluminum alloy or aramid fiber. The aluminum honeycomb has high strength and rigidity for bearing weight, good heat insulation and economy; the aramid honeycomb has wide density range, extremely high shear strength, high toughness, high damage resistance and easy molding and processing, and compared with the metal honeycomb, the aramid honeycomb has the advantages of being bendable, more convenient to process and more convenient and faster to operate.

In some embodiments, the composite material further comprises a hot melt adhesive film disposed between the core and the corresponding substrate, the hot melt adhesive film being used for bonding between the core and the corresponding substrate, the hot melt adhesive film being made of one of polyethersulfone and thermoplastic polyurethane elastomer rubber. The substrate and the core body can be integrally formed by using the hot melt adhesive film, and the forming method comprises compression molding and RTM (resin transfer molding) forming, so that the process is simple.

In some embodiments, the fibers of the fiber-reinforced resin substrate are one or more of hemp fibers, cotton fibers, bamboo fibers, carbon fibers, glass fibers, and aramid fibers; the fiber in the fiber reinforced resin substrate is one or more of fiber cloth, fiber felt, unidirectional fiber and short fiber; the resin is one or more of polypropylene (PP), polyether ether ketone (PEEK), nylon 6 (PA 6), nylon 66 (PA 66), ABS, polyether imide (PEI), polyphenylene sulfide (PPS) and polylactic acid (PLA). The fiber reinforced resin substrate is manufactured into a laminated board by mixing fibers and resin and combining the fibers and the resin in a pressurizing and heating mode, namely a fiber reinforced resin-based panel, wherein the pressurizing and heating mode comprises compression molding, resin transfer molding, fiber automatic laying molding, long fiber reinforced thermoplastic resin direct molding, 3D printing molding and the like. The mixing mode of the fiber and the resin comprises mixing and layering of the fiber and the resin film, impregnating the fiber by liquid resin and solid phase blending of the fiber resin. The molding and processing modes of the fiber reinforced resin substrate are selected from common fiber materials, so that the process is simpler.

According to another object of the present invention, there is also provided a method for preparing a composite material having a negative poisson's ratio honeycomb with a density gradient, comprising mixing fibers and a resin, and heating under pressure to form a fiber-reinforced resin substrate; manufacturing the core body through 3D printing; in the first direction, the top and the bottom of the core body are respectively paved with a hot melt adhesive film and a base plate in sequence and then integrally formed. It will be appreciated that the aramid fibers described above are co-molded with a resin, typically a phenolic resin, by 3D printing during the process of making the core.

Specifically, the fiber and the resin are mixed and combined by a pressurizing and heating mode to manufacture a laminated board, namely a fiber reinforced resin-based panel;

designing dimension parameters of the density gradient negative poisson ratio honeycomb material according to the mechanical energy level required to be absorbed by the material, wherein the dimension parameters comprise thickness and concave angle, and manufacturing a core body of the negative poisson ratio honeycomb structure with the density gradient through 3D printing;

and sequentially layering the upper substrate, the hot melt adhesive film, the core body, the hot melt adhesive film and the lower substrate from top to bottom, and then integrally forming.

The above composite materials are prepared in a variety of ways, and several specific methods are given below:

example 1

The preparation method of the composite material with the density gradient and the negative poisson ratio honeycomb structure provided by the embodiment comprises the following steps:

s100: mixing carbon fiber cloth and a PP resin film layer, and combining the carbon fiber cloth and the PP resin film layer by compression molding to manufacture a laminated plate; the compression molding temperature is 200 ℃ and the molding pressure is 8MPa, so as to obtain the carbon fiber reinforced PP substrate;

s200: designing the size parameters of the negative poisson ratio honeycomb material, wherein the wall thickness is 1mm, the concave angle is 80 degrees, the concave angle is gradually decreased by 3 degrees to 68 degrees, and the negative poisson ratio aluminum honeycomb structure core body with the density gradient is manufactured through 3D printing;

s300: and paving the upper carbon fiber reinforced PP substrate, the polyether sulfone hot-melt adhesive film, the core body, the polyether sulfone hot-melt adhesive film and the lower carbon fiber reinforced PP substrate, and combining through compression molding to obtain the composite material.

Example 2

S100: mixing a carbon fiber felt and a PEEK resin film layer, and combining the carbon fiber felt and the PEEK resin film layer by compression molding to manufacture a laminated plate; the compression molding temperature is 350 ℃, and the molding pressure is 7MPa, so as to obtain the carbon fiber reinforced PEEK substrate;

s200: designing the size parameters of the negative poisson ratio honeycomb material, wherein the wall thickness is 1.5mm, the concave angle is 80 degrees, the concave angle is gradually decreased by 2 degrees to 72 degrees, and the negative poisson ratio aramid fiber honeycomb structure core body with the density gradient is manufactured through 3D printing;

s300: the composite material is obtained by spreading an upper carbon fiber reinforced PEEK substrate, a thermoplastic polyurethane elastomer rubber hot melt adhesive film, a core body, a thermoplastic polyurethane elastomer rubber hot melt adhesive film and a lower carbon fiber reinforced PEEK substrate and combining through compression molding.

Example 3

S100: mixing jute fiber felt and PLA resin film layer, and making them combine by means of compression molding so as to obtain the laminated plate; the compression molding temperature is 190 ℃ and the molding pressure is 6MPa, so as to obtain the jute fiber reinforced PLA substrate;

s200: designing the size parameters of the negative poisson ratio honeycomb material, wherein the wall thickness is 1mm, the concave angle is 80 degrees, the concave angle is gradually decreased by 2.5 degrees to 70 degrees, and the negative poisson ratio aluminum honeycomb structure core body with the density gradient is manufactured through 3D printing;

s300: and paving the upper carbon fiber reinforced PLA substrate, the polyether sulfone hot-melt adhesive film, the core body, the polyether sulfone hot-melt adhesive film and the lower carbon fiber reinforced PLA substrate, and combining through compression molding to obtain the composite material.

Comparative example 1

The comparative example differs from example 1 only in that the internal recess angles in the core honeycomb structure are all 80 ° and do not decrease.

The composite properties of several examples are set forth below, see Table 1, wherein the impact test method is performed using ASTM D7136/D7136M-12.

Table 1 composite properties

As shown in Table 1, the density gradient-free honeycomb structure of examples 1-3 significantly improved impact resistance and excellent comprehensive mechanical properties as compared with that of comparative example 1, while ensuring good flexural strength, tensile properties and other mechanical properties. Therefore, compared with a core with a constant inner concave angle, the core of the composite material provided by the embodiment of the invention has the advantages that the material is more saved on the premise of the same layer number, the shock resistance is better than that of the core with the same layer number and the constant inner concave angle, and meanwhile, the preparation process is simple, the operability is strong, and the application prospect is wide.

In the description of the present specification, reference to the terms "one embodiment/manner," "some embodiments/manner," "example," "specific example," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment/manner or example is included in at least one embodiment/manner or example of the present application. In this specification, the schematic representations of the above terms are not necessarily for the same embodiment/manner or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments/modes or examples. Furthermore, the various embodiments/modes or examples described in this specification and the features of the various embodiments/modes or examples can be combined and combined by persons skilled in the art without contradiction.

Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include at least one such feature. In the description of the present application, the meaning of "plurality" is at least two, such as two, three, etc., unless explicitly defined otherwise.

It will be appreciated by persons skilled in the art that the above embodiments are provided for clarity of illustration only and are not intended to limit the scope of the invention. Other variations or modifications will be apparent to persons skilled in the art from the foregoing disclosure, and such variations or modifications are intended to be within the scope of the present invention.

Claims

1. The composite material with the density gradient and the negative poisson ratio honeycomb structure is characterized by comprising two substrates and a core body arranged between the two substrates, wherein the substrates are fiber reinforced resin substrates, and the core body is a honeycomb member formed by splicing a plurality of pipe bodies and a plurality of plate bodies;

2. The negative poisson ratio honeycomb composite according to claim 1, wherein the central axes of the plurality of tubes spliced in sequence are in the same plane along the first direction; and/or the number of the groups of groups,

3. The negative poisson's ratio honeycomb composite of claim 1 wherein each of the tubes has a first wall, a second wall and each of the plates having the same thickness.

4. The negative poisson's ratio honeycomb composite according to claim 1, wherein the width of the plate body between two adjacent pipe bodies having the largest concave angle is the same as the width of the first wall plate, and the width direction of the plate body, the width direction of the first wall plate, and the second direction are the same.

5. The negative poisson's ratio honeycomb composite of claim 1 wherein the internal recess angle is α, wherein α is 50 ° or less and 85 ° or less.

6. The negative poisson ratio honeycomb composite according to claim 5, wherein the number of the tubes spliced to each other along the first direction is n, and a difference between the internal concave angles of two adjacent tubes is less than 35 °/n, and a difference between the internal concave angles of each adjacent tube is the same.

7. The negative poisson ratio honeycomb composite according to any one of claims 1 to 6, wherein the core is made of an aluminum alloy or aramid fiber.

8. The negative poisson ratio honeycomb composite according to any one of claims 1 to 6, further comprising a hot melt adhesive film disposed between the core and the corresponding substrate, the hot melt adhesive film being used for bonding between the core and the corresponding substrate, the hot melt adhesive film being made of one of polyethersulfone and thermoplastic polyurethane elastomer rubber.

9. The negative poisson ratio honeycomb composite according to any one of claims 1 to 6, wherein the fibers of the fiber-reinforced resin substrate are one or more of fibrilia, cotton fiber, bamboo fiber, carbon fiber, glass fiber, and aramid fiber;

10. A method for preparing a composite material with a negative poisson's ratio honeycomb structure having a density gradient, the method comprising:

fabricating the core of any one of claims 1-9 by 3D printing;