Bistable vibration absorption unit, bistable mechanical metamaterial structure and preparation method of bistable vibration absorption unit and bistable mechanical metamaterial structure

Abstract

The invention discloses a bistable vibration absorption unit, a bistable mechanical metamaterial structure and a preparation method of the bistable mechanical metamaterial structure, and the bistable vibration absorption unit is characterized by comprising a track frame, a vibrator and an elastic mechanism; rails which are oppositely arranged are arranged on the two sides of the rail frame, and the molded lines of the rails are parabolas; the vibrator is located between the tracks on the two sides of the track frame, the first end of the elastic mechanism is connected with the side portion of the vibrator, and the second end of the elastic mechanism is slidably connected with the track on the corresponding side; the elastic mechanism has the degree of freedom of compression or extension, and the elastic mechanism has the stroke of displacement along the track. The invention is applied to the fields of vibration and noise control and nonlinear metamaterial structures, can be applied to impact energy absorption structures, has higher strength and stability, and realizes low-frequency, broadband and efficient vibration suppression and efficient impact attenuation effects under the condition of small additional mass.

Description

Technical Field

[0001] The present invention relates to the fields of mechanical engineering, mechanics, vibration and noise control, and nonlinear metamaterial structure technology, and in particular to a bistable vibration absorbing unit, a bistable mechanical metamaterial structure, and a preparation method thereof. Background Art

[0002] Structural vibration and shock are widely present in the fields of aerospace, shipbuilding, ocean and nuclear industries. Structural vibration and shock suppression are crucial in terms of equipment service safety and acoustic stealth performance. Especially in aerospace and equipment with harsh service environments, lightweight design and vibration shock control are equally important. The vibration shock generated by the structure under the excitation of flow shock and various vibration sources will not only reduce the safety and stability of the equipment and the performance of precision instruments, but also directly lead to accidents such as loss of control, structural vibration fatigue, and fracture in severe cases. At the same time, vibration will also radiate noise, affecting the stealth performance and survivability of the equipment. In manned equipment, it will damage the hearing and vision of personnel and endanger health. Designing material structures with shock suppression and vibration control is of great significance to improving the safety and stability of equipment. For equipment such as aerospace, its size, weight, environmental adaptability and other engineering requirements are stringent. Traditional vibration reduction and damping technologies are difficult to effectively solve its low-frequency vibration and shock problems. It is urgent to develop new vibration reduction and noise reduction technologies.

[0003] Mechanical metamaterials are still extraordinary structures that have elastic wave control to achieve extraordinary mechanical properties. Compared with traditional material structures, metamaterials have many novel phenomena in statics and dynamics. By rationally designing periodic microstructures, special properties such as elastic wave band gap, extraordinary mechanical properties, negative Poisson's ratio, light weight and high strength can be obtained. They have broad application prospects in the fields of vibration reduction, noise reduction and impact protection.

[0004] Research has shown that mechanical metamaterials specially designed based on local resonance excitation can produce local resonance band gaps, effectively suppress elastic wave propagation, and achieve control of elastic waves, providing new ideas for the study of vibration and noise control of beam-plate structures. At present, a large number of mechanical metamaterials research still focuses on linear metamaterials.

[0005] However, the local resonance bandgap of linear mechanical metamaterials is narrow, and it is impossible to coordinate and resolve the contradiction between light weight, low frequency and broadband elastic wave suppression. Moreover, the spectrum passband of linear metamaterials of limited size is composed of dense resonance peaks. The more cells there are, the more resonance peaks there are in the passband. That is, the narrow elastic wave bandgap of linear metamaterials can attenuate structural vibrations, but the response in its wider passband is amplified by resonance.

[0006] Nonlinear mechanical metamaterials refer to mechanical metamaterials with nonlinear dynamic properties. Studies have shown that the introduction of nonlinear factors is expected to break through the limitations of the vibration suppression bandwidth of traditional linear metamaterials and achieve ultra-low frequency, ultra-wideband, and efficient vibration suppression. As an important component of nonlinear mechanical metamaterials, bistable mechanical metamaterials can achieve dynamic properties such as sudden bounce change, negative stiffness, and tunability, and have broad application prospects in elastic wave control and impact protection.

[0007] The properties of bistable mechanical metamaterials depend to a large extent on the design of the cellular unit. The design of lightweight and small-sized bistable structures is rarely involved at present, and the design technology of bistable nonlinear cells needs to be innovated. The design of lightweight and adjustable bistable units can promote the vibration reduction and impact resistance applications of bistable mechanical metamaterials. Summary of the invention

[0008] In view of the deficiencies in the above-mentioned prior art, the present invention provides a bistable vibration absorption unit, a bistable mechanical metamaterial structure and a preparation method thereof, which can be applied to impact energy absorption structures, have higher strength and stability, and achieve low-frequency, broadband, and efficient vibration suppression and efficient impact attenuation effects under the condition of small additional mass.

[0009] To achieve the above-mentioned purpose, the present invention provides a bistable vibration absorbing unit, comprising a track frame, a vibrator and an elastic mechanism; Oppositely arranged tracks are provided on both sides of the track frame, and the track has a parabola profile; The vibrator is located between the tracks on both sides of the track frame, the first end of the elastic mechanism is connected to the side of the vibrator, and the second end of the elastic mechanism is slidably connected to the track on the corresponding side; The elastic mechanism has a degree of freedom of compression or extension, and the elastic mechanism has a stroke of displacement along the track.

[0010] In one embodiment, the elastic mechanism includes a spring and a sleeve, a countersunk hole is provided on the side of the vibrator, and the sleeve is a cylindrical structure with one end open; The first end of the spring is connected to the bottom of the counterbore, the second end of the spring is embedded in the open end of the sleeve and connected to the bottom of the sleeve, and the closed end of the sleeve is in contact with the track.

[0011] In one embodiment, the open end of the sleeve is coaxially embedded in the counterbore, and the outer wall of the sleeve is gap-matched with the hole wall of the counterbore.

[0012] In one embodiment, the number of the rails and the number of the elastic mechanisms are both four, and the elastic mechanisms correspond one to one with the rails; The four tracks are distributed in a rectangular array on the track frame, the first end of the elastic mechanism is connected to the side of the vibrator, and the second end of the elastic mechanism is slidably connected to the corresponding track.

[0013] In one embodiment, the springs in the four elastic mechanisms have the same stiffness and are prestressed.

[0014] To achieve the above object, the present invention further provides a bistable mechanical metamaterial structure, comprising a plurality of the above bistable vibration absorbing units; The bistable vibration absorbing units are distributed in an array in one direction; or The bistable vibration absorbing units are distributed in arrays in two orthogonal directions; or The bistable vibration absorbing units are distributed in arrays in three orthogonal directions; or The bistable vibration absorbing units are distributed in a circular array; or The bistable vibration absorbing units are distributed in a cylindrical array.

[0015] To achieve the above object, the present invention also provides a method for preparing the above bistable mechanical metamaterial structure, comprising the following steps: Step 1, determining the resonant frequency of the bistable vibration absorbing unit based on the target vibration frequency band; Step 2, determining the equivalent negative stiffness and nonlinear stiffness coefficient of the bistable vibration absorbing unit based on the resonance frequency and the additional mass limit of the bistable vibration absorbing unit; Step 3, determining the track coefficient, protrusion height and spring stiffness coefficient of the track according to the equivalent negative stiffness and the nonlinear stiffness coefficient; Step 4, designing a bistable vibration absorbing unit according to the parameters determined in steps 1 to 3, and combining it with a matrix designed for vibration reduction and impact resistance to form a cell of a bistable mechanical metamaterial; Step 5: Arrange multiple cells of the bistable mechanical metamaterial according to a preset array to form a bistable mechanical metamaterial structure.

[0016] Compared with the prior art, the present invention has the following beneficial technical effects: The bistable vibration absorbing unit in the present invention slides on a parabolic track through an elastic mechanism to produce a steady-state jump and a sliding damping effect, thereby realizing a bistable effect. The nonlinear stiffness coefficient and the local resonance band gap position of the bistable vibration absorbing unit can be controlled by controlling the stiffness coefficient of the elastic mechanism, the track height and the track length. At the same time, the damping coefficient can be adjusted by controlling the roughness of the track and the elastic mechanism, thereby controlling the impact energy absorption efficiency. The cells constituting the bistable vibration absorbing unit are periodically arranged on the base beam structure to construct a bistable mechanical metamaterial structure, which can achieve low-frequency, broadband, and efficient vibration suppression and efficient impact attenuation effects under the condition of additional mass. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0018] Figure 1 is an axonometric diagram of the bistable vibration absorbing unit in Example 1 of the present invention; Figure 2 is a cross-sectional view of a bistable vibration absorbing unit in Example 1 of the present invention; Figure 3 It is a partial schematic diagram of the track frame and the elastic mechanism in Example 1 of the present invention; Figure 4 is a partial schematic diagram of the vibrator in Example 1 of the present invention; Figure 5 It is a schematic diagram of force analysis at the contact position between the sleeve and the track in the bistable vibration absorbing unit in Example 2 of the present invention; Figure 6 Schematic diagram of reaction force-displacement curve in Example 2 of the present invention; Figure 7 This is a schematic diagram of the arrangement, installation and testing of the bistable mechanical metamaterial cantilever beam in Example 2 of the present invention, wherein: Figure 7 (a) is a schematic diagram of the test scheme for the impact transient vibration characteristics of the bistable metamaterial cantilever beam. Figure 7 (b) Schematic diagram of the impact excitation application scheme; Figure 8 Schematic diagram of the one-dimensional cantilever beam impact transient vibration test results in Example 2 of the present invention, wherein: Figure 8 (a) is a speed-time diagram. Figure 8 (b) is a schematic diagram of amplitude-frequency; Reference numerals: track frame 1 , track 101 , vibrator 2 , counterbore 201 , elastic mechanism 3 , spring 301 , sleeve 302 , base 4 .

[0019] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0020] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0022] In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that ordinary technicians in the field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0023] Example 1 like Figure 1 The bistable vibration absorbing unit disclosed in the present embodiment is shown, which mainly includes a track frame 1 made of structural steel material, a vibrator 2 and an elastic mechanism 3. The track frame 1 is fixedly connected to the base 4 that needs vibration reduction and impact resistance by bolts. Oppositely arranged tracks 101 are provided on both sides of the track frame 1. The length direction of the track 101 is perpendicular to the plane where the base 4 is located, and the profile of the track 101 is a parabola. The vibrator 2 is located between the tracks 101 on both sides of the track frame 1, and is slidably matched with the track 101 through the elastic mechanism 3. The first end of the elastic mechanism 3 is connected to the side of the vibrator 2, and the second end of the elastic mechanism 3 is slidably connected to the track 101 on the corresponding side. The elastic mechanism 3 has the freedom of compression or extension, and the elastic mechanism 3 has a displacement stroke along the track 101, that is, the elastic mechanism 3 can drive the vibrator 2 to slide along the track 101 under the action of external force.

[0024] In this embodiment, the elastic mechanism 3 includes a spring 301 and a sleeve 302. A circular countersunk hole 201 is provided on the side of the vibrator 2 at the connection position corresponding to the elastic mechanism 3, and the sleeve 302 is a cylindrical structure with one end open. The first end of the spring 301 is fixedly connected to the bottom of the countersunk hole 201 by gluing, fixing with a connecting piece, etc., the second end of the spring 301 is embedded in the open end of the sleeve 302 and is fixedly connected to the bottom of the sleeve 302 by gluing, fixing with a connecting piece, etc., the closed end of the sleeve 302 is in contact with the track 101, and the closed end of the sleeve 302 is a spherical or curved structure to avoid interference when the sleeve 302 slides on the track 101. In the specific application process, the friction coefficient of the two can be controlled by controlling the surface roughness of the contact surface between the sleeve 302 and the track 101.

[0025] During the specific implementation process, the open end of the sleeve 302 is coaxially embedded in the countersunk hole 201, and the outer wall of the sleeve 302 is gap-matched with the hole wall of the countersunk hole 201. In specific applications, even if the sleeve 302 slides to the most recessed position of the track 101, the open end of the sleeve 302 is still located in the countersunk hole 201, so as to avoid the spring 301 being exposed and causing the spring 301 to bend during the sliding process.

[0026] In the specific implementation process, the number of rails 101 and elastic mechanisms 3 are both four, and the elastic mechanisms 3 correspond to the rails 101 one by one. The four rails 101 are distributed in a rectangular array on the rail frame 1, the first end of the elastic mechanism 3 is connected to the side of the vibrator 2, and the second end of the elastic mechanism 3 is slidably connected to the corresponding rail 101. Among them, the stiffness of the springs 301 in the four elastic mechanisms 3 is the same, and the springs 301 have prestress, which can be controlled by designing the wire diameter, number of turns and length of the springs 301.

[0027] The bistable vibration absorbing unit in this embodiment slides on the parabolic track 101 through the elastic mechanism 3 to produce steady-state jump and sliding damping effects, thereby realizing a bistable effect. The nonlinear stiffness coefficient and the local resonance band gap position of the bistable vibration absorbing unit can be controlled by the stiffness coefficient of the spring 301, the height of the track 101 and the length of the track 101. At the same time, the damping coefficient can be adjusted by controlling the roughness of the track 101 and the elastic mechanism 3, thereby controlling the impact energy absorption efficiency. The cells constituting the bistable vibration absorbing unit are periodically arranged on the beam-plate structure of the substrate 4 to construct a bistable mechanical metamaterial structure, which can achieve low-frequency, broadband, and efficient vibration suppression and efficient impact attenuation effects under the condition of additional mass.

[0028] Example 2 This embodiment discloses a bistable mechanical metamaterial structure, which includes several bistable vibration absorbing units in Embodiment 1. Specifically, each bistable vibration absorbing unit is distributed in an array in one direction on a substrate that needs vibration reduction and impact resistance, or each bistable vibration absorbing unit is distributed in an array in two orthogonal directions on a substrate that needs vibration reduction and impact resistance, and each bistable vibration absorbing unit can also be distributed in an array in three orthogonal directions on a substrate that needs vibration reduction and impact resistance, or each bistable vibration absorbing unit is distributed in a circular array or a cylindrical array on a substrate that needs vibration reduction and impact resistance.

[0029] This embodiment also discloses a method for preparing the above-mentioned bistable mechanical metamaterial structure, which mainly involves determining the resonance frequency, equivalent negative stiffness coefficient, nonlinear stiffness coefficient, track coefficient, track protrusion height, and spring stiffness coefficient of the bistable vibration absorption unit in Example 1. Specifically, the method for preparing the bistable mechanical metamaterial structure in this embodiment mainly includes the following steps: Step 1, determining the resonant frequency of the bistable vibration absorbing unit based on the target vibration frequency band; Step 2, determining the equivalent negative stiffness and nonlinear stiffness coefficient of the bistable vibration absorbing unit based on the resonance frequency and the additional mass limit of the bistable vibration absorbing unit; Step 3, determining the track coefficient, protrusion height and spring stiffness coefficient of the track according to the equivalent negative stiffness and the nonlinear stiffness coefficient; Step 4, designing a bistable vibration absorbing unit according to the parameters determined in steps 1 to 3, and combining it with a matrix that needs vibration reduction and impact resistance to form a cell of a bistable mechanical metamaterial; Step 5: Arrange multiple cells of the bistable mechanical metamaterial according to a preset array to form a bistable mechanical metamaterial structure.

[0030] According to the principle of local resonance type mechanical metamaterial, the local resonance band gap of the mechanical metamaterial composed of the bistable vibration absorption unit in this embodiment is determined by the resonance frequency of the bistable vibration absorption unit. In order to achieve the low-frequency and broadband vibration suppression and shock attenuation effects of the bistable mechanical metamaterial, this embodiment sets the resonant frequency The design is near the first-order natural frequency of the matrix (generally considering 80%~100% of the first-order natural frequency of the matrix).

[0031] In the specific application process of the bistable mechanical metamaterial in this embodiment, when the vibration amplitude or impact excitation is small, the vibrator mainly vibrates near the steady-state position, mainly showing the linear metamaterial characteristics, and limitedly suppressing vibration and impact near the band gap frequency; when the vibration amplitude is large or the impact excitation is severe, the vibrator will undergo a steady-state jump, thereby generating negative stiffness and nonlinear dynamic effects, efficiently dissipating the energy of the transfer matrix, and achieving low-frequency broadband vibration suppression and impact attenuation. The resonant frequency of the bistable vibration absorption unit The equivalent linear stiffness of the bistable vibration absorbing unit near the steady-state position and the vibrator mass are jointly determined. Analysis shows that the vibrator mass has little effect on the vibration suppression and impact attenuation effects of the bistable mechanical metamaterial, so a smaller vibrator mass can be selected to achieve low-frequency vibration suppression and impact attenuation effects while having a lower added mass ratio. In the specific implementation process, when the specific vibration reduction frequency range of the bistable mechanical metamaterial is determined, the linear resonance frequency of the bistable vibration absorbing unit can be determined within 80%~100% of the first-order natural frequency of the matrix according to actual needs. , at the linear resonant frequency Under the premise that the structural dimensions, additional mass ratio and other limiting requirements of the bistable vibration absorbing unit are known, a lower vibrator mass can also be determined while meeting the vibration shock suppression effect. m .

[0032] According to the dynamic characteristics of the bistable vibration absorbing unit, when the response amplitude is small, the oscillator only moves near one of the equilibrium positions, which is close to the linear mechanical metamaterial characteristics, and the resonant frequency is:

[0033] in, is the linear stiffness of the bistable vibration absorbing unit at the equilibrium position; Based on the linear resonant frequency determined in step 1 And the vibrator mass m , the linear stiffness of the bistable vibration absorbing unit at the equilibrium position can be calculated , and the linear stiffness of the bistable vibration absorbing unit at the equilibrium position Also satisfied ,in, k is the equivalent negative stiffness of the bistable vibration absorbing unit, k n is the nonlinear stiffness coefficient of the bistable vibration absorbing unit. Under the premise that the size of the bistable vibration absorbing unit is known and the working load is limited, its stable distance It can be determined according to the actual size of the bistable vibration absorbing unit, and further according to the linear stiffness , the equivalent negative stiffness can be calculated k and nonlinear stiffness coefficient k n .

[0034] According to the dynamic characteristics of a single bistable vibration absorbing unit, the system motion differential equation can be expressed as:

[0035] in, m is the oscillator mass, c is the damping coefficient,u is the excitation displacement, then the absolute displacement of the system motion is x + u ; refer to Figure 5 According to the force analysis of the bistable unit, the bistable effect is achieved by the horizontal spring compression through the track trajectory to generate a vertical force. F ( x ) with displacement x The changing rule is:

[0036] in, y To design the track trajectory, k y is the spring stiffness coefficient, θ is the orbital inclination; In order to realize the bistable unit force displacement relationship is The expression of the orbital trajectory should be In order to ensure the realization of negative stiffness, the track profile equation of this embodiment is designed as .in, a is the parabolic trajectory coefficient, r 1 is the height of the track protrusion, then the stable distance of the bistable unit .consider y Minimum x =0, bring the relevant design parameters into F ( x ) with displacement x The change law of can obtain the bistable unit force displacement relationship:

[0037] It can be seen that the equivalent negative stiffness of the bistable vibration absorbing unit is , nonlinear stiffness coefficient The parabola trajectory coefficient a , Track protrusion height r 1 and horizontal spring stiffness coefficient k y related.

[0038] Due to the limited roughness of the metal structure processing surface, there is a friction coefficient between the contact between one end of the sleeve and the track. f y , when the track protrusion height r 1 Larger, steady-state distance When the orbital inclination is small, θ If it is too small, the sliding friction will cause self-locking. aDetermined by the steady-state distance and the protrusion height (i.e. ), the specific value is set according to the bending vibration amplitude and force of the vibrator in actual use. Theoretically, the larger the steady-state distance, the smaller the protrusion height, and the smaller the trajectory coefficient, the vibrator can produce a steady-state jump under a very weak force, and efficiently dissipate the matrix energy. However, since the equivalent negative stiffness coefficient and nonlinear stiffness coefficient are mainly determined by the parabola trajectory coefficient of the track a , Track protrusion height r 1. Both should not be too small, otherwise the negative stiffness coefficient and nonlinear stiffness coefficient of the bistable vibration absorbing unit will be too small, which is not conducive to vibration control and impact suppression. Therefore, the steady-state distance designed in step 2 in this embodiment is The equivalent negative stiffness has been calculated k and the nonlinear stiffness coefficient k n Under the premise of , as well as , the track protrusion height can be calculated r 1. Orbital parabola trajectory coefficient a Spring rate k y .

[0039] Spring rate k y The calculation formula is:

[0040] in, d is the spring wire diameter, D is the outer diameter of the spring, n is the effective working number of the spring, G is the shear modulus of the material, E is the Young's modulus of the material, is the Poisson's ratio of the material; The spring material in this embodiment is spring steel, and its material parameters are determined. k y After the determination, the appropriate spring wire diameter, outer diameter and number of working turns can be selected according to the structural dimensions, additional mass and other limitations of the bistable vibration absorbing unit. =2.5mm, track protrusion height r 1=1.5mm, calculate the track coefficient a =240; horizontal spring length is 11.5mm, wire diameter d =0.4mm, outer diameter D =4mm, number of turnsn =14, oscillator mass m = 25g. The force-displacement curve of the bistable nonlinear unit is finally calculated as follows: Figure 6 As shown, within the working stroke (-2.5~2.5mm), the curve shows a good bistable effect.

[0041] In the specific implementation process of step 5, the entire bistable mechanical metamaterial is composed of a periodic bistable vibration absorbing unit array. The one-dimensional nonlinear mechanical metamaterial beam is composed of an array of cells in a single direction; the two-dimensional nonlinear mechanical metamaterial plate is composed of an array of cells in two orthogonal directions; the three-dimensional nonlinear mechanical metamaterial structure is composed of a periodic array of cells in the circumferential direction or in three orthogonal directions. The circumferential direction is arranged according to a periodic angle or in an axial array.

[0042] According to the above steps 1 to 5, bistable vibration absorbing units and bistable mechanical metamaterials of various specific structures can be obtained. In order to verify the vibration suppression effect of the bistable mechanical metamaterial obtained by the preparation method in this embodiment, further description is made below in combination with a specific one-dimensional cantilever beam bistable mechanical metamaterial example.

[0043] According to the linear natural frequency of the bistable vibration absorbing unit near the stable position, the bistable nonlinear local resonance frequency is determined f 0. The natural frequency vibration of the bistable vibration absorbing unit is caused by the exciter, and the velocity signal of the vibrator is tested by the laser vibrometer to analyze its natural frequency. f 0=40Hz.

[0044] The bistable mechanical metamaterial structure is constructed by periodically arranging the above bistable vibration absorbing units on the finite beam plate structure. Taking a one-dimensional cantilever beam as an example, 4×1 bistable vibration absorbing units are attached to the cantilever beam substrate to form a bistable mechanical metamaterial cantilever beam structure, such as Figure 7 As shown in (a), the average mass of the attached oscillator is m r =25g. Mechanical metamaterial cantilever beam thickness h =16mm, length L =500mm, lattice constant a =100mm.

[0045] Next, impact vibration test experiments will be carried out to test the dynamic response characteristics of the bistable mechanical metamaterial cantilever beam under impact excitation and verify the effectiveness of the design method of the lightweight, low-frequency, broadband, and high-efficiency impact-resistant bistable vibration absorption unit.

[0046] For the one-dimensional cantilever beam structure, in the experimental test, one end of the metamaterial cantilever beam is fixedly suspended on the bracket to simulate the fixed constraint boundary, such as Figure 7(a) As shown. Impact excitation is applied to the side of the bistable metamaterial cantilever beam near the free end. The specific excitation method is a swinging steel ball falling impact form. Different excitation amplitudes can be achieved by adjusting the mass of the steel ball and the drop height, as shown in Figure 7 (b) The vibration response near the center of the cantilever beam is measured using a laser vibrometer.

[0047] The vibration response of the cantilever beam without the bistable vibration absorbing unit is used as a reference value. The bistable mechanical metamaterial one-dimensional cantilever beam is composed of four bistable vibration absorbing units arranged periodically on the cantilever beam. At this time, the added mass ratio of the structure is 11.57%. The transient vibration response and spectrum of the metamaterial cantilever beam under the same impact excitation are shown in Figure 2. Figure 8 As shown. Compared with the cantilever beam without the bistable vibration absorption unit, the dense resonance peaks of the bistable metamaterial cantilever beam in the range of 30-500Hz are attenuated by an average of 9.3dB, and the vibration reduction effect is obvious. Compared with the impact time domain peak, the time domain peak can be effectively reduced, and the first impact peak can be reduced by 35%. At the same time, the addition of the bistable vibration absorption unit can accelerate the attenuation of the impact peak and effectively resist the impact. It shows that under impact excitation, strong bistable jumps and nonlinear effects can be achieved, achieving low-frequency broadband vibration reduction and efficient impact resistance.

[0048] The above experimental results show that the bistable mechanical metamaterial cantilever beam constructed according to the bistable vibration absorbing unit designed in this embodiment can achieve low-frequency, broadband, high-efficiency vibration reduction and high-efficiency impact attenuation effects with light additional mass.

[0049] The above description is only a preferred embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification and drawings under the inventive concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A bistable vibration absorbing unit, characterized in that: It includes a track frame, a vibrator and an elastic mechanism; Oppositely arranged tracks are provided on both sides of the track frame, and the profile of the tracks is a parabola; The vibrator is located between the tracks on both sides of the track frame, the first end of the elastic mechanism is connected to the side of the vibrator, and the second end of the elastic mechanism is slidably connected to the track on the corresponding side; The elastic mechanism has a degree of freedom of compression or extension, and the elastic mechanism has a stroke of displacement along the track.

2. The bistable vibration absorbing unit according to claim 1, characterized in that: The elastic mechanism includes a spring and a sleeve, a countersunk hole is provided on the side of the vibrator, and the sleeve is a cylindrical structure with one end open; The first end of the spring is connected to the bottom of the counterbore, the second end of the spring is embedded in the open end of the sleeve and connected to the bottom of the sleeve, and the closed end of the sleeve is in contact with the track.

3. The bistable vibration absorbing unit according to claim 2, characterized in that: The open end of the sleeve is coaxially embedded in the counterbore, and the outer wall of the sleeve is gap-matched with the hole wall of the counterbore.

4. The bistable vibration absorbing unit according to claim 2 or 3, characterized in that: The number of the rails and the number of the elastic mechanisms are both four, and the elastic mechanisms correspond one to one with the rails; The four tracks are distributed in a rectangular array on the track frame, the first end of the elastic mechanism is connected to the side of the vibrator, and the second end of the elastic mechanism is slidably connected to the corresponding track.

5. The bistable vibration absorbing unit according to claim 4, characterized in that: The springs in the four elastic mechanisms have the same stiffness and are prestressed.

6. A bistable mechanical metamaterial structure, characterized in that: A bistable vibration absorbing unit comprising any one of claims 1 to 5; The bistable vibration absorbing units are distributed in an array in one direction; or The bistable vibration absorbing units are distributed in arrays in two orthogonal directions; or The bistable vibration absorbing units are distributed in arrays in three orthogonal directions; or The bistable vibration absorbing units are distributed in a circular array; or The bistable vibration absorbing units are distributed in a cylindrical array.

7. A method for preparing a bistable mechanical metamaterial structure according to claim 6, characterized in that: The steps include: Step 1, determining the resonant frequency of the bistable vibration absorbing unit based on the target vibration frequency band; Step 2, determining the equivalent negative stiffness and nonlinear stiffness coefficient of the bistable vibration absorbing unit based on the resonance frequency and the additional mass limit of the bistable vibration absorbing unit; Step 3, determining the track coefficient, protrusion height and spring stiffness coefficient of the track according to the equivalent negative stiffness and the nonlinear stiffness coefficient; Step 4, designing a bistable vibration absorbing unit according to the parameters determined in steps 1 to 3, and combining it with a matrix designed for vibration reduction and impact resistance to form a cell of a bistable mechanical metamaterial; Step 5: Arrange multiple cells of the bistable mechanical metamaterial according to a preset array to form a bistable mechanical metamaterial structure.

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