Mechanical metamaterial

Abstract

The invention discloses a mechanical metamaterial which comprises one or more configuration units. The configuration unit comprises an upper outer frame (1) and a lower outer frame (4) opposite to the upper outer frame (1); an upper coupling structure (2) and a lower coupling structure (3) are arranged between the upper outer frame (1) and the lower outer frame (4); the lower end of the upper coupling structure (2) is fixedly connected with the upper end of the lower coupling structure (3) through an independent middle support column (5); the upper coupling structure (2) or / and the lower coupling structure (3) are / is a cross elliptical ring-curved beam coupling structure. The mechanical metamaterial is high in energy absorption performance and good in recoverability, can effectively restrain high-frequency impact, and is more suitable for buffering multiple continuous strong transient impact scenes.

Description

Technical Field

[0001] The invention belongs to the technical field of high-performance buffer materials, and in particular to a mechanical buffer metamaterial suitable for buffering multiple continuous strong transient impacts. Background Art

[0002] High-performance buffer materials are an important component of many military and daily life equipment that are subject to mechanical impact. For example, helmets with impact buffer components can protect the survival of passengers in traffic accidents; missile fuzes with impact buffer components can work reliably and accurately detonate ammunition when penetrating multi-story building walls. For these applications, higher energy absorption performance and better recoverability are permanent goals, but this is limited by traditional rubber, foam metal and other buffer materials. For example, rubber has a relatively low energy absorption ratio, and the thickness of the buffer component must be increased to ensure the reliable operation of the equipment under impact conditions. However, such a bulky buffer component is obviously not ideal in devices with limited size such as helmets and fuzes. When metal foams are subjected to continuous multiple impacts, they are easily compacted and cannot rebound. Therefore, mechanical metamaterials have become a good choice. It achieves the modulation of nonlinear mechanical properties through special microstructure design, so that it can obtain high energy absorption ratios through different deformation mechanisms of various microstructures. In addition, the impact frequency selectivity has been less involved in previous studies. In fact, high-frequency mechanical loads are more destructive than low-frequency mechanical loads, so the high-frequency suppression ability of buffer materials under mechanical impact is also of great value.

[0003] Existing mechanical metamaterials, such as the Chinese invention patent "A high-energy-absorbing and recoverable buffer structure suitable for penetrating ammunition detonation buffering" (application number: CN202311488754.1, publication date: 2023-12-29), include: a first symmetrically curved cross-crossed hyperbolic beam structure is provided at the lower end of the upper support plate of the unit cell structure; the first symmetrically curved cross-crossed hyperbolic beam structure is connected to the upper support plate through four first support columns; a second symmetrically curved cross-crossed hyperbolic beam structure is provided at the upper end of the lower support plate; the second symmetrically curved cross-crossed hyperbolic beam structure is connected to the lower support plate through four second support columns; the first symmetrically curved cross-crossed hyperbolic beam structure and the second symmetrically curved cross-crossed hyperbolic beam structure are connected through four third support columns, and every two third support columns divide a single curved beam into four equal parts; the four first support columns correspond to the four second support positions.

[0004] However, the above-mentioned mechanical metamaterial has technical defects such as serious degradation of structural stiffness under large deformation and poor structural recovery after impact due to the fact that the cross double arc curved beam and the support plate only rely on the fixed connection of the surrounding support columns and there is a lack of force-bearing interlayer between the support plate and the arc curved beam. Summary of the invention

[0005] The purpose of the present invention is to provide a mechanical metamaterial with high energy absorption, good recoverability, and the ability to effectively suppress high-frequency impacts, making it more suitable for buffering multiple continuous strong transient impact scenarios.

[0006] The technical solution for realizing the present invention is:

[0007] A mechanical metamaterial comprises one or more configuration units; the configuration unit comprises an upper outer frame and a lower outer frame opposite to the upper outer frame; an upper coupling structure and a lower coupling structure are arranged between the upper outer frame and the lower outer frame; the lower end of the upper coupling structure is fixedly connected to the upper end of the lower coupling structure via an independent intermediate support; the upper coupling structure and / or the lower coupling structure are cross-crossed elliptical ring-curved beam coupling structures.

[0008] Preferably, the upper coupling structure includes two upper curved beams whose two ends are bent toward the upper outer frame, and the two upper curved beams are cross-intersected at the midpoint; two upper elliptical rings with their long axes cross-intersecting and their short axes coaxial are provided between the upper curved beams and the upper outer frame; the two ends of the upper curved beams are fixedly connected to the lower end surface of the upper outer frame through an upper support column.

[0009] Preferably, the lower coupling structure includes two lower curved beams whose two ends are bent toward the lower outer frame, and the two lower curved beams are cross-intersected at the midpoint; two lower elliptical rings with their long axes cross-intersecting and their short axes coaxial are provided between the lower curved beams and the lower outer frame; the two ends of the lower curved beams are fixedly connected to the upper end of the lower outer frame through a lower support column.

[0010] Furthermore, the upper end of the independent middle pillar is fixedly connected to the lower ends of the cross intersection of the two upper curved beams, and the lower end thereof is fixedly connected to the upper ends of the cross intersection of the two lower curved beams.

[0011] Compared with the prior art, the present invention has the following significant advantages:

[0012] 1. High energy absorption: The present invention adopts an elliptical ring-curved beam coupling structure. Due to the mutual coupling of the elliptical ring structure with positive stiffness and the curved beam structure with negative stiffness, the force-displacement response curve of the mechanical metamaterial of the present invention is enhanced, and the stiffness degradation under large deformation is avoided, so that the mechanical metamaterial has higher energy absorption. In comparison with the unit cell structure of the same size (3.8mm*3.8mm*3.8mm), the energy absorption of the existing mechanical metamaterial is 123.81mJ, while the energy absorption of the mechanical metamaterial of the present invention can reach 162.62mJ, an increase of 31.35%.

[0013] 2. Good recoverability: Under compression load, the mechanical metamaterial of the present invention uses an elliptical ring with large deformation capacity as an additional support for the curved beam. The elliptical ring fills the gap in the intermediate layer between the curved beam and the upper frame to enhance the internal support of the structure. In addition, through the coordination of the bending deformation of the elliptical ring structure and the curved beam structure, the elastic potential energy storage of the buffer structure during the compression deformation process can be achieved, thereby enhancing the recoverability of the overall structure. By comparing the natural recovery of the unit cell structure of the same size (3.8mm*3.8mm*3.8mm) at different compression heights, the structural recoverability of the mechanical metamaterial of the present invention increases by an average of 20%.

[0014] 3. Effectively suppress high-frequency impact: In the mechanical metamaterial of the present invention, due to the use of an elliptical ring structure, which shows a small displacement transmission rate in both experimental and theoretical analysis, the mechanical metamaterial of the present invention can effectively reduce the transmission of high-frequency vibrations during the impact process, and reduce the actual destructive power of the impact through self-filtering, thereby protecting the core components from external vibration interference and maintaining the stability and accuracy of the system. By analyzing the power share of each frequency domain of the signal buffered by the mechanical metamaterial of the present invention, for the high-frequency frequency domain of 3000Hz to 10000Hz, the high-frequency power share of the original impact signal is 21.02%, while the high-frequency power share of the signal buffered by the mechanical metamaterial of the present invention is only 3.1%.

[0015] 4. More suitable for buffering in multiple continuous strong transient impact scenarios: In the mechanical metamaterial of the present invention, due to the mutual coupling of the elliptical ring and the curved beam, the structure has the characteristics of close to zero stiffness and good support, making the energy absorption process of the structure more uniform during the compression process, avoiding excessive concentration of energy when encountering continuous impacts in a short period of time and causing stress concentration in some internal structures, making the structure more adaptable to the energy absorption capacity under continuous impacts. Using multiple impact table experiments, a single cell structure of the same size (3.8mm*3.8mm*3.8mm) was compared. Under four consecutive impacts of about 10,000g, the impact buffering rate of the existing mechanical metamaterials was maintained between 45% and 50%, while the impact buffering rate of the mechanical metamaterial of the present invention was maintained above 60%. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the appearance structure of the mechanical metamaterial of the present invention.

[0017] Figure 2 yes Figure 1 Schematic diagram of the three-dimensional structure of the mesostructured unit.

[0018] Figure 3 yes Figure 2 Top view of the .

[0019] Figure 4 yes Figure 2 according to Figure 3 Cross-sectional view along the AA direction.

[0020] Figure 5 yes Figure 2 according to Figure 3 Cross-sectional view along the BB direction.

[0021] Figure 6 yes Figure 1 Schematic diagram of the compression deformation process of the medium configuration unit. Figure 6 (a) shows the initial state when the structure is not deformed; Figure 6 (b) is the state when the structure is slightly deformed; Figure 6 (c) is the state when the structure is moderately deformed; Figure 6 (d) is the state when the structure is fully deformed.

[0022] Figure 7 Schematic diagram of static compressive stress-strain comparison between the mechanical metamaterial of the present invention and the existing mechanical metamaterial.

[0023] Figure 8 It is a schematic diagram comparing the structural recovery of the mechanical metamaterial of the present invention and the existing mechanical metamaterial at different compression heights.

[0024] In the figure, 1 is an upper outer frame, 2 is an upper coupling structure, 3 is a lower coupling structure, 4 is a lower outer frame, and 5 is an independent middle support.

[0025] 11, 12, 13, 14 are support columns, 21, 22 are curved beams, 23, 24 are elliptical rings,

[0026] 31, 32 are curved beams, 33, 34 are elliptical rings, 41, 42, 43, 44 are supporting columns. DETAILED DESCRIPTION

[0027] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0028] like Figure 1 As shown, the mechanical metamaterial of the present invention includes at least one configuration unit, or is formed by splicing a plurality of configuration units to form a plate-like structure.

[0029] like Figure 2 , 3 As shown, the configuration unit includes an upper outer frame 1 and a lower outer frame 4 placed parallel to and opposite to the upper outer frame 1;

[0030] An upper coupling structure 2 and a lower coupling structure 3 are provided between the upper outer frame 1 and the lower outer frame 4;

[0031] The lower end of the upper coupling structure 2 is fixedly connected to the upper end of the lower coupling structure 3 via an independent middle support 5;

[0032] The upper end of the upper coupling structure 2 is fixedly connected to the lower end of the upper outer frame 1;

[0033] The lower end of the lower coupling structure 3 is fixedly connected to the upper end of the lower outer frame 4 .

[0034] like Figure 4 , 5 As shown, the upper coupling structure 2 is a cross-crossed elliptical ring-curved beam coupling structure;

[0035] The upper coupling structure 2 includes two upper curved beams 21 and 22 with both ends bent toward the upper outer frame 1. Figure 3 , 4 As shown; the two upper curved beams 21, 22 are cross-intersected at the midpoint;

[0036] Two upper elliptical rings 23 and 24 are provided between the upper curved beams 21 and 22 and the upper outer frame 1, with their major axes crossing each other and their minor axes being coaxial.

[0037] Both ends of the upper curved beams 21, 22 are fixedly connected to the lower end of the upper outer frame 1 through upper support columns 11, 12, 13, 14 respectively.

[0038] like Figure 4 , 5 As shown, the lower coupling structure 3 is a cross-crossed elliptical ring-curved beam coupling structure;

[0039] The lower coupling structure 3 includes two lower curved beams 31 and 32 with both ends bent toward the lower outer frame 4. Figure 3 , 4 As shown; the two lower curved beams 31, 32 are cross-intersected at the midpoint;

[0040] Two lower elliptical rings 33 and 34 are provided between the lower curved beams 31 and 32 and the lower outer frame 4, with their long axes crossing each other and their short axes coaxial.

[0041] Both ends of the lower curved beams 31 , 32 are fixedly connected to the upper end of the lower outer frame 4 through lower support columns 41 , 42 , 43 , 44 , respectively.

[0042] like Figure 2 , 4 As shown in FIG. 5 , the lower side of the cross point of the two upper curved beams 21 and 22 is fixedly connected to the upper end of the independent middle pillar 5 , and the upper side of the cross point of the two lower curved beams 31 and 32 is fixedly connected to the lower end of the independent middle pillar 5 .

[0043] The mechanical metamaterial of the present invention is composed of at least one configuration unit or a plurality of configuration units spliced ​​together.

[0044] When multiple configuration units are used for splicing, the upper surfaces of the upper outer frames 1 of each configuration unit are coplanar, and the lower surfaces of the lower outer frames 4 of each configuration unit are coplanar.

[0045] Preferably, when multiple configuration units are used for splicing, each configuration unit is arranged uniformly in an array. Figure 1 What is shown is a flat plate material formed by 64 structural units arranged in 8X8.

[0046] The "upper" and "lower" in this article are not limited to the "upper" and "lower" in the geographical sense. "Up" can be understood as the direction from which the external force is applied, and "lower" can be understood as the side opposite to the "upper". For example, when a flat plate-like material is placed horizontally on an object below and the external force comes from the upper surface, the upper surface of the flat plate-like material has the same meaning as the "upper" in this article. When a flat plate-like material is horizontally attached to the lower surface of an object and the external force comes from the lower surface, the lower surface of the flat plate-like material has the same meaning as the "upper" in this article. When a flat plate-like material is non-horizontally attached to the side of an object and the external force comes from the outside of the object, the surface of the flat plate-like material that is attached to the side of the object is the lower surface, and the side of the flat plate-like material away from the object is the upper surface.

[0047] The entire array unit can be integrally formed using 3D printing technology.

[0048] In addition, regarding the selection of structural parameters. For the elliptical ring structure, when the eccentricity of the elliptical ring is 0.73, the dynamic response peak and resonance frequency can be as low as possible in most stages of the entire compression process, which is more in line with the requirements for weakening high-frequency signals. Therefore, for the design of the elliptical ring structure, the eccentricity is preferably 0.6 to 0.8. The best is 0.73.

[0049] For the curved beam structure, the change in stiffness of its force-displacement curve is mainly related to the ratio of the height of the curved beam to the thickness of the curved beam. When the ratio of the height of the curved beam to the thickness of the curved beam is greater than 2.31, the stiffness of the force-displacement curve will drop rapidly after the elastic zone and a region where the force is less than zero will appear. This region is in an energy release state, which will cause the structure to be bistable, which will seriously affect the recoverability of the structure. Therefore, based on the demand for high recoverability of the structure, it is necessary to avoid the appearance of the energy release region as much as possible, that is, the ratio of the height to the thickness of the curved beam structure needs to be less than 2.31. Combined with the optimal solution of the eccentricity of the elliptical ring of 0.73, the ratio of the height to the thickness of the curved beam structure is between 2.31 and 1.

[0050] The deformation process of the mechanical metamaterial of the present invention when subjected to external force impact is schematically shown as follows: Figure 6 As shown. Among them, Figure 6(a) shows the initial state when the structure is not deformed; Figure 6 (b) is the state when the structure is slightly deformed; Figure 6 (c) is the state when the structure is moderately deformed; Figure 6 (d) is the state when the structure is fully deformed.

[0051] The working process of the mechanical metamaterial of the present invention is as follows:

[0052] 1. When there is no external impact, each component is in its initial state and the structure is not deformed.

[0053] 2. When impacted by external force, the elliptical ring and the curved beam will deform to a corresponding degree at the same time according to the magnitude of the external force.

[0054] For the curved beam structure, the curved beam is a cosine structure, which will first deform along the center and the two ends. It is manifested as a decrease in the height of the waveform (i.e., the amplitude), and at the same time, there will be a tendency to expand in the lateral direction (horizontally), but due to the effect of the external frame, the expansion of the curved beam will be prevented, trying to keep the volume of the structure unchanged. Its compression process shows a nonlinear response. Initially, the structure shows greater rigidity, but as the compression continues, the curved beam will enter the negative stiffness stage, making deformation easier.

[0055] For the elliptical ring structure, due to its geometric characteristics, deformation will first be reflected in the direction of the short axis, that is, the height of the ellipse (in the direction of the short axis) decreases, and the stretching in the direction of the long axis will increase accordingly. During the continuous compression process, the bending stiffness of the elliptical ring will gradually increase, especially after being compressed to a certain extent in the direction of the short axis, the deformation resistance of the structure will be significantly enhanced. This nonlinear effect is more significant in the early stage of compression, but as the compression deepens, the structural stiffness is further enhanced and the deformation rate will slow down. The overall performance is positive stiffness behavior.

[0056] Therefore, the mutual coupling of the positive stiffness elliptical ring structure and the negative stiffness curved beam structure enhances the force-displacement response curve of the mechanical metamaterial of the present invention, avoids stiffness degradation under large deformation, and makes the mechanical metamaterial more energy absorbing.

[0057] 3. When the external force disappears, the elastic potential energy stored in the buffer structure during the compression deformation process is released, and the curved beam recovers according to the degree of plastic deformation after the compression force disappears. The elliptical ring also shows a similar effect. The structure will recover according to the degree of plastic deformation after the force disappears, showing a good deformation recovery ability.

[0058] 4. When subjected to multiple continuous strong transient impacts, the elliptical ring and the curved beam will deform to corresponding degrees at the same time according to the magnitude of the external force.

[0059] For curved beam structures, under the action of multiple consecutive strong transient impacts, the waveform of the curved beam will be subjected to high-frequency dynamic loads. Due to its natural curvature, the curved beam structure can gradually bend or expand under the action of impact force, making the force action area wider, thereby achieving a higher energy absorption effect. However, each strong transient impact will cause the curved beam to undergo a brief but drastic deformation. Under the action of large impact energy, the curved beam may produce local buckling during a certain impact process, especially in places where the waveform curvature is large. Multiple impacts will aggravate the buckling phenomenon and may even cause nonlinear buckling or overall instability of the entire structure.

[0060] For the elliptical ring structure, it shows good energy absorption capacity when subjected to multiple impacts, especially in the direction of the short axis. The short axis will be compressed first when it is impacted, thus acting as a "cushion". This compression process can effectively absorb the impact energy and reduce the impact force directly transmitted to other parts. Compared with other shapes, the elliptical ring can gradually deform in a softer way, thereby absorbing the impact energy in stages and avoiding instantaneous stress concentration. Compared with irregular structures, the closed symmetry of the elliptical ring gives it better elastic deformation capacity.

[0061] Therefore, due to the advantages brought by the elliptical ring, it can bring better structural recovery, share the load of the curved beam structure in multiple impacts, and prevent the structure from failing due to severe instantaneous deformation caused by instantaneous high-energy impact due to stress concentration, so that the curved beam structure can play a better role. Therefore, the mechanical metamaterial structure of the present invention is more suitable for buffering multiple continuous strong transient impact scenarios.

[0062] Figure 7 Schematic diagram of static compressive stress-strain comparison between the mechanical metamaterial of the present invention and the existing mechanical metamaterial.

[0063] from Figure 7 It can be seen that the plastic region of the stress-strain curve of the mechanical metamaterial of the present invention has a larger platform stress than that of the existing mechanical metamaterials, and the structural stiffness changes smoothly, which can achieve large energy absorption. Through integral calculation, the energy absorption of the existing mechanical metamaterial is 123.81mJ, while the energy absorption of the mechanical metamaterial of the present invention can reach 162.62mJ, an increase of 31.35%.

[0064] Figure 8 Schematic diagram showing the comparison of the structural recovery of the mechanical metamaterial of the present invention and the existing mechanical metamaterial at different compression heights. Figure 8 It can be seen that under the same compression height condition, the structural recovery of the mechanical metamaterial of the present invention is much higher than that of the existing mechanical metamaterial structure, with an average improvement of 20%.

[0065] The mechanical metamaterial of the present invention can be preferably used in high-penetration projectile fuzes. Experimental verification shows that its energy absorption efficiency exceeds 60% under continuous multiple impacts of 10,000g, and exceeds 50% under high-energy impacts of 25,000g, both of which are significantly better than the level of less than 50% of existing mechanical metamaterials. For multiple impact signals buffered by the mechanical metamaterial of the present invention, the power share of the buffered high-frequency signal component (3000-10,000Hz) is greatly reduced, from 21.02% to 3.1%, further indicating that it can effectively reduce high-frequency impact energy transfer. In addition, the recovery ability of the mechanical metamaterial after multiple strong impacts is also far superior to that of existing materials. Through structural comparison of the same size (3.8mm*3.8mm*3.8mm) after three 25000g impacts, the structural height of the mechanical metamaterial of the present invention is reduced to 3.29mm (structural integrity: 86.58%), while the structural height of the existing mechanical metamaterial is reduced to 2.98mm (structural integrity: 78.42%). The advantages are obvious, ensuring stability and durability after multiple strong impacts.

Claims

1. A mechanical metamaterial, comprising one or more configuration units; the configuration unit comprises an upper outer frame (1) and a lower outer frame (4) opposite to the upper outer frame (1); characterized in that: An upper coupling structure (2) and a lower coupling structure (3) are provided between the upper outer frame (1) and the lower outer frame (4); The lower end of the upper coupling structure (2) is fixedly connected to the upper end of the lower coupling structure (3) via an independent middle support (5); The upper coupling structure (2) and / or the lower coupling structure (3) are cross-crossed elliptical ring-curved beam coupling structures.

2. The mechanical metamaterial according to claim 1, characterized in that: The upper coupling structure (2) comprises two upper curved beams (21, 22) with both ends bent toward the upper outer frame (1), and the two upper curved beams (21, 22) are cross-intersected at the midpoint; Two upper elliptical rings (23, 24) with their major axes crossing each other and their minor axes coaxial are provided between the upper curved beams (21, 22) and the upper outer frame (1); Both ends of the upper curved beams (21, 22) are fixedly connected to the lower end surface of the upper outer frame (1) via upper support columns (11, 12, 13, 14) respectively.

3. The mechanical metamaterial according to claim 2, characterized in that: The lower coupling structure (3) comprises two lower curved beams (31, 32) with both ends bent toward the lower outer frame (4), and the two lower curved beams (31, 32) are cross-intersected at the midpoint; Two lower elliptical rings (33, 34) with their major axes crossing each other and their minor axes coaxial are provided between the lower curved beams (31, 32) and the lower outer frame (4); The two ends of the lower curved beams (31, 32) are fixedly connected to the upper end of the lower outer frame (4) via a lower support column (41, 42, 43, 44) respectively.

4. The mechanical metamaterial according to claim 3, characterized in that: The upper end of the independent middle support (5) is fixedly connected to the lower ends of the cross intersection of the two upper curved beams (21, 22), and the lower end is fixedly connected to the upper ends of the cross intersection of the two lower curved beams (31, 32).

5. The mechanical metamaterial according to any one of claims 2 to 4, characterized in that: The eccentricity of the upper elliptical ring (23, 24) and / or the lower elliptical ring (33, 34) is 0.6 to 0.

8.

6. The mechanical metamaterial according to any one of claims 2 to 4, characterized in that: The eccentricity of the upper elliptical ring (23, 24) and / or the lower elliptical ring (33, 34) is 0.

73.

7. The mechanical metamaterial according to any one of claims 2 to 4, characterized in that: The ratio of the bending height of the upper curved beam (21, 22) and / or the lower curved beam (31, 32) to the beam thickness is between 2.3 and 1.

8. The mechanical metamaterial according to any one of claims 1 to 4, characterized in that: When multiple configuration units are spliced ​​together, the configuration units are arranged in an array to form an overall array of mechanical metamaterials.

9. The mechanical metamaterial according to claim 8, characterized in that: The mechanical metamaterial of the overall array is integrally formed by using 3D printing technology.

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