Lattice structure design method of multi-level configuration

Abstract

The invention relates to the field of helmets, in particular to a multilevel configuration lattice structure design method, a multilevel unit cell structure is constructed, the multilevel unit cell structure is adopted as a helmet lining, and the specific steps for constructing the multilevel unit cell structure are as follows: S1, a cubic space is constructed, the cubic space is averagely divided into four equal parts, combining the second-layer region and the third-layer region into a middle region; s2, constructing a first structure body, deleting connecting rods at the upper end and the lower end of the first structure body to obtain a second structure body, sequentially connecting four vertexes at the upper end and the lower end of the second structure body by adopting first connecting rods to obtain a third structure body, and placing the third structure body in the middle area; s3, the four corners of the upper end and the four corners of the lower end of the third structure body are connected with the two corresponding edges in a one-to-one correspondence mode through second connecting rods, and a multi-layer unit cell structure is obtained; and three-dimensional nesting and multi-level configuration are realized on the unit cell scale.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of helmets, in particular to a lattice structure design method of multi-level configuration. 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 fracture, skull injury, and concussion. 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 adding and offsetting 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 The purpose of the present application is to provide a lattice structure design method of multi-level configuration capable of realizing three-dimensional multi-stage deformation.

[0005] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows: A lattice structure design method of multi-level configuration, 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: 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; S2: Use a hexagon as a design unit, rotate the design unit by 90° along the symmetry axis in the Z-axis direction on the plane of the diagonal line of the cubic space to obtain a first body, delete the connecting rods at the upper end and the lower end of the first body to obtain a second body, and connect the four vertices at the upper end and the lower end of the second body with first connecting rods in sequence to obtain a third body. The quadrilateral surrounded by the first connecting rod is a square, and the third body is placed in the middle region; S3: using the second connecting rod to connect the four corners of the upper end of the third structure with the four edges of the upper end of the first layer region one by one, using the second connecting rod to connect the four corners of the lower end of the third structure with the four edges of the lower end of the fourth layer region one by one, and the second connecting rod is perpendicular to the connected edge, to obtain a multi-level unit cell structure.

[0006] Preferably, it further comprises the following steps: 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 surrounded by the first connecting rod, and the distance 2H between the upper and lower first connecting rods on the same side; S5: setting the unit cell side length L of the multi-level unit cell structure to 10 mm, setting the size parameters of M and H respectively, and adjusting 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, generating a lattice structure with a cell number of 3*3*3 in X, Y and Z directions, to obtain a lattice structure database; S6: based on the structure performance sensitivity analysis of single parameter gradual change control, and comparing and analyzing the results, and obtaining the lattice structure with the optimal performance according to the comparison and analysis results. Preferably, in step S6, the structure performance sensitivity analysis based on single parameter gradual change control is to perform multiple sets of gradual value taking on one geometric parameter under the condition that a single geometric parameter M or H is kept unchanged, to obtain stress-strain curves, deformation modes and key mechanical performance indicators under different parameter combinations through finite element simulation, and to obtain the lattice structure with the optimal performance.

[0007] Preferably, the key mechanical performance indicators include densification strain, platform stress, SEA, platform stress normalized value, SEA normalized value and performance sensitivity.

[0008] By adopting the foregoing design scheme, the application has the beneficial effects that: the multi-level unit cell structure constructed by the application divides the multi-level unit cell structure into three layers, the middle region is a third structure with a tortoise shell structure, the upper layer region and the lower layer region use a second connecting rod to construct a tree-like branch, so that the multi-level unit cell structure has a hierarchical feature and a multi-level fractal structure combined with a tree-like branch, and three-dimensional nesting and multi-level configuration are realized on the unit cell scale, thereby providing a new implementation approach for multi-stage deformation of the structure. BRIEF DESCRIPTION OF DRAWINGS

[0009] Figure 1 It is a schematic diagram of the cubic space division structure of the application; Figure 2 It is a schematic diagram of the tortoise shell and tree structure analysis of the application; Figure 3 It is a schematic diagram of the steps of constructing the multi-level unit cell structure of the application; Figure 4 A schematic diagram of the lattice structure of the present application; Figure 5 A schematic diagram of the finite element model of the present application and the compression process of its corresponding physical sample; Figure 6 A stress-strain curve diagram of the lattice structure of the present application; Figure 7 A flowchart of the lattice structure design method of the present application; Figure 8 A deformation mode diagram of the lattice structure of the present application. DETAILED DESCRIPTION

[0010] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be described in further detail below with reference to the accompanying drawings. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work shall fall within the scope of protection of the present application.

[0011] The terms "first", "second", "third" and the like in the specification and claims of the present application and the above-described drawings are used to distinguish different objects, and are not used to describe a particular order. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but can optionally include steps or units not listed, or can optionally include other steps or units inherent to the process, method, product or device.

[0012] A lattice structure design method of a 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 of constructing the multi-level unit cell structure are as follows: S1: For a multi-stage deformation structure and its stiffness distribution characteristics, a cubic space is constructed, and an XYZ coordinate axis as shown in Figure 3 part (1) is constructed with the geometric center of the bottom surface of the cubic space as the 0 point. 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 force transmission guidance and boundary stability.

[0013] S2: Inspired by the structure of the natural world (turtle shell and tree branch), the structural mechanism is analyzed and the characteristics are extracted. The turtle shell is an overall elliptical 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 has a "hard-soft-hard" sandwich configuration, including an outer keratin layer, a middle three-dimensional honeycomb cancellous bone foam layer, and an inner dense bone plate providing rigid support. The tree branch structure has a multi-level branch configuration in macro, forming a binary tree fractal network, which helps to uniformly disperse the load. The branch nodes have a conical transition zone in the node connection characteristics. The analysis of the two kinds of bionic characteristics is shown in Figure 2 .

[0014] Based on the geometric characteristics of a large number of keratin scutes on the surface of the turtle shell, the shape is mostly hexagonal or irregular polygon, 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 parallel to each other, and the four diagonal edges are connected to form two vertices on both sides of the horizontal edge, as shown in Figure 3 . The design unit is placed on the plane of the diagonal line of the cubic space, and the two vertices are located at the midpoints of the opposite two edges of the cubic space. The two vertices of the design unit are placed in the Y-axis direction, and the symmetric axis of the design unit is rotated by 90° in the Z-axis direction to obtain a first structure. At this time, a cross-shaped connection appears in the first structure, and the connecting rods at the upper and lower ends of the first structure are deleted to obtain a second structure as shown in Figure 3 . The four vertices of the upper and lower ends of the second structure are connected in turn by a first connecting rod to obtain a third structure as shown in Figure 3 . The quadrilateral surrounded by the first connecting rod is a square, and the third structure is placed in the middle region. S3: According to the binary tree structure design, 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 a second connecting rod, and 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 a second connecting rod, and the second connecting rod is perpendicular to the connected edge, as shown in Figure 3 parts (4) and (5), 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 the two edges adjacent to the corresponding region one by one, forming a structure similar to a tree.

[0015] S5: The size parameters of the multi-level unit cell structure are defined: 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. S6: Set the cell edge length L of the multi-level cellular structure to 10 mm, set the size parameters of M and H to 1.5 mm, 2.0 mm, 2.5 mm and 3.0 mm respectively, and ensure that the relative density of the multi-level cellular structure is the same under different size parameter combinations by adjusting the connecting rod diameter D. Based on the set size parameters and the multi-level cellular structure, a lattice structure with a cell number of 3x3x3 is generated along the X, Y and Z directions, and a lattice structure database is obtained. Set M=H=2.5 mm to obtain the lattice structure as shown in FIG. 6. Figure 4 In this embodiment, the relative density is set to 30.9%, and other parameter combinations can be set according to actual application requirements.

[0016] S7: Perform structure performance sensitivity analysis based on single parameter gradual control, and perform comparative analysis on the results to obtain the lattice structure with the optimal performance. In this embodiment, based on the performance data of the TPU material suitable for 3D printing obtained by experiment, 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. 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.

[0017] To truly reflect the super-elasticity and viscoelasticity of the TPU material, super-elasticity and viscoelasticity are introduced into the material constitutive, and the super-elasticity part is fitted with the tensile sample data by using the Marlow model. 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 FIG. 7. Figure 5

[0018] 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.

[0019] In step S7, the structure performance sensitivity analysis based on single parameter gradual control is to perform multiple gradual value taking on one geometric parameter under the condition that a single geometric parameter M or H is kept unchanged. The stress-strain curve, deformation mode and key mechanical performance index under different parameter combinations are obtained by finite element simulation. In this embodiment, the key mechanical performance index includes densification strain, platform stress, SEA, platform stress normalized value, SEA normalized value and performance sensitivity. The lattice structure with the optimal performance is obtained. ​

[0020] In this embodiment, the deformation mode refers to the deformation state of the structure under different compression amounts, such as Figure 8 As shown, the deformation mode under the M2.5-H2.5 parameter combination is shown.

[0021] In order to better illustrate the lattice design method of the present application, the following specific embodiment analysis is carried out.

[0022] Table 1 shows a geometric parameter combination scheme based on single parameter gradual control. According to the combination scheme, 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) in this group has the optimal mechanical performance.

[0023] Table 1 shows a geometric parameter combination scheme based on single parameter gradual control.

[0024] Table 2 shows the MDCM structure performance sensitivity analysis under single parameter gradual control (M=2.5 mm).

[0025] The comprehensive analysis results show that the structure generally appears a significant stress-strain curve drop phenomenon after a strain of 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 minimum (1.5 mm), the rigidity of the inner layer imitating the tortoise shell structure is weakened, the multi-stage deformation characteristic disappears, and the stress-strain curve shows a monotonous and stable increase. When the parameters increase to H≥2.5 mm, the length of the imitating tree structure rod decreases, resulting in a decrease in overall rigidity, and the compression response tends to be stable. It is further found that a decrease in M value will cause the stress drop to occur later in the densification stage, indicating that it has a significant control effect on the instability timing. 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. In contrast, the combination of M≤H has more uniform stress distribution and more stable compression response. The geometrically symmetric configuration (M=H) generally has a higher platform stress, a larger densification strain and a more optimal specific energy absorption. The asymmetric configuration is prone to induce local buckling and yield prematurely, reducing the energy absorption performance. Overall, this sensitivity analysis method can realize the quantitative correlation of geometric parameters and mechanical performance, and provides an effective design basis for the stability optimization and energy absorption performance improvement of multi-stage deformation lattice structures.

[0026] 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 the key factor affecting the energy absorption efficiency and structural stability. The sensitivity analysis results show that when M and H are symmetrical, the structural stiffness distribution is more uniform, the load transfer is more continuous, the tree-like branch and the shell-like configuration can form a good synergistic effect, which significantly prolongs the deformation stage in the compression process, effectively inhibits the local premature instability, and thus greatly improves the stability of the platform stress and the energy absorption performance. On the contrary, when M and H are asymmetrical, 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 enhancement of stress curve fluctuation and the advance of densification, resulting in a significant reduction in energy dissipation capacity. Therefore, the sensitivity analysis method of the present application clearly 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 energy absorption, and the use of the lattice structure as a helmet liner significantly improves the buffering and energy absorption effect, which can effectively improve the safety performance of the helmet.

[0027] The above specific embodiments further illustrate 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. within the spirit and principles of the present application should 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, thus obtaining a multi-level unit cell structure.

2. The method for designing a multi-level lattice structure as described in claim 1, characterized in that: It also includes the following steps: 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.

3. The method for designing a multi-level lattice structure as described in claim 2, 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.

4. The method for designing a multi-level lattice structure as described in claim 3, 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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