A high-ductility multi-stage flexible structure based on node design

Abstract

The application discloses a high-ductility multistage flexible structure based on node design, which is a multistage lattice flexible structure formed by periodic array of multistage unit cells; each unit cell is composed of a central structured node and a circular-arc microstructure connected with the structured node; the structured node is composed of a plurality of central symmetrical circular-arc segments, and has bending, stretching and rotating coupling deformation capabilities; and the circular-arc microstructure is connected with the structured node in the form of being tangent to an auxiliary circle of the structured node. The structured node of the application has bending, stretching and rotating coupling deformation, improves the deformation capability of the flexible lattice structure under the action of tensile load, greatly improves the limit ductility, guarantees the tensile strength, expands the design space and application range of the flexible lattice structure, and can be applied not only to flexible electronic device substrates but also to large deployable structures and other fields.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of flexible structure, and particularly relates to a high-ductility multi-stage flexible structure based on node design. BACKGROUND

[0002] Flexible electronic devices have important application value in the fields of health monitoring, disease treatment, posture recognition and soft robot, and therefore have developed rapidly in recent years. Inorganic stretchable electronic devices are concerned due to the combination of high electrical properties and high stretchability. The flexibility of the device system depends not only on the design method of the wire connecting the hard electronic element, but also on the mechanical properties of the device substrate and the packaging layer. In order to enable the device system to be stably combined with the human body or other organisms for a long time, the key is to propose a soft material or flexible structure design method suitable for the device substrate / packaging layer. For solid soft materials based on chemical synthesis method such as silicone rubber, the mechanical properties are difficult to accurately and quantitatively control according to the target requirements. The flexible lattice structure with periodic characteristics can realize adjustable biomimetic "J-shaped" stress-strain response, and has high air permeability and defect insensitivity, and therefore has unique advantages when applied to flexible electronic devices. How to improve the ductility of the flexible lattice structure without reducing the tensile strength is an important and challenging technical method.

[0003] In the prior art, the design method of the flexible lattice structure is limited to two aspects, one is to design the microstructure shape between the nodes of the lattice, such as horseshoe-shaped, zigzag-shaped microstructure, etc.; the other is to design the topological form of the lattice, such as triangle, honeycomb, etc. These structures can realize the regulation of stress-strain curve and Poisson's ratio, but the improvement effect of the limit mechanical properties (such as ductility, strength, etc.) of the structure is very small, and the ductility of the flexible lattice structure still has great room for improvement. At present, there is no flexible lattice structure proposed from the perspective of node design. SUMMARY

[0004] In view of the problems in the prior art, the purpose of the present application is to provide a high-ductility multi-stage flexible structure based on node design, so as to solve the problem of insufficient ductility of the existing flexible lattice structure, and to broaden the design space and application range of the flexible lattice structure.

[0005] In order to achieve the above purpose, the present application realizes the following technical scheme:

[0006] A high ductility multi-level flexible structure based on node design, the high ductility multi-level flexible structure is a multi-level lattice flexible structure formed by periodic array of multi-level unit cells; each unit cell is composed of a central structured node and a circular arc microstructure connecting the structured node, the structured node is composed of a plurality of circular arc segments which are central symmetric, the structured node has bending, stretching and rotational coupling deformation ability; the circular arc microstructure is connected with the structured node in the form of tangent to the auxiliary circle of the structured node.

[0007] The multi-level lattice flexible structure is realized by structured node design, the number of levels n of the multi-level lattice flexible structure, for multi-level lattice flexible structures with different levels, the number of circular arc segments in the structured node is n times the number of circular arc microstructures in the corresponding unit cell; when n is 0, the structured node degenerates into a point node in the traditional lattice structure, when n is 1, a one-level multi-level lattice structure is formed which is the most representative; the number of circular arc microstructures is related to the periodic topological form, corresponding to triangle, square and honeycomb, the number of circular arc microstructures is 6, 4 and 3 respectively, the geometric shape is controlled by the microstructure central angle φ0 and the microstructure radius r0;

[0008] The width of each circular arc segment in the structured node and the circular arc microstructure is uniform, the size of the structured node is described by the auxiliary circle radius r of the structured node, the node arc central angle is described by φ which is independent of the microstructure arc central angle; the circular arc in the circular arc microstructure is connected with the structured node in the form of tangent to the auxiliary circle of the structured node, the included angle between the connecting line from the connection point to the center of the structured node and the horizontal direction is the connection angle θ; the microstructure central angle φ0 and the microstructure radius r0 are obtained from the unit cell span L, the connection angle θ and the node radius r, the calculation formula is as follows:

[0009]

[0010] On this basis, the relevant parameters are standardized by the unit cell span L, and the unit cell of the high ductility multi-level flexible structure can be completely described and designed by the four standardized parameters w / L, r / L, θ and φ.

[0011] The ultimate ductility of the multi-level lattice flexible structure is related to the critical strain ε cr The critical strain ε cr The critical strain ε cr The calculation formula is as follows:

[0012]

[0013] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0014] (A) The structured node of the present application improves the deformation ability of the flexible lattice structure under tensile load by bending, stretching and rotating coupling deformation, thereby achieving a substantial increase in ultimate ductility.

[0015] (B) The multi-level flexible structure of the present application does not need to reduce the cross-sectional size of the microstructure compared with the existing fractal structure, and ensures the tensile strength while improving the ductility, to a certain extent, solving the problem that high ductility and high strength are difficult to be compatible.

[0016] (C) The present application introduces new structural design freedoms such as structural level, node size and node shape, which expands the design space and application range of the flexible lattice structure, and can be applied not only to flexible electronic device substrates, but also to large deployable structures and other fields.

[0017] (D) The present application can realize precise control of the overall nonlinear mechanical response and extreme mechanical properties of the structure through structural parameter control, which has important application value in the field of flexible electronic devices;

[0018] (E) The multi-level flexible structure of the present application is easy to realize, compatible with various high-precision planar preparation techniques, and the types of parent materials are not limited, which can fully play the advantages of structural performance. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a schematic diagram of the unit cell of the present application under different topologies and structural levels.

[0020] Figure 2 is a schematic diagram of the geometric parameters of the present application.

[0021] Figure 3a , Figure 3b and Figure 3c are schematic diagrams of the overall structure of the present application corresponding to the periodic topologies of triangle, square and honeycomb, respectively.

[0022] Figure 4a and Figure 4b are stress-strain curves, ductility and strength comparison diagrams of the present application and traditional flexible lattice structures, respectively.

[0023] Figure 5 is a schematic diagram of the ductility and strength performance space of the present application and the prior art structure and material. DETAILED DESCRIPTION

[0024] The present application will be further described in detail below in combination with the drawings and specific embodiments. It should be noted that the present application is not limited to the following specific embodiments, and any equivalent variations and improvements made on the basis of the technical solutions of the present application fall within the scope of the present application.

[0025] AsFigures 1 to 5 As shown in the drawings, the embodiment gives a high ductility multistage flexible structure based on node design, which realizes a substantial improvement in ductility without loss of tensile strength.

[0026] The multistage flexible structure of the application is composed of multistage unit cells through periodic arraying. Figure 1 As shown, the multistage flexible structure is realized through structured node design, so that the node structure of the n-stage unit cell has a similar geometric configuration to the overall structure of the n-1-stage unit cell. The structured node is composed of a plurality of central symmetric circular arcs, and the number of circular arcs is related to the topological form and the structure stage number n, and is 6n, 4n and 3n respectively for triangular, square and honeycomb unit cells.

[0027] In one specific embodiment, a one-stage multistage lattice structure of square topology is composed of a central structured node and four circular arc microstructures connecting the nodes, as shown in the drawings. Figure 2 The width of the circular arc of the structured node and the arc segment of the circular arc microstructure is uniform as w, and the horizontal span of the unit cell is L. The geometric shape of the circular arc microstructure is controlled by the microstructure center angle φ0 and the microstructure radius r0. The size of the structured node is described by the auxiliary circle radius r of the structured node, and the node circular arc center angle is described by φ which is independent of the microstructure circular arc center angle. The arc segment of the circular arc microstructure is connected with the structured node in the form of tangency with the auxiliary circle of the structured node, and the angle between the connecting line from the connection point to the center of the structured node and the horizontal direction is the connection angle θ. The unit cell of the high ductility multistage flexible structure can be completely described and designed by the four standardized parameters w / L, r / L, θ and φ.

[0028] The ultimate ductility of the application can be calculated by the critical strain ε cr As described, the critical strain ε cr is related to the structure stage number n and the standardized parameters r / L, θ and φ. In one specific embodiment, the arc segment in the structured node and the microstructure is a semicircular arc, which satisfies θ = φ = 180°, and the critical strain ε cr The calculation formula is as follows:

[0029]

[0030] In one specific embodiment, the four standardized parameters are w / L = 0.01, r / L = 0.3, θ = 180° and φ = 180° respectively, the structure stage number n = 1, and the unit cell is periodically extended in different ways to obtain a multistage flexible structure, as shown in the drawings. Figure 3a 、 Figure 3b and Figure 3c The application is compatible with various high-precision planar preparation technologies such as photolithography and laser cutting, and the types of parent materials are not limited, which can be selected from polymers, elastomers, metals and the like.

[0031] The structured node of the present application has bending, stretching and rotating coupling deformation ability, compared with the traditional flexible lattice structure, the deformation ability and ductility is greatly improved, and the tensile strength is ensured. In one specific embodiment, the multistage lattice flexible structure of the present application is prepared by taking polymer as the matrix material and through 3D printing technology, which can provide more than 4 times ductility of the traditional structure with the same microstructure parameters without loss of tensile strength, as shown in Figure 4a and Figure 4b .

[0032] As shown in Figure 5 , the present application can provide higher ductility than the existing flexible lattice structure technology, and within the range of achievable ductility, it can provide higher tensile strength than typical soft materials, providing a technical approach to solve the problem of high ductility and high strength difficult to be considered in the field of flexible structure and soft material.

Claims

1. A highly ductile, multi-level flexible structure based on node design, characterized in that: The highly ductile multi-level flexible structure is a multi-level lattice flexible structure formed by periodically arraying multi-level unit cells; each unit cell consists of a central structured node and arc-shaped microstructures connecting the structured nodes. The structured node consists of multiple centrally symmetrical arc segments and has the ability to bend, stretch, and rotate coupled deformation. The arc-shaped microstructure is connected to the structured node in a manner that is tangent to the auxiliary circle of the structured node; The multi-level lattice flexible structure is implemented through a structured node design, and the number of levels in the multi-level lattice flexible structure is: n For multi-level lattice flexible structures with different numbers of levels, the number of arc segments in the structured nodes is equal to the number of arc-shaped microstructures in the corresponding unit cell. n times; when n When the value is 0, the structured node degenerates into a point node in the lattice structure. n When the value is 1, a multi-level lattice structure is formed; the number of arc-shaped microstructures is related to the periodic topological form, corresponding to triangles, squares, and honeycomb shapes, with the numbers of arc-shaped microstructures being 6, 4, and 3 respectively. The geometric shape is determined by the central angle of the microstructure. φ 0 and microstructure radius r 0 control; The width of each arc segment in the structured nodes and arc-shaped microstructures is uniformly set to... w The size of a structured node is determined by the radius of its auxiliary circle. r describe ， The central angle of the node arc is independent of the central angle of the microstructure arc. φ Description: In the arc-shaped microstructure, the arc connects to the structured node in a tangent manner to the auxiliary circle of the structured node. The angle between the line connecting this connection point to the center of the structured node and the horizontal direction is called the connection angle. θ Microstructure central angle φ 0 and microstructure radius r 0 is the span of a single cell L Connecting angle θ and node radius r The calculation formula is as follows: Based on this, use unit cell span L By standardizing relevant parameters, the unit cell energy of a highly ductile, multi-level flexible structure can be obtained from... w / L , r / L , θ , φ These four standardized parameters fully describe and design; The ultimate ductility of the multi-level lattice flexible structure is determined by the critical strain. ε cr Description, critical strain ε cr With structural hierarchy n Related to geometric parameters, the critical strain is when the arc segment in the structured node and microstructure is a semi-circular arc. ε cr The calculation formula is as follows: 。

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