JP6790697B2 - Structural members and vehicles - Google Patents

Description

The present invention relates to a structural member having impact resistance and a vehicle using the same.

Structural members used as vehicle reinforcing members are required to have high strength and weight reduction. For example, International Publication No. 2005/058624 (Patent Document 1) discloses a metal tube for impact resistance, which is attached to the vehicle body of an automobile with a structure of supporting both ends. This metal tube has a full length or a partially bent part. The outer peripheral side of the bent portion is arranged so as to substantially match the impact direction applied to the vehicle body. This metal pipe has excellent impact resistance for vehicle body reinforcement as compared with a reinforcing member using a straight pipe.

International Publication 2005/08624

When thinning the structural members in order to reduce the weight, usually, the strength is also increased. The structural member bends when it receives an impact exceeding the yield strength, and the bent portion protrudes. When the structural member is thinned, the degree of protrusion when it is broken by an impact tends to increase. On the other hand, for example, when a structural member is used for a vehicle, the degree to which the structural member deformed by the impact of a collision bends and protrudes is preferably smaller. This is because the fact that the bent portion protrudes greatly means that energy absorption is locally generated, and that the energy absorption capacity of the member as a whole is small. Since the structural member absorbs the impact energy more efficiently, the impact energy applied to the occupants in the vehicle can be further suppressed.

Therefore, the present application discloses a structural member capable of efficiently absorbing impact energy and a vehicle using the structural member.

The structural member in the embodiment of the present invention is a tubular structural member having a quadrangular cross section. The structural member is a top surface portion corresponding to one side of a quadrangular side of the cross section, a pair of side walls extending from both ends of the top surface portion and facing each other, and a bottom portion facing the top surface portion. The side wall is provided with a bottom portion formed between the other end portion on the opposite side to the one end portion on the top surface side. Each of the pair of side walls has a low-strength region in a region from one end of the side wall to a position at a predetermined distance. The predetermined distance is 20 to 40% of the height of the side wall. The yield strength of the low-strength region is 60 to 85% of the yield strength at a position of half the height of the side wall.

According to the disclosure of the present application, it is possible to provide a structural member capable of efficiently absorbing impact energy when subjected to an impact.

FIG. 1A is a cross-sectional view of a structural member according to an embodiment of the present invention. FIG. 1B is a plan view of the structural member shown in FIG. 1A. FIG. 1C is a side view of the structural member shown in FIG. 1A. FIG. 2 is a diagram schematically showing a state of a collision test. FIG. 3 is a diagram showing deformation when an impact is applied to a structural member having a uniform strength distribution. FIG. 4 is a diagram showing deformation when an impact is applied to a structural member having a low strength region. FIG. 5 is a diagram for explaining the deformation behavior of a structural member having a uniform strength distribution. FIG. 6 is a diagram for explaining the deformation behavior of the structural member having the low strength region. FIG. 7A is a diagram showing how the structural member is deformed by receiving an impact load. FIG. 7B is a diagram showing how the structural member is deformed by receiving an impact load. FIG. 7C is a diagram for explaining the deformation behavior of the structural member having the low strength region. FIG. 8A is a diagram showing an example of H and Sh when R is formed on the shoulder portion. FIG. 8B is a diagram showing an example of H and Sh when recesses (grooves) are formed at both ends of the side wall. FIG. 8C is a diagram for explaining the height direction of the side wall when the top surface portion is tilted. It is a side view which shows the example of the structural member curved in the longitudinal direction. It is a side view which shows the example of the structural member curved in the longitudinal direction. It is a side view which shows the example of the structural member curved in the longitudinal direction. It is a side view which shows the example of the structural member curved in the longitudinal direction. FIG. 10 is a diagram showing an example of structural members arranged in a vehicle. FIG. 11 is a diagram showing a B-pillar composed of structural members in the present embodiment. FIG. 12 is a diagram showing an example of a vehicle having a vehicle body having a space frame structure. FIG. 13 is a diagram schematically showing the configuration of the analysis model in the simulation. FIG. 14 shows each dimension of the structural member used in the simulation. FIG. 15 is a graph showing the amount of deformation due to bending deformation when an impact is applied by changing the strength ratio between the low strength region and the other region. FIG. 16A is a diagram showing a cross-sectional shape of the structural member used in the analysis. FIG. 16B is a diagram showing the side shape of the structural member used in the analysis. FIG. 17 is a graph showing the analysis results. FIG. 18 is a diagram showing an analysis result of deformation behavior.

The structural member of the first configuration in the embodiment of the present invention is a tubular structural member having a quadrangular cross section. The structural member is a top surface portion corresponding to one side of a quadrangular side of the cross section, a pair of side walls extending from both ends of the top surface portion and facing each other, and a bottom portion facing the top surface portion. The side wall is provided with a bottom portion formed between the other end portion on the opposite side to the one end portion on the top surface side. Each of the pair of side walls includes a high-strength region including the center of the side wall in a direction perpendicular to the top surface portion and a low-strength region having a yield strength of 60 to 85% of the yield strength of the center of the side wall. The low-strength region extends from one end of the side wall to the other end at a distance of 20-40% of the height of the side wall in a direction perpendicular to the top surface. It is formed over a distance equal to or greater than the height of the side wall in the longitudinal direction of the side wall.

That is, the low-strength region in each of the pair of side walls is formed in a region from one end of the side wall to a position at a predetermined distance (a distance of 20 to 40% of the height of the side wall). That is, the low-strength region is formed from one end of the side wall over the boundary between the high-strength region and the low-strength region. The distance from one end of the side wall to the boundary of the boundary in the height direction of the side wall is 20 to 40% of the height of the side wall.

Further, the width of the low-strength region in each of the pair of side walls in the longitudinal direction of each side wall is equal to or larger than the width in the height direction of each side wall (that is, the height of the side wall).

In the first configuration, the height direction of each side wall is a direction perpendicular to the top surface portion. The height of the side wall is the distance from one end to the other end of the side wall in a direction perpendicular to the top surface. Also in the second and fourth configurations described later, the height direction of the side wall is the direction perpendicular to the top surface portion.

The longitudinal direction of each side wall is the longitudinal direction of the structural member and also the longitudinal direction of the top surface portion. The structural member is an elongated member having a longitudinal direction (major axis). The longitudinal direction of each side wall is the same as the extending direction of the ridge line (first ridge line) formed between each side wall and the top surface portion. The longitudinal direction of the side wall is substantially perpendicular to the height direction of the side wall.

The yield strength of the low-strength region in each of the pair of side walls is 60 to 85% of the yield strength of the center of the side wall in the direction perpendicular to the top surface portion. Here, the center of the side wall in the direction perpendicular to the top surface is at a position of half the height of the side wall.

The high-strength region is provided in the height direction of the side wall from the boundary between the low-strength region and the high-strength region to the other end of the side wall (the end on the bottom side).

The first configuration can be rephrased as the second configuration below. The structural member in the second configuration is a tubular structural member having a quadrangular cross section. The structural member includes a top surface portion corresponding to one side of a quadrangular side of the cross section, two first ridge lines at both ends of the top surface portion, a bottom portion facing the top surface portion, and both ends of the bottom portion. It is provided with two second ridges in the portion and two side walls located between the two first ridges and the two second ridges. Each of the two side walls is up to 20-40% of the distance between the first ridge and the second ridge in the direction perpendicular to the top surface from the first ridge to the second ridge. In addition, the first ridge line is provided in a region having a length equal to or longer than the distance between the first ridge line and the second ridge line in the direction perpendicular to the top surface portion in the extending direction of the first ridge line, and is perpendicular to the top surface portion. It comprises a low-strength region having a yield strength of 60-85% of the yield strength at the center of the side wall in the direction. The center of the first ridge line and the second ridge line is the same as the center of the side wall in the direction perpendicular to the top surface portion.

Each of the two side walls includes the low-strength region and a high-strength region having a higher yield strength than the low-strength region. The high-strength region is provided in a region perpendicular to the top surface of each side wall from the second ridgeline to the boundary between the low-strength region and the high-strength region. The central side wall of the side wall in the direction perpendicular to the top surface is included in the high strength region.

In the first and second configurations, the two side walls facing each other in the structural member have a high strength region including the center in the height direction of the side wall and a low strength region having a yield strength lower than the high strength region. Be prepared. The low-strength region extends from one end (first ridgeline) on the top surface side of each side wall to a position 20 to 40% of the height of each side wall, and the low-strength region of each side wall of the low-strength region. It is formed over a distance equal to or greater than the height of each side wall (that is, the distance in the direction perpendicular to the top surface from the first ridge line to the second ridge line) in the longitudinal direction (that is, the extending direction of the first ridge line). The inventors have found that such a low-strength region can increase the absorption efficiency of impact energy of a structural member when an impact is applied to the top surface portion. Specifically, when an impact is applied in the direction perpendicular to the top surface portion, the stress due to the impact is applied in the direction perpendicular to the impact direction in the low strength region formed in the region of 20 to 40% on the top surface portion side of each side wall. It was found that the deformation of the structural member can be suppressed by dispersing in the (longitudinal direction of the side wall) and utilizing the rigidity of the high strength region including the center of each side wall in the height direction. Further, by setting the yield strength of the low-strength region of each side wall to 60 to 85% of the yield strength at the central position in the height direction of each side wall, the impact energy absorption efficiency of the structural member can be set to the required level. It was found to be enhanced. That is, the structural members having the first and second configurations can efficiently absorb the impact energy when they receive an impact.

In the first or second configuration, it is desirable that the yield strength distribution of one side wall of the pair of side walls and the yield strength distribution of the other side wall have a mirror image relationship with each other. This is because the impact energy absorption efficiency when an impact is received from the top surface portion can be further enhanced by forming the intensity distribution of the pair of side walls facing each other in a mirror image relationship in the square tube.

In the first to third configurations, it is desirable that the tensile strength at the center position of the side wall in the direction perpendicular to the top surface portion is 980 MPa or more. This is because, in such a high-strength structural member, the effect of improving the absorption efficiency of impact energy can be preferably obtained.

In the first to fourth configurations, the structural member may be curved so as to be convex toward the top surface in the longitudinal direction. In this configuration, the structural member is less likely to bend when an impact load is applied to the top surface portion, as compared with the case where the structural member is not curved.

In the first to fifth configurations, it is desirable that the low-strength region is arranged at the center of the side wall in the longitudinal direction. The reason is as follows. The longitudinal center of the side wall is separated from both longitudinal ends. The vicinity of these both ends is often supported by being connected to other members. When a load is applied to the center while both ends are supported, the bending moment becomes large. By arranging the low-strength region in the center of the side wall in the longitudinal direction, the low-strength region is arranged at a position where deformation due to impact is likely to increase. As a result, the absorption efficiency of impact energy can be further increased. The longitudinal direction of the side wall is the extending direction of the first ridgeline between the side wall and the top surface.

In the first to sixth configurations, the top surface portion or the bottom portion may include at least two connecting portions that are connected to other members at positions separated from each other in the longitudinal direction of the side wall. It is desirable that the low strength region be centrally located between the at least two connecting portions in the longitudinal direction of the side wall. The reason is as follows. The center of the two connecting portions is separated from the position supported by the other member. When a load acts on the center of the two connecting portions, the bending moment increases. Therefore, in the structural member supported by at least two connecting portions, by providing the low strength region in the center of at least two connecting portions, the low strength region is arranged at a position where deformation due to impact is likely to be large. As a result, the absorption efficiency of impact energy can be further increased.

A vehicle including any of the structural members having the first to seventh configurations is also included in the embodiment of the present invention. In such a vehicle, it is desirable that the structural member is arranged so that the top surface portion is on the outside of the vehicle and the bottom portion is on the inside of the vehicle. As a result, when an impact is applied to the top surface of the structural member from the outside of the vehicle, the structural member can efficiently absorb the impact.

[Embodiment]
1A is a cross-sectional view of the structural member according to the embodiment of the present invention, FIG. 1B is a plan view of the structural member shown in FIG. 1A, and FIG. 1C is a side view of the structural member shown in FIG. 1A.

The structural member 10 shown in FIGS. 1A to 1C has a quadrangular cross section. The structural member 10 is formed in a tubular shape whose axial direction is the longitudinal direction. The structural member 10 has four walls corresponding to each side of a quadrangle in cross section.

As shown in FIG. 1A, the structural member 10 has a top surface portion 1a, a pair of side walls 1b, and a bottom portion 1c as the four walls. The top surface portion 1a corresponds to one of the four sides of the quadrangle in the cross section. The pair of side walls 1b extend from both ends of the top surface portion 1a and face each other. The bottom portion 1c faces the top surface portion 1a and is formed between the other end portions on the side opposite to one end portion on the top surface portion 1a side of the pair of side walls 1b. That is, the bottom portion 1c is formed between the other end portion of one side wall 1b of the pair of side wall 1b and the other end portion of the other side wall 1b.

In the configuration shown in FIG. 1, both ends of each of the four walls of the top surface portion 1a, the pair of side walls 1b, and the bottom portion 1c are continuous with the ends of the adjacent walls. That is, these four walls are composed of one continuous member. For example, the four walls of the structural member 10 can be welded pipes formed by deforming one plate material. In this case, the structural member 10 is a square tube formed by bending one plate material. The structural member 10 does not have a member (for example, a flange or the like) that protrudes outward from the outer circumference of the square pipe.

As shown in FIG. 1B, the boundary portion (shoulder portion) 1ab between the top surface portion 1a and the pair of side wall portions 1b forms a ridge extending in the longitudinal direction (hereinafter, referred to as a first ridge line 1ab). The first ridge line 1ab is a bent portion (bent portion) of the structural member 10. Both ends of the top surface portion 1a in the direction perpendicular to the longitudinal direction (x direction) form a pair of first ridge lines 1ab. A pair of side walls 1b extend from the pair of first ridge lines 1ab. The pair of side walls 1b extend in the same direction (z direction). That is, in the structural member 10, the dimensions in the extending direction of the ridge (first ridge line 1ab) formed by the top surface portion 1a and the pair of side walls 1b, that is, in the axial direction (y direction) of the pipe are such that the pair of side walls 1b face each other. It is longer than the dimension in the direction (x direction). The longitudinal direction of the structural member 10 is the same as the extending direction of the first ridge line 1ab formed between the top surface portion 1a and the side wall 1b.

As shown in FIGS. 1A and 1C, the boundary portion 1bc between the bottom portion 1c and each of the pair of side walls 1b forms a ridge extending in the longitudinal direction (hereinafter, referred to as a second ridge line 1bc). The second ridge line 1bc is a bent portion (bent portion) of the structural member 10. In each of the pair of side walls 1b, a second ridge line 1bc is formed at the other end of both ends of each side wall 1b, which is opposite to one end on the top surface portion 1a side. That is, the bottom 1c is formed between the pair of second ridges 1bc at each other end of the pair of side walls 1b.

As shown in FIGS. 1A and 1C, each of the pair of side walls 1b has a low-strength region 1s in a region from one end of the side wall 1b to a position at a distance Sh. The low-strength region 1s is a region having a lower strength than the periphery. In the pair of side walls 1b, the portion other than the low-strength region 1s is a high-strength region having a higher strength than the low-strength region 1s. In the height direction of each side wall 1b (direction perpendicular to the top surface portion 1a), the low-strength region 1s is located at a distance Sh from one end portion (first ridge line 1ab) on the top surface portion 1a side to the first ridge line 1ab. It is formed in the part up to the position. That is, there is a boundary 1sk between the low-intensity region 1s and the high-intensity region at a position at a distance Sh from the first ridge line 1ab. The distance between the boundary 1sk and the first ridge line ab in the height direction of the side wall 1b is the distance Sh. The portion from the boundary 1sk between the low-strength region 1s and the high-strength region to the second ridge line 1bc (bottom 1c) is the high-strength region.

Further, as shown in FIG. 1C, the low-strength region 1s is formed over a distance equal to or greater than the height H of the side wall 1b in the longitudinal direction of the side wall 1b (extending direction (y direction) of the first ridge line 1ab). Will be done. That is, the length Sn in the longitudinal direction of the side wall 1b of the low-strength region 1s is equal to or greater than the height H of the side wall 1b. Here, the height of the side wall 1b is from the first ridge line 1ab (one end portion of the side wall 1b) to the second ridge line 1bc (the other end portion of the side wall 1b) in the direction perpendicular to the top surface portion 1a (z direction). The distance is. As described above, the low-strength region 1s is provided from the first ridge line 1ab to the position of the distance Sh in the height direction of the side wall 1b, and in the longitudinal direction of the side wall 1b over a distance equal to or greater than the height H of the side wall 1b. ..

In this way, in the structural member 10, by providing the low-strength region 1s on a part of the side wall 1b on the top surface portion 1a side, the degree of deformation in the bending direction when an impact is applied to the structural member 10 is further reduced. be able to. This is based on the following findings obtained as a result of the inventors carefully observing the state of deformation of the structural member due to impact. The inventors conducted a collision test (simulation) in which an indenter collided with a structural member having a tubular structure having a quadrangular cross section, and observed the deformation behavior of the structural member. FIG. 2 is a diagram schematically showing a state of a collision test. In the collision test, the structural member 10a is placed over the two bases 12. The indenter 11 is made to collide with the structural member 10a at a position intermediate between the two bases 12.

FIG. 3 is a diagram showing deformation when an impact is applied to the structural member 10b having a uniform strength distribution. FIG. 4 is a diagram showing deformation when the same impact as in FIG. 3 is applied to the structural member 10c having the same low strength region as in FIGS. 1A to 1C. As shown in FIG. 3, in the case of the structural member 10b having a uniform strength distribution, the bent portion is bent so as to protrude sharply. This deformation mode is called folding. On the other hand, in the case of the structural member 10c having a low-strength portion on the side wall, as shown in FIG. 4, the impacted top surface portion and a part of the side wall extending from both ends thereof are crushed by the impact. This deformation mode is called cross-section collapse. Compared with the case of FIG. 3, in the case of FIG. 4, the area of the member that deforms when the same impact load is applied and contributes to the impact absorption is wider, and as a result, in the bending direction of the deformed portion of the structural member. The degree of protrusion is small.

FIG. 5 is a diagram for explaining the deformation behavior of the structural member 10b having a uniform strength distribution. FIG. 6 is a diagram for explaining the deformation behavior of the structural member 10c having a low strength region as shown in FIGS. 1A to 1C. 5 and 6 show a configuration seen from the side surface of the structural member, that is, the side wall side.

As shown in FIG. 5, in the structural member 10b having a uniform strength distribution, the deformation generated at the bending deformation starting point P due to the impact is the height of the side wall so that the top surface and the side wall are wedge-shaped in the side view. Proceed in the direction. As a result, it bends so as to project sharply in the bending direction (the height direction of the side wall). In some cases, the side walls may be cracked.

As shown in FIG. 6, in the structural member 10c having the low-strength region 1sc (the region indicated by the dots in FIG. 6) on the top surface side of the side wall, the deformation progressing inward from the bending deformation starting point P is the low-strength region 1sc. When the boundary is reached, it tends to proceed in the lateral direction (longitudinal direction of the structural member 10c) where the strength is relatively low, without going to the region where the strength is stronger than the low strength region 1sc. Therefore, the deformation spreads in the longitudinal direction, and the degree of deformation in the bending direction (height direction of the side wall) becomes small.

Further, when the structural member formed of a tubular structure having a quadrangular cross section is bent and deformed in the direction perpendicular to the top surface portion, the vicinity of the center in the height direction of the side wall is likely to break. That is, the vicinity of the position of half the height of the side wall is likely to be the starting point of bending deformation. 7A and 7B show a state in which a structural member 10d having a top surface portion 1da, a side wall 1db extending from both ends thereof, and a bottom portion 1dc facing the top surface portion 1da and continuous with the side wall 1db is deformed by an impact load. It is a figure. When an impact load is input to the top surface portion 1da, the angle of the shoulder portion of the structural member 10d (the bent portion at the boundary between the top surface portion 1da and the side wall 1db) is deformed, and the central region of the side wall 1db in the height direction is bent. As a result, the structural member 10d is crushed. In order to prevent the side wall 1db from being easily bent, the structural member 10 shown in FIGS. 1A to 1C has a high strength in the central region of the side wall 1b in the height direction.

That is, in the structural member 10, the strength of the position 1mid at the center (1/2) of the height of the side wall 1b is strengthened to some extent, and the center is closer to the top surface portion 1a than the position 1mid at the center in the height direction of the side wall 1b. A low-strength region 1s having a strength lower than that of the position 1mid is provided. By appropriately setting the range of the low-strength region 1s and the strength ratio of the low-strength region 1s to the central position 1mid in the height direction, it is possible to prevent the side wall 1b from being easily broken at the central position 1mid, and further. , The degree of crushing of the side wall 1b on the top surface portion 1a side from the central position 1mid in the longitudinal direction can be increased. As a result, as shown in FIG. 6, the deformation behavior can be such that the degree of deformation in the bending direction is reduced.

The deformation behavior shown in FIGS. 7A and 7B is not limited to the case where the indenter collides with the top surface of the structural member. For example, when the structural member is bent and deformed by an axial force that compresses it in the longitudinal direction, or when an indenter is pressed against the top surface and a force in the direction perpendicular to the longitudinal direction is statically applied as in a three-point bending test. Bending deformation can have the same deformation behavior.

Further, as shown in FIG. 6, the inventors have found that the width of the low-strength region 1s in the longitudinal direction (the extending direction of the first ridge line 2) is also important in order to reduce the degree of deformation in the bending direction. Has been found. FIG. 7C is a diagram for explaining the deformation behavior when the length Sn in the longitudinal direction of the low-strength region 1sc is made shorter than half (H / 2) of the height H of the side wall 1b. As shown in FIG. 7C, when the width of the low-strength region in the longitudinal direction is narrow, the deformation progressing inward from the bending deformation starting point P quickly reaches the boundary between the low-strength region 1sc and the high-strength region in the longitudinal direction. .. As a result, the collapse in the longitudinal direction is restricted, and the deformation in the height direction is likely to proceed.

As a result of bending tests and analysis of the structural member under various conditions, the inventors have found that when the structural member is bent and deformed, the range of deformation in the longitudinal direction is about the same as the height of the side wall. Furthermore, the inventors have found that by making the width of the low-strength region 1sc in the longitudinal direction equal to or greater than the height of the side wall, the deformation due to impact can be dispersed in the longitudinal direction and the degree of deformation in the bending direction can be reduced. ..

Based on the above findings, the inventors have come up with the idea of constructing the structural member 10 as follows. Each of the pair of side walls 1b shown in FIGS. 1A and 1C has a low-strength region 1s in a region from one end of the side wall 1b to a position at a distance Sh. The distance Sh of the low-strength region 1s of the side wall 1b can be 20 to 40% of the height H of the side wall 1b. The yield strength of the low-strength region 1s can be 60 to 85% of the yield strength at the position 1mid (that is, the position 1mid at the center in the height direction) which is half the height H of the side wall 1b.

That is, in the cross section of the structural member 10, 50% of the height H of the side wall 1b (that is, the side wall 1b) from the end of the side wall 1b on the top surface 1a side to a length of 20 to 40% of the height H of the side wall 1b. A low-strength region with a yield strength of 60 to 85% is continuous from the position (center in the height direction). In other words, the low-intensity region 1s is 20 to 20 to the distance between the first ridge 1ab and the second ridge 1bc in the direction perpendicular to the top surface 1a from the first ridge 1ab to the second ridge 1bc. It is provided up to the 40% position. The yield strength of the low-strength region 1s is 60 to 85% of the yield strength of the side wall 1b at the center of the first ridge line 1ab and the second ridge line 1bc.

As a result, for example, the deformation behavior when an impact is applied to the top surface portion 1a tends to cause the cross-sectional collapse as shown in FIG. As a result, the degree of bending deformation in the direction perpendicular to the top surface portion 1a can be reduced. In this way, when the structural member 10 receives an impact, it can absorb a larger impact energy with a small deformation. That is, the structural member 10 can efficiently absorb the impact energy.

Further, in the configurations shown in FIGS. 1A to 1C, the low strength region 1s is provided on both of the pair of side surfaces 1b of the structural member 10 facing each other. Therefore, when an impact is applied to the top surface portion 1a, the possibility that only one side surface 1b of the pair of side surface 1b is bent is reduced.

The distance Sh of the low-strength region 1s is more preferably 35% or less of the height H of the side wall 1b, and even more preferably 30% or less. Further, the distance Sh is more preferably 25% or more of the height H of the side wall 1b. The ratio (strength ratio) of the strength of the low-strength region 1s on the side wall 1b to the strength of the position 1mid at the center in the height direction is preferably 83% or less, and more preferably 80% or less. Further, this strength ratio is more preferably 70% or more.

It is desirable that the intensity distribution of one side wall of the pair of side walls 1b and the intensity distribution of the other side wall have a mirror image relationship with each other. This makes it less likely that one of the pair of side walls 1b will collapse first.

For example, in the example shown in FIG. 1, the distance Sh of the low-strength region 1s of one side wall 1b of the pair of side walls 1b and the distance Sh of the low-strength region 1s of the other side wall 1b facing each other are the same. Further, the pair of side walls 1b have the same height as each other, and the angle with the top surface portion 1a is also the same. Therefore, in the cross section perpendicular to the longitudinal direction shown in FIG. 1, the strength distribution of the structural member 10 is symmetrical with respect to the vertical bisector A of the top surface portion 1a. As a result, the bias of stress due to impact is reduced.

Further, the low-strength region 1s is preferably formed over a distance equal to or greater than the height H of the side wall 1b in the longitudinal direction of the side wall 1b. That is, the low-strength region 1s is provided in a region having a length equal to or longer than the distance between the first ridge line 1ab and the second ridge line 1bc in the extending direction of the first ridge line 1ab and in the direction perpendicular to the top surface portion 1a. .. As a result, it is possible to facilitate the deformation in the longitudinal direction and further suppress the displacement in the bending direction. The dimension of the first ridge line 1ab in the low-strength region 1s in the extending direction is preferably 1.5 times (3H / 2) or more the height of the side wall 1b, and twice the height of the side wall 1b (2H). ) It is more preferable to make the above.

It is desirable that the tensile strength at the position 1mid at the center of the side wall 1b in the height direction is, for example, 980 MPa or more (yield strength 500 MPa or more). As a result, the strength of the side wall 1b at the center position 1mid in the height direction can be secured, and the side wall 1b can be made difficult to break at this position 1mid. The region other than the low-strength region 1s of the structural member 10 can have the same strength as the position 1mid at the center in the height direction.

Between the first ridge line 1ab and the second ridge line 1bc, the region from the end of the low-strength region 1s to the second ridge line 1bc (flange 1c) is a high-strength region. The yield strength in the high-strength region is higher than the yield strength in the low-strength region 1s. The intensity distribution in the high intensity region does not have to be uniform.

A low-strength region may be provided in at least a part of the top surface portion 1a, or a low-strength region may not be provided in the top surface portion 1a. It has been found by the inventors that the influence of the strength of the side wall 1b is dominant in the bending deformation of the structural member 10. The strength of the top surface portion 1a has less influence on bending deformation than the strength of the side wall 1b.

As shown in FIG. 1A, the structural member 10 is opposite to the top surface portion 1a, a pair of side walls 1b that are bent from both ends of the top surface portion 1a and extend vertically, and one end of the pair of side walls 1b on the top surface portion 1a side. A bottom portion 1c that bends inward from the other end on the side and connects between the other ends of the pair of side walls 1b is provided. In the example shown in FIG. 1A, the side wall 1b is perpendicular to the top surface portion 1a and the bottom portion 1c. That is, the cross section of the surface of the structural member 10 perpendicular to the longitudinal direction is rectangular.

The configuration of the structural member 10 is not limited to the example shown in FIG. 1A. For example, the angle between the side wall 1b and the bottom 1c does not have to be 90 degrees (right angle). Similarly, the angle between the side wall 1b and the top surface portion 1a is not limited to 90 degrees (right angle). For example, the cross section of the structural member 10 perpendicular to the longitudinal direction may be trapezoidal. In this case, the cross-sectional shape is a symmetrical trapezoid, and the strength distributions of the pair of side walls 1b can be mirror images of each other. The cross-sectional shape may be a trapezoid that is not symmetrical. For example, the pair of side walls 1b may have different lengths. As a result, the top surface portion 1a and the bottom portion 1c do not have to be parallel.

Further, R (rounded or curved portion) may be formed in the cross-sectional shape of the corner (shoulder portion) that is the boundary between the side wall 1b and the top surface portion 1a. Similarly, R (rounded or curved portion) may be formed in the cross-sectional shape of the corner (shoulder portion) of the boundary between the side wall 1b and the bottom portion 1c. Further, at least one surface of the top surface portion 1a, the side wall portion 1b, and the bottom portion 1c can be a curved surface instead of a flat surface. That is, at least one of the top surface portion 1a, the side wall 1b, and the bottom portion 1c may be curved. If the radius of curvature of R at the angle between the side wall 1b and the top surface portion 1a is too large, the function of the side wall 1b to support the load in the height direction deteriorates. Therefore, the radius of curvature inside the R (curvature) of the corner between the side wall 1b and the top surface portion 1a is set to, for example, 15 mm or less. Alternatively, the radius of curvature inside the R (curvature) at the angle between the side wall 1b and the top surface portion 1a is set to, for example, one-third or less of the height H of the side wall 1b (R ≦ H / 3).

At least one of the pair of side walls 1b may be provided with a recess (groove), a protrusion (ridge), a step or a hole. The top surface portion 1a or the bottom portion 1c may be provided with a concave portion (groove), a convex portion (ridge), a step or a hole. However, the concave portions (grooves), convex portions (ridges), steps or holes provided on the top surface portion 1a, the side wall 1b or the bottom portion 1c shall be of a size that does not significantly affect the deformation behavior of the structural member 10. There is a need. For example, a convex portion may be formed on the top surface portion 1a.

When R (rounded or curved portion) is formed at the corner of the boundary between the side wall 1b and the top surface portion 1a or the corner of the boundary between the side wall 1b and the bottom portion 1c, among the portions where R is formed in the cross section perpendicular to the longitudinal direction. The height H of the side wall 1b and the distance Sh of the low-strength region are determined by setting the R stop (end of the curved portion) farther from the position 1mid at the center in the height direction of the side wall 1b as the end of the side wall 1b.

That is, the height H of the side wall 1b and the low-strength region 1s are set with the end (R stop) on the top surface 1a side of the curved portion (curved portion) between the side wall 1b and the top surface 1a as one end of the side wall 1b. The distance Sh in the height direction is determined. Further, the height H of the side wall 1b and the height of the low strength region 1s are set with the end (R stop) on the flange 1c side of the curved portion (curved portion) between the side wall 1b and the flange 1c as the other end of the side wall 1b. Determine the distance Sh in the direction.

Similarly, the height H of the side wall 1b and the distance Sh in the height direction of the low-strength region 1s are determined with reference to the first ridge line 1ab and the second ridge line 1bc. In this case, specifically, the first ridge line 1ab is the end (R stop) of the R (curved portion) between the side wall 1b and the top surface portion 1a on the top surface portion 1a side, that is, the R (curved portion). The R stop (the end of the curved portion) farther from the position 1mid at the center of the side wall 1b in the height direction. The second ridge line 1bc is the end (R stop) of the R (curved portion) between the side wall 1b and the flange 1c on the flange 1c side, that is, the position 1mid at the center of the side wall 1b of the R (curved portion) in the height direction. Let it be the R stop (the end of the curved part) farther from.

Here, the height of the side wall 1b is a dimension in the height direction from one end to the other end of the side wall 1b. In other words, the height of the side wall 1b is a dimension in the direction perpendicular to the top surface portion 1a from the first ridge line 1ab to the second ridge line 1bc of the side wall 1b. The distance Sh of the low-strength region 1s is a dimension in the height direction from one end of the side wall 1b to the boundary of the low-strength region 1s of the side wall 1b. That is, the distance Sh of the low-strength region 1s is a dimension in the direction perpendicular to the top surface portion 1a from the first ridge line 1ab to the boundary between the low-strength region 1s and the high-strength region of the side wall 1b. The position 1mid, which is half the height of the side wall 1b, is the central position in the height direction of the side wall 1b. That is, the position 1mid, which is half the height of the side wall 1b, is the position of the central side wall 1b of the first ridge line 1ab and the second ridge line 1bc in the direction perpendicular to the top surface portion 1a.

The height direction of the side wall 1b is perpendicular to the top surface portion 1a. Specifically, the direction perpendicular to the top surface portion 1a is the direction perpendicular to the plane of the surface of the top surface portion 1a. When the top surface portion 1a includes a concave portion, a convex portion, a step or a curved portion in a cross section perpendicular to the longitudinal direction, the direction perpendicular to the virtual plane connecting the two first ridge lines 1ab is defined as the direction perpendicular to the top surface portion. To do.

FIG. 8A is a diagram showing an example of the height H of the side wall 1b and the distance Sh of the low strength region 1s when R is formed on the shoulder portion. In the example shown in FIG. 8A, the height H of the side wall 1b is the dimension (height) in the z direction (direction perpendicular to the bottom 1c) from one end to the other end of the side wall 1b in the cross section of the structural member 10. The distance Sh of the low-strength region 1s is the dimension (height) of the low-strength region 1s of the side wall 1b in the z direction.

Even if the side wall 1b has a concave portion, a convex portion, a step or a hole (hereinafter referred to as a concave portion or the like), the portion where the concave portion or the like is formed in the cross section perpendicular to the longitudinal direction is from the central position 1mid of the side wall 1b. The height H of the side wall 1b and the distance Sh of the low-strength region are determined by using the far R stop (the end of the curved portion) as the end of the side wall 1b. FIG. 8B is a diagram showing an example of the height H of the side wall 1b and the distance Sh of the low strength region when recesses (grooves) are formed at both ends of the side wall 1b. In this case, in the cross section perpendicular to the longitudinal direction, the portion farthest from the center position 1mid of the side wall 1b (the end of the recess) is defined as the end of the side wall 1b. In the example shown in FIG. 8B, the dimension in the z direction from one end to the other end of the side wall 1b, that is, the height from the lowest position to the highest position of the side wall 1b is H, and the low strength region 1s of the side wall 1b. Let Sh be the height from the lowest position to the highest position.

FIG. 8C is a diagram for explaining the height direction of the side wall 1b when the top surface portion 1a is tilted. In the structural member 10 shown in FIG. 8C, the top surface portion 1a and the bottom portion 1c are not parallel to each other. Further, the lengths of one side wall 1br and the other side wall 1bh in the z direction are different. The height direction of the side walls 1br and 1bh is the direction perpendicular to the top surface portion 1a. The heights HL and HR of each side wall 1br and 1bh and the distances ShR and ShL from one end of each low-intensity region 1sr and 1sh (first ridge line 1bcr, 1bch) to the boundary 1skr and 2sk are the side wall 1br and 1bh. It is decided based on the height direction of. Therefore, the distance from one end (first ridge 1abr, 1anh) to the other end (second ridge 1bcr, 1bch) on the surface of the side wall 1br and 1b is different from the heights HR and HL.

In the above embodiment, at least one of the first ridge line and the second ridge line may be a curved line. For example, at least one of the first ridge and the second ridge may be curved in the height direction of the side wall or in the direction perpendicular to the side wall. Further, the height of the side wall (distance between the first ridge line and the second ridge line) may change in the longitudinal direction (extending direction of the first ridge line). When the height of the side wall differs depending on the position in the longitudinal direction, the height of the side wall that is the reference for the height distance Sh and the longitudinal distance Sn of the low-strength region is the height of the side wall in the portion where the low-strength region is formed. The average height.

In the example shown in FIG. 1B, the structural member 10 is formed so as to extend linearly in the longitudinal direction. On the other hand, the structural member 10 may be curved in the longitudinal direction. For example, the shape can be curved so as to be convex toward the top surface portion 1a side (z + direction) when viewed from the side surface (x direction). Further, the structural member 10 may be curved when viewed from above (z direction). Further, the width of the top surface portion 1a (the length in the direction perpendicular to the longitudinal direction (x direction)) does not have to be uniform. The height (length in the z direction) of the side wall 1b does not have to be uniform.

9A-9D are side views showing an example of the structural member 10 curved in the longitudinal direction. In the examples shown in FIGS. 9A to 9D, the structural member 10 is curved so as to be convex toward the top surface portion 1a side (z + direction) when viewed from the side surface (x direction). That is, the structural member 10 is curved so as to be convex toward the top surface portion 1a in the longitudinal direction. In FIG. 9A, the structural member 10 is curved with a constant curvature over the entire longitudinal direction. In FIGS. 9B and 9C, the curvature changes according to the position of the structural member 10 in the longitudinal direction. In FIG. 9D, the structural member 10 is curved in a part in the longitudinal direction.

By bending the structural member 10 so as to be convex from the bottom portion 1c toward the top surface portion 1a, when an impact load is input to the top surface portion 1a, it is not curved (a linear configuration in the longitudinal direction). ), The structural member 10 is less likely to bend.

[Example of application to vehicles]
A vehicle provided with the above structural member 10 is also included in the embodiment of the present invention. In the vehicle, the structural member 10 can be arranged so that the top surface portion 1a is on the outside of the vehicle and the bottom portion 1c is on the inside of the vehicle. That is, the structural member 10 is attached so that the impact input surface is on the outside of the vehicle. As a result, when an impact is received from the outside of the vehicle, the degree to which the structural member 10 protrudes inside the vehicle is reduced. Therefore, the possibility that the structural member 10 comes into contact with the device or person in the vehicle is reduced. For example, it is possible to prevent the structural member from breaking toward the inside of the cabin in the event of a collision. This further improves safety.

As described above, the structural member 10 may be curved so as to be convex toward the top surface portion 1a side. In this case, the top surface portion 1a can be arranged on the outside to support both ends of the structural member 10. As a result, the structural member 10 can be made difficult to break when an impact is received from the outside of the vehicle.

Further, the structural member 10 may be used in a state of being supported at two positions separated in the longitudinal direction. In this case, the structural member 10 has two connecting portions which are portions connected to other members. That is, the structural member 10 is supported by another member at the connecting portion. The connecting portion may also be referred to as a supporting portion. The connecting portion is provided on at least one of the side wall 1b, the top surface portion 1a, and the bottom portion 1c.

At the connecting portion, the structural member 10 is fixed to other members. The connecting portion of the structural member 10 is joined to another member by, for example, a fastening member or welding. The number of connecting portions may be three or more.

Further, the connecting portion may be configured to support the structural member 10 in a state of being inserted into the internal space of the structural member 10. For example, in the case of the structural member 10, a through hole may be formed in the bottom portion 1c, another member may be inserted through the through hole, and the end portion of the other member may be joined to the inner surface of the top surface portion 1a. In this way, the connecting portion may be provided inside the member of the top surface portion 1a of the structural member 10. Alternatively, a through hole may be formed in the top surface portion 1a, another member may be inserted through the through hole, and the end portion of the other member may be joined to the inner surface of the bottom portion 1c. In this way, the connecting portion may be provided inside the member of the bottom portion 1c of the structural member 10.

The low-strength region 1s is preferably provided between the two connecting portions. That is, it is preferable that at least a part of the low-strength region 1s is formed on the side wall 1b between the two connecting portions. As a result, it is possible to reduce bending deformation when an impact is applied to a portion of the structural member that is not supported by the connecting portion. Further, it is desirable that the low strength region 1s is provided at the center of the two connecting portions. That is, it is preferable that the low-strength region 1s is formed on the side wall 1b at the center of the two connecting portions. As a result, it is possible to increase the impact energy absorption efficiency at a position where a strong impact is likely to be applied. As a result, the degree of bending deformation of the structural member due to impact can be reduced.

Further, it is desirable to arrange the low strength region 1s at the center of the structural member 10 in the longitudinal direction. This is because the structural member 10 is connected to other members in the vicinity of both ends away from the center in the longitudinal direction. As a result, regardless of whether there is a connecting portion or not, in the structural member 10, the moment due to the impact is the largest and the portion that is easily broken (the center in the longitudinal direction of the structural member or the intermediate portion between the connecting portions) is broken. Deformation can be effectively suppressed.

As described above, the structural member 10 can be used for a high-strength vehicle structural member. The structural members for vehicles include, for example, A-pillars, B-pillars, side sills, roof rails, floor members, front side members, and other members that make up the vehicle body, and door impact beams, bumpers, and other vehicle bodies that are attached to the vehicle body from external impacts. Includes equipment inside the vehicle and members that protect the occupants. The vehicle structural member absorbs the impact energy at the time of a vehicle collision.

FIG. 10 is a diagram showing an example of structural members arranged in a vehicle. In the example shown in FIG. 10, the A pillar 15, the B pillar 16, the side sill 17, the roof rail 18, the bumper 19, the front side member 20, the door impact beam 21, the floor member 22, and the rear side member 23 are used as structural members for the vehicle. Be done. At least one of these vehicle structural members can be provided with a low-strength region 1s as in the structural member 10 described above.

FIG. 11 is a diagram showing a bumper 19 composed of structural members in the present embodiment. In the example shown in FIG. 11, the pumper-19 has a top surface 19a, a pair of side walls 19b, and a bottom 19c. A pair of side walls 19b extend from both ends in a direction perpendicular to the longitudinal direction of the top surface 19a so as to face each other. A bottom portion 19c is formed between one end of the pair of side walls 19b on the top surface portion 19a side and the other end on the opposite side. The top surface portion 19a, the pair of side walls 19b, and the bottom portion 19c are composed of one continuous plate material. The top surface portion 19a is arranged on the outside of the vehicle. The bottom 19c is located inside the vehicle. A low-strength region 19s is provided on a part of the side wall 19b on the top surface portion 19a side. The low-strength region 19s is provided in a region from the boundary between the top surface portion 19a and the side wall 19b to a position at a distance of 20 to 40% of the length between one end of the side wall 19b and the other end. The yield strength in the low-strength region 19s is 60 to 85% of the yield strength in the other regions (yield strength at the center position in the height direction of the side wall 19b).

The structural member 10 can be applied not only to a vehicle having a monocoque structure but also to a vehicle body having a frame structure. FIG. 12 is a vehicle having a vehicle body having a space frame structure disclosed in Japanese Patent Application Laid-Open No. 2011-37313. The vehicle body having a space frame structure includes a plurality of pipes 31 and joints 32 for connecting the pipes 31. The pipe 31 is arranged inside the body 30 that covers the surface of the vehicle body. The plurality of pipes 31 include a pipe extending in the vertical direction, a pipe extending in the front-rear direction, and a pipe extending in the left-right direction. At least a part of the plurality of pipes 31 can be formed of the steel pipe 1 described above. As described above, applying the steel pipe 1 to the pipe (pipe material) constituting the vehicle body having the space frame structure is effective because the pipe does not bend deeply inside the vehicle body where the occupant or the engine is located.

Structural members for vehicles that absorb impact energy are roughly classified into two types: those that are deformed by axial compression and those that are bent and deformed. An object that bends and deforms absorbs impact energy due to bending or cross-section collapse deformation. It is required to improve the impact energy absorption efficiency by using a high-strength material for members such as B-pillars and side sills. Therefore, the structural member 10 of the present embodiment is provided with an ultra-high strength steel having a tensile strength (tensile strength in a region other than the low strength region) of 980 MPa or more (yield strength of 500 MPa or more) at a position 1 mid in the center of the side wall 1b in the height direction. When applied, the above effects are noticeable. Further, by setting the strength of the central position 1mid of the side wall 1b of the structural member 10 (strength of a region other than the low strength region 1s) to 1 GPa or more in terms of tensile strength, more effect can be obtained.

The structural member 10 is not limited to a four-wheeled vehicle such as the automobile shown in FIG. 10, and can be used, for example, as a structural member of a two-wheeled vehicle. Further, the use of the structural member 10 is not limited to the vehicle. For example, the structural member 10 can be used as a structural member of an impact-resistant container, a building, a ship, an aircraft, or the like.

[Manufacturing process]
The structural member 10 can be entirely made of the same material. The structural member 10 can be formed of, for example, a steel plate. A tubular structural member (square tube) having a quadrangular cross section can be formed by bending one steel plate and joining one end of the steel plate and the other end facing each other by welding or the like. it can. When bending a square tube, for example, a bending method such as press bending, tensile bending, compression bending, roll bending, push-through bending, or eccentric plug bending can be used.

The manufacturing process of the structural member 10 includes a step of forming a low-strength region in the material. The method for forming the low-strength region is not particularly limited, but for example, the structural member 10 including the cured region can be produced by locally heating and quenching the material by a method such as laser or high-frequency heating. it can. In this case, the region where quenching is not performed is a low-strength region having relatively low strength. Further, after quenching to strengthen the entire square tube, partial annealing treatment can be performed to form a low-strength region.

Alternatively, the structural member 10 curved in the longitudinal direction can be produced by sequentially applying heating, bending moment, and cooling while moving the tubular member in the axial direction. In this method, an induction heating coil is arranged on the outer periphery of the tubular member to locally heat the tubular member to a plastically deformable temperature. A bending moment is applied by moving a movable gripping means such as a movable roller die provided on a tubular member downstream of the induction heating coil while moving the heating portion in the tubular direction. The portion curved in this way is cooled by a cooling device between the induction heating coil and the movable gripping means. In this step, for example, by making the heating and cooling conditions different in the outer peripheral direction of the tubular member, a low-strength region can be formed in the tubular member.

The method for manufacturing the structural member 10 is not limited to the above example. A tailored blank or other known method can be used to form the structural member 10 having a low strength region.

In this embodiment, the deformation of the structural member when the indenter is made to collide with the tubular structural member having a quadrangular cross section is analyzed by simulation. FIG. 13 is a diagram schematically showing the configuration of the analysis model in the simulation. In this simulation, the deformation behavior when the indenter 110 collides with the central portion in the longitudinal direction of the structural member 30 in a state where the structural member 30 is bridged between the two bases 120 is analyzed. The radius of curvature of the indenter 110 was 150 mm, and the initial velocity of the indenter was 4 m / sec.

FIG. 14 shows each dimension in the cross section perpendicular to the longitudinal direction of the structural member 30 used in the simulation. The structural member 30 has a top surface portion 3a, a pair of side wall portions 3b, and a bottom portion 3c. The pair of side walls 3b extend from both ends of the top surface portion 3a and face each other. The bottom portion 3c corresponds to the top surface portion 3a and is formed between the other end portion of the pair of side walls 3b on the side opposite to the top surface portion 3a side. Each of the pair of side walls 3b has a low-strength region 3s in a region from one end of the side wall 3b to a position at a distance Sh.

In FIG. 14, the height of the side wall is H = 50 mm, the width of the top surface (bottom) is W1 = 50 mm, and the plate thickness is t = 1.4 mm. A collision simulation was performed by changing the distance Sh in the low-intensity region 3s. Further, the collision simulation was performed by changing the intensities of the low intensity region 3s and the other regions. The length SL (see FIG. 13) in the longitudinal direction of the low-strength region 3s was set to H / 2.

FIG. 15 is a graph showing the amount of deformation due to bending deformation when an impact load is input by changing the strength ratio between the low strength region 3s and the other regions, where Sh = (2/5) H. In FIG. 15, the vertical axis indicates the amount of penetration (protrusion amount) of the structural member in the direction (z direction) perpendicular to the top surface portion 3a. The horizontal axis indicates the ratio (strength ratio = strength of the low-strength region / strength of the high-strength region) to the strength of the other high-strength region (= the center position 3mid of the side wall 3b) of the strength of the low-strength region 3s. In the graph of FIG. 15, the diamond plot shows the result when the yield intensity in the high intensity region is 120 kgf, and the square plot shows the result when the yield intensity in the high intensity region is 145 kgf.

In the section where the intensity ratio is 0.60 to 0.85, the amount of intrusion decreases as the intensity ratio increases (arrow Y1). In this section, the deformation mode is the cross-section collapse shown in FIG. In this section, when the strength of the low-strength region is low (strength ratio is 0.60 or less), the cross-section is deformed, but the intrusion amount is large and the intrusion amount is almost the same as when the strength ratio exceeds 0.85. It became. When the intensity ratio exceeded 0.85, the amount of intrusion increased sharply (arrow Y2). Further, when the intensity ratio was increased at an intensity ratio of 0.85 or more, the amount of penetration increased as the intensity ratio increased (arrow Y3). It is considered that this is because the deformation mode changed from the cross-sectional crush shown in FIG. 4 to the crease shown in FIG. 3 at the strength ratio of 0.85. As described above, when the strength of the low-strength region is too high (the strength ratio is high), it bends and deforms, and the amount of penetration becomes large. From the results of FIG. 15, it was confirmed that the strength ratio is preferably 60 to 85% and the strength ratio is more preferably 70 to 85% from the viewpoint of reducing the amount of bending deformation due to impact.

Table 1 below shows the deformation behavior when the strength ratio is 0.83 (yield strength in the low strength region is YP100 MPa, yield strength in other regions is YP120 MPa), and the height Sh in the low strength region is changed. Is shown. In Table 1, the up arrow represents the same value as the column directly above. Circles (◯) in the deformation behavior column indicate cross-sectional collapse shown in FIG. 4, and cross sections (x) indicate breaks shown in FIG.

In the results shown in Table 1 above, when the low intensity region is not provided (Sh = 0), Sh = H / 2 (Sh is 50% of H), and Sh = H / 10 (Sh is 10% of H). In the case of, the deformation behavior was broken (see FIG. 3). Deformation behavior when Sh = 2H / 5 (Sh is 40% of H), Sh = H / 3 (Sh is about 33% of H), and Sh = H / 5 (Sh is 20% of H). Was a crushed cross section (Fig. 4). From this result, by setting the distance Sh from one end of the side wall 3b of the low-strength region 3s on the top surface 3a side to 20 to 40% of the height H of the side wall 3b, the deformation behavior is regarded as a cross-sectional collapse and intrusion. It was confirmed that the amount could be reduced.

Further, in the analysis model shown in FIG. 13, the deformation behavior when the indenter 110 was made to collide was analyzed by further changing the strength distribution of the structural member. Specifically, the analysis was performed by changing the dimensions of the low-strength region 3s in the longitudinal direction (y direction). FIG. 16A is a diagram showing a cross-sectional shape of the structural member 30 used in the analysis. FIG. 16B is a diagram showing the side shape of the structural member 30 used in the analysis. As shown in FIG. 16A, the cross-sectional shape of the structural member 30 is trapezoidal. In FIG. 16A, the height of the side wall is H = 50 mm, the width of the top surface is W1 = 70 mm, the width of the bottom is W2 = 90 mm, the plate thickness is t = 1.4 mm, and the radius of curvature R = 5 mm inside the R of the first ridgeline. did. As shown in FIG. 16B, the height direction (z direction) of the low strength region 3s was set to H / 5. The analysis was performed by changing the dimensions of the low-strength region 3s in the longitudinal direction (y direction) to 0, 2H / 3, and 4H. That is, the simulation was performed under the conditions of case1 to case3 below. The yield stress in the low strength region 3s was set to 1100 MPa. The yield stress in the region other than the low strength region, that is, the high strength region was set to 1400 MPa.
case1: SL = 0, Sh = 0 (no low intensity region)
case2: SL = H / 3, Sh = H / 5
case3: SL = 2H, Sh = H / 5

FIG. 17 is a graph showing the analysis results of case1 to case3. FIG. 17 is a graph of load-stroke lines (FS lines) of cases 1 to case 3. The analysis result of FIG. 17 will be described. Under any of the conditions of case1 to case3, the value of the load with respect to the stroke is almost the same from 0 mm to 20 mm of the stroke. However, in Case 2, the load becomes lower than other conditions from around the stroke of 20 mm. In Case 2, the load peaks around the stroke of 25 mm, and then the load decreases as the stroke increases. This is because, in Case 2, the structural member broke around the stroke of 25 mm. In Case 1 and Case 3, Case 3 has a larger load peak stroke. This is because Case 3 broke with a higher stroke than Case 1. In Case 3, the load peak is higher and the stroke at which the load peak appears is larger than in other conditions because the structural member breaks after bearing the load while the cross section is crushed. Case 3 has the highest integration in the stroke of the load, which means the impact energy absorption performance of the structural member. From this, it was found that when the width of the low-strength region 3s in the longitudinal direction was set to the height of the side wall of 4H, the impact energy absorption efficiency was higher and the bending was suppressed than when the height of the side wall was set to 2H / 3.

FIG. 18 shows the analysis results of the deformation behavior of case 2 and case 3. In the analysis result shown in FIG. 18, in the case of case3 in which SL = 2H, the deformation spreads in the longitudinal direction and the bending is suppressed as compared with the case of case2 in which SL = H / 3. That is, the deformation modes of case3 and case2 are different. The deformation mode of case 3 is cross-section collapse. The deformation mode of case2 is folding.

Although one embodiment of the present invention has been described above, the above-described embodiment is merely an example for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and the above-described embodiment can be appropriately modified and implemented within a range that does not deviate from the gist thereof.

1a: Top surface 1b: Side wall 1c: Bottom 1s: Low strength region 10: Structural member

Claims (10)

Have a square cross-section, a structural member having no tubular flange projecting outwardly from the outer periphery of the rectangle,
The top surface corresponding to one side of the quadrangular side of the cross section and
A pair of side walls extending continuously from both ends of the top surface and facing each other,
A bottom portion facing the top surface portion, which is formed continuously with the other end portion between the other end portions on the opposite side of the one end portion continuous with the top surface portion of the pair of side walls. With,
Each of the pair of side walls has a uniform plate thickness and has a high strength region including the center of the side wall in a direction perpendicular to the top surface portion and a yield strength of 60 to 85% of the yield strength of the center of the side wall. The low-strength region includes a low-strength region, and the low-strength region includes 20 of the height of the side wall from the one end portion continuous with the top surface portion of the side wall toward the other end in a direction perpendicular to the top surface portion. It is formed up to a position at a distance of ~ 35% and in the longitudinal direction of the side wall over a distance equal to or greater than the height of the side wall, and the high-strength region has a higher yield strength than the low-strength region. wherein in a region from the other end to the boundary of the high intensity region and the low intensity regions in the longitudinal direction of the side wall, Ru provided over a distance of more than the height of the side wall, structural member. Have a square cross-section, a structural member having no tubular flange projecting outwardly from the outer periphery of the rectangle,
The top surface corresponding to one side of the quadrangular side of the cross section and
Two first ridges at both ends of the top surface and
The bottom facing the top surface and
Two second ridges at both ends of the bottom,
It is provided with two side walls continuous with the top surface and the bottom , respectively, located between the two first ridges and the two second ridges.
Each of the two side walls has a uniform plate thickness.
From the first ridge line between the continuous top surface portion and the side wall toward the second ridge line, 20 to 20 to the distance between the first ridge line and the second ridge line in the direction perpendicular to the top surface portion. The top surface portion is provided in a region having a length equal to or greater than the distance between the first ridge line and the second ridge line in a direction perpendicular to the top surface portion in the extending direction of the first ridge line up to 35%. A low-strength region having a yield strength of 60 to 85% of the yield strength at the center of the side wall in a direction perpendicular to the low-strength region and a high-strength region having a higher yield strength than the low-strength region, from the second ridgeline. A region extending to the boundary between the low-strength region and the high-strength region, the first ridge line and the second ridge line in a direction perpendicular to the top surface portion in the extending direction of the first ridge line. A structural member including a high-strength region provided in a region having a length equal to or longer than the above distance . A tubular structural member with a quadrangular cross section
The top surface corresponding to one side of the quadrangular side of the cross section and
A pair of side walls extending from both ends of the top surface and facing each other,
It is provided with a bottom portion facing the top surface portion and formed between the other end portions on the opposite side of the top surface portion side of the pair of side walls.
Each of the pair of side walls has a uniform plate thickness, and has a high strength region including the center of the side wall in a direction perpendicular to the top surface portion and a yield strength of 60 to 85% of the yield strength of the center of the side wall. The low-strength region includes a low-strength region, which is a distance of 20 to 35% of the height of the side wall from the one end of the side wall to the other end in a direction perpendicular to the top surface. It is formed up to the position and in the longitudinal direction of the side wall over a distance equal to or greater than the height of the side wall.
The low intensity regions in the longitudinal direction of the side wall, are provided at four times the length of the region of the height of the side wall, structural member. The structural member according to any one of claims 1 to 3, wherein the yield strength distribution of one side wall and the yield strength distribution of the other side wall of the pair of side walls are in a mirror image relationship with each other. The structural member according to any one of claims 1 to 4 , wherein the tensile strength at the center position of the side wall in the direction perpendicular to the top surface portion is 980 MPa or more. The structural member according to any one of claims 1 to 5 , wherein the structural member is curved so as to be convex toward the top surface portion in the longitudinal direction. The structural member according to any one of claims 1 to 6 , wherein the low-strength region is arranged at the center in the longitudinal direction of the side wall. The top or bottom comprises at least two connecting parts that are connected to other members at positions apart from each other in the longitudinal direction of the side wall.
The structural member according to any one of claims 1 to 7 , wherein the low-strength region is arranged at the center between the at least two connecting portions in the longitudinal direction of the side wall. The structural member according to any one of claims 1 to 8 , wherein the region other than the low-strength region has a higher yield strength than the low-strength region in the side wall having a uniform plate thickness. A vehicle including the structural member according to any one of claims 1 to 9.
The structural member is a vehicle in which the top surface portion is arranged on the outside of the vehicle and the bottom portion is arranged on the inside of the vehicle.