Mechanical Metastructure with Opposite-Signed Poisson's Ratios under Lateral Expansion-Type Tension and Compression

Abstract

The present invention relates to a mechanical superstructure with a transverse expansion type and a Poisson's ratio of different signs under tension and compression. The four outer diagonal rods of the transverse expansion type combined hexagonal structural unit and the two middle long vertical rods form an outward convex hexagon, and the four inner diagonal rods and the two middle long vertical rods form an inward concave hexagon. The hinges of the two outer diagonal rods at the upper and lower ends are respectively connected to the hinges of the two inner diagonal rods by a short vertical rod; the middle parts of the outer diagonal rods and the inner diagonal rods are each provided with a composite hinge, and the composite hinge includes four short rods, which are hinged and connected end to end in sequence to form a foldable or unfoldable quadrilateral, and two oppositely arranged hinges are respectively connected to the outer diagonal rods / inner diagonal rods. In the initial state, the composite hinge is in a folded state and perpendicular to the outer diagonal rods / inner diagonal rods. At this time, the composite hinge can only withstand pressure but not tension. The present invention can achieve a cross-sectional deformation characteristic that exhibits transverse expansion under in-plane tension or compression, and has a high material utilization rate and a large absolute value of the Poisson's ratio.

Description

Technical Field

[0001] The present invention relates to the technical field of mechanical superstructures, and in particular to a transversely expanding mechanical superstructure with Poisson's ratios of different signs in tension and compression states. Background Art

[0002] Mechanical metamaterials / structures have attracted considerable attention for their exceptional mechanical properties, such as exceptional specific strength, specific stiffness, and superior impact energy absorption. Mechanical metastructures achieve exceptional mechanical properties not possessed by natural materials through their inherent structural design, rather than their chemical composition. The design of mechanical metastructures focuses on the mechanical properties of their structural functional units, typically including elastic modulus, shear modulus, bulk modulus, Poisson's ratio, or thermal expansion coefficient. Depending on the mechanical parameters modulated by the metamaterial's structural functional units, mechanical metastructures can be further categorized as arbitrary Poisson's ratio metamaterials, shear modulus-blanking five-mode anti-expansion metamaterials, negative compressibility metamaterials, negative / zero thermal expansion metamaterials, and tunable stiffness metamaterials. Furthermore, by modulating properties such as the Poisson's ratio, compressibility, and thermal expansion in positive, negative, or negative ways, materials can be shaped and deformed in various ways under various conditions, such as temperature and force fields. Therefore, mechanical metastructures hold significant potential for precision instruments (such as robotics, medical devices, and aerospace equipment), as well as other applications.

[0003] When a negative Poisson's ratio mechanical superstructure is stretched, the structure can expand laterally, but when it is compressed, it contracts laterally. Due to its anomalous Poisson's ratio performance, negative Poisson's ratio mechanical superstructures have attracted much attention in fields such as medical devices, aerospace, and impact protection. However, the Poisson's ratio of negative Poisson's ratio mechanical superstructures is negative in both tension and compression, making it impossible to achieve constant expansion or contraction in the laterally direction. In practical applications, there is a demand for the structure to expand or contract laterally regardless of whether it is in tension or compression. Currently, there are few mechanical superstructures with Poisson's ratios of opposite signs in tension and compression, and low material utilization or small absolute values of Poisson's ratio are common problems of this type of mechanical superstructure.

[0004] Chinese patent CN115163717A discloses a novel composite metamaterial capable of achieving positive-negative Poisson's ratio conversion and its design method. The composite metamaterial comprises a concave hexagonal frame structure, with outwardly protruding corner structures disposed on both sides of the frame structure, and a quadrilateral material disposed between the frame structure and the corner structure. The quadrilateral material is made of a polymer material that is resistant to tension but not compression. This novel composite metamaterial can exhibit both positive and negative Poisson's ratios. Regardless of whether it is subjected to compression or tension in the longitudinal direction, its lateral deformation always contracts inward, enriching the functionality of the metamaterial and expanding its practical application range. However, this novel composite metamaterial is composed of at least two materials, which, compared to a single material, presents problems with complex processing procedures and higher costs. In addition, the first quadrilateral material of the composite metamaterial is a filler material, resulting in a low overall material utilization rate for the composite metamaterial. Furthermore, the Poisson's ratio conversion performance of the composite metamaterial relies on the special properties of a certain polymer material (i.e., resistant to tension but not compression), which is a limitation. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the deficiencies in the above-mentioned existing technologies and provide a mechanical superstructure with a transverse expansion type and a Poisson's ratio of different signs under tension and compression. The superstructure can achieve a cross-sectional deformation characteristic of transverse expansion regardless of in-plane tension or compression, and has a high material utilization rate and a large absolute value of the Poisson's ratio.

[0006] The technical solution adopted by the present invention to solve the above-mentioned technical problems is:

[0007] A mechanical superstructure with a transversely expanding type and a Poisson's ratio of different signs under tension and compression states, comprising a plurality of transversely expanding type combined hexagonal structural units; each of the transversely expanding type combined hexagonal structural units comprises four outer oblique rods, four inner oblique rods, two long vertical rods, two short vertical rods and a plurality of composite hinges, wherein the upper end of the transversely expanding type combined hexagonal structural unit comprises two outer oblique rods and two inner oblique rods, and the lower end comprises two outer oblique rods and two inner oblique rods, the four outer oblique rods and the two middle long vertical rods form a convex hexagon, the four inner oblique rods and the two middle long vertical rods form a concave hexagon, the hinge points of the two outer oblique rods at the upper end are connected to the two The hinges of the inner diagonal rods are connected by a short vertical rod, and the hinges of the two outer diagonal rods at the lower ends are connected to the hinges of the two inner diagonal rods by another short vertical rod, and all the rods are hinged; at least one composite hinge is provided in the middle of all the outer diagonal rods and the inner diagonal rods, and the composite hinge includes four short rods, and the four short rods are hingedly connected end to end in sequence to form a foldable or unfoldable quadrilateral, wherein two oppositely arranged hinges are respectively connected to the outer diagonal rods / inner diagonal rods. In the initial state, the composite hinge is in a folded state and perpendicular to the outer diagonal rods / inner diagonal rods. At this time, the composite hinge can only withstand pressure but not tension.

[0008] In the above solution, when the laterally expandable combined hexagonal structural unit is compressed, the direction of the external load points to the inside of the structure along the length direction of the short vertical rod. At this time, the composite hinges on all the inner diagonal rods unfold to extend the inner diagonal rods, and the structure expands laterally outward.

[0009] In the above scheme, when the laterally expandable combined hexagonal structural unit is subjected to tension, the direction of the external load points to the outside of the structure along the length direction of the short vertical rod. At this time, the composite hinges on all the external diagonal rods unfold to extend the external diagonal rods, and the structure expands laterally outward.

[0010] In the above solution, the four short rods of the composite hinge are of equal length, and in the folded state, the composite hinge is in a straight line.

[0011] In the above solution, a composite hinge is provided at the midpoint of each outer diagonal rod and inner diagonal rod.

[0012] In the above solution, a plurality of the compound hinges having the same number are provided on each outer diagonal rod and each inner diagonal rod, and the plurality of the compound hinges are arranged in sequence along the length direction of the rod.

[0013] In the above solution, the composite hinge further includes four rotatable hinges, and the two short rods are connected via the rotatable hinges.

[0014] In the above solution, the composite hinge is made of plastic material, and the two short rods are connected by a plastic hinge caused by the deformation of the structure itself.

[0015] In the above scheme, the laterally expanding mechanical superstructure with different Poisson's ratios in the tensile and compressive states includes a plurality of laterally expanding combined hexagonal structural units distributed in a matrix, wherein two laterally adjacent combined hexagonal structural units share a long vertical pole; and two vertically adjacent combined hexagonal structural units are connected to each other by short vertical poles.

[0016] The beneficial effects of the present invention are:

[0017] 1. The mechanical superstructure proposed in this invention utilizes transversely expanding composite hexagonal structural units, enabling the structural units to exhibit transversely expanding cross-sectional deformation characteristics regardless of in-plane tension or compression. This means that the structure exhibits the characteristic of Poisson's ratios with opposite signs in tension and compression. Furthermore, the transversely expanding composite hexagonal structural units designed in this invention utilize composite hinges with movable quadrilateral structures, achieving a theoretical material utilization rate of up to 71.4% and a theoretical Poisson's ratio absolute value exceeding 2.

[0018] 2. The present invention obtains a mechanical superstructure with Poisson's ratio of different signs under tension and compression by periodically arranging and combining transversely expanded combined hexagonal structural units.

[0019] 3. Compared to existing technologies, the present invention can be composed of a single material, offering advantages such as simple processing and low cost. The present invention does not employ a filler structure, resulting in higher material utilization. Furthermore, the Poisson's ratio convertibility of the present invention is entirely determined by the structure, independent of material properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0021] Figure 1 It is a schematic diagram of a mechanical superstructure with different Poisson's ratios under transverse expansion tension and compression;

[0022] Figure 2 It is a structural diagram of a laterally expanded combined hexagonal structural unit;

[0023] Figure 3 It is a structural diagram of a composite hinge of laterally expanded combined hexagonal structural units;

[0024] Figure 4 It is a schematic diagram of the lateral deformation of the laterally expanded combined hexagonal structural unit.

[0025] In the figure: 100, transversely expanded combined hexagonal structural unit; 10, outer diagonal rod; 20, inner diagonal rod; 30, compound hinge; 31, short rod; 32, rotatable hinge; 40, long vertical rod; 50, short vertical rod;

[0026] 200. Mechanical superstructures with different Poisson's ratios under transverse expansion tension and compression;

[0027] 300. External load. DETAILED DESCRIPTION

[0028] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described in detail with reference to the accompanying drawings.

[0029] like Figure 1 As shown, a transversely expanding mechanical superstructure 200 with different Poisson's ratios under tension and compression provided by an embodiment of the present invention includes a plurality of transversely expanding combined hexagonal structural units 100 distributed in a matrix.

[0030] like Figure 2As shown, each laterally expandable composite hexagonal structural unit 100 includes four outer diagonal rods 10, four inner diagonal rods 20, two long vertical rods 40, two short vertical rods 50, and a plurality of composite hinges 30. Specifically, the upper end of the laterally expandable composite hexagonal structural unit 100 includes two outer diagonal rods 10 and two inner diagonal rods 20, and the lower end includes two outer diagonal rods 10 and two inner diagonal rods 20. The four outer diagonal rods 10 and the two middle long vertical rods 40 form an outwardly convex hexagon, and the four inner diagonal rods 20 and the two middle long vertical rods 40 form an inwardly concave hexagon. A short vertical rod 50 connects the hinge points of the two outer diagonal rods 10 and the two inner diagonal rods 20 at the upper end of the structural unit, and another short vertical rod 50 connects the hinge points of the two outer diagonal rods 10 and the two inner diagonal rods 20 at the lower end of the structural unit. All rods are hinged. At least one composite hinge 30 is provided in the middle of all outer diagonal bars 10 and inner diagonal bars 20. Figure 3 As shown, the composite hinge 30 comprises four short rods 31, which are hingedly connected end to end to form a foldable or unfoldable quadrilateral. Two of the four short rods 31 are connected to the outer diagonal rods 10 and inner diagonal rods 20, respectively. In the initial state, the composite hinge 30 of the laterally expandable combined hexagonal structural unit 100 is folded and perpendicular to the outer diagonal rods 10 and inner diagonal rods 20. At this time, the composite hinge 30 can only withstand compression but not tension.

[0031] like Figure 4 As shown, when the laterally expandable composite hexagonal structural unit 100 is compressed, the external load 300 is directed inward along the length of the short vertical rods 50, compressing the outer diagonal rods 10 and stretching the inner diagonal rods 20. Since the composite hinges 30 can only withstand compression but not tension, the inner diagonal rods 20 are free to extend. The structural deformation is similar to that of an outwardly convex hexagon, i.e., it expands laterally outward.

[0032] When the laterally expandable composite hexagonal structural unit 100 is subjected to tension, the external load 300 is directed outward along the length of the short vertical rods 50, causing the outer diagonal rods 10 to be stretched and the inner diagonal rods 20 to be compressed. Since the composite hinges 30 can only withstand compression, not tension, the outer diagonal rods 10 are free to extend. The structural deformation is similar to that of a concave hexagon, namely, laterally expanding outward.

[0033] Therefore, the mechanical superstructure proposed by the present invention can achieve a cross-sectional deformation characteristic of lateral expansion, whether under in-plane tension or compression, that is, the structure has the characteristic of Poisson's ratio with opposite signs in tension and compression. In addition, the transversely expandable combined hexagonal structural unit 100 designed by the present invention adopts a composite hinge 30 with an active quadrilateral structure, which enables the structural unit to have the property of Poisson's ratio with opposite signs in tension and compression. At the same time, the theoretical material utilization rate is as high as 71.4%, and the absolute value of the theoretical Poisson's ratio is as high as 2 or more. It should be explained that the theoretical material utilization rate refers to the ratio of the structural mass involved in resisting deformation to the total mass. For the present invention, when subjected to tension, the outer diagonal rod 10 does not participate in resisting deformation. Assuming that the length and mass ratio of the outer diagonal rod 10, the inner diagonal rod 20, the long vertical rod 40, and the short vertical rod 50 are all 1:1:2:1, its material utilization rate is (14-4) / 14=71.4%. The theoretical Poisson's ratio of a material refers to the ratio between the load lateral deformation and the load direction deformation. For the present invention, assuming that the angle between the inner oblique rod 20 and the short vertical rod 50 is θ, the theoretical Poisson's ratio is: In the formula, d represents the derivative sign, and l is the length of the outer diagonal rod 10. Clearly, when θ is small, 1 / tanθ is greater than 2. In fact, when the inner diagonal rod 20 and the outer diagonal rod 10 are equal in length, the smaller θ is, the greater the ratio of the length of the short vertical rod 50 to the length of the outer diagonal rod 10 is, and the greater the material utilization rate. In other words, the smaller θ is, the greater the material utilization rate and the theoretical Poisson's ratio are.

[0034] As a further optimization, the four short rods 31 of the composite hinge 30 are of equal length, and in the folded state, the composite hinge 30 is in a straight line.

[0035] Further optimization, a composite hinge 30 is set at the midpoint of each outer diagonal rod 10 and inner diagonal rod 20. It is also possible to set the same number of composite hinges 30 on each outer diagonal rod 10 and inner diagonal rod 20 as needed, and the multiple composite hinges 30 are arranged in sequence along the length direction of the rod.

[0036] In a further optimization, the composite hinge 30 further includes four rotatable hinges 32, and the two short rods 31 are connected via the rotatable hinges 32. When the composite hinge 30 is made of plastic material, the composite hinge 30 may not include the rotatable hinges 32, and the two short rods 31 are connected via a plastic hinge caused by the deformation of the structure itself.

[0037] Further optimization, two adjacent combined hexagonal structural units in the horizontal direction share a long vertical rod 40; two adjacent combined hexagonal structural units in the vertical direction are connected to each other through a short vertical rod 50. Figure 1 The cross section of the two-dimensional mechanical superstructure shown is stretched in a direction perpendicular to the paper surface to form a honeycomb-like mechanical superstructure.

[0038] In the description of the present invention, it should be understood that the terms "long vertical pole", "short vertical pole", "inner oblique pole", "outer oblique pole", "short pole", etc. are used to indicate and distinguish structural components, which is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the referred components must have the characteristics included in the terms. Therefore, they cannot be understood as limitations on the present invention.

[0039] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are protected by the present invention.

Claims

1. A transversely expanding mechanical superstructure with Poisson's ratios of opposite signs under tension and compression, characterized in that: It includes several laterally expanded combined hexagonal structural units; Each of the laterally expanded combined hexagonal structural units comprises four outer oblique rods, four inner oblique rods, two long vertical rods, two short vertical rods and a plurality of composite hinges, wherein the upper end of the laterally expanded combined hexagonal structural unit comprises two outer oblique rods and two inner oblique rods, and the lower end comprises two outer oblique rods and two inner oblique rods, the four outer oblique rods and the two middle long vertical rods form an outward convex hexagon, the four inner oblique rods and the two middle long vertical rods form an inward concave hexagon, the hinge points of the two outer oblique rods at the upper end are connected to the hinge points of the two inner oblique rods by a short vertical rod, and the two at the lower end are connected to the two inner vertical rods by a short vertical rod. The hinge point of the outer diagonal rod is connected to the hinge points of the two inner diagonal rods through another short vertical rod, and each rod is hinged; at least one composite hinge is provided in the middle of all outer diagonal rods and inner diagonal rods, and the composite hinge includes four short rods, and the four short rods are hingedly connected end to end to form a foldable or unfoldable quadrilateral, wherein two oppositely arranged hinge points are respectively connected to the outer diagonal rod / inner diagonal rod. In the initial state, the composite hinge is in a folded state and perpendicular to the outer diagonal rod / inner diagonal rod. At this time, the composite hinge can only withstand pressure but not tension.

2. The transverse expansion type mechanical superstructure with Poisson's ratios of opposite signs under tension and compression according to claim 1, characterized in that: When the laterally expandable combined hexagonal structural unit is compressed, the external load is directed toward the interior of the structure along the length of the short vertical rod. At this time, the composite hinges on all the inner diagonal rods are unfolded to extend the inner diagonal rods, and the structure expands laterally outward.

3. The transverse expansion type mechanical superstructure with Poisson's ratios of opposite signs under tension and compression according to claim 2, characterized in that: When the laterally expandable combined hexagonal structural unit is subjected to tension, the external load direction points to the outside of the structure along the length direction of the short vertical rod. At this time, the composite hinges on all the external diagonal rods are unfolded to extend the external diagonal rods, and the structure expands laterally outward.

4. The transverse expansion type mechanical superstructure with Poisson's ratios of opposite signs under tension and compression according to claim 1, characterized in that: The four short rods of the composite hinge are of equal length, and in the folded state, the composite hinge is in a straight line.

5. The transverse expansion type mechanical superstructure with Poisson's ratios of opposite signs under tension and compression according to claim 1, characterized in that: A composite hinge is provided at the midpoint of each outer diagonal rod and each inner diagonal rod.

6. The transverse expansion type mechanical superstructure with Poisson's ratios of opposite signs under tension and compression according to claim 1, characterized in that: Each outer diagonal rod and inner diagonal rod is provided with a plurality of the compound hinges of the same number, and the plurality of the compound hinges are arranged in sequence along the length direction of the rod.

7. The transverse expansion type mechanical superstructure with Poisson's ratios of opposite signs under tension and compression according to claim 1, characterized in that: The composite hinge further comprises four rotatable hinges, and the two short rods are connected via the rotatable hinges.

8. The transversely expandable mechanical superstructure with Poisson's ratios of opposite signs under tension and compression according to claim 1, characterized in that: The composite hinge is made of plastic material, and the two short rods are connected via a plastic hinge caused by self-deformation of the structure.

9. The transversely expandable mechanical superstructure with Poisson's ratios of opposite signs under tension and compression according to claim 1, characterized in that: The laterally expanding mechanical superstructure with different Poisson's ratios in the tensile and compressive states includes a plurality of laterally expanding combined hexagonal structural units distributed in a matrix, wherein two laterally adjacent combined hexagonal structural units share a long vertical rod; and two vertically adjacent combined hexagonal structural units are connected to each other via short vertical rods.

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