Frame member, vehicle body, and method for manufacturing frame member

Abstract

The closed cross section portion (10) of the skeleton member (1) has: a first flat portion (21); a second flat portion (22); and a ridge line portion (23) connecting the first flat portion (21) and the second flat portion (22) and having a curvature radius (R) smaller than the curvature radii of the first flat portion (21) and the second flat portion (22). An axial vertical cross section in the closed cross section portion (10) is shaped so that, when the skeleton member (1) is hourglass deformed by a compression load in the length direction Z, the first flat portion (21) and the second flat portion (22) are deformed so as to protrude in the same phase in a direction toward the inside of the closed cross section portion (10) and a direction toward the outside of the closed cross section portion (10).

Description

Technical Field

[0001] This invention relates to a frame component, a vehicle body, and a method for manufacturing the frame component. Background Technology

[0002] In the body of a passenger car, a type of vehicle, the rear portion includes a rear frame. This rear frame incorporates skeletal components such as rear longitudinal beams as impact-absorbing elements (see, for example, Patent Documents 1 and 2). Furthermore, in a rear-end collision involving another vehicle or similar object, the rear frame undergoes axial crushing to absorb the impact load, thereby protecting the occupants, fuel tank, and battery within the passenger compartment. For vehicle rear structures with such functions, there is a need to find ways to more appropriately protect the occupants during rear-end collisions.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2008-32227

[0006] Patent Document 2: Japanese Patent Application Publication No. 2005-121144 Summary of the Invention

[0007] The problem the invention aims to solve

[0008] Typically, the steel plate rear frame included in the lower part of a vehicle's rear structure is manufactured by stamping plates with uniform strength in the thickness direction, thus achieving uniform strength in that direction. In a rear-end collision of a passenger car including such a rear frame, an axial load is generated in the rear frame, causing the rear longitudinal beams to compress axially and deform into a serpentine shape. For the lower part of a vehicle's rear structure containing such rear longitudinal beams, superior impact energy absorption efficiency is required. The same challenge exists in other impact-absorbing components, such as the front longitudinal beams, particularly in axially crushable components.

[0009] Patent document 2 discloses an invention of an aluminum alloy impact-absorbing component (energy-absorbing component for automobile frames). Specifically, it discloses an aluminum alloy energy-absorbing component for automobile frames, characterized in that the component is composed of a heat-treated aluminum alloy hollow profile, wherein the hollow profile has a square or rectangular cross-section with a hollow portion, a wall thickness exceeding 2 mm, and a cross-sectional area of ​​350 mm² excluding the hollow portion. 2The above describes the relationships satisfying 0 < R / a ≤ 0.2, t / a ≤ 0.2, and R / a < 5 × (t / a) - 0.37 when the average length of each side in the cross-section of the hollow profile is set as 'a', the radius of the corner is set as 'R', and the average wall thickness of each side is set as 't'. It is also disclosed that in such an energy-absorbing member, under axial impact load, all sides within the same cross-section perpendicular to the axis bend in the same direction.

[0010] However, the invention in Patent Document 2 is limited to the composition of aluminum alloys. Furthermore, as a specific embodiment, an aluminum extrusion profile is envisioned, and from a strength perspective, a structure with a thicker wall and a larger cross-sectional area is desired.

[0011] One of the purposes of this disclosure is to provide a method for manufacturing a frame component, a body, and a frame component that can achieve superior impact energy absorption efficiency without being limited by materials.

[0012] Solution for solving the problem

[0013] The subject of this invention is the following skeleton component, vehicle body, and method for manufacturing the skeleton component.

[0014] (1) A skeleton member having a closed section portion with a closed section perpendicular to the length direction, wherein,

[0015] The closed section portion includes: a first flat portion; a second flat portion; and a ridge portion that connects the first flat portion and the second flat portion, and whose radius of curvature is smaller than either the radius of curvature of the first flat portion or the radius of curvature of the second flat portion.

[0016] The cross section in the closed section has the following shape: when the skeleton member undergoes serpentine deformation due to compressive load along the length direction, the first flat section and the second flat section bulge with the same phase in the direction toward the inside of the closed section and the direction toward the outside of the closed section.

[0017] (2) The skeleton component according to (1), wherein,

[0018] The radius of curvature of the ridge portion in the cross section is 15 mm or more.

[0019] (3) The skeleton component according to (1) or (2), wherein,

[0020] When the Young's modulus of the skeleton component is set to E, the plate thickness of the closed section is set to t, the radius of curvature of the ridge section is set to R, and the length of at least one of the flat sections in the section is set to bf, R / bf satisfies the following formula (1).

[0021] R / bf ≥ (1.49 × 10) -7 ×Et 3 )+0.153 …(1).

[0022] (4) The skeleton member according to any one of (1) to (3), wherein,

[0023] The frame component is a steel plate component.

[0024] When the plate thickness of the skeleton member is set to t, the radius of curvature of the ridge portion is set to R, and the length of at least one of the flat portions in the cross section is set to bf, R / bf satisfies the following equation (2).

[0025] R / bf≥0.1616t+0.0235…(2).

[0026] (5) The skeleton component according to (4), wherein,

[0027] The skeleton component is formed by joining the first half and the second half together.

[0028] The first half is formed in a cap shape in the cross-section.

[0029] The first half includes the first flat portion, a portion of the second flat portion, a first ridge portion that serves as the ridge portion, a flange that engages with the second half, and a second ridge portion that connects a portion of the second flat portion to the flange.

[0030] When the radius of curvature of the second edge is set to R2, R2 / bf satisfies the following equation (3).

[0031] R2 / bf<0.1616t+0.0235…(3).

[0032] (6) The skeleton member according to any one of (1) to (5), wherein,

[0033] When the radius of curvature of the ridge portion is set to R and the length of at least one of the flat portions in the cross section is set to bf, then 0.20≤R / bf≤0.60.

[0034] (7) The skeleton member according to any one of (1) to (6), wherein,

[0035] When the smaller of the lengths of the closed section portion in the width direction and the height direction of the closed section portion in the cross-section is defined as b, then b ≥ 75 mm.

[0036] When the skeleton component is a steel plate component, the thickness of the closed section portion in the section is 0.8mm to 2.6mm.

[0037] When the skeleton component is an aluminum alloy plate component, the thickness of the closed section in the section is 1.1mm to 3.7mm.

[0038] (8) The skeleton member according to any one of (1) to (7), wherein,

[0039] When the length of at least one of the flat portions in the cross section is set to bf, bf is 75 mm or more.

[0040] (9) The skeleton member according to any one of (1) to (8), wherein,

[0041] The Vickers hardness of the central portion of the closed cross-section in the thickness direction is above 300 HV.

[0042] (10) The skeleton member according to any one of (1) to (9), wherein,

[0043] In the cross section, the Vickers hardness of the surface of the closed cross section in the thickness direction is at least 100 HV lower than the Vickers hardness of the central part of the closed cross section in the thickness direction.

[0044] (11) The skeleton member according to (10), wherein,

[0045] In the cross-section, the closed section portion has a softening layer extending from the surface along the plate thickness direction.

[0046] The Vickers hardness of the central portion in the thickness direction of the closed cross-section is above 300 HV.

[0047] The thickness of the softening layer is 80 μm or more, and is more than 5% and less than 20% of the thickness of the plate at the portion where the softening layer is provided.

[0048] The Vickers hardness of the softening layer on the surface is more than 0.5 times and less than 0.9 times the Vickers hardness of the central portion of the plate in the thickness direction where the softening layer is located.

[0049] The softening layer has: a first hardness variation region, which is a region extending from the surface to 40% of the thickness of the softening layer in the thickness direction of the plate; and a second hardness variation region, which is a region in the softening layer that is not the first hardness variation region.

[0050] The absolute value of the hardness change in the thickness direction of the first hardness change region, ΔHV1, is greater than the absolute value of the hardness change in the thickness direction of the second hardness change region, ΔHV2.

[0051] (12) A vehicle body, wherein the vehicle body comprises the frame member of any one of (1) to (11).

[0052] (13) A method for manufacturing a skeleton component, the skeleton component having a closed section portion with a closed section perpendicular to the length direction, the closed section portion comprising: a first flat portion; a second flat portion; and an edge portion connecting the first flat portion and the second flat portion, wherein the edge portion has a radius of curvature smaller than either the radius of curvature of the first flat portion or the radius of curvature of the second flat portion, wherein,

[0053] In this manufacturing method,

[0054] The shape of the closed section is set such that, when the skeleton member undergoes serpentine deformation due to compressive load along the length direction, the first flat portion and the second flat portion in the section exhibit deformation in which the phase of the deformation is the same in both the direction toward the inside of the closed section and the direction toward the outside of the closed section.

[0055] The closed section is manufactured in such a way that it becomes the shape of the predetermined closed section.

[0056] (14) The method for manufacturing the skeleton component according to (13), wherein,

[0057] In the shape setting of the closed section, when the Young's modulus of the skeleton member is set to E, the plate thickness of the closed section is set to t, the radius of curvature of the edge section is set to R, and the length of at least one of the flat sections in the section is set to bf, R / bf is set to a value that satisfies the following formula (1).

[0058] R / bf ≥ (1.49 × 10) -7 ×Et 3 )+0.153 …(1).

[0059] (15) The method for manufacturing the skeleton component according to (13) or (14), wherein,

[0060] In the shape setting of the closed cross-section, when the radius of curvature of the edge portion is set to R, and the length of at least one of the flat portions in the cross-section is set to bf.

[0061] Set it to 0.20≤R / bf≤0.60.

[0062] (16) A method for manufacturing a skeleton component according to any one of (13) to (15), wherein,

[0063] In the shape setting of the closed cross-section portion

[0064] When the smaller of the lengths of the closed section portion in the width direction and the height direction of the closed section portion in the cross-section is defined as b, then b ≥ 75 mm.

[0065] When the skeleton component is a steel plate component, the thickness of the closed section portion in the section is 0.8mm to 2.6mm.

[0066] When the skeleton component is an aluminum alloy plate component, the thickness of the closed section in the section is 1.1mm to 3.7mm.

[0067] The effects of the invention

[0068] According to the present invention, it is possible to achieve superior impact energy absorption efficiency without being limited by materials. Attached Figure Description

[0069] Figure 1 It is a three-dimensional diagram showing the state of axial crushing deformation of existing skeleton components, marked with color shades corresponding to the strain.

[0070] Figure 2 This is a perspective view showing the state of axial crushing deformation of a skeleton member in one example of this disclosure, marked with shades of color corresponding to the strain.

[0071] Figure 3 It means Figure 2 A schematic three-dimensional view of the skeleton component before it undergoes axial crushing deformation.

[0072] Figure 4 The diagram represents the skeleton component using a cross-section perpendicular to the axis orthogonal to the length direction of the skeleton component.

[0073] Figure 5A and Figure 5B This is a schematic diagram used to illustrate the bending test. Figure 5A This is a top view of the test piece before the experiment. Figure 5BThis refers to the test piece, punch, and roller.

[0074] Figure 6 This is a vertical sectional view of the main part of the modified example 1, with the inner side of the section omitted.

[0075] Figure 7 This is a conceptual diagram illustrating an example of a method for measuring the boundary between the softened layer and the central portion.

[0076] Figure 8 This is a conceptual diagram used to illustrate an example of the Vickers hardness variation in a softened layer.

[0077] Figure 9 This is a vertical sectional view along the axis of a modified example 2, where the skeleton component is composed of the first half and the second half.

[0078] Figure 10A The graphs showing the energy absorption when R / bf is varied are provided for Experiments 2-6. Figure 10B The graphs for Experiments 2-6 show the energy absorption (energy absorption efficiency) per 1 kg of the skeleton component when R / bf is varied.

[0079] Figure 11A The graphs showing the relationship between R / bf and buckling stress for Experiments 7-11 are presented in a way that distinguishes between inverse deformation and in-phase deformation. Figure 11B The graphs for Experiments 7-11 show the relationship between plate thickness t and R / bf when the deformation changes from reverse phase to in-phase.

[0080] Figure 12 The graphs for the minimum R / bf that constitutes the antiphase deformation are plotted for experimental examples 6-11. Detailed Implementation

[0081] [Reflecting on the development of this invention]

[0082] The inventors of this application have focused on a skeleton member having a closed cross-section as an axially crushing member that plastically crushes in the axial (length direction) direction when absorbing impact. The closed cross-section is formed, for example, by combining a pair of cap-shaped members in a cross-section (axis-perpendicular cross-section) orthogonal to the length direction (axial direction) of the skeleton member. Figure 1This is a perspective view showing the state of axial crush deformation of the existing skeleton member 1x, marked with shades of color corresponding to the strain. The skeleton member 1x has two cap-shaped portions 11x and 12x. The flanges 25ax, 25bx, 25cx, and 25dx of each cap-shaped portion 11x and 12x are joined together by welding or the like, thereby forming the skeleton member 1x. The skeleton member 1x has a closed section portion 10x with a closed cross-section perpendicular to the axis orthogonal to the length direction of the skeleton member 1x. The closed section portion 10x is formed into a roughly rectangular shape in the cross-section perpendicular to the axis, having two first flat portions 21ax and 21bx on the top and bottom, two second flat portions 22ax and 22bx on the left and right, and four edge portions 23x (corner portions).

[0083] The inventors of this application focused on the relationship between the width (length) of the flat portion (the first flat portion 21ax, which is the shorter flat portion) in the axially perpendicular section of such a closed cross-section 10x and the radius of curvature of the ridge portion 23x. More specifically, when the skeleton member 1x is subjected to an impact load along its length, each flat portion 21ax, 21bx, 22ax, 22bx is compressed while repeatedly deforming outward and inward towards the axially perpendicular section of the closed cross-section 10x. Figure 1 The diagram shows an outer convex deformation portion 51x and an inner convex deformation portion 52x. This deformation behavior is generally referred to as axial collapse deformation or serpentine deformation. When the radius of curvature of the ridge portion 23x in the member undergoing serpentine deformation is smaller than the width of the first flat portions 21ax, 21bx, the ridge portion 23x acts as a "joint" following the convex deformation of the first flat portions 21ax, 21bx and the second flat portions 22ax, 22bx. Therefore, adjacent portions 21ax, 22ax or portions 21ax, 22bx, adjacent portions 21bx, 22ax or portions 21bx, 22bx exhibit opposite phase deformation behavior, convex in opposite directions to each other in the inner and outer directions of the closed section portion 10x. That is, both the outer convex deformation portion 51 and the inner convex deformation portion 52 appear in a section perpendicular to the axis. Furthermore, the following will also refer to the deformation of opposite phases in which adjacent flat portions in the vertical section of the axis bulge outwards in opposite directions in the inner and outer directions of the closed section portion 10x as anti-phase deformation.

[0084] On the other hand, such as Figure 2As shown, when the radius R of the ridge portion 23 is in a certain or greater proportion to the width bf of the first flat portion 21 (21a), the ridge portion 23 serves to rigidly separate adjacent first flat portions 21a and second flat portions 22a or first flat portions 21a and second flat portions 22b from each other, and adjacent first flat portions 21b and second flat portions 22a or first flat portions 21b and second flat portions 22b from each other in the cross section perpendicular to the axis (preventing the ridge portion 23 from rotating about the central axis of the skeleton member 1). Figure 2 This is a perspective view showing the state of axial crush deformation of the skeleton member 1 in one example of this disclosure, marked with shades of color corresponding to the strain. In this case, for example, adjacent flat portions 21a, 22a (21b, 22b) deform in the same phase, protruding towards the same side in both the inner and outer directions of the closed section portion 10. That is, in a section perpendicular to the axis, either the outwardly convex deformation portion 51 or the inwardly convex deformation portion 52 appears. Furthermore, hereafter, the deformation in the same phase in which adjacent flat portions in a section perpendicular to the axis deform towards the same side in both the inner and outer directions of the closed section portion 10 will also be referred to as in-phase deformation.

[0085] exist Figure 1 In the opposite-phase deformation behavior of the existing structure shown, the strain of the introduced ridge portion 23x is relatively small, so the possibility of the skeleton member 1x undergoing parent material fracture is relatively small. However, in the middle of the axial collapse deformation of the skeleton member 1x, the supporting effect of the ridge portion 23x relative to the impact load is not so sufficient, so there is a tendency for the average load acting on the skeleton member 1x to be small and the energy absorption to be small.

[0086] Compared to the existing structures described above, in the skeleton member 1x of this disclosure, the flat portions 21 and 22 adjacent to the ridge portion 23 undergo deformation behavior in the same phase relative to the inner and outer sides of the closed section portion 10 during axial crushing. As a result, the strain introduced into the ridge portion 23 is relatively large. Therefore, during the axial crushing of the skeleton member 1, the ridge portion 23 provides sufficient support against the impact load, thus tending to generate a larger average load and a larger energy absorption in the skeleton member 1. Based on this understanding, the inventors of this application conceived of the present invention.

[0087] [Composition of the skeleton components]

[0088] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In this embodiment, a frame member applied to the body of an automobile will be described.

[0089] Figure 3 It means Figure 2 A schematic three-dimensional view of the skeleton component 1 before it undergoes axial crushing deformation. Figure 4 The diagram shows the skeleton member 1 represented by a cross section perpendicular to the axis orthogonal to the length direction Z of the skeleton member 1.

[0090] like Figure 3 and Figure 4 As shown, the frame member 1 is a long strip-shaped member, and its length direction (axial direction) is the length direction Z. The frame member 1 constitutes part of the structural members of the body of a vehicle such as a passenger car, and is a member that absorbs impact energy while deforming in a serpentine manner in the length direction Z during a vehicle collision. Examples of such frame members 1 include front longitudinal beams, rear longitudinal beams, lower side beams, A-pillars, B-pillars, roof longitudinal beams, floor crossbeams, roof crossbeams, and lower reinforcement members.

[0091] The shape of the skeleton member 1 in the cross-section perpendicular to the axis, which is orthogonal to the length direction Z, is the same in at least a portion of the length direction Z. Furthermore, through holes such as inspection holes may be formed in the skeleton member 1. The skeleton member 1 has a closed section portion 10, which is closed circumferentially in the cross-section perpendicular to the axis. The cross-section of the closed section portion 10 perpendicular to the length direction Z is a closed section. In the cross-section perpendicular to the axis, mutually orthogonal directions are defined as the width direction X and the height direction Y.

[0092] The skeleton member 1, including the closed section portion 10, is formed by a first half 11 and a second half 12 that are in the shape of a hat.

[0093] The first half 11 and the second half 12 of the frame member 1 can be formed into a thin sheet by stamping a steel plate, or by stamping or extruding an aluminum alloy plate, or by using a resin material other than metal. In other words, the first half 11 and the second half 12 of the frame member 1 can be components obtained by processing and joining steel plates, components obtained by processing and joining aluminum alloy plates, or components obtained by processing and joining resin materials other than metal.

[0094] When the skeleton member 1 is formed of a steel plate, the steel plate is preferably a high-strength steel plate with a tensile strength of 590 MPa or more, preferably 780 MPa or more. More preferably, the steel plate is an ultra-high-strength steel plate, in which case the tensile strength is preferably 980 MPa or more, more preferably 1180 MPa, and even more preferably 1470 MPa or more. As a method for determining the tensile strength of the skeleton member 1, for example, a portion of the first flat portion 21 or a portion of the second flat portion 22 (described later) can be taken as a test piece, and a tensile test can be performed on the test piece using the method according to JIS Z 2241:2022.

[0095] In this way, by forming the skeleton member 1 as an impact absorption member from high-strength steel plate, the thickness of the skeleton member 1 can be reduced and the energy absorption can be increased.

[0096] "Energy absorption" is calculated based on the relationship between the impactor's reaction force (load) and stroke when the skeleton member undergoes serpentine deformation. The impactor's reaction force (load) and stroke can be determined, for example, by arranging the skeleton member 1 vertically along its length, and then, with the lower end fully constrained, colliding a rigid planar impactor with the skeleton member 1 from the upper end along the length direction (vertical direction). "Energy absorption efficiency" is the energy absorption per unit area (plate thickness × section length) perpendicular to the axis of the skeleton member 1. When the skeleton member 1 does not have uniform cross-sections along the length direction Z, the energy absorption per unit area (plate thickness × section length) of the closed cross-section perpendicular to the length direction Z is the energy absorption efficiency.

[0097] When the frame component 1 is formed of an aluminum alloy plate, the aluminum alloy is preferably composed of Al-Mg alloy (5000 series aluminum alloy), Al-Mg-Si alloy (6000 series aluminum alloy) or Al-Zn-Mg alloy (7000 series aluminum alloy).

[0098] The skeleton component 1 may contain blanks other than steel plates and aluminum alloy plates, and may be formed using blanks other than metal materials such as resin materials and carbon materials.

[0099] The first half 11 and the second half 12 are each formed into a cap shape when viewed from the longitudinal direction Z (in a section perpendicular to the axis). The first half 11 and the second half 12 are integrally joined by a flange to form the skeleton member 1. Furthermore, as shown in the modified example 2 described later, either the first half 11 or the second half 12 may also be formed into a flat plate that is not bent when viewed from the longitudinal direction X. Alternatively, the first half 11 and the second half 12 may also be integrally formed from a tubular member that is formed into a ring shape (e.g., a rectangular or other polygonal ring shape) when viewed from the longitudinal direction Z. Hereinafter, unless otherwise specified, the skeleton member 1 will be described based on its state when viewed from a section perpendicular to the axis orthogonal to the longitudinal direction Z.

[0100] The first half 11 has a first flat portion 21 (21a), a pair of ridge portions 23, 23 (23a, 23b), a pair of flat halves 24, 24 (24a, 24b) connected to the first flat portion 21 (21a) via the pair of ridge portions 23, 23 (23a, 23b, and the first ridge portion), and a pair of flanges 25, 25 (25a, 25b) projecting outward in the width direction X from the pair of flat halves 24, 24 (24a, 24b). Each flat half 24, 24 (24a, 24b) is connected to the corresponding flange 25, 25 (25a, 25b) via the second ridge portions 26, 26 (26a, 26b).

[0101] In this embodiment, the second half 12 is formed in a shape that is symmetrical to the first half 11 in the height direction Y.

[0102] The second half 12 has a first flat portion 21 (21b), a pair of ridge portions 23, 23 (23c, 23d, the first ridge portion), a pair of flat halves 24, 24 (24c, 24d) connected to the first flat portion 21 (21b) via the pair of ridge portions 23, 23 (23c, 23d), and a pair of flanges 25, 25 (25c, 25d) projecting outward in the width direction X from the pair of flat halves 24, 24 (24c, 24d). Each flat half 24, 24 (24c, 24d) is connected to the corresponding flange 25, 25 (25c, 25d) via the second ridge portions 26, 26 (26c, 26d).

[0103] From the perspective of ensuring more uniform deformation of each part in the cross-section perpendicular to the axis of the skeleton member 1 during axial crushing deformation, the radius of curvature R of each edge portion 23 is preferably the same. When the radii of curvature of each edge portion 23 are not uniform, the minimum value of the radii of curvature of each edge portion 23 is called the radius of curvature R. The radius of curvature R refers to the radius of curvature at the center in the thickness direction of the plate. Furthermore, when each edge portion 23 is not a smooth arc, the radius of curvature R is defined as the radius of curvature when the first flat portion 21 and the corresponding flat half portion 24, which are connected by a smooth arc as a straight line.

[0104] The first half 11 and the second half 12 are fixed to each other by joining a pair of flanges 25, 25 (25a, 25b) and a pair of flanges 25, 25 (25c, 25d). These flanges 25 are arranged in a posture that projects outward from the frame member 1 in a section perpendicular to the axis. The joining methods of the pair of flanges 25a, 25b and the pair of flanges 25c, 25d include welding such as spot welding, laser welding, arc welding, riveting, crimping, bolting, and other mechanical joining, as well as bonding based on adhesives. The joining portions (joints) of the pair of flanges 25a, 25b and the pair of flanges 25, 25 (25c, 25d) can be formed at multiple locations separated in the length direction Z, or they can be continuously formed in the length direction Z using structural adhesives or the like.

[0105] When the frame member 1 is a rear longitudinal beam, it is preferable that the cross-sectional shape of the connection portion between the member at the front end of the frame member 1 and the connection portion between the member at the rear end of the frame member 1 and the frame member 1 is the same. This allows for efficient transfer of impact loads to the frame member 1, thereby improving the energy absorption efficiency of the frame member 1.

[0106] In this embodiment, the first flat portion 21 (21a, 21b) forms transverse walls at both ends in the height direction Y of the skeleton member 1. Figure 3 , Figure 4 The upper first flat portion 21a is formed by a first half 11, and the lower first flat portion 21b is formed by a second half 12. Furthermore, the second flat portions 22 (22a, 22b) form longitudinal walls at both ends in the width direction X of the frame member 1. Figure 4 In this embodiment, the second flat portion 22a is composed of the flat half 24a of the first half 11 and the flat half 24c of the second half 12, and the second flat portion 22b is composed of the flat half 24b of the first half 11 and the flat half 24d of the second half 12. In this embodiment, since the first half 11 and the second half 12 are firmly joined by welding or the like, the first half 11 and the second half 12 can be treated as a single component. Furthermore, since the flanges 25a, 25b are firmly joined to the flanges 25c, 25d, the radius of curvature R26 of each of the second ridge portions 26 (26a, 26b, 26c, 26d) can be smaller than the radius of curvature R of the ridge portion 23. The radius of curvature R26 refers to the radius of curvature at the center of the plate in the thickness direction. Furthermore, in cases where each of the second edge portions 26 is not a smooth arc, the radius of curvature is set to the radius of curvature R26 when a smooth arc is used to connect the flat half portion 24, which is a straight line, and the corresponding flange 25.

[0107] In this embodiment, the axial perpendicular section of the closed section portion 10 has the following shape: when the skeleton member 1 undergoes serpentine deformation due to a compressive load along the length direction Z, the first flat portion 21 and the second flat portion 22 protrude with the same phase in the direction towards the inside of the closed section portion 10 and the direction towards the outside of the closed section portion 10. More details of this shape will be described below.

[0108] As described above, the closed section portion 10, which is composed of the first half portion 11 and the second half portion 12, includes a first flat portion 21, a second flat portion 22, and an edge portion 23 that connects the first flat portion 21 and the second flat portion 22 and has a radius of curvature R smaller than either the radius of curvature R21 of the first flat portion 21 or the radius of curvature R22 of the second flat portion 22.

[0109] The first flat portion 21 and the second flat portion 22 have radii of curvature in the cross section perpendicular to the axis that are larger than the maximum external dimension W of the skeleton member 1. The maximum external dimension refers to the straight-line length in the cross section perpendicular to the axis of the skeleton member 1 where the distance between the ends of any two points is the greatest.

[0110] In this embodiment, the first flat portion 21 and the second flat portion 22 are orthogonal to each other, but this is not the case. The angle between the second flat portion 22 and the first flat portion 21 can also be an angle other than 90°.

[0111] (Radius of curvature of the edge portion)

[0112] The ridge portion 23 connects adjacent first flat portions 21 and second flat portions 22, and the radius of curvature of each ridge portion 23 in the cross section perpendicular to the axis is a radius of curvature R. The radius of curvature R is preferably 15 mm or more. By making the radius of curvature R 15 mm or more, the torsional stiffness of the ridge portion 23 can be further improved. As a result, the amount of torsion of each part of the ridge portion 23 in the length direction Z when subjected to external force can be further reduced. Thus, the ridge portion 23 can be constructed as a more "rigid" part. As a result, the ridge portion 23 can rigidly separate adjacent first flat portions 21 and second flat portions 22 in the cross section perpendicular to the axis, and when an impact load in the length direction Z is applied, the rotation of flat portions 21 and 22 about the axis along the length direction Z can be suppressed. As a result, in the skeleton member 1, deformation behavior of adjacent flat portions 21 and 22 deforming towards each other in the same phase can be generated, thereby further improving the impact load efficiency.

[0113] Furthermore, the shorter of the two lengths in the vertical cross-sections of the first flat portion 21 and the second flat portion 22 is defined as length bf. In this embodiment, the length of the first flat portion 21 is length bf. Additionally, the radius of curvature R refers to the radius of curvature of the portion of the ridge portion 23 located at the center of the closed cross-section portion 10 in the plate thickness direction.

[0114] (Lower limit of R / bf)

[0115] When the Young's modulus of the skeleton member 1 is set to E and the plate thickness of the closed section portion 10 is set to t, it is preferable that R / bf satisfies the following formula (1).

[0116] R / bf ≥ (1.49 × 10) -7 ×Et 3 )+0.153 …(1)

[0117] When equation (1) is not satisfied, the deformation mode of the skeleton member 1 during axial crushing deformation tends to be an antiphase deformation. On the other hand, when equation (1) is satisfied, the deformation mode of the skeleton member 1 during axial crushing deformation tends to be an in-phase deformation. That is, taking the equality of the right and left sides of equation (1) as the boundary, the value of R / bf will more clearly determine whether it is an antiphase deformation or an in-phase deformation. The bending stiffness of the flat plate and Et 3 Proportional. Therefore, based on the variable Et, which is proportional to the bending stiffness. 3 This allows for the prediction of whether the skeleton member 1 will experience either inverse or in-phase deformation. Such a variable, Et, is proportional to the bending stiffness. 3 The insight into predicting whether the skeleton member 1 will undergo either inverse or in-phase deformation is the result of in-depth research conducted by the inventors of this application. Thus, it is possible to predict whether the skeleton member 1 will undergo either inverse or in-phase deformation using Young's modulus E and the plate thickness t of the skeleton member 1.

[0118] When the skeleton member 1 is made of steel plate, Young's modulus E is approximately 210 GPa. When the skeleton member 1 is made of aluminum alloy plate, Young's modulus E is approximately 70 GPa. Furthermore, the radius of curvature R26 of the second ridge portions 26 (26a, 26b, 26c, 26d) can also be configured to not satisfy equation (1). That is, it can also be...

[0119] R26 / bf < (1.49 × 10) -7 ×Et 3 )+0.153.

[0120] With this configuration, the second ridge portions 26 (26a, 26b, 26c, 26d) can be made compact. Therefore, high energy absorption efficiency of the skeleton member 1 can be achieved, and the skeleton member 1 can be made more compact in the width direction X and the height direction Y.

[0121] (Especially the lower limit of R / bf when the frame members are steel plate members)

[0122] In particular, when the skeleton member 1 is a steel plate member, when the plate thickness of the closed section 10 is set to t and the length of at least one flat part (the first flat part 21 in this embodiment) in the section perpendicular to the axis is set to bf, it is preferable that R / bf satisfies the following formula (2).

[0123] R / bf≥0.1616t+0.0235…(2)

[0124] When equation (2) is not satisfied, the deformation mode of the skeleton member 1 during axial crushing deformation is prone to be an antiphase deformation. On the other hand, when equation (2) is satisfied, the deformation mode of the skeleton member 1 during axial crushing deformation is prone to be an in-phase deformation. That is, taking the equality of the right and left sides of equation (2) as the boundary, the value of R / bf will more clearly determine whether it is an antiphase deformation or an in-phase deformation. In this way, by setting R / bf based on equation (2) specifically for the case where the skeleton member 1 is a steel plate member, the skeleton member 1 can be designed by simpler calculation. In addition, the radius of curvature R26 of the second ridge portion 26 (26a, 26b, 26c, 26d) (equivalent to the radius of curvature R2 of this disclosure) can also be configured not to satisfy equation (2). That is, it can also be that

[0125] R26 / bf<0.1616t+0.0235…(3).

[0126] With this configuration, the second ridge portions 26 (26a, 26b, 26c, 26d) can be made compact. Therefore, high energy absorption efficiency of the skeleton member 1 can be achieved, and the skeleton member 1 can be made more compact in the width direction X and the height direction Y.

[0127] Thus, it is preferable to set the lower limit value of R / bf based on the above-mentioned equations (1) and (2). The lower limit value of R / bf is preferably 0.20 (0.2≤R / bf). By setting R / bf to a value above the preferred lower limit value, the radius of curvature R of the ridge portion 23 can be increased. As a result, the ridge portion 23 serves to rigidly separate the adjacent first flat portion 21 and second flat portion 22 from each other (preventing the ridge portion 23 from rotating around the central axis of the skeleton member 1). As a result, the skeleton member 1 undergoes in-phase deformation during axial crushing deformation, which can increase the amount of impact energy absorbed. In addition, examples of the lower limit of R / bf are 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, and 0.30.

[0128] (Upper limit of R / bf)

[0129] The upper limit of R / bf is preferably 0.60 (R / bf ≤ 0.60). If R / bf exceeds the preferred upper limit, the axial crushing deformation (herringbone deformation) easily becomes unstable. In order to stably generate herringbone deformation, it is necessary to generate appropriate flexure in the flat portions 21 and 22 to cause the skeleton member 1 to perform a contraction action like herringbone deformation. At this time, if R / bf is too large, the width of the ridge portion 23 in the section perpendicular to the axis is too wide, so the closed section portion 10 is prone to excessive flexure, and the herringbone deformation easily becomes unstable. As a result, it is difficult to stabilize the amount of impact energy absorbed.

[0130] (Summary of the upper and lower bounds of R / bf)

[0131] As explained above, it is preferable that 0.20 ≤ R / bf ≤ 0.60. Any of the values ​​described above can be used as examples of the lower limit for R / bf. By configuring it in this way, R / bf becomes a value outside the scope of the invention in Patent Document 2.

[0132] (Thickness of frame component 1)

[0133] When the frame member 1 is a steel plate member, the plate thickness t of the closed section portion 10 (the first half 11 and the second half 12) is preferably 0.8 mm to 2.6 mm. By making the plate thickness t above or above the aforementioned lower limit, the frame member 1 can generate a sufficient impact load during a vehicle collision, and the impact energy absorption can be further improved. In addition, by making the plate thickness t below or above the aforementioned upper limit, when the frame member 1 undergoes axial crushing deformation due to the impact load, serpentine deformation can be smoothly generated, and in-phase deformation can be generated more reliably.

[0134] Furthermore, when the skeleton member 1 is an aluminum alloy member, for the same reasons as above, the plate thickness t of the closed section portion 10 (the first half 11 and the second half 12) is preferably 1.1 mm to 3.7 mm, or it can be 1.1 mm to 2.0 mm.

[0135] (Width of the flat portion, bf)

[0136] The length bf of at least one of the flat portions 21 and 22 in the axial perpendicular section of the closed section portion 10 (the first flat portion 21 in this embodiment) is preferably 75 mm or more. The reason for preferring bf ≥ 75 mm is that the preferred minimum value for the radius of curvature R is 15 mm, and the preferred minimum value for R / bf is 0.2. That is, the length bf is 75 mm when R / bf = 15 / 75 = 0.2. Thus, by sufficiently ensuring the length bf of the first flat portion 21, when the skeleton member 1 undergoes heliotropic deformation due to impact load, the flat portions 21 and 22 will deflect with moderate resistance, stabilizing the heliotropic deformation. As a result, the energy absorption efficiency of the skeleton member 1 can be improved.

[0137] (b) is the length of the smaller of the width and height of the closed section.

[0138] In this embodiment, the smaller of the lengths of the closed section portion 10 in the width direction X of the section perpendicular to the axis of the closed section portion 10 and the lengths of the closed section portion 10 in the height direction Y of the section is set as b. In this embodiment, since the closed section portion 10 is longitudinally elongated, the length of the closed section portion 10 in the width direction X is length b. This length b is preferably b ≥ 75 mm. By setting b ≥ 75 mm, the length of the flat portion 21 in the section perpendicular to the axis can be sufficiently ensured, and the radius of curvature R of the ridge portion 23 can be sufficiently ensured. As a result, when the skeleton member 1 undergoes serpentine deformation due to impact load, the flat portions 21 and 22 will flex with moderate resistance, and the serpentine deformation shape can be stabilized. The length b is preferably b ≤ 150 mm. By setting b ≤ 150 mm, the skeleton member 1 can be made less heavy, and the skeleton member 1 can be made lighter.

[0139] (t / b)

[0140] As described above, the relatively smaller length b of the width and height of the closed section portion 10 is preferably 75mm to 150mm. Furthermore, when the skeleton member 1 is a steel plate member, the plate thickness t of the closed section portion 10 is preferably 0.8mm to 2.6mm, as described above. Therefore, the maximum t / b is 2.6 / 150 ≈ 0.035, which is a value outside the scope of the invention in Patent Document 2. Furthermore, when the skeleton member 1 is an aluminum alloy member, the plate thickness t of the closed section portion 10 is preferably 1.1mm to 3.7mm, as described above. Therefore, the maximum t / b is 3.7 / 75 ≈ 0.049, which is a value outside the scope of the invention in Patent Document 2.

[0141] (Vickers hardness of the closed section)

[0142] The Vickers hardness of the central portion of the closed section portion 10 in the thickness direction is preferably 300 HV or higher. By forming the central portion of the closed section portion 10 in the thickness direction with such a high hardness, the impact energy absorption can be further improved without increasing the plate thickness. The lower limit of the Vickers hardness of the central portion of the closed section portion 10 in the thickness direction can be 300 HV, 350 HV, 400 HV, 500 HV, 550 HV, 600 HV, or 650 HV.

[0143] (Method for determining the Vickers hardness of a closed section)

[0144] In this embodiment, the method for measuring the Vickers hardness of the central portion of the closed section 10 in the thickness direction is as follows. A section perpendicular to the plate surface of the specimen is cut from, for example, the first flat portion 21 or the second flat portion 22 of the closed section 10, and a measuring surface of the specimen is prepared for hardness testing. The method for preparing the measuring surface is performed according to JIS Z 2244:2020. After grinding the measuring surface with silicon carbide paper of #600 to #1500, it is polished into a mirror finish using a liquid made by dispersing diamond powder with a particle size of 1μm to 6μm in a diluent such as alcohol and pure water. The hardness test is performed according to JIS Z 2244:2020. Using a micro Vickers hardness tester, 10 points are measured at 1 / 2 position of the specimen thickness, under a test force of 1 kgf, such that the distance between the centers of the indentation is more than 3 times the average diagonal length of the indentation, and the average value is taken as the Vickers hardness of the closed section 10.

[0145] (Maximum bending angle of closed section 10)

[0146] When the skeleton member 1 is a steel plate member, the maximum bending angle of the steel plate constituting the skeleton member 1 (the first half 11 and the second half 12) is preferably 30 degrees to 130 degrees. By setting the maximum bending angle within the above range, high bending performance can be achieved even in the skeleton member 1, which has a high Vickers hardness and high strength. Therefore, even if the skeleton member 1 undergoes heliotropic deformation during axial crushing deformation, the deformation capacity of the skeleton member 1 can be improved, and the possibility of fracture of the skeleton member 1 can be suppressed.

[0147] The maximum bending angle can be determined by the VDA bending test (VDA238-100:2017) standardized by the German Association of the Automotive Industry (VDA). Figure 5A and Figure 5B This is a schematic diagram used to illustrate the bending test. Figure 5A This is a top view of test piece S before the experiment. Figure 5B The test piece S, punch P, and roller R are shown. Figure 5A and Figure 5B As shown, the VDA bending test involves pressing a test piece S, placed on two rollers R1 and R2, between rollers R1 and R2 using a punch P with a top radius of 0.4 mm, thereby deforming the test piece S into a V-shape. The length of the test piece S is set within the range of 60 mm, obtained by adding 10 mm to the distance between the centers of rollers R1 and R2. The width of the test piece S is set within the range of 10 mm to 60 mm. The test piece S is cut from the closed section 10 with its length direction having a radius of curvature of 500 mm or more. Figure 5B As shown, the test piece S deforms in a V-shape when viewed along its width. The ridge line L generated by the bending of the test piece S at this time is a line along the width direction of the test piece S. The load and stroke of the punch P are measured at this time. Then, the load of the punch P is increased from the start of the test, and the maximum bending angle is calculated based on the stroke when the load of the punch P decreases by 60N from the maximum load as the test piece S fractures at the apex of the bend, thereby evaluating the fracture resistance characteristics of the test piece S. For the formula for calculating the maximum bending angle based on the stroke, the formula described in Annex D of VDA238-100 above is used. Furthermore, when the stroke is 14mm and the test piece S does not fracture, the value obtained from the formula for calculating the maximum bending angle based on the bending angle at a stroke of 14mm is taken as the maximum bending angle of the test piece S. In this embodiment, the number of tests of the test piece S in the VDA bending test is 3, and the average value of the measurement results of the 3 test pieces S is taken as the maximum bending angle of the closed section 10.

[0148] The shape of the closed section 10 is designed (set) so that the skeleton member 1 with the above general structure undergoes in-phase deformation when it undergoes serpentine deformation due to compressive load along the length direction Z, and the closed section 10 is manufactured in such a way that it becomes the shape of the designed closed section 10.

[0149] (Effect)

[0150] As explained above, according to this embodiment, such as Figure 2 As shown, when the frame member 1 undergoes axial crushing deformation due to impact load, adjacent flat portions 21 and 22 undergo in-phase deformation, where they bulge towards the same side in both the inner and outer directions of the closed section portion 10. Under such deformation, the ridge portion 23 exhibits higher torsional stiffness, allowing the flat portions 21 and 22 to withstand greater impact loads and achieve superior impact energy absorption efficiency. By improving energy absorption efficiency during a collision, the amount of intrusion into the vehicle can be reduced, thus improving occupant protection. Furthermore, it also enables the weight reduction of the frame member.

[0151] The embodiments of the present invention have been described above. However, the present invention is not limited to the embodiments described above. Various modifications can be made to the present invention within the scope of the claims. Furthermore, the following mainly describes configurations that differ from the above-described embodiments and variations, and detailed descriptions are omitted for the same configurations, using the same reference numerals.

[0152] [Variation Example 1]

[0153] In the above embodiment, an example was described where the strength distribution in the thickness direction of the steel plate base material is substantially the same when the frame member 1 is a steel plate. However, this is not necessarily the case. Figure 6 This is a sectional view perpendicular to the axis of the main part of variant example 1, omitting the illustration of the inner side of the section. For example... Figure 6 As shown, for the first half 11 and the second half 12 of the skeleton member 1, at least one of the softening layers 33 may be present near the outer surface 31 and the inner surface 32. In Modified Example 1, softening layers 33 are present near both the outer surface 31 and the inner surface 32, and a central portion 34 is present between the softening layers 33. Preferably, the entire area of ​​the outer surface 31 is formed by the softening layer 33, and also preferably, the entire area of ​​the inner surface 32 is formed by the softening layer 33.

[0154] (Summary of the thickness range of the softening layer)

[0155] Each softening layer 33 is formed, for example, by making the carbon content of the portion of the blank that forms the outer side surface 31 and the portion that forms the inner side surface 32 (the portion that forms the softening layer 33) less than the carbon content of the portion that forms the central part 34 in the blank. The method of forming the softening layer 33 is not particularly limited and can be any method. In this modified example 1, from the viewpoint of being able to increase the maximum bending angle of each half 11 and 12 and sufficiently ensure the strength of each half 11 and 12, it is preferable that each softening layer 33 has a predetermined thickness, for example, from the corresponding side surface 31 or 32. The lower limit of the predetermined thickness is, for example, 80 μm, and the upper limit is, for example, 200 μm.

[0156] (A summary of the Vickers hardness distribution in the softened layer and a summary of the Vickers hardness in the central part)

[0157] In each softening layer 33, the Vickers hardness decreases as one half of the plate thickness is moved away from each half 11, 12. The portions of each softening layer 33 that become surfaces 31, 32 have the lowest Vickers hardness in each half 11, 12, and are at least 100 HV lower than the Vickers hardness of the central portion 34. Examples of upper limits for the difference in Vickers hardness between the surfaces 31, 32 and the central portion 34 in each half 11, 12 include 250 HV, 300 HV, 350 HV, 400 HV, 500 HV, 550 HV, 600 HV, and 650 HV. Furthermore, when only "Vickers hardness of each half 11, 12" is mentioned, it refers to the Vickers hardness of the central portion 34.

[0158] In this modified example 1, where each half 11 and 12 is provided with a softening layer 33, the maximum bending angle of each half 11 and 12 can be increased by, for example, about 20 degrees, compared to the case where no softening layer 33 is provided (implementation).

[0159] Thus, the Vickers hardness of the surfaces 31 and 32 in the thickness direction of each half 11 and 12 is at least 100 HV lower than the Vickers hardness of the central portion 34 in the thickness direction of each half 11 and 12. This allows for a further increase in the maximum bending angle of each half 11 and 12. Therefore, during serpentine deformation, crack formation in each half 11 and 12 can be suppressed, thereby improving impact absorption performance.

[0160] Here is an example to further illustrate the composition of each half, 11 and 12.

[0161] (Vickers hardness of the central part of each half)

[0162] The Vickers hardness of the central portion 34 in the thickness direction where the softening layer 33 is provided is preferably 300 HV or higher. When the Vickers hardness of the central portion 34 is 300 HV or higher, the effect of improving the deformability of the softening layer 33 in each half 11, 12 becomes significant. The Vickers hardness of the central portion 34 is preferably 500 HV or higher, more preferably 600 HV or higher, and even more preferably 700 HV or higher. There is no particular upper limit to the Vickers hardness of the central portion 34, but considering formability, it is preferably 900 HV or lower, and even more preferably 800 HV or lower. Thus, as an example of the preferred lower limit of the Vickers hardness of the central portion 34, 300 HV, 350 HV, 400 HV, 450 HV, 500 HV, 550 HV, 600 HV, 700 HV, 720 HV, and 750 HV can be listed. Furthermore, as an example of a preferred upper limit for the Vickers hardness of the central part 34, 1100HV, 1050HV, 1000HV, 950HV, 900HV, 850HV, and 800HV can be listed.

[0163] (Details on the thickness of each softening layer)

[0164] The thickness of each softening layer 33 in the plate thickness direction is preferably 80 μm or more, and is 5% or more and 20% or less of the plate thickness t at the portion where the softening layer 33 is provided. If the thickness of each softening layer 33 is 20% or less of the plate thickness t, the proportion of each softening layer 33 in the steel plate used as the material of each half 11, 12 is small, thus maintaining the required load-bearing performance of each half 11, 12. The thickness of each softening layer 33 is preferably 17% or less of the aforementioned plate thickness, and more preferably 14% or less. On the other hand, when the softening layer 33 is provided over the entire surface area of ​​the steel plate used as the material of each half 11, 12, if the thickness of each softening layer 33 is 80 μm or more and is 5% or more of the aforementioned plate thickness t, the deformation capacity based on the softening layer 33 can be fully utilized. The thickness of each softening layer 33 is more preferably 8% or more of the aforementioned plate thickness.

[0165] (Method for determining the thickness of the interface between the softening layer and the central part)

[0166] Next, the method for measuring the boundary between the softening layer 33 and the central portion 34 will be explained. Figure 7This is a conceptual diagram illustrating an example of a method for measuring the boundary between the softening layer 33 and the central portion 34. A cross-section perpendicular to the plate surface is taken from each half 11 and 12 of the sample, and the measurement surface of the sample is prepared for hardness testing. In preparing the measurement surface, to accurately measure the Vickers hardness near the sample surface, the method is implemented with minimal unevenness and no edge collapse near the surface. Here, a cross-section polisher manufactured by NEC Corporation is used to sputter the measurement surface using an argon ion beam. At this time, to suppress the formation of striped unevenness on the measurement surface, a sample rotation stand manufactured by NEC Corporation is used to irradiate the measurement surface with an argon ion beam from a 360-degree direction.

[0167] The Vickers hardness of the specimen after the test surface has been prepared was measured using a micro Vickers hardness tester. The test force was 50 gf, applied to the area corresponding to the softened layer of the specimen, along a direction perpendicular to the surface (thickness direction).

[0168] The measurement position on the outermost side of the sample is set at a thickness of 20 μm from either surface 31 or 32 (in the case of a coating, this refers to the surface of the steel base material directly below the coating; in the case of an alloy layer between the coating and the steel base material, this refers to the surface of the steel base material directly below the alloy layer). Regarding the measurement point at the junction of the softening layer 33 and the central portion 34, it is set at equal intervals of 5 μm to 15 μm in the thickness direction, and the distance between the centers of the indentations is at least three times the average diagonal length of the indentation. Depending on the average diagonal length of the indentation, it is sometimes impossible to ensure a center-to-center distance of at least three times the average diagonal length of the indentation along the thickness direction. In such cases, the measurement is performed at different positions in a direction orthogonal to the thickness direction and also at different positions in the thickness direction. Therefore, it is possible to meet the measurement conditions of equal intervals of 5 μm to 15 μm in the thickness direction, and the distance between the centers of the indentations being more than three times the average diagonal length of the indentations. The measurement is performed from a thickness position of 20 μm from the surface to a position halfway through the thickness direction.

[0169] (A method for calculating the slope of Vickers hardness at various thickness locations after measuring the interface between the softened layer and the central part)

[0170] When measuring the boundary between the softened layer 33 and the central portion 34, the slope of the Vickers hardness at each thickness position after the Vickers hardness measurement is, for example, set as the slope Δbi obtained from the Vickers hardness at multiple consecutive points (3 points). The slope Δbi is calculated according to the following formula (4).

[0171] [Mathematical Formula 1]

[0172]

[0173] Here,

[0174] Δbi: The slope (HV / μm) calculated from the three points from the i-th point to the (i+2)-th point.

[0175] xi: The thickness position (μm) of the i-th measurement point measured from the surface of each half 11 and 12.

[0176] xk: Thickness position (μm) measured from the surface of each half 11 and 12.

[0177] yk: The average Vickers hardness (HV) at three different points at the thickness location of xk.

[0178] The thickness position of the measurement point closest to the steel plate surface among the three measurement points obtained by formula (4) from the surface side of each half 11 and 12 is set as the thickness position of the junction between the softening layer 33 and the central part 34.

[0179] (The relationship between the Vickers hardness of the softened layer and the Vickers hardness of the central part)

[0180] The Vickers hardness of the softening layer 33 on the surfaces 31 and 32 of each half 11 and 12 is preferably more than 0.5 times and less than 0.9 times the Vickers hardness of the central part 34 of the part where the softening layer 33 is provided.

[0181] (Method for determining the Vickers hardness of the central part of each half)

[0182] The Vickers hardness of the central portion 34 is determined as follows. A cross-section perpendicular to the plate surface is cut from each half 11 and 12 of the specimen, and the test surface of the specimen is prepared for hardness testing. The preparation method of the test surface is performed according to JIS Z2244:2020. After grinding the test surface with #600 to #1500 silicon carbide paper, it is then polished to a mirror finish using a liquid made by dispersing diamond powder with a particle size of 1μm to 6μm in an alcohol-based diluent and pure water. The hardness test is performed according to JIS Z 2244:2020. Using a micro Vickers hardness tester, 10 indentations are measured at a distance between the centers of the indentation at a distance of more than three times the average diagonal length of the indentation, at a position half the thickness of the specimen, under a test force of 1 kgf. The average value of these indentations is taken as the Vickers hardness of the central portion 34.

[0183] (Method for determining the Vickers hardness of the surface of each half)

[0184] The Vickers hardness of surfaces 31 and 32 of each half 11 and 12 was measured according to the Vickers hardness test described in JIS Z 2244:2020, on the cross sections obtained by cutting along the thickness direction of each half 11 and 12.

[0185] For the aforementioned cross-section, after preparing the test surface of the specimen, it is used for hardness testing. In preparing the test surface, to accurately measure the Vickers hardness near the surface of the specimen, the preparation is carried out in a manner that minimizes unevenness and prevents edge collapse near the surface. Here, a cross-section polisher manufactured by NEC Corporation is used to sputter the test surface using an argon ion beam. At this time, to suppress the formation of striation-like unevenness on the test surface, a specimen rotation stand manufactured by NEC Corporation is used to irradiate the test surface with an argon ion beam from a 360-degree direction.

[0186] The Vickers hardness of the specimens after the test surfaces were prepared was measured using a micro Vickers hardness tester. The test point was set at a thickness of 20 μm from surfaces 31 and 32 of each half 11 and 12. If a coating was present in each half 11 and 12, the test point was set at a thickness of 20 μm from the surface of the steel base material directly below the coating. If an alloy layer existed between the coating and the steel base material in each half 11 and 12, the test point was set at a thickness of 20 μm from the surface of the steel base material directly below the alloy layer. Ten indentations were measured at the aforementioned thickness points along a direction perpendicular to the plate surface (thickness direction) under a test force of 10 gf, with a distance between the centers of each indentation at least three times the average diagonal length of the indentation. The average value of these indentations was taken as the Vickers hardness of surfaces 31 and 32 of each half 11 and 12.

[0187] If the Vickers hardness of the surfaces 31 and 32 of each half 11 and 12 is 0.5 times or more than the Vickers hardness of the central half 34, the load-bearing capacity during impact, especially in the later stages of the impact stroke, can be improved. More preferably, the softening layer 33 has a Vickers hardness of 0.6 times or more than the Vickers hardness of the central half 34 on the surfaces 31 and 32 of each half 11 and 12. On the other hand, if the Vickers hardness of the surfaces 31 and 32 of each half 11 and 12 is less than 0.9 times the Vickers hardness of the central half 34, the deformation capacity can be sufficiently improved. More preferably, the softening layer 33 has a Vickers hardness of less than 0.8 times the Vickers hardness of the central half 34 on the surfaces 31 and 32 of each half 11 and 12.

[0188] (Vickers hardness variation of the softened layer)

[0189] Figure 8 This is a conceptual diagram illustrating an example of the Vickers hardness variation in the softening layer 33. (e.g.) Figure 8As shown, the softening layer 33 has: a first hardness variation region, which is a region extending from the surfaces 31 and 32 to 40% of the thickness of the softening layer 33 in the thickness direction; and a second hardness variation region, which is a region in the softening layer 33 that is not in the first hardness variation region. Preferably, the absolute value ΔHV1 of the hardness variation in the thickness direction in the first hardness variation region is greater than the absolute value ΔHV2 of the hardness variation in the thickness direction in the second hardness variation region. If ΔHV1 is greater than ΔHV2, sufficient load-bearing characteristics can be obtained.

[0190] The absolute value of the hardness change ΔHV1 in the first hardness variation region is preferably 100 HV or more and less than 200 HV. If ΔHV1 is 100 HV or more, stress concentration in bending deformation during serpentine deformation can be further mitigated, and bending characteristics can be further improved. Furthermore, if ΔHV1 is less than 200 HV, the effect of mitigating stress concentration during bending deformation is further enhanced, resulting in better bending characteristics. Therefore, when ΔHV1 is 100 HV or more and less than 200 HV, good bending characteristics can be obtained, and the deformation capacity of each half 11 and 12 can be improved. Specifically, in the later stage of the impact stroke, the load decrease immediately following the load peak can be smoothed out. Therefore, as described above, the absolute value of the hardness change ΔHV1 in the first hardness variation region is preferably 100 HV or more and less than 200 HV. Furthermore, the lower limit of ΔHV1 is preferably 100 HV, while the upper limit can be less than 200 HV, less than 300 HV, or less than 400 HV.

[0191] (Method for determining the Vickers hardness of the first and second hardness variation regions of the softened layer)

[0192] Next, the method for measuring the hardness of the first and second hardness variation regions will be described. A cross-section perpendicular to the plate surface is taken from each half 11 and 12 of the specimen, and the test surface of the specimen is prepared for hardness testing. In preparing the test surface, to accurately measure the Vickers hardness near the surface of the specimen, the preparation is carried out in a manner that minimizes unevenness and prevents edge collapse near the surface. Here, a cross-section polisher manufactured by NEC Corporation is used to sputter the test surface using an argon ion beam. To suppress the formation of striped unevenness on the test surface, a specimen rotation stand manufactured by NEC Corporation is used to irradiate the test surface with an argon ion beam from a 360-degree direction.

[0193] The Vickers hardness of a specimen with a prepared test surface is measured using a micro Vickers hardness tester. The test is performed on the area corresponding to the softened layer of the specimen, perpendicular to the surface (thickness direction), under a test force of 10 gf. The total number of test points varies depending on the specimen thickness, but the number of test points used to calculate ΔHV1 and ΔHV2 (described later) is set according to JIS Z 2244:2020.

[0194] The thickness of the softening layer 33 is 80 μm or more, and is 5% to 20% of the thickness of the plate at the portion where the softening layer 33 is provided. The first hardness variation region is the region of the softening layer 33 from the surface to 40% of its thickness. In this embodiment, it exists at a thickness position starting from the surfaces 31 and 32 of each half 11 and 12, with a minimum of, for example, 40 μm and a maximum of, for example, 80 μm.

[0195] The measurement position on the outermost side of the sample is set at a thickness of 20 μm from the surface (in the case of a coating, this refers to the surface of the steel base material directly below the coating; in the case of an alloy layer between the coating and the steel base material, this refers to the surface of the steel base material directly below the alloy layer). This 20 μm thickness position is a point different from the measurement point used for the Vickers hardness measurement of surfaces 31 and 32 of the aforementioned halves 11 and 12. In the measurement of the first hardness variation region, indentations are measured at at least two locations along the thickness direction, with a distance between the centers of equally spaced indentations of 15 μm or less and at least three times the average diagonal length of the indentation. Depending on the average diagonal length of the indentation, sometimes only one point can be measured in the column along the thickness direction for the first hardness variation region. In this case, the measurement is performed with different positions in both the direction orthogonal to the thickness direction and the thickness direction itself. Therefore, it is possible to measure Vickers hardness at at least two points in the first hardness variation region while meeting the measurement conditions of equal intervals of less than 15 μm in the plate thickness direction and the distance between the centers of the indentations being more than three times the average diagonal length of the indentations.

[0196] The softening layer 33 has a thickness of 80 μm or more, and is 5% to 20% of the plate thickness at the portion where the softening layer 33 is provided. The Vickers hardness of the second hardness variation region is measured in the area excluding the first hardness variation region within this thickness range. When the thickness of the softening layer 33 is 80 μm to 200 μm, the second hardness variation region exists in a range with a minimum thickness of 32 μm to 80 μm (48 μm thickness range) and a maximum thickness of 80 μm to 200 μm (120 μm thickness range), starting from the surfaces 31 and 32 of each half 11 and 12. For the second hardness variation region, indentations are measured at at least two locations in the plate thickness direction, provided that the distance between the centers is at least 15 μm or less at equal intervals and the average diagonal length of the indentation is at least three times the length of the average diagonal. Depending on the average diagonal length of the indentation, it may be impossible to measure the hardness of two adjacent points at a defined interval along the plate thickness direction for the second hardness variation region. In this case, the measurements are performed by varying the positions in the direction orthogonal to the plate thickness direction and by varying the positions in the plate thickness direction. This allows for the measurement of the Vickers hardness of the second hardness variation region while simultaneously meeting the measurement conditions of equal intervals of 15 μm or less in the plate thickness direction and a distance between the centers of the indentations that is at least three times the average diagonal length of the indentation. The second hardness variation region can also be measured on the same column as the first hardness variation region. For example, the second hardness variation region can be measured at a total of four points: one point near the boundary with the first hardness variation region, one point near the boundary with the central portion 58, and two points between these two points. When the second hardness variation region exists up to 200 μm from the steel plate surface, the measurement points of the first and second hardness variation regions can be measured at various thickness locations at distances from the steel plate surface, such as 20 μm, 35 μm, 50 μm, 65 μm, 80 μm, 95 μm, 110 μm, 125 μm, 140 μm, 155 μm, 170 μm, 185 μm, and 200 μm.

[0197] When a sample with a softening layer 33 is disposed on both sides of the central portion 34 of each half 11, 12, the same measurement is performed from the first surface side of the sample, and further, the same measurement is performed from the second surface side opposite to the first surface.

[0198] (Calculation method of the absolute value ΔHV1 of the hardness change in the first hardness change region after measurement)

[0199] ΔHV1 is calculated using the following steps. Specifically, the hardness gradient Δa of the first hardness variation region is calculated using equation (5) based on all measurement points contained in the region (first hardness variation region) from the surfaces 31 and 32 of the specimen cut from each half 11 and 12 up to 40% of the overall thickness of the softened layer 33. Here, ai is the percentage (%) of the distance from the i-th measurement point to the surface in the overall thickness of the softened layer, ci is the Vickers hardness (HV) corresponding to ai, and n is the sum of all measurement points contained in the region (first hardness variation region) from the surface up to 40% of the overall thickness of the softened layer.

[0200] [Mathematical Formula 2]

[0201]

[0202] Here,

[0203] Δa: Gradient of hardness change in the thickness direction of the plate in the first hardness variation region (HV / %)

[0204] ai: The proportion (%) of the distance from the i-th measurement point to the surface in the overall thickness of the softening layer.

[0205] ci: The average Vickers hardness (HV) at three different points at the thickness location of the i-th measurement point.

[0206] n: The sum of all measurement points contained in the first hardness variation region on the first surface side.

[0207] In the case of a sample with softening layers 33 arranged on both sides of the central portion 34, Δa1 on the first surface side is calculated by Equation (5) based on the Vickers hardness measured from the first surface side, and further, Δa2 on the second surface side is calculated by Equation (5) based on the Vickers hardness measured from the second surface side. The arithmetic mean of Δa1 and Δa2 can be set as Δa.

[0208] ΔHV1 can be obtained by multiplying Δa obtained by equation (5) by the proportion of the thickness of the first hardness variation region in the overall thickness of the softening layer.

[0209] (Calculation method of the absolute value ΔHV2 of the hardness change in the second hardness change region after measurement)

[0210] ΔHV2 is calculated through the following steps. That is, based on all the measurement points contained in the area (second hardness variation area) of the overall thickness of the softening layer 33 on the surface side of the sample (40%~100%), the hardness gradient ΔA of the second hardness variation area is calculated using equation (6). Here, Ai is the proportion (%) of the distance from the i-th measurement point to the surface in the overall thickness of the softening layer, Ci is the Vickers hardness (HV) corresponding to Ai, and N is the sum of all measurement points contained in the area (second hardness variation area) of the overall thickness of the softening layer on the surface side (40%~100%).

[0211] [Mathematical Formula 3]

[0212]

[0213] Here,

[0214] ΔA: Gradient of hardness change in the thickness direction within the second hardness variation region (HV / %)

[0215] Ai: The proportion (%) of the distance from the i-th measurement point to the surface in the total thickness of the softening layer.

[0216] Ci: The average Vickers hardness (HV) at three different points at the thickness location of the i-th measurement point.

[0217] N: The sum of all measurement points contained in the second hardness variation region on the first surface side.

[0218] In the case of a sample with softening layers 33 arranged on both sides of the central portion 34, ΔA1 on the first surface side is calculated by Equation (6) based on the Vickers hardness measured from the first surface side, and further, ΔA2 on the second surface side is calculated by Equation (6) based on the Vickers hardness measured from the second surface side. The arithmetic mean of ΔA1 and ΔA2 can be set as ΔA.

[0219] ΔHV2 can be obtained by multiplying ΔA obtained by equation (6) by the proportion of the thickness of the second hardness variation region in the overall thickness of the softening layer.

[0220] (Effect)

[0221] According to the configuration described in Modified Example 1, by utilizing the softening layer 33 to improve the bending deformation capacity of the skeleton member 1, the possibility of fracture of the skeleton member 1 can be further reduced. During in-phase deformation of the skeleton member 1, the strain introduced into the ridge portion 23 is relatively large, but by improving the bending deformation capacity of the skeleton member 1 during serpentine deformation, the possibility of strain-induced fracture of the skeleton member 1 can be further reduced. Therefore, the impact energy absorption of the skeleton member 1 can be made more stable. Thus, by combining the design for achieving in-phase deformation with the use of surface-modified steel in the skeleton member 1, a higher energy absorption capacity can be achieved.

[0222] [Variation Example 2]

[0223] In the above-described embodiments and variations, the example given is that both the first half 11 and the second half 12 of the skeleton member 1 are hat-shaped in the cross-section perpendicular to the axis. However, this is not always the case. Figure 9 This is a sectional view along the axis of a modified example 2 of the skeleton member 1, which is composed of the first half 11 and the second half 12A. (See attached image.) Figure 9 As shown, the second half 12A is formed entirely flat and does not have a ridge portion 23. In this case, the flanges 25c and 25d of the second half 12A join with the flanges 25a and 25b of the first half 11, and these flanges 25c and 25d are continuous with the first flat portion 21b. In this frame member 1, the flat halves 24a and 24b of the first half 11 become the second flat portions 22A and 22A (22aA and 22bA). In this case, the frame member 1 can be a steel plate member, an aluminum alloy member, or a composite member composed of multiple materials.

[0224] Example

[0225] (Relationship between R / bf and energy uptake)

[0226] Will Figure 3 The skeleton component 1 shown was modeled on a computer and manufactured as Test Examples 1 to 6. The common specifications of Test Examples 1 to 4 in Test Examples 1 to 6 are as follows.

[0227] Common specifications of test examples 1-4

[0228] Material: Steel plate

[0229] Tensile strength: 1300MPa

[0230] Plate thickness t: 1.2mm

[0231] Length in the Z direction: 480mm

[0232] The radius of curvature R of the edge portion 23: 5, 10, 15, 20, 25, 30 mm

[0233] Length of the flat portion (bf): 100, 90, 80, 70, 60, 50 mm

[0234] The maximum bending angle settings for each of Experiments 1 to 4 are as follows.

[0235] Experimental Example 1: 50 degrees

[0236] Experimental Example 2: 65 degrees

[0237] Experimental Example 3: 80 degrees

[0238] Test Example 4: 110 degrees

[0239] Test Example 5 is the same as Test Examples 1-4, except that the tensile strength is set to 590 MPa and the setting is to prevent bending fracture. Test Example 6 is the same as Test Examples 1-4, except that the material is set to 6000 series aluminum alloy, the tensile strength is set to 425 MPa, the plate thickness is set to 2.4 mm and the setting is to prevent bending fracture.

[0240] For each of the test examples 1-6, the energy absorption and energy absorption efficiency were calculated using FEM (finite element method) under the following conditions: the base end was fixed in the Z-direction along the length, and an impact load along the Z-direction was applied to the top end. More specifically, the fracture prediction software NSafe (registered trademark)-MAT, developed by Nippon Steel Corporation, was used. The surface strain fracture function of this software was used when calculating the energy absorption.

[0241] The shape of the impactor: a flat, rigid body.

[0242] The impact speed of the impactor was 14.4 km / h.

[0243] For each of the experimental examples 1 to 6, the energy absorption was calculated sequentially while changing R / bf to 0.05, 0.11, 0.19, 0.29, 0.42, and 0.60.

[0244] The results are expressed in Figure 10A and Figure 10B middle. Figure 10A The graphs showing the energy absorption of the skeleton component 1 when R / bf is varied are provided for test examples 2-6. Figure 10B The graphs for Experimental Examples 2-6 show the energy absorption (energy absorption efficiency) per 1 kg of the skeleton component 1 when R / bf is varied.

[0245] exist Figure 10A and Figure 10BIn Test Example 1 (maximum bending angle 50 degrees), a large base material fracture occurred when R / bf > 0.00, therefore the energy absorption could not be calculated and is not shown in the graph. Test Example 2 (maximum bending angle 60 degrees) also experienced a large base material fracture when R / bf > 0.19, therefore the energy absorption up to R / bf = 0.19 is shown in the graph. On the other hand, for Test Examples 3-6, the energy absorption up to R / bf = 0.60 is shown in the graph.

[0246] like Figure 10A and Figure 10B As shown, in Test Examples 3-6, the energy absorption significantly increased when R / bf was between 0.20 and 0.60, exceeding 0.19, with 0.20 ≤ R / bf ≤ 0.60 being preferred. Furthermore, in Test Example 5 with a tensile strength of 590 MPa, due to the relatively low Vickers hardness, there was no significant difference in the strain induction mechanism between in-phase and out-of-phase deformation; therefore, the energy absorption did not change significantly regardless of the value of R / bf.

[0247] (The preferred lower limit of R / bf from the perspective that the blank of the skeleton component is steel plate)

[0248] Will Figure 3 The skeleton component 1 shown was modeled on a computer and manufactured as Test Examples 7 to 11. The common specifications of Test Examples 7 to 11 are as follows.

[0249] Common specifications of test examples 7-11

[0250] Material: Steel plate

[0251] The radius of curvature R of the ridge section 23: 5~30mm

[0252] The plate thicknesses for Experiments 7-11 are as follows.

[0253] Test Example 7: 0.8mm

[0254] Test Example 8: 1.0 mm

[0255] Test Example 9: 1.2mm

[0256] Test Example 10: 1.4mm

[0257] Test Example 11: 1.6mm

[0258] For each of the test examples 7-11, the buckling stress was calculated using the finite strip method (FSM). The results are expressed as follows: Figure 11A and Figure 11B middle.

[0259] Figure 11AThe graphs showing the relationship between R / bf and buckling stress for Experiments 7-11 are presented in a way that distinguishes between inverse deformation and in-phase deformation. Figure 11B The graphs for Experiments 7-11 show the relationship between plate thickness t and R / bf when the deformation changes from reverse phase to in-phase.

[0260] exist Figure 11A In this model, the horizontal axis is set to R / bf, and the vertical axis is set to the buckling stress (MPa). Additionally, in... Figure 11A In the examples, R / bf during antiphase deformation is marked with a △ symbol, and R / bf during in-phase deformation is marked with an ○ symbol. Furthermore, in each of the experimental examples 7-11, sections with consecutive △ symbols are connected by straight lines, and sections with consecutive ○ symbols are also connected by straight lines; however, there are no straight lines connecting the △ and ○ symbols. For each of the experimental examples 7-11, the sections where there are no straight lines connecting the △ and ○ symbols represent the boundary between R / bf during antiphase deformation and R / b during in-phase deformation. Figure 11B In the figure, the horizontal axis is set as the plate thickness t (mm) and the vertical axis is set as R / bf. For each of the experimental examples 7 to 11, R / bf is shown when the deformation changes from the opposite phase to the same phase.

[0261] exist Figure 11B If we use the regression line to represent R / bf when the deformation changes from antiphase to in-phase, as shown in each of the experimental examples 7 to 11, then we know that R / bf = 0.1616t + 0.0235. That is, it is confirmed that when the skeleton member 1 is a steel plate member, R / bf ≥ 0.1616t + 0.0235 is preferred.

[0262] (Preferred lower limit of R / bf from the viewpoint that the blank of the skeleton component is a metallic material)

[0263] For test examples 7-11, based on the above analysis, the minimum value of R / bf under the condition of in-phase deformation during axial crushing deformation is calculated as shown in Table 1 below.

[0264] [Table 1]

[0265]

[0266] Table 1 records the plate thickness t, Young's modulus E, and Et for test examples 7-11. 3 .

[0267] Furthermore, for Test Example 6 made of aluminum alloy, the minimum value of R / bf under the condition of in-phase deformation during axial crushing deformation was calculated using the same analysis as Test Examples 7-11. This minimum value is related to the plate thickness, Young's modulus E, and Et. 3 They are shown together in Table 1.

[0268] In the Et of test examples 6-11 in Table 1 3 When plotting the various R / bf values ​​in Table 1 with R / bf as the horizontal axis and R / bf as the vertical axis, it becomes... Figure 12 The chart shown. Figure 12 The graphs for the minimum R / bf that constitutes the antiphase deformation are plotted for experimental examples 6-11. Figure 12 The trend line is R / bf = (1.49 × 10) / (bf + bf ...) / (bf) / ( -7 ×Et 3 The result of +0.153 confirms that reverse deformation occurs when the value of R / bf is above this value.

[0269] Industrial availability

[0270] This invention can be widely applied to the manufacturing methods of frame components, vehicle bodies, and frame components.

[0271] Explanation of reference numerals in the attached figures

[0272] 1. Skeleton component; 10. Closed section; 11. First half; 12, 12A, Second half; 21. First flat section; 22. Second flat section; 23. Ridge section (First ridge section); 26. Second ridge section; 24. Flat half; 25. Flange; 31. Outer surface; 32. Inner surface; 33. Softening layer; 34. Central section; b. Length; bf. Length; R26. Radius of curvature (radius of curvature R2); X. Width direction; Y. Height direction; Z. Length direction; W. Maximum external dimension.

Claims

1. A skeleton member having a closed section portion with a closed section perpendicular to the length direction, wherein, The closed section portion includes: a first flat portion; a second flat portion; and a ridge portion that connects the first flat portion and the second flat portion, and whose radius of curvature is smaller than either the radius of curvature of the first flat portion or the radius of curvature of the second flat portion. The cross section in the closed section has the following shape: when the skeleton member undergoes serpentine deformation due to compressive load along the length direction, the first flat section and the second flat section bulge with the same phase in the direction toward the inside of the closed section and the direction toward the outside of the closed section.

2. The skeleton component according to claim 1, wherein, The radius of curvature of the ridge portion in the cross section is 15 mm or more.

3. The skeleton component according to claim 1, wherein, When the Young's modulus of the skeleton component is set to E, the plate thickness of the closed section is set to t, the radius of curvature of the ridge section is set to R, and the length of at least one of the flat sections in the section is set to bf, R / bf satisfies the following formula (1). R / bf≥(1.49×10 -7 ×Et 3 )+0.153 …(1)。 4. The skeleton component according to claim 1, wherein, The frame component is a steel plate component. When the plate thickness of the skeleton member is set to t, the radius of curvature of the ridge portion is set to R, and the length of at least one of the flat portions in the cross section is set to bf, R / bf satisfies the following equation (2). R / bf≥0.1616t+0.0235…(2).

5. The skeleton component according to claim 4, wherein, The skeleton component is formed by joining the first half and the second half together. The first half is formed in a cap shape in the cross-section. The first half includes the first flat portion, a portion of the second flat portion, a first ridge portion that serves as the ridge portion, a flange that engages with the second half, and a second ridge portion that connects a portion of the second flat portion to the flange. When the radius of curvature of the second edge is set to R2, R2 / bf satisfies the following equation (3). R2 / bf<0.1616t+0.0235…(3).

6. The skeleton component according to claim 1, wherein, When the radius of curvature of the ridge portion is set to R and the length of at least one of the flat portions in the cross section is set to bf, then 0.20≤R / bf≤0.

60.

7. The skeleton component according to claim 1, wherein, When the smaller of the lengths of the closed section portion in the width direction and the height direction of the closed section portion in the cross-section is defined as b, then b ≥ 75 mm. When the skeleton component is a steel plate component, the thickness of the closed section portion in the section is 0.8mm to 2.6mm. When the skeleton component is an aluminum alloy plate component, the thickness of the closed section in the section is 1.1mm to 3.7mm.

8. The skeleton component according to claim 1, wherein, When the length of at least one of the flat portions in the cross section is set to bf, bf is 75 mm or more.

9. The skeleton component according to claim 1, wherein, The Vickers hardness of the central portion of the closed cross-section in the thickness direction is above 300 HV.

10. The skeleton member according to claim 1, wherein, In the cross section, the Vickers hardness of the surface of the closed cross section in the thickness direction is at least 100 HV lower than the Vickers hardness of the central part of the closed cross section in the thickness direction.

11. The skeleton member according to claim 10, wherein, In the cross-section, the closed section portion has a softening layer extending from the surface along the plate thickness direction. The Vickers hardness of the central portion in the thickness direction of the closed cross-section is above 300 HV. The thickness of the softening layer is 80 μm or more, and is more than 5% and less than 20% of the thickness of the plate at the portion where the softening layer is provided. The Vickers hardness of the softening layer on the surface is more than 0.5 times and less than 0.9 times the Vickers hardness of the central portion of the plate in the thickness direction where the softening layer is located. The softening layer has: a first hardness variation region, which is a region extending from the surface to 40% of the thickness of the softening layer in the plate thickness direction; And a second hardness variation region, which is a region in the softened layer that is not the first hardness variation region. The absolute value of the hardness change in the thickness direction of the first hardness change region, ΔHV1, is greater than the absolute value of the hardness change in the thickness direction of the second hardness change region, ΔHV2.

12. A vehicle body, wherein, The vehicle body includes the frame member as described in any one of claims 1 to 11.

13. A method for manufacturing a skeleton member, the skeleton member having a closed section portion with a closed cross-section perpendicular to its length direction, the closed section portion comprising: a first flat portion; a second flat portion; and an edge portion connecting the first flat portion and the second flat portion, wherein the edge portion has a radius of curvature smaller than either the radius of curvature of the first flat portion or the radius of curvature of the second flat portion, wherein... In this manufacturing method, The shape of the closed section is set such that, when the skeleton member undergoes serpentine deformation due to compressive load along the length direction, the first flat portion and the second flat portion in the section exhibit deformation in which the phase of the deformation is the same in both the direction toward the inside of the closed section and the direction toward the outside of the closed section. The closed section is manufactured in such a way that it becomes the shape of the predetermined closed section.

14. The method for manufacturing a skeleton component according to claim 13, wherein, In the shape setting of the closed section, when the Young's modulus of the skeleton member is set to E, the plate thickness of the closed section is set to t, the radius of curvature of the edge section is set to R, and the length of at least one of the flat sections in the section is set to bf, R / bf is set to a value that satisfies the following formula (1). R / bf≥(1.49×10 -7 ×Et 3 )+0.153 …(1)。 15. The method for manufacturing a skeleton component according to claim 13, wherein, In the shape setting of the closed cross-section, when the radius of curvature of the edge portion is set to R, and the length of at least one of the flat portions in the cross-section is set to bf. Set it to 0.20≤R / bf≤0.

60.

16. The method for manufacturing a skeleton component according to claim 13, wherein, In the shape setting of the closed section portion When the smaller of the lengths of the closed section portion in the width direction and the height direction of the closed section portion in the cross-section is defined as b, then b ≥ 75 mm. When the skeleton component is a steel plate component, the thickness of the closed section portion in the section is 0.8mm to 2.6mm. When the skeleton component is an aluminum alloy plate component, the thickness of the closed section in the section is 1.1mm to 3.7mm.

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