JP7648879B2 - Automotive body structural components - Google Patents

Description

The present invention relates to structural components for automobile bodies.

In recent years, the use of high-tensile steel plates in automotive parts has expanded with the aim of improving the collision safety performance of automobiles and reducing the weight of the vehicle body. By using high-tensile steel plates, it is possible to obtain parts with better collision safety performance, or to achieve both collision safety performance and weight reduction through thinner parts.

However, when the thickness of the material is reduced, not only does the rigidity of the steel plate before processing decrease, but the rigidity of the parts after processing also decreases, so simply using high-strength, thin steel plate may not provide sufficient strength to ensure crash safety performance.

The collision safety performance of automobile body parts includes the bending crush characteristics of side sills and B-pillars in side collisions, and bumpers in frontal collisions. There is a demand for improving the three-point bending characteristics in local buckling mode to achieve higher collision safety performance even when using thin plate materials.

Patent Document 1 discloses a vehicle crashworthiness reinforcement material with excellent buckling resistance that is designed to have a recessed bead extending along the longitudinal direction of the main body portion to the center of the width of the main body portion.
Patent Document 2 discloses a metal vehicle absorber having concave or convex beads that are approximately parallel to the front-rear direction of the vehicle on one or both of an upper web and a lower web.

Patent No. 5119477 Patent No. 4330652

However, the techniques of Patent Documents 1 and 2 were unable to fully demonstrate the three-point bending characteristics of the local buckling mode of the more highly bent crushed parts that are required.

The present invention was made in consideration of the above problems, and the object of the present invention is to provide a structural member that can exhibit superior collision safety performance by improving the load-bearing capacity and impact energy absorption at the beginning of the stroke of deformation in local buckling mode.

Specific aspects of the present invention are as follows:

(1) A first aspect of the present invention is a hat-shaped member having a top plate portion extending in the longitudinal direction, a pair of side wall portions extending through first corner portions formed at both widthwise ends of the top plate portion, and a pair of flange portions extending through second corner portions formed at ends of the pair of side wall portions opposite the first corner portions; a joining member having a pair of joining portions joined to the pair of flange portions of the hat-shaped member and a top plate opposing portion opposing the top plate portion of the hat-shaped member;
a composite bead extending along the longitudinal direction is formed on the top plate portion or the top plate opposing portion, the composite bead comprising a pair of bead side walls extending and bending inward from the top plate portion or the top plate opposing portion, a pair of bead bottom walls extending and bending inward from the pair of bead side walls in directions facing each other, and a bulge portion formed between the pair of bead bottom walls, in a cross section perpendicular to the longitudinal direction, the bulge portion comprises a pair of inclined portions extending from first ends, which are ends of the pair of bead bottom walls opposite the pair of bead side walls, such that the distance between them increases as the bulge portion extends outward in a height direction, and a central portion connecting second ends, which are ends of the pair of inclined portions opposite the pair of bead bottom walls ,
(2) In the structural component for an automobile body described in (1) above, two or more of the composite beads may be formed in parallel in the width direction.
(3) In the structural component for an automobile body described in (1) or (2) above, the composite bead may be formed on the top plate portion of the hat-shaped component.
(4) In the structural component of an automobile body described in (3) above, the composite bead may be formed so that, in a cross section perpendicular to the longitudinal direction, the center of the composite bead in the width direction is located in the region from the boundary point between the top plate portion and the first corner portion to a point that is spaced apart in the width direction by 1/4 of the width of the top plate portion.
(5) In the structural component of an automobile body described in (3) above, the composite bead may be formed so that, in a cross section perpendicular to the longitudinal direction, the boundary point between the composite bead and the top plate portion is located in the region from the boundary point between the top plate portion and the first corner portion to a point spaced 20 mm apart.
(6) In the structural component for an automobile body described in any one of (3) to (5) above, an imaginary straight line connecting the boundary points between the top plate portion and the bead side wall may overlap at least a portion of the central portion of the bulge portion.
(7) In the structural component for an automobile body described in any one of (3) to (6) above, the hat-shaped component may be formed from a steel plate having a thickness of 1.2 mm or less.
(8) In the structural component for an automobile body described in any one of (3) to (7) above, the hat-shaped component may be formed from a steel plate having a tensile strength of 980 MPa or more.
(9) In the structural component for an automobile body according to any one of (3) to (8) above, the hat-shaped component may be a hardened component.
(10) In the structural component for an automobile body described in (1) or (2) above, the composite bead may be formed on the portion of the joining member facing the top plate.
(11) In the structural component of an automobile body described in (10) above, the composite bead may be formed so that, in a cross section perpendicular to the longitudinal direction, the center of the composite bead in the width direction is located in a region from the inner end of the joint of the joining member to a point that is spaced apart by a distance of 1/4 of the width of the top plate opposing portion in the width direction.
(12) In the structural component of an automobile body described in (10) above, the composite bead may be formed so that, in a cross section perpendicular to the longitudinal direction, the boundary point between the composite bead and the joining member is located in a region from an inner end of the joining portion of the joining member to a point spaced 20 mm apart.
(13) In the structural component of an automobile body described in any one of (10) to (12) above, a virtual straight line connecting the boundary points between the top plate opposing portion and the bead side wall may overlap at least a portion of the central portion of the bulge portion.
(14) In the structural component for an automobile body according to any one of (10) to (13) above, the joining member may be formed from a steel plate having a thickness of 1.2 mm or less.
(15) In the structural component for an automobile body according to any one of (10) to (14) above, the joining member may be formed from a steel plate having a tensile strength of 980 MPa or more.
(16) In the structural component for an automobile body according to any one of (10) to (15) above, the joining member may be a hardened member.
(17) In the structural component for an automobile body described in any one of (1) to (16) above, the first ends may be in contact with each other.
(18) In the structural component for an automobile body described in (17) above, the first ends may be fixed to each other.
(19) In the structural component for an automobile body according to any one of (1) to (18) above, the bulge and the bead side wall may be in contact with each other.
(20) In the structural component for an automobile body described in (19) above, the bulge and the bead side wall may be fixed together.
(21) In the structural component of an automobile body described in any one of (1) to (20) above, the distance between the second ends may be 1.2 times or more the distance between the first ends.
(22) In the structural component for an automobile body according to any one of (1) to (21) above, the width of the composite bead may be 5 mm to 20 mm, and the depth of the composite bead may be 5 mm to 20 mm.
(23) In the structural component for an automobile body according to any one of (1) to (22) above, the aspect ratio calculated by the depth/width of the composite bead may be 0.25 to 4.0.
(24) In the structural component for an automobile body described in any one of (1) to (23) above, a height direction bead extending along the height direction may be formed on the side wall portion.
(25) In the structural component for an automobile body described in (24) above, the height direction bead may extend from the first corner portion.
(26) In the structural component for an automobile body described in (24) above, the height direction bead may extend from the second corner portion.
(27) In the structural component for an automobile body described in (24) above, the height direction bead may extend from the first corner portion to the second corner portion.
(28) In the structural component for an automobile body described in any one of (24) to (27) above, the width of the height direction bead may be 10 mm to 60 mm, and the depth of the height direction bead may be 2 mm to 10 mm.
(29) In the structural component for an automobile body according to any one of (24) to (28) above, the aspect ratio calculated by the depth/width of the height direction bead may be 0.05 to 1.0.

The present invention improves the load-bearing capacity and impact energy absorption at the beginning of the stroke in the local buckling mode of deformation, thereby achieving better collision safety performance.

FIG. 1A is a schematic diagram for explaining three-point bending characteristics in local buckling mode, FIG. 1B is a schematic diagram for explaining three-point bending characteristics in wall buckling mode, and FIG. 1C is a schematic diagram for explaining moment bending characteristics. FIG. 2 is a perspective view showing a structural member according to the first embodiment. FIG. 2B is a schematic cross-sectional view of the structural member according to the first embodiment, taken along line A1-A1' in FIG. 2A. FIG. 4 is a perspective view showing a state after deformation of the structural member according to the first embodiment. FIG. 2 is a schematic cross-sectional view showing a composite bead. FIG. 4 is a schematic cross-sectional view showing a composite bead after deformation. FIG. 2 illustrates a first step of an example of a molding method. FIG. 4 illustrates a second step of the exemplary molding method. FIG. 4 illustrates a third step of the exemplary molding method. FIG. 11 is a schematic cross-sectional view showing a structural member according to a first modified example. FIG. 11 is a perspective view showing a structural member according to a second modified example. FIG. 11 is a schematic cross-sectional view showing a composite bead of a structural member according to a third modified example. FIG. 11 is a schematic cross-sectional view showing a composite bead of a structural member according to a fourth modified example. FIG. 11 is a perspective view showing a structural member according to a second embodiment. FIG. 11 is a plan view showing a structural member according to a second embodiment. FIG. 13 is a partially enlarged view of portion B of FIG. 12. FIG. 2 is a schematic diagram for explaining three-point bending conditions.

The bending crush characteristics of automobile parts can be broadly divided into three-point bending characteristics, in which the impact of the collision is applied directly to the crushed part of the part, causing deformation, and moment bending characteristics, in which the impact of the collision is applied indirectly to the crushed part of the part, causing deformation.
Among these, the three-point bending characteristics are classified into three-point bending characteristics in a local buckling mode and three-point bending characteristics in a wall buckling mode.
The three-point bending characteristics in the local buckling mode and the three-point bending characteristics in the wall buckling mode are often evaluated based on the three-point bending characteristics obtained by conducting a three-point bending test in which an impactor directly collides with a component, as shown in (a) and (b) of Figure 1.
In the three-point bending characteristic of the local buckling mode, as shown in FIG. 1A, when the distance between the supports supporting the load in the three-point bending test is long, bending deformation occurs mainly at the position where the load is applied by the impactor.
In the three-point bending characteristics of the wall buckling mode, as shown in FIG. 1B, when the distance between the supports supporting the load in the three-point bending test is short, the main deformation is that the side wall is crushed in the part height direction, centered on the position where the load is applied by the impactor.
Furthermore, the moment bending characteristics are often evaluated based on the moment bending characteristics obtained by conducting a moment bending test in which an impactor or the like does not come into contact with the crushed portion of the part, as shown in FIG. 1(c).

The present inventors have studied component shapes for improving collision safety performance against deformation in the local buckling mode as shown in FIG. 1(a) and have obtained the following findings.
(a) In three-point bending where the crushed part comes into contact with the impactor, a combination of compressive stress along the longitudinal direction occurs on the inside of the bent part, compressive stress along the height direction occurs on the side wall of the part, and tensile stress along the longitudinal direction occurs on the outside of the bent part.
(i) Because compressive stress along the height direction occurs in the side walls, the side walls can easily buckle and deform due to compressive stress along the height direction, particularly when the material plate thickness is thin. Even in parts designed to operate in local buckling mode, the deformation state may approach that of wall buckling mode in the early stages of deformation.
(c) When the deformation state approaches the wall buckling mode, if buckling deformation of the side wall easily occurs, not only will good three-point bending characteristics for the wall buckling mode not be obtained, but the crushed side wall will reduce the height of the crushed part, and the bending rigidity in the height direction of the cross section that intersects the longitudinal direction will decrease. Therefore, even if the deformation state reaches the local buckling mode in the subsequent deformation, good three-point bending characteristics for the local buckling mode may not be obtained.
(e) Therefore, by designing a part shape that can simultaneously increase the deformation resistance to compressive stress along the longitudinal direction, the deformation resistance to compressive stress along the height direction, and the deformation resistance to tensile stress along the longitudinal direction, it is possible to improve the load-bearing capacity in deformation in local buckling mode, especially at the beginning of the stroke.
(e) By forming a composite bead consisting of a bead side wall, a bead bottom wall, and a bulge on the surface that comes into contact with the impactor, the height directional component of the bead side wall and the bulge can be used to increase the deformation resistance, and the interference between the bead side wall and the bulge during deformation can be used to increase the impact absorption energy, thereby enabling the implementation of even better collision safety performance.

The present invention, which was completed based on the above findings, will be described in detail below with reference to the embodiments. Note that in this specification and drawings, components having substantially the same functional configuration are designated by the same reference numerals, and duplicated explanations will be omitted.

In the following description, the axial direction of a structural member, i.e., the direction in which the axis extends, will be referred to as the longitudinal direction Z.
In addition, in a plane perpendicular to the longitudinal direction Z, a direction parallel to the top plate portion is referred to as a width direction X, and a direction perpendicular to the longitudinal direction Z and the width direction X is referred to as a height direction Y.
The direction away from the axis of the structural member is referred to as outward and the opposite direction is referred to as inward.

First Embodiment
Hereinafter, a structural member 100 for an automobile body according to a first embodiment of the present invention (hereinafter, referred to as structural member 100) will be described.

First, the schematic configuration of the structural member 100 will be described with reference to FIGS. 2A and 2B.
FIG. 2A is a perspective view of the structural member 100, and FIG. 2B is a cross-sectional view taken along the line A1-A1' of FIG. 2A.
2A and 2B , the structural member 100 is a member with a closed cross-sectional structure composed of a hat-shaped member 110 and a joining member 120. Examples of applications of the structural member 100 include B-pillars, side sills, and bumper reinforcements.

The structural member 100 according to this embodiment is a component that is intended to be installed in an automobile with the hat-shaped member 110 facing the outside of the vehicle and the joining member 120 facing the inside of the vehicle.

Therefore, when an impact load from the outside of the vehicle is input to the hat-shaped member 110 and bending deformation occurs in the structural member 100, as shown in FIG.
A compressive stress (A) along the longitudinal direction Z in the hat-shaped component 110;
A compressive stress (B) along the height direction Y in the hat-shaped component 110;
Tensile stress (C) along the longitudinal direction Z in the joining member 120;
will occur in a complex manner.
In addition, the "compressive stress (B) along the height direction Y of the hat-shaped component 110" can also be rephrased as "compressive stress (B) along a direction perpendicular to the longitudinal direction Z of the hat-shaped component 110."

As shown in FIGS. 2A and 2B , the hat-shaped component 110 has a top plate portion 111 extending along the longitudinal direction Z, a pair of side walls 115 , 115 , and a pair of flange portions 119 , 119 .
The hat-shaped member 110 may be a member made of a metal plate such as a steel plate, an aluminum plate, an aluminum alloy plate, a stainless steel plate, or a titanium plate, or further, a resin plate or a CFRP (Carbon Fiber Reinforced Plastic) plate.

(Top plate)
The top plate portion 111 corresponds to a portion that comes into direct contact with an impactor in the three-point bending test of the local buckling mode shown in FIG.
The structural member 100 in this embodiment is installed in an automobile with the hat-shaped member 110 facing the outside of the vehicle, so that when an impact load from the outside of the vehicle is input to the top plate portion 111, causing bending deformation in the structural member 100, a compressive stress (A) along the longitudinal direction Z is generated in the top plate portion 111.

The width W of the top plate portion 111 may be 40 mm or more and 200 mm or less. As shown in FIG. 2B, the width W of the top plate portion 111 is the distance in the width direction X between the boundary points of the top plate portion 111 and the first corner portions 113, 113 at both ends of the top plate portion 111 in a cross section perpendicular to the longitudinal direction Z of the structural member 100.

(Side wall portion)
The pair of side walls 115, 115 extend via first corners 113, 113 formed at both ends in the width direction X of the top plate portion 111. The first corners 113, 113 have an R portion with a curvature radius of, for example, 1 mm to 10 mm in a cross section perpendicular to the longitudinal direction Z of the structural member 100.
The structural member 100 in this embodiment is installed in an automobile with the hat-shaped member 110 facing the outside of the vehicle, so that when an impact load from the outside of the vehicle is input to the top plate portion 111, causing bending deformation in the structural member 100, a compressive stress (B) along the height direction Y is generated in the pair of side wall portions 115, 115.

The height H of the side wall 115 may be 20 mm or more and 150 mm or less. As shown in FIG. 2B, the height H of the side wall 115 is the distance in the height direction Y between the boundary point between the side wall 115 and the first corner 113 and the boundary point between the side wall 115 and the second corner 117 in a cross section perpendicular to the longitudinal direction Z of the structural member 100. The second corners 117, 117 have an R portion with a radius of curvature of, for example, 1 mm to 10 mm in a cross section perpendicular to the longitudinal direction Z of the structural member 100.

(Flange part)
2A , second corner portions 117, 117 are formed at ends of the pair of side wall portions 115, 115 opposite the first corner portions 113, 113. A pair of flange portions 119, 119 extend outward via the second corner portions 117, 117.
The flange portion 119 has spot welds 170 formed at a predetermined pitch in the longitudinal direction Z for joining to the joining member 120. Note that spot welding is one example of a joining means, and laser welding or brazing may also be used.

(Composite bead)
In the structural member 100 according to this embodiment, a single composite bead 150 is formed along the longitudinal direction Z in the central portion in the width direction X of the top plate portion 111 .
4 is a schematic cross-sectional view showing the composite bead 150. As shown in FIG 4, the composite bead 150 is formed by a pair of bead side walls 151, 151, a pair of bead bottom walls 153, 153, and a bulge portion 155.

(Bead side wall and bead bottom wall)
The pair of bead side walls 151, 151 are formed at the center of the top plate portion 111 in the width direction X so as to bend inward from the top plate portion 111 in the height direction Y. In the structural member 100 according to this embodiment, the angle θ on the inner side between the bead side wall 151 and the top plate portion 111 is approximately 90 degrees, but the angle θ may be 90 degrees or more.
The pair of bead bottom walls 153, 153 are formed so as to bend in directions facing each other from the ends of the pair of bead side walls 151, 151 opposite the top plate portion 111.

(Bulging part)
The bulging portion 155 is formed between the pair of bead bottom walls 153, 153 so as to bulge outward from the end portions of the pair of bead bottom walls 153, 153 opposite the pair of bead side walls 151, 151.
More specifically, the bulge 155 is formed by a pair of inclined portions 155a, 155a and a central portion 155b.
The pair of inclined portions 155a, 155a extend from the first end portion Q1, Q1 to the second end portion Q2, Q2 such that the distance between them increases as they extend outward in the height direction Y.
The first ends Q1, Q1 are ends of the pair of bead bottom walls 153, 153 opposite to the pair of bead side walls 151, 151.
The second ends Q2, Q2 are ends of the pair of inclined portions 155a, 155a opposite the pair of bead bottom walls 153, 153. Since the bulging portion 155 has the pair of inclined portions 155a, 155a, the distance D1 between the first ends Q1, Q1 is smaller than the distance D2 between the second ends Q2, Q2.
In the drawings of the present application, the first ends Q1, Q1 and the second ends Q2, Q2 are indicated by black dots having a diameter equal to the plate thickness of the bulging portion. Therefore, as shown in Fig. 4, the distance D1 is the distance between the inner end points of the first ends Q1, Q1, and the distance D2 is the distance between the inner end points of the second ends Q2, Q2.
The central portion 155b is a portion that connects the second ends Q2, Q2 to each other.

FIG. 5 is a schematic cross-sectional view showing the composite bead 150 after it has been deformed.
As described above, compressive stress (A) is generated in the top plate portion 111 along the longitudinal direction Z. This compressive stress also acts on the entire cross section of the composite bead 150 formed in the top plate portion 111 along the longitudinal direction Z. Compared to a normal concave bead (a concave bead having no bulging portions), the composite bead 150 has a greater number of ridges and walls in the height direction in the cross section, which increases the deformation resistance to the compressive stress (A) along the longitudinal direction Z, thereby improving the load-bearing capacity at the beginning of the stroke.
In addition, in the case of a normal concave bead, there is a space between a pair of bead side walls, and the pair of bead side walls are widely separated from each other, so that the bead side walls tend to collapse inward. On the other hand, in the structural member 100 in which the composite bead 150 is formed, the second end portion Q2 is close to the bead side wall 151, and the second end portions Q2, Q2 are connected to each other by the central portion 155b, so that the bead side wall 151 is unlikely to collapse. Therefore, the deformation of the top plate portion 111 is relatively small, and the cross-sectional shape of the hat-shaped member 110 is also unlikely to collapse, so that the deformation resistance against the compressive stress (A) along the longitudinal direction Z can be maintained at a high state even after the maximum load stroke has passed.
Therefore, the structural member 100 having the composite bead 150 formed thereon can improve the load resistance in the initial stage of the stroke in the local buckling mode of deformation, and can exhibit high impact absorption energy.

Further, as shown in FIG. 4, the distance D2 between the second ends Q2, Q2 is larger than the distance D1 between the first ends Q1, Q1. According to this configuration, the inclined portions 155a, 155a of the bulging portion 155 are inclined toward the pair of bead side walls 151, 151, so that after an impact load is input to the structural member 100, the deformation of the structural member 100 progresses while the vicinity of the second end Q2 of the inclined portion 155a of the bulging portion 155 interferes with the pair of bead side walls 151, 151. The central portion 155b connecting the second ends Q2, Q2 acts to support the pair of bead side walls 151, 151 that are falling inward through the second ends Q2, Q2. This allows the load capacity to be maintained high even after the maximum load has been exceeded, and the impact absorption energy to be improved.
In order to obtain this effect more reliably, the separation distance D2 between the second ends Q2, Q2 of the bulge portion 155 is preferably at least 1.2 times the separation distance D1 between the first ends Q1, Q1, and more preferably at least 1.5 times.

Moreover, the width of the outward side of the bulge 155 (i.e., the distance between the widthwise outer end points of the second ends Q2, Q2) is preferably 60% or more, and more preferably 80% or more, of the distance between the pair of bead side walls 151, 151 at the same height position. With this configuration, after an impact load is input to the structural member 100, the deformation of the structural member 100 can proceed more reliably while the vicinity of the second end Q2 interferes with the pair of bead side walls 151, 151.
In order to obtain a similar effect, the distance in the width direction X between the second end Q2 and the bead side wall 151 at the same height position (i.e., the distance between the widthwise outer end point of the second end Q2 and the bead side wall 151) is preferably 2 mm or less, and more preferably 1 mm or less.

The shape of the central portion 155b of the bulging portion 155 is not particularly limited as long as it connects the second ends Q2, Q2 to each other. For example, in a cross section perpendicular to the longitudinal direction Z, the central portion 155b may have a shape that protrudes outward in the height direction Y, or may have a shape that protrudes inward in the height direction Y.
However, it is preferable that the shape of the central portion 155 b of the bulge 155 is such that an imaginary line connecting the boundary points between the top plate portion 111 and the bead side wall 151 overlaps at least a portion of the central portion 155 b of the bulge 155 .
According to this configuration, after an impact load is input to the structural member 100, the deformation of the structural member 100 can be more reliably promoted while the bulging portion 155 interferes with the pair of bead side walls 151, 151. Therefore, the impact absorption energy can be further improved.

Moreover, as in the structural member 100 according to this embodiment, it is more preferable that the central portion 155b of the bulge portion 155 is formed in a planar shape, and that this planar central portion 155b overlaps, over its entire length, with an imaginary straight line connecting the boundary points between the top plate portion 111 and the bead side wall 151.

The composite bead 150 does not necessarily have to be formed over the entire length of the top plate portion 111 in the longitudinal direction Z, but may be formed over a portion of the entire length of the top plate portion 111. The position where the composite bead 150 is formed may be selected as the position where the bending crushing characteristics of the structural member 100 should be most strengthened, for example, the position where the impactor comes into contact and its vicinity. The composite bead 150 may also be formed at multiple locations in the longitudinal direction Z.

As shown in FIG. 2B, the composite bead 150 has a predetermined depth d1 and a predetermined width w1.

The depth d1 of the composite bead 150 is the distance in the height direction Y from the outer surface of the top plate portion 111 to the outer surface of the bead bottom wall 153 in the composite bead 150. If the composite bead 150 has a shape whose depth changes along the longitudinal direction Z, the maximum value of the distance in the height direction Y from the top plate portion 111 to the bead bottom wall 153 is defined as the depth d1.

The greater the depth d1 of the composite bead 150, the greater the deformation resistance against the compressive stress (A) along the longitudinal direction Z generated in the top plate portion 111, and the more suppressed early buckling deformation in the top plate portion 111. This improves the load resistance at the beginning of the stroke.
Therefore, the depth d1 of the composite bead 150 is preferably 5 mm or more, and more preferably 8 mm or more.

On the other hand, if the depth d1 of the composite bead 150 is too large, the width w1 of the composite bead 150 becomes relatively small, which may make it difficult to mold the composite bead 150. Therefore, the depth d1 of the composite bead 150 is preferably 20 mm or less, and more preferably 16 mm or less.

The width w1 of the composite bead 150 is the distance between the intersection of a virtual line extending the outer surface of one bead side wall 151 of the composite bead 150 with a virtual line extending the outer surface of the top plate portion 111, and the intersection of a virtual line extending the outer surface of the other bead side wall 151 of the composite bead 150 with a virtual line extending the outer surface of the top plate portion 111, in a cross section perpendicular to the longitudinal direction Z.
When the composite bead 150 has a shape in which the width changes along the longitudinal direction Z, the separation distance in the cross section where the separation distance is maximum is defined as width w1.

The smaller the width w1 of the composite bead 150, the higher the deformation resistance against the compressive stress (A) along the longitudinal direction Z generated in the top plate portion 111, suppressing early buckling deformation in the top plate portion 111 and increasing the maximum load. Therefore, the width w1 of the composite bead 150 is preferably 20 mm or less, and more preferably 15 mm or less.

On the other hand, if the width w1 of the composite bead 150 is too small, the depth d1 of the composite bead 150 becomes relatively large, which may make it difficult to form the composite bead 150.
For this reason, the width w1 of the composite bead 150 is preferably 5 mm or more, and more preferably 8 mm or more.

As described above, the depth d1 and width w1 of the composite bead 150 affect the deformation resistance to the compressive stress (A) along the longitudinal direction Z that occurs in the top plate portion 111. When the aspect ratio A1 calculated by the depth d1 relative to the width w1 of the composite bead 150 (depth d1/width w1) is 0.25 or more and 4.0 or less, this is preferable because it can more reliably exert the effect of increasing the deformation resistance to the compressive stress (A) along the longitudinal direction Z that occurs in the top plate portion 111. It is even more preferable that the aspect ratio A1 is 0.5 or more and 2.0 or less.

The hat-shaped member 110 can be formed, for example, by subjecting a plate material to cold pressing or warm pressing.
The hat-shaped member 110 may also be formed by hot stamping, in which a steel plate is heated to a high temperature in the austenite region, and then press-formed in a die, and simultaneously quenched in the die. Thus, the hat-shaped member 110 may be a quenched member.

Here, an example of a method for forming the hat-shaped member 110 by cold pressing will be described with reference to FIGS. 6A, 6B, and 6C.
6A, a plate material is placed on a lower die 1001 having a pair of grooves formed therein, and an upper die 1002 having a pair of protrusions corresponding to the pair of grooves is pressed into the plate material until it reaches the bottom dead center. This produces a first intermediate molded body M1.
6B , in a state where the first intermediate molded body M1 is sandwiched between the lower mold 2001 and the upper mold 2002, the pair of slide molds 2003, 2003 arranged on both sides of the first intermediate molded body M1 are pressed toward the center while the upper mold 2002 is pressed toward the lower mold 2001. In this way, a second intermediate molded body M2 having a composite bead 150 is obtained.
Finally, as shown in FIG. 6C, the second intermediate molded body M2 is press-molded into a generally hat-shaped shape using a lower mold 3001 and an upper mold 3002, thereby obtaining a hat-shaped member 110 having a composite bead 150.

From the viewpoint of reducing weight, the hat-shaped component 110 is preferably formed from a steel plate having a thickness of 1.2 mm or less, and more preferably from a steel plate having a thickness of 1.0 mm or less.
The lower limit of the thickness of the hat-shaped component 110 is not particularly limited, and may be 0.3 mm or more.
Furthermore, from the viewpoint of collision safety performance, the hat-shaped member 110 is preferably formed from a steel plate having a tensile strength of 980 MPa or more, and more preferably from a steel plate having a tensile strength of 1470 MPa or more.

(Joining member)
The joining member 120 will be described below.
The joining member 120 is a member that is joined to the hat-shaped member 110. The structural member 100 according to this embodiment is installed in an automobile with the joining member 120 facing the inside of the vehicle. Therefore, when an impact load from the outside of the vehicle is input to the top plate portion 111 and bending deformation occurs in the structural member 100, a tensile stress (C) along the longitudinal direction Z is generated in the joining member 120.
Therefore, by joining the joining member 120 to the hat-shaped member 110, it is possible to increase the deformation resistance against the tensile stress (C) along the longitudinal direction Z. This makes it possible to improve the load resistance at the beginning of the stroke.
Furthermore, by being joined to the hat-shaped member 110, the joining member 120 can prevent the side wall portion 115 from opening in the width direction X when bending deformation occurs in the structural member 100. Therefore, it is possible to sufficiently increase the deformation resistance of the side wall portion 115 against the compressive stress (B) along the height direction Y, and to improve the load resistance at the beginning of the stroke.

2A and 2B, in the structural member 100 according to this embodiment, a single flat plate material is used as the joining member 120. However, instead of the flat plate material, for example, a hat-shaped member may be used.
The joining member 120 may be a member made of a metal plate such as a steel plate, an aluminum plate, an aluminum alloy plate, a stainless steel plate, or a titanium plate, or further, a resin plate or a CFRP (Carbon Fiber Reinforced Plastic) plate.
The tensile strength and thickness of the joining member 120 are not particularly limited. As described above, when an impact load from the outside of the vehicle is input to the top plate portion 111 and bending deformation occurs in the structural member 100, a tensile stress (C) along the longitudinal direction Z occurs in the joining member 120. If compressive stress occurs, the plate thickness and strength of the member greatly affect the buckling deformation due to the compressive stress, but in the case of tensile stress, a material with a thin plate thickness or low strength can be used within a range in which the member does not break due to tensile deformation. Therefore, for example, the tensile strength and thickness of the joining member 120 may be lower than those of the hat-shaped member 110, or may be thinner than those of the hat-shaped member 110.
The joining member 120 may also be a hardened member.

As shown in FIG. 2B , the joint member 120 has a pair of joint portions 121, 121 provided at both ends in the width direction X, and a top plate facing portion 123 provided in the center in the width direction X.
The pair of joint portions 121, 121 are locations where the pair of flange portions 119, 119 of the hat-shaped component 110 are joined by spot welding or the like.
The top plate facing portion 123 is a portion of the joining member 120 excluding the joint portion 121 , and is a portion facing the top plate portion 111 of the hat-shaped member 110 .
In the structural member 100 according to this embodiment, the joint member 120 is formed from a single flat steel plate, so that the joint portion 121 and the top plate facing portion 123 are adjacent regions on the same plane.

The width of the top plate facing portion 123 may be 40 mm or more and 200 mm or less. It is preferable that the width of the top plate facing portion 123 is larger than the width W of the top plate portion 111. In this case, the pair of side wall portions 115, 115 incline in a direction expanding outward from the first corner portion 113, 113 to the second corner portion 117, 117. When an impact load from the outside of the vehicle is input to the top plate portion 111, the pair of side wall portions 115, 115 tend to collapse in a direction in which the first corner portions 113, 113 approach each other. As a result, the pair of bead side walls 151, 151 of the composite bead 150 also tend to collapse in a direction toward the bulge portion 155, but when the collapse occurs, they interfere with the bulge portion 155. The pair of bead side walls 151, 151 interfere with the bulge portion 155 to suppress further collapse, and the collapse of the pair of side wall portions 115, 115 is also suppressed. As a result, the cross-sectional shape of the hat-shaped member 110 can be prevented from collapsing, further improving the impact absorption energy. In addition, because the pair of side walls 115, 115 are inclined in a direction expanding outward from the first corners 113, 113 to the second corners 117, 117, when the hat-shaped member 110 is press-molded, a negative angle can be eliminated when the height direction Y is the press direction, which makes molding easier.

According to the structural member 100 of this embodiment, when an impact load from outside the vehicle is input to the top plate portion 111 and bending deformation occurs in the structural member 100, it is possible to exert a combination of deformation resistance to compressive stress (A) along the longitudinal direction Z, deformation resistance to compressive stress (B) along the height direction Y, and deformation resistance to tensile stress (C) along the longitudinal direction Z.
In particular, the formation of the composite bead 150 more effectively generates deformation resistance against the compressive stress (A) along the longitudinal direction Z. Therefore, early buckling deformation in the top plate portion 111 is suppressed, and the load resistance at the beginning of the stroke can be improved.
Furthermore, after an impact load is input to the structural member 100, the deformation of the structural member 100 progresses as the bulging portion 155 interferes with the pair of bead side walls 151, 151. This makes it possible to maintain a high load capacity even after the maximum load is exceeded, and improve the impact absorption energy.

(First Modification)
7 shows a cross-sectional view of a structural member 100A according to a first modified example. In the structural member 100 described above, the hat-shaped member 110 has a top plate portion 111 on which one composite bead 150 is formed, but in the structural member 100A according to the first modified example, the hat-shaped member 110A has two composite beads 150A, 150A formed on both sides of the top plate portion 111A in the width direction X.

In this way, when two composite beads 150A, 150A are formed in parallel in the width direction X along the longitudinal direction Z on the top plate portion 111A, as shown in Figure 7, each composite bead 150A, 150A is formed so that the widthwise center of the composite bead 150A (i.e., the central position of the width w1 of the composite bead 150A) is located in the vicinity portion P of both ends of the top plate portion 111A in the width direction X.

More specifically, the vicinity portion P is the region from the boundary point between the top plate portion 111A and the first corner portion 113 in a cross section perpendicular to the longitudinal direction Z of the structural member 100A to a point that is 1/4 of the width W of the top plate portion 111A in the width direction X.

From another perspective, each composite bead 150A, 150A may be formed such that the bead side wall 151 protrudes inward from the top plate portion 111A so that the boundary point between the composite bead 150A and the top plate portion 111A is located in the region from the boundary point between the top plate portion 111A and the first corner portion 113 to a point that is 20 mm apart in a cross section perpendicular to the longitudinal direction Z.

In this way, when two composite beads 150A, 150A are formed on both sides of the top plate portion 111A in the width direction X, the first corner portion 113 and the composite bead 150A are positioned at a close distance. Therefore, in the region from the first corner portion 113 to the composite bead 150A, the bending rigidity in the height direction Y of the cross section intersecting with the longitudinal direction Z can be effectively improved. Therefore, the load capacity and impact absorption energy at the beginning of the stroke can be more reliably improved.

(Second Modification)
8 is a perspective view of a structural member 100B according to a second modified example. In the above-described structural member 100, the composite bead 150 is formed on the top plate portion 111 of the hat-shaped component 110. In this structural member 100B, however, the composite bead 150B is not formed on the top plate portion 111B of the hat-shaped component 110B, but is formed on the top plate facing portion 123B of the joining member 120B.

This structural member 100B is different from the structural member 100, and is a part that is assumed to be installed in an automobile with the hat-shaped member 110B facing the inside of the vehicle and the joining member 120B facing the outside of the vehicle.
According to this structural member 100B, when it is installed in an automobile with the hat-shaped member 110B facing the inside of the vehicle and the joining member 120B facing the outside of the vehicle, it is possible to obtain the same effects as the structural member 100.
Furthermore, in the structural member 100B, when two composite beads are formed on both sides in the width direction X of the top plate facing portion 123B, the load resistance and impact absorption energy at the beginning of the stroke can be improved more reliably.
Therefore, in the case where the composite bead 150B is formed on the top plate facing portion 123B of the joining member 120B, the following aspect is preferable.
(1) In a cross section perpendicular to the longitudinal direction Z, the composite bead 150B is formed so that the center of the composite bead 150B in the width direction X is located in the region from the inner end of the joint 121 of the joint member 120B to a point that is spaced apart in the width direction X by 1/4 of the width of the top plate opposing portion 123B.
(2) In a cross section perpendicular to the longitudinal direction Z, the composite bead is formed so that the boundary point between the composite bead 150B and the joining member 120B is located in the region from the inner end of the joining portion 121 of the joining member 120B to a point that is 20 mm apart.

Furthermore, in the structural member 100B according to this modified example, it is preferable that an imaginary line connecting the boundary points between the top plate facing portion 123B and the bead side wall of the composite bead 150B overlaps at least a part of the central portion of the bulging portion.
Moreover, it is preferable that the joint member 120B is formed from a steel plate having a thickness of 1.2 mm or less.
Moreover, it is preferable that the joining member 120B is formed from a steel plate having a tensile strength of 980 MPa or more.
The joining member 120B is preferably a hardened member.

9 is a cross-sectional view showing a composite bead 150C of a structural member 100C according to a third modification. In this composite bead 150C, second ends Q2, Q2 of a bulge 155 are in contact with a pair of bead side walls 151, 151.
According to this configuration, since the bulge 155 and the bead side wall 151 are in contact with each other in advance, after an impact load is input to the structural member 100C, the deformation of the structural member 100C can be more reliably progressed in a state where the bulge 155 and the bead side wall 151 interfere with each other. This makes it possible to increase the deformation resistance against the compressive stress (A) along the longitudinal direction Z at an earlier timing, and to maintain a high load capacity even after the maximum load stroke has passed, thereby improving the impact absorption energy.
Furthermore, the bulge 155 may be in contact with and fixed to the pair of bead side walls 151, 151. Laser welding, brazing, or application of an adhesive may be used as a means for contacting and fixing the bulge 155. When the shape is fixed in this manner, the collapse of the cross-sectional shape of the hat-shaped component 110 can be effectively suppressed, and the effect of improving the impact absorption energy can be more stably obtained.
On the other hand, in consideration of the electrocoatability of the structural member 100C, it may be preferable that the second end portions Q2, Q2 of the bulging portion 155 of the composite bead 150C are spaced apart from the pair of bead side walls 151, 151. By having the second end portions Q2, Q2 of the bulging portion 155 spaced apart from the pair of bead side walls 151, 151, it is possible to improve the electrocoatability of the pair of regions surrounded by the pair of inclined portions 155a, 155a of the bulging portion 155, the pair of bead side walls 151, 151, and the pair of bead bottom walls 153, 153. In order to achieve both an improvement in impact absorption energy and electrocoatability, the ranges in which the bulging portion 155 and the pair of bead side walls 151, 151 contact each other and the ranges in which they are spaced apart may be provided alternately or mixed.

10 is a cross-sectional view showing a composite bead 150D of a structural member 100D according to a fourth modification. In this composite bead 150D, the first ends Q1, Q1 are in contact with each other. That is, the separation distance D1 between the first ends Q1, Q1 of the composite bead 150D is 0 mm.
In this case, after an impact load is input to the structural member 100D, the pair of bead side walls 151, 151 come into contact with the bulging portion 155 early on, so that the deformation of the structural member 100D can proceed more reliably with the bulging portion 155 interfering with the bead side walls 151. This makes it possible to maintain a high load capacity even after the maximum load stroke has passed, and improve the impact absorption energy.
Furthermore, the first ends Q1, Q1 of the composite bead 150D may be in contact with and fixed to each other. Laser welding, brazing, or application of an adhesive may be used as a means for contacting and fixing the first ends Q1, Q1 of the composite bead 150D. When the shape is fixed in this manner, the deformation of the cross-sectional shape of the hat-shaped component 110 can be effectively suppressed, and the effect of improving the impact absorption energy can be more stably obtained.
On the other hand, in consideration of the electrocoatability of the structural member 100D, it may be preferable that the first ends Q1, Q1 of the composite bead 150D are spaced apart. By spaced apart the first ends Q1, Q1 of the composite bead 150D, it is possible to improve the electrocoatability of the region surrounded by the pair of inclined portions 155a, 155a and the central portion 155b of the bulging portion 155. In order to achieve both improved impact absorption energy and electrocoatability, the ranges in which the first ends Q1, Q1 of the composite bead 150D contact each other and the ranges in which they are spaced apart may be provided alternately or mixed.

Second Embodiment
A structural member 200 according to a second embodiment of the present invention will now be described.
The structural member 200 according to this embodiment differs from the structural member 100 according to the first embodiment in that a bead extending in the height direction Y is formed on the side wall portion.
The same components as those described in the first embodiment, such as the composite bead 150 and the joining member 120, are designated by the same reference numerals and will not be described.

First, a schematic configuration of a structural member 200 according to this embodiment will be described with reference to FIGS.
Fig. 11 is a perspective view of the structural member 200. Fig. 12 is a schematic plan view, and Fig. 13 is an enlarged view of a portion B of Fig. 12.
As shown in FIGS. 11 to 13, the structural member 200 is a member having a closed cross-sectional structure composed of a hat-shaped member 210 and a joining member 120 .

As shown in FIG. 11, the hat-shaped member 210 has a top plate portion 111 extending along the longitudinal direction Z, a pair of side wall portions 215, 215 extending through first corner portions 113, 113 formed at both ends of the top plate portion 111 in the width direction X, and a pair of flange portions 119, 119 extending through second corner portions 117, 117 formed at the ends of the pair of side wall portions 215, 215 opposite the first corner portions 113, 113.

(Height bead)
A plurality of height direction beads 260 are formed in parallel on the side wall portion 215 along a direction intersecting the longitudinal direction Z.
In the example shown in FIG. 11, the height direction bead 260 is formed over the entire height of the side wall portion 215 in the height direction, but the height direction bead 260 may be formed over only a portion of the entire height direction.
The height direction bead 260 is formed so as to protrude inward from the side wall portion 215 .
The height direction bead 260 may have an R portion with a predetermined radius of curvature at the end portion on the side wall portion 215 side. In this case, the height direction bead 260 is connected to the side wall portion 215 via the R portion of the height direction bead 260.
The provision of such height direction beads 260 can increase the deformation resistance against the compressive stress (B) along the height direction Y generated in the side wall portion 215. As a result, early buckling deformation in the side wall portion 215 is suppressed, and the maximum load is increased.

In the structural member 200 according to this embodiment, the height direction bead 260 is formed so as to extend from the first corner portion 113 to the second corner portion 117 .
Since the height direction bead 260 is formed to extend from the first corner portion 113, the height direction bead 260 also contributes to the deformation resistance of the first corner portion 113 against the compressive stress (B) along the height direction Y, making the first corner portion 113 less likely to be crushed. Since the first corner portion 113 is less likely to be crushed, the upper portion of the side wall portion 215 connected to the first corner portion 113 is also less likely to be crushed. Since the first corner portion 113 and the side wall portion 215 are less likely to be crushed, a decrease in bending rigidity in the height direction Y of the cross section intersecting the longitudinal direction Z due to a decrease in the height of the structural member 200 is suppressed, and a decrease in the three-point bending characteristics in the local buckling mode can be prevented, which is preferable. Furthermore, when the height-direction bead 260 is formed so as to extend from the first corner portion 113 in this manner, a step is formed in the first corner portion 113 along the longitudinal direction Z between the portion of the bead bottom wall 262 of the height-direction bead 260 and the portion of the side wall portion 215 where the height-direction bead is not formed.

Furthermore, since the height direction bead 260 is formed to extend from the first corner portion 113 to the second corner portion 117, the height direction bead 260 also contributes to the deformation resistance of the second corner portion 117 against the compressive stress (B) along the height direction Y, and the second corner portion 117 is also less likely to be crushed. Therefore, since the first corner portion 113, the side wall portion 215, and the second corner portion 117 are less likely to be crushed, the decrease in bending rigidity in the height direction Y of the cross section intersecting the longitudinal direction Z due to the reduction in the height of the structural member 200 is further suppressed, and the decrease in the three-point bending characteristics in the local buckling mode can be further prevented, which is preferable.

The height direction bead 260, like the composite bead 150, may be molded simultaneously using the same mold when the top plate portion 111, the side wall portion 215, and the flange portion 119 are press molded, or may be molded using a different mold or tool before the top plate portion 111, the side wall portion 215, and the flange portion 119 are press molded.

As shown in FIG. 13 , the height direction bead 260 is formed by a pair of bead side walls 261 , 261 and a bead bottom wall 262 .
The pair of bead side walls 261, 261 are bent from the side wall portion 215 and extend inwardly.
The bead bottom wall 262 extends to connect the ends of the pair of bead side walls 261 , 261 opposite the side wall portion 215 .

As shown in FIG. 13, the height bead 260 has a predetermined depth d2 and a predetermined width w2.

The depth d2 of the height direction bead 260 is the distance in the width direction X from the outer surface of the side wall portion 215 to the outer surface of the bead bottom wall 262 in the height direction bead 260. If the height direction bead 260 has a shape whose depth changes along the height direction Y, the maximum value of the distance in the width direction X from the side wall portion 215 to the bead bottom wall 262 is defined as the depth d2.

The greater the depth d2 of the height direction bead 260, the greater the deformation resistance against the compressive stress (B) along the height direction Y that occurs in the side wall portion 215. Therefore, the depth d2 of the height direction bead 260 is preferably 2 mm or more, and more preferably 4 mm or more.

On the other hand, if the depth d2 of the height direction bead 260 is too large, the dimension in the width direction X of the structural member 200 becomes locally small, and the bending rigidity in the cross section intersecting the longitudinal direction Z becomes too small, so that the desired three-point bending characteristics may not be obtained. In addition, in a configuration in which the composite bead 150 is formed in the portion near the end of the width direction X of the top plate portion 111, if the depth d2 of the height direction bead 260 is too large, the composite bead 150 may not be formed at the desired position. Furthermore, if the depth d2 of the height direction bead 260 is too large, it may be difficult to mold the height direction bead 260 if the width w2 of the height direction bead 260 is relatively small. Therefore, the depth d2 of the height direction bead 260 is preferably 10 mm or less, and more preferably 8 mm or less.

The multiple height direction beads 260 are preferably formed with an inter-bead distance of 50 mm or less in the longitudinal direction Z of the side wall portion 215, and more preferably with an inter-bead distance of 30 mm or less. In this case, it is possible to further increase the deformation resistance against the compressive stress (B) along the height direction Y generated in the side wall portion 215. Note that the inter-bead distance means the distance between one end of the height direction bead 260 and the other end of the adjacent height direction bead 260, as shown in FIG. 13.

The plurality of height-direction beads 260 do not need to be formed over the entire length of the side wall portion 215 in the longitudinal direction Z, but may be formed over a portion of the entire length of the side wall portion 215 in the longitudinal direction Z. As positions at which the plurality of height-direction beads 260 are formed, positions at which the bending crushing characteristics of the structural member 200 should be most strengthened, for example, a position where the impactor comes into contact and its vicinity may be selected.
Furthermore, the multiple vertical beads 260 do not need to be formed side by side on the side wall portion 215 with equal bead-to-bead distances; for example, when three vertical beads 260 are formed, the two bead-to-bead distances may be different values.
Furthermore, the plurality of height direction beads 260 do not necessarily have to be formed at the same position in the longitudinal direction Z on the pair of side wall portions 215, 215. For example, at the same position in the longitudinal direction Z as the height direction bead 260 formed on one side wall portion 215, the height direction bead 260 does not have to be formed on the other side wall portion 215.

The width w2 of the height-wise bead 260 is the distance between the intersection of a virtual line extending the outer surface of one bead side wall 261 of the height-wise bead 260 with a virtual line extending the outer surface of the side wall portion 215, and the intersection of a virtual line extending the outer surface of the other bead side wall 261 of the height-wise bead 260 with a virtual line extending the outer surface of the side wall portion 215, in a cross section perpendicular to the height direction Y.
When the height direction bead 260 has a shape whose width changes along a direction intersecting the longitudinal direction Z, the separation distance in the cross section where the separation distance is maximum is defined as width w2.

The smaller the width w2 of the height direction bead 260, the higher the deformation resistance against the compressive stress (B) along the height direction Y generated in the side wall portion 215. Therefore, the width w2 of the height direction bead 260 is preferably 60 mm or less, and more preferably 40 mm or less.

On the other hand, if the width w2 of the height direction bead 260 is too small, and the depth d2 of the height direction bead 260 is relatively large, it may be difficult to mold the height direction bead 260. Therefore, it is preferable that the width w2 of the height direction bead 260 is 10 mm or more, and it is even more preferable that it is 15 mm or more.

As described above, the depth d2 and width w2 of the height direction bead 260 affect the deformation resistance to the compressive stress (B) along the height direction Y that occurs in the side wall portion 215. When the aspect ratio A2 calculated by the depth d2 to the width w2 of the height direction bead 260 (depth d2/width w2) is 0.05 or more and 1.0 or less, this is preferable because it can more reliably exert the effect of increasing the deformation resistance to the compressive stress (B) along the height direction Y that occurs in the side wall portion 215. It is even more preferable that the aspect ratio A2 is 0.1 or more and 0.5 or less.

According to the structural member 200 according to the present embodiment described above, when an impact load from the outside of the vehicle is input to the top plate portion 111 and bending deformation occurs in the structural member 200, it is possible to exert a composite deformation resistance against the compressive stress (A) along the longitudinal direction Z generated in the top plate portion 111, a deformation resistance against the compressive stress (B) along the height direction Y generated in the side wall portion 215, and a deformation resistance against the tensile stress (C) along the longitudinal direction Z generated in the joining member 120. In particular, it is possible to increase the deformation resistance against the compressive stress (B) along the height direction Y generated in the side wall portion 215. This improves the load resistance, especially at the beginning of the stroke, and improves collision safety performance.

Since the thinner the plate material, the lower the deformation resistance, the conventional method has been one of the barriers to weight reduction by using thin, high-strength materials. That is, even if the deformation resistance of the top plate against the compressive stress (A) along the longitudinal direction Z is increased by increasing the strength or designing the part shape, the structural member cannot exhibit good three-point bending characteristics if the thin-walled side wall easily buckles due to bending deformation, etc. Conversely, even if the deformation resistance of the side wall in the direction intersecting the longitudinal direction Z is increased by increasing the strength or designing the part shape, the structural member cannot exhibit good three-point bending characteristics if the thin-walled top plate easily buckles due to bending deformation, etc.
As described above, the structural member 200 of this embodiment can exert a composite deformation resistance at each portion, making it possible to exert excellent collision safety performance even when using a thin-walled, high-strength material.

(Example)
The effects of the present invention will be specifically described below with reference to examples. Note that the examples described below are merely examples of the present invention and do not limit the present invention.

A simulation model of a structural member was prepared, which was composed of a hat-shaped member made of steel plate with a thickness of 1.6 mm and a tensile strength of 1.5 GPa, and a joining member made of steel plate with a thickness of 0.8 mm and a tensile strength of 440 MPa, or a thickness of 1.6 mm and a tensile strength of 1.5 GPa.
A simulation model of the structural member was appropriately given a composite bead and a height-direction bead, and a simulation assuming three-point bending was performed to evaluate the maximum load at the beginning of the stroke and the absorbed energy up to a stroke of 100 mm. In addition, some three-point bending simulations were also performed in which a conventional concave bead was given instead of the composite bead as a standard or comparative example. The basic conditions were as follows. In this embodiment, the inclination angle of the bead side wall of the composite bead and the concave bead, which are longitudinal beads arranged on the top plate portion or the top plate facing portion, was 90° with respect to the top plate portion. In addition, in the three-point bending simulation, when the hat-shaped member was arranged facing the impactor side, a steel plate with a plate thickness of 0.8 mm and a tensile strength of 440 MPa was used for the joining member, and when the joining member was arranged facing the impactor side, a steel plate with a plate thickness of 1.6 mm and a tensile strength of 1.5 GPa was used for the joining member.
Width of top plate: 90mm
Side wall height H: 60 mm
Radius of curvature of first corner (inner side of bend): 5 mm
Curvature radius of the second corner (inner bend): 5 mm
Total length of structural member L: 800 mm
Spot welding: 40mm pitch Width of top plate facing part: 130mm
Longitudinal bead depth d1: 10 mm
Longitudinal bead width w1: 10 mm
Height direction bead depth d2: 5 mm
Height direction bead width w2: 24 mm
Distance between beads in the height direction: 16 mm

The three-point bending conditions were set as shown in FIG. 14, with the impactor's curvature radius being 50 mm and the support stand's separation distance being 700 mm.
Tables 1 to 4 show the evaluation results of the bead application conditions and the maximum load at the beginning of the stroke.

Experiment No. 1, Experiment No. 1A, and Experiment No. 1B are experimental data for confirming the effect of forming a composite bead on the hat-shaped member under three-point bending conditions in which the hat-shaped member is disposed facing the impactor side.
Experiment No. 1 was a benchmark and was an experimental example in which no longitudinally extending beads were formed.
Experiment No. 1A is an example of an experiment in which one recessed bead of a conventional shape was formed in the center of the top plate portion of the hat-shaped member.
Experiment No. 1B is an experimental example in which one composite bead of the present invention is formed in the center of the top plate portion of the hat-shaped member.

According to Experiment No. 1A, the maximum load was improved by 126% and the energy absorption amount was improved by 116% compared to Experiment No. 1.
On the other hand, in Experiment No. 1B, the maximum load was improved to 132% and the energy absorption amount was improved to 128% compared to Experiment No. 1.
Therefore, it was confirmed that the composite bead of the present invention exhibits superior collision safety performance compared to the conventional concave bead.

Experiment No. 2 and Experiment No. 2A are experimental data for verifying the effect of forming two composite beads on the ridge line side of the top plate portion of the hat-shaped component.
Experiment No. 2 was the evaluation standard, and was an experimental example in which two conventional concave beads were formed on the ridge line side of the top plate of the hat-shaped member.
Experiment No. 2A is an experimental example in which two composite beads of the present invention are formed on the ridge line side of the top plate portion of the hat-shaped member.

According to Experiment No. 2A, the maximum load was improved to 110% and the energy absorption amount was improved to 111% compared to Experiment No. 2.
Therefore, it was confirmed that by forming two composite beads of the present invention on the ridge side of the top plate, superior collision safety performance is exhibited compared to the case where two conventional concave beads are formed on the ridge side of the top plate.

Furthermore, Experiment No. 2B is an experimental example in which two composite beads of the present invention are formed on the ridge line side of the top plate of the hat-shaped member, and in addition, a height direction bead is formed on the side wall portion of the hat-shaped member.
According to Experiment No. 2B, the maximum load was improved to 149% and the energy absorption amount was improved to 146% compared to Experiment No. 2.
Therefore, it was confirmed that when two composite beads of the present invention are formed on the ridge line side of the top plate of the hat-shaped component, and a height-direction bead is formed on the side wall portion of the hat-shaped component, even better collision safety performance is achieved.

Experiment No. 3, Experiment No. 3A, and Experiment No. 3B are experimental data for confirming the effect of forming a composite bead on the portion of the joint member facing the top plate under three-point bending conditions in which the joint member is disposed facing the impactor side.
Experiment No. 3 was the evaluation standard, and was an experimental example in which no longitudinally extending beads were formed.
Experiment No. 3A is an example of an experiment in which one concave bead of a conventional shape was formed in the center of the portion of the joining member facing the top plate.
Experiment No. 3B is an example of an experiment in which one composite bead of the present invention is formed in the center of the portion of the joining member facing the top plate.

According to Experiment No. 3A, the maximum load was improved to 127% and the energy absorption amount was improved to 129% compared to Experiment No. 3.
On the other hand, in Experiment No. 3B, the maximum load was improved to 130% and the energy absorption amount was improved to 139% compared to Experiment No. 3.
Therefore, it was confirmed that the composite bead of the present invention exhibits superior collision safety performance compared to the conventional concave bead.

Experiment No. 4 and Experiment No. 4A are experimental data for confirming the effect of forming two composite beads on both sides of the joining member facing the top plate.
Experiment No. 4 is an evaluation standard, and is an experimental example in which two conventional concave beads are formed on both sides of the joining member facing the top plate.
Experiment No. 4A is an example of an experiment in which two composite beads of the present invention were formed on both sides of the top plate facing portion of the joining member.

According to Experiment No. 4A, the maximum load was improved to 111% and the energy absorption amount was improved to 105% compared to Experiment No. 4.
Therefore, it was confirmed that by forming two composite beads of the present invention on both sides of the top plate facing portion of the joining member, superior collision safety performance is exhibited compared to the case where two conventional concave beads are formed on both sides of the top plate facing portion of the joining member.

Furthermore, Experiment No. 4B is an experimental example in which, in addition to forming two composite beads of the present invention on both sides of the top plate facing portion of the joining member, a height direction bead is formed on the side wall portion of the hat-shaped member.
According to Experiment No. 4B, the maximum load was improved to 125% and the energy absorption amount was improved to 190% compared to Experiment No. 4.
Therefore, it was confirmed that when two composite beads of the present invention are formed on both sides of the top plate facing portion of the joining member, and a height-direction bead is formed on the side wall portion of the hat-shaped member, even better collision safety performance is achieved.

The present invention provides a structural member that can provide superior collision safety performance by improving the load-bearing capacity and impact energy absorption at the beginning of the stroke in local buckling mode deformation.

100, 100A, 100B, 100C, 100D, 200 Structural member 110, 210 Hat-shaped member 111 Top plate portion 113 First corner portion 115, 215 Side wall portion 117 Second corner portion 119 Flange portion 120, 120B Joint member 121 Joint portion 123, 123B Top plate opposing portion 150, 150A, 150B, 150C, 150D Composite bead 151 Bead side wall 153 Bead bottom wall 155 Bulging portion 155a Inclined portion 155b Central portion 260 Height direction bead 261 Bead side wall 262 Bead bottom wall A1, A2 Aspect ratio D1 Distance between first ends D2 Distance between second ends X Width direction Y Height direction Z Longitudinal direction

Claims (29)

A top plate portion extending in a longitudinal direction;
A pair of side walls extending through first corners formed at both ends of the top plate in a width direction;
a pair of flange portions extending through second corner portions formed at ends of the pair of side wall portions opposite to the first corner portions;
A hat-shaped member having
A pair of joints joined to the pair of flange portions of the hat-shaped member;
a top plate facing portion facing the top plate portion of the hat-shaped member;
A joining member having
Equipped with
A composite bead is formed on the top plate portion or the top plate opposing portion, the composite bead extending along the longitudinal direction,
The composite bead is
A pair of bead side walls extending inwardly from the top plate portion or the top plate opposing portion;
a pair of bead bottom walls extending from the pair of bead side walls in a bent manner toward each other;
a bulge formed between the pair of bead bottom walls;
Equipped with
In a cross section perpendicular to the longitudinal direction, the bulge portion has
a pair of inclined portions extending from first ends of the pair of bead bottom walls opposite the pair of bead side walls so that the distance between them increases toward the outside in a height direction;
a central portion connecting second ends of the pair of inclined portions opposite to the pair of bead bottom walls;
The width of the outer side of the bulge is 80% or more of the distance between the pair of bead side walls at the same height direction position.
A structural member for an automobile body. 2. The structural member for an automobile body according to claim 1, wherein two or more of the composite beads are formed in parallel in the width direction. 3. The structural member for an automobile body according to claim 1, wherein the composite bead is formed on the top plate portion of the hat-shaped member. A structural member of an automobile body as described in claim 3, characterized in that, in a cross section perpendicular to the longitudinal direction, the composite bead is formed so that its center in the width direction is located in the region from the boundary point between the top plate portion and the first corner portion to a point that is spaced apart in the width direction by 1/4 of the width of the top plate portion. A structural member of an automobile body as described in claim 3, characterized in that, in a cross section perpendicular to the longitudinal direction, the composite bead is formed so that the boundary point between the composite bead and the top plate portion is located in the region from the boundary point between the top plate portion and the first corner portion to a point spaced 20 mm apart. 6. A structural member for an automobile body as claimed in any one of claims 3 to 5, characterized in that an imaginary straight line connecting boundary points between the top plate portion and the bead side wall overlaps at least a portion of the central portion of the bulge portion. 7. A structural member for an automobile body according to claim 3, wherein the hat-shaped member is formed from a steel plate having a thickness of 1.2 mm or less. 8. A structural member for an automobile body according to claim 3, wherein the hat-shaped member is formed from a steel plate having a tensile strength of 980 MPa or more. 9. The structural member for an automobile body according to claim 3, wherein the hat-shaped member is a hardened member. 3. The structural member for an automobile body according to claim 1, wherein the composite bead is formed on the portion of the joining member facing the top plate. A structural member for an automobile body as described in claim 10, characterized in that, in a cross section perpendicular to the longitudinal direction, the composite bead is formed so that its center in the width direction is located in a region from the inner end of the joint of the joining member to a point that is spaced apart in the width direction by a distance of 1/4 of the width of the top plate opposing portion. 11. The structural member of an automobile body according to claim 10, characterized in that, in a cross section perpendicular to the longitudinal direction, the composite bead is formed so that a boundary point between the composite bead and the joining member is located in a region from an inner end of the joining portion of the joining member to a point spaced 20 mm apart. A structural member for an automobile body as described in any one of claims 10 to 12, characterized in that an imaginary straight line connecting the boundary points between the top plate opposing portion and the bead side wall overlaps at least a portion of the central portion of the bulge portion. 14. The structural member of an automobile body according to claim 10, wherein the joining member is formed from a steel plate having a thickness of 1.2 mm or less. 15. The structural member of an automobile body according to claim 10, wherein the joining member is formed from a steel plate having a tensile strength of 980 MPa or more. The structural member for an automobile body according to any one of claims 10 to 15, characterized in that the joining members are hardened members. The structural member for an automobile body according to any one of claims 1 to 16, characterized in that the first ends are in contact with each other. 18. The automotive vehicle body structural member of claim 17, wherein the first ends are fixed together. 19. The automobile body structural member according to claim 1, wherein the bulge and the bead side wall are in contact with each other. 20. The automotive vehicle body structural member according to claim 19, wherein the bulge and the bead side wall are fixed together. 21. The structural member of an automobile body according to claim 1, wherein the distance between the second ends is at least 1.2 times the distance between the first ends. The width of the composite bead is 5 mm to 20 mm;
22. A structural member for an automotive body according to any one of claims 1 to 21, characterized in that the depth of the composite bead is between 5 mm and 20 mm. 23. The structural member of an automobile body according to claim 1, wherein the aspect ratio calculated by depth/width of the composite bead is 0.25 to 4.0. A height direction bead extending along the height direction is formed on the side wall portion.
A structural member for an automobile body according to any one of claims 1 to 23. 25. The automotive vehicle body structural member of claim 24, wherein said elevational bead extends from said first corner portion. 25. The automotive vehicle body structural member of claim 24, wherein said elevational bead extends from said second corner portion. 25. The automotive vehicle body structural member of claim 24, wherein the elevational bead extends from the first corner to the second corner. The width of the height direction bead is 10 mm to 60 mm,
28. The structural member for an automobile body according to claim 24, wherein the depth of the bead in the height direction is 2 mm to 10 mm. 29. A structural member for an automobile body according to any one of claims 24 to 28, characterized in that an aspect ratio calculated by dividing the depth/width of the height direction bead is 0.05 to 1.0.

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