Novel rotating star-shaped negative Poisson's ratio structure

Abstract

The invention discloses a novel rotating star-shaped negative Poisson's ratio structure. A unit cell structure of the novel rotating star-shaped negative Poisson's ratio structure is composed of a rotating shaft symmetric star-shaped structure and four right-angle ligaments distributed on the star-shaped structure and extending outwards. The symmetrical star-shaped structure of the rotating shaft is composed of side lengths L01 and L02, an included angle theta 0 and a width t0. The four outwards-extending right-angle ligaments extend outwards from the star-shaped structure and penetrate through the intersection point of the two sides of the obtuse-angle (or acute-angle) concave side of the star-shaped structure, and the lengths of the four outwards-extending right-angle ligaments are L11 (or L21) respectively; the second center line is perpendicular to the first center line, and the length of the second center line is L12 (or L22); the width of each of the four extended right-angled ligaments is t; and the length of the horizontal (or vertical) line segment connected with the tail end of the right-angled ligament is L13 (or L23). The novel rotating star-shaped negative Poisson's ratio unit cells are combined into an n * n complete structure through transverse and longitudinal arrays. The novel rotating star-shaped negative Poisson's ratio structure provided by the invention has obvious negative Poisson's ratio effect and energy absorption capability.

Description

Technical Field

[0001] The invention relates to the technical field of metamaterials / superstructures, and in particular to a novel rotating star-shaped negative Poisson's ratio structure. Background Art

[0002] In the field of physics in the 21st century, the concept of "metamaterial" was proposed. It is defined as a type of artificial composite structure or material with extraordinary physical properties that natural materials do not have. Metamaterials cover acoustics, optics, thermals, mechanics and electromagnetism. Negative Poisson's ratio material / structure is a kind of mechanical metamaterial / structure, which is different from the common positive Poisson's ratio material / structure in nature.

[0003] The Poisson's ratio of materials in nature is mostly positive, which is manifested as the phenomenon that the structure shrinks in the vertical (or horizontal) direction under the action of tensile load in the horizontal (or vertical) direction. However, negative Poisson's ratio metamaterials / superstructures show the opposite characteristics, that is, axial tension-lateral expansion, axial compression-lateral contraction. Negative Poisson's ratio metamaterials / superstructures have great advantages in shear resistance, fracture resistance, energy absorption performance, etc., and show excellent physical properties such as lightweight, high damping, sound absorption and energy absorption, vibration reduction and heat insulation.

[0004] Negative Poisson's ratio metamaterials / superstructures have broad application prospects in aerospace, biomedicine, mechanical electronics, and national defense engineering. In the aerospace field, in order to improve flight stability, efficiency and safety, the research on deformable airfoils has been developed. Negative Poisson's ratio structures can promote airfoil deformation, reduce aerodynamic drag and control vibration. In the biomedical field, negative Poisson's ratio structures can be used to manufacture cardiovascular stents and lumbar disc implants, so that the structure provides better support and stability when subjected to stress. In the field of smart sensors, the unique deformation behavior of negative Poisson's ratio structures can improve the sensitivity and accuracy of flexible strain sensors. In addition, negative Poisson's ratio structures also perform well in the fields of automotive lightweight and anti-collision protection, and can effectively absorb impact energy and provide better protection performance.

[0005] There are many types of negative Poisson's ratio structures, each of which has its own unique advantages and disadvantages and is suitable for different application scenarios. At present, common negative Poisson's ratio structures include: concave hexagonal structure, double arrow structure, star structure, chiral structure, rotating rigid body structure, etc.

[0006] Star-shaped structures often have complex geometries and symmetries and are suitable for applications that require high energy absorption and special mechanical properties. Their negative Poisson's ratio effect causes the material to expand laterally when under tension, providing additional structural stability.

[0007] Rotational rigid structures consist of rigid geometries connected by hinges at their corners. When stretched, the geometries rotate around the hinges, producing expansion in the axial and lateral directions, i.e., a negative Poisson's ratio response. The diversity of rotational rigid structures can be attributed to the differences in geometries.

[0008] Traditional single star-shaped structures and rotating rigid structures have a short stress platform area, the structure enters the densification stage prematurely, and has poor deformation stability, which makes the structure perform poorly in terms of compressive strength and energy absorption efficiency.

[0009] At present, the rapid development of 3D printing and additive manufacturing technology can produce various structures with complex topological configurations. This has further promoted researchers to conduct in-depth research on the basic deformation mechanism of various negative Poisson's ratio materials / structures. Summary of the invention

[0010] In view of the above problems, the purpose of the present invention is to propose a novel rotating star-shaped negative Poisson's ratio structure, which is composed of a rotating axis symmetrical star-shaped structure with four right-angled ligaments extending from four inner concave parts to form a novel rotating star-shaped unit cell structure. On this basis, the unit cells are arrayed in the horizontal and vertical directions to form an n×n structure. The novel rotating star-shaped negative Poisson's ratio structure has a good negative Poisson's ratio effect and the ability to resist external impact. The change of the geometric parameters of the unit cell structure has an important influence on the mechanical properties of the overall structure.

[0011] To achieve the purpose of the present invention, the present invention is implemented by the following technical solutions:

[0012] A further improvement is that the novel rotating star-shaped negative Poisson's ratio structure is made of metal, shape memory alloy (nickel-titanium alloy, copper-zinc-aluminum alloy, iron-titanium alloy) or thermoplastic polyurethane (TPU) superelastic material, which can be prepared by 3D printing technology.

[0013] A further improvement is that the novel rotating star-shaped negative Poisson's ratio unit cell is composed of a rotating axis symmetrical star-shaped structure and four right-angled ligaments extending outward from the concave side of the star-shaped structure. 01 and L 02 , angle θ0 and width t0. The four outward-extending right-angle ligaments all extend outward from the center of the star-shaped structure, passing through the intersection of the two sides of the concave side of the obtuse (or acute) angle of the star-shaped structure, and the lengths are L 11 (or L 21 ); the second center line is perpendicular to the first center line and has a length of L 12 (or L 22 ); the width of the four outward-extending right-angled ligaments is t; the length of the horizontal (or vertical) line segment connecting the ends of the right-angled ligaments is L 13 (or L 23), the angle formed by it and the width t of the right-angle ligament can be expressed as arccos(t / L 13 )(or arccos(t / L 23 ))express.

[0014] A further improvement is that the novel rotating star-shaped negative Poisson's ratio unit cell is combined into a complete n×n structure by lateral and longitudinal arrays. When the array is lateral, the vertical line segment L of the right-angle ligament extending outward at the acute angle of the two adjacent star-shaped unit cells on the left and right is 23 The sizes are equal and they are kept in the same straight line. When arranged in the longitudinal direction, the horizontal line segment L of the right-angle ligament extending outward from the obtuse angle of the two adjacent star-shaped cells above and below 13 Equal in size and in the same straight line.

[0015] Further improvements are as follows: In the ABAQUS software pre-processing module, firstly, material parameters are set for the structure, the finite element mesh of the structure is divided, the analysis steps are set, the boundary conditions and load conditions are set, and the contact properties are set, so as to perform out-of-plane quasi-static compression simulation on the structure.

[0016] Further improvements are as follows: using finite element ABAQUS simulation software to simulate the out-of-plane quasi-static compression of the new rotating star-shaped negative Poisson's ratio structure, and obtaining the deformation process cloud diagram, stress-strain curve, Poisson's ratio-strain curve and specific energy absorption-strain curve of the new rotating star-shaped negative Poisson's ratio structure under the action of in-plane quasi-static compression load.

[0017] Further improvements are as follows: the mechanical properties and energy absorption efficiency of the new rotating star-shaped negative Poisson's ratio structure under quasi-static compression loads can be determined by adjusting the slenderness ratio, angle of the central star-shaped cell wall structure and the slenderness ratio of the surrounding right-angle ligaments.

[0018] The beneficial effects of the present invention are as follows: the novel rotating star-shaped negative Poisson's ratio structure of the present invention has light weight, high specific strength, high resistance to external impact and good negative Poisson's ratio performance, and the change of the geometric parameters of the structure has an important influence on the overall mechanical properties of the structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is the geometric cell configuration of the novel rotating star-shaped negative Poisson's ratio structure in Example 1 of the present invention.

[0020] Figure 2 This is a novel rotating star-shaped negative Poisson's ratio 6×6 structure according to Example 1 of the present invention.

[0021] Figure 3 This is a deformation cloud diagram of the novel rotating star-shaped negative Poisson's ratio structure of Example 2 of the present invention under the action of a quasi-static compression load.

[0022] Figure 4This is the stress-strain curve of the novel rotating star-shaped negative Poisson's ratio structure under quasi-static compression load in Example 2 of the present invention.

[0023] Figure 5 This is the Poisson's ratio-strain curve of the novel rotating star-shaped negative Poisson's ratio structure under quasi-static compression load in Example 2 of the present invention.

[0024] Figure 6 The specific energy absorption-strain curve of the novel rotating star-shaped negative Poisson's ratio structure under quasi-static compression load in Example 2 of the present invention DETAILED DESCRIPTION

[0025] In order to deepen the understanding of the present invention, the present invention will be further described in detail below in conjunction with examples. The examples are only used to explain the present invention and do not constitute a limitation on the protection scope of the present invention.

[0026] Example 1

[0027] according to Figure 1 As shown, this embodiment provides a novel rotating star-shaped negative Poisson's ratio structure, whose unit cell structure is composed of a rotating axis symmetrical star-shaped structure and four right-angle ligaments extending outward from the concave side of the star-shaped structure. 01 and L 02 , angle θ0 and width t0. The four outward extending right-angle ligaments are as follows: (1) The first center line of the right-angle ligament on the obtuse concave side of the star-shaped structure extends outward from the center of the star-shaped structure, passes through the intersection of the two sides of the obtuse concave side of the star-shaped structure, and has a length of L 11 ; The second center line extends in a direction perpendicular to the first center line, with a length of L 12 ; The width of the right-angle ligament is t; The length of the horizontal line segment connecting the ends of the right-angle ligament is L 13 The angle formed by the right angle ligament width t can be expressed as arccos(t / L 13 ) (2) The first center line of the right-angle ligament on the acute concave side of the star-shaped structure extends from the center of the star-shaped structure, passes through the intersection of the two sides of the acute concave side of the star-shaped structure, and has a length of L 21 ; The second center line extends in a direction perpendicular to the first center line, with a length of L 22 ; The width of the right-angle ligament is also t; The length of the vertical line segment connecting the ends of the right-angle ligament is L 23 The angle formed by the right angle ligament width t can be expressed as arccos(t / L 23 )express.

[0028] according to Figure 2As shown, this embodiment provides a novel rotating star-shaped negative Poisson's ratio structure, wherein the novel rotating star-shaped negative Poisson's ratio unit cell is combined into an n×n complete structure by lateral and longitudinal arrays. When the array is lateral, the vertical line segment L of the right-angle ligament extending outward at the acute angle of the two adjacent star-shaped unit cells on the left and right 23 The sizes are equal and they are kept in the same straight line. When arranged in the longitudinal direction, the horizontal line segment L of the right-angle ligament extending outward from the obtuse angle of the two adjacent star-shaped cells above and below 13 Equal in size and in the same straight line.

[0029] The novel rotating star-shaped negative Poisson's ratio structure is made of a material of metal, shape memory alloy (nickel-titanium alloy, copper-zinc-aluminum alloy, iron-titanium alloy) or thermoplastic polyurethane (TPU) superelastic material.

[0030] Example 2

[0031] In the pre-processing module of ABAQUS finite element software, firstly, the material parameters of the structure are set, the structural finite element mesh is divided, the analysis step is set, the boundary conditions and load conditions are set, and the contact properties are set, so as to perform out-of-plane quasi-static compression simulation calculation on the structure.

[0032] The material parameters were set in the ABAQUS finite element simulation software, and titanium alloy TC4 was selected as the research object. The material elastic modulus was E = 110 GPa, the material Poisson's ratio was μ = 0.3, and the yield stress was σ = 820 MPa.

[0033] according to Figure 3 As shown, this embodiment provides a deformation cloud diagram of a new type of rotating star-shaped negative Poisson's ratio structure under a quasi-static compression load. It can be seen from the figure that when ε=3.5%, the upper and lower edge ligaments of the structure shrink and contact with the middle star-shaped structure, and the structure exhibits negative Poisson's ratio performance. As the strain increases, both the external ligaments and the middle star-shaped structure shrink, and when the strain ε=52%, plasticity and stress plateaus are exhibited. When the strain reaches ε=73%, the structure further shrinks and contacts, showing a more obvious densification.

[0034] according to Figure 4 As shown, this embodiment provides a stress-strain curve of a novel rotating star-shaped negative Poisson's ratio structure under a quasi-static compression load. As can be seen from the figure, the stress-strain response of the novel rotating star-shaped negative Poisson's ratio structure can be divided into three stages. First, at a small strain, the stress rises linearly with the strain. This region is called the linear elastic region. During this stage, the structure does not undergo plastic deformation until the peak stress is reached. Then it enters a longer platform region. When the strain is about 0.65, the stress rises rapidly and reaches the densification region. The novel rotating star-shaped negative Poisson's ratio structure has a longer stress plateau period, which can effectively increase the energy absorption of the structure.

[0035] according to Figure 5 As shown in FIG. 1 , this embodiment provides a Poisson's ratio-strain curve of a novel rotating star-shaped negative Poisson's ratio structure under a quasi-static compression load. As can be seen from the figure, the novel rotating star-shaped negative Poisson's ratio structure exhibits a good negative Poisson's ratio effect in the linear elastic stage, and from the plateau stage, the structural Poisson's ratio increases with the increase of strain.

[0036] according to Figure 6 As shown, this embodiment provides a specific energy absorption-strain curve of a novel rotating star-shaped negative Poisson's ratio structure under quasi-static compression load. As can be seen from the figure, the specific energy absorption of the novel rotating star-shaped negative Poisson's ratio structure increases with the increase of strain, and the structure exhibits a good energy absorption effect.

[0037] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A novel rotating star-shaped negative Poisson's ratio structure, characterized in that: The structure is formed by connecting a plurality of periodic unit cells in an array along the horizontal and vertical directions. Each of the periodic unit cells comprises an axisymmetric star-shaped structure and four right-angled ligaments extending outward from the concave side of the star-shaped structure.

2. A novel rotating star-shaped negative Poisson's ratio structure according to claim 1, characterized in that: The rotation axis symmetric star structure consists of a side length L 01 and L 02 , angle θ0 and width t0. The four outward extending right-angle ligaments are as follows: (1) The first center line of the right-angle ligament on the obtuse concave side of the star-shaped structure extends outward from the center of the star-shaped structure, passes through the intersection of the two sides of the obtuse concave side of the star-shaped structure, and has a length of L 11 ; The second center line extends in a direction perpendicular to the first center line, with a length of L 12 ; The width of the right-angle ligament is t; The length of the horizontal line segment connecting the ends of the right-angle ligament is L 13 The angle formed by the right angle ligament width t can be expressed as arccos(t / L 13 ) (2) The first center line of the right-angle ligament on the acute concave side of the star-shaped structure extends from the center of the star-shaped structure, passes through the intersection of the two sides of the acute concave side of the star-shaped structure, and has a length of L 21 ; The second center line extends in a direction perpendicular to the first center line, with a length of L 22 ; The width of the right-angle ligament is also t; The length of the vertical line segment connecting the ends of the right-angle ligament is L 23 The angle formed by the right angle ligament width t can be expressed as arccos(t / L 23 )express.

3. The novel rotating star-shaped negative Poisson's ratio structure according to claim 1 is characterized in that: The new rotating star-shaped negative Poisson's ratio unit cell is combined into a complete n×n structure through transverse and longitudinal arrays. When arrayed transversely, the vertical line segment L of the right-angle ligament extending outward from the acute angle of the two adjacent star-shaped unit cells on the left and right 23 The sizes are equal and they are kept in the same straight line. When arranged in the longitudinal direction, the horizontal line segment L of the right-angle ligament extending outward from the obtuse angle of the two adjacent star-shaped cells above and below 13 The out-of-plane thickness of the new rotating star-shaped negative Poisson's ratio structure is H z , which is not reflected in the floor plan.

4. The novel rotating star-shaped negative Poisson's ratio structure according to claim 1 is characterized in that: Prepared using 3D printing technology.

5. The novel rotating star-shaped negative Poisson's ratio structure according to claim 1 is characterized in that: The rotating star-shaped negative Poisson's ratio structure is made of a material such as metal, shape memory alloy (nickel-titanium alloy, copper-zinc-aluminum alloy, iron-titanium alloy) or thermoplastic polyurethane (TPU) superelastic material.

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