Double-material double-layer curved beam negative stiffness multistable energy absorption structure

Abstract

The invention discloses a double-material double-layer curved beam negative stiffness multi-stable-state energy absorption structure, and relates to the technical field of mechanical metamaterial printing. The problems that an existing negative stiffness multistable metamaterial is high in peak force and low in energy absorption efficiency can be solved. The multistable energy absorption structure comprises a plurality of cell elements; each cell element comprises a first curved beam, a second curved beam, an upper horizontal supporting beam and a lower horizontal supporting beam; a middle connecting beam is arranged on the lower surface of the upper horizontal supporting beam; two side edge connecting beams are arranged on the upper surface of the lower horizontal supporting beam; the middle of the first curved beam is connected to the middle connecting beam, and the two ends are connected to the side connecting beams. The second curved beam is located below the first curved beam and is the same as the first curved beam in bending direction, the middle of the second curved beam is connected to the middle connecting beam through a first embedding structure, and the two ends of the second curved beam are connected to the side edge connecting beams through second embedding structures. The first curved beam is made of hard materials, and the second curved beam is made of soft materials. The method is used for improving the performance of the negative stiffness multistable metamaterial.

Description

Technical Field

[0001] The present application relates to the technical field of mechanical metamaterials, and in particular to a dual-material double-layer curved beam negative stiffness multi-stable energy absorption structure. Background Art

[0002] Mechanical metamaterials can exhibit unique physical properties that surpass natural materials by designing their internal structures. They have important application value in the fields of biomedicine, aerospace, marine engineering, and multifunctional intelligent structures. Among them, negative stiffness multistable metamaterials are an important branch of mechanical metamaterials. Negative stiffness multistable metastructures have significant advantages in energy absorption, impact shock absorption, etc. After the negative stiffness multistable material is subjected to an impact, it can still maintain its deformed shape even in the absence of external loads, and store energy in the structure through elastic deformation, thereby effectively avoiding or reducing secondary damage and providing excellent buffering protection performance.

[0003] With the advancement of science and technology, ships are facing higher requirements for safety under extreme loads and complex environments. Negative stiffness multistable metamaterials undergo layer-by-layer buckling within the elastic range under impact, and absorb energy efficiently through elastic deformation of the structure, which is particularly suitable for ships in extreme environments such as deep sea and polar ice areas. In addition, negative stiffness multistable metamaterials are also widely used in protective packaging of precision parts, aerospace engineering, vehicle engineering and other fields. However, existing negative stiffness multistable energy-absorbing materials have the problems of high peak force and low energy absorption efficiency. Summary of the invention

[0004] The embodiments of the present application provide a dual-material dual-layer curved beam negative stiffness multi-stable energy absorption structure, which solves the problems of high peak force and low energy absorption efficiency of existing negative stiffness multi-stable metamaterials.

[0005] To achieve the above-mentioned objectives, an embodiment of the present application provides a dual-material double-layer curved beam negative stiffness multi-stable energy absorption structure, comprising a plurality of cells; the cells comprise a first curved beam, a second curved beam, an upper horizontal support beam and a lower horizontal support beam; an intermediate connecting beam is provided on the lower surface of the upper horizontal support beam; two side connecting beams are provided on the upper surface of the lower horizontal support beam; the middle portion of the first curved beam is connected to the intermediate connecting beam, and the two ends are connected to the side connecting beams; the second curved beam is located below the first curved beam and has the same bending direction as the first curved beam, the middle portion of the second curved beam is connected to the intermediate connecting beam through a first interlocking structure, and the two ends are connected to the side connecting beams through a second interlocking structure; the first curved beam is made of hard material, and the second curved beam is made of soft material.

[0006] Furthermore, the number of cells is eight; the eight cells are arranged in four layers; the cells of two adjacent layers are arranged in opposite directions, and the first curved beam and the second curved beam in the cells of the top layer are both bent downward; the first curved beam and the second curved beam in the cells of the bottom layer are both bent upward.

[0007] Furthermore, the horizontal projection lengths of the first curved beam and the second curved beam are equal, and the cross-sectional thickness and vertical height of the second curved beam are greater than those of the first curved beam.

[0008] Furthermore, the geometric shape of the first curved beam in its natural state satisfies the functional relationship Wherein, w1 is the coordinate variable of the first curved beam along the height direction; h1 is the height of the first curved beam; l is the horizontal projection length of the first curved beam or the second curved beam; x1 is the coordinate variable of the first curved beam along the length direction;

[0009] The geometric shape of the second curved beam in its natural state satisfies the functional relationship Among them, w2 is the coordinate variable of the second curved beam along the height direction; h2 is the height of the second curved beam; x2 is the coordinate variable of the second curved beam along the length direction.

[0010] Furthermore, the first curved beam, the middle connecting beam, the side connecting beam, the upper horizontal supporting beam and the lower horizontal supporting beam are all made of nylon or polylactic acid.

[0011] Furthermore, the second curved beam is made of thermoplastic polyurethane.

[0012] Furthermore, the first engaging structure includes a first groove and a first engaging portion matched with the first groove; the first groove is provided on the lower surface of the middle connecting beam; and the first engaging portion is provided on the upper surface of the second curved beam.

[0013] Furthermore, the second engaging structure includes a second groove and a second engaging portion matched with the second groove; the second groove is provided on the side surface of the side connecting beam; and the second engaging portion is provided on the end surface of the second curved beam.

[0014] Furthermore, the upper horizontal support beam and the lower horizontal support beam have the same structure; the middle connecting beam and the side connecting beam have the same structure; the first curved beam, the upper horizontal support beam, the lower horizontal support beam, the middle connecting beam and the side connecting beam are integrally formed.

[0015] Furthermore, when the ratio of the height to the thickness of the first curved beam Q1 ≥ 5 and the ratio of the height to the thickness of the second curved beam Q2 ≤ 2.31, the force-displacement curve of the cell during the buckling process includes three segments, in which the force F1 in the first segment satisfies the formula:

[0016]

[0017] Wherein, h1 is the height of the first curved beam; t1 is the thickness of the first curved beam; E1 is the elastic modulus of the first curved beam; I1 is the moment of inertia of the cross section of the first curved beam; l is the horizontal projection length of the first curved beam or the second curved beam; d is the displacement during the buckling process; h2 is the height of the second curved beam; t2 is the thickness of the second curved beam; E2 is the elastic modulus of the second curved beam; I2 is the moment of inertia of the cross section of the second curved beam;

[0018] The force F2 in the second paragraph satisfies the formula:

[0019]

[0020] The force F3 in the third paragraph satisfies the formula:

[0021]

[0022] Compared with the prior art, this application has the following beneficial effects:

[0023] 1. The dual-material double-layer curved beam negative stiffness multi-stable energy absorption structure of the embodiment of the present application utilizes the difference in the buckling position of curved beams of different thicknesses and heights to make the peak forces of the first curved beam and the second curved beam appear at different displacement stages, and uses hard materials and soft materials to respectively construct the two curved beams of the cell, thereby effectively reducing the peak force of the structure and improving the energy absorption efficiency per unit volume, while realizing a bistable characteristic.

[0024] 2. The double-material double-layer curved beam negative stiffness multi-stable energy-absorbing structure of the embodiment of the present application obtains the force-displacement relationship expression during the cell buckling process through theoretical derivation, verifies its mechanical properties, and significantly improves the efficiency of structural design. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present application 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 application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0026] Figure 1 This is a schematic diagram of the three-dimensional structure of the double-material double-layer curved beam negative stiffness multi-stable energy absorption structure according to an embodiment of the present application;

[0027] Figure 2 This is a front view of a double-material double-layer curved beam negative stiffness multi-stable energy absorption structure according to an embodiment of the present application;

[0028] Figure 3 A cell model and a decomposition diagram of a double-material double-layer curved beam negative stiffness multi-stable energy absorption structure in an embodiment of the present application;

[0029] Figure 4 This is a deformation diagram of a cell in a double-material double-layer curved beam negative stiffness multi-stable energy-absorbing structure when it is compressed in an embodiment of the present application;

[0030] Figure 5 It is a theoretical curve diagram of the superposition of the force-displacement curves of the first curved beam and the second curved beam in the double-material double-layer curved beam negative stiffness multi-stable energy absorption structure of the embodiment of the present application;

[0031] Figure 6 This is a comparison diagram of the force-displacement curves of the double-material double-layer curved beam negative stiffness multi-stable energy absorption structure and the double-layer 1mm nylon curved beam in the embodiment of the present application;

[0032] Figure 7 This is a comparison chart of the unit volume energy absorption curves of the double-material double-layer curved beam negative stiffness multi-stable energy absorption structure of the embodiment of the present application and the double-layer 1mm nylon curved beam. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0034] In the description of the present application, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0035] In the description of the present application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected" and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection. For ordinary technicians in this field, they can understand the specific meanings of the above terms in this application according to specific circumstances.

[0036] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" can explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise specified, "plurality" means two or more.

[0037] Reference Figures 1 to 4 The embodiment of the present application provides a double-material double-layer curved beam negative stiffness multi-stable energy absorption structure, including eight cells 9 arranged in four layers. Each cell 9 includes a first curved beam 1, a second curved beam 2, an upper horizontal support beam 3, a lower horizontal support beam 4, a middle connecting beam 5 and two side connecting beams 6.

[0038] The middle connecting beam 5 is connected to the middle part of the lower surface of the upper horizontal supporting beam 3 , and the two side connecting beams 6 are connected to the left and right ends of the upper surface of the lower horizontal supporting beam 4 .

[0039] The middle part of the first curved beam 1 is connected to the middle connecting beam 5, and the two ends are connected to the side connecting beams 6. The second curved beam 2 is located below the first curved beam 1 and has the same bending direction as the first curved beam 1. The middle part of the second curved beam 2 is connected to the middle connecting beam 5 through a first interlocking structure 7, and the two ends are connected to the side connecting beams 6 through a second interlocking structure 8.

[0040] The cells 9 of two adjacent layers are arranged facing each other or facing each other, that is, the bending directions of the first curved beams 1 and the second curved beams 2 in the cells 9 of the two adjacent layers are opposite. Specifically, the first curved beams 1 and the second curved beams 2 in the cells 9 of the top layer and the third layer from top to bottom are bent downward, and the first curved beams 1 and the second curved beams 2 in the cells 9 of the second layer and the bottom layer are bent upward, thereby improving the energy absorption per unit volume and providing good buffer protection capability.

[0041] The height of the first curved beam 1 is h1=6mm, and the thickness is t1=1mm; the height of the second curved beam 2 is h2=5mm, and the thickness is t2=2.6mm; the horizontal projection length of the first curved beam 1 and the second curved beam 2 is l=85mm, and the thickness in the out-of-plane direction is b=20mm.

[0042] Substitute h1=6mm, l=85mm into the functional relationship The geometric shape function relationship of the first curved beam 1 in the embodiment of the present application can be obtained. Wherein, w1 is the coordinate variable of the first curved beam along the height direction, and x1 is the coordinate variable of the first curved beam 1 along the length direction.

[0043] Then substitute h2=5mm, l=85mm into the functional relationship The geometric shape function relationship of the second curved beam 2 in the embodiment of the present application can be obtained. Among them, w2 is the coordinate variable of the second curved beam along the height direction, and x2 is the coordinate variable of the second curved beam 1 along the length direction.

[0044] The first curved beam 1, the middle connecting beam 5, the two side connecting beams 6, the upper horizontal support beam 3 and the lower horizontal support beam 4 are all made of nylon (PA) or polylactic acid (PLA) material, and the elastic modulus is 1000MPa and the Poisson's ratio is 0.3. The first curved beam 1, the middle connecting beam 5, the two side connecting beams 6, the upper horizontal support beam 3 and the lower horizontal support beam 4 are processed in one piece.

[0045] The second curved beam 2 is connected to the middle connecting beam 5 by a first interlocking structure 7. The second curved beam 2 is connected to the side connecting beam 6 by a second interlocking structure 8. The material of the second curved beam 2 is thermoplastic polyurethane (TPU), with an elastic modulus of 80 MPa and a Poisson's ratio of 0.3.

[0046] The first curved beam 1 and the second curved beam 2 have a spacing of 4 mm at both ends and a spacing of 3 mm in the middle. The middle connecting beam 5 and the side connecting beam 6 are both 11.5 mm long and 6 mm wide. The upper horizontal support beam 3 and the lower horizontal support beam 4 are both 85 mm long and 6 mm wide.

[0047] The first interlocking structure 7 includes a first groove 71 and a first interlocking portion 72 matched with the first groove 71. The first groove 71 is provided on the lower surface of the middle connecting beam 5, and the first interlocking portion 72 is provided on the upper surface of the second curved beam 2. The second interlocking structure 8 includes a second groove 81 and a second interlocking portion 82 matched with the second groove 81. The second groove 81 is provided on the inner side surface of the side connecting beam 6, and the second interlocking portion 82 is provided on the end surface of the second curved beam 2. Both the first groove 71 and the second groove 81 are "T"-shaped grooves.

[0048] Reference Figure 3 When preparing the energy absorbing structure, first prepare the first curved beam 1, the middle connecting beam 5, the two side connecting beams 6, the upper horizontal support beam 3 and the lower horizontal support beam 4 as an integrated part and the second curved beam 2 respectively, and then embed the second curved beam 2.

[0049] Figure 4 The deformation diagram of the cell 9 in the energy absorption structure of the embodiment of the present application when it is compressed is shown. It can be seen from the figure that when the cell 9 is subjected to external compressive force, due to the difference in thickness and height between the first curved beam 1 and the second curved beam 2, that is, the difference in the buckling position between the two, the peak forces of the two curved beams appear at different displacement stages. In addition, due to the different materials of the two curved beams, the peak force of the energy absorption structure is effectively reduced and the energy absorption efficiency per unit volume is improved, while achieving a bistable characteristic.

[0050] When the ratio of the height to the thickness of the first curved beam 1 is The ratio of the height to the thickness of the second curved beam 2 When , the force-displacement curve of cell 9 during the buckling process includes three sections. The force F1 in the first section satisfies the formula:

[0051]

[0052] Wherein, h1 is the height of the first curved beam 1; t1 is the thickness of the first curved beam 1; E1 is the elastic modulus of the first curved beam 1; I1 is the moment of inertia of the cross section of the first curved beam 1; l is the horizontal projection length of the first curved beam 1 or the second curved beam 2; d is the displacement during the buckling process; h2 is the height of the second curved beam 2; t2 is the thickness of the second curved beam 2; E2 is the elastic modulus of the second curved beam 2; I2 is the moment of inertia of the cross section of the second curved beam 2;

[0053] The force F2 in the second paragraph satisfies the formula:

[0054]

[0055] The force F3 in the third paragraph satisfies the formula:

[0056]

[0057] Set h1 = 6 mm, t1 = 1 mm, E1 = 1000 MPa, l=85mm, h2=5mm, t2=2.6mm; E2=80MPa, Substituting the above three formulas, we can obtain the three-stage force-displacement curves of the cell 9 in the buckling process in the embodiment of the present application:

[0058] F1=0.082d 3 -1.484d 2 +14.740dd∈(0,1.17)

[0059] F2=0.082d 3 -1.484d 2 +4.970d+11.416d∈(1.17,9.20)

[0060] F3=0.082d 3 -1.484d 2 +17.016d+99.393d∈(9.20,10.13)

[0061] like Figure 5 As shown, the force-displacement curve of the compression deformation of cell 9 shows that the structural load presents a gentle change area near the peak value, and then the load gradually decreases. There is a negative stiffness area, and the minimum value of the curve is below zero, which has obvious bistable characteristics.

[0062] Comparison of mechanical properties between double-material double-layer curved beam negative stiffness multi-stable energy absorption structure and single-material negative stiffness multi-stable structure Figure 6 , Figure 7 shown.

[0063] Depend on Figure 6 and Figure 7 It can be seen that the two-layer cell structure composed of 1mm nylon (PA) and 2.6mm thermoplastic polyurethane (TPU) has a 14.78% lower peak force and a 25.4% higher energy absorption per unit volume compared to the two-layer 1mm nylon (PA) cell structure. The optimized structure reduces the peak force while increasing the energy absorption per unit volume. After impact, it can maintain a stable state after deformation without external force. It stores energy in the structure through elastic deformation, effectively avoiding or reducing secondary damage, and providing good buffer protection capabilities.

[0064] The above are only specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A double-material double-layer curved beam negative stiffness multi-stable energy absorption structure, characterized in that: It comprises a plurality of cells; the cells comprise a first curved beam, a second curved beam, an upper horizontal support beam and a lower horizontal support beam; a middle connecting beam is arranged on the lower surface of the upper horizontal support beam; two side connecting beams are arranged on the upper surface of the lower horizontal support beam; the middle part of the first curved beam is connected to the middle connecting beam, and both ends are connected to the side connecting beams; the second curved beam is located below the first curved beam and has the same bending direction as the first curved beam, the middle part of the second curved beam is connected to the middle connecting beam through a first interlocking structure, and both ends are connected to the side connecting beams through a second interlocking structure; the first curved beam is made of hard material, and the second curved beam is made of soft material.

2. The double-material double-layer curved beam negative stiffness multi-stable energy absorption structure according to claim 1 is characterized in that: The number of the cells is eight; the eight cells are arranged in four layers; the cells of two adjacent layers are arranged in opposite directions, and the first curved beam and the second curved beam in the cells of the top layer are both bent downward; the first curved beam and the second curved beam in the cells of the bottom layer are both bent upward.

3. The double-material double-layer curved beam negative stiffness multi-stable energy absorption structure according to claim 1 is characterized in that: The horizontal projection lengths of the first curved beam and the second curved beam are equal, and the cross-sectional thickness and vertical height of the second curved beam are greater than those of the first curved beam.

4. The double-material double-layer curved beam negative stiffness multi-stable energy absorption structure according to claim 3 is characterized in that: The geometric shape of the first curved beam in its natural state satisfies the functional relationship Wherein, w1 is the coordinate variable of the first curved beam along the height direction; h1 is the height of the first curved beam; l is the horizontal projection length of the first curved beam or the second curved beam; x1 is the coordinate variable of the first curved beam along the length direction; The geometric shape of the second curved beam in its natural state satisfies the functional relationship Among them, w2 is the coordinate variable of the second curved beam along the height direction; h2 is the height of the second curved beam; x2 is the coordinate variable of the second curved beam along the length direction.

5. The double-material double-layer curved beam negative stiffness multi-stable energy absorption structure according to claim 1 is characterized in that: The first curved beam, the middle connecting beam, the side connecting beam, the upper horizontal supporting beam and the lower horizontal supporting beam are all made of nylon or polylactic acid, and the first curved beam, the upper horizontal supporting beam, the lower horizontal supporting beam, the middle connecting beam and the side connecting beam are integrally formed.

6. The double-material double-layer curved beam negative stiffness multi-stable energy absorption structure according to claim 1 is characterized in that: The second curved beam is made of thermoplastic polyurethane.

7. The double-material double-layer curved beam negative stiffness multi-stable energy absorption structure according to claim 1 is characterized in that: The first engaging structure comprises a first groove and a first engaging portion matched with the first groove; the first groove is arranged on the lower surface of the middle connecting beam; and the first engaging portion is arranged on the upper surface of the second curved beam.

8. The double-material double-layer curved beam negative stiffness multi-stable energy absorption structure according to claim 7 is characterized in that: The second engaging structure comprises a second groove and a second engaging portion matched with the second groove; the second groove is arranged on the side surface of the side connecting beam; and the second engaging portion is arranged on the end surface of the second curved beam.

9. The double-material double-layer curved beam negative stiffness multi-stable energy absorption structure according to claim 8, characterized in that: The upper horizontal support beam and the lower horizontal support beam have the same structure; the middle connecting beam and the side connecting beam have the same structure.

10. The double-material double-layer curved beam negative stiffness multi-stable energy absorption structure according to claim 1, characterized in that: When the ratio of the height to the thickness of the first curved beam Q1 ≥ 5 and the ratio of the height to the thickness of the second curved beam Q2 ≤ 2.31, the force-displacement curve of the cell during the buckling process includes three segments, among which the force F1 in the first segment satisfies the formula: Wherein, h1 is the height of the first curved beam; t1 is the thickness of the first curved beam; E1 is the elastic modulus of the first curved beam; I1 is the moment of inertia of the cross section of the first curved beam; l is the horizontal projection length of the first curved beam or the second curved beam; d is the displacement of the upper horizontal support beam of the cell during the buckling process; h2 is the height of the second curved beam; t2 is the thickness of the second curved beam; E2 is the elastic modulus of the second curved beam; I2 is the moment of inertia of the cross section of the second curved beam; The force F2 in the second paragraph satisfies the formula: The force F3 in the third paragraph satisfies the formula:

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