Controllable buffering energy-absorbing negative stiffness metamaterial

Abstract

The invention relates to the technical field of metamaterials, in particular to a controllable buffering and energy-absorbing negative-stiffness metamaterial which is formed by periodically arranging a plurality of same unit cells. The unit cell includes: a frame; the curved beam is arranged in the frame; the push rod is movably arranged on the frame and is in transmission connection with the curved beam; the air bag is arranged between the frame and the curved beam, and the air bag and the push rod are located on the two sides of the curved beam respectively; adjacent unit cells on different layers are connected with the middle parts of the curved beams and the bottom of the frame through push rods; the adjacent unit cells located on the same layer are connected through a shared frame. The curved beam is of a bistable structure, and after the curved beam is subjected to geometric deformation under the action of an external load, the curved beam can be converted from an initial first stable state to a second stable state and keep a configuration. A curved beam with a buckling step property and an air bag with controllable gas pressure are used, and through combination of the curved beam with the buckling step property and the air bag with controllable gas pressure, the negative stiffness metamaterial with the curved beam capable of being controlled to reset and used for buffering and energy absorption is constructed.

Description

Technical Field

[0001] This invention relates to the field of metamaterials technology, specifically to a controllable buffer energy-absorbing negative stiffness metamaterial. Background Technology

[0002] Negative stiffness metamaterials are a class of reusable, artificially designed metamaterials. Their reusability helps reduce maintenance costs, leading to widespread attention and significant progress in the field of reusable energy absorption buffers. The main mechanism by which these materials achieve energy absorption buffering lies in utilizing their negative stiffness to suppress the growth of structural reaction forces and absorbing energy through the multi-stable transition process of the structure. However, after absorbing energy through multi-stable transitions, negative stiffness metamaterials often fail to controllably return to their initial configuration, making them ineffective against the same or subsequent loads. This limitation has become a bottleneck restricting the further development and practical application of negative stiffness metamaterials in the field of energy absorption buffering. Summary of the Invention

[0003] To address the technical problems existing in the background art, the present invention provides a controllable buffer energy-absorbing negative stiffness metamaterial, which uses a curved beam with buckling step properties and an air bladder with controllable gas pressure, and constructs a negative stiffness metamaterial for buffer energy absorption with controllable reset of the curved beam through the combination of the two.

[0004] The technical solution adopted by this invention to solve its technical problem is: A controllable buffer-absorbing negative stiffness metamaterial, consisting of several identical unit cell periods arranged in a cycle; Single cells include: frame; Curved beams are installed inside the frame; The push rod is movably mounted on the frame and connected to the curved beam drive; An airbag is positioned between the frame and the curved beam, with the airbag and push rod located on opposite sides of the curved beam. Adjacent cells on different levels are connected by push rods between the middle of the curved beam and the bottom of the frame; adjacent cells on the same level are connected by a shared frame.

[0005] Furthermore, the curved beam has a bistable structure. After the curved beam undergoes geometric deformation under external load, it can transform from the initial first steady state to the second steady state and maintain its configuration.

[0006] Furthermore, the curved beam has a predetermined geometry, and its centerline is defined by the following formula: ; in, It is the ordinate of any point on the center line of the curved beam. It is the x-coordinate of that point. It is the arc height of the curved beam. It is the span of the curved beam.

[0007] Furthermore, the airbag is connected to a pressure regulating device via a hose, which can adjust the shape of the airbag and the internal gas pressure.

[0008] Furthermore, curved beams include: The middle beam connects to the push rod; The connecting beams are symmetrically arranged on both sides of the middle beam and are in a curved shape; The edge beam is located at the end of the connecting beam furthest from the middle beam and is fixedly connected to the frame.

[0009] Furthermore, the frame is a hollow frame structure, including: First border; The second frame is vertically set at both ends of the first frame and is fixedly connected to the side beam; The third frame is positioned across the upper end of the second frame and is slidably connected to the push rod.

[0010] Furthermore, the second frame has a groove, and the side beam is fixedly installed in the groove.

[0011] Furthermore, the pusher includes: beam; The longitudinal beam is vertically positioned in the middle of the transverse beam and is slidably connected to the third frame.

[0012] Furthermore, a hole is provided in the middle of the third frame, and the longitudinal beam is slidably inserted into the hole and abuts against the middle beam.

[0013] Furthermore, the thickness of the curved beam is 1 / 3 of the thickness of the third frame, and the thickness of the curved beam is 1 / 4 of the thickness of the second frame.

[0014] The beneficial effects of this invention are: (1) Breaking through the limitations of existing negative stiffness metamaterial buffer energy absorption design, a curved beam with buckling step properties and a gas bladder with controllable gas pressure are used. By combining the two, a negative stiffness metamaterial for buffer energy absorption with controllable reset of the curved beam is constructed. After the curved beam in the negative stiffness metamaterial enters the second stable state due to buffer energy absorption, the gas pressure inside the gas bladder can be adjusted by the pressure regulating device to allow the curved beam to return to its initial configuration in order to cope with subsequent impact loads.

[0015] (2) The curved beam adopts a bistable design, which can undergo a geometric configuration jump from the first steady state to the second steady state under external load. This process is accompanied by obvious negative stiffness characteristics, which can smoothly absorb impact energy and effectively suppress rebound, avoiding secondary impact. This makes the energy absorption process controllable and predictable, improving the reliability of the buffer.

[0016] (3) By connecting the airbag to the external pressure regulating device through a hose, the internal air pressure and shape of the airbag can be adjusted in real time, thereby changing the supporting effect and constraint conditions on the curved beam, and realizing the active control of the overall stiffness, critical buckling load and energy absorption characteristics of the structure. It can adapt to different impact velocities and energy levels and has good environmental adaptability.

[0017] (4) The curved beam adopts a combination structure of intermediate beams, connecting beams and edge beams. The curved connecting beams can distribute stress more evenly during deformation, delay local yielding or fracture, and improve the deformation capacity and recyclability of the curved beam. The fixed connection between the edge beams and the frame enhances interface stability and ensures deformation coordination.

[0018] (5) The push rod passes through the pre-reserved hole in the frame. The push rod is constrained by the hole in the frame and can only slide along the hole. This avoids the push rod deflection and the second-order unstable deformation mode of the curved beam, which is conducive to the generation of negative stiffness and improves the impact protection effect.

[0019] (6) By setting the thickness of the curved beam to 1 / 3 of the thickness of the third frame and 1 / 4 of the thickness of the second frame, the frame has the necessary support stiffness while ensuring that the curved beam is flexible enough to undergo steady-state change, thus achieving an optimized balance between lightweight and load-bearing capacity in the overall structure.

[0020] (7) Push rods, frames and curved beams can be directly processed using additive manufacturing technology, and the relevant steps are completed by machines to achieve mass production. Attached Figure Description

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0022] Figure 1 This is a three-dimensional structural diagram of a curved beam in a unit cell in the first steady state; Figure 2 This is a schematic diagram of a three-dimensional structure of a curved beam in a unit cell in the second steady state; Figure 3 This is a three-dimensional structural diagram of the push rod; Figure 4 This is a three-dimensional structural diagram of the frame; Figure 5 This is a three-dimensional structural diagram of the curved beam; Figure 6 This is a three-dimensional structural diagram of the metamaterial in its first stable state after the airbag is pressurized; Figure 7 This is a three-dimensional structural diagram of the metamaterial in its second stable state after the airbag is depressurized; Figure 8 This is a schematic diagram of the structure of the test specimen used for experimental testing of this invention; Figure 9It is a diagram of the experimental process used to obtain the force-displacement curves of metamaterials; Figure 10 These are force-displacement curves of metamaterials obtained through experiments; Figure 11 This is a schematic diagram illustrating the principle of changing the mechanical properties of a unit cell by adjusting the gas pressure inside the airbag.

[0023] In the picture: 1. Push rod, 2. Frame, 3. Curved beam, 4. Airbag, 5. Hose, 6. Pressure regulating device; 11. Horizontal beam; 12. Longitudinal beam; 21. First border; 22. Second border; 23. Third border; 24. Hole; 25. Groove; 31. Intermediate beam, 32. Connecting beam, 33. Edge beam. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to the accompanying drawings.

[0025] like Figure 1 , 2 As shown, a controllable buffer-absorbing negative stiffness metamaterial is composed of several identical unit cells arranged periodically. The specific structure of each unit cell includes a frame 2, with a curved beam 3 installed inside the frame 2. A push rod 1 is movably mounted on the frame 2 and is drively connected to the curved beam 3. An air bladder 4 is disposed between the frame 2 and the curved beam 3, with the air bladder 4 and push rod 1 located on opposite sides of the curved beam 3. Adjacent unit cells in different layers are connected to the middle of the curved beam 3 and the bottom of the frame 2 via push rod 1; adjacent unit cells in the same layer are connected via a shared frame 2. Multiple unit cells are connected to form a multicellular metamaterial structure.

[0026] The curved beam 3 has a bistable structure. After undergoing geometric deformation under external load, the curved beam 3 can transform from the initial first stable state to the second stable state while maintaining its configuration. In a specific embodiment, the curved beam 3 has a preset geometric shape, and its centerline is defined by the following formula: ; in, It is the ordinate of any point on the center line of the curved beam 3. It is the x-coordinate of that point. It is the arc height of curved beam 3. It is the span of the curved beam 3.

[0027] The airbag 4 is connected to a pressure regulating device 6 via a flexible tube 5. The pressure regulating device 6 can adjust the shape and internal gas pressure of the airbag 4, thereby changing the stable state of the curved beam 3. The change in the stable state of the curved beam 3 also alters the mechanical properties of the metamaterial. In a specific embodiment, the pressure regulating device 6 can be selected as a syringe. When the curved beam 3 in the unit cell is in the first steady state, the airbag 4 is in a depressurized state. After the curved beam 3 in the unit cell reaches the second steady state due to external loads, the airbag 4 is pressurized and expanded, causing the curved beam 3 to return from the second steady state to the initial first steady state in order to cope with subsequent loads.

[0028] This invention features controllable reset. After the curved beam 3 deforms under stress and enters a second stable state, the gas pressure inside the airbag 4 can be controllably adjusted by the pressure regulating device 6, thereby changing the load acting on the curved beam 3 and controlling the curved beam 3 to return from the second stable state to the first stable state. During loading, the force transmission path in the unit cell is push rod 1-curved beam 3-airbag 4. When controlling the gas pressure of the airbag 4 to restore the curved beam 3 to its initial configuration, the force transmission path is airbag 4-curved beam 3-push rod 1, using the gas pressure inside the airbag 4 to push the curved beam 3 from the second stable state back to the first stable state.

[0029] like Figure 5 As shown, the specific structure of the curved beam 3 includes a central beam 31, which is connected to the push rod 1. Connecting beams 32 are symmetrically arranged on both sides of the central beam 31 and are curved. Side beams 33 are located at the end of the connecting beams 32 away from the central beam 32 and are fixedly connected to the frame 2. When the curved beam 3 is in its first stable state, the bending direction is upward; when it is in its second stable state, the bending direction is downward. The central part of the curved beam 3 is a planar central beam 31, which is fixedly connected to the longitudinal beam 12 of the push rod 1. The side beams 33 at the ends of the curved beam 3 are fixedly connected to the grooves 25 reserved in the frame 2.

[0030] The upper surface of the airbag 4 is fixedly connected to the middle beam 31 of the curved beam 3. When subjected to external load, causing the curved beam 3 to transition from the first stable state to the second stable state, the airbag 4 is in a depressurized state. When it is necessary to restore the curved beam 3 from the second stable state to the first stable state, the airbag 4 is pressurized through the pressure regulating device 6, thereby providing thrust to the curved beam 3, and the airbag 4 is in a pressurized state.

[0031] like Figure 4 As shown, frame 2 is a hollow frame structure, specifically including a first frame 21. A second frame 22 is vertically disposed at both ends of the first frame 21 and is fixedly connected to the side beam 33. A third frame 23 is horizontally disposed across the upper end of the second frame 22 and is slidably connected to the push rod 1. The second frame 22 has a groove 25, and the side beam 33 is fixedly disposed in the groove 25.

[0032] like Figure 3As shown, the specific structure of the push rod 1 includes a crossbeam 11. A longitudinal beam 12 is vertically disposed in the middle of the crossbeam 11 and is slidably connected to the third frame 23. A hole 24 is provided in the middle of the third frame 23, and the longitudinal beam 12 is slidably inserted into the hole 24 and abuts against the intermediate beam 31. The hole 24 can constrain the push rod 1 so that it can only slide in the hole 24 and cannot deflect. The longitudinal beam 12 of the push rod 1 is fixedly connected to the intermediate beam 31 in the middle of the curved beam 3.

[0033] Furthermore, the thickness of the curved beam 3 is 1 / 3 of the thickness of the third frame 23, and the thickness of the curved beam 3 is 1 / 4 of the thickness of the second frame 22. The length of the longitudinal beam 12 is 3 / 25 to 4 / 25 of the length of the transverse beam 11. The length of the second frame 22 is 33 / 100 to 34 / 100 of the length of the first frame 21.

[0034] Figure 6 and Figure 7 This is a schematic diagram of the metamaterial structure in the first and second stable states according to an embodiment of the present invention. As shown in the figure, the metamaterial structure consists of multiple periodically arranged unit cells. Adjacent unit cells on the left and right sides are fixedly connected to each other by a shared frame 2, and adjacent unit cells on the top and bottom are connected by push rods 1 to the middle of the curved beam 3 and the bottom of the frame 2. When the air bladders 4 in the unit cells of the metamaterial are pressurized, the metamaterial is in the first stable state. When the air bladders 4 in the unit cells of the metamaterial are depressurized due to load, the metamaterial is in the second stable state.

[0035] like Figure 8 This is a schematic diagram of the specimen used for experimental testing of the present invention. Figure 9 Figure 1 shows the experimental process for obtaining the force-displacement curve of the metamaterial in this embodiment of the invention. Figure 2 shows the first step: initially, the airbag 4 is unpressurized, and the air pressure inside the airbag 4 is close to 0 MPa. Figure 3 shows the second step: when the air pressure in the airbag 4 is close to 0 MPa, a load is applied to the metamaterial, causing the curved beam 3 in the single-cell structure to undergo elastic deformation, transitioning from the first steady state to the second steady state. Figure 4 shows the third step: when the air pressure in the airbag 4 is close to 0 MPa, a load is continuously applied to the metamaterial, causing the two-cell structure to transition from the first steady state to the second steady state. Through the above process, force-displacement images of the curved beam 3's stiffness change in three segments—positive stiffness, negative stiffness, and positive stiffness—are obtained. Figure 5 shows the fourth step: the air pressure inside the airbag 4 is adjusted to 6.7 MPa by the pressure regulating device 6. The pressurized airbag 4 applies an upward load to the curved beam 3, thereby restoring the single-cell structure to the first steady state. As shown in Figure (V), in the fifth step, when the air pressure inside airbag 4 is 6.7 MPa, an upward load is continuously applied to the curved beam 3 through airbag 4, and finally both unit cell structures recover to the first steady state. The above experimental process demonstrates the tunability of the mechanical properties of this negative stiffness metamaterial and its buffering and energy absorption effect.

[0036] Figure 10This is a graph showing the force and displacement of the metamaterial obtained experimentally in an embodiment of the present invention. Figure 9 The experiment shows the force and displacement images of the stiffness changes of the curved beam 3 in the metamaterial structure, which are divided into three stiffness segments: positive stiffness, negative stiffness, and positive stiffness. Because the metamaterial specimen has a two-layer unit cell structure, the image shows the force and displacement images of the three stiffness segments: positive stiffness, negative stiffness, and positive stiffness.

[0037] Figure 11 This is a schematic diagram illustrating the principle of changing the mechanical properties of a unit cell by adjusting the internal gas pressure of the airbag in an embodiment of the present invention. Figure (a) shows the pressure regulating device and airbag 4 in this embodiment. By changing the internal pressure of the airbag 4 through the pressure regulating device, the airbag 4 exhibits different force-displacement curves under external force, achieving adjustable positive stiffness. Figure (b) shows the force-displacement response curve of the curved beam 3 under the constraint of the push rod 1 and the frame 2. The stiffness change of the curved beam 3 is divided into three segments: positive stiffness, negative stiffness, and positive stiffness. Figure (c) shows the force-displacement curve of the unit cell. Because the airbag 4 and the curved beam 3 in the unit cell are connected in parallel, the contact area between the airbag 4 and the curved beam 3 shown in the figure is 80 mm². 2 The force-displacement curve of the unit cell is generated by superimposing the force-displacement curves of airbag 4 and curved beam 3. When the pressure of airbag 4 is close to zero, the force-displacement curve of the unit cell exhibits three stiffness variations: positive stiffness, negative stiffness, and positive stiffness. When the pressure of airbag 4 is sufficiently high (4 kPa in the figure), the force-displacement curve of the unit cell exhibits three stiffness variations: positive stiffness, quasi-zero stiffness, and positive stiffness. The presence of negative stiffness and quasi-zero stiffness indicates that the structure can absorb energy while limiting structural reaction forces, achieving good buffering and energy absorption. Furthermore, as the pressure of airbag 4 increases, the envelope area of ​​the force-displacement curve of the unit cell with the horizontal axis gradually increases. This indicates that the increase in airbag 4 pressure improves the energy absorption capacity of the unit cell, enabling the unit cell to cope with larger impact loads.

[0038] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A controllable buffer energy-absorbing negative stiffness metamaterial, characterized in that, It is composed of several identical unit cells arranged in a cycle; The unit cell includes: Framework (2); A curved beam (3) is installed inside the frame (2); The push rod (1) is movably mounted on the frame (2) and is connected to the curved beam (3) in a transmission manner; An airbag (4) is disposed between the frame (2) and the curved beam (3), and the airbag (4) and the push rod (1) are respectively located on both sides of the curved beam (3); Adjacent units located on different layers are connected by push rods (1) to the middle of the curved beam (3) and the bottom of the frame (2); adjacent units located on the same layer are connected by a shared frame (2).

2. The controllable buffer energy-absorbing negative stiffness metamaterial according to claim 1, characterized in that, The curved beam (3) has a bistable structure. After the curved beam (3) undergoes geometric deformation under external load, the curved beam (3) can transform from the initial first stable state to the second stable state and maintain its configuration.

3. The controllable buffer energy-absorbing negative stiffness metamaterial according to claim 2, characterized in that, The curved beam (3) has a preset geometric shape, and its centerline is defined by the following formula: ； in, It is the ordinate of any point on the center line of the curved beam (3). It is the x-coordinate of that point. It is the arc height of the curved beam (3). It is the span of the curved beam (3).

4. The controllable buffer energy-absorbing negative stiffness metamaterial according to claim 1, characterized in that, The airbag (4) is connected to a pressure regulating device (6) via a hose (5), which can adjust the shape of the airbag (4) and the internal gas pressure.

5. The controllable buffer energy-absorbing negative stiffness metamaterial according to claim 1, characterized in that, The curved beam (3) includes: The intermediate beam (31) is connected to the push rod (1); The connecting beam (32) is symmetrically arranged on both sides of the intermediate beam (31) and is in a curved shape; Side beam (33) is located at one end of the connecting beam (32) away from the middle beam (32) and is fixedly connected to the frame (2).

6. The controllable buffer energy-absorbing negative stiffness metamaterial according to claim 5, characterized in that, The frame (2) is a hollow frame structure, including: First border (21); The second frame (22) is vertically disposed at both ends of the first frame (21) and is fixedly connected to the side beam (33); The third frame (23) is positioned across the upper end of the second frame (22) and is slidably connected to the push rod (1).

7. The controllable buffer energy-absorbing negative stiffness metamaterial according to claim 6, characterized in that, The second frame (22) has a groove (25), and the side beam (33) is fixedly disposed in the groove (25).

8. The controllable buffer energy-absorbing negative stiffness metamaterial according to claim 6, characterized in that, The push rod (1) includes: Crossbeam (11); The longitudinal beam (12) is vertically disposed in the middle of the transverse beam (11) and is slidably connected to the third frame (23).

9. A controllable buffer energy-absorbing negative stiffness metamaterial according to claim 8, characterized in that, The third frame (23) has a hole (24) in the middle, and the longitudinal beam (12) is slidably inserted into the hole (24) and abuts against the middle beam (31).

10. The controllable buffer energy-absorbing negative stiffness metamaterial according to claim 1, characterized in that, The thickness of the curved beam (3) is 1 / 3 of the thickness of the third frame (23), and the thickness of the curved beam (3) is 1 / 4 of the thickness of the second frame (22).

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