Star-shaped chiral impact-resistant energy-absorbing metamaterial and adjustment method of metamaterial structure

Abstract

The invention provides a star-shaped chiral impact-resistant energy-absorbing metamaterial and an adjusting method of a metamaterial structure. The metamaterial comprises a multi-layer structure formed by permutation and combination of a plurality of star-shaped chiral structure unit cells. Wherein each star-shaped chiral structure unit cell has rotation similarity and comprises a chiral structure star-shaped structure located at the center position and four corners of the star-shaped structure arranged on the periphery of the chiral structure; the metamaterial forms a transition structure and has second-order plateau stress when subjected to rapid impact force. By utilizing the metamaterial, the problems that an existing metamaterial cannot realize load reduction and energy absorption at the same time, and the posture of the structure is unstable under large deformation can be solved.

Description

Technical Field

[0001] This invention relates to the field of metamaterials technology, and more specifically, to a star-shaped chiral impact-resistant energy-absorbing metamaterial and a method for adjusting the metamaterial structure. Background Technology

[0002] The front ends of vehicles such as automobiles and airplanes are frequently subjected to impacts, posing a significant challenge to the stable operation of internal mechanical and electronic components. Faced with the strong impact loads and substantial energy absorption requirements of high-speed impacts, designing lightweight and highly efficient energy-absorbing and load-reducing buffer structures has become an urgent problem. Traditional foam buffer materials possess a single stable plateau stress, exhibiting good energy absorption consistency under the same strain. However, due to the lack of tensile expansion characteristics in foam honeycomb materials, compared to negative Poisson's ratio superstructures, their stress in the final compaction stage of compression is lower, resulting in relatively poor energy absorption efficiency. Furthermore, some existing negative Poisson's ratio structures exhibit poor deformation stability under impact, making the load-reducing structure prone to displacement, thus preventing most of the structure from participating in energy absorption. Eccentric loads can also easily cause structural attitude deviations. Negative stiffness superstructures primarily rely on deformation transitions between two stable states to absorb energy and reduce load, resulting in a shorter energy absorption stroke and lower energy absorption. Related patents are as follows:

[0003] (1) Patent “A Multi-Node Negative Poisson Ratio Concave Honeycomb Structure and Its Design Method” 202411498695.0 discloses a multi-node negative Poisson ratio concave honeycomb structure and its design method. The negative Poisson ratio configuration is obtained by periodically arranging concave polygons, but it only has first-order plateau stress and cannot meet the requirements of reducing peak load and improving overall energy absorption.

[0004] (2) Patent No. 202311833257.0, entitled “A Tile-like Negative Poisson’s Ratio Honeycomb Metamaterial”, proposes a tile-like negative Poisson’s ratio honeycomb metamaterial. This material is composed of several tile-like negative Poisson’s ratio honeycomb unit cells arranged in an alternating manner. Under impact, the main structure is unstable in its left and right deformation and is prone to displacement, which greatly reduces the part of the structure that participates in energy absorption and fails to achieve the best energy absorption effect of the structure.

[0005] (3) Patent “A design method for a multi-stable metamaterial with ideal energy absorption characteristics” 202411532938.8 proposes a snap-fit ​​energy-absorbing metamaterial. By connecting a negative stiffness bistable curved beam with a bottom snap-fit ​​locking structure, energy absorption is achieved by switching between two stable states of the hyperbolic beam and friction between the snaps when subjected to impact. However, the overall structure has too little energy absorption stroke and low energy absorption efficiency.

[0006] In summary, existing energy-absorbing metamaterial structures cannot simultaneously achieve the functions of load reduction, energy absorption, and deformation stability. Summary of the Invention

[0007] In view of the above problems, the purpose of this invention is to provide a star-shaped chiral impact-resistant energy-absorbing metamaterial and a method for adjusting the metamaterial structure, so as to solve the problem that existing metamaterials cannot simultaneously achieve load reduction and energy absorption, and that the structure is unstable under large deformation.

[0008] On one hand, this invention provides a star-shaped chiral impact-resistant energy-absorbing metamaterial, comprising: a multilayer structure formed by the arrangement and combination of several star-shaped chiral structural unit cells; wherein,

[0009] Each star-shaped chiral unit cell has rotational similarity, including a chiral structure located at the center and four corners of a star-shaped structure disposed around the chiral structure;

[0010] The metamaterial forms a transition structure and has a second-order plateau stress when subjected to high-velocity impact.

[0011] One option is that the star-shaped chiral structure unit cells are arranged in a staggered or gradient manner.

[0012] One option is that the chiral structure includes a ring at the center and spiral ligaments uniformly arranged around the ring; wherein,

[0013] The ring includes a circular ring, an elliptical ring, or a polygonal ring.

[0014] One option is that the star-shaped structure has at least three angles, and the inclined cell walls of the star-shaped structure are arc-shaped or wavy.

[0015] One option is that the matrix material of the metamaterial is a metallic material, a composite material, or a shape memory alloy, wherein...

[0016] The metallic materials include aluminum alloys and titanium alloys, and the composite materials include carbon fiber reinforced polymers and highly elastic recoverable rubber.

[0017] On the other hand, the present invention also provides a method for structural adjustment of a metamaterial, wherein the metamaterial is the aforementioned star-shaped chiral impact-resistant energy-absorbing metamaterial, comprising:

[0018] The metamaterial forms a transitional structure and has two-stage plateau stress when subjected to low-speed impact, namely the first-stage plateau stress and the second-stage plateau stress.

[0019] The structural parameters of the metamaterial are adjusted according to the stress of the first-order platform.

[0020] The structural parameters of the metamaterial are adjusted according to the second-order plateau stress.

[0021] One optional approach is that adjusting the structural parameters of the metamaterial based on the first-order plateau stress includes:

[0022] When subjected to the first-order plateau stress, the star-shaped chiral unit cell is compressed in the y-direction and forms a transition state;

[0023] Based on the transition state, the geometric relationship of the star-shaped chiral structure unit cell is obtained;

[0024] Based on the law of conservation of energy and the aforementioned geometric relationships, the first-order platform stress is obtained;

[0025] Based on the stress of the first-order platform, the length of the tilted cell wall, the length of the surrounding cell wall, and the angle are adjusted.

[0026] One optional approach is that the geometric relationship formula for the star-shaped chiral unit cell is:

[0027] l sin(α) + OCsin(β) = h / 2

[0028] l cos(α) + OCcos(β) = h / 2

[0029] R 2 +d 2 =OC 2

[0030] Where l is the length of the inclined cell wall; R is the radius of the ring; d is the length of the ligament; h is the length of the surrounding cell walls; α is the angle between adjacent inclined cell walls; and β is the angle between the line connecting the intersection of the adjacent inclined cell walls in the transitional form and the center of the ring and the vertical direction.

[0031] Initially, the horizontal length of the star-shaped chiral unit cell is L0, the vertical height is H0, L0 = h - 2l cos(θ) + 2l sin(θ), and H0 is equal to L0;

[0032] According to the law of conservation of energy, the energy E1 absorbed by the star-shaped chiral unit cell during the first stage of deformation is:

[0033] E1=σ p1 L0b(H0-H1)

[0034] =8M1(θ-α)+8M2(π / 2-α-θ)+8M3(β-π / 4)

[0035] The first-order plateau stress of the star-shaped chiral unit cell is:

[0036]

[0037] Where b is the thickness in the outward direction of the structure, σ p1 Let H1 be the first-order plateau stress, and H1 be the vertical height of the unit cell in the transition state. Since the thickness of the cell wall is always t, then:

[0038] M1=M2=M3=M p1

[0039] M p1 =σ ys bt 2 / 4

[0040] Among them, M p1 Let σ be the total plastic moment of a cell wall with a wall thickness of t. ys This refers to the yield stress of the material itself.

[0041] One optional approach is that adjusting the structural parameters of the metamaterial based on the second-order plateau stress includes:

[0042] When subjected to the second-order plateau stress, the star-shaped chiral unit cell continues to compress in the y-direction to form a dense state, and the total height of the star-shaped chiral unit cell in the dense state is obtained.

[0043] Based on the law of conservation of energy and the total height, the second-order platform stress is obtained;

[0044] Based on the second-order plateau stress, the length of the cell walls around the metamaterial, the radius of the annulus, the ligament length, and the unit wall thickness are adjusted.

[0045] One possible approach is that, according to the law of conservation of energy, the energy absorbed by the star-shaped chiral unit cell during the second stage of deformation is:

[0046]

[0047] Second stage platform stress values:

[0048]

[0049] in, M p2 =σ ys bt 2 ,

[0050] E2 represents the total energy absorbed by a single cell in the second stage, L1 represents the horizontal length of the upper and lower cell walls in the transitional state, H2 represents the total height of a single cell in the compact state, and M represents the total energy absorbed by a single cell in the compact state. p2 The total plastic moment of a cell wall with a wall thickness of 2t.

[0051] As can be seen from the above technical solution, the star-shaped chiral impact-resistant energy-absorbing metamaterial and the method for adjusting the metamaterial structure provided by this invention combine a star-shaped structure with a chiral structure to form a multilayer metamaterial with star-shaped chiral structural cells. These star-shaped chiral structural cells form a stable transition structure during deformation and maintain central stability during subsequent large deformation. By deriving the theoretical plateau stress model formula, the travel of the plateau stress and the second-order plateau stress can be adjusted for different load reduction requirements. The metamaterial of this invention can solve the problem that existing metamaterials cannot simultaneously achieve load reduction, energy absorption, and structural stability under large deformation.

[0052] To achieve the foregoing and related objectives, one or more aspects of the invention include the features that will be described in detail below. The following description and accompanying drawings illustrate certain exemplary aspects of the invention. However, these aspects indicate only a few of the various ways in which the principles of the invention can be used. Furthermore, the invention is intended to encompass all such aspects and their equivalents. Attached Figure Description

[0053] Other objects and results of the invention will become more apparent and readily understood with reference to the following description taken in conjunction with the accompanying drawings. In the drawings:

[0054] Figure 1 A schematic diagram of a star-shaped chiral structure unit cell according to an embodiment of the present invention;

[0055] Figure 2 This is a schematic diagram of a representative unit cell of a star-shaped chiral structure under low-velocity impact according to an embodiment of the present invention.

[0056] Figure 3 This is a schematic diagram of a representative unit cell of a star-shaped chiral structure under high-speed impact according to an embodiment of the present invention.

[0057] Figure 4 This is a compression deformation diagram of a star-shaped chiral structure distribution arrangement according to an embodiment of the present invention;

[0058] Figure 5 Stress-strain diagrams for experimental and simulation calculations of the SCHH structure according to an embodiment of the present invention.

[0059] In all the accompanying drawings, the same reference numerals indicate similar or corresponding features or functions. Detailed Implementation

[0060] In the following description, numerous specific details are set forth for illustrative purposes and to provide a thorough understanding of one or more embodiments. However, it will be apparent that these embodiments may also be implemented without these specific details. In other instances, well-known structures and devices are shown in block diagram form for ease of description of one or more embodiments.

[0061] In this invention, unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0062] To address the aforementioned problem that existing metamaterials cannot simultaneously achieve load reduction and energy absorption while maintaining structural stability under large deformations, this invention provides a star-shaped chiral impact-resistant energy-absorbing metamaterial and a method for adjusting the metamaterial structure.

[0063] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0064] To illustrate the star-shaped chiral impact-resistant energy-absorbing metamaterial provided by this invention Figure 1 The structure of a star-shaped chiral shock-absorbing metamaterial according to an embodiment of the present invention is shown.

[0065] like Figure 1 As shown, the star-shaped chiral impact-resistant energy-absorbing metamaterial provided in this embodiment includes: a multilayer structure formed by arranging and combining several star-shaped chiral structural unit cells; wherein, each star-shaped chiral structural unit cell has rotational similarity, including a chiral structure located at the center and four corners of the star-shaped structure arranged around the chiral structure, and the metamaterial forms a transition structure and has a second-order plateau stress when subjected to a high-velocity impact force.

[0066] Specifically, in Figure 1 In the illustrated embodiment, the star-shaped structure has four corners. In a star-shaped structure (such as...) Figure 1 (a) inserts chiral structures into the four corners ( Figure 1 (b) forms a star-shaped chiral unit cell with four corners, resulting in a structure like... Figure 1 As shown in (c).

[0067] Figure 1 The geometry of the star-shaped structure in (a) can be determined by the length of the inclined cell wall, the length of the horizontal cell wall, and the angle. Figure 1 The geometry of the chiral structure in (b) can be determined by the ligament length, the radius of the annulus, and the wall thickness. The geometry of the SCHH (Star-Chirality Honeycomb) can be determined by the length l of the inclined cell wall, the length h of the surrounding cell wall, the radius R of the annulus, the ligament length d, the unit wall thickness t, and the angle θ.

[0068] The star-shaped chiral unit cells are arranged in either a staggered or gradient configuration. In other words, the arrangement of the star-shaped chiral unit cells is not limited to a staggered arrangement; a gradient arrangement (such as a gradient in wall thickness or size) can also be used to achieve differentiated energy absorption effects in different regions. Randomly arranged chiral structures can be introduced into the star-shaped structure to disperse impact loads and reduce local stress concentration.

[0069] The chiral structure comprises a central ring and helical ligaments evenly distributed around its periphery. The ring can be circular, elliptical, or polygonal. In other words, the central ring and the ligaments around its periphery can also be of other geometric shapes; elliptical or polygonal rings can replace the circular ring, and helical ligaments can be used. In specific applications, the number of ligaments can be increased or decreased as needed (e.g., from four to three or six) to adjust the structure's rotational characteristics and energy absorption efficiency.

[0070] The star-shaped structure has at least three angles, and its inclined cell walls are either arc-shaped or wavy. In other words, the number of angles can be adjusted; for example, a hexagonal or triangular star shape can be used. The inclined cell walls can be designed to be arc-shaped or wavy to accommodate different load distribution requirements.

[0071] The matrix material of metamaterials can be a metal, a composite material, or a shape memory alloy. Metal materials include aluminum alloys and titanium alloys, while composite materials include carbon fiber reinforced polymers and highly elastic recoverable rubber. In specific applications, different materials can be selected based on their varying mechanical properties (such as lightweight, high toughness, or recoverability). Furthermore, the wall thickness of the star-shaped chiral unit cell can be designed to be gradually or non-uniformly distributed to optimize the distribution of plateau stress.

[0072] This invention combines star-shaped chiral unit cells with other types of unit cells (such as honeycomb and concave structures) to form multi-level metamaterials, enabling the simultaneous realization of multiple energy absorption mechanisms, such as the negative Poisson's ratio effect and multi-stable state switching. In this invention, the star-shaped structure is combined with a chiral structure to form a star-shaped chiral structure, giving the structure central stability under compression and creating a transitional structure with second-order plateau stress, suitable for use in automotive and aircraft nose-mounted load-reduction scenarios.

[0073] On the other hand, the present invention also provides a method for adjusting the structure of a metamaterial, wherein the metamaterial is the aforementioned star-shaped chiral impact-resistant energy-absorbing metamaterial. The method for adjusting the structure of the metamaterial includes: when the metamaterial is subjected to a low-speed impact, it forms a transition structure and has two-stage plateau stresses, wherein the two-stage plateau stresses are the first-stage plateau stress and the second-stage plateau stress, respectively; adjusting the corresponding structural parameters of the metamaterial according to the first-stage plateau stress; and adjusting the corresponding structural parameters of the metamaterial according to the second-stage plateau stress.

[0074] Specifically, to achieve the best impact resistance in superstructures, the structural deformation patterns under different load impact velocities must generally be considered in the design of honeycomb structures. Under different impact velocities, the structure will induce different stress waves, resulting in plateau stress distributions with varying patterns. The area enclosed by the plateau stress and the strain axis represents the strain energy absorbed by the structure; therefore, the stress plateau value is an important indicator for evaluating the load reduction and energy absorption performance of superstructures. This invention derives the plateau stress of a star-shaped chiral structure under different compression velocities to adjust the plateau stress of the structure for load reduction requirements under different working conditions.

[0075] First, a theoretical analysis is performed on the two-stage plateau stress that occurs in the SCHH structure during low-speed impact. In this invention, adjusting the structural parameters of the metamaterial based on the first-stage plateau stress includes: when subjected to the first-stage plateau stress, the star-shaped chiral unit cell is compressed in the y-direction and forms a transition state; based on the transition state, the geometric relationship of the star-shaped chiral unit cell is obtained; based on the law of conservation of energy and the geometric relationship, the first-stage plateau stress is obtained; based on the first-stage plateau stress, the length of the tilted cell wall, the length of the surrounding cell walls, and the angle are adjusted.

[0076] Specifically, Figure 2 (a) is a schematic diagram of the SCHH structure under in-plane impact, σ y The average stress in the y-direction is given. Since the unit cell structure has rotational similarity, one-quarter of the entire unit cell structure is used for analysis.

[0077] like Figure 2 As shown in (b), during the first stage of deformation, cell wall AC rotates around points A and C simultaneously under the action of bending moment M1; cell wall BC rotates around points B and C simultaneously under the action of bending moment M2, until points A and B coincide. Cell wall CD rotates around points B and C under the action of bending moment M3, simultaneously causing the ring of the intermediate chiral structure to rotate. A total of six plastic hinge points in one-quarter of the unit cell generate plastic deformation energy absorption, such as... Figure 2 (b) shows the circled area. The remaining horizontal and vertical cell walls only undergo translational movement without deformation or energy absorption, eventually resulting in a single cell forming as shown in the diagram. Figure 2(c) shows the transition structure. In the diagram, points A and B, E and F, I and J, and M and N are actually overlapping, but are avoided to clearly represent two distinct cell walls. In the transitional form, the angle between cell walls AC and AN becomes α, and the angle between line OC and the vertical direction is β. Based on the geometric relationships of the cell element, we can obtain:

[0078]

[0079] Assume that under low-velocity impact, the work done by stress in the y-direction is equal to the energy dissipated by the plastic hinges of the structure. Initially, the horizontal length of the unit cell is L0, which is given by L0 = h - 2l cos(θ) + 2l sin(θ), and the vertical height is H0, which is equal to L0. According to the law of conservation of energy, the energy E1 absorbed by the unit cell in the first stage of deformation is:

[0080]

[0081] Where b is the thickness in the outward direction of the structure, σ p1 Let H1 be the first-order plateau stress, and H1 be the vertical height of the unit cell in the transition state. Since the thicknesses of the cell walls AC, BC, and CD are all t, then:

[0082] M1=M2=M3=M p1 (3)

[0083] Where M p1 Let be the total plastic moment of the cell wall with thickness t, and its calculation formula is:

[0084] M p1 =σ ys bt 2 / 4 (4)

[0085] σ ys The yield stress is the material's own. Substituting equations (3) and (4) into equation (2), we can obtain the first-order plateau stress of the SCHH structure as:

[0086]

[0087] In this invention, the structural parameters of the metamaterial are adjusted according to the second-order plateau stress, including: when subjected to the second-order plateau stress, the star-shaped chiral unit cell continues to compress in the y-direction to form a dense state, and the total height of the star-shaped chiral unit cell in the dense state is obtained; the second-order plateau stress is obtained according to the law of conservation of energy and the total height; and the length of the cell walls around the metamaterial, the radius of the annulus, the ligament length, and the unit wall thickness are adjusted according to the second-order plateau stress.

[0088] Specifically, under the impact load, the cell continues to compress in the y-direction. At this point, the cell structure changes. Since the star-shaped inclined edges overlap, the equivalent wall thickness after overlap is 2t, while the remaining wall thicknesses remain unchanged, ultimately forming a structure like... Figure 2 (d) shows the dense morphology, where circles represent plastic hinge points and arrows indicate the direction of rod rotation. The vertical cell wall buckles under impact, dividing into upper and lower segments. Each cell wall has four plastic hinges, which rotate π / 2 under torque M4. The eight star-shaped inclined edges merge into four groups of thick walls, which adhere tightly to the upper and lower horizontal cell walls under the compression of the deformed vertical cell wall. Under torque M5, two groups rotate α, and two groups rotate π / 2-α. The four ligaments of the chiral structure undergo large deformation buckling, adhering tightly to the central ring structure, and each rotates (d-3t) / (R+2t)-β under torque M6.

[0089] Based on the law of conservation of energy, regarding the second impact process:

[0090]

[0091] Where: E2 is the total energy absorbed by the unit cell in the second stage; L1 is the horizontal length of the upper and lower cell walls in the transitional state; H2 is the total height of the unit cell in the dense state. Combining the above analysis of the cell wall thickness in the second stage, we can obtain:

[0092]

[0093] Among them, M p2 The fully plastic moment of a cell wall with a wall thickness of 2t is calculated as follows:

[0094] M p2 =σ ys bt 2 (8)

[0095] Substituting equations (7) and (8) into equation (6), we can obtain the second-order plateau stress of the SCHH structure:

[0096]

[0097] The above describes the derivation of the platform stress in metamaterials under low-velocity impact. Furthermore, under high-velocity impact loading, the compressive deformation of the SCHH structure follows a periodic crushing mode, and the stress state of the cell during impact is as follows: Figure 3 As shown. At this point, the vast majority of the work done by the impact force is converted into the kinetic energy of the structural mass, while the energy dissipated by the plastic deformation of the structure accounts for a very small proportion. Therefore, the inertial effect is significant under high-speed impact. For example... Figure 3 As shown, the analysis focuses on two adjacent cell structures, with the upper and lower layers subjected to stress σ. H The lower surface is subjected to stress σ.S The effect of this is that the horizontal length of the cell is L0. Due to the excessively high impact velocity, the structure does not have time to undergo lateral necking deformation at the impact end, and the cell is crushed. Therefore, momentum conservation is used to obtain the stress on the high-speed platform:

[0098]

[0099] Where T0 is the initial time; T1 is the time when the upper unit cell is compressed to a dense state while the lower unit cell is not compressed; This represents the momentum of the upper cell at time T1; This represents the momentum of the lower-level cell at time T2. This represents the momentum possessed by the upper-level cell at the initial moment. This represents the momentum possessed by the lower-level cell at the initial moment.

[0100] Because the structure exhibits periodic crushing characteristics, at time T1, the momentum of the lower cell is equal to the initial momentum of the upper cell, i.e.:

[0101]

[0102] At the initial moment, there is Therefore, equation (10) can be simplified to:

[0103]

[0104] During the time interval T0 to T1, the upper unit cell is crushed, causing the entire structure to move downwards at an impact velocity. Therefore, the momentum of the unit cell and T1 can be expressed as:

[0105]

[0106] Where ρ0 is the density of the matrix material; v is the impact velocity; ρ r Let be the relative density of a unit cell, expressed as:

[0107]

[0108] Substituting equations (14) and (13) into equation (12), we obtain the expression for the high-speed platform stress of the SCHH structure as follows:

[0109]

[0110] Where, σ SLet σ be the stress at the fixed end during the impact. Since inertia dominates under high-speed impact, the stress at the fixed end is nearly equal to the stress under quasi-static conditions. Furthermore, the cell deformation at the fixed end is very similar to that under low-speed impact. Therefore, it is assumed that the stress at the fixed end under high-speed impact is equal to the first-order plateau stress under low-speed impact, and σ is taken as... S =σ p1 .

[0111] If all chiral structures in a structure rotate in the same direction under compression, the entire structure will tilt to one side. The cells at one corner will undergo compaction deformation first due to the overall tilt, resulting in uneven and unstable overall deformation. To address this lateral deformation, half of the chiral structures in the honeycomb are replaced with anti-chiral structures, and the chiral and anti-chiral cells are arranged in a staggered pattern to form a periodic structure of four cells per group, thus counteracting the effect of chiral rotation. Figure 4 As shown in (a), the final compressed form of the structure is as follows Figure 4 As shown in (b).

[0112] The two stages of the SCHH deformation process and the two plateau stress regions on the stress-strain curve have clear boundaries, which can be represented by the critical strain ε. c To describe it. Its definition is... Figure 2 (c) The strain at which the unit cell just reaches the transition state; the theoretical value of the critical strain can be calculated:

[0113]

[0114] Where H0 is Figure 2 In (a), the height of the original cell SCHH, H1, is... Figure 2 The height of the deformed cell in (c).

[0115] In this invention, a quasi-static compression Abaqus simulation analysis was performed on the structure to obtain its stress-strain curve, and a physical test experiment was conducted to verify the feasibility of the simulation. The results are as follows: Figure 5 As shown, the simulation results are highly consistent with the actual test results, and in Figure 5 It can be seen from the data that the structure does indeed have obvious second-order plateau stress.

[0116] The plateau stress of the structure under different compression rates was simulated using Abaqus to verify the feasibility of the theoretical derivation formula. The results are shown in Table 1. It can be seen that the theoretical derivation model of plateau stress can predict the plateau stress of the SCHH structure to a certain extent.

[0117] Based on the derived theoretical formulas, the platform stress and critical strain of the structure can be adjusted to meet different load reduction requirements under impact conditions.

[0118] Table 1 Comparison of theoretical calculations and simulation numerical values ​​of the SCHH structure at different speeds.

[0119]

[0120] In embodiments of this invention, a star-chirality honeycomb (SCHH) superstructure combining a star-shaped structure and a chiral structure is constructed. This honeycomb forms a stable transition structure during deformation and maintains central stability during subsequent large deformations. The plateau stresses in this metamaterial at different impact velocities are derived, and simulation software is used to verify the accuracy of the theoretical results. The derived two-order plateau stress formula is used to optimize the new structure, improving its energy absorption and load reduction performance.

[0121] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A star-shaped chiral impact-resistant energy-absorbing metamaterial, characterized in that, include: A multilayered structure formed by the arrangement and combination of several star-shaped chiral unit cells; among which, Each star-shaped chiral unit cell has rotational similarity, including a chiral structure located at the center and four corners of a star-shaped structure disposed around the chiral structure; The metamaterial forms a transition structure and has a second-order plateau stress when subjected to high-velocity impact.

2. The star-shaped chiral impact-resistant energy-absorbing metamaterial as described in claim 1, characterized in that, The star-shaped chiral unit cells are arranged in a staggered or gradient manner.

3. The star-shaped chiral impact-resistant energy-absorbing metamaterial as described in claim 1, characterized in that, The chiral structure includes a centrally located annular ring and spiral ligaments uniformly distributed around the periphery of the annular ring; wherein, The ring includes a circular ring, an elliptical ring, or a polygonal ring.

4. The star-shaped chiral impact-resistant energy-absorbing metamaterial as described in claim 1, characterized in that, The star-shaped structure has at least three angles, wherein the inclined cell walls of the star-shaped structure are arc-shaped or wavy.

5. The star-shaped chiral impact-resistant energy-absorbing metamaterial as described in claim 1, characterized in that, The matrix material of the metamaterial is a metallic material, a composite material, or a shape memory alloy, wherein... The metallic materials include aluminum alloys and titanium alloys, and the composite materials include carbon fiber reinforced polymers and highly elastic recoverable rubber.

6. A method for structural adjustment of metamaterials, characterized in that, The metamaterial is a star-shaped chiral impact-resistant energy-absorbing metamaterial as described in any one of claims 1-5, and the method includes: The metamaterial forms a transitional structure and has two-stage plateau stress when subjected to low-speed impact, namely the first-stage plateau stress and the second-stage plateau stress. The structural parameters of the metamaterial are adjusted according to the stress of the first-order platform. The structural parameters of the metamaterial are adjusted according to the second-order plateau stress.

7. The method for adjusting the structure of metamaterials as described in claim 6, characterized in that, The step of adjusting the structural parameters of the metamaterial according to the first-order plateau stress includes: When subjected to the first-order plateau stress, the star-shaped chiral unit cell is compressed in the y-direction and forms a transition state; Based on the transition state, the geometric relationship of the star-shaped chiral structure unit cell is obtained; Based on the law of conservation of energy and the aforementioned geometric relationships, the first-order platform stress is obtained; Based on the stress of the first-order platform, the length of the tilted cell wall, the length of the surrounding cell wall, and the angle are adjusted.

8. The method for adjusting the structure of metamaterials as described in claim 7, characterized in that, The geometric relationship formula for the star-shaped chiral unit cell is: lsin(α) + OCsin(β) = h / 2 lcos(α) + OCcos(β) = h / 2 R 2 +d 2 =OC 2 Where l is the length of the inclined cell wall; R is the radius of the ring; d is the length of the ligament; h is the length of the surrounding cell walls; α is the angle between adjacent inclined cell walls; and β is the angle between the line connecting the intersection of the adjacent inclined cell walls in the transitional form and the center of the ring and the vertical direction. Initially, the horizontal length of the star-shaped chiral unit cell is L0, the vertical height is H0, L0 = h - 2lcos(θ) + 2lsin(θ), and H0 is equal to L0; According to the law of conservation of energy, the energy E1 absorbed by the star-shaped chiral unit cell during the first stage of deformation is: E1=σ p1 L0b(H0-H1) =8M1(θ-α)+8M2(π / 2-α-θ)+8M3(β-π / 4) The first-order plateau stress of the star-shaped chiral unit cell is: Where b is the thickness in the outward direction of the structure, σ p1 Let H1 be the first-order plateau stress, and H1 be the vertical height of the unit cell in the transition state. Since the thickness of the cell wall is always t, then: M1=M2=M3=M p1 M p1 =σ ys bt 2 / 4 Among them, M p1 Let σ be the total plastic moment of a cell wall with a wall thickness of t. ys This refers to the yield stress of the material itself.

9. The method for adjusting the structure of metamaterials as described in claim 8, characterized in that, The step of adjusting the structural parameters of the metamaterial according to the second-order plateau stress includes: When subjected to the second-order plateau stress, the star-shaped chiral unit cell continues to compress in the y-direction to form a dense state, and the total height of the star-shaped chiral unit cell in the dense state is obtained. Based on the law of conservation of energy and the total height, the second-order platform stress is obtained; Based on the second-order plateau stress, the length of the cell walls around the metamaterial, the radius of the annulus, the ligament length, and the unit wall thickness are adjusted.

10. The method for adjusting the structure of metamaterials as described in claim 9, characterized in that, According to the law of conservation of energy, the energy absorbed by the star-shaped chiral unit cell in the second stage of deformation is: Second stage platform stress values: in, M p2 =σ ys bt 2 , E2 represents the total energy absorbed by a single cell in the second stage, L1 represents the horizontal length of the upper and lower cell walls in the transitional state, H2 represents the total height of a single cell in the compact state, and M represents the total energy absorbed by a single cell in the compact state. p2 The total plastic moment of a cell wall with a wall thickness of 2t.

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