JP2023008339A - Vehicle skeleton member - Google Patents

Abstract

To facilitate an improvement effect of collision resistance performance per member unit mass by a high-strength material in a structure having a reinforcement member added to a hat-shaped member.SOLUTION: A vehicle skeleton member 10 has a hat-shaped member 1, a closing plate 2, a reinforcement member 6, and a plurality of welding parts 31. The hat-shaped member 1 has a first top plate 1a, two first vertical walls 1b and two flanges 1c. The reinforcement member 6 has a second top plate 6a and two second vertical walls 6b. A plurality of spot welding parts 31 join the first vertical wall 1b with the second vertical wall 6b. At least one of the hat-shaped member 1 and the reinforcement member 6 has a tensile strength exceeding 1.1 GPa. The whole of a HAZ softening part 31b of the spot welding part 31 on the vertical wall of the member having a tensile strength exceeding 1.1 GPa is positioned between a height position Lc of the center of the first vertical wall 1b and a ridge line 1ab between the first vertical wall 1b and the first top plate 1a, and is at a position that does reach an R-stop of the ridge line 1ab between the vertical wall and the top plate.SELECTED DRAWING: Figure 1

Description

The present invention relates to a vehicle frame member including reinforcing members.

For example, vehicle frame members such as B-pillars and side sills are required to have crash resistance. As a vehicle frame member, there is a case where a member having a hat-shaped cross section and a reinforcing member joined thereto is used. For example, in Japanese Patent Application Laid-Open No. 2013-189173 (Patent Document), a first molded body having a hat-shaped cross-sectional shape and a second molded body having a groove-shaped cross-sectional shape are closely attached to each other. A structural member is disclosed. By setting the cross-sectional peripheral length of the vertical wall portion of the second molded body to a specific range with respect to the cross-sectional peripheral length of the vertical wall portion of the first molded body, the vertical wall portion of the first molded body can be formed at an early stage. Buckling is prevented.

JP 2013-189173 A

In the above-described prior art, it is taught about the relationship between the strength of a member having a hat-shaped cross-sectional shape (hereinafter referred to as a hat-shaped member) and the reinforcing member, and the arrangement of the HAZ softened portion around the spot welding that joins them. not The inventors studied improving the collision resistance performance per unit mass of the member by forming the hat-shaped member and the reinforcing member from a high-strength material. The collision resistance performance per unit mass of a member is represented by, for example, the maximum load and energy absorption amount per unit mass of the member at the time of collision. In the study, it was found that when at least one of the hat-shaped member and the reinforcing member is formed of a high-strength material, the HAZ softened portion of the spot welding that joins the reinforcing member and the hat-shaped member tends to be the starting point of fracture. Hereinafter, the fracture originating from such a HAZ softened portion is referred to as HAZ fracture. Occurrence of HAZ fracture can be a factor that reduces the effect of improving impact resistance performance per unit mass of a member by using a high-strength material.

In the present application, a reinforcing member is added to the hat-shaped member, and in a structure using a high-strength material for at least one of the hat-shaped member or the reinforcing member, by suppressing the occurrence of HAZ fracture, the per unit mass of the member made of the high-strength material Disclosed is a vehicle frame member that can more easily obtain an effect of improving collision resistance performance.

A vehicle frame member according to an embodiment of the present invention includes a hat-shaped member, a closing plate, a reinforcing member, and a plurality of spot welds.
The hat-shaped member comprises a first top plate, two first vertical walls and two flanges. The first top plate is arranged between the two first vertical walls. The first vertical wall is arranged between the first top plate and the flange. The flange is joined with the closing plate.
The reinforcing member comprises a second top plate and two second vertical walls. The second top plate is arranged between the two second vertical walls.
The first vertical wall and the second vertical wall are superimposed. The plurality of spot welds join the first vertical wall and the second vertical wall.
At least one of the hat-shaped member and the reinforcing member has a tensile strength greater than 1.1 GPa.
Of the hat-shaped member and the reinforcing member, the entire HAZ softened portion of the plurality of spot welds in the vertical wall of the member having a tensile strength exceeding 1.1 GPa is in the direction perpendicular to the surface of the flange, the second It is located between the central height position of the vertical wall and the R stop on the first vertical wall side of the ridgeline between the first vertical wall and the first top plate, and has a tensile strength of 1.1. It is located at a position that does not reach the R stop on the vertical wall side of the ridge between the vertical wall of the member and the top plate exceeding 1 GPa.

According to the disclosure of the present application, a reinforcing member is added to the hat-shaped member, and in a structure using a high-strength material for at least one of the hat-shaped member or the reinforcing member, by suppressing the occurrence of HAZ fracture, the member unit made of high-strength material It becomes easier to obtain the effect of improving the collision resistance performance per mass.

It is a sectional view showing composition of a structural member in this embodiment. FIG. 2 is an enlarged view of the vertical wall of FIG. 1 near a spot weld; 2 is a side view of the structural member shown in FIG. 1; FIG. FIG. 2 is a diagram showing the hardness distribution of spot-welded portions of the structural member shown in FIG. 1; FIG. 3 is a cross-sectional view showing a modification of the structural member shown in FIG. 1; FIG. 4 is a cross-sectional view showing another modification of the structural member shown in FIG. 1; It is a figure which shows the application example to the vehicle frame|skeleton of the structural member in this embodiment. It is a figure which shows the four-point bending model in this analysis example. FIG. 9 is a diagram showing a model used for the four-point bending model of FIG. 8; FIG. 10 shows the stress field resulting from a four-point bending simulation performed on the model shown in FIG. 9; FIG. 10 is a graph showing the load-displacement relationship and the maximum load per unit mass as a result of running a four-point bending simulation on the model shown in FIG. 9; FIG. 10 is a graph showing the maximum load per member unit mass of the model shown in FIG. 9; FIG. FIG. 10 is a graph showing the amount of energy absorbed per unit mass of the member of the model shown in FIG. 9; FIG. It is a figure which shows the size of the test piece used for the measurement of tensile strength.

The inventors have studied a configuration in which a closed cross-section structure including a hat-shaped member and a closing plate is reinforced with a groove-shaped reinforcing member as a vehicle frame member. When at least one of the hat-shaped member and the reinforcing member is a high-strength member such as a hot-stamped material or a cold-pressed ultra-high tensile strength material, and the joining of the reinforcing member and the hat-shaped member is by spot welding, It was found that a HAZ softened portion was present in the spot welded portion. The HAZ softened portion is a region softened by thermal influence (tempering) during welding. For example, in a 1.5 GPa-class hot stamp material, the hardness of the base material is about 450 HV in Vickers hardness, while the hardness of the most softened portion of the HAZ softened portion is reduced to about 300 HV.

As a result of investigation, the inventors found that when a high-strength member exceeding 1.1 GPa is used as a vehicle frame member, strain is concentrated in the HAZ softened portion when a large tensile force is applied to the spot welded portion during a collision. It was found that the member breakage is more likely to occur when When such HAZ fracture occurs, the effect of improving the collision resistance per unit mass of the member by using a high-strength member is diminished. It becomes difficult to exhibit the improvement effect.

As a result of further trial and error, the inventors set the HAZ softened portion of the spot welded portion in the high-strength member exceeding 1.1 GPa to the top plate side of the hat-shaped member from the height of the center of the vertical wall of the hat-shaped member. It was found that HAZ fracture can be suppressed by arranging it in a region that does not reach the R stop on the vertical wall side of the ridgeline between the vertical wall and the top plate in a high-strength member exceeding 1.1 GPa. .

A vehicle frame member according to an embodiment of the present invention includes a hat-shaped member, a closing plate, a reinforcing member, and a plurality of spot welds.
The hat-shaped member comprises a first top plate, two first vertical walls and two flanges. The first top plate is arranged between the two first vertical walls. The first vertical wall is arranged between the first top plate and the flange. The flange is joined with the closing plate.
The reinforcing member comprises a second top plate and two second vertical walls. The second top plate is arranged between the two second vertical walls.
The first vertical wall and the second vertical wall are superimposed. The plurality of spot welds join the first vertical wall and the second vertical wall.
At least one of the hat-shaped member and the reinforcing member has a tensile strength greater than 1.1 GPa.
Among the hat-shaped member and the reinforcing member, the vertical wall of the member having a tensile strength exceeding 1.1 GPa (the tensile strength of the portion other than the spot welded portion of the first vertical wall and the second vertical wall is 1 .The entire HAZ softened portion of the plurality of spot welds in the vertical wall exceeding 1 GPa) is located at the height of the center of the first vertical wall and the first vertical wall in the direction perpendicular to the plane of the flange. The vertical wall and the top plate (first top plate and the second top plate whose tensile strength exceeds 1.1 GPa) does not reach the R stop on the vertical wall side of the ridgeline.

According to the above configuration, by using a material of more than 1.1 GPa for at least one of the hat-shaped member and the reinforcing member, and by setting the spot welded portion and the HAZ softened portion to the above arrangement configuration, the first top plate It is possible to suppress HAZ breakage in a high-strength member at the time of collision with load. This makes it easier to obtain the effect of improving the collision resistance performance per unit mass of the member by using the high-strength member. As a result, it is possible to realize a collision resistant member with high mass efficiency.

More specifically, in the above configuration, between the central height position of the first vertical wall of the hat-shaped member and the R stop on the first vertical wall side of the ridgeline between the first vertical wall and the first top plate , the entirety of the HAZ softening of multiple spot welds in the longitudinal walls of members with a tensile strength greater than 1.1 GPa. Here, the HAZ softened portion is defined as a region in which the Vickers hardness is 30 HV or more smaller than the Vickers hardness of the member around the nugget of the spot welded portion. A spot weld includes the nugget and its surrounding heat affected zone (HAZ). The HAZ softening zone is included in the heat affected zone. A nugget is the part that melts during welding. The center of the spot-welded portion is the center of the nugget viewed from the plate thickness direction of the first vertical wall.

When a load is applied to the first top plate due to a collision, the vehicle frame member receives a bending moment and deforms. Due to this bending moment, compressive bending is applied to the first top plate side and tensile bending is applied to the closing plate side. In the region on the side of the first top plate from the center of the height of the first vertical wall, both the first vertical wall and the second vertical wall tend to generate compressive force in the longitudinal direction. That is, in the above region, no or a small tensile force in the longitudinal direction tends to occur. By arranging the spot welded portions as described above, a compressive force rather than a tensile force is likely to be generated in the HAZ softened portion during a collision. When a large longitudinal tensile force is applied to the HAZ softened portion, HAZ fracture is likely to occur in the HAZ softened portion, whereas HAZ fracture does not occur even if a longitudinal compressive force is applied to the HAZ softened portion. Hateful. Therefore, HAZ fracture is suppressed in the member having a tensile strength exceeding 1.1 GPa due to the arrangement structure of the spot welding. As a result, the collision resistance per unit mass of the vehicle frame member can be improved.

The position of the height of the center of the first vertical wall is such that the first vertical wall and the first vertical wall are separated from each other in a cross section on a plane passing through the center of each of the plurality of welding spots and perpendicular to the longitudinal direction of the hat-shaped member. The center of the first vertical wall is defined as the height of the first vertical wall from the R stop on the first top plate side of the ridge between the top plates to the R stop on the flange side of the ridge between the first vertical wall and the flange. shall determine the position of the height of the The height direction of the first vertical wall is the direction perpendicular to the surface of the flange extending from the first vertical wall via the ridgeline in the cross section. That is, let the height of the part including the ridgeline of the both ends of a 1st vertical wall be the height of a 1st vertical wall. More specifically, the height of the first vertical wall is from the R stop at the boundary between the lower surface of the flange and the ridgeline in the direction perpendicular to the surface of the flange extending from the first vertical wall through the ridgeline to the height of the first top plate. It is the dimension up to the R stop at the boundary between the top surface and the ridge line. If the upper and lower surfaces of the flange are not parallel, the direction perpendicular to the lower surface of the flange shall be the direction perpendicular to the plane of the flange. In addition, the above upper surface and lower surface are the upper surface and the lower surface when the vertical direction is defined with the first vertical wall as the reference, the first top plate as the upper side, and the flange as the lower side in the height direction of the first vertical wall. . Also, the height of the first vertical wall is determined for each of the two first vertical walls in one hat-shaped member. Let the height of each 1st vertical wall be the height of the part including the ridgeline of the both ends of each 1st vertical wall.

In the spot-welded portion, a region in which the Vickers hardness is lower than the Vickers hardness of the member by 30 HV or more is defined as the HAZ softened portion. The Vickers hardness of the member is the Vickers hardness of the portion of the member other than the spot-welded portion. The HAZ softened portion in the vertical wall of the hat-shaped member or the reinforcing member has a Vickers hardness lower than that of the portion other than the spot-welded portion of the vertical wall by 30 HV or more. Among the hat-shaped member and the reinforcing member, the Vickers hardness of the vertical wall of the member having a tensile strength exceeding 1.1 GPa is the first vertical wall and the The interface of the second vertical wall (if there is a small gap between the first vertical wall and the second vertical wall, the It shall be measured at a position 1/4 of the plate thickness from the surface in contact with the gap) to the direction of the first vertical wall or the second vertical wall where the tensile strength exceeds 1.1 GPa. Vickers hardness is measured according to the Vickers hardness test method specified in JIS Z 2244-1:2020. Vickers hardness measurement conditions are a load (test force) of 3 N and a measurement pitch of 0.5 mm. The Vickers hardness of the member is measured at five points separated by 10 mm or more from the spot weld. Let the average value of the Vickers hardness measured at these five points be the Vickers hardness of the member.

The tensile strength of the hat-shaped member and the reinforcing member is the tensile strength obtained by measuring the test piece taken from the portion excluding the spot welded portion of the hat-shaped member and the reinforcing member, and other portions where the strength has changed locally. Strengthen. The test piece is an ASTM half-size test piece shown in FIG. The unit of numerical values for the dimensions shown in FIG. 14 is mm. The thickness of the test piece shall be the thickness of the member. The tensile strength is measured by a tensile test at a tensile speed (crosshead displacement speed) of 10 mm/min according to JIS Z 2241 (2011). Specimens may be taken from either the vertical wall or the top plate. In the form in which the tensile strength of the member exceeds 1.1 GPa, in addition to the case where the tensile strength exceeds 1.1 GPa in all regions except the spot welded portion of the member, a part of the member has a slight 1.1 GPa. A case where the tensile strength as a whole of the member can be regarded as having strength equivalent to exceeding 1.1 GPa, even though there are minute regions where the tensile strength does not exceed 1.1 GPa, is also included.

The R stop on the vertical wall side of the ridgeline between the vertical wall and the top plate in the hat-shaped member or reinforcing member is rounded between the vertical wall and the top plate in the cross section perpendicular to the ridgeline of the hat-shaped member or reinforcing member It is the end on the vertical wall side (not the top plate side) of both ends of the portion, that is, the R-shaped portion (R portion). In addition, in the state in which the two members are superimposed, the two members are in contact at least partially.

In the above configuration, the tensile strength of the reinforcing member may exceed 1.1 GPa, and the tensile strength of the hat-shaped member may be 1.1 GPa or less. As a result, the hat-shaped member has a tensile strength of 1.1 GPa or less to ensure ductility, and a portion where it is desired to increase deformation resistance (difficulty in deformation) against a collision load has a tensile strength of more than 1.1 GPa. of reinforcing members can be arranged. As a result, it is possible to properly arrange the portion that is made ductile to make the material less likely to break and the portion that is made less deformable by the reinforcing member, thereby further improving the crash resistance performance as a whole. Further, it is possible to further suppress the occurrence of breakage (HAZ breakage) originating from the softened HAZ portion in the spot-welded portion of the first vertical wall of the hat-shaped member.

For example, the tensile strength of the hat-shaped member may be 980 MPa or more and less than 1.1 GPa. This makes it easier for the hat-shaped member to have appropriate strength and to ensure ductility. Material fracture can be suppressed by ensuring ductility.

In the above configuration, the tensile strength of both the hat-shaped member and the reinforcing member may exceed 1.1 GPa. As a result, the vehicle frame member as a whole can ensure higher collision resistance performance.

A ridge line between the first vertical wall and the first top plate in a direction perpendicular to the flange face in a cross section on a plane passing through the center of each of the plurality of spot welds and perpendicular to the longitudinal direction of the hat-shaped member It is preferable that the distance from the R stop on the side of the vertical wall to the end of the second vertical wall is one-third or less of the height of the first vertical wall. Thereby, the spot-welded portion can be arranged at a position close to the ridge line between the first vertical wall and the first top plate and not interfering with the anti-collision performance. As a result, it is possible to further improve the collision resistance per unit mass of the vehicle frame member against the bending of the vehicle frame member due to a collision. From this point of view, it is more preferable that the distance is equal to or less than a quarter of the height of the first vertical wall.

When a vehicle frame member including a hat-shaped member and a reinforcing member is collided from the top plate side, the vehicle frame member receives a bending moment due to the impact load that causes compression bending on the top plate side. The inventors have found that the top plate and the ridgeline are mainly responsible for bearing the load in the deformation due to the collision load. In such bending deformation, the degree of contribution of the vertical wall to the load resistance is considered to be lower than that of the top plate and the ridge line. In addition, when the tensile strength of at least one of the hat-shaped member and the reinforcing member exceeds 1.1 GPa, the spot welded portion is arranged at a position close to the ridgeline, thereby making it difficult for the spot welded portion to separate during cross-sectional deformation. The inventor has found that this makes it difficult for the reinforcing member to come off from the hat-shaped member. Based on this knowledge, by arranging the spot welds near the ridgeline, the stress in the peeling direction (perpendicular to the vertical wall) applied to the spot welds can be reduced, and the peeling of the spot welds can be reduced. can be suppressed. This improves the energy absorption during the deformation period after the maximum load is reached. It should be noted that the higher the strength of the member, the more likely it is that the spot-welded portion will peel off. Therefore, in a configuration in which the tensile strength of at least one of the hat-shaped member and the reinforcing member exceeds 1.1 GPa, the effect of suppressing separation due to the above arrangement of the spot welded portions becomes more pronounced. In a configuration in which the tensile strength of both the hat-shaped member and the reinforcing member exceeds 1.1 GPa, peeling of spot welding is more likely to occur than in a configuration in which only one of the tensile strength exceeds 1.1 GPa. , the effect of suppressing peeling by the arrangement of the spot-welded portions becomes more pronounced.

From the viewpoint of the maximum load and energy absorption per unit mass of the member, from the R stop on the vertical wall side of the ridgeline between the first vertical wall and the first top plate in the cross section to the end of the second vertical wall is preferably 10 to 50 mm, for example. From the same point of view, the minimum value of this distance is more preferably 15 mm or more, more preferably 20 mm or more. Moreover, the maximum value of this distance is more preferably 40 mm or less, and even more preferably 30 mm or less. In addition, the center of the plurality of welding spots is located 5 to 15 mm from the R stop on the vertical wall side of the ridgeline between the vertical wall and the top plate of the hat-shaped member and the reinforcing member whose tensile strength exceeds 1.1 GPa. Preferably. As a result, the spot-welded portion can be arranged at a position close to the ridgeline while avoiding reaching the softened portion of the HAZ and the ridgeline.

It is preferable that the centers of the plurality of spot-welded portions are positioned 5 to 15 mm from the end of the second vertical wall of the reinforcing member. Here, the end portion of the second vertical wall of the reinforcing member is the end portion on the side opposite to the ridge line between the second vertical wall and the second top plate with respect to the spot welded portion. That is, the spot weld is arranged between the end of the reinforcing member and the ridgeline. The ridgeline side portion from the spot welded portion to the ridgeline between the second vertical wall and the second top plate of the reinforcing member contributes to the load bearing performance to some extent. On the other hand, it is considered that the end portion side portion from the spot welded portion to the end portion of the second vertical wall of the reinforcing member contributes less to the load bearing performance. Therefore, by reducing the size of the end portion side portion, it is possible to improve the load bearing performance with respect to the weight of the vehicle frame member. On the other hand, from the viewpoint of ensuring the joint strength of the spot welds, it is preferable to ensure a sufficient area for the spot welds in the reinforcing member. From these points of view, the inventor has come up with a configuration in which the centers of the plurality of spot-welded portions are provided at positions 5 to 15 mm from the end of the second vertical wall of the reinforcing member.

The end of the second vertical wall of the reinforcing member is positioned between the central height position of the first vertical wall and the ridge line between the first vertical wall and the first top plate in the direction perpendicular to the plane of the flange. may be The inventors have found that it is important that the first top plate does not buckle against the bending moment at the time of collision when a load is applied to the first top plate. We find that strengthening the vicinity is effective. The end of the reinforcing member is positioned between the central height of the first vertical wall and the ridgeline between the first vertical wall and the first top plate. The weight of the reinforcing member can be suppressed while ensuring a high height. Furthermore, the portion of the second vertical wall closer to the ridge line than the spot welded portion contributes to load bearing performance more than the portion of the second vertical wall closer to the flange than the spot welded portion. Therefore, in addition to the arrangement of the ends of the second vertical wall described above, the centers of the plurality of spot-welded portions are provided at positions 5 to 15 mm from the ends of the second vertical walls of the reinforcing member. It is possible to further enhance the effect of reducing the weight of the reinforcing member while ensuring higher load performance.

Of the hat-shaped member and the reinforcing member, the HAZ softened portion of the vertical wall of the member having a tensile strength exceeding 1.1 GPa has a Vickers hardness of 50 HV higher than the Vickers hardness of the portion other than the spot welded portion of the vertical wall. It may have a large softening region that is smaller than or equal to. When the difference in Vickers hardness between the HAZ softened portion of the vertical wall and the portion other than the spot welded portion of the vertical wall is 50 HV or more, strain concentration tends to occur in the HAZ softened portion under the condition that a tensile force is applied, and the HAZ Breakage (HAZ breakage) starting from the softened portion is likely to occur. By arranging on the compression side the HAZ softened portion having a Vickers hardness difference of 50 HV or more from the portion other than the spot-welded portion of the vertical wall, the effect of suppressing HAZ fracture becomes remarkable.

A vehicle frame including the vehicle frame member configured as described above is also included in the embodiments of the present invention. In this case, the first top plate may be arranged outside the vehicle, and the closing plate may be arranged inside the vehicle. As a result, it is possible to form a vehicle frame with improved collision resistance performance against a collision load from the outside of the vehicle.

The reinforcing member may be arranged outside the closed cross-sectional structure formed by the hat-shaped member and the closing plate. Alternatively, the reinforcing member may be placed inside the closed section structure, ie between the hat-shaped member and the closing plate.

The second top plate may be closer to the first top plate than the central height position of the first vertical wall. Further, the second top plate may be arranged between the central height position of the first vertical wall and the first top plate. Thereby, the reinforcement effect of the ridge line between the first vertical wall and the first top plate by the reinforcing member is improved. As a result, the vehicle frame member can more efficiently absorb energy during bending crushing deformation.

The neutral axis of the vehicle frame member is the position at which the tensile and compressive forces in the longitudinal direction of the member are balanced and the stress is zero when a bending moment is applied to the member. When a bending moment occurs in a member, the stress at the neutral axis becomes zero, the tensile force increases with distance from the neutral axis toward the tension side, and the compressive force increases with distance from the neutral axis toward the compression side. The position of the neutral axis in a member changes depending on structural conditions such as the shape of the member. The inventors have found that due to the structure of the vehicle frame member, the position of the neutral axis is often positioned near the center height of the first vertical wall of the hat-shaped member or on the closing plate side. Based on this, by arranging the entire HAZ softening part with reference to the height position of the center of the first vertical wall as in the embodiment of the present invention, even under various structural conditions, collision It has been realized that sometimes the softened HAZ can be loaded with a compressive force or with a relatively small tensile force. That is, according to the embodiments of the present invention, HAZ fracture in high-strength members can be suppressed under various structural conditions.

According to the results of studies by the inventors, it has been found that the strength of the ridgeline decreases when the HAZ softening portion is arranged on the ridgeline between the vertical wall and the top plate. Therefore, it is preferable that the spot welded portion is arranged so that the HAZ softened portion does not exist on either the ridge line between the first vertical wall and the first top plate or the ridge line between the second vertical wall and the second top plate. From a similar point of view, the spot welds may also be arranged so that the nuggets and HAZ softened portions are not present on any ridgeline. Further, for example, it is preferable to arrange the spot welded portions 31 so that the difference between the R-stop Vickers hardness on the vertical wall side of the ridge line and the Vickers hardness of the portion of the vertical wall other than the spot welded portion is 30 HV or less.

The said structure WHEREIN: A said 1st top plate and a said 2nd top plate may be piled up. Thereby, the reinforcement effect by a reinforcement member can be heightened more. In this case, a top plate spot weld may be provided for joining the first top plate and the second top plate. Further, in the hat-shaped member, the first vertical wall, the first top plate and the flange are integrally formed of the same plate material. In the reinforcing member, the second vertical wall and the second top plate are integrally formed of the same plate material. Therefore, at least one of the first top plate and the second top plate has a tensile strength exceeding 1.1 GPa. The HAZ softened portion of the top plate spot welded portion is the R stop on the top plate side of the ridgeline between the top plate and the vertical wall of the hat-shaped member and the reinforcing member having a tensile strength exceeding 1.1 GPa. The top plate spot welds may be positioned so that they do not reach. This can further enhance the effect of suppressing HAZ fracture in a high-strength member.

A method for manufacturing the vehicle frame member having the above configuration is also included in the embodiments of the present invention. The manufacturing method of the present embodiment includes a step of forming the hat-shaped member by press molding, a step of forming the reinforcing member by press molding separately from the hat-shaped member, and a first vertical wall of the hat-shaped member. A step of joining the reinforcing member to the second vertical wall by spot welding, and a step of joining the closing plate to the flange of the hat-shaped member. In joining the hat-shaped member and the reinforcing member, spot welding is performed so that the HAZ softened portion is positioned as described above, so that the impact resistance performance per unit mass of the member is improved by using a high-strength member. A simplified vehicle frame member can be provided. At least one of the hat-shaped member and the reinforcing member can be made a member having a tensile strength exceeding 1.1 GPa, for example, by quenching during press molding by hot stamping (hot press). Alternatively, a hat-shaped member or reinforcing member having a tensile strength exceeding 1.1 GPa can be obtained by cold-pressing an ultra-high tensile strength material. Although the closing plate is not particularly limited, it may be formed by hot pressing or cold pressing, for example. For example, a closing plate can be obtained by cold-pressing a high-tensile material.

[Embodiment]
FIG. 1 is a cross-sectional view showing the configuration of a vehicle frame member (hereinafter simply referred to as "structural member") 10 in this embodiment. FIG. 2 is an enlarged view of the vertical wall of FIG. 1 near spot welding. FIG. 3 is a side view of structural member 10 shown in FIG. FIG. 1 is a cross section of a plane perpendicular to the longitudinal direction of the structural member 10 (that is, the longitudinal direction of the hat-shaped member 1). FIG. 3 is a side view of the structural member 10 shown in FIG. 1 viewed from a direction perpendicular to the longitudinal direction (x direction) and height direction (z direction), that is, the width direction (y direction).

A structural member 10 includes a hat-shaped member 1 , a closing plate 2 and a reinforcing member 6 . The hat-shaped member 1 has a hat-shaped cross section. A portion of the hat-shaped member 1 and a portion of the closing plate 2 are overlapped and joined. The hat-shaped member 1 and the closing plate 2 are joined together to form a closed cross-sectional structure. A portion of the reinforcing member 6 and a portion of the hat-shaped member 1 are joined together.

As shown in FIGS. 1 and 3, the hat-shaped member 1 has a first top plate 1a, two first vertical walls 1b, and two flanges 1c. The two first vertical walls 1b extend from both ends in the width direction of the first top plate 1a via the ridgeline 1ab and face each other. The two flanges 1c of the two first vertical walls 1b extend in directions away from each other from the other end of the first vertical wall 1b on the side opposite to the first top plate 1a side. That is, the two flanges 1c extend outward from the other ends of the two first vertical walls 1b via the ridge line 1bc in the facing direction of the two first vertical walls 1b. The two flanges 1c and the closing plate 2 are overlapped and joined. The closing plate 2 and the two flanges 1 c are joined by a plurality of flange spot welds 33 .

A boundary portion (shoulder portion) between the first top plate 1 a and the two first vertical walls 1 b is a bent portion of the hat-shaped member 1 . This bent portion forms a ridgeline 1ab extending in the longitudinal direction (x direction) of the structural member 10 . A boundary portion between each of the two first vertical walls 1b and each flange 1c serves as a bent portion of the hat-shaped member 1. As shown in FIG. This bent portion also forms a ridgeline 1bc extending in the x direction.

The reinforcing member 6 is a channel member having a second top plate 6a and two second vertical walls 6b. Two second vertical walls 6b extend from both ends of the second top plate 6a in the width direction via ridge lines 6ab. That is, the second top plate 6a is arranged between the two second vertical walls 6b. The two second vertical walls 6b face each other.

A boundary portion (shoulder portion) between the second top plate 6a and the two second vertical walls 6b serves as a bent portion of the reinforcing member 6. As shown in FIG. This bent portion forms a ridgeline 6ab extending in the longitudinal direction (x-direction) of the structural member 10 .

The ridgelines 1ab, 1bc, and 6ab have an R shape in a cross section perpendicular to the longitudinal direction of the hat-shaped member. The R-shaped end is an R stop. In FIG. 1, the R stops of the ridgelines 1ab, 6ab, and 1bc are indicated by broken lines. As shown in FIG. 2, in this cross section, the ridgeline 1ab is a portion between the R stop 1ab1 on the vertical wall side and the R stop 1ab2 on the top plate side. The ridge line 6ab is a portion between the R stop 6ab1 on the vertical wall side and the R stop 6ab2 on the top plate side.

The second top plate 6a is overlapped with the first top plate 1a of the hat-shaped member 1 . The second top plate 6a and the second vertical wall 6b are overlapped with the first vertical wall 1b. The second vertical wall 6 b is joined to the first vertical wall 1 b of the hat-shaped member 1 by a plurality of spot welds 31 . The first top plate 1a and the second top plate 6a may be joined by spot welding.

In the examples shown in FIGS. 1 to 3, both the hat-shaped member 1 and the reinforcing member 6 are made of a material with a tensile strength exceeding 1.1 GPa. Therefore, the portions of the flange 1c, the first top plate 1a, the second top plate 6a, the first vertical wall 1b, and the second vertical wall 6b other than the spot welded portions 31 and 33 all have a tensile strength of 1.1 GPa. exceeds

As shown in FIG. 2, in the first vertical wall 1b and the second vertical wall 6b, the spot welded portion 31 includes a nugget 31c, a HAZ hardened portion 31a around the nugget 31c, and a HAZ softened portion around the HAZ hardened portion 31a. and a portion 31b. Note that the flange spot welded portion 33 also includes a nugget, a HAZ hardened portion, and a HAZ softened portion. A nugget is a part that melts and hardens during welding. In spot welds, the nugget mainly contributes to the joint. In addition, a part of HAZ hardening part may contribute to joining.

In the example shown in FIGS. 1 and 3, the neutral axis G1 passes through the center of the height H in the direction perpendicular to the lower surface of the flange 1c extending from the first vertical wall 1b via the ridgeline 1bc.

As shown in FIG. 2, the HAZ softened portions 31b of the plurality of spot-welded portions 31 that join the first vertical wall 1b and the second vertical wall 6b are located at the center height position Lc of the first vertical wall 1b and at the second vertical wall 1b. It is positioned between the first vertical wall 1b and the ridgeline 1ab between the first top plate 1a and does not reach the R stop of the ridgeline between the first vertical wall 1b and the first top plate 1a. The central height position Lc of the first vertical wall 1b is a half position of the height H of the first vertical wall (H/2 height position). The height H of the first vertical wall is measured from the R stop at the boundary between the lower surface of the flange 1c and the ridgeline 1bc in the direction perpendicular to the lower surface of the flange 1c extending from the first vertical wall 1b through the ridgeline 1bc to the first top plate. It is the dimension up to the R stop of the boundary between the upper surface of 1a and the ridgeline 1ab.

FIG. 4 is a diagram showing an example of the cross-sectional structure and hardness distribution of the HAZ softened portion 31b in the spot welded portion 31. As shown in FIG. The upper part of FIG. 4 is a cross-sectional view of a portion of the spot welded portion 31 including the nugget 31c, the HAZ hardened portion 31a, and the HAZ softened portion 31b. The lower portion of FIG. 4 is a graph showing an example of Vickers hardness distribution along line S2 in the cross-sectional view. A line S2 is a line at a distance of 1/4 of the plate thickness t of the first vertical wall 1b from the interface 16b between the first vertical wall 1b and the second vertical wall 6b.

In FIG. 4, the spot welded portion 31 is heated until it melts during welding and then cooled. The nugget 31c is a portion that melts and hardens during welding, that is, a melted portion. After the nugget 31c is melted by welding, the heat is removed by the electrode or the steel plate portion and quenched. At this time, the periphery of the nugget 31c is also quenched after being austenitized by reaching the A3 point or higher. As a result, the nugget 31c and the area adjacent to its periphery have substantially the same hardness as the vertical walls 1b and 6b. As a result, a HAZ hardened portion 31a is formed around the nugget 31c. A HAZ softened portion 31b is formed around the nugget 31c at a distance from the nugget 31c. The HAZ softened portion 31b is a portion softened by tempering (hard phase is softened). Note that the hardness distribution of the spot-welded portion is not limited to the example shown in FIG. For example, the hardness of the nugget can vary depending on the components of the hat-shaped member and stiffening member.

Here, the Vickers hardness measured at the first vertical wall 1b and the second vertical wall 6b at a distance of SD = 10 mm or more from the spot welded portion 31 is It is regarded as the Vickers hardness of the portion other than the HAZ softened portion. The HAZ softened portion 31b of the first vertical wall 1b has a Vickers hardness lower than the Vickers hardness H1 of the base material of the first vertical wall 1b by 30 HV or more. The HAZ softened portion 31b of the second vertical wall 6b has a Vickers hardness lower than that of the base material of the second vertical wall 6b by 30 HV or more.

The Vickers hardness is the interface 16b between the first vertical wall 1b and the second vertical wall 6b on the cut plane including the center of the spot welded portion 31 of the first vertical wall 1b and the second vertical wall 6b (that is, the center of the nugget 31c). From the first vertical wall 1b and the second vertical wall 6b, the tensile strength shall be measured at the position of 1/4 distance (t / 4) of the plate thickness t toward the member exceeding 1.1 GPa . If there is a small gap between the first vertical wall 1b and the second vertical wall 6b, the member of the first vertical wall 1b and the second vertical wall 6b having a tensile strength exceeding 1.1 GPa is in contact with the gap. The Vickers hardness is measured at a position of 1/4 of the plate thickness t (t/4) from the surface in the plate thickness direction of the member. Vickers hardness measurement conditions are a load of 3 N and a measurement pitch of 0.5 mm. In the case of FIG. 4, since both members of the first vertical wall 1b and the second vertical wall 6b exceed 1.1 GPa, the Vickers hardness is measured for both the first vertical wall 1b and the second vertical wall 6b.

The HAZ softened portions 31b of the first vertical wall 1b and the second vertical wall 6b are located at the center height position Lc of the first vertical wall 1b and the first vertical wall 1b and the first vertical wall 1b in the direction perpendicular to the surface of the flange 1c. It is positioned between the edge line 1ab between the top plates 1a. Furthermore, the HAZ softened portion 31b is a position that does not reach the R stop on the vertical wall side of the ridge line 1ab of the first vertical wall 1b and the first top plate 1a, and the second vertical wall 6b and the second top plate 6a A spot welded portion 31 is formed so as not to reach the R stop on the vertical wall side of the ridgeline 6ab between them. That is, in both the hat-shaped member 1 and the reinforcing member 6, the entire HAZ softened portion 31b is positioned closer to the vertical wall than the R stop on the vertical wall side of the ridgeline between the vertical wall and the top plate. Furthermore, in both the hat-shaped member 1 and the reinforcing member 6, the softened HAZ portion 31b is on the compression side with respect to the neutral axis G1 of bending due to the load applied to the first top plate 1a. Accordingly, when the structural member 10 is deformed by the load applied to the first top plate 1a, a compressive force is generated in the HAZ softened portion 31b. Therefore, HAZ breakage originating from the HAZ softened portion 31b is less likely to occur.

According to the study results of the inventors, when the hardness difference ΔHV between the minimum hardness of the HAZ softened portion of the vertical wall and the hardness of the portion other than the spot welded portion of the vertical wall is 50 HV or more, the HAZ softened portion under tensile load conditions It is known that strain concentration is more likely to occur, and as a result, fracture starting from the HAZ softened portion is more likely to occur. FIG. 4 shows an example in which the HAZ softened portion 31b includes a portion where the hardness difference ΔHV is 50HV or more. In such a case, by arranging the spot welding so that the HAZ softened portion 31b is positioned on the compression side of the bending, HAZ breakage in the high-strength member can be effectively suppressed.

FIGS. 1 to 4 are examples in which the tensile strength exceeds 1.1 GPa in both the hat-shaped member and the reinforcing member. The tensile strength of one of the hat-shaped member and the reinforcing member may exceed 1.1 GPa, and the tensile strength of the base material of the other may be 1.1 GPa or less. For example, the tensile strength of one of the hat-shaped member 1 and the reinforcing member 6 may exceed 1.1 GPa, and the tensile strength of the base material of the other may be 1.1 GPa or less.

FIG. 5 is a cross-sectional view showing an example in which the tensile strength of the reinforcing member 6 exceeds 1.1 GPa and the tensile strength of the hat-shaped member 1 is 1.1 GPa or less. In the example shown in FIG. 4, the spot-welded portion 31 of the first vertical wall 1b and the first top plate 1a of the hat-shaped member 1 has a HAZ softening such that the difference in hardness from the portion other than the spot-welded portion of the vertical wall is 30 HV or more. part is not formed. In other words, no HAZ softened portion, which can be a starting point for HAZ fracture, is formed. In such a case, in the second vertical wall 6b of the reinforcing member 6 exceeding 1.1 GPa, the HAZ softened portion 31b does not reach, and the entire HAZ softening portion 31b is located on the first top plate 1a side (that is, on the compression side of the neutral axis G1) from the position Lc of the height of the center of the first vertical wall. , the spot welds 31 are arranged. As a result, HAZ fracture in a high-strength member can be effectively suppressed.

FIG. 6 is a sectional view showing an example in which the tensile strength of the base material of the hat-shaped member 1 exceeds 1.1 GPa and the tensile strength of the base material of the reinforcing member 6 is 1.1 GPa or less. In the example shown in FIG. 6, the spot welded portion 31 of the second vertical wall 6b of the reinforcing member 6 is not formed with a HAZ softened portion that can become a starting point of HAZ fracture. In such a case, in the first vertical wall 1b of the hat-shaped member 1 that exceeds 1.1 GPa, HAZ The entire HAZ softening portion 31b is located so that the softening portion 31b does not reach and on the first top plate 1a side (that is, the compression side from the neutral axis G1) from the central height position Lc of the first vertical wall 1b. The spot welds 31 are arranged so as to do. As a result, HAZ fracture in a high-strength member can be effectively suppressed.

1, 2, 5 and 6, the first top plate 1a and the second top plate 6a are in contact with each other. The first top plate 1a and the second top plate 6a may be joined by spot welding. Alternatively, the first top plate 1a and the second top plate 6a may not be joined and may be separated from each other.

In a cross section perpendicular to the longitudinal direction of the hat-shaped member 1, the neutral axis G1 is near the center height of each of the two first vertical walls 1b, or at the center of each of the two first vertical walls 1b. It is positioned closer to the closing plate 2 than the height position. Therefore, in the structural member 10, even if the height position of the center of the first vertical wall 1b is replaced with the neutral axis, the same effect can be obtained. When structural conditions such as the shape of the structural member 10 change, the position of the neutral axis G1 also changes. Here, for example, as shown in FIGS. 1 and 2, in a cross section on a plane perpendicular to the longitudinal direction of the hat-shaped member 1, the entire HAZ softened portion 31b of the spot welded portion 31 is located at the center of the first vertical wall 1b. and the R stop on the first vertical wall 1b side of the ridge line 1ab between the first vertical wall 1b and the first top plate 1a, and the tensile strength is 1.1 GPa The spot welded portion 31 can be arranged so that it does not reach the R stop on the vertical wall side of the ridge between the vertical wall of the member exceeding the top plate and the top plate. This allows the softened HAZ to be loaded with compressive forces or with relatively small tensile forces during a crash under various structural conditions. Therefore, under various structural conditions, HAZ fracture in high-strength members can be suppressed. That is, under various structural conditions, it is possible to more easily obtain the effect of improving the collision resistance performance per unit mass of the member by using the high-strength member.

In a cross section passing through the center of each of the plurality of spot-welded portions 31 and perpendicular to the longitudinal direction of the hat-shaped member 1, from the R stop on the vertical wall side of the ridge line 1ab between the first vertical wall 1b and the first top plate 1a to the first The distance h1 in the direction perpendicular to the flange surface to the end 6bt of the second vertical wall 6b is one-third or less of the height H in the direction perpendicular to the flange surface of the first vertical wall 1b (h1 ≤ ( H/3)) is preferred. As a result, both the maximum load per unit mass of the structural member 10 and the amount of energy absorption per unit mass of the structural member 10 can be improved. From the same point of view, it is more preferable to set h1≦(H/4). For example, the distance h1 in the direction perpendicular to the surface of the flange 1c from the R stop on the vertical wall side of the ridgeline 1ab between the first vertical wall 1b and the first top plate 1a to the end 6bt of the second vertical wall 6b is , 10-50 mm. Further, for example, the distance s1 from the R stop on the vertical wall side of the ridgeline between the vertical wall and the top plate of the hat-shaped member 1 and the reinforcing member 6 having a tensile strength exceeding 1.1 GPa to the center of the spot welded portion 31 can be 5-15 mm. Here, the center of the spot-welded portion 31 is the center of the nugget 31c viewed from the plate thickness direction of the first vertical wall 1b.

Next, an example of the positional relationship between the spot welded portion 31 and the end portion 6bt of the reinforcing member 6 will be described with reference to FIGS. 1 and 2. FIG. A distance s between the center of the spot-welded portion 31 and the end portion 6bt of the second vertical wall 6b of the reinforcing member 6 can be, for example, 5 to 15 mm. It is considered that the portion from the spot welded portion 31 to the end portion 6bt of the second vertical wall 6b hardly contributes to load bearing performance. Therefore, by making this portion smaller, the weight of the reinforcing member 6 can be reduced. As a result, the load bearing performance of the structural member 10 can be further improved.

The end portion 6bt of the second vertical wall 6b of the reinforcing member 6 may be located closer to the first top plate 1a than the central height position Lc of the first vertical wall 1b in the direction perpendicular to the flange surface. good. Also in this case, the reinforcing effect of the reinforcing member 6 can be obtained. As an example, a portion that is not actively crushed is assumed, such as a vehicle frame member such as a B-pillar upper. In this case, it is important that the top plate does not buckle against the bending moment applied when the top plate collides. To withstand this buckling, it is effective to strengthen the top plate and ridgeline. For example, it is effective to reinforce the vicinity of the ridgeline 1ab between the first top plate 1a and the first vertical wall 1b of the hat-shaped member 1 with the reinforcing member 6. FIG. This is because the contribution to the improvement of impact resistance performance by reinforcing the first vertical wall 1b up to the flange 1c side is greater than the contribution by reinforcing the ridge line 1ab of the first vertical wall 1b and the first top plate 1a. This is because the Therefore, even if the length of the second vertical wall 6b of the reinforcing member 6 is arranged only on the compression side (first top plate 1a side) from the neutral axis, it is possible to improve the anti-collision performance. In addition, with this configuration, the reinforcing member 6 can be shortened and further reduced in weight.

<Example of application to a vehicle>
FIG. 7 is a diagram showing an example of a state in which the structural member 10 having the characteristics shown in FIGS. 1 to 6 is mounted on a vehicle as a vehicle frame. In the example of FIG. 7, the structural member 10 is used as a B-pillar (center pillar). The structural member 10 is mounted such that the hat-shaped member 1 is arranged on the outside of the vehicle and the closing plate 2 is arranged on the inside of the vehicle. The first top plate 1a surface of the hat-shaped member 1 faces the outside of the vehicle. The reinforcing member 6 is provided at a position covering the center of the hat-shaped member 1 in the longitudinal direction. The surface of the second top plate 6a of the reinforcing member 6 also faces the outside of the vehicle.

In the example shown in FIG. 7, it is assumed that an object collides with the structural member 10 from the outside of the side surface of the vehicle. At the time of collision, a bending moment is generated in the structural member 10 due to the load applied to the first top plate 1a of the hat-shaped member 1 . As an example, crash loads create bending moments in the structural member 10 . A four-point bending test is known as a test method for reproducing and evaluating such bending moments. A four-point bending test can generate a region where the bending moment is constant. It is possible to evaluate the collision performance of the B-pillar by applying the maximum bending moment generated at the time of collision deformation in a four-point bending test.

In the example shown in FIG. 7, since the central portion B2 of the B-pillar is provided with the reinforcing member 6, the load-bearing performance against the load due to the collision is high, and the deformation toward the inside of the vehicle is suppressed. The base material of the reinforcing member 6 is made of, for example, a material with a hardness exceeding 1.1 GPa. On the other hand, the reinforcing member 6 is not provided on the lower portion B1 of the B pillar. Therefore, it is more likely to be crushed by a collision load than the central portion B2. The lower portion B1 is crushed and deformed to absorb the impact load. For example, the hat-shaped member 1 is made of a base material of 1.1 GPa or less. In this way, by appropriately arranging the reinforcing member 6 according to the assumed collision, the deformation behavior at the time of collision can be brought closer to the target. In addition, the aspect of the structural member 10 is not restricted to said example. The structural member 10 may be used not only for B-pillars but also for other vehicle frame members such as A-pillars, roof rails, bumpers, door beams, and the like. Also, the combination of the tensile strengths of the hat-shaped member 1 and the reinforcing member 6 is not limited to the above example. For example, the tensile strength of both the hat-shaped member 1 and the reinforcing member 6 may exceed 1.5 GPa.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. For example, the hat-shaped member and stiffening member may be curved in the longitudinal direction. In this case, at least one of the edge line between the first top plate and the first vertical wall of the hat-shaped member and the edge line between the first vertical wall and the flange extends curvedly. The ridge line between the first top plate and the first vertical wall of the hat-shaped member and the ridge line between the first vertical wall and the flange may or may not be parallel.

The first top plate and the first vertical wall of the hat-shaped member may be formed of a flat plate, or may have a shape in which a part of the flat plate has unevenness. The second top plate and the second vertical wall of the reinforcing member may be formed of a flat plate, or may have a shape in which a part of the flat plate has unevenness. The first top plate of the hat-shaped member and the flange may or may not be parallel. Also, the closing plate is not limited to a flat plate. For example, the closing plate may have a top plate, two vertical walls extending from both ends of the top plate via ridgelines, and flanges extending from ends of the vertical walls via ridgelines. In this case, the flange of the hat-shaped member and the flange of the closing plate are joined. The first longitudinal wall of the hat-shaped member and the longitudinal wall of the closing plate extend in opposite directions from the flange. That is, the cross-sectional shape of the closing plate may be hat-shaped. In this case, the hat-shaped member and the closing plate constitute a structural member having a so-called double hat-shaped closed cross-sectional structure.

<Analysis example>
FIG. 8 is a diagram showing a four-point bending model used for analysis. A structural member 10E to be analyzed is configured to include a hat-shaped member 1E, a reinforcing member, and a closing plate 2E. In addition, in FIG. 8, the reinforcing member is omitted. As shown in FIG. 8, in four-point bending, the lower surface of the structural member 10E is supported by two longitudinally spaced supports SE, and two longitudinally spaced indenters PE between the two supports SE. , apply a load to the upper surface of the structural member 10E. The reinforcing member is provided over the entire longitudinal direction of the structural member 10E. The two support portions SE serve as two fulcrums, and the point at which the two indenters PE contact the upper surface serves as a power point. In four-point bending, a bending moment due to loading occurs between two fulcrums. Between two points of force, the bending moment is constant and maximum. For example, as shown in FIG. 10, which will be described later, this bending moment causes the vertical wall of the hat-shaped member to generate a compressive force on the top plate side and a tensile force on the closing plate side between the two fulcrums. Further, bending of the structural member occurs largely between two points of force. FIG. 9 is a diagram showing a model of the structural member 10E used in the four-point bending model of FIG. Models A to E in FIG. 9 are a group of models in which the spot welding positions (welding point positions) on the vertical walls of the hat-shaped member 1E and the reinforcing member 6E and the length of the vertical wall of the reinforcing member 6E are varied. In FIG. 9, the positions of spot welds are represented by squares. In model A and model B, there is a spot welded portion between the central height position Lc of the first vertical wall of the hat-shaped member 1E and the flange. In model C and model D, there is a spot weld between the central height position Lc of the first vertical wall and the first top plate. The position of the spot-welded portion of the vertical wall of model D is located farther from the central height position Lc of the first vertical wall than the position of the spot-welded portion of the vertical wall of model C. The position of the spot welded part of the vertical wall of model E is the R stop on the vertical wall side of the ridge between the first vertical wall and the first top plate, and the R on the vertical wall side of the ridge between the second vertical wall and the second top plate Both stops are reached. In any of models A to D, the distance s from the end of the second vertical wall to the center position of the spot weld is s=5 mm, which is in the range of 5 to 15 mm. In models A to C, the end of the second vertical wall is closer to the closing plate than the central height position Lc of the first vertical wall. In models D and E, the end of the second vertical wall of the reinforcing member 6E is closer to the second top plate than the central height position Lc of the first vertical wall. Further, the distance h1 from the R stop on the vertical wall side of the ridgeline 1ab between the first vertical wall 1b and the first top plate 1a to the end 6bt of the second vertical wall 6b is as follows. Model A has h1=50 mm, model B has h1=32 mm, model C has h1=24 mm, and model D has h1=12 mm. For model E, h1=12 mm. That is, in models A to C, h1>(H/3), and in models D and E, h1≦(H/3). In models A to E, the height H of the first vertical wall is 60 mm. In Models A to E, the tensile strength of the hat-shaped member 1E is 1.5 GPa, and the plate thickness of the hat-shaped member 1E is 2.0 mm. The reinforcing member 6E has a tensile strength of 1.5 GPa and a plate thickness of 1.6 mm. The closing plate 2E has a tensile strength of 780 MPa and a thickness of 1.2 mm. Models A to E are provided with a spot welded portion for joining the first top plate and the second top plate, and a spot welded portion for joining the flange of the hat-shaped member 1E and the closing plate 2E. A four-point bending simulation shown in FIG. 8 was performed using models A to E shown in FIG.

FIG. 10 is a diagram showing stress fields calculated as a result of executing a four-point bending simulation with the models A to D shown in FIG. In FIG. 10, illustration of the reinforcing member 6E and illustration of the spot-welded portion between the top plate and the flange are omitted. In FIG. 10, regions where tensile force is generated are indicated by no hatching, and regions where compressive force is generated are indicated by dots. In FIG. 10, the spot welds on the vertical wall are indicated by circles. The results shown in FIG. 10 show that the spot welds broke (HAZ fracture) in models A and B in which a large tensile force was generated in the spot welds. In model A and model B, a tensile force is generated at the spot weld between the two force points (see FIG. 8). On the other hand, in the case of models C and D, there was no breakage of spot welds (HAZ breakage). In model C, the tensile and compressive forces are nearly zero at the spot weld between the two force points. In model D, a compressive force is generated in the spot weld. From this, it was found that by arranging the position of the spot welded portion between the central height position Lc of the first vertical wall and the first top plate, the breakage of the spot welded portion (HAZ breakage) can be avoided. .

FIG. 11 is a graph showing the load-displacement relationship of Models AE. In the results shown in FIG. 11, in model A and model B, a large tensile force was generated in the HAZ softened portion, strain was concentrated in the HAZ softened portion, and therefore the HAZ fractured before reaching the maximum load. The tensile force of model A is even greater than that of model B. Model A had a faster HAZ rupture than model B. In Model C, after the maximum load was reached, the reinforcing member was separated from the hat-shaped member due to peeling of the spot-welded portion. In model C, the load drops abruptly after this peeling.

FIG. 12 is a graph showing the maximum load per unit mass of members for Models A to E. FIG. From this graph, it was found that models C and D, in which the length of the vertical wall of the reinforcing member is short, have a higher maximum load per unit mass of the member than models A and B, in which the vertical wall of the reinforcing member is long. In addition, the maximum load per unit mass of the member was significantly higher in model D where h1≦(H/3) than in model C where h1>(H/3). Model E, in which the spot-welded portion reaches the ridgeline, has a significantly lower maximum load per unit mass of the member.

FIG. 13 is a graph showing energy absorption per unit mass of members of Models A to E. FIG. From this graph, it can be seen that models C and D, in which the length of the vertical wall of the reinforcing member is short, have a higher energy absorption amount (energy absorption efficiency) per unit mass of the member than models A and B, in which the vertical wall of the reinforcing member is long. I found out. In addition, the energy absorption amount (energy absorption efficiency) per unit mass of the member was significantly higher in model D where h1≦(H/3) than in model C where h1>(H/3). . In model E, which has a configuration in which the spot weld reaches the ridgeline, the energy absorption amount (energy absorption efficiency) is lower than that in model D.

Thus, in this analysis example, the bending moment is applied by arranging the position of the spot welding between the reinforcing member and the hat-shaped member on the ridge line side from the height of the center of the first vertical wall and not reaching the ridge line. Under such conditions, it is possible to suppress HAZ fracture originating from the HAZ softened portion of spot welding. As a result, by using high-strength materials for the reinforcing member and the hat-shaped member, it is possible to easily obtain the effect of improving the maximum load and energy absorption amount per unit mass of the member, that is, the impact resistance performance per unit mass of the member. It has been found that mass efficiency enables the realization of superior reinforcement structures. In particular, by arranging the spot welds so that h1 ≤ (H / 3) and the HAZ softened portion does not reach the ridgeline, it was found that the maximum load and energy absorption per unit mass of the member can be further improved. rice field.

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 can be implemented by appropriately modifying the above-described embodiment without departing from the scope of the invention.

1: Hat-shaped member 2: Closing plate 31, 33: Joint 6: Reinforcing member 10: Structural member 1a: First top plate 1b: First vertical wall 1c: Flange 6a: Second top plate 6b: Second vertical wall

Claims (7)

A vehicle frame member,
a hat-shaped member;
a closing plate;
a reinforcing member;
with multiple spot welds,
The hat-shaped member includes a first top plate, two first vertical walls and two flanges,
The first top plate is arranged between the two first vertical walls,
The first vertical wall is arranged between the first top plate and the flange,
the flange is joined with the closing plate;
The reinforcing member includes a second top plate and two second vertical walls,
The second top plate is arranged between the two second vertical walls,
the first vertical wall and the second vertical wall are superimposed;
the plurality of spot welds join the first vertical wall and the second vertical wall;
At least one of the hat-shaped member and the reinforcing member has a tensile strength of more than 1.1 GPa,
Of the hat-shaped member and the reinforcing member, the entire HAZ softened portion of the plurality of spot welds in the vertical wall of the member having a tensile strength exceeding 1.1 GPa is in the direction perpendicular to the surface of the flange, the second It is located between the central height position of the vertical wall and the R stop on the first vertical wall side of the ridgeline between the first vertical wall and the first top plate, and has a tensile strength of 1.1. A vehicle frame member located at a position not reaching the R stop on the vertical wall side of the ridge line between the vertical wall and the top plate of the member exceeding 1 GPa. The tensile strength of the reinforcing member is greater than 1.1 GPa,
The tensile strength of the hat-shaped member is 1.1 GPa or less,
The vehicle frame member according to claim 1. The tensile strength of both the hat-shaped member and the reinforcing member is greater than 1.1 GPa,
The vehicle frame member according to claim 1 or 2. A ridge line between the first vertical wall and the first top plate in a direction perpendicular to the flange face in a cross section on a plane passing through the center of each of the plurality of spot welds and perpendicular to the longitudinal direction of the hat-shaped member The distance from the R stop on the vertical wall side of the reinforcing member to the end of the second vertical wall of the reinforcing member is one-third or less of the height of the first vertical wall,
A vehicle frame member according to any one of claims 1 to 3. The centers of the plurality of spot welds are located 5 to 15 mm from the end of the second vertical wall of the reinforcing member,
A vehicle frame member according to any one of claims 1 to 4. Of the hat-shaped member and the reinforcing member, the HAZ softened portion of the vertical wall of the member having a tensile strength exceeding 1.1 GPa has a Vickers hardness of 50 HV higher than the Vickers hardness of the portion other than the spot welded portion of the vertical wall. having a large softening region smaller than or equal to
A vehicle frame member according to any one of claims 1 to 5. A vehicle frame member according to any one of claims 1 to 6,
The first top plate is arranged outside the vehicle,
A vehicle skeleton, wherein the closing plate is arranged inside the vehicle.

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