Title of Invention CRASH ENERGY ABSORBING PART Technical Field [OOOI] The present invention relates to a crash energy absorbing part which may be used in transport vehicles such as automobiles. 10 Background Art [0002] Safety level of transport vehicles has been increasing every year, and it is essential to protect occupants in a cabin even if the function of the transport vehicle 15 is damaged in collision. Tlierefore, in order lo make a fianie around the cabin absorb the energy that is generated in collision and reduce the sl~ocktr ansmitted to the cabin, a high strength steel sheet is actively used for the fiame, whereby the collision safety is improved. [0003] 20 Moreover, in recent years, considering the repairability after collision in addition to the collision safety, a vehicle type, in which an exchangeable crash energy absorbing part such as a crash box is used for absorbing the shock, has been increased. This crash energy absorbing part may be mounted at a front surface and a rear surface of a cabin so that the shock-absorbing direction of the crash energy 25 absorbing part is in a longitudinal direction of an automobile. The crash energy absorbing part is collapsingly deformed into a bellows shape in tlle shock-absorbing direction in collision and thereby absorbs the crash energy. Although it slightly differs depending on the vehicle type, there is a limitation in tlie shape of the crash energy absorbing part due to the space wvbere the crash energy absorbing part is to be 30 arranged. [0004] Here, as shown by the views (A) to (E) in FIG. 1, the collapsing deformation into the bellows shape is perfornled by repeating defom~ation such that buckling creases bw, which are formed at a certain buckling wavelength H, are folded. Other than this deformation, there are cases in wvhich the entirety of a part is bent, whereby 5 deformation occurs unstably. In such deformation, the crash energy is difficult to absorb sufficiently. [OOOS] Ful-ther~norea, collision of an automobile does not.necessarily occur in a direction parallel to the shock-absorbing direction of the crash energy absorbing part. 10 Therefore, the crash energy must be absorbed even when a crash load is applied in a direction crossing the shock-absorbing direction (for example, a direction that is oblique to the shock-absorbing direction by an intersection angle of 10 degrees). [O006] Accordingly, a crash energy absorbing part is required to be made so that the 15 collapsing deformation into the bellows shape will occur reliably and stably regardless of the direction of a crash load that is applied, from tie viewpoint of absorbing all crash energy, which is generated in a light collision (for example, a collision occurring at the speed of 15 kmkour), and thereby preventing damages to other members. In addition, it is very important to reduce the weight of a member 20 fiom the viewpoint of improvenient in fuel efficiency. [0007] Techniques for strictly co~itrollingt he material and the shape parameters of a crash energy absorbing part have been developed heretofore in order to make the crasli energy absorbing part so that the collapsing deformation into the bellows shape 25 will occur more stably. [OOOS] For example, according to Non-Patent Literature 1, the behavior of collapsing of a thin cylindrical lnelnber \vhich receives a compressive load in an axial direction is controlled by a ratio oy/E, in \vllich op represents yield stress of a 30 material and E represents a longitudinal elastic coefficient (Young's modulus). In this case, when the ratio ojlE is small, an axial symmetric buckling mode tends to occur, and when the ratio oylE is great, an axial asynlmetric buckling mode tends to occur. [0009] Also, according to Non-Patent Literature 2, regarding the beha~lior of 5 collapsing of a thin cylindrical menlbel; thc collapsing mode is changed by a ratio dlt of a diameter "d" of the metnber and the thickness "t" of the member. [OOlO] On the other hand, Patent Literature I discloses a technique for configuring a crash energy absorbing part to be collapsingly defonned into a bellows shape. In 10 this case, the crash energy absorbing part has a cross section of a polygon shape of a rectangle or more, and a ratio t/M of the thickness "t" and a circu~nferentialle ngth R/i of the cross section is controlled to be not less than 0.0025. [OO 111 Patent Literature 2 also discloses a technique for configuring a crash energy 15 absorbing part to be collapsingly deformed into a bellows shape. In this case, the crash energy absorbing part has a polygonal cross section, and a ratio of lengths of adjacent sides among the sides of the polygon of the cross section is controlled to be not seater than 2.3. [0012] 20 The above techniques of strictly controlling the material and the shape paralneters of the crash energy absorbing part are findings that are effective for configuring a crash energy absorbing part, which is made of an ordinary metal material, to be collapsingly defonned into a bellows shape. Howevel; in the case of a crash energy absorbing part that is co~lstmcted of a sandwich metal sheet, in which 25 a surface layer that is formed of a metal sheet is laminated on each side surface of a core layer and is bonded together, it is difficult to pro\dde a crash energy absorbing part by h l l y utilizing the followitig characteristics of the satid\vich metal sheet, only by controlling the material and the shape parameters as described above. That is, the sandwich tnetal sheet is light in weight con~pared to a metal sheet and can be 30 deformed at a short buckling \vavelength. [00 1 31 It is repo~ted that a crash energy absorbing part that is constrncted of a sandwich metal sheet is collapsingly deformed into a bellows shape at a shoi-t buckling wavelength by co~ltrollinga ratio of the Young's modulus of the nmtal sheet of a surface layer and the Young's modulus of a core layel: The ~nechanis~onf this 5 deformation is described below. [00 141 Since the core layer restricts the metal sheet on each surface of the core layer by bonding, the sandwich metal sheet can be modeled by two metal sheets 12 which are restricted relative to each other by elastic springs 11 (the view (A) in FIG. 10 2). Although a degree of fieedotn of defor~nationo f the nletal sheet 12 is different, the collapsing deformation mode of each of the two metal sheets 12 is equivalent to the collapsing deforination mode of a metal sheet 12 on an elastic floor 13 (the view (B) in FIG. 2). Tlie elastic floor 13 corresponds to restricting elastic springs. Both of the two metal sheets 12 (the view (A) in FIG. 2) that are restricted by the elastic 15 springs 11 are unfixed, whereas only the metal sheet 12 (the view (B) in FIG. 2) on the elastic floor 13 is unfixed. Therefore, the deformation of the elastic springs 11 corresponds to sllear defor~nationin the case of collapsingly deforming the two metal sheets 12 that are restricted by the elastic springs 11, and the deformation of the elastic springs 11 corresponds to elongatio~di eforination in the case of collapsingly 20 deforming the metal sheet 12 on the elastic floor 13. Nevertheless, the collapsing energy is absorbed by the deformation of the elastic body and the defornlation of the metal sheet in each of the cases. In this case, the deformation is perfor~ned so that the total of the deformation energy will be the minirnum. When the metal sheet 12 of the surface layer is deformed at a buckling wavelength HI (the view (C) it1 FIG. 2), 25 which is equal to the length of the straight portion of the metal sheet 12, an energy er is the minirnum. On the other hand, in the deformation of the elastic floor, the energy can be made smaller when the elongation is made as sinall as possible. Thus, when the metal sheet 12 is deformed at a short buckling wavelength Hz as shown in the view (D) in FIG. 2, an energy e, is the minimum. Accordingly, the buckling 30 wavelength of the sheet on the elastic floor depends on the balance of the amount of the energy e, and ef and is thereby a value which is smaller than the bucking wavelength HI and is greater than the buckling \vavelength 1-12 (the views (C) and (D) in FIG. 2). [0015] The sandwich metal sheet is collapsingly defommed at a short buckling 5 wavelength by the same pri~lciplea s in the case in FIG. 2. That is, in the surface layer, the defor~uation energy is small when the surface layer is defor~ned at a long buckling wavelength, whereas in the core layel; the deformation energy is s~nall when the core layer is deformed at a short buckling wavelength. The sandwich metal sheet is defornled at a buckling wavelength, at which the alnount of the 10 deformation energy of the surface layer and the core layer is balanced and the total of the defonnation energy of the surface layer and the core layer will be minimum. Since the core layer is deformed at a short buckling wavelength because the deformation energy is decreased, a crash energy absorbing part that is constructed of the sandwich metal sheet is collapsingly deformed at a shorter wavelength compared 15 to a crash energy absorbing part that is made of a single material. However, in a sandwich metal sheet, in which a core layer has a high Young's nlodulus, and in which a hardly deformable material such as a brazing material is used as a bonding ~naterial, the core layer is hardly deformed and is difficult to deform at a short buckling wavelength. Therefore, in such a crash energy absorbing part, the 20 collapsing defonnation into the bellows shape may not occur stably. [0016] In another example, Patent Literature 3 discloses a crash energy absorbing part which has a polygonal closed cross section with an inwardly recess portion, and in which a bending mo~llent is differentiated at a part of the cross section. By 25 forming such a co~nplicated cross sectional shape, the buckling wavele~igth is made short, the collapsing deformation into the bellows shape stably occurs even in a collision from an oblique direction, and the crash energy is absorbed sufficiently. Howevel; this technique can be used in the case of using a metal sheet. Therefore, if a sandwich metal sheet is formed into the same co~nplicateds hape as in the above 30 technique, there is a high probability that a forming defect such as rupture of a surface layer occurs in the for~l~inangd a desired shape is not obtained. [0017] As described above, in general, the r~~aterianl d the shape paratneters of a crash energy absorbing part are colltrolled so that the. crash energy absorbing part will be collapsingly deformed into a bello\vs shape even when an in~pacits applied in 5 a direction crossing the shock-absorbing direction of the crash energy absorbing part. However, a technique for in~proving the fuel efficiency of a transportation vehicle and for obtaining sufficie~~abt sorbable amount of the crash energy by forming a crash energy absorbing part with a light weight material and making collapsing deformation into a bellows shape occur more stably, has not yet been developed. 10 Citation List Patent Literature [0018] Patent Literature 1 : Patent Literature 2: Patent Literature 3: Nan-Patent Literature 1001 91 I Non-PatentLiteratuel: Materials & Mechanics Conference 2008, 20 "OSO905-1"-"OSO905-2" Non-Patent Literature 2: Journal of the Japan Society of Mechanical Engineers Kansai branch, 2005 (80) Sumn~a~ofy I nvention 25 Technical Problem [0020] An object of the present invention is to provide a crash energy absorbing part which is light in weight, and in which collapsing deformation into a bellows shape occurs more stably even when a crash load is applied in a direction crossing 30 the shock-absorbing direction of the crash energy absoxbing part. Solution to Proble~n [0021] The inventors of the present invention researched the crash energy absorbing part which is constmcted of a sandwich nietal sheet in more detail in order 6 to solve the above problenl. As a result, the inventors of the present invention found that there is a probability that in a sandwich tiletal sheet, in which a core layer has a high Young's n~odulus,a nd in which a hardly deformable material suc11 as a brazing material is used as a bonding material, collapsing defornlation into a bellows shape does not stably occur depending on the direction of a load that is applied, 10 because the core layer is hardly deformed and is difficult to deform at a short buckling wavelength. [0022] Then, the inventors of the present invention conducted an intensive research on the problem and concluded that the deformation of a layer, which is formed of the 15 core layer and the bonding layers, should be strictly cot~trolled because the defornlation characteristics of the bonding layers are also important parameters in order to make the sandwich metal sheet so that collapsing deformation will occur more stably at a short buckling wavelength. [0023] 20 The inventors of the present invention and found the following items as a technique for solving the above problem that is specific to the sandwich metal sheet providing a crash energy absorbing part which is light in weight, and in which collapsing deformation into a bellows shape occurs tllore stably even when a crash load is applied in a direction crossing the sl~ock-absorbing direction of the crash 25 energy absorbing part. (1) A crash energy absorbing part configured to absorb crash energy when a crash load is applied to one of end portions in a shock-absorbing direction of the crash energy absorbing part, 30 the crash energy absorbing part being constructed by fornling a sandwich metal sheet including surface layers and a core layes, in which each of the surface layers is formed of a n~etals heet, and the sui.face layer is laminated on each surface of the core layer and is bonded together, wherein the center layer other that1 the surface layers has a defornlation rate of not less than 7.0 % arid not greater than 75.0 %, and the deformation rate is a rate 5 of decrease i n flexural rigidity, which is measured by an experiment, from a calculated rigidity, which is calculated based 011 the structure of the sandwich metal sheet. (2) The crash energy absorbing part according to (I), 10 wherein each of the surface layers is formed of a metal sleet which has a Young's modulus that is greater than the Young's modulus of the core layer, and wherein a thickness ratio tJtf of the thickness tf of each of the surface layers and the thickness t, of the core layer is not less than 2.0 and not greater than 7.0. (3) 15 The crash energy absorbing part according to (I), wherein each of the surface layers is formed of a metal sheet which has a Young's tnodulus that is greater than the Young's nlodulus of the core layel; and wherein a thickness ratio tJtf of the thickness trof each of the surface layers and the thickness t, of the core layer is not less than 3.5 and not greater than 5.0. 20 (4) The crash energy absorbing part according to (l), wherein a ratio E&E, of the Young's n~odnlnsE f of each of the surface layers and the Young's modulus E, of the core layer is not less than 1 x lo5 and not greater than 1 x 10". 25 (5) The crash energy absorbing part according to (I), wliereit~t he deformation rate of the center layer is not less than 7.0 % and not greater than 50.0 %. (6) The crash energy absorbing part according to (I), wherein the shape of any cross section that is perpendicular to the shockabsorbing direction has a curved portion, of ~vhic11m ininlum curvature radius is not less than 7.0 nnn, at not less than 30.0 % of a circumferential length of the cross section, and wherein the shape of the cross section has a closed structure or has an 5 opening at less than 15.0 % of the circumferential length of the cross section. (7) The crash energy absorbing part according to (I), including 4 or nlore recess portions in a cross section perpendicular to the shock-absorbing direction, each of the recess portions being formed of a curved portion which is formed of a curve having a 10 curvature radius of not less than 7.0 mm and not greater than 15 mm and which is inwardly recessed toward the center of the cross section. (8) The crash energy absorbing part according to (I), wherein the surface layer has yield stress of not less than 100 MPa and not 15 greater than 1000 MPa. (9) The crash energy absorbing part according to (I), wherein a ratio pJprof a density p, of the core layer and a density prof each of the surface layers is not less than 11300 and not greater than 112. 20 (10) The crash energy absorbing part according to (I), wherein the sandwich nletal sheet further includes a bonding layer between the surface layer and the core layer, and wherein the bonding layer has a shear modulus of not less than 50 MPa and not 25 greater than 500 MPa. Advantageous Effects of Invention [0024] According to the present invention, a crash energy absorbing part which is 30 light in weight, and in which collapsing deformation into a bellows shape occurs nlore stably even when an impact is applied in a direction crossing the shockabsorbing direction of the crash energy absorbing part, is provided. As a rcsult, by using the crash energy absorbing part of the present invention, the collapsing defornlation into the bellows shape occurs not only by an impact applied from a fiont direction but also by an impact applied from an oblique direction, atid the crash 5 energy is absorbed. Moreover, being formed of a light weight material, the part itself can be reduced in ~veight. Thus, the crasli energy absorbing part of the preselit invention is effective for inlproving the file1 efficiency of an autolnobile or the like. [0025] The crash energy absorbing part of the present invention has the above 10 effects and therefore can be suitably used as a crash energy absorbing part not only for ordinary auton~obiles but also for transport vehicles such as each type of automobiles from light autonlobiles to large automobiles such as trucks and buses, trains, etc. 15 Brief Description of Drawings [0026] [FIG. 11 FIG. 1 is a sche~natic view showing typical defonnatiorl behavior whet1 a crash load is applied in a shock-absorbing direction, and FIG.1 shows defornlation steps in views (A) to (D) and sho\vs a photograph after the deformation in view (E). 20 [FIG. 21 FIG. 2 is a schematic view showing deformation behavior of a surface layer and a core layer xvhen a sandwich metal sheet is collapsingly deformed. [FIG. 31 FIG. 3 is an explanatory drawing showing a stlx~cture of a crash energy absorbing part according to an embodiment of the present invention. [FIG. 41 FIG. 4 is a schenlatic view of collapsing behavior of a crasli energy 25 absorbing part having an opening. [FIG. 51 FIG. 5 is a schematic view sho\ving a shape of a center line of a cross section of a crash energy absorbing part according to an embodiment of the present invention. [FIG. 61 FIG. 6 is a schematic view showing a shape of a center line of a cross section of a crash energy absorbing part according to another enlbodiment of the present 30 invention. [FIG. 71 FIG. 7 is a schematic view of a crash energy absorbing part having openillgs at portions of the crash energy absorbing part. [FIG. 81 FIG. 8 is a schematic view sho\vi~iga shape of a center line of a cross section of a crash energy absorbing past that is used in Examples. [FIG 91 FIG. 9 is a schematic view sho~vinga shape of a center line of a cross section 5 of a crash energy absorbing part that is used in Examples. [FIG. 101 FIG. 10 is a sclien~aticv iew showing a shape of a center line of a cross section of a crash energy absorbing part that is used in Examples. [FIG. 111 FIG. 11 is a schematic view showing a shape of a center line of a cross section of a crasll energy absorbing part that is used in Examples. 10 [FIG. 121 FIG. 12 is a schematic view showing a shape of a center line of a cross section of a crash energy absorbing part that is used in Exanlples. [FIG. 131 FIG. 13 is a schematic view showing a shape of a center line of a cross section of a crash energy absorbing part that is used in Exatnples. [FIG. 141 FIG. 14 is a schematic view showing a shape of a center line of a cross 15 section of a crash energy absorbing past that is used in Comparative Examples. [FIG. 151 FIG. 15 is a schematic view showing a shape of a center line of a cross section of a crash energy absorbing part that is used in Cotnparative Exatnples. [FIG. 161 FIG. 16 is a schematic view showing a sandwich metal sleet that is used in Exan~plesa nd showing a shape of a center line of a cross section of a crash energy 20 absorbing part that is formed of the sandwich metal sheet. [FIG. 171 FIG. 17 is a schematic view showing a shape of a center line of a cross section of a crash energy abso~bingp art that is used in Coniparative Exanlples. [FIG. 181 FIG. 18 is a schematic view showing a shape of a center line of a cross section of a crash energy absohing part that is used in Comparative Examnples. 25 [FIG. 191 FIG. 19 is a schematic view showing a shape of a center line of a cross section of a crash energy absorbing part that is used in Exatnples. [FIG. 201 FIG. 20 is a schematic view sl~owitiga test method for applying an oblique load to a crash energy absorbing past. [FIG. 211 FIG, 21 is an explanatory drawing showing a shape of a crash energy 30 absorbing part according to Second Exaniple of the present invention. [FIG. 221 FIG. 22 is a graph sho\ving an average buckling \vavelength with respect to a value of E JEf of each of an exatnple 24 and comparative exaillples 14 and 15. [FIG. 231 FIG. 23 is a graph showing an average buckling wavelength with respect to a shape of a crash energy absorbing part. 5 Reference Signs List [0027] I sand~vichm etal sheet 3A, 3B surface layer 5 core layer 10 7A, 773 bonding layer 11 elastic spring 12 metal sheet 2 1 end surface of opening 22 recess portion 15 Description of Embodiments [0028] Hereinafter, (a) preferred embodiment(s) of the present disclosure will be described in detail wit11 reference to the appended drawings. In this specification 20 and the drawvings, eleniet~tsth at have substantially the same fiinction and structure are denoted with the same reference signs, and repeated explallation is omitted. [0029] The crash energy absorbing part of the present invention is a crash energy absorbing part which absorbs crash energy when a crash load is applied to one of end 25 portions in the sl~ock-absorbingd irection. [0030] Moreover, the crash energy absorbing part of the present inventioll is tnade so that the collapsing defornlation into the bellows shape will occur more stably and thereby absorbs crash energy even wllen a crash load is applied in a direction 30 crossing the shock-absorbing direction. Here, in the present inve~~tiotnl,~ ed irection crossing the shock-absorbing direction is a direction that crosses the shock-absorbing direction by not less than 0 degree to less than 60 degrees. In addition, the direction at an angle of from greater than 0 degree to less than 60 degrees is defined as an oblique direction, and a crash load that is applied froni the oblique direction is defined as an oblique load. When tlie angle is 60 degrees or greatel; the 5 defbrniation mode of the crash energy absorbing part due to the crash load may not be the collapsing deformation, but a defor~liationm ode, in which the entirety of the part is folded by a lateral load (load that is perpendicular to the shock-absorbing direction), may mainly occur in most cases. Preferably, the ccrsh energy absorbing part is arranged so that the crash load will be applied in a direction of not greater than 10 45 degrees, more preferably not greater than 30 degrees, with respect to the shockabsorbing direction. Thus, the ratio of the mode of collapsing defor~nationi nto the bellows shape is more increased, and the crash energy is absorbed further efficiently. [003 11 The stn~cture of the crash energy absorbing part according to an 15 embodiment of the present invention mentioned above will be described with reference to FIG. 3 hereinaftee FIG. 3 is an explanatory drawing showing the str~~cturoef the crash energy absorbing part according to an embodiment of the present invention. [0032] 20 (Sttucture of sandwich metal sheet) First, a sandwich metal sheet for constructing the crash energy absosbing part of the present invention will be described with reference to FIG. 3. [0033] The sandwich metal sheet of the present invention is a sheet that is formed 25 by laminating a metal sheet on each side surface of a core layer as a surface layer and bonding the metal sheet with a bonding material. The core layer of the sandwich metal sheet is a sheet-like layer having a density that is lower than the density of the metal sheet of the surface layer. [0034] 30 As shown in FIG. 3, a sandwich metal sheet 1 for constructing the crash energy absorbing part according to an embodinlent of the present illvention is a sandwich tnetal sheet, in which surface layers 3A and 3B, which are formed of a nietal sheet, are lanlinated on both surfaces of a core layer 5, respectively, and arc bonded with bonding layers 7A and 7B, respectively. The Young's IIIO~LI~LIoSf the core layer 5 is smaller than the Young's tnodulus of each of the surface layers 3A and 5 3B. [0035] The surface layers 3A and 3B can be formed of any metal sheet as long as the metal sheet has a Young's ~nodulus that is greater than tlie Young's modulus of tlie core layer 5, preferably a metal sheet having a yield stress of not less than 100 10 MPa and not greater than 1000 MPa, and the metal sheet can be appropriately selected depending on the necessary absorbable amount of the crash energy. If the yield stress of the surface layer is less than 100 MPa, in order to obtain a snfficient absorbable amount of the crash energy, the thickness of the surface layer must be increased or a circutnferential length of a cross section of the crash energy absorbing 15 part must be increased, whereby the weight of the crash energy absorbing part is undesirably increased. On the other hand, if a nletal sheet having a yield stress of greater than 1000 MPa is used as the surface layer, the metal sheet generally tends to be a thick metal sheet, and the weight is undesirably increased. Accordingly, in order to provide a shock-absorbing member which is lighter than the weight of a 20 conventional one by greatly increasing the effect of reducing the weight of the crash energy absorbing part, a metal sheet having a yield stress of not less than 100 MPa and not greater than 1000 MPa is preferably used as the surface layer. Moreover, if the crash energy absorbing part is used for absorbing all crash energy in light collision only by itself so as to avoid damages to other connected members, 25 deforniation resistance of the crash energy absorbing part must be less than the deformation resistance of the connected members, and therefore, the yield stress of the surface layer is preferably not less than 100 MPa and riot greater than 590 A4Pa. As the enaterial for forming tlie surface layers 3A and 3B, specifically, a carboll steel, an aluminum alloy, a pure titanium, a titanium alloy, a niagnesiunl alloy, or the like, 30 may be used. In this case, the surface layers 3A and 3B are more preferably made of a carbon steel, an alunti~ium alloy, or the like, from tlie viewpoint of the production cost of tlie sa~idxvichln ctal sheet 1. Moreoves, the surface layers 3A and 3B may be subjected to each kind of plating treatments (for exanlple, zinc plating or alloy plating) so as to have corrosio~rle sistance and may be subjected to a publicly known surface treatment such as a chromate treatment, a phosphate treatment, an 5 organic resin treatment, etc. [0036] The thickness of each of the surface layers 3A and 3B is preferably not less than 0.2 mtn. If the thickness of eacli of the surface layers 3A and 3B is less than 0.2 mm, the surface layers 3A atid 3B tend to rupture iii bending in a productiot~ of 10 the crash energy absorbing part. Therefore, it is not preferable that the thickness of each of the surface layers 3A and 3B is less than 0.2 mnl. On the other hand, if the thickness of each of the surface layers 3A and 3B is greater than 2.0 mm, the total thickness of the sandwich metal sheet 1 is increased, and the Inass of the sandwich metal sheet 1 is undesirably increased. Therefore, the thickness of each of the 15 surface layers 3A and 3B is preferably not greater than 2.0 mtn from the viewpoint of the reduction in weight of the crash energy absorbing part. [0037] The material for the core layer 5 is not specifically limited as long as the material has a Young's niodulus that is smaller than the Young's modulus of tlie 20 surface layers 3A and 3B, and a publicly known material can be appropriately selected and be used. As the tnaterial for forniing the core layer 5, specifically, a metal material such as an aluminutii alloy, titanium, copper, or tlie like, a non-metal material sncli as ceramics, resin, fiber-reinforced resin, paper, or the like, or a cotnposite material, in whicli any of these materials are combined and composited, 25 may be used. The composite material may include a composite material, in which voids of a hot~eycomb structural body are filled with foanled resin, and a co~iiposite material, in which a resin sheet arid a network structural body are sequentially laminated, for example. [0038] 30 The sandwich tnetal sheet is preferably rnore reduced in weight in order to improve tlie fitel eficieticy of an automobile or the like, which is ~noutited \\lit11 the crash energy absorbing part constructed of the sandwich nletal sheet. In the core layer which is suitably used for constructing such a sandwich metal sheet tliat is reduced in weight, a material, in which a publicly known structure having openings is applied in a metal tnaterial described above, an Fe alloy, or a stainless steel, is 5 preferably used. The publicly known structure having openings may include a network structure, a hone~~comsbtr ucture, a structure provided wit11 holes that are fornied by expanding or punching, a \