Energy absorbing structure and design method

Abstract

The present invention discloses an energy absorbing structure and a design method, and relates to the fields of structural mechanics and material engineering. Traditional energy absorbing structures have the problems of low energy absorption efficiency, poor performance under complex force conditions, and poor structural reusability. The present invention provides an energy absorbing structure and a design method, including an energy absorbing structure; the front and back sides of the energy absorbing structure are symmetrically arranged and have energy absorbing components with the same arrangement and configuration, and two groups of energy absorbing components are connected by a connecting plate; each group of energy absorbing components is a modular structure composed of 4 energy absorbing units, and the 4 energy absorbing units are arranged in a square array at the four corners of the connecting plate, and the directions of every two energy absorbing units are perpendicular to each other, so that the energy absorbing components form a self-locking shape; multiple energy absorbing components and connecting plates form a large-scale energy absorbing group through self-locking, and the large-scale energy absorbing group will not detach or splash under impacts from all directions. The present invention can effectively reduce the damage to the main structure caused by impact.

Description

Technical Field

[0001] The invention relates to the field of structural mechanics and material engineering technology, and in particular to an energy absorbing structure and a design method thereof. Background Art

[0002] In modern engineering structure design, energy-absorbing structures are increasingly used, especially in the fields of automobiles, aerospace, construction and industrial equipment. The design and optimization of energy-absorbing structures are of great significance for improving safety and reliability. The main function of energy-absorbing structures is to effectively absorb energy through structural deformation when impacted by external forces, reduce the damage to the main structure caused by the impact force, and ensure the safety of equipment and personnel. However, existing energy-absorbing structures have some limitations, such as:

[0003] The energy absorption efficiency of traditional energy-absorbing structures is low. Most traditional energy-absorbing structures rely on a single deformation mechanism, such as plastic deformation or elastic deformation, and cannot effectively absorb energy within the full impact range. When impacted, the energy absorption efficiency is low, and the performance is unstable under different impact conditions, making it difficult to provide consistent protection. Poor performance under complex stress conditions. Under multi-directional impact or complex stress conditions, many existing energy-absorbing structures cannot adapt well to stress distribution in different directions and can often only be optimized for a single direction, resulting in poor energy absorption performance in complex environments.

[0004] Poor structural reusability. Some traditional energy-absorbing structures often produce irreversible plastic deformation after a large deformation or impact, and lose the ability to continue to be used, resulting in increased maintenance costs. Although some structures can be reused through partial elastic recovery, they have limitations in energy absorption performance. Difficult to adjust and optimize. Traditional energy-absorbing structures usually rely on material selection and geometric design to optimize energy absorption, and rarely involve modular and multi-level structural design. This method is difficult to adapt to the needs of various occasions, and it is impossible to flexibly adjust the energy absorption characteristics of the structure according to different impact conditions.

[0005] Therefore, how to design an energy-absorbing structure that can adapt to multi-directional impacts, has high energy absorption capacity and has a certain degree of reusability has become an important issue in the current research field. In addition, the modular design of the energy-absorbing structure and the optimization of the arrangement method are also important directions to solve the low energy absorption efficiency under complex impact conditions. Summary of the invention

[0006] The present invention proposes an energy absorption structure and design method to solve the defects in the above-mentioned prior art. It has the advantages of efficient energy absorption, adaptability to multi-directional impact, reusability and strong structural stability, and is intended to ensure equipment safety and personnel protection under complex impact conditions, thereby effectively reducing the damage to the main structure caused by the impact, extending the service life of the equipment and reducing maintenance costs.

[0007] To achieve the above purpose, the technical idea of ​​the present invention is:

[0008] (1) The energy absorption structure of the present invention adopts energy absorption components that are symmetrically arranged on the front and back sides to ensure that the energy absorption performance of the structure is consistent in multi-directional impacts. Each group of energy absorption components includes multiple energy absorption units, which are interconnected by unit connecting plates to ensure the stability and consistency of the overall structure. The energy absorption units are arranged in a matrix at the four corners of the connecting plate, and the directions of every two energy absorption units are perpendicular to each other, ensuring that energy can be effectively absorbed in different impact directions.

[0009] (2) Each energy absorption unit of the present invention includes a bistable beam and a plastic shell. The bistable beam provides negative stiffness energy absorption by state switching under the action of external force, which is suitable for absorbing small impact energy; when the impact intensity is large, the plastic shell enters the plastic deformation stage, and further absorbs the impact energy through deformation, thereby protecting the main structure under large impact. The upper and lower ends of the energy absorption unit are respectively provided with an upper connecting plate and a lower connecting plate, which are used to keep the bistable beam fixed and the force transmitted, thereby enhancing the overall stability of the structure. At the same time, the energy absorption units are connected by connecting plates to ensure that the units work together during the impact process and effectively disperse the impact force.

[0010] (3) Multiple energy-absorbing components and connecting plates are connected through self-locking modules to form a large-scale energy-absorbing group. The design of the self-locking module ensures that the structure can remain stable under impact in all directions without additional fixing devices, without detachment or splashing, thereby enhancing the impact resistance and safety of the energy-absorbing group, and is suitable for complex impact environments in multiple scenarios.

[0011] To achieve the above purpose, the technical solution adopted by the present invention is:

[0012] An energy absorbing structure and a design method, comprising an energy absorbing structure; energy absorbing components of the front and back sides of the energy absorbing structure are symmetrically arranged and have the same arrangement and configuration, and two groups of energy absorbing components are connected by a connecting plate; each group of energy absorbing components is a modular structure composed of four energy absorbing units, and the four energy absorbing units are arranged in a square array at four corners of the connecting plate, and the directions of every two energy absorbing units are perpendicular to each other, so that the energy absorbing components form a self-locking shape; multiple energy absorbing components and the connecting plate form a large-scale energy absorbing group through self-locking, and the large-scale energy absorbing group will not separate and splash under impact from all directions.

[0013] Furthermore, the energy absorption unit includes: a bistable beam having two stable states, which can switch states under the action of external force and repeatedly absorb energy through negative stiffness during the switching process; a plastic energy absorption part, the front and rear surfaces and the bottom surface are hollowed out to form a hollow structure, and its hollow part is connected to the bistable beam, and after absorbing energy through negative stiffness, it enters the plastic deformation stage and continues to absorb energy efficiently and in large quantities.

[0014] Furthermore, each energy absorbing unit also includes an upper connecting plate and a lower connecting plate, wherein the upper connecting plates are arranged at intervals at the bottom of the plastic energy absorbing member, and a hollow portion of the bottom surface of the plastic energy absorbing member is formed by the two upper connecting plates; the lower connecting plate is arranged at the bottom of the bistable beam to maintain the structural stability of the energy absorbing unit and provide effective force transmission.

[0015] Furthermore, the cross section of the plastic energy absorbing member is a semicircular structure.

[0016] Furthermore, a flat plate is provided on the top of the plastic energy absorbing member.

[0017] Furthermore, the bistable beam is an arc-shaped plate structure composed of a first convex arc segment, a second concave arc segment and a third convex arc segment with smooth transition.

[0018] Furthermore, the first convex arc segment and the second convex arc segment are symmetrical to two sides of the second concave arc segment.

[0019] Furthermore, the final parameters of the bistable beam are selected as h0=4 mm, t0=0.2 mm, and d0=18 mm.

[0020] To achieve the above object, the present invention comprises the following steps:

[0021] S1. Determine the optimal parameters of the bistable beam structure:

[0022] Constructing the theoretical model: drawing the parameter design domain and determining the maximum width d of the bistable beam 0max Minimum width d with upper connecting plate 1min ;

[0023] Construct a finite element model: select different parameter groups in the bistable beam parameter design domain, draw the model and simulate it in the finite element software ABAQUS / Explicit to study the stability of the negative stiffness energy absorption of the bistable beam structure under impact conditions;

[0024] Determine the influence of thickness and height on the dynamic performance of the bistable beam: According to the simulation results, the influence of comprehensive parameters on energy absorption performance is selected to select the final parameters of the bistable beam;

[0025] S2. Determine the parameters of plastic energy absorbing parts

[0026] Build theoretical model: Establish a plastic hinge theoretical model, predict the structural performance of plastic energy absorbers through theoretical calculation, and study the performance difference of plastic energy absorbers in two stages and the overall energy absorption performance of the structure;

[0027] Establish finite element model: draw energy absorbing unit models with different plastic energy absorbing parts geometric parameters and simulate them in finite element software ABAQUS / Explicit to study the performance of plastic energy absorbing parts structure under different plastic energy absorbing parts parameters;

[0028] S3. Determine the optimal configuration of the energy absorbing structure

[0029] According to the two-stage stroke ratio, two-stage force ratio, two-stage energy absorption ratio, and effective energy absorption stroke U eff , total energy absorption EA, mass specific energy absorption SEA m , volume specific energy absorption SEA V , deformation stability, it is concluded that the plastic energy absorbing structure has better load-bearing and energy-absorbing performance when it is thicker, round in shape and has a small flat plate on the top;

[0030] S4. Dynamic response of the test system at different impact velocities.

[0031] The parameters in step S2 specifically include determining the plastic shell thickness t: through the simulation results of structures with different plastic shell thicknesses t and the theoretical prediction results, it is concluded that the thickness t of the plastic shell mainly affects the force ratio and energy absorption ratio of the two stages, and the structure has better energy absorption performance when the thickness is larger;

[0032] Determine the height h of the plastic shell: Through the simulation results and theoretical prediction results of structures with different plastic shell heights h, it is concluded that the height h of the plastic shell mainly affects the stroke ratio of the two stages. When the plastic shell is circular, the structure has better energy absorption performance;

[0033] Determine the length p of the plastic shell plate: Designing a flat plate at the top of the plastic shell is beneficial to the deformation stability of the structure, and the length of the plate should be small.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1. The energy absorption structure of the present invention ensures that the energy absorption performance can be maintained consistently in multi-directional impacts through energy absorption components symmetrically arranged on the front and back sides. Each energy absorption component is composed of multiple energy absorption units, which are arranged in a matrix at the four corners of the connecting plate, and the directions of every two energy absorption units are arranged perpendicular to each other. This design can not only absorb energy in the horizontal and vertical directions at the same time, but also optimize the force distribution of the structure, thereby improving the energy absorption efficiency in complex force environments and ensuring effective protection of the structure under various impact conditions.

[0036] 2. The present invention adopts a combined design of a bistable beam and a plastic shell. Each energy absorption unit provides negative stiffness energy absorption through the bistable beam in the event of a small impact. When the impact intensity is large, the plastic shell enters the plastic deformation stage to further absorb the impact energy. This dual-mechanism energy absorption structure effectively improves the energy absorption efficiency, especially it can provide multi-level energy absorption under different impact intensities. In addition, the energy absorption unit is fixed by the upper connecting plate and the lower connecting plate, which ensures the stability of the bistable beam and the transmission of force. At the same time, the synergy between the units is achieved through the connecting plate, so that the entire energy absorption structure has good stability and consistent mechanical performance.

[0037] 3. The present invention realizes the rapid and stable connection between the energy absorption component and the connecting plate through the design of the self-locking module, without the need for additional fixing devices, thereby greatly improving the assembly efficiency. The self-locking module can ensure that the structure does not detach or splash under impact from all directions, enhances the stability and impact resistance of the energy absorption group, and avoids structural failure in high-stress environments. This design is suitable for a variety of complex impact scenarios, such as traffic collisions or industrial protection, ensuring the safety and reliability of the energy absorption system under different impact conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0039] Figure 1 is a structural diagram of an energy absorbing structure according to the present invention;

[0040] Figure 2 yes Figure 1 Structural diagram of the middle energy absorption unit;

[0041] Figure 3 yes Figure 2 The structural exploded diagram of the energy absorbing unit;

[0042] Figure 4 is the geometric parameter of the multi-mechanism self-locking energy-absorbing structure;

[0043] Figure 5 is the deformation of the multi-mechanism self-locking energy-absorbing structure under distributed load impact: (a) deformation of the energy-absorbing unit, (b) deformation of the unit, (c) deformation of the system;

[0044] Figure 6 These are the following: (a) force-displacement curves of three different scales for the multi-mechanism self-locking energy-absorbing structure under distributed load impact; (b) the areas enclosed by the three force-displacement curves;

[0045] Figure 7 It is the loading and unloading of the multi-mechanism self-locking energy-absorbing structure under the impact of distributed loads;

[0046] Figure 8 It is a schematic diagram of the geometric parameters of the bistable beam;

[0047] Fig. 9 is the design domain of bistable beam parameters;

[0048] Fig.10 is the peak force F in the negative stiffness segment 1,max Comparison of simulation and theoretical calculation results;

[0049] Fig.11 The load-bearing and energy-absorbing performance of the bistable beam varies with the parameters in the design domain: (a) Peak force F 1，max , (b) energy absorption EA1, (c) mass specific energy absorption SEA m , (d) Volumetric specific energy absorption SEA V ;

[0050] Fig.12 It is an energy absorbing unit model with different bistable beam geometric parameters;

[0051] Fig.13 It is the simulation result of loading-unloading of bistable beams with different parameters at a certain speed;

[0052] Fig.14 is the initial force F in the plastic stage 2,0 Derivation: (a) distribution of plastic point hinges in the structure, (b) stress conditions of the structure;

[0053] Fig.15 is the initial force F in the plastic stage 2,0 Comparison of simulation and theoretical calculation results;

[0054] Fig.16 The influence of the plate at the top of the plastic shell on the deformation mode of the negative stiffness section of the system: (a) unstable deformation without the plate, (b) adding a plate design at the top of the plastic shell, (c) stable deformation with the plate;

[0055] Fig.17 is the effect of the plastic shell thickness t on the structural bearing capacity;

[0056] Fig.18 The influence of the plastic shell thickness t on the structural performance: (a) two-stage stroke ratio, (b) two-stage force ratio, (c) two-stage energy absorption ratio, (d) effective energy absorption stroke u eff , total energy absorption EA, mass specific energy absorption SEA m And volume specific energy absorption SEA V ;

[0057] Fig.19 The influence of the height h of the plastic shell on the bearing capacity of the structure: (a) the force-displacement curve of the structure under different h, (b) the segmented bearing phenomenon of the plastic section when h is small;

[0058] Fig. 20The influence of the plastic shell height h on the structural performance: (a) two-stage stroke ratio, (b) two-stage force ratio, (c) two-stage energy absorption ratio, (d) effective energy absorption stroke u eff , total energy absorption EA, mass specific energy absorption SEA m And volume specific energy absorption SEA V ;

[0059] Fig.21 is the effect of the plate length p on the deformation mode of the negative stiffness section of the system: (a) Models with different plate lengths, (b) Deformation of the system with different plate lengths in the negative stiffness section;

[0060] Fig. 22 is the effect of the plate length p on the bearing capacity of the structure;

[0061] In the figure: 1. energy absorbing component; 11. energy absorbing unit; 111. bistable beam; 1111. first convex arc segment; 1112. second concave arc segment 1112; 1113. third convex arc segment; 112. plastic shell; 113. upper connecting plate; 114. lower connecting plate; 2. connecting plate. DETAILED DESCRIPTION

[0062] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings.

[0063] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0064] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0065] Embodiment 1

[0066] Combination Figures 1 to 22The present invention discloses an energy absorbing structure and a design method, including energy absorbing components 1 symmetrically arranged on the front and back sides and having the same arrangement and configuration, two groups of energy absorbing components 1 are connected by a connecting plate 2; each group of energy absorbing components 1 is a modular structure composed of four energy absorbing units 11, and the four energy absorbing units 11 are arranged in a square array at the four corners of the connecting plate 2, and the directions of every two energy absorbing units 11 are perpendicular to each other, so that the energy absorbing components 1 form a self-locking shape; multiple energy absorbing components 1 and the connecting plate 2 form a large-scale energy absorbing group through self-locking, and the large-scale energy absorbing group will not be separated or splashed under impact from all directions.

[0067] Specifically, the front and back sides of the energy absorbing structure both use symmetrically arranged energy absorbing components 1, which have the same arrangement and configuration. The front and back energy absorbing components 1 are connected to each other through a unit connecting plate 2, so that when impacted, the energy absorbing behaviors of the front and back sides remain consistent.

[0068] Specifically, the energy absorption assembly 1 is composed of four energy absorption units 11, and the four energy absorption units 11 are arranged in a matrix form through the unit connection plate 2, and the directions of every two energy absorption units 11 are perpendicular to each other. The upper and lower energy absorption units 11 are connected by the connection plate 2 in the vertical direction, and the left and right energy absorption units 11 are connected to each other by the connection plate 2 in the horizontal direction. This arrangement not only ensures that each energy absorption unit 11 can deform and absorb energy independently, but also through the mutual support between adjacent units, the entire energy absorption structure can evenly distribute the force transmission and deformation when subjected to a large range of impacts, providing a stable energy absorption effect.

[0069] Specifically, each energy absorbing unit 11 includes a bistable beam 111, which has two stable states and can switch states under the action of external force and repeatedly absorb energy through negative stiffness during the switching process; a plastic energy absorbing member 112, the front and rear surfaces and the bottom surface are hollowed out to form a hollow structure, and its hollowed-out part is connected to the bistable beam 111, and after absorbing energy through negative stiffness, it enters the plastic deformation stage and continues to absorb energy efficiently and in large quantities.

[0070] It is worth noting that the core feature of the bistable beam 111 is that it has two stable states, and when subjected to external force, it can switch from one stable state to another stable state. During the state switching process, the bistable beam 111 will experience a negative stiffness stage, which can effectively absorb impact energy. The existence of the negative stiffness stage enables the structure to absorb initial impact energy through elastic deformation when it is slightly deformed.

[0071] like Figure 2The bistable beam 111 is a cosine beam, and two upper and lower connecting plates 2 are added to the top and bottom of the bistable beam 111. The lower connecting plate 114 not only limits the rotational freedom of the midpoint of the beam, but also allows the bistable beam 111 to fully deform and switch to a stable state across the critical point; the upper connecting plate 113 constrains the translational and rotational freedoms of both ends of the beam, achieving an effect similar to that of a fixed support constraint. The above design enables the bistable beam 111 structure to achieve a stable state switch in the negative stiffness energy absorption stage without rebound, thereby achieving an effective energy absorption effect.

[0072] Specifically, the bistable beam 111 is an arc-shaped plate structure formed by a first convex arc segment 1111, a second concave arc segment 1112 and a third convex arc segment 1113 formed in one piece, and the first convex arc segment 1111 and the second convex arc segment 1113 are symmetrical on both sides of the second concave arc segment 1112.

[0073] Specifically, the geometric shape of the bistable beam 111 affects its stability and energy absorption capacity. Experiments show that when the height of the bistable beam 111 is high and the thickness is small, its stability is the best. This is because the taller beam can withstand a larger displacement, while the thinner thickness enables it to provide a longer energy absorption time in the negative stiffness stage, so that the overall structure exhibits better energy absorption during the impact process.

[0074] Specifically, the plastic energy absorbing member 112 is wrapped around the outside of the bistable beam 111. When the cross-section of the plastic energy absorbing member 112 is a semicircular structure and a flat plate is provided on the top, the impact force can be dispersed in a larger range, the bearing capacity is stronger, and more energy can be absorbed during the plastic deformation process.

[0075] Specifically, the plastic energy absorbing member 112 can further absorb more impact energy after the bistable beam 111 undergoes state switching and absorbs part of the energy. The plastic energy absorbing member 112 will enter the plastic deformation stage when the impact energy is large, and absorb additional energy through deformation, thereby further improving the energy absorption effect.

[0076] Specifically, each energy absorbing unit 11 also includes an upper connecting plate 113 and a lower connecting plate 114. The upper connecting plate 113 is arranged at intervals at the bottom of the plastic energy absorbing member 112, and a hollow portion of the bottom surface of the plastic energy absorbing member is formed by the two upper connecting plates; the lower connecting plate 114 is arranged at the bottom of the bistable beam 111 to maintain the structural stability of the energy absorbing unit 11 and provide effective force transmission. The upper connecting plate 113 is connected to the unit connecting plate 2 to provide support for the energy absorbing unit 11 in the upper and lower directions during the impact process. The lower connecting plate 114: provides support for the bistable beam 111 in the lower direction, and is interconnected with the lower energy absorbing unit 11 to form a stable overall structure. These connecting plates 2 not only play a role in force transmission inside the energy absorbing unit 11, but also can ensure the coordinated work of each unit in the multi-unit modular structure when subjected to external forces, thereby ensuring structural stability.

[0077] 2. Example of performance analysis of multi-mechanism self-locking energy absorption structure

[0078] The geometric features of the multi-mechanism self-locking energy absorption structure are as follows: Figure 4 As shown. Since the unit has a high degree of symmetry, we take the energy absorbing unit 11 as an example to introduce the structural parameters: the span of the cosine bistable beam 111 is l0, the height is h0, the thickness is t0, and the width is d0; the lower connecting plate 114 of the bistable beam 111 is h0, the thickness is t, the width is d0, and the spacing is l'; the upper connecting plate 113 is t, the width is d1, the length is l, and the spacing with the bistable beam 111 is d2; the shape of the plastic energy absorbing member 112 is circular, with a diameter of l, a height of h, a thickness of t, and a width of d. There is a correlation between the parameters, which is expressed by the following formula:

[0079] l=l0+l'=11l'=2d=2(d0+2d1+2)=2h=10l', (1.1)

[0080] That is, the unit can be completely defined by 6 independent parameters: the span l0, height h0, thickness t0, and width d0 of the cosine beam; the spacing d2 between the upper connecting plate 113 and the bistable beam 111; and the thickness t of the plastic energy absorber 112. The spacing d2 between the upper connecting plate 113 and the bistable beam 111 is to ensure that the deformation of the bistable beam 111 is not affected by the connecting plate 2.

[0081] Finite element software ABAQUS / Explicit was used to load the multi-mechanism self-locking energy absorption unit 11, the single unit and the system. Five layers were staggered, containing a total of 35 units. A rigid plate was used to simulate the distributed load. Since the mass of the impact object in actual situations is usually much larger than the mass of a small number of energy absorption units, it is approximately assumed that the velocity of the plate remains unchanged during the impact process, v z =-1m / s, simulating low-speed impact.

[0082] The deformation of each model is as follows Figure 5 As shown. Structures at different levels show the same deformation characteristics, which can be mainly divided into three stages: In the first stage, before u / H=0.26, the bistable beam 111 part of the structure deforms and undergoes a steady-state switch, and the plastic energy absorber 112 and the connecting plate 2 basically maintain their original shape. In this stage, basically no plastic deformation occurs in the structure, and the negative stiffness of the bistable beam 111 structure is mainly used to absorb energy, which is called the negative stiffness section. In the second stage, between u / H=0.26-0.82, the plastic energy absorber 112 and the upper connecting plate 113 are compressed to produce large plastic deformation. This stage mainly uses the plastic deformation of the structure to absorb energy, which is called the plastic section. When u / H=0.82, the third stage begins, the lower connecting plate 114 begins to deform, and the entire structure is gradually compacted, which is called the compaction section. The above results show that the structures corresponding to different energy absorption mechanisms in the structural design deform at different stages, and different energy absorption mechanisms can be used to cope with impacts of different compression degrees.

[0083] The force-displacement curves of the three scale models of the structure under impact are highly similar, showing three obvious stages, and the positions of the dividing points of each stage are similar to Figure 5 The characteristic positions of the deformation in the structure completely correspond, that is, the structural characteristics correspond to the energy absorption characteristics, and a quantitative relationship between the unit structural characteristics and the unit performance can be established. In the first stage of the negative stiffness section, for the energy absorption unit 11 (black line), the structure contains only one bistable beam 111, so there is only one peak value of the force. After the beam undergoes a steady-state jump, it is separated from the impact plate and no longer bears the load until the plastic energy absorption part 112 begins to deform; for a single unit (red line), it contains two layers of bistable beams 111. When compressed, the bistable beams 111 deform in layers and in sequence, and there are two peaks of force; for the system, it contains multiple layers of bistable beams 111. When the layers are deformed in sequence, there are multiple peaks of force, and the distance between the peaks is close, so that the force exhibits characteristics similar to a platform. In the second stage of the plastic section, the load-bearing characteristics of the energy absorption unit 11 are basically the same as those of the single unit. As the structure is gradually compressed, the force gradually increases. The bearing characteristics of the system and the unit in this stage are slightly different. They have the same force at the beginning of the plastic stage, but then the system force continues to rise and presents a platform feature. This is because the staggered arrangement of the self-locking units makes the system denser relative to the unit. A 2×2 unit arrangement is inserted into the 3×3 unit arrangement in the lower layer. The system deforms more evenly in the plastic stage and the bearing is more stable. In the third stage of compaction, the bearing of the structure suddenly increases, which is not conducive to energy absorption. The characteristics of the structural deformation and force-displacement curves show that when the impact energy or stroke is small, the structure absorbs energy through the negative stiffness mechanism; when the impact energy or stroke is large, the negative stiffness of the structure is not enough to absorb all the energy / bear all the deformation, and the structure needs to enter the plastic deformation stage to absorb energy.

[0084] Combining the symmetry of the structure and the arrangement of the system, the load values ​​of models of different scales are compared. A single unit can be regarded as a combination of two layers, with 4 energy-absorbing units 11 on each layer. When impacted, the load of a single unit is 4 times that of the energy-absorbing unit 11. The system is arranged with 5 layers and 9 units on the bottom layer. When impacted, the load of the system is about 9 times that of a single unit. The shapes and characteristic points of the three curves are basically the same, and the loads of models at different levels have extremely high similarity and numerical correlation. Figure 6 (a) The areas under the three curves were further calculated to characterize the energy absorption performance of each model. Figure 6 As shown in (b), at the end of the plastic stage, the areas under the three curves are basically the same, that is, the three models have similar energy absorption characteristics. The same results were obtained after comparison using models with elliptical plastic energy absorbers 112 of h = 10 mm and h = 30 mm. The above results show that the performance of the macro system can be predicted by the unit performance and arrangement, and the relationship between unit performance and system performance can be established in combination with structural deformation. Since the energy absorption unit 11 has similar load-bearing and energy absorption characteristics as the system, it can be approximately replaced. Therefore, in subsequent simulation studies, the energy absorption unit 11 is mainly simulated to save computing resources.

[0085] We also performed loading-unloading simulations on the energy absorbing unit 11 and a single unit in the negative stiffness section, with a speed of 1 m / s. The results are as follows Figure 7 As shown in the figure, the structure will not rebound after unloading after steady-state switching, and can remain stable, and can effectively absorb energy in the negative stiffness section. The structure can also be restored to its original state by reverse loading after unloading, achieving the design goal of reusability.

[0086] 3. Example of a method for constructing a multi-mechanism self-locking energy-absorbing structure system

[0087] S1. Determine the optimal parameters of the bistable beam 111 structure

[0088] 1. Construct theoretical model: draw parameter design domain and determine the maximum width d of bistable beam 111 0max The minimum width d of the upper connecting plate 113 1min ;

[0089] The geometric parameters of the bistable beam 111 negative stiffness structure in the multi-mechanism self-locking energy absorption structure are as follows: Figure 8 , as shown in Table 1 and formula (1.2).

[0090]

[0091] According to the results of the literature [Qiu J. An Electrothermally-Actuated Bistable Mems Relay for Power Applications [D]. Boston; Massachusetts Institute of Technology, 2003], the width d0 of the bistable beam 111 has no effect on the steady-state switching. However, if the steady-state switching of the cosine beam in the symmetric mode is to be achieved, the parameters must satisfy:

[0092] h0 / t0>2.31,(1.3)

[0093] In addition, according to the results of the literature [Tan X, Chen S, Zhu S, et al. Reusable Metamaterial Via Inelastic Instability for Energy Absorption [J]. International Journal of Mechanical Sciences, 2019, 155: 509-517.], if the bistable beam 111 has no plastic deformation during the stable state switching process, it must meet the following requirements:

[0094]

[0095] Where ε max is the maximum elastic strain of the material used for the bistable beam 111. For 40CrMnSiMoV spring steel, ε max =0.01.

[0096] Equations (1.3) and (1.4) together give the feasible domain of parameters h0, t0 and l0. The parameter design domain is plotted with t0 / l0 and h0 / l0 as the horizontal and vertical coordinates, as shown in Fig. 9 According to this diagram, when l0 is given, h0 and t0 can be selected from the diagram.

[0097] The literature [Qiu J.An Electrothermally-Actuated Bistable Mems Relay for Power Applications [D]. Boston; Massachusetts Institute of Technology, 2003] also uses the energy variation method to deduce the change of the lateral force F along the negative direction of the y-axis with the midpoint displacement, where the peak force F 1,max for:

[0098]

[0099] Where I is the cross-sectional inertia moment of the beam, I = d0t03 / 12. The maximum axial force of the beam along the x direction is P max It can also be obtained by the energy variation method:

[0100]

[0101] According to the design, P max The load is borne by the upper connecting plate 113. In order to meet the requirement that the connecting plate 2 has no plastic deformation during the deformation of the bistable beam 111, the width of the upper connecting plate 113 should meet the following requirements:

[0102]

[0103] When l0 is given (l0 = 40 mm in this section), the width d of the plastic energy absorber 112 can be calculated as 22 mm according to the self-locking design requirements and formula (1.1). The distance d2 between the upper connecting plate 113 and the bistable beam 111 only needs to take a smaller value (d2 = 1 mm in this section). After selecting h0 and t0 in the design domain, the maximum width d of the bistable beam 111 can be solved by combining formulas (1.6) and (1.7): 0max The minimum width d of the upper connecting plate 113 1min :

[0104]

[0105] In the subsequent parameter selection of d0 and d2, appropriate adjustments will be made to avoid the structure from continuously working under the limit state and causing plastic deformation or failing to achieve stable steady-state switching, which will affect reusability.

[0106] Table 1 Geometric parameters of the multi-mechanism self-locking energy absorption structure

[0107]

[0108] The system has the characteristic of multiple peaks connected to form a platform in the negative stiffness section. This phenomenon is the same as in the literature [Pan F, Li Y, Li Z, et al. 3d Pixel Mechanical Metamaterials [J]. Advanced Materials, 2019]. When multiple bistable units are connected in series to form a multi-stable structure, the force of the structure fluctuates slightly around the peak force of the bistable state. It can be approximately considered that the system is based on the peak force F 1,max Stable load bearing. Fig.10 , comparing formula (1.5) with the force of the negative stiffness section of the system obtained by simulation calculation, the result obtained by theoretical calculation is basically the same as the platform force of the system in simulation. According to the above results, when the energy absorption unit 11 is used to represent the energy absorption characteristics of the system in the future, the energy absorption EA1 of the negative stiffness section is approximately replaced by the peak force F by the direct integral of force over displacement.1,max × displacement u1 of the negative stiffness segment, that is,

[0109] EA1=F 1，max u1,(1.10)

[0110] Using mass ratio energy absorption SEA m Energy absorption SEA with volume ratio V Evaluation of the energy absorption performance of the bistable beam 111, SEA m It is given by formula (2.3), SEA V It can be expressed as

[0111]

[0112] Wherein V is the volume of the circumscribed cube of the model. For the bistable beam 111, V=h0d0l0.

[0113] According to equations (1.5), (1.10), and (1.11), the F of the bistable beam 111 in the parameter design domain is plotted. 1,max , EA1, SEA m With SEA V Changes such as Fig.11 shown. Fig.11 (a) shows the peak force F at the intersection of the upper and lower bounds of the parameter design domain. 1,max It reaches the maximum value, at which time the height h0 is small and the thickness t0 reaches the maximum value. Fig.11 (b) shows that the energy absorption EA1 is maximum at the upper limit of the parameter close to the intersection of the upper and lower limits, and at this time t0 has a larger range to choose from. Fig.11 (c) shows that the energy absorption from the mass ratio SEA m The parameter selection has the best energy absorption performance at the upper limit. Fig.11 (d) shows the energy absorption from volume ratio SEA V According to the above phenomenon, in order to make the structure have better load-bearing and energy-absorbing performance, the parameters h0 and t0 of the bistable beam 111 should be selected at the upper boundary close to the intersection of the upper and lower boundaries.

[0114] 2. Construct the finite element model: select different parameter groups in the parameter design domain of the bistable beam 111, draw the model and simulate it in the finite element software ABAQUS / Explicit to study the stability of the negative stiffness energy absorption of the bistable beam 111 structure under impact conditions;

[0115] The parameters of the plastic energy absorber 112 are kept constant at t = 0.8 mm and d2 = 1 mm, and only the parameters of the bistable beam 111 and the upper connecting plate 113 are changed. Given l0 = 40 mm, different heights h0 and thicknesses t0 are selected, and the maximum width d of the bistable beam 111 is calculated according to equations (1.6) and (1.7): 0max The minimum width d of the upper connecting plate 113 1min , d0 is rounded down and d1 is rounded up to avoid the structure working continuously in the limit state. Fig.12 As shown, using Figure 4 The parameter group used in modeling the similar energy absorbing unit 11 is shown in Table 2.

[0116] Table 2 Geometric parameters of bistable beam 111 of different models

[0117]

[0118] 3. Determine the influence of thickness and height on the dynamic performance of the bistable beam 111: According to the simulation results, the influence of comprehensive parameters on the energy absorption performance is considered to select the final parameters of the bistable beam 111.

[0119] The simulation results are as follows Fig.12 As shown. For some models with a larger thickness t0, the steady-state switching during loading is not stable. Dynamic loading causes fluctuations in the beam, which causes the bistable beam 111 to rebound during unloading, and the structure cannot effectively absorb energy. When t0 is small, the bistable beam 111 can achieve stable steady-state switching and effectively absorb energy. Considering the influence of comprehensive parameters on energy absorption performance, the final parameters of the bistable beam 111 are selected as h0 = 4mm, t0 = 0.2mm, and d0 = 18mm, as shown in Fig.13 As shown by the red dot in the middle, the bistable beam 111 structure in subsequent studies all uses this parameter.

[0120] S2. Determine the parameters of the plastic energy absorption structure

[0121] The structure of the plastic energy absorbing member 112 in the multi-mechanism self-locking energy absorbing structure is relatively simple. When the span l0 of the bistable beam 111 is given, the shape of the circular plastic energy absorbing member 112 is completely determined, and only the thickness t can be adjusted. If the shape of the plastic energy absorbing member 112 is changed to an ellipse, the height h becomes an independent parameter, and the stroke of the plastic energy absorbing section of the structure can be greatly adjusted. In addition, it was found in the study that designing the top of the plastic energy absorbing member 112 as a platform is conducive to the stability of the deformation of the negative stiffness section, and the influence of the platform length p on the structural performance is also discussed.

[0122] according to Figure 5 and Figure 6 The characteristics of the deformation and force-displacement curve of the structural energy absorption unit 11 shown in the figure provide the following structural performance evaluation indicators:

[0123] Two-stage stroke ratio: u2 / u1. u2 is the stroke of the plastic stage, and u1 is the stroke of the negative stiffness stage, which is used to characterize the ratio of different energy absorption mechanisms in deformation;

[0124] Two-stage force ratio: F 2,0 / F 1,max . F 2,0 is the initial force of the plastic stage, F 1,max is the platform force in the negative stiffness segment, which represents the degree of change in the bearing capacity of the structure when the energy absorption mechanism is switched;

[0125] Two-stage energy absorption ratio: EA2 / EA1. EA2 is the energy absorption of the structure in the plastic stage, and EA1 is the energy absorption of the structure in the negative stiffness stage, which represents the difference in energy absorption of different energy absorption mechanisms when the structure is fully deformed;

[0126] Effective energy absorption stroke u eff : (u1+u2) / total height of the structure H. Characterizes the proportion of the structure that can effectively bear load before the compaction stage;

[0127] Total energy absorption EA: EA1+EA2. Characterizes the energy absorption capacity of the structure;

[0128] Mass specific energy absorption SEA m :EA / m . m is the mass of the structure;

[0129] Volumetric energy absorption SEA V :EA×2 / V. V is the volume of the circumscribed cube of the structure. When the structural units are arranged in a staggered system, the circumscribed cube of a single unit actually contains two complete units, so the total energy absorption is twice.

[0130] The parameters F involved in the above indicators 1,max , EA1, SEA V They are given by equations (1.5), (1.10), and (1.11) respectively. The initial force F in the plastic stage 2,0 According to the force-displacement curve of the simulation results, the remaining parameters are calculated by the following formulas:

[0131] u1=2h0, (1.12)

[0132] u2=h-l0-t-t0, (1.13)

[0133]

[0134] 1. Build a theoretical model: Establish a plastic hinge theoretical model, predict the structural performance of the plastic energy absorbing member 112 through theoretical calculation, and study the performance difference between the two stages of the plastic energy absorbing member 112 and the overall energy absorption performance of the structure;

[0135] When the plastic energy absorbing member 112 begins to deform, the upper connecting plate 113 for maintaining the stable switching of the bistable beam 111 begins to play a role in restricting the displacement of the two ends of the plastic energy absorbing member 112. Figure 5 The deformation of the plastic energy absorbing member 112 can be simplified as the deformation of a semicircular metal shell connected at the diameter. The initial force F of the plastic segment can be directly calculated from the parameters of the plastic energy absorbing member 112 by applying the plastic hinge theory. 2,0 , which is convenient for structural design and parameter optimization. Fig.14 (a) shows the distribution of plastic strain in the structure, and the following assumptions are made to establish a plastic hinge theory model: there is no elastic deformation, plastic deformation only occurs at the plastic hinge, the plastic hinge is five points equidistantly distributed on the arc, and the influence of axial stress is ignored. Fig.14 Take the 1 / 4 arc containing three plastic hinges A, B, and C in (a). The stress condition when it just becomes a plastic structure is as follows: Fig.14 (b), where Mp is the plastic hinge moment. According to the moment equilibrium, for points B and C:

[0136]

[0137] Where M p =σ s t 2 d / 4. The two equations can be solved as follows:

[0138]

[0139] Substituting the structural parameters in Table 1 into formula (1.19), we can calculate F 2,0 =497.5N, compared with the simulation results Fig.15 The two are highly consistent, so the theoretical model can be applied to the subsequent analysis of F 2,0 Make predictions.

[0140] 2. Establish a finite element model: draw energy absorbing units with different geometric parameters of the plastic energy absorbing parts 112 and simulate them in the finite element software ABAQUS / Explicit to study the performance of the structure under different parameters of the plastic energy absorbing parts 112.

[0141] When simulating the system, it was found that part of the plastic energy absorber 112 in the negative stiffness section was torsion-induced, resulting in asymmetric deformation of the bistable beam 111, such as Fig.16 (a) is shown. This is because the contact position between the units in the system is only at the top of the plastic energy absorber 112, and the units are in line contact, which is prone to sliding and twisting. Therefore, it is considered to design a Fig.16(b) shows a plate with a length of p to increase the constraint on the in-plane rotational freedom of the plastic energy absorber 112. The simulation results of the system after adding the plate with a length of p = 20 mm are shown in FIG. Fig.16 As shown in (c), the deformation of the system in the negative stiffness section is relatively stable, and the bistable beam 111 in the structure deforms in a symmetrical mode, and can effectively absorb energy in this stage. Therefore, the plate length p is also studied as an independent parameter of the plastic energy absorber 112.

[0142] The three independent geometric parameters of the plastic energy absorbing member 112, thickness t, height h, and plate length p, are studied respectively, and the data range of the parameters is 0.3mm≤t≤1mm, 10mm≤h≤34mm, and 0mm≤p≤38mm. When t changes, h=22mm, p=0mm; when h changes, t=0.8mm, p=0mm; when p changes, h=22mm, t=0.8mm.

[0143] Then, the thickness t, height h, and plate length p of the plastic energy absorbing member 112 are studied respectively:

[0144] 1. Determine the thickness t of the plastic energy absorbing member 112: Through the simulation results and theoretical prediction results of the structures with different thickness t of the plastic energy absorbing member 112, it is concluded that the thickness t of the plastic energy absorbing member 112 mainly affects the force ratio and energy absorption ratio of the two stages. When the thickness is larger, the structure has better energy absorption performance;

[0145] The simulation results of structures with different thickness t of plastic energy absorber 112 and the peak force F of the negative stiffness segment using equations (1.5) and (1.19) 1，max and the initial force F in the plastic stage 2,0 The theoretical prediction results are as follows Fig.17 shown.

[0146] The thickness t of the plastic energy absorber 112 mainly affects the load-bearing capacity of the structure in the plastic section, and also affects whether the negative stiffness section can effectively absorb energy. Substituting the parameters in Table 1 into equations (1.6) and (1.7), and taking t as the unknown number, the minimum thickness t of the connecting plate 113 without plastic deformation is obtained. min ≈0.35mm. In order to meet the condition that the structure can be reused in the first stage, the stable state switching of the bistable beam 111 should precede the plastic deformation of the plastic energy absorber 112, which requires the peak force F 1，max Less than the initial force F2,0 of the plastic stage. Substituting the parameters in Table 1 into equations (1.5) and (1.19), and taking t as the unknown, the solution is to satisfy the condition F 1，max <F 2,0 Minimum thickness t min ≈0.4mm. The black and red solid lines in the figure are the simulation results of t=0.3 and 0.4mm respectively. t does not meet or approach the requirements of the above two conditions.min This results in the bistable beam 111 and the plastic energy absorber 112 of the two groups of models deforming simultaneously during the compression process, which does not meet the design requirements, and the structural load is quite different from the theory and is unpredictable. For the model with t>0.4mm, the action stages of the two energy absorption mechanisms are clearly demarcated, and the simulation and theoretical calculation values ​​are relatively close. As the thickness t increases, the load of the structure in the plastic section increases.

[0147] The performance index of the model with t>0.4mm varies with t as shown in Fig.18 As shown in the figure, the thickness t has almost no effect on the two-stage stroke ratio; the two-stage force ratio and the two-stage energy absorption ratio increase with the increase of thickness t, and are approximately linear within the current parameter variation range; the effective energy absorption stroke u eff Almost unaffected; total energy absorption EA, mass specific energy absorption SEA m , volume specific energy absorption SEA V It increases with the increase of thickness t.

[0148] Based on the above results, the thickness t of the plastic energy absorbing member 112 mainly affects the force ratio and energy absorption ratio of the two stages; when the thickness is larger, the structure has better energy absorption performance, but the force changes greatly when the two energy absorption mechanisms are switched.

[0149] 2. Determine the height h of the plastic energy absorbing member 112: Through the simulation results and theoretical prediction results of the structures with different heights h of the plastic energy absorbing member 112, it is concluded that the height h of the plastic energy absorbing member 112 mainly affects the stroke ratio of the two stages. When the plastic energy absorbing member 112 is circular, the structure has better energy absorption performance;

[0150] Simulation results of structures with different plastic energy absorbers 112 heights h, and the peak force F of the negative stiffness segment using equations (1.5) and (1.19) 1，max and the initial force F in the plastic stage 2,0 Theoretical predictions made Fig.19 (a) According to the research results of Wu et al., the change of h has an effect on F 2,0 No effect, F under different h 2,0 The values ​​of are the same as those of the circular plastic energy absorbing member 112 (h=22 mm).

[0151] The height h of the plastic energy absorbing member 112 mainly affects the travel of the structure in the plastic section and also has an impact on the stability of the load-bearing of the plastic section. Fig.19 As shown in (a), structures of different heights have clear boundaries between the two energy absorption mechanisms, and the simulation and theoretical calculation values ​​are basically the same. As the height h increases, the travel of the structure in the plastic section increases, and the travel of stable load increases. In the force-displacement curves of the three models with h < 22 mm (h = 10, 14, 18 mm), the increase in load in the plastic section is not continuous, and an obvious inflection point appears, such as Fig.19 (b) This is because during the compression deformation process of the plastic energy absorbing member 112, part of the shell first contacts the bistable beam 111 and the lower connecting plate 114, and the deformation mode of the plastic energy absorbing member 112 changes. This phenomenon causes the structure to be deformed before reaching the effective energy absorption stroke u eff The front load increases sharply, and the smaller h is, the faster the load increases after the inflection point. eff The smaller the height, the worse the energy absorption performance. This phenomenon basically disappears when the plastic energy absorber 112 is circular (h = 22 mm), so when designing the plastic energy absorber 112, the shape should be circular or a higher ellipse. However, when simulating the system with h = 34 mm, it is found that the relatively thin and tall plastic energy absorber 112 is prone to instability during deformation, so the height h should not be too high.

[0152] The performance indicators of the model with h≥22mm vary with h as follows Fig. 20 As shown in the figure, the two-stage stroke ratio increases with the increase of height h, and is approximately linear within the current parameter variation range; the height h has almost no effect on the two-stage force ratio; the two-stage energy absorption ratio increases with the increase of height h, but the overall change is small; the effective energy absorption stroke u eff The total energy absorption EA increases with the increase of height h; the mass specific energy absorption SEA m , volume specific energy absorption SEA V It decreases with the increase of height h.

[0153] Based on the above results, the stroke ratio of the two stages is mainly affected by adjusting the height h; when the plastic energy absorbing member 112 is circular, the structure has better energy absorbing performance.

[0154] 3. Determine the length p of the plate of the plastic energy absorbing member 112: Designing a plate at the top of the plastic energy absorbing member 112 is beneficial to the deformation stability of the structure, and the length of the plate should be small;

[0155] When the platform length p changes from 0 to 38 mm, the plate gradually grows and the total height of the unit gradually becomes shorter, such as Fig.21 (a) is shown. The deformation mode of the system in the negative stiffness section under different plate lengths p is shown as follows Fig.21 (b) After adding the flat plate, the deformation of the system tends to be stable, and the design of adding the flat plate is effective.

[0156] The force-displacement curves of the energy absorbing unit 11 corresponding to each system are as follows: Fig. 22As shown. The length p of the plate affects both the force and stroke of the plastic section. As p increases, the load of the structure in the plastic section increases and the stroke decreases. In addition, as the plate becomes longer, the load of the structure in the plastic section changes from a steady rise to a large fluctuation, and the longer the plate is, the more unstable the load. (This situation also exists in the system). When the plate is small (p = 10mm), the load characteristics of the structure and the initial force of the plastic section are close to those without a plate, and can be approximately predicted using the theory without a plate.

[0157] Considering the deformation stability and load-bearing characteristics of the structure, designing a flat plate at the top of the plastic energy absorbing member 112 is beneficial to the deformation stability of the structure, and the length of the flat plate should be relatively small.

[0158] S4. Determine the optimal configuration of the energy absorbing structure

[0159] According to the two-stage stroke ratio, two-stage force ratio, two-stage energy absorption ratio, and effective energy absorption stroke U eff , total energy absorption EA, mass specific energy absorption SEA m , volume specific energy absorption SEA V , deformation stability, it is concluded that the plastic energy absorbing member (112) has better load-bearing and energy absorbing performance when the structure is thicker, round in shape and has a small flat plate at the top.

[0160] S5. Dynamic response of the test system at different impact velocities

[0161] The structure can effectively absorb energy at all impact velocities, and the reusability feature takes effect at lower impact velocities.

[0162] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention; therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is limited by the attached claims rather than the above description. Therefore, it is intended to include all changes within the meaning and scope of the equivalent elements of the claims in the present invention, and any figure marks in the claims should not be regarded as limiting the claims involved.

[0163] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An energy absorbing structure, characterized in that: It comprises energy absorbing components (1) which are symmetrically arranged on the front and back sides and have the same arrangement and configuration, and two groups of energy absorbing components (1) are connected by a connecting plate (2); Each energy absorbing assembly (1) is a modular structure composed of four energy absorbing units (11), the four energy absorbing units (11) are arranged in a square array at the four corners of the connecting plate (2), and the directions of every two energy absorbing units (11) are perpendicular to each other, so that the energy absorbing assembly (1) forms a self-locking shape; A plurality of energy absorbing components (1) and connecting plates (2) form a large-scale energy absorbing group through self-locking, and the large-scale energy absorbing group will not separate or splash under impact from all directions.

2. An energy absorbing structure according to claim 1, characterized in that: Each energy absorbing unit (11) comprises: A bistable beam (111) has two stable states, can switch states under the action of external force and repeatedly absorb energy through negative stiffness during the switching process; A plastic energy absorbing member (112) has its front and rear surfaces and bottom surface hollowed out to form a hollow structure, and its hollowed-out portion is connected to the bistable beam (111). After negative stiffness energy absorption, it enters the plastic deformation stage to continue to absorb energy in high efficiency and large quantities.

3. The energy absorbing structure according to claim 1, characterized in that: Each energy absorbing unit (11) further comprises an upper connecting plate (113) and a lower connecting plate (114), wherein: Upper connecting plates (113) are arranged at intervals on the bottom of the plastic energy absorbing member (112), and a hollow portion of the bottom surface of the plastic energy absorbing member is formed by two upper connecting plates; The lower connecting plate (114) is arranged at the bottom of the bistable beam (111) to maintain the structural stability of the energy absorbing unit (11) (11) and provide effective force transmission.

4. An energy absorbing structure according to claim 3, characterized in that: The cross section of the plastic energy absorbing member (112) is a semicircular structure.

5. An energy absorbing structure according to claim 4, characterized in that: A flat plate is provided at the top of the plastic energy absorbing member (112).

6. The energy absorbing structure according to claim 2, characterized in that: The bistable beam (111) is an arc-shaped plate structure composed of a first convex arc segment (1111), a second concave arc segment (1112) and a third convex arc segment (1113) in a smoothly transitioned manner.

7. An energy absorbing structure according to claim 6, characterized in that: The first convex arc segment (1111) and the second convex arc segment (1113) are symmetrical to the two sides of the second concave arc segment (1112).

8. The energy absorbing structure according to claim 6, characterized in that: The final parameters of the bistable beam (111) are selected as h0=4 mm, t0=0.2 mm, and d0=18 mm.

9. The design method of the energy absorbing structure according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1. Determine the optimal parameters of the bistable beam (111) structure: Constructing a theoretical model: drawing a parameter design domain, determining the maximum width d0max of the bistable beam (111) and the minimum width d1min of the upper connecting plate (113); Construct a finite element model: select different parameter groups in the parameter design domain of the bistable beam (111), draw the model and simulate it in the finite element software ABAQUS / Explicit to study the stability of the negative stiffness energy absorption of the bistable beam (111) structure under impact conditions; Determine the influence of thickness and height on the dynamic performance of the bistable beam (111): select the final parameters of the bistable beam (111) based on the simulation results and the influence of the parameters on the energy absorption performance; S2. Determine the parameters of plastic energy absorbing parts Establishing a theoretical model: establishing a plastic hinge theoretical model, predicting the structural performance of the plastic energy absorbing member (112) through theoretical calculation, and studying the performance difference between the two stages of the plastic energy absorbing member (112) and the overall energy absorption performance of the structure; Establishing a finite element model: drawing an energy absorbing unit model with different geometric parameters of the plastic energy absorbing member (112) and simulating it in the finite element software ABAQUS / Explicit to study the performance of the plastic energy absorbing member structure under different plastic energy absorbing member (112) parameters; S3. Determine the optimal configuration of the energy absorbing structure According to the two-stage stroke ratio, two-stage force ratio, two-stage energy absorption ratio, and effective energy absorption stroke U eff , total energy absorption EA, mass specific energy absorption SEA m , volume specific energy absorption SEA V , deformation stability, it is concluded that the plastic energy absorbing member (112) has better load-bearing and energy-absorbing performance when the structure is thicker, round in shape and has a small flat plate at the top; S4. Dynamic response of the test system at different impact velocities.

10. The parameters in step S2 specifically include determining the thickness t of the plastic shell (112): through simulation results of structures with different plastic shell (112) thicknesses t and theoretical prediction results, it is concluded that the thickness t of the plastic shell (112) mainly affects the force ratio and energy absorption ratio of the two stages, and the structure has better energy absorption performance when the thickness is larger; Determining the height h of the plastic shell (112): Through simulation results and theoretical prediction results of structures with different heights h of the plastic shell (112), it is concluded that the height h of the plastic shell (112) mainly affects the stroke ratio of the two stages, and when the plastic shell (112) is circular, the structure has better energy absorption performance; Determine the length p of the flat plate of the plastic shell (112): Designing a flat plate at the top of the plastic shell (112) is beneficial to the deformation stability of the structure, and the length of the flat plate should be small.

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