JP7785288B2 - Impact absorbing member and manufacturing method thereof - Google Patents

Description

The present invention relates to an impact absorbing member and a manufacturing method thereof.

Shock-absorbing materials are used for a variety of purposes. For example, in space development, the development of shock-absorbing materials to protect probes from impacts during landing is an important issue. Furthermore, various shock-absorbing materials have traditionally been used in automobiles and other vehicles to protect passengers.

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 cannot be determined three-dimensionally, such as when the attitude changes during a drop impact, it is not desirable to use them as shock-absorbing materials. Furthermore, for landing missions on gravitational celestial bodies, it is desirable to use materials with three-dimensional shock-absorbing properties so that they can also accommodate landing surfaces with large undulations.

Japanese Patent Application Laid-Open No. 2021-099116 Japanese Patent Application Laid-Open No. 2021-098464 Japanese Patent Application Laid-Open No. 2021-085462 Japanese Patent Application Laid-Open No. 2021-070206 Japanese Patent Application Laid-Open No. 2019-157916

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 absorption properties. Foam materials exhibit relatively good impact absorption properties, but as the porosity increases, it becomes more difficult to control the size and distribution of the pores, making control of the properties more difficult. Furthermore, regular lattice structures have a repeating structure of regular or periodic unit cells, and while it is easy to control the cell size and distribution, they exhibit anisotropic compressive deformation that depends on this regularity and periodicity. However, when the impact direction is not specified, it is desirable for the compressive deformation properties to be isotropic.

The present invention was made in consideration of the above circumstances, and provides an impact absorbing component with more isotropic compressive deformation characteristics than conventional components, as well as a method for manufacturing the same.

To solve the above problems, the present invention provides the following means.

The shock-absorbing member according to the first aspect of the present invention has an irregular lattice structure.

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

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:
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.

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

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 the three-dimensional Voronoi tessellation method of a predetermined regular lattice structure.

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

The present invention provides an impact absorbing component with more isotropic compressive deformation characteristics than conventional components.

FIG. 1 is a diagram illustrating the Voronoi division method. 1A and 1B are schematic diagrams showing unit cells of a regular lattice structure, in which (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. 1 is a graph showing the relationship between VG value and CV value. 2(a) is a projection view of a cylindrical sample having a regular lattice structure, in which (a) is a cylindrical sample obtained by stacking the unit cells shown in FIG. 2(a) in the [001] direction, (b) is a cylindrical sample obtained by stacking the unit cells shown in FIG. 2(a) in the [101] direction, (c) is a cylindrical sample obtained by stacking the unit cells shown in FIG. 2(a) in the [111] direction, and (d) is a cylindrical sample obtained by stacking the unit cells shown in FIG. 2(b) in the [001] direction. ] direction, (e) is a cylindrical sample in which the unit cells shown in FIG. 2(b) are stacked in the [101] direction, (f) is a cylindrical sample in which the unit cells shown in FIG. 2(b) are stacked in the [111] direction, (g) is a cylindrical sample in which the unit cells shown in FIG. 2(c) are stacked in the [0001] direction, and (h) is a cylindrical sample in which the unit cells shown in FIG. 2(c) are stacked in the [0001] direction. This is a cylindrical sample in which unit cells are stacked.
10. (b) is a cylindrical sample obtained by applying a three-dimensional displacement to the BCC arrangement and Voronoi division, where the cylinder axis direction and the BCC [001] direction coincide with each other, resulting in a CV value of 0.21; and (c) is a cylindrical sample obtained by applying a three-dimensional displacement to the BCC arrangement and Voronoi division, where the cylinder axis direction and the BCC [001] direction coincide with each other, resulting in 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 triangulation, so that the cylinder 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 triangulation, so that the cylinder 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 triangulation, so that the cylinder axis direction coincides with the FCC [001] direction and the CV value is 0.27. 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, and the CV value is 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, and the CV value is 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, and the CV value is 0.38. FIG. 1 is a cross-sectional schematic diagram showing a configuration used in a compression test. 4(a)-(l) are graphs showing the energy absorption up to 50% strain obtained for structures including the cylindrical samples of the regular lattice structure shown in Figures 3(a)-(c) and the cylindrical samples of the irregular lattice structure shown in Figures 4(a)-(l). (a) shows the average energy absorption of the regular and irregular lattice structures based on the BCC configuration, (b) shows the average energy absorption of the regular and irregular lattice structures based on the FCC configuration, (c) shows the average energy absorption of the regular and irregular lattice structures based on the HCP configuration, and (d) shows the anisotropy of the energy absorption in the regular and irregular lattice structures.

The following describes in detail, with reference to the drawings, an impact absorbing member and a manufacturing method thereof according to an embodiment of the present invention.

(shock absorbing member)
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 three-dimensional Voronoi tessellation method.

Here, 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 the element is divided so that all division lines are equidistant from the kernel point on both sides. The diagram obtained by the Voronoi tessellation method is called a Voronoi diagram.

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 placed 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.

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 (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.
When each cell is a convex hull (convex polyhedron), the cells do not contain elements that cause stress concentration, making them preferable for impact absorbing components.In contrast, when each cell is a concave polyhedron, stress concentration occurs in elements with dihedral angles exceeding 180°, making the cells more susceptible to fracture and reducing energy absorption characteristics.
When three-dimensional structure data is created using the Voronoi division method, each cell of the lattice structure is always a convex hull.

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.

Here, v _is the average volume of the cells that make up the impact absorbing member, and N is the total number of cells that make up the impact absorbing member. CV is expressed as (standard deviation of the volume distribution of the cells that make up the impact absorbing member) / (average volume of the cells that make up the impact absorbing member) as in formula (1), and is an index that indicates the degree of uniformity of the cell volume. A smaller CV value indicates a higher degree of uniformity, and a larger CV value indicates a lower degree of uniformity. CV is the coefficient of variation of the cell volume distribution.

Regular lattice structures are easy to control, but have anisotropic compression properties. The anisotropy of the compression properties comes from the unit cell structure, which consists of the same cells repeated regularly. Therefore, reducing the uniformity of the cells and introducing irregularity reduces the anisotropy of the compression properties, making them more isotropic. However, making the unit cell structure randomly irregular without control significantly reduces the energy absorption properties of the component. Therefore, it is necessary to make the unit cell structure irregular enough to exhibit isotropy, but not so irregular that the energy absorption properties are excessively reduced. By controlling the irregular cell structure and designing a component so that the CV expressed by equation (1) is in the range of 0.05 to 0.35, an irregular lattice structure with a volume distribution in which the CV expressed by equation (1) is in the range of 0.05 to 0.35 can be obtained.

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

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 base 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 Voronoi tessellation 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, or a simple trigonal lattice belonging to a trigonal crystal structure as generating points can be used for the unit cells of the regular lattice structure.

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.

The impact absorbing member according to this embodiment preferably has an anisotropy of the amount of energy absorption of 10% or less, and more preferably 5% or less.
In this specification, the "anisotropy of energy absorption amount" in "the 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 the difference in the amount of energy absorption in the two directions is defined as "the maximum difference between the amounts of energy absorption in the two directions." In other words, "the anisotropy of the amount of energy absorption is 10% or less" means that, among the differences in the amounts of energy absorption in any two selected directions of the impact absorbing component expressed by the formula (2), the difference in the maximum amount of energy absorption is 10% or less.

The shock-absorbing member can be made from 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 resin and metal.

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).

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.

(Method for 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.

Methods for creating three-dimensional structural data for impact absorbing components include, for example, three-dimensional Voronoi tessellation and three-dimensional Delaunay tessellation. In the three-dimensional Delaunay tessellation, the unit cells are tetrahedrons, so the three-dimensional Voronoi tessellation is preferable for manufacturing impact absorbing components.

This article uses illustrations to explain how to create 3D structure data with an irregular lattice structure using the 3D Voronoi tessellation method.

First, a unit cell of a regular lattice structure before introducing irregularity is created by the three-dimensional Voronoi tessellation method.
Next, the arrangement of the kernel points in the Voronoi tessellation method is determined so that the arrangement of the kernel points forms a predetermined structure. At this time, a crystalline structure such as BCC, FCC, or HCP can be used as the predetermined structure. The regular lattice structure shown in FIG. 2, which will be described later, is a structure obtained by using the BCC arrangement, FCC arrangement, or HCP arrangement as the arrangement of the kernel points 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 the displacement becomes a predetermined CV value (not zero). The volume of each cell obtained in this way is distributed so that it has the 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.

The molding method used in the manufacturing method of the impact 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, as it can layer cross-sectional shapes based on three-dimensional form data created with three-dimensional software to create a three-dimensional object.

As a 3D printer, for example, a powder bed fusion (PBF) printer can be used, which can create high-resolution, complex shapes without support materials. This method is also known as selective laser melting (SLM). In this method, resin or metal powder particles are laid flat to form a powder layer, and a laser is irradiated onto the shaped portion of this powder layer to sinter or melt the powder particles and bond them together, forming a solidified layer. Further powder particles are laid on top of this solidified layer to form a next powder layer, which is then irradiated with a laser to melt and bond the powder particles, forming a next solidified layer. This process is repeated, stacking the solidified layers to produce a structure of the desired shape.
Here, the term "solidified layer" refers to a "melted and solidified layer", a "melted and bonded layer", or a "sintered layer".

By adjusting the laser intensity, the laser scanning interval, and the powder diameter, it is possible to form structures with complex shapes, such as porous structures.

When using a powder bed fusion 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).

In addition, 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 types.

Other 3D printers that can be used include the Stereo Lithography Apparatus (SLA), which uses ultraviolet light to cure photo-curable liquid resin, layer by layer, to create a three-dimensional object; the inkjet printer (multi-jet printing), which replaces the ink in an inkjet printer with UV-curable resin; the inkjet powder layering method (color-jet printing), which, like the inkjet printer, ejects coloring material and adhesive from the print head and builds up layers of plaster powder while it hardens; and the Fused Deposition Modeling (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 builds up layers to create a model.

Next, specific examples of the present invention will be described. However, the present invention is not limited to these examples.

(Sample Preparation)
Regular and irregular lattice structures were designed using the 3D Voronoi tessellation method.

The unit cell of the regular lattice structure is a structure consisting of the edges (edges) of solids obtained as the BCC, FCC, and HCP configurations of the crystal structure, with the kernel point configuration in the Voronoi tessellation method, as shown in Figure 2. The lattice spacing for this BCC configuration is 7.50 mm, the lattice spacing for the FCC configuration is 9.45 mm, and the lattice spacing for the HCP configuration is 6.68 mm, and the number of kernel points per unit volume is the same.
FIG. 2 is a schematic diagram showing a unit cell of a regular lattice structure, in which (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.

The irregular lattice structure was obtained by using the Voronoi tessellation method to create a group of points obtained by three-dimensionally displacing the BCC, FCC, and HCP configurations. The displacement was given a random displacement u of normal distribution in each of the X, Y, and Z directions in space, as shown in the following equation (2).

VG in the formula (2) was set to 10%, 20%, 40%, and 60% of the lattice spacing of the BCC configuration, FCC configuration, and HCP configuration.
Figure 3 shows a graph showing the relationship between the VG value and the CV value. Increasing the VG value, a design parameter that controls the irregularity, also increases the CV value. When the VG value is sufficiently large, the CV value saturates. Theoretically, when the irregularity increases, the density of the mother points remains the same, so it becomes unclear whether the base is BCC, FCC, or HCP. This can be considered a random state, and a CV value of 0.35 or more can be considered a random lattice structure from the graph.

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

By designing both regular and irregular lattice structures in the above manner, the number of kernel points per unit volume of the lattice structure is the same. Furthermore, by using the Voronoi tessellation method, each cell in the lattice structure is guaranteed to be a convex hull. Furthermore, the CV value of a regular lattice structure is 0 (zero).

Next, cylindrical samples with an outer dimension of φ40 mm × H40 mm (diameter × height) were designed, each 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 included in the cylindrical sample.

4(a) to 4(c) show three types of cylindrical samples of regular lattice structure, each having a different cylindrical axis direction relative to the direction of arrangement of the unit cells shown in FIG. 2(a) that are stacked (repeated).
Figure 4(a) shows a cylindrical sample with a regular lattice structure whose axis direction is oriented to 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 direction is oriented to 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 direction is oriented to 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 [001], [101], and [111] directions of the BCC configuration, which are the Voronoi generating points.
The [001], [101] and [111] directions have azimuthal symmetry.
4(d) to 4(f) show three types of cylindrical samples of regular lattice structure with different cylindrical axis directions 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 direction is aligned with 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 direction is aligned with 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 direction is aligned with the [111] direction of the unit cell shown in Figure 2(b). Therefore, the axis direction of each of the cylindrical samples in Figures 4(d) to 4(f) is parallel to the [001], [101], and [111] directions of the FCC configuration, which are the Voronoi generating points.
4(g) and 4(h) show two types of cylindrical samples of regular lattice structure, which have different cylindrical axis directions relative to the arrangement direction of the unit cells shown in FIG. 2(c) that are stacked (repeated).
FIG. 4(g) shows a cylindrical sample of a regular lattice structure in which the cylinder axis direction is oriented to the [0001] direction of the unit cell shown in FIG. 2(c), and FIG. 4(h) shows a cylindrical sample of a regular lattice structure in which the cylinder axis direction is oriented to the [0001] direction of the unit cell shown in FIG.
The cylindrical samples in Figures 4(g) and 4(h) are cylindrical samples with a regular lattice structure in which the cylindrical axis direction is oriented to the [0001] direction of the HCP arrangement, which is the Voronoi generating point.
Five cylindrical samples of the same type were designed.

Figures 5(a) to (d) show irregular lattice structures obtained by using the Voronoi tessellation method with a point cloud obtained by three-dimensionally displacing the BCC configuration as Voronoi generating points. The cylinder axis direction coincides with the [001] direction of the BCC configuration, and the four types of irregular lattice structure cylinder samples have different CV values.
5(a) shows a cylindrical sample in which the regular lattice structure shown in FIG. 4(a) is three-dimensionally displaced to form an irregular lattice structure such that the CV value becomes 0.10; FIG. 5(b) shows a cylindrical sample in which the regular lattice structure shown in FIG. 4(a) is three-dimensionally displaced to form an irregular lattice structure such that the CV value becomes 0.21; FIG. 5(c) shows a cylindrical sample in which the regular lattice structure shown in FIG. 4(a) is three-dimensionally displaced to form an irregular lattice structure such that the CV value becomes 0.34; and FIG. 5(d) shows a cylindrical sample in which the regular lattice structure shown in FIG. 4(a) is three-dimensionally displaced to form an irregular lattice structure such that the CV value becomes 0.39.
Figures 5(e) to (h) show irregular lattice structures obtained by using the Voronoi tessellation method with a point cloud obtained by three-dimensionally displacing 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 different CV values.
FIG. 5( e ) shows a cylindrical sample obtained by three-dimensionally displacing the regular lattice structure shown in FIG. 4( d ) so that the CV value becomes 0.13, resulting in an irregular lattice structure. FIG. 5( f ) shows a cylindrical sample obtained by three-dimensionally displacing the regular lattice structure shown in FIG. 4( d ) so that the CV value becomes 0.27, resulting in an irregular lattice structure. FIG. 5( g ) shows a cylindrical sample obtained by three-dimensionally displacing the regular lattice structure shown in FIG. 4( d ) so that the CV value becomes 0.37, resulting in an irregular lattice structure. FIG. 5( h ) shows a cylindrical sample obtained by three-dimensionally displacing the regular lattice structure shown in FIG. 4( d ) so that the CV value becomes 0.41, resulting in an irregular lattice structure.
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 configuration as the Voronoi generating points. The cylinder axis direction coincides with the [0001] direction of the HCP configuration, and these are four types of cylindrical samples with different CV values.
FIG. 5(i) shows a cylindrical sample in which the regular lattice structure shown in FIG. 4(g) has been three-dimensionally displaced to form an irregular lattice structure such that the CV value is 0.09; FIG. 5(j) shows a cylindrical sample in which the regular lattice structure shown in FIG. 4(g) has been three-dimensionally displaced to form an irregular lattice structure such that the CV value is 0.20; FIG. 5(k) shows a cylindrical sample in which the regular lattice structure shown in FIG. 4(g) has been three-dimensionally displaced to form an irregular lattice structure such that the CV value is 0.33; and FIG. 5(l) shows a cylindrical sample in which the regular lattice structure shown in FIG. 4(g) has been three-dimensionally displaced to form an irregular lattice structure such that the CV value is 0.38.

In addition to the above-mentioned Figure 5, we designed cylindrical samples with an outer diameter of φ40 mm × H40 mm (diameter × height) and different cylindrical axis directions, which have an irregular lattice structure obtained by using the Voronoi tessellation method with point clouds that have been three-dimensionally displaced in the BCC arrangement, FCC arrangement, and HCP arrangement as Voronoi generating points.
For the BCC configuration, irregular lattice structures with CV values of approximately 0.10, 0.21, 0.34, and 0.39 were designed, with the cylinder axes parallel to the [001], [101], and [111] directions of the BCC configuration. For the FCC configuration, irregular lattice structures with CV values of approximately 0.13, 0.27, 0.37, and 0.41 were designed, with the cylinder axes parallel to the [001], [101], and [111] directions of the FCC configuration. For the HCP configuration, irregular lattice structures with CV values of approximately 0.09, 0.20, 0.33, and 0.38 were designed, with the cylinder axes parallel to the [0001] and [2110] directions of the HCP configuration. Five cylindrical samples of each type were designed, and a total of 160 types of cylindrical samples with irregular lattice structures were designed.

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

(Compression test)
A compression test was carried out on the cylindrical samples described above. Next, the amount of energy absorbed up to 50% strain (20 mm displacement) was calculated from the load-displacement curve of the compression test to confirm the degree of anisotropy.

The compression test was carried out in accordance with JIS K7220:2006 as follows.
As shown in FIG. 6, a cylindrical sample S was placed on a steel sample mounting jig 10, and a compression test was performed from the upper surface side 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.

The energy absorption amount up to 50% strain and the anisotropy of the energy absorption amount obtained for the cylindrical samples are shown in Figure 7. The anisotropy of the energy absorption amount was calculated using the following formula (3).
Figure 7(a) shows the energy absorption of a regular lattice structure (CV value: 0) and an irregular lattice structure with a BCC configuration as the generating point. At a CV value of 0, the energy absorption varies significantly depending on the weighting direction ([001], [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 energy absorption varies significantly depending on the weighting direction ([001], [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 the HCP configuration as the generating point. When the CV value is 0, the [0001] direction and
It can be seen that the amount of energy absorption varies greatly depending on the loading direction, indicating strong anisotropy. On the other hand, Figure 7(d) shows that the anisotropy decreases as the CV value increases, and the average energy absorption at each CV value also decreases monotonically. When the CV value is around 0.20, the anisotropy is 1.5%, and the average energy absorption is 10.2 J. On the other hand, when the CV value is around 0.38, the anisotropy is 1.8%, and the average energy absorption is 9.4 J.

As described above, it has been confirmed that irregular lattice structures with a CV value of 0.05 or greater and 0.35 or less have a low anisotropy of energy absorption, as shown in equation (3), of 10% or less, and have a greater energy absorption than structures with a CV value of 0.35 or greater.

The shock-absorbing member of the present invention can be applied to any part that requires protection from impact, such as space probes, vehicles, electronic devices, and furniture.

10 Sample mounting jig 20 Compressor S Cylindrical sample

Claims (5)

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 :
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. The shock absorbing element of claim 1, wherein each cell of the irregular lattice structure is a convex hull. 3. The impact absorbing member according to claim 1, wherein the anisotropy of the energy absorption amount is 10% or less. 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. 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:
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.