Structural member

Abstract

To enhance the strength of a structural member for an automobile.SOLUTION: A structural member (100) includes a first member (10) and a second member (20). The first member (10) includes a top plate (11), a pair of vertical walls (12, 121, 122), and a pair of flanges (13, 131, 132). The second member (20) is joined to the flanges (13, 131, 132) by a weld and an adhesive (40). The adhesive (40) includes an extrusive portion (41). The extrusive portion (41) extrudes from a joint portion (50) between each flange (13, 131, 132) and the second member (20) into a space (S) defined by the first member (10) and the second member (20) and is in contact with the first member (10) and the second member (20). When a length of a portion of the extrusive portion (41) in contact with the second member (20) is defined as a contact width (W), the contact width (W) is 0.50 times or more a curvature radius (R) of a bent portion (15, 151, 152).SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to structural members for automotive vehicles. [Background technology]

[0002] There is a demand for lighter automobile bodies to improve fuel economy or electricity consumption. Automobile bodies are made up of many structural members. To reduce the weight of automobile bodies, the materials used for the structural members are becoming stronger and thinner.

[0003] Some automotive structural components are made up of multiple components joined by spot welding. The strength of a spot weld against loads in the shear direction increases depending on the material strength of the components. On the other hand, the strength of a spot weld against loads in the peel direction increases depending on the material strength of the components until the material strength of the components reaches a certain value. However, once the material strength of the components exceeds a certain value, the strength of the spot weld against loads in the peel direction decreases. Therefore, when each component is made of high-strength material, there is a concern about fracture of the spot weld, especially fracture in the peel direction.

[0004] One known method for preventing fracture of spot welds is to join components together using spot welding and adhesive (weld bonding). For example, Patent Document 1 discloses a structural component in which a first component, which is a hat material, and a second component, which is a flat plate material, are joined by spot welding. Patent Document 1 describes a closed cross-section formed by the first and second components, in which a resin is interposed between a bent portion of the first component near the flange and the second component. The resin interposition width is, for example, 0.5 to 2.0 times the radius of curvature of the bent portion of the first component. The interposition width refers to the linear distance from the flange-side end of the resin portion in contact with the first component to the opposite end in the cross-section of the structural component. Patent Document 1 also describes that the resin is preferably an epoxy-based structural adhesive. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-168082 Summary of the Invention [Problem to be solved by the invention]

[0006] Patent Document 1 explains that when a load acts on a structural member in a direction perpendicular to the longitudinal direction, both vertical walls of the first member deform so as to collapse inward. On the other hand, Patent Document 1 also describes that by interposing a resin (adhesive) between the bent portion of the first member and the second member, the collapse of the vertical walls is suppressed, and the bending strength and absorbed energy of the structural member are increased.

[0007] However, especially when the first member is made of a high-strength, thin-walled material, this type of collapse of the vertical wall is likely to occur and persist for a relatively long time. Specifically, when a load is input to the structural member from the second member side, for example, due to a car collision, the bent portion near the flange of the first member continues to intrude into the inside of the structural member when viewed in cross section. To further increase the strength of the structural member, it is preferable to continuously suppress this intrusion of the bent portion.

[0008] An object of the present disclosure is to further increase the strength of structural members for automobiles. [Means for solving the problem]

[0009] The structural member for an automobile according to the present disclosure has an elongated shape. The structural member includes a first member and a second member. The first member includes a top plate, a pair of vertical walls, and a pair of flanges. The vertical walls are arranged to face each other. The vertical walls are connected to the top plate. The flanges are connected to the vertical walls via bent portions on opposite sides of the top plate. The flanges protrude from the vertical walls to the outside of the vertical walls. The second member is arranged to face the top plate. The second member is joined to the flanges by welding and adhesive. The adhesive includes a protruding portion. The protruding portion protrudes from the joint between each flange and the second member into a space formed by the first member and the second member and contacts the first member and the second member. When the length of the protruding portion that contacts the second member is defined as the contact width in a cross section perpendicular to the longitudinal direction of the structural member, the contact width is 0.50 times or more the radius of curvature of the bent portion. [Effects of the Invention]

[0010] According to the present disclosure, the strength of structural members for automobiles can be further increased. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a perspective view that schematically shows a structural member for an automobile according to an embodiment. [Figure 2] FIG. 2 is a cross-sectional view of the structural member shown in FIG. 1 taken along line II-II. [Figure 3] FIG. 3 is a partially enlarged cross-sectional view of the structural member shown in FIG. [Figure 4A] FIG. 4A is a schematic diagram showing the deformation behavior of a structural member including a first member and a second member when a load is input from the second member side. [Figure 4B] FIG. 4B is a schematic diagram showing the deformation behavior of the structural member when a load is input to the structural member from the second member side. [Figure 4C] FIG. 4C is a schematic diagram showing the deformation behavior of the structural member when a load is input to the structural member from the second member side. [Figure 5]FIG. 5 is a schematic diagram showing a cross section of a model of a structural member used in the analysis. DETAILED DESCRIPTION OF THE INVENTION

[0012] A structural member for an automobile according to an embodiment has an elongated shape. The structural member includes a first member and a second member. The first member includes a top plate, a pair of vertical walls, and a pair of flanges. The vertical walls are arranged to face each other. The vertical walls are connected to the top plate. The flanges are connected to the vertical walls via bent portions on opposite sides of the top plate. The flanges protrude from the vertical walls to the outside of the vertical walls. The second member is arranged to face the top plate. The second member is joined to the flanges by welding and adhesive. The adhesive includes a protruding portion. The protruding portion protrudes from the joint between each flange and the second member into a space formed by the first member and the second member and contacts the first member and the second member. When the length of the protruding portion that contacts the second member is defined as the contact width in a cross section perpendicular to the longitudinal direction of the structural member, the contact width is 0.50 times or more the radius of curvature of the bent portion (first configuration).

[0013] In a structural member according to the first configuration, the second member is joined to both flanges of the first member by welding and adhesive. The adhesive includes portions (protruding portions) that protrude from the joints between the flanges of the first member and the second member toward the inside of the structural member. When a load is input to the structural member from the second member side, a bending deformation occurs in the structural member with the second member side on the inside of the bending and the top plate side of the first member on the outside of the bending, and a longitudinal compressive force is generated in the second member. As a result, the flange sides of both vertical walls of the first member deform inward relative to the top plate sides, causing the bent portions near the flanges to move toward the inside of the structural member. The protruding portions of the adhesive can function as resistance to this bending.

[0014] In the structural member according to the first embodiment, the contact width of the adhesive protrusion with the second member is ensured to be at least 0.50 times the radius of curvature of the bent portion. In other words, the adhesive protrusion extends along the direction of movement of the bent portion of the first member, a length at least 0.50 times the radius of curvature of the bent portion. In this case, the adhesive protrusion can provide continuous resistance to the bent portion, which gradually moves inward of the structural member. Therefore, movement of the bent portion and tilting of the vertical wall are continuously suppressed, making it easier to maintain the cross-sectional shape of the structural member. As a result, the structural member can be made stronger than ever against loads input from the second member.

[0015] In the structural member according to the first configuration, in a cross section perpendicular to the longitudinal direction of the structural member, when the direction perpendicular to the contact surface between the protruding portion and the second member is defined as the height direction, the maximum length of the protruding portion in the height direction may be 0.50 times or more the radius of curvature (second configuration).

[0016] In the structural member according to the second configuration, the maximum length in the height direction of the protruding portion of the adhesive is ensured to be 0.50 times or more the radius of curvature of the bent portion. In this case, when the structural member is bent, the bent portion moving inward of the structural member is less likely to overcome the protruding portion of the adhesive, improving the effectiveness of the protruding portion as resistance to the bent portion. As a result, the structural member is more likely to have high strength against loads input from the second member side.

[0017] In the structural member according to the first or second configuration, the adhesive may have a Young's modulus of 1.2 GPa or more (third configuration).

[0018] In the third configuration, the adhesive has a high Young's modulus of 1.2 GPa or more. In this case, the protruding portion of the adhesive can function as a greater resistance to the bending portion that moves inward of the structural member during bending deformation of the structural member. As a result, the structural member is more likely to have higher strength against loads input from the second member side.

[0019] In a structural member according to any one of the first to third configurations, when the tensile strength of the first member is TS (MPa) and the plate thickness of the first member is t (mm), TS / t may be 900 or more (fourth configuration).

[0020] In the structural member according to the embodiment, when the thickness t (mm) of the first member is small, the rigidity of the first member is low, which makes it easy for the bending portion to move and the resulting tilting of the vertical wall as described above to occur. On the other hand, when the tensile strength TS (MPa) of the first member is large, the first member has a large amount of elastic deformation and is less likely to yield. Therefore, when the structural member receives a load from the second member, the bending portion moves and the vertical wall tilts for a relatively long period of time. Because the above structural member provides continuous resistance to the bending portion moving inward of the structural member by the protruding portion of the adhesive, it is particularly effective when the first member is made of a high-strength, thin-walled material, in other words, a material with a high tensile strength TS relative to the thickness t.

[0021] In the fourth configuration, the first member is made of a material with a high tensile strength TS relative to the plate thickness t, specifically a material with a TS / t ratio of 900 or more. In this case, the protruding portion of the adhesive can significantly enhance the strength of the structural member.

[0022] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In these drawings, the same or equivalent components are designated by the same reference numerals, and the same description will not be repeated.

[0023] [Structural member configuration] FIG. 1 is a perspective view schematically illustrating a structural member 100 for an automobile according to this embodiment. The structural member 100 is used in the body of an automobile. The structural member 100 is, for example, a bumper beam. When the structural member 100 is a bumper beam, the structural member 100 is disposed at the front or rear of the automobile body.

[0024] 1, structural member 100 has an elongated shape. When assembled into the body of an automobile, structural member 100 extends, for example, in the left-right direction of the body. Structural member 100 includes a first member 10 and a second member 20.

[0025] The first member 10 and the second member 20 extend in the longitudinal direction of the structural member 100. When the structural member 100 is installed in a vehicle body, the first member 10 and the second member 20 typically extend in the left-right direction of the vehicle body.

[0026] The second member 20 is disposed on the outside of the first member 10 on the vehicle body. When the structural member 100 is a front bumper beam, the second member 20 is disposed in front of the first member 10 on the vehicle body. When the structural member 100 is a rear bumper beam, the second member 20 is disposed behind the first member 10 on the vehicle body. The second member 20 is the collision surface of the structural member 100, and the collision load during a vehicle collision is input from the second member 20 toward the first member 10. When the structural member 100 is a bumper beam, the first member 10 and the second member 20 may be curved along the longitudinal direction of the structural member 100 so that the first member 10 is on the inside of the curve and the second member 20 is on the outside of the curve.

[0027] The first member 10 includes a top plate 11, a pair of vertical walls 121, 122, and a pair of flanges 131, 132.

[0028] The vertical walls 121, 122 are arranged to face each other. The vertical walls 121, 122 are connected by the top plate 11. The vertical wall 121 is connected to one of both side edges of the top plate 11 extending in the longitudinal direction of the structural member 100. The vertical wall 122 is connected to the other side edge of the top plate 11 on the side opposite the vertical wall 121. The flanges 131, 132 are connected to the vertical walls 121, 122, respectively, on the side opposite the top plate 11. The flanges 131, 132 protrude from the vertical walls 121, 122 to the outside of the vertical walls 121, 122, respectively.

[0029] The second member 20 is disposed so as to face the top plate 11 of the first member 10. The second member 20 is joined to the flanges 131 and 132 of the first member 10.

[0030] Fig. 2 is a cross-sectional view taken along line II-II of the structural member 100 shown in Fig. 1. Fig. 2 shows a cross section (transverse section) of the structural member 100 cut along a plane perpendicular to the longitudinal direction thereof.

[0031] 2, the first member 10 has a substantially hat-like shape in a cross-sectional view of the structural member 100. When the structural member 100 is installed in the vehicle body, in the cross-section of the structural member 100, the top plate 11 extends substantially in the up-down direction of the vehicle body, and the vertical walls 121, 122 face each other substantially in the fore-and-aft direction of the vehicle body. The vertical walls 121, 122 may be arranged parallel to each other or non-parallel to each other. For example, the vertical walls 121, 122 may be arranged so that they become more spaced apart as they move away from the top plate 11 in a cross-sectional view of the structural member 100.

[0032] In this embodiment, one vertical wall 121 is connected to the top plate 11 via a bent portion 141. The other vertical wall 122 is connected to the top plate 11 via a bent portion 142. The bent portions 141 and 142 are corner portions between the top plate 11 and the vertical walls 121 and 122, respectively. The bent portions 141 and 142 may have an arc shape that protrudes outward from the first member 10 in a cross-sectional view of the structural member 100.

[0033] The flanges 131, 132 are connected to the vertical walls 121, 122 via bent portions 151, 152, respectively. One flange 131 is connected to the vertical wall 121 via the bent portion 151 on the opposite side of the top plate 11. The bent portion 151 is a corner portion between the vertical wall 121 and the flange 131. The other flange 132 is connected to the vertical wall 122 via the bent portion 152 on the opposite side of the top plate 11. The bent portion 152 is a corner portion between the vertical wall 122 and the flange 132. The bent portions 151, 152 may have a concave arc shape on the inside of the first member 10 in a cross-sectional view of the structural member 100.

[0034] When the structural member 100 is installed in the vehicle body, the flanges 131 and 132 protrude substantially in the up-and-down direction of the vehicle body from the vertical walls 121 and 122, respectively. In the example of Fig. 2, one flange 131 protrudes upward from the vertical wall 121 of the vehicle body. The other flange 132 protrudes downward from the vertical wall 122 of the vehicle body.

[0035] In the example of FIG. 2, the second member 20 has a flat plate shape. However, the second member 20 does not necessarily have to be a completely flat plate shape. The second member 20 may have an uneven or curved shape. When the structural member 100 is installed in the vehicle body, the second member 20 extends substantially in the vertical direction of the vehicle body in the cross section of the structural member 100. The second member 20 is joined to the flanges 131, 132 so as to close the openings of the first member 10 on the flange 131, 132 side. In other words, the first member 10 and the second member 20 form a closed cross section.

[0036] FIG. 3 is a cross-sectional view of the structural member 100, showing an enlarged view of the joint region between the first member 10 and the second member 20. On the paper surface of FIG. 3, the second member 20 is disposed above the first member 10. In the structural member 100, the configuration of the joint region between the first member 10 and the second member 20 is substantially the same on the flange 131 side and the flange 132 side. Hereinafter, when there is no need to particularly distinguish between the flanges 131 and 132, the flanges 131 and 132 will be collectively referred to as flange 13. Similarly, when there is no need to particularly distinguish between the vertical walls 121 and 122 and the bending portions 151 and 152, the vertical walls 121 and 122 will be collectively referred to as vertical wall 12, and the bending portions 151 and 152 will be collectively referred to as bending portion 15.

[0037] Referring to FIG. 3 , the second member 20 is joined to the flange 13 by welding. The second member 20 may be joined to the flange 13 by resistance welding. The second member 20 is typically joined to the flange 13 by spot welding. In this case, a nugget 30 is formed at the overlapping portion between the second member 20 and the flange 13. A plurality of nuggets 30 are formed at the overlapping portion between the second member 20 and the flange 13. These nuggets 30 are arranged at intervals in the longitudinal direction of the structural member 100.

[0038] In addition to being welded, the second member 20 is joined to the flange 13 by adhesive 40. The second member 20 and the flange 13 are joined by adhesive 40 along the longitudinal direction of the structural member 100. The second member 20 and the flange 13 may be joined by adhesive 40 over substantially the entire longitudinal length of the structural member 100.

[0039] The adhesive 40 includes a protruding portion 41. The protruding portion 41 is a portion of the adhesive 40 that protrudes from the joint (overlap portion) 50 between the second member 20 and the flange 13 into the space S formed by the first member 10 and the second member 20. The adhesive 40 joins the second member 20 and the flange 13 along the longitudinal direction of the structural member 100, so that the protruding portion 41 extends along the longitudinal direction of the structural member 100. For example, the protruding portion 41 extends along the longitudinal direction of the structural member 100, passing through the center of the structural member 100. The protruding portion 41 may be provided over substantially the entire longitudinal length of the structural member 100.

[0040] The protruding portion 41 contacts the second member 20. The protruding portion 41 directly contacts one of both surfaces of the second member 20 that is located inside the structural member 100. The protruding portion 41 also contacts the first member 10. The protruding portion 41 directly contacts at least the bent portion 15 adjacent to the flange 13. When viewed in cross section of the structural member 100, the protruding portion 41 may contact the second member 20 over a wider area than the first member 10.

[0041] In the cross section of the structural member 100, the protruding portion 41 extends from an end 51 of a joint 50 between the second member 20 and the flange 13 toward the inside of the structural member 100, while contacting the surface of the second member 20. The joint 50 is the portion where the second member 20 and the flange 13 of the first member 10 are overlapped. Of both ends of the joint 50 in the cross section of the structural member 100, the end 51 is the end that is located on the inside of the structural member 100. The end 51 of the joint 50 typically coincides with the position of the end (R end) 153 of the bent portion 15 on the flange 13 side.

[0042] The contact width W of the protruding portion 41 is at least 0.50 times the radius of curvature R of the bent portion 15. The contact width W is the length of the portion of the protruding portion 41 of the adhesive 40 that contacts the second member 20 in the cross section of the structural member 100. The radius of curvature R of the bent portion 15 is the radius of curvature of the surface of the bent portion 15 on the inside of the structural member 100.

[0043] The contact width W is preferably 1.00 times or more, and more preferably 1.50 times or more, the radius of curvature R of the bent portion 15. The contact width W is, for example, 2.50 times or less the radius of curvature R of the bent portion 15. Although not particularly limited, the radius of curvature R of the bent portion 15 may be 4.0 mm or more and 15.0 mm or less.

[0044] The maximum height H of the protruding portion 41 is 0.50 times or more the radius of curvature R of the bent portion 15. The maximum height H is the maximum length of the protruding portion 41 in the height direction, when the height direction is defined as the direction perpendicular to the contact surface 411 between the protruding portion 41 of the adhesive 40 and the second member 20 in the cross section of the structural member 100. The maximum height H is preferably 1.00 times or more, and more preferably 2.00 times or more the radius of curvature R of the bent portion 15. The maximum height H is, for example, 5.00 times or less the radius of curvature R of the bent portion 15.

[0045] The contact width W and maximum height H of the protruding portion 41 can be measured as follows. First, the structural member 100 is cut at its longitudinal center to obtain a sample including a measurement cross section. The longitudinal center of the structural member 100 is the portion extending, for example, 200 mm on both sides from the longitudinal center of the structural member 100. The measurement cross section is a cross section obtained by cutting the structural member 100 perpendicular to the longitudinal direction and includes the protruding portion 41 of the adhesive 40. The measurement cross section of this sample is observed, for example, with an optical microscope, and the length of the portion of the protruding portion 41 that contacts the second member 20 is measured. In other words, the linear distance from the end point E1 on the flange 13 side of the contact surface 411 of the protruding portion 41 with the second member 20 to the end point E2 on the opposite side is measured and determined as the contact width W. In addition, the measurement cross section of the sample is observed, for example, with an optical microscope, and the distance between the straight line connecting the end points E1 and E2 of the contact surface 411 of the protruding portion 41 and the straight line L that is parallel to this line and touches the protruding portion 41 at a position away from the second member 20 is measured and determined as the maximum height H.

[0046] The radius of curvature R of the bent portion 15 may also be measured by observing the cross section of the sample with an optical microscope. For example, in the cross section of the sample observed with an optical microscope, the radius of curvature R of the bent portion 15 can be determined as the radius of curvature of an arc passing through three points on the outer surface of the bent portion 15, specifically, the end portion (R end) 153 on the flange 13 side, the end portion (R end) 154 on the vertical wall 12 side, and the midpoint thereof.

[0047] [Manufacturing methods for structural components] An example of a manufacturing method for the structural member 100 according to this embodiment will be briefly described below. When manufacturing the structural member 100, a first member 10 and a second member 20 are prepared. The first member 10 and the second member 20 are each formed from a metal plate. The first member 10 and the second member 20 may each be formed from a steel plate.

[0048] The first member 10 is formed, for example, by pressing a metal plate. When the tensile strength of the first member 10 is TS (MPa) and the plate thickness is t (mm), TS / t is preferably 900 or more. TS / t is more preferably 1500 or more, and even more preferably 2000 or more. TS / t is, for example, 3000 or less. Although not particularly limited, the tensile strength TS of the first member 10 may be 1180 MPa or more, and is preferably 1470 MPa or more.

[0049] The tensile strength TS and thickness t of the first member 10 can be measured at a position where thickness reduction due to press working is relatively unlikely to occur. For example, the structural member 100 is cut at the center in the longitudinal direction to obtain a test piece from the top plate 11, and a tensile test in accordance with JIS Z 2241:2022 is performed using this test piece to measure the tensile strength TS of the first member 10. Alternatively, for example, the structural member 100 is cut at the center in the longitudinal direction to obtain a sample, and the thickness of the top plate 11 is measured at five locations at 10 mm intervals on the cross section of this sample using a vernier caliper. The average value of the measured thicknesses of the top plate 11 can be used as the thickness t of the first member 10.

[0050] When the second member 20 is given a certain shape, the second member 20 may be formed by pressing a metal plate. The tensile strength of the second member 20 may be the same as or different from the tensile strength TS of the first member 10. The plate thickness of the second member 20 may be the same as or different from the plate thickness t of the first member 10.

[0051] A liquid adhesive 40, for example, is applied to the prepared first member 10 and second member 20. The adhesive 40 is applied to at least one of the flanges 131, 132 of the first member 10 and the second member 20, for example, along the longitudinal direction thereof. Next, the second member 20 is placed on the flanges 131, 132 of the first member 10. Then, the flanges 131, 132 of the first member 10 and the second member 20 are welded together. The flanges 131, 132 of the first member 10 and the second member 20 are joined together by, for example, spot welding.

[0052] The flanges 131, 132 of the first member 10 and the second member 20 are held so as to be pressed against each other during welding. Therefore, the adhesive 40 is extruded into and out of the space S from between the flanges 131, 132 of the first member 10 and the second member 20. The portion of the adhesive 40 extruded into the space S hardens to form a protruding portion 41. The protruding portion 41 may be formed in a shape that protrudes from the second member 20 side toward the top plate 11 side of the first member 10. The height of the protruding portion 41 may, for example, gradually decrease from the position of the maximum height H toward the end points E1 and / or E2 of the contact surface 411 with the second member 20. As the adhesive 40 hardens, the flanges 131, 132 of the first member 10 and the second member 20 are bonded together.

[0053] The contact width W and maximum height H of the protruding portion 41 can be adjusted by changing the amount and position of the adhesive 40 applied. Although not particularly limited, for example, the contact width W and maximum height H of the protruding portion 41 can be increased by increasing the amount of adhesive 40 applied or by applying adhesive 40 to the flange 13 of the first member 10 and / or the second member 20 at a position closer to the bent portion 15. Furthermore, for example, to increase the contact width W of the protruding portion 41, the adhesive 40 may be applied and then welded with the second member 20 positioned below the first member 10. In this case, gravity can be used to cause the adhesive 40 to flow toward (downward from) the second member 20.

[0054] The adhesive 40 is preferably a heat-curing adhesive. In this case, the adhesive 40 may be cured by the heat generated during welding. Although not particularly limited, the heat-curing adhesive may be, for example, a one-component heat-curing epoxy adhesive.

[0055] The adhesive 40 after curing preferably has a Young's modulus of 1.2 GPa or more. The Young's modulus of the adhesive 40 is more preferably 3.0 GPa or more, and even more preferably 4.5 GPa or more. The Young's modulus of the adhesive 40 may be 5.0 GPa or less.

[0056] The Young's modulus of the adhesive 40 can be measured using a nanoindenter. The specific measurement procedure is as follows: The structural member 100 is cut at the center in the longitudinal direction, and a sample is taken with the protruding portion 41 exposed on the cross section. An indenter is pressed into the protruding portion 41 on the cross section of the sample so that only the adhesive 40 is compressively deformed, and a load is applied. After the load reaches the maximum load, the load is released. The maximum indenter pressing amount is about 100 nm. A load-displacement curve is obtained from the start of loading to the end of unloading. The slope S (N / mm) of the load-displacement curve during unloading, and the contact area A (mm 2 ), the Young's modulus E of the adhesive 40 can be calculated using the following formula (1). E=(√π / 2)×(S / √A) (1)

[0057] [effect] The structural member 100 according to this embodiment can have high strength against a load input from the second member 20 side. This will be explained in detail below.

[0058] 4A to 4C are schematic diagrams showing the deformation behavior of a structural member including a first member 10 and a second member 20 when a load P is input from the second member 20 side. When the load P is input, the cross section of the structural member deforms in the order of FIGS. 4A, 4B, and 4C. Referring to FIGS. 4A to 4C, when the load P is applied to the second member 20, the structural member undergoes bending deformation with the second member 20 side on the inside of the bend. As a result, a compressive force acts on the second member 20 along the longitudinal direction of the structural member, and a tensile force acts on the top plate 11 of the first member 10 along the longitudinal direction of the structural member. A compressive force also acts on a portion of the first member 10 close to the second member 20, specifically, on the bent portion 15 near the flange 13 along the longitudinal direction of the structural member. Due to the action of the compressive force, the bent portions 15 move toward the inside of the structural member so as to approach each other in a cross-sectional view of the structural member. As a result, deformation occurs in the vertical wall 12, with the flange 13 side tilting more inwardly of the structural member than the top plate 11 side. The distance between the top plate 11 of the first member 10 and the second member 20 gradually decreases as the bent portion 15 moves and the vertical wall 12 tilts. When the vertical wall 12 finally buckles, the distance between the top plate 11 of the first member 10 and the second member 20 suddenly decreases.

[0059] However, in the structural member 100 according to this embodiment, the flange 13 of the first member 10 is joined to the second member 20 not only by welding but also by adhesive 40. The protruding portion 41 of the adhesive 40 is adjacent to the bent portion 15 of the first member 10 on the inside of the structural member 100. In this case, the protruding portion 41 of the adhesive 40 can suppress the movement of the bent portion 15 described above. Therefore, tilting of the vertical wall 12 is suppressed, and the cross-sectional shape of the structural member 100 is more easily maintained.

[0060] When a load is input to the structural member 100 from the second member 20 side and a compressive force acts on the bent portion 15 of the first member 10 in the longitudinal direction of the structural member 100, the bent portion 15 moves toward the inside of the structural member 100. If the protruding portion 41 of the adhesive 40 does not extend in the direction of movement of the bent portion 15, the bent portion 15 will easily climb over the protruding portion 41 and penetrate into the inside of the structural member 100. If the bent portion 15 climbs over the protruding portion 41, the protruding portion 41 will no longer be able to provide resistance to the bent portion 15. In contrast, in the structural member 100 according to this embodiment, the contact width W of the protruding portion 41 is 0.50 or more times the radius of curvature R of the bent portion 15. In other words, the protruding portion 41 extends along the direction of movement of the bent portion 15 of the first member 10, a length that is 0.50 or more times the radius of curvature R of the bent portion 15. In this case, it becomes difficult for the bent portion 15, which attempts to move toward the inside of the structural member 100, to overcome the protruding portion 41, and the protruding portion 41 can continuously provide resistance to the bent portion 15. Therefore, tilting of the vertical wall 12 is continuously suppressed, and the cross-sectional shape of the structural member 100 is more likely to be maintained. This makes it possible to further increase the strength of the structural member 100 against a load input from the second member 20 side.

[0061] In the structural member 100 according to this embodiment, the first member 10 and the second member 20 are joined together by a combination of welding and adhesive 40. This makes it less likely that the welded portion of the first member 10 and the second member 20 will break, particularly in the peeling direction, compared to when the first member 10 and the second member 20 are joined together by welding alone.

[0062] In the structural member 100 according to this embodiment, the maximum height H of the protruding portion 41 of the adhesive 40 is preferably at least 0.50 times the radius of curvature R of the bent portion 15. This makes it more difficult for the bent portion 15, which gradually moves inward of the structural member 100, to overcome the protruding portion 41, improving the effect of providing resistance to the bent portion 15. This therefore makes it possible to further increase the strength of the structural member 100 against a load input from the second member 20 side.

[0063] In the structural member 100 according to this embodiment, the adhesive 40 preferably has a Young's modulus of 1.2 GPa or more. In this case, the effect of the protruding portion 41 as a resistance to the bent portion 15 can be further improved. Therefore, the strength of the structural member 100 against a load input from the second member 20 side can be further increased.

[0064] In the structural member 100 according to this embodiment, the ratio of the tensile strength TS to the thickness t of the first member 10 (TS / t) is preferably 900 or greater. When TS / t≧900, the thickness t is small relative to the tensile strength TS, and the rigidity of the first member 10 is relatively low. Therefore, when the structural member 100 receives a load from the second member 20, the movement of the bent portion 15 and the accompanying tilting of the vertical wall 12 as described above are likely to occur. Furthermore, when TS / t≧900, the tensile strength TS is large relative to the thickness t, and the amount of elastic deformation of the first member 10 is relatively large. Therefore, the movement of the bent portion 15 and the tilting of the vertical wall 12 occur for a relatively long period of time. In this embodiment, the protruding portion 41 of the adhesive 40 continuously provides resistance to the bent portion 15, thereby continuously suppressing the movement of the bent portion 15. Therefore, when the bent portion 15 in the first member 10 is likely to move and the bent portion 15 moves for a relatively long period of time, that is, when TS / t≧900, the effect of increasing the strength of the structural member 100 is likely to be significantly achieved.

[0065] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present disclosure. [Example]

[0066] The present disclosure will be described in more detail below with reference to examples, although the present disclosure is not limited to the following examples.

[0067] In order to confirm the effects of the present disclosure, a load application simulation analysis (three-point bending simulation analysis) was performed on a structural member including a first member 10 having a hat-shaped cross section and a second member 20 serving as a closing plate, using general-purpose CAE analysis software (LS-DYNA, manufactured by Ansys).

[0068] FIG. 5 is a schematic diagram showing a cross section of the structural member model used in this analysis. Referring to FIG. 5, in this analysis, the width w1 of the top plate 11 of the first member 10 was 80 mm, the height h1 of the vertical wall 12 was 60 mm, and the width w2 of the second member 20 was 120 mm. Furthermore, the distance between supports was set to 500 mm, and a load was applied toward the first member 10 with respect to the longitudinal center of the second member 20, thereby performing three-point bending of the structural member. Table 1 shows the assumed conditions of the first member 10 and the second member 20, as well as the specifications of the adhesive 40, for each structural member subjected to three-point bending. The "Maximum Load" in Table 1 is the maximum load value on the load-displacement curve obtained in the load application simulation analysis.

[0069] [Table 1]

[0070] In Table 1, in Comparative Example 4 and Examples 1 to 12, the first member 10 and the second member 20 are joined together using both welding (spot welding) and adhesive 40. In Comparative Example 4 and Examples 1 to 12, as shown in FIG. 3, there is a protruding portion 41 of adhesive 40 adjacent to the bent portion 15 near the flange 13 of the first member 10. On the other hand, in Comparative Examples 1 to 3 and 5, the first member 10 and the second member 20 are joined together only by welding (spot welding), and adhesive 40 is not used. Therefore, there is no protruding portion 41 of adhesive 40 in Comparative Examples 1 to 3 and 5. When Comparative Example 3 and Comparative Example 4 are compared, which differ only in the presence or absence of adhesive 40, the maximum load in Comparative Example 4 is slightly higher than that of Comparative Example 3.

[0071] In Comparative Example 4, the contact width W of the protruding portion 41 with the second member 20 is less than 0.50 times the radius of curvature R of the bent portion 15 (W / R<0.50). On the other hand, in Examples 4 to 7, the conditions of the first member 10 and the second member 20 are the same as in Comparative Example 4, but the contact width W is ensured to be 0.50 times or more the radius of curvature R of the bent portion 15 (W / R≧0.50). In Comparative Example 4, the increase in maximum load compared to Comparative Example 3 was less than 1.0 kN, but in Examples 4 to 7, the maximum load increased by 5.0 kN or more compared to Comparative Example 3. Therefore, if a protruding portion 41 of the adhesive 40 is present and its contact width W is 0.50 times or more the radius of curvature R of the bent portion 15, the maximum load (strength) of the structural member is greatly improved.

[0072] The results of Examples 4 to 7 show that the strength of the structural member increases as the ratio of the contact width W of the protruding portion 41 to the radius of curvature R of the bent portion 15 increases. In Example 6, where the contact width W is close to 1.00 times the radius of curvature R of the bent portion 15, the maximum load increased by 9.0 kN compared to Comparative Example 3, and in Example 7, where the contact width W is 1.50 times or more the radius of curvature R of the bent portion 15, the maximum load increased by 15.0 kN or more compared to Comparative Example 3. Therefore, the contact width W is preferably 1.00 times or more the radius of curvature R of the bent portion 15, and more preferably 1.50 times or more.

[0073] Examples 8 and 10 differ only in the maximum height H of the protruding portion 41 of the adhesive 40. In Example 8, the maximum height H is 0.50 times the radius of curvature R of the bent portion 15 (H / R=0.50), while in Example 10, the maximum height H is 0.70 times the radius of curvature R of the bent portion 15 (H / R=0.70). The maximum load of Example 10 was greater than the maximum load of Example 8. Therefore, the greater the ratio of the maximum height H of the protruding portion 41 to the radius of curvature R of the bent portion 15, the greater the strength of the structural member. It is preferable that the maximum height H of the protruding portion 41 be, for example, 0.50 or more times the radius of curvature R of the bent portion 15.

[0074] Examples 8, 11, and 12 differ only in the Young's modulus of the adhesive 40. Among Examples 8, 11, and 12, the Young's modulus of the adhesive 40 is the largest in Example 12 and the smallest in Example 11. Comparing Examples 8, 11, and 12, Example 12, which had the largest Young's modulus of the adhesive 40, had the largest maximum load. Furthermore, among Examples 8, 11, and 12, Example 11, which had the smallest Young's modulus of the adhesive 40, had the smallest maximum load. Therefore, it can be said that the greater the Young's modulus of the adhesive 40, the greater the strength of the structural member.

[0075] Comparing Examples 8, 11, and 12 with Comparative Example 5, which had the same conditions for the first member 10 and the second member 20, the maximum loads of Examples 8, 11, and 12 were all increased relative to Comparative Example 5. The results of Examples 8, 11, and 12 indicate that the Young's modulus of the adhesive 40 is preferably 1.2 GPa or greater. Furthermore, in Examples 8 and 12, where the Young's modulus of the adhesive 40 was 3.0 GPa or greater, the increase in maximum load from Comparative Example 5 was greater than in Example 11, where the Young's modulus of the adhesive 40 was less than 3.0 GPa. In Example 11, the increase in maximum load relative to Comparative Example 5 was 6.5 kN, whereas in Examples 9 and 12, the maximum load was approximately 10.0 kN higher than Comparative Example 5. Based on these results, it is more preferable that the Young's modulus of the adhesive 40 be 3.0 GPa or greater.

[0076] Comparing Examples 2, 3, 7, and 8 with Comparative Examples 1, 2, 3, and 5, which share the same conditions for the first member 10 and the second member 20, it is clear that the degree of improvement in maximum load increases as TS / t increases. Specifically, in Example 2, where TS / t = 492, the maximum load was 1.34 times that of Comparative Example 1. In Example 3, where TS / t = 983, the maximum load was 1.39 times that of Comparative Example 2. In Example 7, where TS / t = 1500, the maximum load was 1.41 times that of Comparative Example 3. In Example 8, where TS / t = 2250, the maximum load was 1.43 times that of Comparative Example 5. Therefore, it can be seen that the greater the TS / t, the greater the improvement in the strength of the structural member due to the protruding portion 41 of the adhesive 40, and the more pronounced the effect of the protruding portion 41. TS / t is preferably 900 or greater. [Explanation of symbols]

[0077] 100: Structural members 10: First member 11: Top plate 12, 121, 122: Vertical wall 13, 131, 132: Flanges 15, 151, 152: Bent section 20: Second member 40: Adhesive 41: Protruding part 411: Contact surface 50: Joint

Claims

1. A structural member for an automobile having a long shape, a first member including a top plate, a pair of vertical walls arranged to face each other and connected to the top plate, and a pair of flanges connected to the vertical walls via bent portions on opposite sides of the top plate and protruding from the vertical walls to the outside of the vertical walls; a second member disposed opposite the top plate and joined to the flange by welding and adhesive; Equipped with the adhesive includes a protruding portion that protrudes from a joint portion between each of the flanges and the second member into a space formed by the first member and the second member and that contacts the first member and the second member, A structural member, wherein, in a cross section perpendicular to the longitudinal direction of the structural member, when the length of the portion of the protruding portion that contacts the second member is defined as a contact width, the contact width is 0.50 times or more the radius of curvature of the bent portion.

2. 10. The structural member of claim 1, A structural member, wherein, in a cross section perpendicular to the longitudinal direction of the structural member, when a direction perpendicular to a contact surface between the protruding portion and the second member is defined as a height direction, the maximum length of the protruding portion in the height direction is 0.50 times or more the radius of curvature.

3. 10. The structural member of claim 1, A structural member, wherein the adhesive has a Young's modulus of 1.2 GPa or greater.

4. 10. The structural member of claim 1, A structural member, wherein TS / t is 900 or more, where TS (MPa) is the tensile strength of the first member and t (mm) is the plate thickness of the first member.

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