Impact absorbing member and manufacturing method thereof

Abstract

To provide a shock absorbing member that has isotopic compressive deformation property more than before, and to provide a method for manufacturing the same.SOLUTION: A shock absorbing member has an irregular lattice structure.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an impact absorbing member and a method for manufacturing the same. [Background technology]

[0002] Impact-absorbing materials are used in a variety of applications. For example, in space development, the development of impact-absorbing materials to protect probes from impacts during landing is an important issue. Furthermore, various impact-absorbing materials have traditionally been used in automobiles and other vehicles to protect passengers.

[0003] Currently, most shock absorbing materials are one-dimensional or two-dimensional (see, for example, Patent Documents 1 to 3). However, in cases where the impact direction is not specified three-dimensionally, such as when the attitude changes during a drop impact, it is not desirable to use them as shock absorbing materials. Furthermore, in landing missions to gravity-bearing celestial bodies, it is desirable to use materials with three-dimensional shock absorbing properties so that they can also be used on landing surfaces with large undulations. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-099116 [Patent Document 2] Patent Publication No. 2021-098464 [Patent Document 3] Patent Publication No. 2021-085462 [Patent Document 4] Patent Publication No. 2021-070206 [Patent Document 5] Japanese Patent Application Publication No. 2019-157916 Summary of the Invention [Problem to be solved by the invention]

[0005] Conventionally, foam materials (see, for example, Patent Document 4) and lattice structures (hereinafter referred to as "regular lattice structures"; see, for example, Patent Document 5) are known as materials with three-dimensional shock absorption properties. Foam materials exhibit relatively good shock absorption properties, but as the porosity increases, it becomes more difficult to control the size and distribution of the pores, and control of the properties also becomes more difficult. Furthermore, regular lattice structures have a repeating structure of regular or periodic unit cells, and while it is easy to control the size and distribution of the cells, they exhibit anisotropic compressive deformation that depends on the regularity and periodicity. However, when the impact direction is not specified, it is desirable for the compressive deformation properties to be isotropic.

[0006] The present invention has been made in view of the above circumstances, and provides a shock absorbing member having more isotropic compressive deformation characteristics than conventional shock absorbing members, and a method for manufacturing the same. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides the following means.

[0008] The impact absorbing member according to the first aspect of the present invention has an irregular lattice structure.

[0009] In the impact absorbing member according to the above aspect, each cell of the irregular lattice structure may be a convex hull.

[0010] The impact absorbing member according to the above aspect may have cells with a volume distribution in which the CV value represented by the following formula (1) is in the range of 0.05 to 0.35:

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[0011] The impact absorbing member according to the above aspect may have an anisotropy of energy absorption of 10% or less.

[0012] A second aspect of the present invention relates to a method for manufacturing an impact absorbing member having an irregular lattice structure, and includes a structure data creation process for creating three-dimensional structure data for the impact absorbing member, and a modeling process for modeling the impact absorbing member based on the three-dimensional structure data. The structure data creation process creates the irregular lattice structure by applying displacements to the arrangement of generating points in a three-dimensional Voronoi tessellation method for a predetermined regular lattice structure.

[0013] In the method for manufacturing the impact absorbing member according to the above aspect, the displacement may be determined so that the CV value expressed by the following formula (1) becomes a predetermined value:

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[0014] According to the present invention, it is possible to provide a shock absorbing member having more isotropic compressive deformation characteristics than conventional shock absorbing members. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram illustrating the Voronoi division method. [Figure 2] Schematic diagrams showing unit cells of a regular lattice structure. (a) is obtained when the kernel point arrangement in the Voronoi tessellation method is a BCC arrangement, (b) is obtained when the kernel point arrangement is an FCC arrangement, and (c) is obtained when the kernel point arrangement is an HCP arrangement. [Figure 3] 1 is a graph showing the relationship between VG value and CV value. [Figure 4]2(a) is a projection of a cylindrical sample consisting of a regular lattice structure. (a) is a cylindrical sample in which the unit cells shown in Fig. 2(a) are stacked in the

[001] direction. (b) is a cylindrical sample in which the unit cells shown in Fig. 2(a) are stacked in the

[101] direction. (c) is a cylindrical sample in which the unit cells shown in Fig. 2(a) are stacked in the

[111] direction. (d) is a cylindrical sample in which the unit cells shown in Fig. 2(b) are stacked in the

[001] direction. ] direction, (e) is a cylindrical sample in which the unit cells shown in Figure 2(b) are stacked in the

[101] direction, (f) is a cylindrical sample in which the unit cells shown in Figure 2(b) are stacked in the

[111] direction, (g) is a cylindrical sample in which the unit cells shown in Figure 2(c) are stacked in the

[0001] direction, and (h) is a cylindrical sample in which the unit cells shown in Figure 2(c) are stacked in the

[101] direction.

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[001] direction coinciding with a CV value of 0.10. (b) is a cylindrical sample obtained by applying a three-dimensional displacement to the BCC arrangement and performing Voronoi division, resulting in the cylinder axis direction and the BCC

[001] direction coinciding with a CV value of 0.21. (c) is a cylindrical sample obtained by applying a three-dimensional displacement to the BCC arrangement and performing Voronoi division, resulting in the cylinder axis direction and the BCC

[001] direction coinciding with a CV value of 0.3. (d) is a cylindrical sample obtained by applying a three-dimensional displacement to the BCC arrangement and performing Voronoi division, where the cylindrical axis direction coincides with the BCC

[001] direction and the CV value is 0.39; (e) is a cylindrical sample obtained by applying a three-dimensional displacement to the FCC arrangement and performing Voronoi division, where the cylindrical axis direction coincides with the FCC

[001] direction and the CV value is 0.13; and (f) is a cylindrical sample obtained by applying a three-dimensional displacement to the FCC arrangement and performing Voronoi division, where the cylindrical axis direction coincides with the FCC

[001] direction and the CV value is 0.27. [Figure 5B] These are projections of cylindrical samples consisting of an irregular lattice structure. (g) is a cylindrical sample obtained by applying a three-dimensional displacement to the FCC arrangement and performing Voronoi division, where the cylindrical axis direction coincides with the FCC

[001] direction and the CV value is 0.37. (h) is a cylindrical sample obtained by applying a three-dimensional displacement to the FCC arrangement and performing Voronoi division, where the cylindrical axis direction coincides with the FCC

[001] direction and the CV value is 0.41. (i) is a cylindrical sample obtained by applying a three-dimensional displacement to the HCP arrangement and performing Voronoi division, where the cylindrical axis direction coincides with the HCP

[0001] direction and the CV value is 0.09. (j) is a cylindrical sample obtained by applying a three-dimensional displacement to the HCP arrangement and performing Voronoi division, so that the cylindrical axis direction and the HCP

[0001] direction coincide with each other, resulting in a CV value of 0.20; (k) is a cylindrical sample obtained by applying a three-dimensional displacement to the HCP arrangement and performing Voronoi division, so that the cylindrical axis direction and the HCP

[0001] direction coincide with each other, resulting in a CV value of 0.33; and (l) is a cylindrical sample obtained by applying a three-dimensional displacement to the HCP arrangement and performing Voronoi division, so that the cylindrical axis direction and the HCP

[0001] direction coincide with each other, resulting in a CV value of 0.38. [Figure 6] FIG. 1 is a cross-sectional schematic diagram showing a configuration used in a compression test. [Figure 7] This graph shows the energy absorption up to 50% strain obtained for structures including the cylindrical samples with the regular lattice structure shown in Figures 3(a)-(c) and the cylindrical samples with the irregular lattice structure shown in Figures 4(a)-(l). (a) shows the average energy absorption of the regular and irregular lattice structures with the BCC configuration as the base kernel, (b) shows the average energy absorption of the regular and irregular lattice structures with the FCC configuration as the base kernel, (c) shows the average energy absorption of the regular and irregular lattice structures with the HCP configuration as the base kernel, and (d) shows the anisotropy of the energy absorption in the regular and irregular lattice structures. DETAILED DESCRIPTION OF THE INVENTION

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An impact absorbing member and a manufacturing method thereof according to an embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

[0017] (shock absorbing material) The impact absorbing member according to this embodiment has an irregular lattice structure. In this specification, a regular "lattice structure" (hereinafter referred to as a "regular lattice structure") refers to a structure in which unit cells are periodically repeated. These unit cells are not solid, but have pores or gaps inside. In contrast, the term "irregular lattice structure" used in this specification refers to a structure in which cells whose unit cells are different in at least one of the shape and volume are included in a given regular lattice structure. For example, an "irregular lattice structure" can be created by including cells whose unit cells are different in at least one of the shape and volume in a regular lattice structure designed using the 3D Voronoi tessellation method.

[0018] The Voronoi tessellation method is a method in which the representative point (kernel point) of an element is set at an arbitrary spatial position, and all division lines are divided so that they are equidistant from the kernel point on both sides. The diagram obtained by the Voronoi tessellation method is called a Voronoi diagram.

[0019] The Voronoi tessellation method will be explained in detail using the Voronoi diagram of a plane shown in Figure 1. In the example shown in Figure 1, five kernel points are arranged on a plane. Partition lines are drawn so that they are equidistant from two adjacent kernel points. The area surrounded by the division lines is called a Voronoi region. The division lines are called Voronoi boundaries. The intersections of the Voronoi boundaries are called Voronoi points. The Voronoi diagram shown in Figure 1 has five Voronoi regions. In a typical Voronoi diagram, the number of kernel points and the number of Voronoi regions are the same.

[0020] In the impact absorbing member according to this embodiment, each cell is preferably a convex hull. Here, a convex hull (also called a convex polyhedron) is a polyhedron whose dihedral angles on all edges are less than 180° and which has no self-intersections. Conversely, a polyhedron containing elements whose dihedral angles on any edge exceed 180° is called a concave polyhedron. If each cell is a convex hull (convex polyhedron), it is preferable as an impact absorbing material because it does not contain elements that cause stress concentration.In contrast, if it is a concave polyhedron, stress concentration occurs in elements with dihedral angles exceeding 180°, making the cell more susceptible to fracture and reducing energy absorption characteristics. When three-dimensional structure data is created using the Voronoi tessellation method, each cell of the lattice structure is always a convex hull.

[0021] The impact absorbing member according to this embodiment preferably has a volume distribution in which the parameter CV expressed by the following formula (1) is in the range of 0.05 to 0.35.

[0022]

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[0023] Regular lattice structures are easy to control, but their compressive properties are anisotropic. The anisotropy of the compressive properties stems from the unit cell structure, which consists of identical cells repeated in a regular pattern. Therefore, reducing the uniformity of the cells and introducing irregularity reduces the anisotropy of the compressive properties, making them more isotropic. However, randomly introducing irregularity into the unit cell structure without control significantly reduces the energy absorption properties of the component. Therefore, it is necessary to create irregularity to the extent that the unit cell structure exhibits isotropy, but not so much that the energy absorption properties are significantly reduced. By controlling the irregular cell structure so that the CV (Equation (1)) is in the range of 0.05 to 0.35, an irregular lattice structure with a volume distribution of CV (Equation (1)) in the range of 0.05 to 0.35 can be obtained.

[0024] The CV expressed by equation (1) is a parameter determined only by the volume distribution of the cells constituting the irregular lattice structure, and is a parameter that is not dependent on variations in cell shape.

[0025] In the case where the irregular lattice structure is a structure obtained by introducing displacements into the generating points in the Voronoi tessellation method that forms the unit cells of a specified regular lattice structure, if the CV value is small, the unit cell or the specified regular lattice structure that was used as the basis can be identified. The unit cells of a predetermined regular lattice structure can be any structure, but for example, a structure similar to a structure obtained by Voronoi tessellation using the lattice points of a crystal structure as the generating points can be used. In other words, a structure similar to a structure obtained by Voronoi tessellation using the lattice points of a triclinic, monoclinic, orthorhombic, tetragonal, cubic, hexagonal, or trigonal crystal structure as the generating points can be used for the unit cells of the regular lattice structure. Specifically, structures similar to those obtained by the Voronoi tessellation method using the lattice points of a simple triclinic lattice belonging to a triclinic crystal structure, a simple monoclinic lattice belonging to a monoclinic crystal structure, a base-centered monoclinic lattice, a simple orthorhombic lattice belonging to an orthorhombic crystal structure, a body-centered orthorhombic lattice, a base-centered orthorhombic lattice, a face-centered orthorhombic lattice, a simple square lattice belonging to a tetragonal crystal structure, a body-centered tetragonal lattice, a simple cubic lattice belonging to a cubic crystal structure, a body-centered cubic lattice (BCC), a face-centered cubic lattice (FCC), a simple hexagonal lattice (hexagonal close-packed lattice: HCP) belonging to a hexagonal crystal structure, and a simple trigonal lattice belonging to a trigonal crystal structure as the generating points can be used for the unit cells of the regular lattice structure.

[0026] Of these crystal structures, the cubic system, particularly the structure obtained by the Voronoi tessellation method using BCC as the generating point, is the truncated octahedron structure shown in Figure 2. The cubic system is preferred because it has a large ratio of cell surface area to cell volume, which is close to that of a spherical shape, resulting in relatively small anisotropy in energy absorption.

[0027] The impact absorbing member according to this embodiment preferably has an anisotropy of the energy absorption amount of 10% or less, and more preferably 5% or less. In this specification, the "anisotropy of energy absorption amount" in "anisotropy of energy absorption amount is 10% or less" means that, when comparing the energy absorption amounts of the impact absorbing member in any two selected directions, the anisotropy is determined by the following formula (2): {(larger energy absorption amount - smaller energy absorption amount) / (average of the two energy absorption amounts)} × 100(%) (2) The difference in the amount of energy absorption in the two directions is calculated using the value evaluated by the formula (2), and this means "the difference in the amount of energy absorption in the two largest directions." In other words, "the anisotropy of the amount of energy absorption is 10% or less" means that, among the differences in the amount of energy absorption in any two selected directions of the impact absorbing component expressed by formula (2), the difference in the maximum amount of energy absorption is 10% or less.

[0028] The shock-absorbing member can be made of any known material used for shock-absorbing members. When modeling using a 3D printer, materials that can be used in various modeling methods are used. Examples include resins and metals.

[0029] Examples of resins include high-density polyethylene (HDPE), low-density polyethylene (LDPE), polypropylene (PP), nylon resin (PA), polyacetal (POM), polybutylene terephthalate (PBT), polyphenylene sulfide (PPS), polyether ether ketone (PEEK), liquid crystal polymer (LCP), polystyrene (PS), polyvinyl chloride (PVC), ABS resin, acrylic resin (PMMA), polycarbonate (PC), polyarylate (PAR), and modified polyphenylene ether (PPE).

[0030] Examples of metals include aluminum, chromium, cobalt, copper, gold, iron, magnesium, silicon, molybdenum, nickel, palladium, platinum, rhodium, silver, tin, titanium, tungsten, and zinc, as well as alloys containing these elements. Examples of alloys include steel and stainless steel. These metal materials may be used alone or in combination of two or more. Lightweight materials are desirable for aerospace and automotive components, and aluminum alloys, titanium alloys, and magnesium alloys with high strength-to-weight ratios are preferred, as are steel and stainless steel, which have high energy absorption-to-weight ratios.

[0031] (Method of manufacturing impact absorbing member) The method for manufacturing a shock absorbing member according to the present invention includes a step of creating three-dimensional structural data of the shock absorbing member, and a step of forming the shock absorbing member based on the three-dimensional structural data.

[0032] Methods for creating 3D structural data for impact absorbing components include, for example, 3D Voronoi tessellation and 3D Delaunay tessellation. In the 3D Delaunay tessellation, the unit cells are tetrahedrons, so the 3D Voronoi tessellation is preferable for manufacturing impact absorbing components.

[0033] A method for creating three-dimensional structure data with an irregular lattice structure using the three-dimensional Voronoi division method will be explained using diagrams.

[0034] First, a unit cell of a regular lattice structure before introducing irregularity is created using the 3D Voronoi tessellation method. Next, the arrangement of the seed points in the Voronoi tessellation method is determined so that the seed point arrangement forms a predetermined structure. At this time, crystal structures such as BCC, FCC, and HCP can be used as the predetermined structure. The regular lattice structure shown in Figure 2, which will be described later, is a structure obtained by using the BCC, FCC, and HCP seed point arrangements in the Voronoi tessellation method. The regular lattice structure obtained in this way is a regular lattice structure consisting of a group of cells with uniform cell volume. Next, a three-dimensional displacement is applied to each generating point so that it becomes a predetermined CV value (not zero). The volume of each cell obtained in this way is distributed so that it has a predetermined CV value (not zero), and three-dimensional structural data of an irregular lattice structure consisting of a group of cells with non-uniform cell volumes is obtained.

[0035] The molding method used in the manufacturing method of the shock-absorbing member is not particularly limited as long as it can be used to create an irregular lattice structure, and any known molding method can be used, but a 3D printer is preferred, which can layer cross-sectional shapes based on three-dimensional shape data created with three-dimensional software to create a three-dimensional shape.

[0036] 3D printers can be used, for example, with powder bed fusion (PBF), which allows for high-resolution, complex modeling without support material. This method is also known as selective laser melting (SLM). With this method, resin or metal powder particles are laid flat to form a powder layer, and a laser is irradiated onto the desired portion of this powder layer, sintering or melting the powder particles to form a solidified layer. Further powder particles are laid on top of this solidified layer to form a new powder layer, which is then irradiated with a laser to melt and bond the powder particles to form the next solidified layer. By repeating this process and stacking the solidified layers, a structure of the desired shape can be manufactured. Here, the term "solidified layer" refers to a "melted and solidified layer", a "melted and bonded layer", or a "sintered layer".

[0037] By adjusting the laser intensity, the scanning interval of the laser, the powder diameter, and the like, it is possible to form porous structures and other structures with complex shapes.

[0038] When using a powder bed fusion type 3D printer, examples of resins that can be used as the powder material include high-density polyethylene (HDPE), low-density polyethylene (LDPE), polypropylene (PP), nylon resin (PA), polyacetal (POM), polybutylene terephthalate (PBT), polyphenylene sulfide (PPS), polyether ether ketone (PEEK), liquid crystal polymer (LCP), polystyrene (PS), polyvinyl chloride (PVC), ABS resin, acrylic resin (PMMA), polycarbonate (PC), polyarylate (PAR), and modified polyphenylene ether (PPE).

[0039] Examples of metals that can be used as powder materials include aluminum, chromium, cobalt, copper, gold, iron, magnesium, silicon, molybdenum, nickel, palladium, platinum, rhodium, silver, tin, titanium, tungsten, and zinc, as well as alloys containing these elements. Examples of alloys include steel and stainless steel. These metal materials may be used alone or in combination of two or more.

[0040] Other types of 3D printers that can be used include the Stereo Lithography Apparatus (SLA), which uses ultraviolet light to cure photocurable liquid resin, hardening the resin layer by layer to create a three-dimensional object; the inkjet method (multi-jet printing), which replaces the ink in an inkjet printer with ultraviolet-curable resin to create models; the inkjet powder deposition method (color jet printing), which, like the inkjet method, ejects coloring material and adhesive from the print head and layers the plaster powder while it hardens, to create a model; and the Fused Deposition Modeling method (FDM), which melts thermoplastic resins such as ABS resin and PLA (polylactic acid), ejects the molten resin from the tip of a thin nozzle about 0.1 to 0.8 mm in diameter, and layers it to create a model. [Example]

[0041] Next, specific examples of the present invention will be described, but the present invention is not limited to these examples.

[0042] (Sample preparation) Regular and irregular lattice structures were designed using the 3D Voronoi tessellation method.

[0043] The unit cell of the regular lattice structure is a structure consisting of the edges (edges) of a solid obtained by using the Voronoi tessellation method as the kernel point arrangement of the crystal structure in the BCC arrangement, FCC arrangement, and HCP arrangement, as shown in Figure 2. The lattice spacing for this BCC arrangement is 7.50 mm, the lattice spacing for the FCC arrangement is 9.45 mm, and the lattice spacing for the HCP arrangement is 6.68 mm, and the number of kernel points per unit volume is the same. Figure 2 is a schematic diagram showing a unit cell of a regular lattice structure, where (a) is obtained when the kernel point arrangement in the Voronoi tessellation method is a BCC arrangement, (b) is obtained when the kernel point arrangement is an FCC arrangement, and (c) is obtained when the kernel point arrangement is an HCP arrangement.

[0044] The irregular lattice structure was obtained by applying the Voronoi tessellation method to the point clouds obtained by applying three-dimensional displacements to the BCC, FCC, and HCP configurations described above. The displacements were given a normal-distributed random displacement u in each of the spatial X, Y, and Z directions, as shown in the following equation (2).

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[0045] The CV value of the structure obtained with a VG of 10% (0.750 mm) in a BCC configuration is approximately 0.10, the CV value of the structure obtained with a VG of 10% (0.945 mm) in an FCC configuration is approximately 0.13, the CV value of the structure obtained with a VG of 10% (0.668 mm) in an HCP configuration is approximately 0.09, the CV value of the structure obtained with a VG of 20% (1.50 mm) in a BCC configuration is approximately 0.21, the CV value of the structure obtained with a VG of 20% (1.89 mm) in an FCC configuration is approximately 0.27, and the CV value of the structure obtained with a VG of 20% (1.336 mm) in an HCP configuration is approximately 0.20. The CV value of the structure obtained with a VG of 40% (3.00 mm) in a BCC configuration is approximately 0.34, the CV value of the structure obtained with a VG of 40% (3.78 mm) in an FCC configuration is approximately 0.37, the CV value of the structure obtained with a VG of 40% (2.672 mm) in an HCP configuration is approximately 0.33, the CV value of the structure obtained with a VG of 60% (4.50 mm) in a BCC configuration is approximately 0.39, the CV value of the structure obtained with a VG of 60% (5.67 mm) in an FCC configuration is approximately 0.41, and the CV value of the structure obtained with a VG of 60% (4.008 mm) in an HCP configuration is approximately 0.38.

[0046] By designing both regular and irregular lattice structures in the above way, the number of kernel points per unit volume of the lattice structure is the same. Note that by using the Voronoi tessellation method, each cell of the lattice structure is always a convex hull. Furthermore, the CV value of the regular lattice structure is 0 (zero).

[0047] Next, we designed cylindrical samples with an outer diameter of φ40 mm × H40 mm (diameter × height) consisting of a regular lattice structure and an irregular lattice structure, as shown in Figures 4 and 5. Figures 4 and 5 are projection views of each structure. The strut diameter of the lattice structure was adjusted so that the porosity of each cylindrical sample was 90%. The cross-sectional shape of the strut was circular, and its diameter was approximately 1 mm, depending on the total length of the struts contained in the cylindrical sample.

[0048] 4(a) to 4(c) show three types of cylindrical samples with regular lattice structures, each with a different cylindrical axis direction relative to the arrangement direction of the unit cells in FIG. 2(a) that are stacked (repeated). Figure 4(a) shows a cylindrical sample with a regular lattice structure whose axis is oriented along the

[001] direction of the unit cell shown in Figure 2(a), Figure 4(b) shows a cylindrical sample with a regular lattice structure whose axis is oriented along the

[101] direction of the unit cell shown in Figure 2(a), and Figure 4(c) shows a cylindrical sample with a regular lattice structure whose axis is oriented along the

[111] direction of the unit cell shown in Figure 2(a). Therefore, the axis directions of the cylindrical samples in Figures 4(a) to 4(c) are parallel to the

[0001] ,

[0101] , and

[0111] directions of the BCC arrangement, which are the Voronoi generating points. The

[0001] ,

[101] and

[111] directions have azimuthal symmetry. 4(d) to (f) show three types of cylindrical samples with regular lattice structures, each with a different cylindrical axis direction relative to the arrangement direction of the unit cells shown in FIG. 2(b) that are stacked (repeated). Figure 4(d) shows a cylindrical sample with a regular lattice structure whose axis is oriented along the

[001] direction of the unit cell shown in Figure 2(b), Figure 4(e) shows a cylindrical sample with a regular lattice structure whose axis is oriented along the

[101] direction of the unit cell shown in Figure 2(b), and Figure 4(f) shows a cylindrical sample with a regular lattice structure whose axis is oriented along the

[111] direction of the unit cell shown in Figure 2(b). Therefore, the axis directions of the cylindrical samples in Figures 4(d) to 4(f) are parallel to the

[0001] ,

[0101] , and

[0111] directions of the FCC arrangement, which are the Voronoi generating points. 4(g) to (h) show two types of cylindrical samples with regular lattice structures whose cylindrical axis directions are different from the direction of arrangement of the unit cells shown in FIG. 2(c) that are stacked (repeated). Figure 4(g) shows a cylindrical sample with a regular lattice structure in which the cylinder axis is oriented to the

[0001] direction of the unit cell shown in Figure 2(c), and Figure 4(h) shows a cylindrical sample with a regular lattice structure in which the cylinder axis is oriented to the

[0001] direction of the unit cell shown in Figure 2(c).

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[0049] Figures 5(a) to (d) show irregular lattice structures obtained by using the Voronoi tessellation method with a point cloud that has been three-dimensionally displaced in a BCC configuration as the Voronoi generating points. The cylinder axis direction coincides with the

[001] direction of the BCC configuration, and these are four types of cylindrical samples with irregular lattice structures and different CV values. Figure 5(a) shows a cylindrical sample in which the regular lattice structure shown in Figure 4(a) has been three-dimensionally displaced to form an irregular lattice structure with a CV value of 0.10. Figure 5(b) shows a cylindrical sample in which the regular lattice structure shown in Figure 4(a) has been three-dimensionally displaced to form an irregular lattice structure with a CV value of 0.21. Figure 5(c) shows a cylindrical sample in which the regular lattice structure shown in Figure 4(a) has been three-dimensionally displaced to form an irregular lattice structure with a CV value of 0.34. Figure 5(d) shows a cylindrical sample in which the regular lattice structure shown in Figure 4(a) has been three-dimensionally displaced to form an irregular lattice structure with a CV value of 0.39. Figures 5(e) to (h) show irregular lattice structures obtained by using the Voronoi tessellation method with a point cloud that has been three-dimensionally displaced in the FCC arrangement as the Voronoi generating points. The cylinder axis direction coincides with the

[001] direction of the FCC arrangement, and these are four types of cylindrical samples with irregular lattice structures and different CV values. Figure 5(e) shows a cylindrical sample in which the regular lattice structure shown in Figure 4(d) was three-dimensionally displaced to form an irregular lattice structure with a CV value of 0.13. Figure 5(f) shows a cylindrical sample in which the regular lattice structure shown in Figure 4(d) was three-dimensionally displaced to form an irregular lattice structure with a CV value of 0.27. Figure 5(g) shows a cylindrical sample in which the regular lattice structure shown in Figure 4(d) was three-dimensionally displaced to form an irregular lattice structure with a CV value of 0.37. Figure 5(h) shows a cylindrical sample in which the regular lattice structure shown in Figure 4(d) was three-dimensionally displaced to form an irregular lattice structure with a CV value of 0.41. Figures 5(i) to (l) show irregular lattice structures obtained by using the Voronoi tessellation method with a point cloud that has been three-dimensionally displaced in the HCP arrangement as the Voronoi generating points. The cylinder axis direction coincides with the

[0001] direction of the HCP arrangement, and these are four types of cylindrical samples with irregular lattice structures and different CV values. Figure 5(i) shows a cylindrical sample in which the regular lattice structure shown in Figure 4(g) was three-dimensionally displaced to form an irregular lattice structure with a CV value of 0.09. Figure 5(j) shows a cylindrical sample in which the regular lattice structure shown in Figure 4(g) was three-dimensionally displaced to form an irregular lattice structure with a CV value of 0.20. Figure 5(k) shows a cylindrical sample in which the regular lattice structure shown in Figure 4(g) was three-dimensionally displaced to form an irregular lattice structure with a CV value of 0.33. Figure 5(l) shows a cylindrical sample in which the regular lattice structure shown in Figure 4(g) was three-dimensionally displaced to form an irregular lattice structure with a CV value of 0.38.

[0050] In addition to the above Figure 5, we designed cylindrical samples with an outer diameter of φ40 mm × H40 mm (diameter × height) and different cylindrical axis directions, with an irregular lattice structure obtained by using the Voronoi tessellation method with point clouds that were three-dimensionally displaced in the BCC, FCC, and HCP configurations as Voronoi generating points. For the BCC configuration, we designed irregular lattice samples with CV values ​​of approximately 0.10, 0.21, 0.34, and 0.39, with the cylinder axes parallel to the

[001] ,

[101] , and

[111] directions of the BCC configuration, respectively. For the FCC configuration, we designed irregular lattice samples with CV values ​​of approximately 0.13, 0.27, 0.37, and 0.41, with the cylinder axes parallel to the

[001] ,

[101] , and

[111] directions of the FCC configuration, respectively. For the HCP configuration, we designed irregular lattice samples with CV values ​​of approximately 0.09, 0.20, 0.33, and 0.38, with the cylinder axes parallel to the

[0001] and

[2110] directions of the HCP configuration, respectively. Five cylinders of each type were designed, for a total of 160 irregular lattice samples.

[0051] The cylindrical sample designed as above was fabricated using powder bed fusion (PBF) with nylon powder and PA12. The recycled powder content was 80%.

[0052] (Compression test) Compression tests were conducted on the cylindrical samples described above. Next, the degree of anisotropy was confirmed by calculating the amount of energy absorbed up to 50% strain (20 mm displacement) from the load-displacement curve of the compression test.

[0053] The compression test was carried out in accordance with JIS K7220:2006 as follows. As shown in Figure 6, a cylindrical sample S was placed on a steel sample mounting jig 10, and a compression test was performed from the top surface of the center of the cylindrical sample using a steel compression tool 20 at a test speed of 24 mm / min, and a load-displacement curve was obtained. The amount of energy absorption up to 50% strain (20 mm displacement) can be obtained by integrating the load value by the displacement up to 20 mm displacement (50% strain) based on the displacement-load curve obtained from the compression test described above.

[0054] The energy absorption amount and the anisotropy of the energy absorption amount up to 50% strain obtained for the cylindrical samples are shown in Figure 7. The anisotropy of the energy absorption amount was calculated using the following formula (3).

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[0001] ,

[101] , and

[111] ), indicating strong anisotropy. Figure 7(d) shows that the anisotropy decreases with increasing CV value, and the average energy absorption at each CV value decreases monotonically above 0.1. At a CV value of around 0.10, the anisotropy was 8.3%, and the average energy absorption was 10.8 J. At a CV value of around 0.39, the anisotropy was 2.1%, and the average energy absorption was 9.4 J. Figure 7(b) shows the energy absorption of a regular lattice structure (CV value: 0) and an irregular lattice structure with FCC configurations as the generating points. At a CV value of 0, the amount of energy absorption varies significantly depending on the weighting direction (

[0001] ,

[101] , and

[111] ), indicating strong anisotropy. Figure 7(d) shows that the anisotropy decreases with increasing CV value, but the average energy absorption at each CV value decreases slightly above 0.1. At a CV value of around 0.13, the anisotropy was 13.4%, and the average energy absorption was 9.7 J. At a CV value of around 0.41, the anisotropy was 5.7%, and the average energy absorption was 9.2 J. Figure 7(c) shows the energy absorption of the regular lattice structure (CV value: 0) and the irregular lattice structure with HCP configuration as the generating point. When the CV value is 0, the energy absorption is in the

[0001] direction,

number

[0055] As described above, it was confirmed that an irregular lattice structure with a CV value of 0.05 or more and 0.35 or less has a low anisotropy of the energy absorption amount shown in equation (3) of 10% or less, and has a larger energy absorption amount than a structure with a CV value of 0.35 or more. [Industrial Applicability]

[0056] The shock absorbing member of the present invention can be applied to any part that needs to be protected from shock, such as a space probe, a vehicle, electronic equipment, or furniture. [Explanation of symbols]

[0057] 10 Sample mounting jig 20 Compressor S cylindrical sample

Claims

1. It has an irregular lattice structure, An impact absorbing member having a volume distribution in which the CV value represented by the following formula (1) is in the range of 0.05 to 0.35: [Equation 1] Here, v mean is the average volume of the cells that make up the impact absorbing member, and Ncell is the total number of cells that make up the impact absorbing member.

2. The impact absorbing element according to claim 1 , wherein each cell of the irregular lattice structure is a convex hull.

3. 3. The impact absorbing member according to claim 1, wherein the anisotropy of the energy absorption amount is 10% or less.

4. A method for manufacturing an impact absorbing member having an irregular lattice structure, comprising: a structure data creation step of creating three-dimensional structure data of the impact absorbing member; a modeling process of modeling an impact absorbing member based on the three-dimensional structure data, In the structure data creation step, an irregular lattice structure is created by applying a displacement to a kernel point arrangement in a three-dimensional Voronoi division method of a predetermined regular lattice structure.

5. The method for manufacturing an impact absorbing member according to claim 4, wherein the displacement is determined so that a CV value expressed by the following formula (1) becomes a predetermined value: [Equation 2] Here, v mean is the average volume of the cells that make up the impact absorbing member, and Ncell is the total number of cells that make up the impact absorbing member.

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