Self-adaptive impact-resistant protective metamaterial with Poisson's ratio autonomous constraint function

Abstract

The invention discloses a self-adaptive impact-resistant protective metamaterial with a Poisson's ratio autonomous constraint function, which comprises a PMP honeycomb, the PMP honeycomb comprises a plurality of honeycomb unit cell structures, and each honeycomb unit cell structure comprises a hexagonal thin-wall structure I and a hexagonal thin-wall structure II internally connected in the hexagonal thin-wall structure I. The invention further discloses a preparation method of the self-adaptive impact-resistant protective metamaterial with the Poisson's ratio autonomous constraint function. Compared with an SHC honeycomb, the PMP honeycomb has the advantages that the dynamic Poisson ratio of the PMP honeycomb is relatively stable in the whole crushing process, and the initial fluctuation range is only 0.1. In addition, the average dynamic Poisson's ratio of the PMP honeycomb is relatively small, indicating that the PMP honeycomb is almost free of transverse deformation without additional assistance. After the PMP honeycomb is compressed to be densified, the transverse length of the PMP honeycomb is only increased by 3.5%. Wherein the PMP honeycomb has better self-constraint capability, so that the PMP honeycomb has a more stable energy absorption mode.

Description

Technical Field

[0001] The present invention relates to the technical field of special materials, and particularly to an adaptive anti - impact protection metamaterial with a self - constrained Poisson's ratio function. Background Art

[0002] Problems existing in the prior art: Due to the characteristics of lightweight and the advantage of effectively preventing impact loads, single - hexagonal honeycomb (SHC) is widely used in a series of engineering fields such as aerospace, transportation, and civil engineering. In the past, researchers found a large number of new honeycomb structures applied to energy absorption. Although these structures improve the mechanical properties of traditional SHC honeycombs, their application scope is relatively narrow and it is difficult to control their energy absorption capacity. These structures will inevitably exhibit positive or negative Poisson's ratios during compression. Designing a new energy - absorbing structure with comprehensive mechanical properties to replace traditional honeycombs remains a long - term challenge.

[0003] In existing findings, the elytron structure of beetles can be used as a defensive structure to resist load threats hundreds or even tens of thousands of times its own body weight from a harsh living environment. However, previous studies mainly focused on out - of - plane mechanical properties, and less on in - plane mechanical properties. Summary of the Invention

[0004] The purpose of the present invention is to provide an adaptive anti - impact protection metamaterial with a self - constrained Poisson's ratio function, so as to solve the problems of the mechanical properties of traditional SHC honeycombs, narrow application scope, and difficulty in controlling their energy absorption capacity.

[0005] To solve the above - mentioned technical problems, the present invention adopts the following technical solutions:

[0006] The present invention provides an adaptive anti - impact protection metamaterial with a self - constrained Poisson's ratio function, including a PMP honeycomb. The PMP honeycomb includes a plurality of honeycomb unit cell structures, and each honeycomb unit cell structure includes a hexagonal thin - wall structure Ⅰ and a hexagonal thin - wall structure Ⅱ inscribed in the hexagonal thin - wall Ⅰ.

[0007] Further in this embodiment, the honeycomb unit cell structures are respectively symmetric about the X1 or X2 axis; the PMP honeycomb is formed by periodically arranging the honeycomb unit cell structures in the X1 or X2 direction.

[0008] Still further in this embodiment, the side length of the hexagonal thin - wall structure Ⅱ and the side lengths of the hexagonal thin - wall structure Ⅱ in two adjacent honeycomb unit cell structures form a triangle.

[0009] Still further in this embodiment, the PMP honeycomb is prepared by laser - melting additive manufacturing technology; the substrate is a metal material with plastic forming characteristics.

[0010] In this embodiment, further, both the hexagonal thin wall Ⅰ and the hexagonal thin wall structure Ⅱ are regular hexagonal structures.

[0011] In this embodiment, further, the corners of the hexagonal thin wall structure Ⅱ are connected to the center of the inner wall of the hexagonal thin wall Ⅰ.

[0012] In this embodiment, further, the wall thicknesses of the hexagonal thin wall Ⅰ and the hexagonal thin wall structure Ⅱ are t1 and t2 respectively, and t1 = t2; their side lengths are l1 and l2 respectively; where l1 and l2 should satisfy l1 = 2l2;

[0013] The ratio of the wall thickness of the hexagonal thin wall structure Ⅱ to the side length of the hexagonal thin wall Ⅱ should be less than 0.125;

[0014] The out-of-plane width can be designed according to actual needs, and in this example, it is 10 mm. There are certain requirements for the wall thickness and side length. After calculation, the ratio of the wall thickness to the side length of the hexagonal thin wall Ⅱ should be less than 0.125, otherwise the mechanism of action will change. Since the designed structure is a regular hexagon inscribed in a regular hexagon, l1 and l2 should satisfy l1 = 2l2. In this design example: the wall thicknesses of the hexagonal thin walls Ⅰ and Ⅱ are both 0.4 mm, the side length of the hexagonal thin wall Ⅰ is 4.6 mm, and the side length of the hexagonal thin wall structure Ⅱ is 4 mm.

[0015] Compared with the prior art, the beneficial technical effects of the present invention: Compared with the SHC honeycomb, the dynamic Poisson's ratio of the PMP honeycomb of the present invention is relatively stable during the entire crushing process, and the initial fluctuation amplitude is only 0.1. In addition, the average dynamic Poisson's ratio of the PMP honeycomb is relatively small, indicating that there is almost no lateral deformation without additional assistance. After the PMP honeycomb is compressed to densification, its lateral length only increases by 3.5%. Among them, the PMP honeycomb has a good self-constraint ability, making it have a more stable energy absorption mode. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present invention will be further described below with reference to the accompanying drawings.

[0017] Figure 1 It is a three-dimensional geometric shape schematic diagram of the PMP honeycomb of the adaptive anti-impact protection metamaterial with Poisson's ratio self-constraint function of the present invention;

[0018] Figure 2 It is a schematic diagram of the unit cell structure of the PMP honeycomb of the adaptive anti-impact protection metamaterial with Poisson's ratio self-constraint function of the present invention;

[0019] Figure 3 It is a schematic diagram of the representative volume unit of the PMP honeycomb;

[0020] Figure 4Theoretical analysis of the PMP honeycomb collapse process (a) original configuration; (b) first stage; (c) second stage; (d) third stage;

[0021] Figure 5 Schematic diagrams of the finite element models of the PMP honeycomb and the SHC honeycomb;

[0022] Figure 6 Schematic diagrams of the PMP honeycomb specimen and the SHC honeycomb specimen;

[0023] Figure 7 Schematic diagram of the deformation process of the SHC honeycomb under quasi-static compression;

[0024] Figure 8 Schematic diagram of the deformation process of the PMP honeycomb under quasi-static compression;

[0025] Figure 9 Crashworthiness analysis test diagrams of the SHC and PMP honeycombs;

[0026] Figure 10 Constitutive curve using the 316L stainless steel substrate;

[0027] Figure 11 Constitutive curve using the Q235 steel substrate;

[0028] Figure 12 Constitutive curve using the Al substrate;

[0029] Figure 13 Constitutive curve using the 316L stainless steel substrate. Specific implementation mode

[0030] Reference Figure 1 and Figure 2 In this embodiment, an adaptive impact-resistant protective metamaterial with a Poisson's ratio self-constraint function is disclosed, including a PMP honeycomb, the PMP honeycomb includes a plurality of honeycomb unit cell structures, and the honeycomb unit cell structure includes a hexagonal thin-walled structure I and a hexagonal thin-walled structure II inscribed in the hexagonal thin-walled I.

[0031] In this embodiment, the honeycomb unit cell structure is symmetric about the X1 or X2 axis respectively; the PMP honeycomb is formed by periodically arranging the honeycomb unit cell structure in the X1 or X2 direction. The side length of the hexagonal thin-wall structure II and the side lengths of the hexagonal thin-wall structure II in two adjacent honeycomb unit cell structures form a triangle. The PMP honeycomb is prepared by laser melting additive manufacturing technology; the substrate is a metal material with plastic properties; for example: 316L stainless steel, aluminum, Q235 steel. Both the hexagonal thin-wall I and the hexagonal thin-wall structure II are regular hexagonal structures. The corners of the hexagonal thin-wall structure II are connected to the center of the inner wall of the hexagonal thin-wall I. The wall thicknesses of the hexagonal thin-wall I and the hexagonal thin-wall structure II are t1 and t2 respectively, and t1 = t2; their side lengths are l1 and l2 respectively; where l1 and l2 should satisfy l1 = 2l2;

[0032] The ratio of the wall thickness of the hexagonal thin-wall structure II to the side length of the hexagonal thin-wall II should be less than 0.125.

[0033] Mechanism of action

[0034] Adopt Figure 3 The structure represented by the solid line in is used for theoretical analysis. This structure is symmetric about the central axis and consists of 6 triangular units ( Figure 3 the blue part in ). During the crushing process of the PMP honeycomb, 2 triangular units in the same horizontal layer ( Figure 3 represented by the red dashed box in ) can be used as the representative volume element (RVE) in the theoretical analysis due to their layer-by-layer collapse behavior. The boundary conditions between adjacent triangular cells (or cell walls) are equivalent to "fixed support" connections. When plastic hinges appear at the connection points, the boundary conditions effectively become "simple support", allowing the cell walls to translate and rotate. The plastic hinges of these two units are symmetric about the central axis, and the energy they absorb is equal. Therefore, a comprehensive analysis of a single triangular unit is sufficient to determine the mechanical properties of the entire PMP honeycomb structure.

[0035] Among them, the crushing process is divided into Figure 4 the three stages shown in. At the beginning of crushing (stage I, Figure 4b), plastic deformation begins at points O, A, and B. Under the crushing load, cell walls OA and OB both rotate towards the axis of symmetry (OO1). Cell wall AB is compressed by cell walls OA and OB, generating plastic hinges at points A, B, and the midpoint C1 respectively. As the crushing process progresses, point A rotates clockwise around O to A1, and point B rotates counterclockwise around O to B1. Meanwhile, the midpoint C1 moves in the opposite direction along the axis of symmetry OO1, driving cell wall C1A1 to rotate clockwise around point A1 and cell wall C1B1 to rotate counterclockwise around point B1. Finally, the straight line AB becomes the broken line A1C1B1. Similarly, the straight lines GA and GB respectively become the broken lines GD1A1 and GE1B1. To simplify the mechanical model, it is assumed that the break points where plastic hinges occur are located at the midpoints of the lines. That is, GD1 = D1A1 and GE1 = E1B1.

[0036] In stage II ( Figure 4 c), cell walls OA1 and OB1 continue to rotate towards the axis of symmetry (OO1). The crushed cell wall A1C1B1 is further compressed to reach the position of the broken line A2C2B2. Similarly, the crushed cell walls GD1A1 and GE1B1 rotate inwards around point G under the action of cell walls OA1 and OB1 respectively, reaching the positions of the broken lines G2D2A2 and G2E2B2. As the compression develops, points G and G2 move in the opposite direction along the axis of symmetry OO1. Subsequently, cell wall OG ( Figure 4 b) is compressed into two equal straight segments (OF2 and F2G2), and a plastic hinge ( Figure 4 c) is generated at the midpoint. Under the compression, cell wall OF2 rotates clockwise around point O until it contacts the outer cell wall OB2.

[0037] In the third stage ( Figure 4 d), all the cell walls of the right - hand representative unit analyzed above ( Figure 4 the blue lines in c) rotate counterclockwise around point O by θ3, causing point O to reach the original line AB. After the third stage, the representative unit forms a relatively densified region and moves downward at a velocity v, where the velocity v is equal to the velocity of the upper plate. At this moment, the crushing cycle of the cell is completed, and then a new cycle begins. During the repeated crushing process, the top and bottom of the representative unit respectively bear the crushing stress σ1 and the supporting stress σ2. The crushing stress σ1 is equal to the contact stress between the upper plate and the PMP honeycomb block because the densified region of the PMP honeycomb block moves at a constant velocity v, which is the same as the compression velocity of the upper plate. The supporting stress σ2 provided by the undeformed unit below is equal to the contact stress between the bottom plate and the PMP honeycomb block, and the undeformed unit below the representative unit is basically in static equilibrium. Theoretical analysis shows that there is a self - constraint mechanism for the lateral deformation of the PMP honeycomb ( Figure 4 ), which explains why the lateral deformation of the PMP honeycomb is almost zero during the crushing process.

[0038] Model Structure Design

[0039] Among them, it is designed according to the distribution of photon micro-columns in the beetle elytra structure, as Figure 1 and Figure 2 shown. The honeycomb unit cell structure includes a hexagonal thin-wall structure I and a hexagonal thin-wall structure II inscribed in the hexagonal thin-wall I. The entire PMP honeycomb( Figure 1 ) is formed by periodically arranging the periodic unit cell structure in the X1 and X2 directions. The deformation caused by loading on the overall plane (X1X2) of the PMP honeycomb is called in-plane response, while the deformation caused by loading in the direction perpendicular to the X1X2 plane is called out-of-plane response. By comparing the in-plane mechanical responses of the PMP honeycomb and the traditional SHC honeycomb, the protection mechanism of the PMP honeycomb is revealed. The representative unit cell structure of the PMP honeycomb is as Figure 2 shown, which is symmetric about the X1 and X2 axes respectively and consists of two hexagonal unit cells.

[0040] Finite Element Simulation of Impact Process

[0041] The in-plane response of the honeycomb under the impact of a rigid plate moving at a constant speed was simulated using the nonlinear explicit finite element program LS-DYNA. The relative density of the honeycomb model was selected as 27.3%, the out-of-plane width was 10 mm, and the base material was selected as 316L stainless steel. The PMP model had 15 units in the X1 direction and 11 units in the X2 direction. The length of the outer cell wall was l1 = l2 = 4.6 mm, the length of the inner cell wall was l3 = l4 = 4 mm, and the cell wall angles α = β = 30°. For comparison, the SHC honeycomb had 17 units in the X1 direction and 13 units in the X2 direction. The length of the cell wall of the SHC honeycomb was l5 = l6 = 4 mm, the cell wall angle γ = 30°, and the cell wall thickness was t3 = 0.946 mm. The schematic diagram of the finite element model is as Figure 5 shown, the finite element model of the honeycomb structure (a) PMP honeycomb; (b) SHC honeycomb.

[0042] During the impact process, all degrees of freedom of the bottom rigid plate were fixed, and a constant vertical downward velocity v (along the X1 direction) was applied to the top rigid plate. The honeycomb model used four-node shell elements with five integration points according to the thickness, and the full integration element formula was adopted. Both the top plate and the bottom plate used eight-node solid elements. The automatic surface-to-surface contact algorithm was used to simulate the contact interaction between the honeycomb and the two rigid plates, and the automatic single-surface contact was used to avoid penetration or intersection between the cell walls of the honeycomb. The contact friction coefficient was 0.2, and compression simulation was carried out.

[0043] Sample Preparation

[0044] As Figure 6As shown in the figure, the PMP honeycomb specimen is on the left side and the SHC honeycomb specimen is on the right side. They are prepared by a selective laser melting (SLM) 3D printer, and the material is 316L stainless steel. The main process parameters are a laser power of 200 W, a hatch spacing of 0.12 mm, a layer thickness of 30 μm, and a scanning speed of 800 mm / s. The samples are as shown in the figure. Quasi-static compression tests were carried out on PMP and SHC honeycomb specimens with the same relative density on an MTS universal testing machine. The specimens were compressed at a constant speed of 10 mm / min, and the corresponding strain rate was 0.0014 s-1. The deformation process and crushing mode of the PMP and SHC honeycomb specimens were recorded with a camera.

[0045] Deformation analysis

[0046] As Figure 7 shown, for the SHC honeycomb, a typical "X"-type failure mode can be observed during the crushing process. As the crushing progresses, the SHC honeycomb expands laterally. This is because the special configuration of the hexagon causes plastic hinges to form at specific positions on the cell walls, resulting in the gradual collapse of the SHC honeycomb and the formation of an "X"-type shear band. This "X"-type shear band causes the cells near the free boundaries on both sides of the SHC honeycomb to be less laterally constrained than the cells near the central region, and they are squeezed and expand outward.

[0047] However, no "X"-type shear band was found in the PMP honeycomb. During the quasi-static compression process, the PMP honeycomb was crushed successively from the loading end to the support end (as Figure 8 shown). A transverse shear band perpendicular to the compression direction was observed at the loading end. As the top plate moved downward, the shear band propagated layer by layer towards the support end. The shape of this transverse shear band is similar to the shape of the "I"-type shear band generated by the SHC honeycomb during high-speed crushing. And the former does not cause obvious lateral contraction or expansion of the PMP honeycomb. Compared with the SHC honeycomb, the PMP honeycomb has a more stable deformation mode and better self-constraint ability, which is beneficial to maintaining stable mechanical properties and reducing the influence on the external structure in practical applications.

[0048] Crashworthiness analysis

[0049] As Figure 9 shown, (a) SHC honeycomb; (b) stress-strain curves of the PMP honeycomb; (c) energy absorption efficiency; (d) changes in the dynamic Poisson's ratio and lateral strain.

[0050] The stress-strain curves of the SHC and PMP honeycombs are shown in a and b respectively in Figure 9 the figure, and the energy absorption efficiency (EAE) curves of the SHC and PMP honeycombs calculated from the numerical results are shown in Figure 8 c. The compaction strain of the PMP honeycomb is 0.721, which is 17.2% higher than that of the SHC honeycomb, indicating that the effective compression distance of the PMP honeycomb proposed in this paper is larger. FromFigure 9 As can be seen from Fig. c, before this, the EAE of both the SHC and PMP honeycombs increased approximately linearly before reaching the maximum value. This is because the stress-strain curves of the two honeycombs were relatively flat during this stage. Since the SHC honeycomb entered the compaction stage earlier, the maximum EAE was only 57.3%.

[0051] The PMP honeycomb had a longer plateau stage and a later compaction stage, ultimately resulting in a maximum EAE of up to 82.1% for the PMP honeycomb. The results show that when the compaction strain was in the range of 0.554 - 0.831, the EAE of the PMP honeycomb was higher than that of the SHC honeycomb, accounting for 46.6% of the entire plateau stage (effective stroke) of the SHC honeycomb; during the compression process, the duration for which the EAE of the PMP honeycomb was greater than 50% was 1.6 times that of the SHC honeycomb.

[0052] Compared with the results of the SHC honeycomb, the stress-strain curve of the PMP honeycomb was flatter and more regular during the plateau stage. This was related to the periodic collapse process and failure mode of the PMP honeycomb. In this example, when the relative density was 27.3%, the plateau stress of the PMP honeycomb reached 35.7 MPa, which was 42.8% higher than that of the SHC honeycomb with the same relative density ( Figure 9 as shown in Figs. a and b). The plateau stress of the PMP honeycomb was greater than the initial peak stress, while the opposite was true for the SHC honeycomb. This enabled the PMP honeycomb to be uniformly loaded during the compression process, greatly reducing the risk of stress mutation and structural failure during the initial compression stage. The PMP honeycomb absorbed 60.6% more energy during the crushing process than the SHC honeycomb. The results prove that the PMP honeycomb proposed in this paper not only improves the energy absorption capacity but also makes the energy absorption process more stable and reliable.

[0053] The changes in the lateral strain and dynamic Poisson's ratio of the PMP and SHC honeycombs are shown in Figure 9 Fig. d. It can be found that during the compression process, the instantaneous lateral strain of the SHC honeycomb gradually increased in the form of an approximate linear function. When the SHC honeycomb was compressed by 80%, its instantaneous lateral strain reached 0.2, which means that its lateral length increased by 20%. When the compaction strain was small (before 10%), the dynamic Poisson's ratio of the SHC honeycomb changed violently, first increasing and then decreasing, with a maximum value of 0.86; when the compression strain was greater than 10%, the dynamic Poisson's ratio curve tended to be flat and fluctuated around 0.24.

[0054] The longitudinal deformation of the PMP honeycomb has little effect on the transverse deformation, showing independence from transverse deformation, and the instantaneous transverse strain is close to zero (about 0.016). Compared with the SHC honeycomb, the dynamic Poisson's ratio of the PMP honeycomb is relatively stable throughout the crushing process, and the initial fluctuation amplitude is only 0.1. In addition, the average dynamic Poisson's ratio of the PMP honeycomb is relatively small (about 0.04), indicating that there is almost no transverse deformation without additional assistance. After the PMP honeycomb is compressed to densification, its transverse length only increases by 3.5%. The results show that the PMP honeycomb has better self-constraint ability, making it have a more stable energy absorption mode.

[0055] Reference Figure 10 , which is the constitutive curve using the 316L stainless steel substrate as the base material; Figure 11 It is the constitutive curve using the Q235 steel substrate as the base material; Figure 12 It is the constitutive curve using the Al substrate as the base material;

[0056] When the ratio of the honeycomb thickness to the side length of the hexagonal thin wall is 0.125, the thickness is selected as 0.5 mm, and the side length of the hexagonal thin wall II is selected as 4 mm. The constitutive curve is as Figure 13 shown, which is the constitutive curve of the S4 substrate 316L stainless steel substrate.

[0057] The above embodiments only describe the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. An adaptive anti-impact protective metamaterial with Poisson's ratio autonomous constraint function, characterized in that: It comprises a PMP honeycomb, wherein the PMP honeycomb comprises a plurality of honeycomb unit cell structures, wherein the honeycomb unit cell structure comprises a hexagonal thin-wall structure I and a hexagonal thin-wall structure II inscribed in the hexagonal thin-wall structure I.

2. The adaptive anti-impact protective metamaterial with Poisson's ratio autonomous constraint function according to claim 1, characterized in that: The honeycomb unit cell structure is symmetrical around the X1 or X2 axis respectively; the PMP honeycomb is formed by periodically arranging the honeycomb unit cell structure in the X1 or X2 direction.

3. The adaptive anti-impact protective metamaterial with Poisson's ratio autonomous constraint function according to claim 2, characterized in that: The side length of the hexagonal thin-walled structure II and the side length of the hexagonal thin-walled structure II in two adjacent honeycomb unit cell structures form a triangle.

4. The adaptive anti-impact protective metamaterial with Poisson's ratio autonomous constraint function according to claim 1, characterized in that: The PMP honeycomb is prepared by laser melting additive technology; the substrate is a metal material with plastic properties.

5. The adaptive anti-impact protective metamaterial with Poisson's ratio autonomous constraint function according to claim 1, characterized in that: The hexagonal thin-wall structure I and the hexagonal thin-wall structure II are both regular hexagonal structures.

6. The adaptive anti-impact protective metamaterial with Poisson's ratio autonomous constraint function according to claim 5, characterized in that: The corner of the hexagonal thin-wall structure II is connected to the center of the inner wall of the hexagonal thin wall I.

7. The adaptive anti-impact protective metamaterial with Poisson's ratio autonomous constraint function according to claim 1, characterized in that: The wall thickness of the hexagonal thin wall I and the wall thickness of the hexagonal thin wall structure II are t1 and t2 respectively, t1=t2; the side lengths of the two are l1 and l2 respectively; wherein l1 and l2 should satisfy l1=2l2; The ratio of the wall thickness of the hexagonal thin-wall structure II to the side length of the hexagonal thin wall II should be less than 0.125.

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