具体实施方式：
[0073]Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following embodiments, identical or common portions are identically denoted in the figures, and will not be described repeatedly.
First Embodiment
[0074]FIG. 1 is a perspective view of a shock absorber according to a first embodiment. FIG. 2 is a perspective view of a unit structure of the shock absorber shown in FIG. 1. FIG. 3 is a front view of the shock absorber seen in a direction indicated by an arrow III shown in FIG. 1. FIG. 4 is a plan view of the shock absorber seen in a direction indicated by an arrow IV shown in FIG. 1. FIG. 5 is a cross section of the shock absorber taken along a line V-V shown in FIG. 4. FIG. 6 is a cross section of the shock absorber taken along a line VI-VI shown in FIG. 4. Hereinafter, a shock absorber 1A according to the present embodiment will be described with reference to FIGS. 1 to 6.
[0075]As shown in FIGS. 1 to 6, shock absorber 1A includes a three-dimensional structure S having a plurality of unit structures U (see FIGS. 1 and 2, in particular). The plurality of unit structures U each have a three-dimensional shape formed by a wall 10 having an external shape defined by a pair of parallel curved surfaces.
[0076]Herein, in FIGS. 1 and 2, in order to facilitate understanding, a reference character U does not denote the unit structure in a strict sense; rather, it denotes a unit space in the form of a rectangular parallelepiped that is a space occupied by the unit structure. Furthermore, in FIGS. 1 to 4, in order to facilitate understanding, of an external surface of shock absorber 1A having an overall external shape generally in the form a rectangular parallelepiped, end surfaces located in the X, Y and Z directions shown in the figures are shown in a deep color and thus distinguished from the remainder of the external surface. As shown in FIG. 2, a dimension of unit structure U in a widthwise direction (the X direction shown in the figures) is represented as Lx, a dimension of unit structure U in a depthwise direction (the Y direction shown in the figures) is represented as Ly, and a dimension of unit structure U in a heightwise direction (the Z direction shown in the figures) is represented as Lz.
[0077]The plurality of unit structures U are repeatedly, regularly and continuously arranged in each of the widthwise, depthwise and heightwise directions. Shock absorber 1A according to the present embodiment has six unit structures U arranged in the widthwise direction or the X direction and the depthwise direction or the Y direction side by side, and has three unit structures U arranged in the heightwise direction or the Z direction side by side.
[0078]Shock absorber 1A according to the present embodiment is intended to exhibit a shock absorbing function in the heightwise direction (the Z direction shown in the figure). Accordingly, when shock absorber 1A receives a load, shock absorber 1A exhibits the shock absorbing function in an axial direction, which will match the heightwise direction described above. The number of unit structures U repeated in the widthwise, depthwise and heightwise directions is not particularly limited, and two or more unit structures arranged in at least one of the three directions suffice.
[0079]As has been described above, the plurality of unit structures U each have a three-dimensional shape formed by wall 10. Therefore, as the plurality of unit structures U are continuously connected to one another, three-dimensional structure S is also composed of a set of walls 10.
[0080]Herein, three-dimensional structure S included in shock absorber 1A has a structure in which a thickness is added to a geometrical surface structure. In shock absorber 1A according to the present embodiment, the surface structure is a Schwarz' P structure, which is a type of mathematically defined triply periodic minimal surface. Note that a minimal surface is defined as a curved surface of those having a given closed curve as a boundary that is minimal in area.
[0081]As shown in FIG. 6, three-dimensional structure S that is a Schwarz' P structure with a thickness added thereto has a meandering portion 11 which is a portion presenting a cross-sectional shape extending in a meandering manner when three-dimensional structure S is cut along a specific plane. In the present embodiment, the specific plane is a plane orthogonal to the plane of the sheet of FIG. 4 and parallel to the line VI-VI.
[0082]While there will be three types of meandering portions 11 in total in terms of the structure of three-dimensional structure S: one extending in the widthwise direction; one extending in the depthwise direction; and one extending in the heightwise direction, herein, meandering portion 11 which appears in the cross section shown in FIG. 6, that is, extends in the heightwise direction (i.e., the Z direction), is noted.
[0083]Meandering portion 11 extending in the heightwise direction has a plurality of turning points 12 located in the heightwise direction, and turning point 12 is provided with an internal corner portion 13 and an external corner portion 14. Of these portions, internal corner portion 13 is a portion which appears in the above cross-sectional shape to have a concave shape on a surface of wall 10, and external corner portion 14 is a portion which appears in the above cross-sectional shape to have a convex shape on a surface of wall 10. Herein, a distance between meandering portion 11 extending in the heightwise direction and meandering portion 11 adjacent thereto varies depending on the location in the heightwise direction, and the distance periodically increases and decreases in the heightwise direction.
[0084]While the above-described dimensions Lx, Ly, and Lz are not particularly limited and are variable, in the present embodiment these dimensions Lx, Ly, and Lz satisfy Lx=Ly=Lz. Note that when, of Lx, Ly, and Lz, dimension Lz in the axial direction in which a shock absorbing function is intended to be exhibited, or the heightwise direction, is represented as L1 and the longer one of the remaining, widthwise and depthwise dimensions Lx and Ly is represented as L2, dimensions L1 and L2 satisfying 1.1≤L1/L2≤4.0 allow large compressive stiffness to be obtained and dimensions L1 and L2 satisfying 0.1≤L1/L2≤0.9 allow compressive stiffness to be reduced and hence high deformability to be obtained. Note, however, that dimensions L1 and L2 do not necessarily satisfy these conditions, and whether these conditions are satisfied is arbitrary.
[0085]As shown in FIG. 1 and FIGS. 3 to 6, shock absorber 1A has a differently shaped portion 30 in addition to wall 10 described above. Differently shaped portion 30 is a portion which does not correspond to wall 10 defining unit structure U, and is distinguished from wall 10.
[0086]Differently shaped portion 30 is locally provided in a shock absorbing region, which is a region in which three-dimensional structure S described above has unit structure U disposed (in the present embodiment, the entirety of shock absorber 1A corresponds to the shock absorbing region). More specifically, in the present embodiment, differently shaped portion 30 is provided at a center portion of shock absorber 1A in a plan view, and is not provided in a peripheral portion which is a portion excluding the center portion.
[0087]Differently shaped portion 30 is in the form of a plate having a thickness in a direction intersecting with the axial direction (that is, the Z direction) in which shock absorber 1A exhibits a shock absorbing function when shock absorber 1A receives a load. More specifically, in the present embodiment, differently shaped portion 30 is in the form of a rectangular tube composed of four plate-shaped portions, and each plate-shaped portion extends in the Z direction shown in the figure. In particular, in the present embodiment, the four plate-shaped portions constituting differently shaped portion 30 traverses the shock absorbing region in the Z direction shown in the figure to reach opposite ends of shock absorber 1A.
[0088]Differently shaped portion 30 is disposed in a space located between meandering portions 11 described above, and is connected to be integrated with unit structure U of an adjacent portion. Accordingly, a portion of shock absorber 1A provided with differently shaped portion 30 will be enhanced in compressive stiffness more than the remaining portion of shock absorber 1A (that is, a portion without differently shaped portion 30).
[0089]This is because, in the portion of shock absorber 1A provided with differently shaped portion 30 that has a shape of a plate extending in the axial direction, the compressive stiffness of differently shaped portion 30 having the shape of the plate is further added to the compressive stiffness of wall 10 of the portion provided with differently shaped portion 30. Thus providing shock absorber 1A with such differently shaped portion 30 allows shock absorber 1A to have a local, significantly stiff portion.
[0090]Note that, as has been described above, when differently shaped portion 30 is configured to reach opposite ends of shock absorber 1A in the axial direction, differently shaped portion 30 will act like a partition, and the above-described effect can be more remarkable.
[0091]A shock absorber which is lightweight and has an excellent shock absorbing function can thus be obtained by adopting a configuration in which differently shaped portion 30 that does not correspond to wall 10 defining unit structure U is locally provided in a shock absorbing region which is a region in which three-dimensional structure S has unit structure U disposed, as in shock absorber 1A according to the present embodiment.
[0092]Herein, while shock absorber 1A may be manufactured in any method, it can be additively manufactured using a three dimensional additive manufacturing apparatus for example. When shock absorber 1A is additively manufactured using a three dimensional additive manufacturing apparatus, wall 10 and differently shaped portion 30 will be identical in material. Note, however, that when a three dimensional additive manufacturing apparatus of a fused deposition modelling (FDM) system is used, it is also possible to form wall 10 of a material and form differently shaped portion 30 of a different material.
[0093]While shock absorber 1A (that is, wall 10 and differently shaped portion 30) may basically be formed of any material having a large elastic force, it is preferably formed of a resin material or a rubber material. More specifically, when shock absorber 1A is formed of resin, shock absorber 1A can be formed for example of thermoplastic resin such as ethylene-vinyl acetate copolymer (EVA) or can be formed for example of thermosetting resin such as polyurethane (PU). When shock absorber 1A is formed of rubber, it can be formed for example of butadiene rubber.
[0094]Shock absorber 1A can be composed of a polymer composition. In that case, an example of a polymer to be contained in the polymer composition includes olefinic polymers such as olefinic elastomers and olefinic resins. Examples of the olefinic polymers include polyolefins such as polyethylene (e.g., linear low density polyethylene (LLDPE), high density polyethylene (HDPE), and the like), polypropylene, ethylene-propylene copolymer, propylene-1-hexene copolymer, propylene-4-methyl-1-pentene copolymer, propylene-1-butene copolymer, ethylene-1-hexene copolymer, ethylene-4-methyl-pentene copolymer, ethylene-1-butene copolymer, 1-butene-1-hexene copolymer, 1-butene-4-methyl-pentene, ethylene-methacrylic acid copolymer, ethylene-methyl methacrylate copolymer, ethylene-ethyl methacrylate copolymer, ethylene-butyl methacrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-ethyl acrylate copolymer, ethylene-butyl acrylate copolymer, propylene-methacrylic acid copolymer, propylene-methyl methacrylate copolymer, propylene-ethyl methacrylate copolymer, propylene-butyl methacrylate copolymer, propylene-methyl acrylate copolymer, propylene-ethyl acrylate copolymer, propylene-butyl acrylate copolymer, ethylene-vinyl acetate copolymer (EVA), propylene-vinyl acetate copolymer, and the like.
[0095]The polymer may be an amide-based polymer such as an amide-based elastomer and an amide-based resin. Examples of the amide-based polymer include polyamide 6, polyamide 11, polyamide 12, polyamide 66, and polyamide 610.
[0096]The polymer may be an ester-based polymer such as an ester-based elastomer and an ester-based resin. Examples of the ester-based polymer include polyethylene terephthalate and polybutylene terephthalate.
[0097]The polymer may be a urethane-based polymer such as a urethane-based elastomer and a urethane-based resin. Examples of the urethane-based polymer include polyester-based polyurethane and polyether-based polyurethane.
[0098]The polymer may be a styrene-based polymer such as a styrene-based elastomer and a styrene-based resin. Examples of the styrene-based elastomer include styrene-ethylene-butylene copolymer (SEB), styrene-butadiene-styrene copolymer (SBS), a hydrogenated product of SBS (styrene-ethylene-butylene-styrene copolymer (SEBS)), styrene-isoprene-styrene copolymer (SIS), a hydrogenated product of SIS (styrene-ethylene-propylene-styrene copolymer (SEPS)), styrene-isobutylene-styrene copolymer (SIBS), styrene-butadiene-styrene-butadiene (SBSB), styrene-butadiene-styrene-butadiene-styrene (SBSBS), and the like. Examples of the styrene-based resin include polystyrene, acrylonitrile styrene resin (AS), and acrylonitrile butadiene styrene resin (ABS).
[0099]Examples of the polymer include acrylic polymers such as polymethylmethacrylate, urethane-based acrylic polymers, polyester-based acrylic polymers, polyether-based acrylic polymers, polycarbonate-based acrylic polymers, epoxy-based acrylic polymers, conjugated diene polymer-based acrylic polymers and hydrogenated products thereof, urethane-based methacrylic polymers, polyester-based methacrylic polymers, polyether-based methacrylic polymers, polycarbonate-based methacrylic polymers, epoxy-based methacrylic polymers, conjugated diene polymer-based methacrylic polymers and hydrogenated products thereof, polyvinyl chloride-based resins, silicone-based elastomers, butadiene rubber (BR), isoprene rubber (IR), chioroprene (CR), natural rubber (NR), styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), butyl rubber (IIR), and the like.
[0100]As has been described above, shock absorber 1A according to the present embodiment will be lightweight and have an excellent shock absorbing function. This is significantly attributed to a structural feature (a feature in shape) of shock absorber 1A. Hereinafter, an effect obtained by shock absorber 1A according to the present embodiment will be described based on a result of a first verification test conducted by the present inventor to simulate the shock absorbing function of the shock absorber composed of three-dimensional structure S in which a thickness is added to a Schwarz' P structure (that is, a shock absorber without differently shaped portion 30 as described above).
[0101]FIG. 7 is a graph showing a result of simulating the shock absorbing functions of the shock absorbers for verification examples 1 and 2.
[0102]In the first verification test, models for shock absorbers for verification examples 1 and 2 were specifically designed and a case in which these models received an external force in a prescribed direction was assumed, and how the models would behave in that case was simulated and their behaviors were individually analyzed. More specifically, a so-called stress-strain curve was obtained for each of these models.
[0103]Herein, as has been described above, the shock absorbers according to the verification examples 1 and 2 are each a shock absorber including three-dimensional structure S in which a thickness is added to a Schwarz' P structure (that is, a shock absorber without differently shaped portion 30 described above), and thus composed of wall 10 alone.
[0104]More specifically, the shock absorber according to the verification example 1 includes unit structure U having widthwise, depthwise and heightwise dimensions each 10 mm with wall 10 having a thickness t of 1.4 mm. This case provides a volume ratio V of about 30%.
[0105]The shock absorber according to the verification example 2 includes unit structure U having widthwise, depthwise and heightwise dimensions each of 10 mm with wall 10 having a thickness t of 1.8 mm. This case provides a volume ratio V of about 40%.
[0106]Further, the shock absorbers according to verification examples 1 and 2 both received external force in the axial direction described above or the heightwise direction. Note that the shock absorbers according to the verification examples 1 and 2 were both assumed to be formed of a urethane-based acrylic polymer.
[0107]To increase compressive stiffness, unit structure U may typically have wall 10 increased in thickness. However, when wall 10 is increased in thickness, volume ratio V will also increase accordingly, so that the larger wall 10 is in thickness, the larger volume ratio V is, resulting in the shock absorber being heavier. That is, there is a so-called trade-off relationship between ensuring compressive stiffness and reducing weight.
[0108]However, for example, when the shock absorbers according to the verification examples 1 and 2 are provided with differently shaped portions 30 as described above locally at a portion, that portion provided with differently shaped portion 30 will provide performance as indicated in FIG. 7 by a broken line DL, and the shock absorbers can as a whole obtain a desired shock absorbing function. When this method is compared with obtaining locally large compressive stiffness by increasing wall 10 of the portion of interest entirely in thickness, the former can significantly suppress an increase in weight of the shock absorber.
[0109]Shock absorber 1A according to the present embodiment described above can thus be a shock absorber which is lightweight and has an excellent shock absorbing function, and can be used for various applications.
[0110]Note that, as a three-dimensional shape formed by a wall having an external shape defined by a pair of parallel curved surfaces, other than that in which a thickness is added to a Schwarz' P structure, as described above, there are also a three-dimensional shape in which a thickness is added to a Schwarz' D structure, a three-dimensional shape in which a thickness is added to a gyroid structure, and the like. Therefore, a shock absorber including as a shock absorbing region a three-dimensional structure in which a thickness is added to the Schwarz' D structure, the gyroid structure or the like may locally be provided with such a differently shaped portion as described above.
[0111](First to Third Variations)
[0112]FIGS. 8 to 10 are plan views of shock absorbers according to first to third variations, respectively. Hereinafter, shock absorbers 1A1 to 1A3 according to the first to third variations based on the first embodiment described above will be described with reference to FIGS. 8 to 10.
[0113]While in the first embodiment, differently shaped portion 30 in the form of a rectangular tube is provided to shock absorber 1A only at a center portion in a plan view by way of example, shock absorbers exhibiting different shock absorbing functions and being also light in weight can be manufactured by variously changing differently shaped portion 30 in position, shape, number and the like. The first to third variations described below exemplify a case in which shock absorber 1A is thus changed.
[0114]As shown in FIG. 8, shock absorber 1A1 according to the first variation is provided with a plurality of differently shaped portions 30 that are identically shaped and independent of one another uniformly throughout a shock absorbing region. More specifically, shock absorber 1A1 according to the first variation has the plurality of differently shaped portions 30 each in the form of a rectangular tube, and differently shaped portions 30 each in the form of the rectangular tube are arranged in a staggered manner in a plan view.
[0115]As shown in FIG. 9, shock absorber 1A2 according to the second variation is provided with a plurality of differently shaped portions differently configured and independent of one another, and provided in a shock absorbing region. More specifically, shock absorber 1A2 according to the second variation is provided with differently shaped portion 30 in the form of a cylinder and a rectangular tube arranged concentrically in a plan view.
[0116]As shown in FIG. 10, shock absorber 1A3 according to the third variation is provided with a plurality of differently shaped portions 30 in the form of plates intersecting one another in a shock absorbing region. More specifically, shock absorber 1A3 according to the third variation has differently shaped portions 30 disposed to together form a number sign, and located along a peripheral edge of shock absorber 1A3 when seen in a plan view.
[0117]Thus, differently shaped portion 30 changed in position, shape, number and the like variously can also be as effective as has been described in the first embodiment. In particular, when differently shaped portion 30 that is locally provided is provided uniformly throughout the shock absorber, the shock absorber can obtain a generally uniform shock absorbing function throughout the shock absorber while having a reduced weight, and when differently shaped portions 30 having different shapes are provided in the shock absorber, the shock absorber can exhibit a different shock absorbing function for each portion of the shock absorber while having a reduced weight.
Second Embodiment
[0118]FIG. 11 is a perspective view of a shock absorber according to a second embodiment. FIG. 12 is a cross section of the shock absorber taken along a line XII-XII shown in FIG. 11. A shock absorber 1B according to the present embodiment will be described below with reference to FIGS. 11 and 12. Shock absorber 1B according to the present embodiment is different from shock absorber 1A according to the first embodiment mainly in how differently shaped portion 30 is configured.
[0119]As shown in FIGS. 11 and 12, shock absorber 1B according to the present embodiment includes a three-dimensional structure S having a plurality of unit structures, and three-dimensional structure S is formed of wall 10 having an external shape defined by a pair of parallel curved surfaces. Shock absorber 1B according to the present embodiment has a Schwarz' P structure as a reference in structure for three-dimensional structure S.
[0120]Shock absorber 1B is intended to exhibit a shock absorbing function in the heightwise direction (the Z direction shown in the figures), and a pair of supports 40 is provided at end portions in the heightwise direction to sandwich three-dimensional structure S. Paired supports 40 are each in the form of a plate. Paired supports 40 may each be a member discrete from three-dimensional structure S and bonded or the like and thus assembled to three-dimensional structure S or may be formed integrally with three-dimensional structure S. The pair of supports 40 is not necessarily formed of a material identical to that of three-dimensional structure S and may be formed of a material different from that of three-dimensional structure S.
[0121]Herein, shock absorber 1B according to the present embodiment has five unit structures U arranged in each of the widthwise direction or the X direction and the depthwise direction or the Y direction side by side, and has three unit structures U arranged in the heightwise direction or the Z direction side by side. In FIG. 11, to facilitate understanding, end surfaces located in the X, Y and Z directions shown in the figure are shown in a dark color and thus distinguished from the remainder of the external surface.
[0122]Shock absorber 1B according to the present embodiment is provided with a plurality of differently shaped portions 30 at a prescribed position in one end portion of a pair of end portions of the shock absorbing region composed of three-dimensional structure S that is located in the Y direction. The plurality of differently shaped portions 30 are provided to close a specific opening of a plurality of openings of three-dimensional structure S.
[0123]That is, when three-dimensional structure S has a Schwarz' P structure as a reference in structure, three-dimensional structure S will have an end with a plurality of first openings 17a aligned in a matrix and independent of one another and a single second opening 17b in the form of a lattice surrounding the plurality of first openings 17a. The plurality of differently shaped portions 30 are provided in the form of a cover so as to close the plurality of first openings 17a.
[0124]Herein, the plurality of differently shaped portions 30 each form a shape of a plate having a thickness in a direction intersecting with the axial direction (that is, the Z direction) in which shock absorber 1B exhibits a shock absorbing function as shock absorber 1B receives a load. That is, the plurality of differently shaped portions 30 each extend along the XZ plane. Thus, a portion of shock absorber 1B that is provided with the plurality of differently shaped portions 30 (That is, one of the pair of end portions of the shock absorbing region located in the Y direction) will be enhanced in compressive stiffness more than the remainder of shock absorber 1B.
[0125]Thus this configuration can also provide the shock absorbing region with a local, significantly stiff portion, and the shock absorber can be lightweight and have an excellent shock absorbing function, and can be used for various applications. Further, adopting the above configuration allows the plurality of differently shaped portions 30 to also function as a type of cover, and a secondary effect is also obtained, that is, can suppress otherwise intrusion of foreign matters into shock absorber 1B through those portions.
[0126]While shock absorber 1B according to the present embodiment is provided with a plurality of differently shaped portions 30 in the form of a cover only at one of a pair of end portions of the shock absorbing region located in the Y direction by way of example, a plurality of differently shaped portions 30 in the form of a cover may further be provided at at least one of the other end portion located in the Y direction and a pair of end portions located in the X direction.
[0127]FIGS. 13 and 14 are diagrams showing first to ninth configuration examples of the end portion of the shock absorber shown in FIG. 11. Hereinafter, with reference to FIGS. 13 and 14, some possible configurations of the end portion of shock absorber 1B will be described as first to ninth configuration examples. Variously changing the end portion in configuration can change the shock absorbing function variously.
[0128]While shock absorber 1B according to the second embodiment described above includes as a configuration of an end portion of shock absorber 1B a configuration in which the plurality of first openings 17a are exposed as they are (the configuration corresponds to the first configuration example shown in FIGS. 13 and 14) and a configuration in which the plurality of first openings 17a are closed by providing differently shaped portion 30 in the form of a plate (more precisely, a flat plate) (the configuration corresponds to the ninth configuration example shown in FIG. 14), differently shaped portion 30 can also be changed in shape variously when the plurality of first openings 17a are closed by differently shaped portion 30.
[0129]For example, as indicated in FIG. 13 by the second to fifth configuration examples, when differently shaped portion 30 is changed in thickness, the end portion can be changed in compressive stiffness accordingly.
[0130]That is, when a differently shaped portion 30b having a medium thickness, as in the third configuration example, serves as a reference, a differently shaped portion 30a having a relatively smaller thickness, as in the second configuration example, allows the end portion to have a relatively small compressive stiffness, and when there is no differently shaped portion provided, as in the first configuration example, the end portion can further be reduced in compressive stiffness. In contrast, a differently shaped portion 30c having a relatively increased thickness, as in the fourth configuration example, can increase the end portion's compressive stiffness to be relatively large.
[0131]Thus increasing or decreasing differently shaped portion 30 in thickness will also increase or decrease compressive stiffness accordingly. In this case, however, the shock absorber as a whole has a weight increasing or decreasing as differently shaped portion 30 is increased or decreased in thickness, and simply increasing differently shaped portion 30 in thickness would invite an increase in weight. In this regard, for example, as in the fifth configuration example, a differently shaped portion 30d varied in thickness to have a relatively increased thickness at a portion while having a relatively reduced thickness at a portion can provide relatively large compressive stiffness while suppressing an increase in weight.
[0132]For example, as indicated in FIG. 14 by the sixth to ninth configuration examples, when differently shaped portion 30 is changed in shape, the end portion can be changed in compressive stiffness accordingly.
[0133]That is, a differently shaped portion 30e in the form of a corrugated plate in cross section, as in the sixth configuration example, allows the end portion to have larger compressive stiffness than providing no differently shaped portion per se, as in the first configuration example, and a differently shaped portion 30f shaped in the form of a curved convex plate, as in the seventh configuration example, allows the end portion to have further larger compressive stiffness than differently shaped portion 30e in the form of a corrugated plate in cross section, as in the sixth configuration. Furthermore, differently shaped portion 30g in the form of a curved concave plate, as in the eighth configuration example, allows the end portion to have further larger compressive stiffness than differently shaped portion 30f shaped in the form of a curved convex plate, as in the seventh configuration example, and in addition, a differently shaped portion 30h in the form of a flat plate, as in the ninth configuration example, allows the end portion to have further larger compressive stiffness than differently shaped portion 30g in the form of a curved concave plate, as in the eighth configuration example.
[0134]Thus changing differently shaped portion 30 in shape will also change compressive stiffness accordingly. In that case, however, the shock absorber's overall weight will change as differently shaped portion 30 changes in shape. Note that when weight is considered, the first configuration example provides a smallest weight, followed by the ninth configuration example, the seventh and eighth configuration examples, and the sixth configuration example.
[0135]As is apparent from the above description, allowing the shock absorber to have an end portion changed in configuration variously for example as in the first to ninth configuration examples described above can provide a shock absorbing function with variations and allows the shock absorber to be used in more various applications.
[0136](Fourth Variation)
[0137]FIG. 15 is a perspective view of a shock absorber according to a fourth variation. Hereinafter, a shock absorber 1B1 according to the fourth variation based on the second embodiment will be described with reference to FIG. 15.
[0138]In the second embodiment described above, the plurality of first openings 17a located at a prescribed end portion of shock absorber 1B are all closed at that end portion by differently shaped portion 30 in the form of a cover by way of example, it is not always necessary to close all of the plurality of first openings 17a located at that end portion by differently shaped portion 30, and it is also possible to limit doing so to a portion to change a shock absorbing function for each portion variously. The fourth variation described below shows one example thereof.
[0139]As shown in FIG. 15, shock absorbe