A method for designing a lattice structure of a multi-level configuration

Abstract

The application relates to the field of helmets, in particular to a lattice structure design method of a multi-level configuration, a multi-level cell structure is constructed, the multi-level cell structure is used as a helmet lining, and the specific steps of constructing the multi-level cell structure are as follows: S1: a cubic space is constructed, the cubic space is equally divided into four equal parts, and a second layer region and a third layer region are combined into a middle region; S2: a first body is constructed, connecting rods at the upper end and the lower end of the first body are deleted to obtain a second body, four top points at the upper end and the lower end of the second body are sequentially connected by first connecting rods to obtain a third body, and the third body is arranged in the middle region; S3: four corners at the upper end and the lower end of the third body are connected with corresponding two edges one by one by second connecting rods to obtain a multi-level cell structure; three-dimensional nesting and multi-level configuration are realized on a cell scale.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of helmets, in particular to a multi-level lattice structure design method. BACKGROUND

[0002] With the development of economy and the improvement of people's living standards, consumers' demand for higher performance and safer protective helmets is also increasing. The main function of protective helmets is to disperse the energy generated by impact when an accident or collision occurs, thereby reducing the risk of head injury, and also effectively preventing serious injuries such as head fractures, skull injuries, and concussions. Among the components of the helmet, the outer shell bears the impact at the moment of collision, and then the inner liner further relieves and absorbs the energy generated by the collision, so the helmet liner structure is an important design element to ensure the safety performance of the helmet.

[0003] Although the existing lattice point array structure has the advantages of light weight, high strength, and adjustable mechanical properties, there are still obvious deficiencies in design concept and performance. Traditional helmet liners often use foam filling materials, which have low space utilization and limited compression resistance.

[0004] Most current structure designs are limited to direct imitation of the shapes of organisms in nature, or achieve local configuration changes by increasing and offsetting the bars, which focuses on shape improvement and lacks design strategies for multi-stage deformation, making it difficult to significantly improve overall performance under complex loads. SUMMARY

[0005] The purpose of the present application is to provide a multi-level lattice structure design method that can achieve three-dimensional multi-stage deformation.

[0006] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0007] A multi-level lattice structure design method, a multi-level unit cell structure is constructed, and the multi-level unit cell structure is used as a helmet liner. The specific steps for constructing the multi-level unit cell structure are as follows:

[0008] S1: Construct a cubic space, divide the cubic space into four equal parts along the Z-axis direction, and combine the second layer region and the third layer region of the cubic space into a middle region;

[0009] S2: using a hexagon as a design unit, on a plane where a diagonal of the cubic space is located, a first structure is obtained by rotating the design unit by 90° in the Z-axis direction with the symmetry axis of the design unit, a second structure is obtained by deleting the connecting rods at the upper end and the lower end of the first structure, the four vertices of the upper end and the lower end of the second structure are sequentially connected by using first connecting rods, the first connecting rods form a square, and the third structure is placed in the middle region;

[0010] S3: the four corners of the upper end of the third structure are connected to the four edges of the upper end of the first layer region one by one by using second connecting rods, the four corners of the lower end of the third structure are connected to the four edges of the lower end of the fourth layer region one by one by using second connecting rods, and the second connecting rods are perpendicular to the connected edges, and a multi-level unit cell structure is obtained.

[0011] Preferably, the method further comprises the following step: S4: defining the size parameters of the multi-level unit cell structure: the diameter D of each connecting rod, the side length L of the unit cell, the side length 2M of the quadrilateral formed by the first connecting rod, and the distance 2H between the upper and lower first connecting rods on the same side;

[0012] S5: setting the side length L of the unit cell of the multi-level unit cell structure to 10 mm, setting the size parameters of M and H respectively, and adjusting the diameter D of the connecting rod to ensure that the relative density of the multi-level unit cell structure is the same under different size parameter combinations, based on the set size parameters and the multi-level unit cell structure, generating a lattice structure with a cell number of 3x3x3 in the X, Y and Z directions, and obtaining a lattice structure database;

[0013] S6: based on the structure performance sensitivity analysis of single parameter gradual change control, and comparative analysis is performed on the results, and the lattice structure with the optimal performance is obtained according to the comparative analysis results.

[0014] Preferably, in step S6, the structure performance sensitivity analysis based on single parameter gradual change control is that a plurality of groups of gradual values are taken for one geometric parameter under the condition that a single geometric parameter M or H is kept unchanged, stress-strain curves, deformation modes and key mechanical performance indicators under different parameter combinations are obtained through finite element simulation, and the lattice structure with the optimal performance is obtained.

[0015] Preferably, the key mechanical performance indicators include densification strain, platform stress, SEA, platform stress normalized value, SEA normalized value and performance sensitivity.

[0016] By adopting the foregoing design scheme, the beneficial effects of the application are: the multi-level cell structure constructed by the application divides the multi-level cell structure into three layers, the middle region is the third structure of the tortoise shell structure, the upper region and the lower region adopt the second connecting rod to construct the tree-like branch, so that the multi-level cell structure has the hierarchical characteristics and the multi-stage fractal structure of the tree-like branch, realizes three-dimensional nesting and multi-level configuration on the cell scale, and provides a new implementation approach for multi-stage deformation of the structure. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 A schematic diagram of the cubic space division structure of the application is shown in the figure.

[0018] Figure 2 A schematic diagram of the tortoise shell and tree-like structure analysis of the application is shown in the figure.

[0019] Figure 3 A schematic diagram of the steps of constructing the multi-level cell structure of the application is shown in the figure.

[0020] Figure 4 A schematic diagram of the lattice structure of the application is shown in the figure.

[0021] Figure 5 A schematic diagram of the finite element model and the corresponding physical sample compression process of the application is shown in the figure.

[0022] Figure 6 A stress-strain curve diagram of the lattice structure of the application is shown in the figure.

[0023] Figure 7 A flowchart of the lattice structure design method of the application is shown in the figure.

[0024] Figure 8 A deformation mode diagram of the lattice structure of the application is shown in the figure. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical scheme and advantages of the application clearer, the application will be further described in detail below in combination with the drawings. Obviously, the described embodiments are only some of the embodiments of the application, not all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the application.

[0026] The terms "first", "second", "third", and the like in the description and claims of the present application and the above drawings, are used for distinguishing between similar objects, and are not necessarily used to describe a particular sequential or chronological order. Also, the terms "comprises", "comprising", "includes", "including", or the like means encompassing, but not limited to, for example, a process, method, object, or apparatus that consists of, or includes, but are not limited to, an element or list of elements in that process, method, object, or apparatus, and that element or list does not, without more constraints, preclude other elements or additional elements, whether related or unrelated to that element or list.

[0027] A lattice structure design method of multi-level configuration, as shown in Figure 7 , a multi-level unit cell structure is constructed, and the multi-level unit cell structure is used as a helmet lining. The specific steps for constructing the multi-level unit cell structure are as follows:

[0028] S1: For a multi-stage deformation structure and its stiffness distribution characteristics, a cubic space is constructed, and an XYZ coordinate axis is constructed with the geometric center of the bottom surface of the cubic as the 0 point, as shown in Figure 3 , the cubic space is evenly divided into four equal parts along the Z-axis direction, and the second layer region and the third layer region of the cubic space are combined into a middle region, i.e. region 1 in Figure 1 , the middle region is mainly used for energy absorption, and the first layer region and the fourth layer region, i.e. region 2 in Figure 1 , are mainly used for load transmission guidance and boundary stability.

[0029] S2: Inspired by the biological structure of the natural world (turtle shell and tree-like branch), the structure mechanism is analyzed and the characteristics are extracted. The turtle shell is an oval arched surface in macro geometry, with non-uniform thickness distribution and asymmetric configuration, and the surface is covered with overlapping keratin scutes to form an additional protective layer. In the hierarchical structure, the turtle shell is a "hard-soft-hard" sandwich structure, including an outer keratin layer, a middle three-dimensional honeycomb cancellous bone foam layer, and an inner dense bone plate for rigid support. The tree-like branch structure is a multi-level branch structure in macro, forming a binary tree-like fractal network, which helps to uniformly disperse the load. The branch nodes have a tapered transition zone. The analysis of the two kinds of bionic characteristics is shown in Figure 2 .

[0030] Starting from the geometric characteristics of a large number of keratin scutes on the surface of the turtle shell, the shape is mostly hexagonal or irregular polygonal, and the thickness distribution is asymmetric. Therefore, this application adopts hexagon as the design unit, which is composed of two horizontal edges and four diagonal edges. The two horizontal edges are arranged in parallel, and the four diagonal edges are connected to the two sides of the horizontal edges to form two vertices, as shown in Figure 3As shown, the design unit is placed on the plane where the diagonals of the cubic space are located, two vertices are respectively located at the midpoints of the opposite edges of the cubic space, two vertices of the design unit are placed in the Y-axis direction, and the first structure is obtained by rotating the symmetry axis of the design unit by 90° in the Z-axis direction. At this time, a cross-shaped connection appears in the first structure, and the connecting rods at the upper end and the lower end of the first structure are deleted to obtain the second structure as shown in Figure 3 Part (2) of the middle. The four vertices at the upper end and the lower end of the second structure are connected in turn by the first connecting rod to obtain the third structure as shown in Figure 3 Part (3) of the middle. The quadrilateral surrounded by the first connecting rod is a square, and the third structure is placed in the middle region.

[0031] S3: According to the binary tree type design, the four corners at the upper end of the third structure are connected to the four edges at the upper end of the first layer region one by one by the second connecting rod, and the four corners at the lower end of the third structure are connected to the four edges at the lower end of the fourth layer region one by one by the second connecting rod, and the second connecting rod is perpendicular to the connected edge, as shown in Figure 3 Parts (4) and (5) of the middle, a multi-level unit cell structure is obtained; in this embodiment, as shown in Figure 3 One corner of the third structure is connected to two edges adjacent to the corresponding region one by one, forming a tree-like structure.

[0032] S5: Define the size parameters of the multi-level unit cell structure: the diameter D of each connecting rod, the side length L of the unit cell, the side length 2M of the quadrilateral surrounded by the first connecting rod, and the distance 2H between the upper and lower first connecting rods on the same side.

[0033] S6: Set the unit cell length L of the multi-level unit cell structure to 10 mm, and set the size parameters M, H to 1.5 mm, 2.0 mm, 2.5 mm and 3.0 mm respectively, and adjust the connecting rod diameter D to ensure that the relative density of the multi-level unit cell structure is the same under different size parameter combinations. Based on the set size parameters and the multi-level unit cell structure, a point array structure with a cell number of 3x3x3 is generated along the X, Y and Z directions to obtain a point array structure database; set M=H=2.5 mm to obtain the point array structure as shown in Figure 4 In this embodiment, the set relative density is 30.9%, and other parameter combinations can be set according to actual application requirements.

[0034] S7: Perform structure performance sensitivity analysis based on single parameter gradual change control, and perform comparative analysis on the results, and obtain the point array structure with the optimal performance according to the comparative analysis results.

[0035] In this embodiment, based on the experimental data of TPU material suitable for 3D printing, a finite element model for mechanical response analysis is constructed, a grid structure is generated by the finite element model, and the generated grid structure is placed between the upper and lower rigid plates, wherein all degrees of freedom of the bottom rigid plate are constrained, and the remaining degrees of freedom of the top rigid plate are also constrained except for the Z direction displacement freedom. The top rigid plate is loaded downward along the Z direction at a constant speed of 200 mm / s to simulate the quasi-static compression condition.

[0036] To truly reflect the super-elasticity and viscoelasticity of TPU material, the super-elasticity and viscoelasticity are introduced into the material constitutive, and the super-elasticity part is fitted by using the Marlow model for the tensile sample data. By comparing with the standard static compression experimental data, the accuracy of the established finite element model is checked to ensure the consistency of the calculation results and the actual mechanical response, which is used to characterize the material properties. The compression process of the finite element model and the corresponding physical sample is shown in Figure 5

[0037] In this embodiment, the material constitutive, also known as the mechanical constitutive equation of the material, or the stress-strain model of the material, is a mathematical expression describing the mechanical properties of the material, i.e. the stress-strain-strength-time relationship.

[0038] In step S7, based on the structure performance sensitivity analysis of single parameter gradual change control, a plurality of groups of gradual change values are obtained for one geometric parameter under the condition that a single geometric parameter M or H is kept unchanged, and stress-strain curves, deformation modes and key mechanical performance indicators are obtained by finite element simulation under different parameter combinations. In this embodiment, the key mechanical performance indicators include densification strain, platform stress, SEA, platform stress normalized value, SEA normalized value and performance sensitivity; and the lattice structure with the best performance is obtained.

[0039] In this embodiment, the deformation mode refers to the deformation state of the structure under different compression amounts, as shown in Figure 8 which shows the deformation mode under the M2.5-H2.5 parameter combination.

[0040] In order to better illustrate the lattice design method of the present application, the following specific embodiment analysis is carried out.

[0041] Table 1 shows the geometric parameter combination scheme based on single parameter gradual change control, according to which 16 groups of performance sensitivity analysis can be carried out. Taking M=2.5 mm as a variable control example, Figure 6 the stress-strain curve comparison results are given, and Table 2 gives the structure performance sensitivity analysis, combined with Figure 6 and the content of Table 2, the combination of (M2.5, H2.5) has the best mechanical performance in this grouping.

[0042] ​Table 1 Geometric parameter combination schemes based on single-parameter gradual control

[0043]

[0044] Table 2 Sensitivity analysis of MDCM structure performance under single-parameter gradual control (M = 2.5 mm)

[0045]

[0046] The comprehensive analysis results show that the structure generally appears a significant stress-strain curve drop phenomenon after the strain is about 0.4, and the drop amplitude, corresponding strain position and response mode change significantly with the parameter combination. When M and H are both the minimum value (1.5 mm), the rigidity of the inner layer imitation tortoise shell structure is weakened, the multi-stage deformation characteristic disappears, and the stress-strain curve shows a monotonous and stable growth; when the parameters increase to H≥2.5 mm, the length of the imitation tree structure rod decreases, which leads to the overall rigidity decrease and the compression response tends to be stable. It is further found that the decrease of M value will make the stress drop appear position delay to the densification stage, which shows that it has a significant control effect on the instability time; and the parameter combination of M>H will cause a wider drop area and a larger fluctuation amplitude, which is not conducive to the stability of energy absorption, compared with the combination of M≤H, which has more uniform stress distribution and more stable compression response. The geometric symmetry configuration (M=H) generally has higher platform stress, larger densification strain and better specific energy absorption; the asymmetric configuration is easy to induce local buckling and yield in advance, which reduces the energy absorption performance. Overall, the sensitivity analysis method can realize the correlation and quantization of geometric parameters and mechanical properties, and provides an effective design basis for the stability optimization and energy absorption performance improvement of multi-stage deformation lattice structure.

[0047] In summary, the sensitivity analysis method proposed in the present application systematically studies the geometric parameters and mechanical properties of the lattice structure, and the results show that the symmetry matching of the unit half side length M and the height H is a key factor affecting the energy absorption efficiency and structural stability. The sensitivity analysis results show that when M and H are symmetrical, the structural rigidity distribution is more uniform, the load transfer is more continuous, the imitation tree branches and the imitation tortoise shell configuration can form a good synergistic effect, which significantly prolongs the deformation stage in the compression process, effectively suppresses the local early instability, and thus greatly improves the stability of the platform stress and the energy absorption performance. On the contrary, when M and H are asymmetric, the sensitivity analysis reveals that the lateral constraint of the structure is weakened, the early buckling and sliding instability are more likely to occur, which is manifested as the stress curve fluctuation enhancement and the densification in advance, resulting in a significant decrease in energy dissipation capacity. As can be seen, the sensitivity analysis method verifies that the geometric symmetry should be the core design strategy of the lattice structure, which provides a basis for multi-stage stable deformation and high-efficiency energy absorption. The use of the lattice structure as a helmet liner can significantly improve the buffering and energy absorption effect, and effectively improve the safety performance of the helmet.

[0048] The above detailed description has further explained the purpose, technical solutions and beneficial effects of the present application. It should be understood that the above description is only a specific embodiment of the present application and is not intended to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for designing a multi-level lattice structure, characterized in that: A multi-level unit cell structure is constructed and used as a helmet liner. The specific steps for constructing the multi-level unit cell structure are as follows: S1: Construct a cubic space, divide the cubic space into four equal parts along the Z-axis, and merge the second and third layers of the cubic space into the middle region; S2: Using a hexagon as the design unit, place the two vertices of the design unit on the plane of the diagonal of the cube space, rotate it 90° in the Z-axis direction about the axis of symmetry of the design unit to obtain the first structure. Delete the connecting rods at the top and bottom of the first structure to obtain the second structure. Use the first connecting rod to connect the four vertices at the top and bottom of the second structure in sequence to obtain the third structure. The quadrilateral enclosed by the first connecting rod is a square. Place the third structure in the middle area. S3: The four corners of the upper end of the third structure are connected one-to-one with the four sides of the upper end of the first layer region by the second connecting rod, and the four corners of the lower end of the third structure are connected one-to-one with the four sides of the lower end of the fourth layer region by the second connecting rod, and the second connecting rod is perpendicular to the connected side to obtain a multi-level unit cell structure. S4: Define the dimensional parameters of the multi-level unit cell structure: the diameter D of each connecting rod, the side length L of the unit cell, the side length 2M of the quadrilateral enclosed by the first connecting rod, and the distance 2H between the upper and lower first connecting rods on the same side. S5: Set the cell side length L of the multi-level unit cell structure, set the size parameters M and H respectively, and ensure that the relative density of the multi-level unit cell structure is the same under different combinations of size parameters by adjusting the diameter D of the connecting rod. Based on the set size parameters and the multi-level unit cell structure, generate a 3×3×3 lattice structure along the X, Y and Z directions to obtain the lattice structure database. S6: Structural performance sensitivity analysis based on single-parameter gradual control, and comparative analysis of the results, to obtain the lattice structure with optimal performance based on the comparative analysis results.

2. The method for designing a multi-level lattice structure as described in claim 1, characterized in that: In step S6, the structural performance sensitivity analysis based on single-parameter gradual control involves taking multiple sets of gradual values ​​for a single geometric parameter while keeping the single geometric parameter M or H constant. Through finite element simulation, stress-strain curves, deformation modes, and key mechanical performance indicators under different parameter combinations are obtained, thus acquiring the lattice structure with optimal performance.

3. The method for designing a multi-level lattice structure as described in claim 2, characterized in that: The key mechanical performance indicators include densification strain, plateau stress, SEA, normalized plateau stress, normalized SEA, and performance sensitivity.

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