Body parts

Abstract

To provide a vehicle body member that is lighter and can ensure high axial compressive strength. [Solution] A car body member is provided that is formed from a steel plate with a thickness of 1.6 mm or less, and where the first line is a straight line extending from one end of a long reference flat portion that is continuous with the end of a reference curved portion having the largest radius of curvature, which is not continuous with the reference flat portion, in a tangential direction to the reference curved portion, and the second line is an extension of the reference flat portion, the length between the intersection of the first line and the second line and the other end of the reference flat portion that is not continuous with the reference curved portion is defined as b0, the length of the reference flat portion is defined as b1, and the radius of curvature of the reference curved portion is defined as R, the following formula is satisfied, and the tensile strength of the steel plate is 1180 MPa or more and R is 15 mm or more, where t is the plate thickness of the reference flat portion, E is Young's modulus, ν is Poisson's ratio, and σ is the yield stress of the reference curved portion. y Let's say. TIFF2023075317000010.tif32170

Description

[Technical Field]

[0001] The present invention relates to a body member for, for example, an automobile. [Background technology]

[0002] Conventionally, hollow members made of steel plate and having a predetermined cross-sectional shape have been used as car body members. These car body members are required to be lightweight and have sufficient load-bearing capacity. For this reason, high-tensile steel plates with high strength have recently been used as materials.

[0003] When a vehicle body is subjected to an impact due to a collision or the like, the vehicle body members may be subjected to an axial compressive load. To ensure that the vehicle body members have sufficient load resistance, it is necessary to ensure that the vehicle body members have high axial compressive strength and, for example, to suppress buckling. Patent Document 1 listed below describes a technology for car body structural members that are subject to axial compressive bending deformation, in which the surface that undergoes compressive deformation is curved outwardly convexly in order to realize a lighter member with high axial compressive bending strength. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-186777 Summary of the Invention [Problem to be solved by the invention]

[0005] The technology described in Patent Document 1 only convexly curves the cross-sectional shape of the component's surface that undergoes compressive deformation, without considering the effect that the cross-sectional shape, including the flat surfaces that are continuous with the curved surface, has on the axial compressive strength of the entire component. Furthermore, thinning and increasing the strength of materials used for body structural components can reduce the component's elastic buckling stress. Therefore, in areas subjected to axial compressive loads, elastic buckling may occur before the material's yield stress is reached, potentially reducing the component's axial compressive strength. However, prior art, including the technology described in Patent Document 1, did not consider this when designing the cross-sectional shape of body components.

[0006] Therefore, the present invention has been made in consideration of the above problems, and an object of the present invention is to provide a new and improved vehicle body member that is lighter and can ensure high axial compressive strength. [Means for solving the problem]

[0007] The gist of the present invention is as follows. (1) A body component such as a roof side rail, side sill, or A-pillar upper, made of steel plate with a thickness of 1.6 mm or less. The cross section perpendicular to the axis is The curved portion has at least one curved portion that is convex outward or inward and at least one flat portion, and the curved portion having the largest radius of curvature is defined as a reference curved portion. When the flat portion is continuous with only one of the longitudinal ends of the reference curved portion, the flat portion is used as the reference flat portion. When the flat portion is continuous with both ends, the longer flat portion of the flat portions is used as the reference flat portion. a straight line extending in a tangential direction of the reference curved portion from one of the longitudinal ends of the reference curved portion to which the reference flat portion is not continuous is defined as a first straight line; An extension line of the reference plane portion is a second straight line, The length between the intersection of the first straight line and the second straight line and one of the longitudinal ends of the reference flat portion that is not continuous with the reference curved portion is defined as b0, The length of the reference plane portion is defined as b1, When the radius of curvature of the reference curved portion is R, The b1 is 12 mm or more, The following formulas (1) and (2) are satisfied: The tensile strength of the steel plate is 1180 MPa or more, The R is 15 mm or more. Any of the following body parts: roof side rails, side sills, or upper A-pillars. Here, the thickness of the steel plate forming the reference plane portion is t, Young's modulus is E, Poisson's ratio is ν, and yield stress is σ y Let's say.

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[0008] As described above, according to the present invention, a vehicle body member that is lighter in weight and can ensure high axial compressive strength is provided. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view taken along a direction perpendicular to an axis, showing an example of a vehicle body member according to a first embodiment of the present invention. [Figure 2] 10 is a graph showing the relationship between the radius of curvature of a reference curved portion of a vehicle body member according to an example and the axial compressive strength. [Figure 3]10 is a graph showing the relationship between the radius of curvature of a reference curved portion and the axial compressive strength of a vehicle body member according to a comparative example. [Figure 4] FIG. 10 is a cross-sectional view taken along a direction perpendicular to the axis, showing a vehicle body member according to a modified example 1-1 of the first embodiment. [Figure 5] FIG. 10 is a cross-sectional view taken along a direction perpendicular to the axis, showing a vehicle body member according to Modification 1-2 of the embodiment. [Figure 6] FIG. 10 is a cross-sectional view taken along a direction perpendicular to the axis, showing a vehicle body member according to Modification 1-3 of the embodiment. [Figure 7] FIG. 10 is a cross-sectional view taken along a direction perpendicular to an axis, showing an example of a vehicle body member according to a second embodiment of the present invention. [Figure 8] FIG. 2 is a cross-sectional view taken along a direction perpendicular to the axis, showing a vehicle body member according to a modified example 2-1 of the embodiment. [Figure 9] FIG. 10 is a cross-sectional view taken along a direction perpendicular to the axis, showing a vehicle body member according to Modification 2-2 of the embodiment. [Figure 10] FIG. 10 is a cross-sectional view taken along a direction perpendicular to the axis, showing a vehicle body member according to Modification 2-3 of the embodiment. [Figure 11] FIG. 10 is a cross-sectional view taken along a direction perpendicular to the axis, showing a vehicle body member according to Modification 2-4 of the embodiment. [Figure 12] 1 is a diagram showing an automobile frame as an example to which a vehicle body member according to an embodiment is applied; DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this specification and drawings, components having substantially the same functional configurations are designated by the same reference numerals, and redundant explanations will be omitted.

[0011] First Embodiment First, the configuration of the first embodiment will be described with reference to FIG. 1. FIG. 1 is a cross-sectional view showing an example of a vehicle body member according to this embodiment. The vehicle body member 1 may be a structural member of the vehicle body, in other words, a frame member. The vehicle body may be, for example, the body of an automobile. The vehicle body member 1 is, for example, a hollow cylindrical member formed from a steel plate. Hereinafter, the longitudinal direction along the axis of the vehicle body member 1 is also referred to as the axial direction. The steel plate used as the material for the vehicle body member 1 is not particularly limited, but may have a tensile strength of 1180 MPa or more. The tensile strength is not limited to 1.2 GPa class, but may be 1.5 GPa class, 1.8 GPa class, 2.5 GPa class, etc. When the thickness of the steel plate is 1.6 mm or less, the vehicle body member 1 according to this embodiment exhibits the effects described below. The thickness of the steel plate may be, for example, 0.4 mm or more, from the viewpoint of the impact absorption characteristics required of the vehicle body member 1. The vehicle body member 1 can be formed by applying various known processing techniques to the steel plate. As an example, a blank may be formed into a predetermined shape by cold drawing press processing to form the vehicle body member 1. Alternatively, the vehicle body member 1 may be formed by, for example, hot stamping.

[0012] As an example, the vehicle body member 1 may have a square tubular shape. FIG. 1 shows a cross section perpendicular to the axial direction (axis-perpendicular cross section) of the vehicle body member 1, which has a square tubular shape. The axis-perpendicular cross section of the vehicle body member 1 is a closed cross section and has four curved portions 100, 101, 102, and 103 and four flat portions 110, 111, 112, and 113. The curved portions 100, 101, 102, and 103 are arc-shaped and convex outward from the vehicle body member 1, and may have the same shape and size. The flat portions 110, 111, 112, and 113 may be linear and may have the same size.

[0013] Among the curved portions 100, 101, 102, and 103, the one with the largest radius of curvature is designated as the reference curved portion 10. Here, the radius of curvature of the curved portion is obtained, for example, as follows. Specifically, in a cross section perpendicular to the axis, three points are determined: two R-end points, which are the start or end points of the bending of the steel plate on the surface of the car body member 1 (in other words, the boundary points between the curve and the straight line), and a bending center point on the curved portion of the surface, which is equidistant along the surface from the two R-end points. The radius of curvature of the curved portion is obtained by calculating the curvature from these three points using a known mathematical method. Note that the surface is the outer surface of the bent steel plate, as shown in FIG. 1 . In the example shown in FIG. 1 , the radii of curvature of the curved portions 100, 101, 102, and 103 are the same, so for example, the curved portion 100 can be designated as the reference curved portion 10. The radius of curvature of the reference curved portion 10 is designated as R.

[0014] In the cross section perpendicular to the axis, flat portions 110, 113 are continuous with both longitudinal ends P, Q of the reference curved portion 10. These ends P, Q are the two R stop points on the surface of the vehicle body member 1. The longer of the flat portions 110, 113 is taken as the reference flat portion 11. In the example shown in FIG. 1 , the flat portions 110, 113 have the same length, so for example, the flat portion 110 can be taken as the reference flat portion 11. Note that if a flat portion is continuous with only one of the longitudinal ends P, Q of the reference curved portion 10, that flat portion may be taken as the reference flat portion 11.

[0015] A first straight line L1 is a line extending in a tangential direction of the reference bending portion 10 from the end P, of both longitudinal ends P, Q of the reference bending portion 10, which end P is not continuous with the reference flat portion 11, in other words, a tangent to the surface of the reference bending portion 10 at the end P. In addition, an extension line of the surface of the reference flat portion 11 (in the example shown in FIG. 1, the surface continuous with the surface on the outer side of the bending of the reference bending portion 10) is a second straight line L2.

[0016] The length between the intersection S of the first straight line L1 and the second straight line L2 and the end T of the reference flat portion 11 in the longitudinal direction, which is not continuous with the reference curved portion 10, is defined as b0.

[0017] The angle formed by the first straight line L1 and the second straight line L2 with the reference bending portion 10 in between is defined as θ. θ may be set within a range of 80° or more and 150° or less. In the example shown in FIG. 1, θ is set to 90° or close to 90°.

[0018] In the cross section perpendicular to the axis, the length (width) of the reference flat portion 11 is b1, the plate thickness is t, the Young's modulus is E, the Poisson's ratio is ν, and the yield stress is σ y In this case, the radius of curvature R of the reference curved portion 10 is set so as to satisfy the following formula (1). Note that the radius of curvature R set in this manner may be 15 mm or more, for example, when the tensile strength of the steel plate used as the material is 1180 MPa or more. Furthermore, there is no particular upper limit to the radius of curvature R, and it is sufficient that the radius of curvature R is such that the length b1 of the reference flat portion 11 exceeds 0, as will be described later.

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[0019] The length b1 of the reference flat portion 11 is set so as to satisfy the following formula (2): Note that the length b1 set in this manner may be, for example, 10 mm or more, as long as it satisfies formula (2).

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[0020] Next, the effects of this embodiment will be described. An axial compressive load (axial compressive load) can act on the vehicle body member 1. Due to their shape, the portions of the vehicle body member 1 corresponding to the curved portions 100-103 have higher rigidity against the axial compressive load than the portions corresponding to the flat portions 110-113, and are less likely to elastically buckle. Therefore, the radius of curvature R of the reference curved portion 10 is set to a predetermined value or greater. As a result, even if one of the flat portions on both sides of the reference curved portion 10 (e.g., the flat portion 110) attempts to elastically buckle, the reference curved portion 10 can block the influence of this deformation on the other (e.g., the flat portion 113), i.e., the flat portions from elastically buckling in unison. Therefore, elastic buckling can be suppressed and the axial compressive strength can be improved for the vehicle body member 1 as a whole. Specifically, by setting the radius of curvature R of the reference curved portion 10 to be equal to or greater than the lower limit defined by the left side of the above formula (1), it is possible to suppress the above-mentioned effects and suppress the overall elastic buckling of the car body member 1. When the tensile strength of the steel plate is 1180 MPa or greater, the radius of curvature R may be, for example, 15 mm or greater, and the inventors have confirmed that in this case, the axial compressive strength can be effectively improved (see Example 1-1 described below).

[0021] Furthermore, by setting the length b1 of the reference flat portion 11 to be equal to or less than the upper limit defined by the right-hand side of the above formula (2), elastic buckling of the flat portion continuous with the reference curved portion 10 can be suppressed. Formula (2) was obtained as a result of extensive research by the present inventors. Formula (2) is used to calculate the effective maximum length of the flat portion, taking into account the deformation mode of the car body member 1 formed from a high-strength, thin-plate steel plate against an axial compressive load. Here, the effective maximum length is the upper limit of the length of the flat portion such that the elastic buckling stress is equal to or greater than the yield stress in a predetermined range (e.g., the entire range) in the longitudinal direction of the flat portion in a cross section perpendicular to the axis, thereby avoiding elastic buckling.

[0022] By setting the length b1 of the reference flat portion 11 to be equal to or less than the effective maximum length, elastic buckling is suppressed within a predetermined range (e.g., the entire range) in the longitudinal direction of the reference flat portion. In other words, within a predetermined range in the longitudinal direction of the reference flat portion, until the axial compressive stress reaches the strength limit of the material, the load applied to the reference flat portion is withstood by the strength of the material and is unlikely to be converted into elastic buckling of the reference flat portion. Of the two flat portions sandwiching the reference curved portion on both sides, the length of the flat portion opposite the reference flat portion is equal to or less than the length of the reference flat portion, by definition of a reference flat portion. Therefore, the length of this flat portion is also equal to or less than the upper limit defined by the right-hand side of the above equation (2), and elastic buckling is suppressed in this flat portion as well. In other words, elastic buckling is suppressed in the flat portions on both sides sandwiching the reference curved portion.

[0023] The lower limit of the radius of curvature R defined on the left side of the above formula (1) is the length b0 minus the effective maximum length of the flat portion. In other words, the lower limit of the radius of curvature R is set so that the radius of curvature R of the standard curved portion can be as large as possible while keeping the length of the standard flat portion equal to or less than the effective maximum length. Therefore, elastic buckling can be suppressed by the flat portions on both sides of the standard curved portion, and even if one of these flat portions were to buckle, the influence that this could have on the other flat portion can be blocked by the standard curved portion interposed between the two flat portions. In this way, the synergistic effect of the lower limit of the radius of curvature R and the upper limit of the length b1 can improve the axial compressive strength of the car body member 1 as a whole and suppress elastic buckling.

[0024] The angle θ between the first straight line L1 and the second straight line L2 may be 80° or more and 150° or less. When the angle θ is 150° or less, the longitudinal end of the flat portion in the cross section perpendicular to the axis is supported by other portions at a certain angle, and can therefore be considered to be simply supported rather than a free end. Therefore, the definition of the effective maximum length of the reference flat portion according to the above formula (2) functions effectively, and the above-mentioned effect can be effectively obtained by length b1 satisfying formula (2). Furthermore, when the angle θ is 80° or more, it becomes easy for the radius of curvature R of the reference curved portion to satisfy formula (1).

[0025] The body member 1 is formed from a steel plate having a tensile strength equal to or greater than a predetermined value and a plate thickness equal to or less than a predetermined value. In this way, by using a thinner and stronger material for the body member 1, the weight of the body member 1 can be reduced and the load capacity can be improved. However, making the material of the body member 1 thinner and stronger can reduce the elastic buckling stress of the flat parts of the member. In other words, a reduction in the plate thickness t of the flat parts significantly reduces the elastic buckling stress of the flat parts. Furthermore, even if the strength of the flat parts against the axial compressive load is the same, as can be seen from the right side of the above formula (2), the smaller the plate thickness t, and the greater the yield stress σ y Therefore, if the length of the flat portion in the direction perpendicular to the axis is not taken into consideration, there is a high possibility that elastic buckling will occur in the area subjected to compressive load before the yield stress of the material is reached.

[0026] In contrast, by setting the length b1 of the reference flat portion 11 to be equal to or less than the upper limit (effective maximum length) defined by the right side of the above formula (2), elastic buckling of the flat portion can be suppressed even if the material is thinned and strengthened. Furthermore, by setting the radius of curvature R of the reference curved portion 10 to be equal to or greater than the lower limit defined by the left side of the above formula (1), elastic buckling of the entire vehicle body member 1 can be effectively suppressed even if the material is thinned and strengthened. Specifically, the vehicle body member 1 is formed from a steel plate having a thickness of 1.6 mm or less. Because of this thickness, the problem of reduced elastic buckling stress as described above is likely to occur. In response, significant effects can be achieved by setting the radius of curvature R or the length b1 using the above formulas (1) and (2). Furthermore, the vehicle body member 1 may be formed from a steel plate having a tensile strength of, for example, 1180 MPa or more. With such a tensile strength, the problem of a decrease in elastic buckling stress as described above is likely to occur, but by setting the radius of curvature R or the length b1 using the above formulas (1) and (2), a significant effect can be obtained.

[0027] By setting the length b1 of the reference flat portion 11 to a value greater than the lower limit defined by the left side of the above formula (2), the rigidity of the car-body member 1 against bending and torsion can be improved. That is, as shown in FIG. 1 , the distance d0 from the neutral axis N to the flat portion 110 (the moment arm about the neutral axis N) is greater than the distance d1 from the neutral axis N of the car-body member 1 to the curved portions 100 and 101 (the moment arm about the neutral axis N). Therefore, by setting the length b1 of the reference flat portion 11 to a value greater than 0, in other words, by providing a flat portion on the car-body member 1, the compressive strength against bending and torsion (small loads) caused by relatively small vibrations of the car-body member 1, such as when the car body vibrates or when the car body runs over a curb, can be improved. From this perspective, it is preferable that the length b1 be as large as possible within a range equal to or less than the effective maximum length of the flat portion. By increasing the length b1, i.e., by increasing the proportion of the flat portion in the cross-sectional shape of the car-body member 1 that is occupied by the flat portion, the rigidity can be further improved.

[0028] The length b1 of the reference flat portion 11 may be equal to or greater than a predetermined lower limit value greater than 0. In this case, the maximum load resistance of the compression surface (for example, on the bending side) of the body member 1 when a large load is input can be increased, thereby increasing the amount of energy absorbed by the body member 1. In other words, when the cross section of the body member 1 in the axis-perpendicular direction is made up of flat portions as well, the circumferential length of the cross section, i.e., the cross-sectional area A, can be larger in the same design space than when the cross section is made up of only curved portions (circular, etc.). The strength of the body member 1 is determined by the yield stress σ of the material. y and the cross-sectional area A. Increasing the cross-sectional area A increases the maximum load-bearing capacity (axial compressive strength) of the compression surface of the body member 1, thereby increasing the amount of energy absorbed by the body member 1. The lower limit of the length b1 is determined by the thickness t and yield stress σ of the steel plate that is the material for the body member 1. y For example, the length b1 may be 10 mm or more. This value of 10 mm is set based on, for example, the thickness t of the steel plate being 0.5 mm and σ y = 2 GPa, this is a value that can be selected as the lower limit value appropriate for suppressing an excessive decrease in the cross-sectional area A.

[0029] [Example] The inventors applied an axial compressive load to test specimens (Examples 1-1 and 1-2) having the cross-sectional shape shown in Figure 1 (angle θ = 90°) and investigated the relationship between the radius of curvature R (mm) of the reference curved portion and the axial compressive strength P (kN) of the test specimens. The axial dimension of the test specimen in Example 1-1 was 288 mm, the outer dimension D was 72 mm, and the steel plate used had a thickness of 1.6 mm, a Young's modulus of 206,000 MPa, a Poisson's ratio of 0.3, a tensile strength of 1,256 MPa, and a yield stress of 943 MPa. The test results for Example 1-1 are shown in Table 1, along with the lengths b0 and b1, the left side of Equation (1), and the right side of Equation (2) (i.e., the effective maximum length of the flat portion).

[0030] [Table 1]

[0031] The axial dimension of the specimen in Example 1-2 was 480 mm, the outer dimension D was 120 mm, and the thickness of the steel plate used as the material was 1.6 mm, with a Young's modulus of 206,000 MPa, a Poisson's ratio of 0.3, a tensile strength of 431 MPa, and a yield stress of 319 MPa. The test results for Example 1-2 are shown in Table 2, along with the length b0, the length b1, the left side of equation (1), and the right side of equation (2) (i.e., the effective maximum length of the flat portion).

[0032] [Table 2]

[0033] When the radius of curvature R of the reference curved portion is small, the lengths b0 and b1 are large, and the left side of equation (1) is large. Therefore, when R is less than a certain threshold R*, R is less than the left side of equation (1), and equation (1) does not hold. Also, when R is less than R*, b1 is greater than the right side of equation (2), and equation (2) does not hold. On the other hand, when R is large, b0 and b1 are small, and the left side of equation (1) is small. Therefore, when R is equal to or greater than the threshold R*, R is equal to or greater than the left side of equation (1), and equation (1) holds. Also, when R is equal to or greater than the threshold R*, b1 is less than the right side of equation (2), and equation (2) holds. In Example 1-1, the right side of equation (2) was 45.0 mm, and R* was 13.5 mm. In Example 1-2, the right side of formula (2) was 77.3 mm, and R* was 21.4 mm.

[0034] FIG. 2 shows the test results of Example 1-1 as a graph. When the curvature radius R of the reference curved portion was equal to or less than a predetermined value (24 mm), the axial compressive strength P was small, less than 315 kN, when the curvature radius R was less than the threshold value R* (13.5 mm). This is thought to be because equations (1) and (2) do not hold, and therefore the flat surfaces on both sides of the curved portion tend to interact with each other, making elastic buckling more likely to occur. When the curvature radius R was equal to or greater than R* (13.5 mm), the axial compressive strength P was large, being equal to or greater than 315 kN. This is thought to be because equations (1) and (2) hold, and therefore the interaction is suppressed, preventing elastic buckling. Note that when the curvature radius R exceeded the predetermined value (24 mm), the axial compressive strength P decreased with increasing curvature radius R. This is thought to be because the proportion of flat surfaces in the cross-sectional shape decreased, resulting in a reduced cross-sectional area.

[0035] FIG. 3 shows the test results of Example 1-2 as a graph. When the curvature radius R of the reference curved portion was equal to or less than a predetermined value (40 mm), the axial compressive strength P was small, less than 197 kN, when the curvature radius R was less than the threshold value R* (21.4 mm). This is thought to be because equations (1) and (2) do not hold, and therefore the flat surfaces on both sides of the curved portion tend to interact with each other, making elastic buckling more likely to occur. When the curvature radius R was equal to or greater than R* (21.4 mm), the axial compressive strength P was large, being equal to or greater than 197 kN. This is thought to be because equations (1) and (2) hold, and therefore the interaction is suppressed, preventing elastic buckling. Note that when the curvature radius R exceeded the predetermined value (40 mm), the axial compressive strength P decreased with increasing curvature radius R. This is thought to be because the proportion of flat surfaces in the cross-sectional shape decreased, resulting in a reduced cross-sectional area.

[0036] In Example 1-1, compared to Example 1-2, not only was a large axial compressive strength P obtained in the range of the radius of curvature R equal to or greater than the threshold value R*, but the increase in the axial compressive strength P due to an increase in the radius of curvature R was also large. This is thought to be because Example 1-1 used a steel plate with a tensile strength of 1180 MPa or more, and therefore the above-mentioned effect of setting the radius of curvature R using formula (1) or setting the length b1 using formula (2) was more pronounced than in Example 1-2.

[0037] [Variation 1-1] FIG. 4 shows a modified example of the cross-sectional shape shown in FIG. 1. The curvature radii of the curved portions 102 and 103 are the same, and the curvature radius of the curved portion 100 is larger than that of the curved portion 103. Because the curvature radii of the curved portions 100 and 101 are the same, for example, the curved portion 100 may be used as the reference curved portion 10. Of the flat portions 110 and 111 that are continuous with both longitudinal ends of the reference curved portion 10, the longer flat portion 110 is used as the reference flat portion 11. If the curvature radius R of the reference curved portion 10 satisfies formula (1) and the length b1 of the reference flat portion 11 satisfies formula (2), the same effect as the example shown in FIG. 1 can be obtained. For example, the curvature radius R may be 15 mm or more, and the length b1 may be 10 mm or more.

[0038] [Variation 1-2] FIG. 5 shows a modified example of the cross-sectional shape shown in FIG. 1. The curvature radii of the curved portions 102 and 103 are the same, and the curvature radius of the curved portion 100 is larger than that of the curved portion 103. Because the curvature radii of the curved portions 100 and 101 are the same, for example, the curved portion 100 may be used as the reference curved portion 10. Of the flat portions 110 and 113 that are continuous with both longitudinal ends of the reference curved portion 10, the longer flat portion 110 is used as the reference flat portion 11. If the curvature radius R of the reference curved portion 10 satisfies formula (1) and the length b1 of the reference flat portion 11 satisfies formula (2), the same effect as the example shown in FIG. 1 can be obtained. For example, the curvature radius R may be 15 mm or more, and the length b1 may be 10 mm or more.

[0039] [Variation 1-3] FIG. 6 shows a modified example of the cross-sectional shape shown in FIG. 1. Of the curved portions 100, 101, 102, and 103, the curved portion 100 with the largest radius of curvature is defined as the reference curved portion 10. Of the flat portions 110, 113 continuous with both longitudinal ends of the reference curved portion 10, the longer flat portion 110 is defined as the reference flat portion 11. The angle θ formed by the first line L1 and the second line L2 across the reference curved portion 10 is 100° to 110°. If the radius of curvature R of the reference curved portion 10 satisfies formula (1) and the length b1 of the reference flat portion 11 satisfies formula (2), the same effects as those of the example shown in FIG. 1 can be obtained. For example, the radius of curvature R may be 15 mm or more, and the length b1 may be 10 mm or more.

[0040] <Second embodiment> The vehicle body member 1 may be formed by joining multiple members formed into a predetermined shape together by welding or the like. FIG. 7 shows an example of an axis-perpendicular cross section of the vehicle body member 1 formed in this manner. This cross section may be a closed cross section. The vehicle body member 1 is formed into a cylindrical shape by joining a first member 1A and a second member 1B by welding. The axis-perpendicular cross section of the first member 1A has two curved portions 100, 101 and three flat portions 110, 111, and 112. The flat portion 112 functions as a joining flange. The curved portion 101 may be a relatively small curve that is typically generated when the flat portion 112 is bent relative to the flat portion 111. The axis-perpendicular cross section of the second member 1B has two curved portions 102, 103 and three flat portions 113, 114, and 115. The flat portion 115 functions as a joining flange. The curved portion 103 may be a relatively small curve that would normally occur when bending the flat portion 115 relative to the flat portion 114. The flat portion 112 of the first member 1A is joined to the longitudinal end of the flat portion 113 of the second member 1B via a weld 131. The longitudinal end of the flat portion 110 of the first member 1A is joined to the flat portion 115 of the second member 1B via a weld 132. The curved portions 101 and 103 are convex toward the inside of the vehicle body member 1. Of the curved portions 100, 101, 102, and 103, the curved portion 100 with the largest radius of curvature is defined as the reference curved portion 10. Of the flat portions 110 and 111 that are continuous with both longitudinal ends of the reference curved portion 10, the longer flat portion 110 is defined as the reference flat portion 11.

[0041] When the radius of curvature R of the reference curved portion 10 satisfies the above formula (1) and the length b1 of the reference flat portion 11 satisfies the above formula (2), the same effects as those of the first embodiment can be obtained. For example, the radius of curvature R may be 15 mm or more, and the length b1 may be 10 mm or more. Note that the length b1 of the flat portion 110 serving as the reference flat portion 11 is the length from the connection point with the curved portion 100 to the welded portion 132, and does not include the length of the free end on the tip side of the welded portion 132.

[0042] [Variation 2-1] FIG. 8 shows a modified example of the cross-sectional shape shown in FIG. 7. The cross section of the first member 1A taken perpendicular to the axis has four curved portions 100, 101, 102, and 103 and five flat portions 110, 111, 112, 114, and 115. The flat portions 112 and 114 function as joining flanges. The curved portions 101 and 102 may be relatively small curved portions that are typically formed when the flat portions 112 and 114 are bent relative to the flat portions 111 and 115, respectively. The second member 1B is flat, and its cross section taken perpendicular to the axis has one flat portion 113. The flat portions 112 and 114 of the first member 1A are joined to the longitudinal ends of the flat portion 113 of the second member 1B via welds 131 and 132, respectively. The curvature radii of the curved portions 101 and 102 are the same, and the curvature radius of the curved portion 100 is larger than that of the curved portion 101. Because the curvature radii of the curved portions 100 and 103 are the same, for example, the curved portion 100 may be used as the reference curved portion 10. Of the flat portions 110 and 111 continuous with both longitudinal ends of the reference curved portion 10, the longer flat portion 110 is used as the reference flat portion 11. If the curvature radius R of the reference curved portion 10 satisfies formula (1) and the length b1 of the reference flat portion 11 is set to satisfy formula (2), the same effect as the example shown in FIG. 7 can be obtained. For example, the curvature radius R may be 15 mm or more, and the length b1 may be 10 mm or more.

[0043] [Variation 2-2] FIG. 9 shows a modified example of the cross-sectional shape shown in FIG. 7. The cross section of the first member 1A taken perpendicular to the axis has four curved portions 100, 101, 102, and 106 and five flat portions 110, 111, 112, 117, and 118. The flat portions 112 and 117 function as joining flanges. The curved portions 102 and 106 may be relatively small curved portions that are typically formed when the flat portions 112 and 117 are bent relative to the flat portions 111 and 118, respectively. The cross section of the second member 1B taken perpendicular to the axis has three curved portions 103, 104, and 105 and four flat portions 113, 114, 115, and 116. The flat portions 113 and 116 function as joining flanges. The curved portions 103 and 105 may be relatively small curved portions that are typically formed when the flat portions 113 and 116 are bent relative to the flat portions 114 and 115, respectively. The flat portions 112 and 117 of the first member 1A are joined to the flat portions 113 and 116 of the second member 1B via welds 131 and 132, respectively. Among the curved portions 100 to 106, the curved portion 100 with the largest radius of curvature is defined as the reference curved portion 10. Of the flat portions 110 and 118 that are continuous with both longitudinal ends of the reference curved portion 10, the longer flat portion 110 is defined as the reference flat portion 11. Setting the radius of curvature R of the reference curved portion 10 to satisfy Equation (1) and the length b1 of the reference flat portion 11 to satisfy Equation (2) provides the same effects as the example shown in FIG. 7 . For example, the radius of curvature R may be 15 mm or more, and the length b1 may be 10 mm or more.

[0044] [Variation 2-3] FIG. 10 shows a modified example of the cross-sectional shape shown in FIG. 7. The cross section of the first member 1A taken perpendicular to the axis has four curved portions 100, 101, 106, and 107 and five flat portions 110, 111, 112, 118, and 119. The flat portions 112 and 118 function as joining flanges. The curved portions 101 and 106 may be relatively small curved portions that are typically formed when the flat portions 112 and 118 are bent relative to the flat portions 111 and 119, respectively. The cross section of the second member 1B taken perpendicular to the axis has four curved portions 102, 103, 104, and 105 and five flat portions 113, 114, 115, 116, and 117. The flat portions 113 and 117 function as joining flanges. The curved portions 102 and 105 may be relatively small curved portions that are typically formed when bending the flat portions 113 and 117 relative to the flat portions 114 and 116, respectively. The flat portions 112 and 118 of the first member 1A are joined to the flat portions 113 and 117 of the second member 1B via welds 131 and 132, respectively. Of the curved portions 100 to 107, the curved portion 100 with the largest radius of curvature is defined as the reference curved portion 10. Of the flat portions 110 and 111 that are continuous with both longitudinal ends of the reference curved portion 10, the longer flat portion 110 is defined as the reference flat portion 11. Setting the radius of curvature R of the reference curved portion 10 to satisfy Equation (1) and the length b1 of the reference flat portion 11 to satisfy Equation (2) provides the same effects as the example shown in FIG. 7 . For example, the radius of curvature R may be 15 mm or more, and the length b1 may be 10 mm or more.

[0045] [Variation 2-4] FIG. 11 shows a modified example of the cross-sectional shape shown in FIG. 7. The cross section of the vehicle body member 1 taken perpendicular to the axis is a closed cross section having a substantially hat shape. The cross section of the first member 1A taken perpendicular to the axis has eight curved portions 100, 101, 102, 103, 104, 105, 106, and 107 and seven flat portions 110, 111, 112, 113, 115, 116, and 117. The flat portions 113 and 115 function as joining flanges. The curved portions 104 and 105 may be relatively small curved portions that are typically formed when the flat portions 113 and 115 are bent relative to the flat portions 112 and 116, respectively. The curved portions 100 and 107 are continuous with each other without a flat portion in between. The curved portions 101 and 102 are continuous with each other without a flat portion in between. The curved portions 100, 101, 102, and 107 and the flat portion 110 form a recessed portion 12 that protrudes from the flat portions 111 and 117 toward the inside of the vehicle body member 1. The recessed portion 12 is groove-shaped and extends along the longitudinal direction (axial direction) of the vehicle body member 1. The second member 1B is flat, and its cross section perpendicular to its axis has one flat portion 114. The flat portions 113 and 115 of the first member 1A are joined to the longitudinal ends of the flat portion 113 of the second member 1B via welded portions 131 and 132, respectively. The curved portions 100 and 101 are convex toward the inside of the vehicle body member 1. The radii of curvature of the curved portions 100 and 101 are larger than the radii of curvature of the other curved portions 102 to 107. Because the radii of curvature of the curved portions 100 and 101 are the same, for example, the curved portion 100 may be used as the reference curved portion 10. Since the flat portion is continuous with only one of the longitudinal ends of the reference bending portion 10 , this flat portion 110 is defined as the reference flat portion 11 .

[0046] If the radius of curvature R of the reference curved portion 10 satisfies Equation (1) and the length b1 of the reference flat portion 11 satisfies Equation (2), the same effects as those of the example shown in FIG. 7 can be obtained. For example, the radius of curvature R may be 15 mm or more, and the length b1 may be 10 mm or more. In this modification, the flat portion of the first member 1A is divided into three, so the lengths of the flat portions 110, 111, and 117 in the cross section perpendicular to the axis are shortened and tend to be equal to or less than the upper limit defined by the right side of Equation (2). This suppresses elastic buckling in each flat portion. Furthermore, the recess 12 in the first member 1A improves the strength of the vehicle body member 1 against bending moments and further improves its impact absorption characteristics.

[0047] [Application examples of body components] A preferred embodiment of the present invention has been described in detail above. Now, an application example of the vehicle body member 1 according to the embodiment will be described with reference to Fig. 12. Fig. 12 is a diagram showing an automobile frame 2 as an example to which the vehicle body member 1 is applied. The vehicle body member 1 can constitute the automobile frame 2 as a cabin frame or an impact absorbing frame.

[0048] Examples of applications of the vehicle body member 1 as a cabin framework include a roof central reinforcement 201, a roof side rail 203, a B-pillar 207, a side sill 209, a tunnel 211, an A-pillar lower 213, an A-pillar upper 215, a kick-in reinforcement 227, a floor cross member 229, an under-reinforcement 231, and a front header 233. Examples of applications of the vehicle body member 1 as an impact absorbing framework include a rear side member 205, an apron upper member 217, a bumper reinforcement 219, a crash box 221, and a front side member 223. In addition to the above, the vehicle body member 1 may be applied to a door impact beam or the like as a reinforcing member provided inside a vehicle door. In short, the vehicle body member 1 of this embodiment can be applied to any part where a compressive force can act in the axial direction.

[0049] When the vehicle body member 1 is used as a cabin frame or an impact absorbing frame in this way, the vehicle body member 1 has high axial compressive strength, which reduces deformation during a collision. In addition, the deformability is improved, which protects the inside of the frame.

[0050] Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to these examples. It is clear that a person skilled in the art to which the present invention pertains can conceive of various modifications and alterations within the scope of the technical ideas set forth in the claims, and it is understood that these also naturally fall within the technical scope of the present invention.

[0051] For example, it is sufficient that there is at least one curved portion in the cross section of the vehicle body member taken perpendicular to the axis, and there may be only one curved portion. Also, it is sufficient that there is at least one flat portion in the cross section of the vehicle body member taken perpendicular to the axis, and there may be only one flat portion. The cross section of the vehicle body member taken perpendicular to the axis does not have to be a closed cross section, and may be an open cross section. For example, in the modified examples shown in Figures 8 to 11, the second member 1B may be omitted, and only the first member 1A may be used as the vehicle body member. In these cases, too, both longitudinal ends of the reference flat portion in the cross section taken perpendicular to the axis can be considered to be simply supported, and therefore the above-mentioned effects can be obtained when the above formula (1) or formula (2) is satisfied. [Explanation of symbols]

[0052] 1 Body parts 10 Reference curve 11 Reference plane part L1 1st straight line L2 2nd straight line

Claims

1. A vehicle body member such as a roof side rail, a side sill, or an A-pillar upper, which is made of a steel plate with a thickness of 1.6 mm or less, The cross section perpendicular to the axis is The curved portion has at least one curved portion that is convex outward or inward and at least one flat portion, and the curved portion having the largest radius of curvature is defined as a reference curved portion. When the flat portion is continuous with only one of the longitudinal ends of the reference curved portion, the flat portion is used as the reference flat portion. When the flat portion is continuous with both ends, the longer flat portion of the flat portions is used as the reference flat portion. a straight line extending in a tangential direction of the reference curved portion from one of the longitudinal ends of the reference curved portion to which the reference flat portion is not continuous is defined as a first straight line; an extension line of the reference plane portion is a second straight line; a length between the intersection of the first straight line and the second straight line and one of the longitudinal ends of the reference flat portion that is not continuous with the reference curved portion is defined as b0; The length of the reference plane portion is defined as b1, When the radius of curvature of the reference curved portion is R, The b1 is 12 mm or more, The following formulas (1) and (2) are satisfied: The tensile strength of the steel plate is 1180 MPa or more, The R is 15 mm or more. Any of the following body parts: roof side rails, side sills, or upper A-pillars. Here, the thickness of the steel plate of the portion forming the reference plane portion is t, Young's modulus is E, Poisson's ratio is ν, and yield stress is σ ｙ Let's say. [Equation 1] [Equation 2]

2. The vehicle body member according to claim 1 , wherein an angle formed between the first straight line and the second straight line across the reference curved portion is equal to or greater than 80° and equal to or less than 150°.

3. The vehicle body member according to claim 1 or 2, wherein the cross section perpendicular to the axis is a closed cross section.

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