structural members

Abstract

To provide a structural member which has improved fatigue strength of a weld part in a concave curved part.SOLUTION: A structural member has a first main surface part, a second main surface part, and a wall part connecting the first main surface part and the second main surface part, wherein the wall part has a first wall constitution part extending from the first main surface part, and a second wall constitution part extending from the second main surface part, the first wall constitution part is arranged inside the second wall constitution part in the wall part, a weld part for fixing the first wall constitution part and the second wall constitution part is arranged on an end of the second wall constitution part, the structural member has a concave curved part and a non-concave curved part when the structural member is viewed in plan view from a height direction of the wall part, and H1X and H1Y at least partially satisfy H1X<H1Y when a height of the first wall constitution part in the wall part is represented by H1, H1 at any position belonging to the concave curved part is represented by H1X, and H1 at any position belonging to the non-concave curved part is represented by H1Y.SELECTED DRAWING: Figure 4

Description

[Technical Field]

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

[0002] A front lower arm, which is a suspension component of an automobile, is an L-shaped component that is connected to a tire and a suspension member. The front lower arm is formed, for example, by welding two components together. Patent Document 1 discloses a suspension arm (front lower arm) having a lower half member and an upper half member that are welded together. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-168640 Summary of the Invention [Problem to be solved by the invention]

[0004] As in Patent Document 1, in structural members having welded parts, cracks due to fatigue at the welded parts are expected. Therefore, there is a demand for improving the fatigue strength of the welded parts. In particular, in structural members using metal plates with high tensile strength, the fatigue strength required of the welded parts is high, so there is a demand for improving the fatigue strength of the welded parts.

[0005] The present inventors focused on reducing residual stress in welds in order to improve the fatigue strength of welds. As a result of a detailed study of residual stress in welds, they found that the residual stress in welds varies greatly depending on the position, and that high tensile residual stress occurs in welds in particular in areas defined as "concave curved portions," which will be described later.

[0006] The present disclosure has been made in consideration of the above-described circumstances, and has as its main object to provide a structural member having improved fatigue strength of a welded portion in a concave curved portion. [Means for solving the problem]

[0007] In the present disclosure, there is provided a structural member having a first main surface portion, a second main surface portion, and a wall portion connecting the first main surface portion and the second main surface portion, wherein the wall portion has a first wall-forming portion extending from the first main surface portion and a second wall-forming portion extending from the second main surface portion, wherein in the wall portion, the first wall-forming portion is disposed inside the second wall-forming portion, and a weld portion for fixing the first wall-forming portion and the second wall-forming portion is disposed at an end portion of the second wall-forming portion, and when the structural member is viewed from above in a height direction of the wall portion, the structural member has a concavely curved portion and a non-concavely curved portion, and wherein a height of the first wall-forming portion in the wall portion is defined as H1, and H1 at any position belonging to the concavely curved portion is defined as H 1X and H1 at any position belonging to the non-concave curved portion is H 1Y In this case, the above H 1X and the above H 1Y is at least partially H 1X <H 1Y To provide a structural member that satisfies the above requirements.

[0008] According to the present disclosure, H 1X and H 1Y At least some of the 1X <H 1Y Since the above condition is satisfied, the structural member has improved fatigue strength of the welded portion at the concave curved portion.

[0009] In the above disclosure, the minimum value of H1 in the concave curved portion is H 1X-MIN The minimum value of H1 in the non-concave curved portion is H 1Y-MIN In this case, the above H 1X-MIN and the above H 1Y-MIN is H 1X-MIN <H 1Y-MIN may be satisfied.

[0010] In the above disclosure, the above H 1X-MIN and the above H 1Y-MIN , 0≦H 1X-MIN / H1Y-MIN ≦0.75 may be satisfied.

[0011] In the above disclosure, the height of the second wall component in the wall portion is H2, and the H 1X-MIN The above H2 at the position where 2XA In this case, the above H 1X-MIN and the above H 2XA , 0≦H 1X-MIN / (H 1X-MIN +H 2XA )≦0.5 may be satisfied.

[0012] In the above disclosure, the average value of H1 in the concave curved portion is H 1X-AVE The average value of H1 in the non-concave curved portion is H 1Y-AVE In this case, the above H 1X-AVE and the above H 1Y-AVE is H 1X-AVE <H 1Y-AVE may be satisfied.

[0013] In the above disclosure, the above H 1X-AVE and the above H 1Y-AVE , 0≦H 1X-AVE / H 1Y-AVE ≦0.75 may be satisfied.

[0014] In the above disclosure, the height of the second wall component in the wall portion is H2, and the average value of H2 in the concave curved portion is H 2X-AVE In this case, the above H 1X-AVE and the above H 2X-AVE , 0≦H 1X-AVE / (H 1X-AVE +H 2X-AVE )≦0.5 may be satisfied.

[0015] Further, in the present disclosure, there is provided a structural member having a first main surface portion, a second main surface portion, and a wall portion connecting the first main surface portion and the second main surface portion, wherein the wall portion has a first wall-forming portion extending from the first main surface portion and a second wall-forming portion extending from the second main surface portion, wherein in the wall portion, the first wall-forming portion is disposed inside the second wall-forming portion, and a welded portion for fixing the first wall-forming portion and the second wall-forming portion is disposed at an end portion of the second wall-forming portion, and when the structural member is viewed from above in a height direction of the wall portion, the structural member has a concavely curved portion and a non-concavely curved portion, and wherein a height of the first wall-forming portion in the wall portion is H1, and H1 at any position belonging to the concavely curved portion is H 1X The height of the second wall component in the wall is H2, and the H 1X The above H2 at the position of H 2X In this case, the above H 1X and the above H 2X is at least partially H 1X ≦H 2X To provide a structural member that satisfies the above requirements.

[0016] According to the present disclosure, H 1X and H 2X At least some of the 1X ≦H 2X Since the above condition is satisfied, the structural member has improved fatigue strength of the welded portion at the concave curved portion.

[0017] In the above disclosure, when the structural member is viewed in a plan view from the height direction of the wall portion, the H 1X and the above H 2X is H 1X ≦H 2X may be satisfied.

[0018] In the above disclosure, the minimum value of H1 in the concave curved portion is H 1X-MIN And the above H 1X-MIN The above H2 at the position where 2XA In this case, the above H 1X-MIN and the above H 2XA , 0≦H 1X-MIN / (H1X-MIN +H 2XA )≦0.5 may be satisfied.

[0019] In the above disclosure, the average value of H1 in the concave curved portion is H 1X-AVE The average value of H2 in the concave curved portion is H 2X-AVE In this case, the above H 1X-AVE and the above H 2X-AVE , 0≦H 1X-AVE / (H 1X-AVE +H 2X-AVE )≦0.5 may be satisfied.

[0020] In the above disclosure, when the structural member is viewed in a plan view from a height direction of the wall portion, the concavely curved portion and the non-concavely curved portion may be disposed adjacent to each other.

[0021] In the above disclosure, the maximum height H of the wall portion MAX may be 200 mm or less.

[0022] In the above disclosure, the structural member may be made of a steel plate, and the tensile strength of the steel plate may be 780 MPa or more.

[0023] In the above disclosure, the tensile strength of the steel plate may be 980 MPa or more.

[0024] In the above disclosure, the thickness of the steel plate may be 3.5 mm or less.

[0025] In the above disclosure, the thickness of the steel plate may be 2.9 mm or less.

[0026] In the above disclosure, the structural member may be a structural member of an automobile.

[0027] In the above disclosure, the structural member may be a front lower arm. [Effects of the Invention]

[0028] The present disclosure has an effect of providing a structural member having improved fatigue strength of the welded portion in the concave curved portion. [Brief explanation of the drawings]

[0029] [Figure 1] 1 is a schematic plan view illustrating a structural member according to the present disclosure. [Figure 2] 2 is a cross-sectional view of the structural member shown in FIG. 1 taken along the line AA. [Figure 3] 3 is a schematic cross-sectional view illustrating a wall portion according to the present disclosure. FIG. [Figure 4] 2A and 2B are cross-sectional views of the structural member shown in FIG. 1 along lines BB and CC. [Figure 5] FIG. 10 is an explanatory diagram illustrating the occurrence of cracks in a wall portion. [Figure 6] FIG. 2 is an explanatory diagram illustrating the mechanism of residual stress generation in a welded portion. [Figure 7] FIG. 10 is an explanatory diagram illustrating residual stress in a concave curved portion. [Figure 8] FIG. 10 is an explanatory diagram illustrating out-of-plane deformation of a wall portion. [Figure 9] 1 is a schematic plan view illustrating a structural member according to the present disclosure. [Figure 10] 1 is a schematic side view illustrating a structural member according to the present disclosure. [Figure 11] 1A and 1B are schematic plan and side views illustrating a structural member according to the present disclosure. [Figure 12] 3 is a schematic cross-sectional view illustrating a wall portion according to the present disclosure. FIG. [Figure 13] 1 is a schematic cross-sectional view illustrating a structural member according to the present disclosure. [Figure 14] 1 is a schematic cross-sectional view illustrating a structural member according to the present disclosure. [Figure 15] 1A to 1C are schematic cross-sectional views illustrating a method for manufacturing a structural member according to the present disclosure. [Figure 16] 10 is a graph showing the relationship between the height HX of the first wall constituent portion in the wall portion and the rate of decrease in maximum tensile residual stress. DETAILED DESCRIPTION OF THE INVENTION

[0030] The structural members of this disclosure will be described in detail below. In the drawings shown below, the size and shape of each part are appropriately exaggerated for ease of understanding. Furthermore, in each drawing, reference numerals may be omitted for convenience.

[0031] Fig. 1 is a schematic plan view illustrating a structural member according to the present disclosure, specifically a front lower arm, Fig. 2 is a cross-sectional view of the structural member shown in Fig. 1 taken along line AA.

[0032] As shown in FIGS. 1 and 2, a structural member 10 has a first main surface portion 11, a second main surface portion 21, and wall portions 31 and 32 connecting the first main surface portion 11 and the second main surface portion 21. In FIG. 2, the first main surface portion 11 and the second main surface portion 21 are positioned opposite each other. Also, as shown in FIG. 2, the wall portion 31 has a first wall-forming portion 12 extending from the first main surface portion 11 and a second wall-forming portion 22 extending from the second main surface portion 21. Also, as shown in FIG. 2, in the wall portion 31, the first wall-forming portion 12 is positioned more inward than the second wall-forming portion 22. An end portion of the first wall-forming portion 12 and an end portion of the second wall-forming portion 22 partially overlap each other to enable lap fillet welding. Also, a weld portion 3 for fixing the first wall-forming portion 12 and the second wall-forming portion 22 is disposed at the end portion of the second wall-forming portion 22.

[0033] In the present disclosure, the height of the first wall-constituting portion in the wall portion is defined as H1. Here, as shown in Fig. 3, in a cross section having the first main surface portion 11, the second main surface portion 21, and the wall portion 31, the first wall-constituting portion 12 in the wall portion 31 is usually linear. As shown in Fig. 3, "the height of the first wall-constituting portion in the wall portion" refers to the distance from position α of the root of the welded portion 3 in the first wall-constituting portion 12 to position β of the end portion of the linear first wall-constituting portion 12 on the first main surface portion 11 side (the boundary between the linear first wall-constituting portion 12 and the bent portion located at the boundary between the first wall-constituting portion 12 and the first main surface portion 11).

[0034] When the structural member is viewed from above in the height direction of the wall portion, the structural member has a concavely curved portion and a non-concavely curved portion. Here, the "height direction of the wall portion" refers to the extension direction of the wall portion (first wall-constituting portion and second wall-constituting portion) in a cross section having the first main surface portion, the second main surface portion, and the wall portion. Also, the "cross section having the first main surface portion, the second main surface portion, and the wall portion" refers to a cross section perpendicular to the extension direction of the space portion partitioned by the first main surface portion, the second main surface portion, and the wall portion. The height direction of the wall portion is, for example, direction D in FIG. 2. H The concavely curved portion and the non-concavely curved portion will be described in detail later, but for example, in FIG. 1, the area near line BB corresponds to the concavely curved portion, and the area near line CC corresponds to the non-concavely curved portion. Also, FIG. 4(a) is a cross-sectional view of the structural member shown in FIG. 1 taken along line BB, and FIG. 4(b) is a cross-sectional view of the structural member shown in FIG. 1 taken along line CC. As shown in FIG. 4(a), H1 (height of the first wall component in the wall) at any position belonging to the concavely curved portion is defined as H 1X As shown in FIG. 4(b), H1 (the height of the first wall component in the wall) at any position belonging to the non-concave curved portion is defined as H 1Y Let's say.

[0035] In the present disclosure, for example, H 1X and H 1Y But at least some of it is H 1X <H 1Y Since the height H of the first wall component in the concave curved portion is satisfied, the fatigue strength of the welded portion in the concave curved portion is improved. 1X is the height H of the first wall component in the non-concave curved section. 1Y By making the height H of the second wall component in the non-concave curved portion smaller than , the occurrence of tensile residual stress can be suppressed, and the fatigue strength of the welded portion can be improved. 2Y is the height H of the second wall component in the concave curved section. 2X If the thickness is larger, for example, it becomes easier to ensure good surface rigidity.

[0036] As shown in FIG. 4(a), H1 (height of the first wall component in the wall) at any position belonging to the concave curved portion is H 1XAnd H 1X H2 (height of the second wall component in the wall) at the position 2X In the present disclosure, for example, H 1X and H 2X But at least some of it is H 1X ≦H 2X Since the above condition is satisfied, the structural member has improved fatigue strength of the welded portion at the concave curved portion.

[0037] As in Patent Document 1, structural components having welds are expected to experience fatigue cracking at the welds. Specifically, as shown in FIG. 5, fatigue cracks C are expected to occur at the toe 3x of the weld 3. Meanwhile, in order to achieve both weight reduction and strength, it is desirable to use metal plates with high tensile strength in structural components (e.g., automobile chassis components). In particular, structural components using metal plates with high tensile strength require higher fatigue strength at the welds, so improving the fatigue strength of the welds is desirable. Furthermore, because concave curved portions are prone to stress concentration when a load is applied, improving the fatigue strength of the welds is important. In particular, suspension components such as lower arms are important safety components that affect human lives. In this respect, improving the fatigue strength of the welds is also important.

[0038] The present inventors focused on reducing residual stress in welds in order to improve the fatigue strength of welds. After conducting a detailed study of residual stress in welds, they discovered that residual stress in welds varies significantly depending on its location, and that high tensile residual stress occurs in welds, particularly in areas defined as "concave curved portions" (described below). Furthermore, they investigated the mechanism and discovered that the occurrence of high tensile residual stress is closely related to the out-of-plane deformation of the wall during welding.

[0039] 1.Relationship between the occurrence of residual stress and out-of-plane deformation of the wall As shown in Fig. 6(a), assume that a first wall constituent part 12 and a second wall constituent part 22 are welded together. As shown in Fig. 6(b), during the heating process in welding a concave curved part, the first wall constituent part 12 and the second wall constituent part 22 are significantly deformed inward out-of-plane to form a welded part 3. Then, during the cooling process, as shown in Fig. 6(c), the first wall constituent part 12 and the second wall constituent part 22 that have been deformed inward out-of-plane deform back outward, and tensile residual stress is generated in the welded part 3.

[0040] Figure 7(a) is a schematic cross-sectional view of a conventional structural member, with the dashed-line X representing a typical concave curved portion. The out-of-plane deformation and residual stress of the wall during the cooling process were evaluated at 10 points in the P and Q regions shown in Figure 7(a) using computer-aided engineering (CAE) analysis. The results are shown in Figure 7(b). The horizontal axis in Figure 7(b) represents the out-of-plane deformation of the weld toe during the cooling process, with positive values ​​corresponding to outward out-of-plane deformation. The vertical axis in Figure 7(b) represents the residual stress divided by the tensile strength of the base material, with positive values ​​corresponding to tensile residual stress and negative values ​​corresponding to compressive residual stress. As shown in Figure 7(b), the out-of-plane deformation of the wall during the cooling process was large at the concave curved portion X, and the tensile residual stress was also high. Therefore, it was suggested that suppressing the out-of-plane deformation of the wall during welding is important for reducing the tensile residual stress of the weld in a concave curved portion.

[0041] In the present disclosure, as shown in the above-mentioned FIGS. 4(a) and 4(b), H 1X and H 1Y At least some of the 1X <H 1Y It is preferable to change the position of the weld 3 in the concave curved portion and the non-concave curved portion so as to satisfy the following. That is, as shown in FIGS. 4(a) and 4(b), 1X (height of the first wall component 12 at the concave curved portion) is defined as H 1Y It is preferable that the height of the first wall component 12 at the non-concave curved portion is smaller than H 1X and H2X At least some of the 1X ≦H 2X It is preferable that the following condition be satisfied. This suppresses out-of-plane deformation of the wall portion during welding in the concave curved portion, and suppresses the generation of tensile residual stress. As a result, a structural member with improved fatigue strength at the welded portion in the concave curved portion is obtained.

[0042] H 1X The reason why out-of-plane deformation of the wall portion during welding is suppressed by reducing the height (of the first wall constituent portion at the concave curved portion) is as follows. Here, FIG. 8(a) is a schematic cross-sectional view illustrating an example of a wall portion in the present disclosure. As shown in FIG. 8(a), the position of the end portion of the linear first wall constituent portion 12 on the first main surface portion 11 side is designated as position β. The reason why out-of-plane deformation of the wall portion during welding is suppressed is that the temperature difference between the welded portion 3 and position β is reduced, thereby reducing the difference in thermal expansion in the welding direction. This point will be explained in more detail using FIGS. 8(b) and 8(c).

[0043] FIG. 8(b) shows the welded portion 3 in FIG. 8(a) in the height direction D of the wall portion. H 8(c) is a schematic cross-sectional view cut in a direction perpendicular to the wall portion 8(a), and FIG. 8(c) is a schematic cross-sectional view cut in a direction perpendicular to the wall portion 8(a). H This is a schematic cross-sectional view taken in a direction perpendicular to the plane of the glass. Here, the amount of thermal expansion is Δl (mm), the length before expansion is l (mm), the linear expansion coefficient is α, and the temperature change is ΔT. In this case, Δl / l = αΔT holds. Note that Δl / l is L.

[0044] As shown in FIG. 8(b), the L at the welded portion 3 is defined as L3. L3 satisfies L3=αΔT3. On the other hand, as shown in FIG. 8(c), the L at the position β is defined as L β Let's say. L β L β = αΔT β When the height H1 of the first wall-forming portion 12 (i.e., the distance between the welded portion 3 and the position β in FIG. 8(a)) is reduced, the temperature difference between the welded portion 3 and the position β (ΔT3 - ΔT β ) becomes smaller. The temperature difference (ΔT3-ΔT β) becomes smaller, the thermal expansion difference (L3-L β ) is also reduced. As a result, the amount of out-of-plane deformation of the wall portion during the heating process is reduced, and the amount of return of the wall portion during the cooling process is also reduced. Therefore, the tensile residual stress in the welded portion 3 is reduced.

[0045] Furthermore, in the present disclosure, the height H1 of the first wall-constituting portion, which is disposed more inward than the second wall-constituting portion, is relatively small, rather than the height H2 of the second wall-constituting portion. Here, the influence of out-of-plane deformation of the wall portion is more pronounced on the first wall-constituting portion, which is disposed on the inside. The reason for this is that the first wall-constituting portion is more susceptible to heat during welding than the second wall-constituting portion, resulting in a greater amount of heat input. Furthermore, the out-of-plane deformation of the second wall-constituting portion is suppressed by the first wall-constituting portion, which is disposed on the inside, acting as a barrier, but the out-of-plane deformation of the first wall-constituting portion does not have a member that acts as a barrier. In this respect, the influence of out-of-plane deformation of the wall portion is more pronounced on the first wall-constituting portion, which is disposed on the inside. Therefore, by relatively reducing the height H1 of the first wall-constituting portion, the out-of-plane deformation of the wall portion during welding is effectively suppressed.

[0046] 2. Concave and non-concave curved sections When the structural member of the present disclosure is viewed in plan view from the height direction of the wall portion, the structural member has a concavely curved portion and a non-concavely curved portion. The concavely curved portion and the non-concavely curved portion are defined as follows.

[0047] First, view the structural member in a plan view from the height direction of the wall portion, and identify one evaluation point corresponding to the end of the welded portion in its plan view shape. Next, identify two points (the ends of the welded portion) that are 4 mm away from the evaluation point. Next, identify the curvature circle from these three points. Next, when the line segment from the evaluation point to the center of curvature overlaps with the structural member 10 as in the left curvature circle shown in FIG. 9, it is considered positive (plus), and when the line segment from the evaluation point to the center of curvature does not overlap with the structural member 10 as in the right curvature circle shown in FIG. 9, it is considered negative (minus). When the radius of curvature R [mm] satisfies -400 ≤ R < 0, the evaluation point is determined to be included in the concave curved portion. On the other hand, the evaluation point with R < -400 is determined not to be included in the concave curved portion because the curvature is small and close to a straight line. Also, the region (set of evaluation points) where the radius of curvature R [mm] satisfies -400 ≤ R < 0 is defined as the concave curved portion.

[0048] The radius of curvature R in the concave curved portion is -400 mm or more and less than 0, and may be -300 mm or more, may be -200 mm or more, and may be -100 mm or more. On the other hand, the radius of curvature R in the concave curved portion is, for example, -3 mm or less. Also, when the structural member is viewed in a plan view from the height direction of the wall portion, the length of the concave curved portion is, for example, 30 mm or more and 1000 mm or less, and may be 50 mm to 200 mm or less.

[0049] In contrast, when the radius of curvature R [mm] satisfies 0 ≤ R or R < -400, the evaluation point is determined to be included in the non-concave curved portion. Also, the region (set of evaluation points) where the radius of curvature R [mm] satisfies 0 ≤ R or R < -400 is defined as the non-concave curved portion. The non-concave curved portion may be a straight line portion (R = 0), may be a convex curved portion (0 < R), or may be a portion that is gently curved in a concave shape so as not to correspond to the concave curved portion defined as above (R < -400). Also, when the structural member is viewed in a plan view from the height direction of the wall portion, the length of the non-concave curved portion is, for example, 10 mm or more and 1000 mm or less, and may be 15 mm or more and 300 mm or less.

[0050] A structural member in the present disclosure may have only one concavely curved portion or may have two or more concavely curved portions, and a structural member in the present disclosure may have only one non-concavely curved portion or may have two or more non-concavely curved portions.

[0051] The concavely curved portion and the non-concavely curved portion may be arranged adjacent to each other. For example, in FIG. 10(a), from the left side of the drawing, the non-concavely curved portion, the concavely curved portion, and the non-concavely curved portion are arranged adjacent to each other in this order. The welds 3 are formed continuously in these three regions. As shown in FIG. 10(a), the welds 3 may be arranged linearly in the concavely curved portion. Also, as shown in FIG. 10(b), the welds 3 may be arranged convexly in the concavely curved portion. In FIGS. 10(a) and (b), the welds 3 in the concavely curved portion have flat portions, but as shown in FIG. 10(c), the welds 3 in the concavely curved portion do not have to have flat portions.

[0052] 11(a) and (b), in the P region having adjacent concavely curved portions and non-concavely curved portions, the welds 3 may be arranged linearly. In that case, in the R region having other non-concavely curved portions, as shown in FIGS. 11(a) and (c), the height of the first wall-forming portion 12 in the wall portion becomes relatively large.

[0053] 3. Structural members In the present disclosure, the structural member has a first main surface portion, a second main surface portion, and a wall portion connecting the first and second main surfaces. The height of the first wall-forming portion in the wall portion is defined as H1. The "height of the first wall-forming portion in the wall portion" refers to the distance from the root position α of the welded portion 3 in the first wall-forming portion 12 to the end position β of the bent portion (the bend stop) located at the boundary between the first wall-forming portion 12 and the first main surface portion 11, as shown in FIG. 3 . Also, in the present disclosure, the height of the second wall-forming portion in the wall portion is defined as H2. The "height of the second wall-forming portion in the wall portion" refers to the distance from the root position α of the welded portion 3 in the second wall-forming portion 22 to the end position γ of the bent portion (the bend stop) located at the boundary between the second wall-forming portion 22 and the second main surface portion 21, as shown in FIG. 3 . Also, in the present disclosure, the height of the wall portion is defined as H. As shown in FIG. 3, the "height of the wall portion" refers to the distance from the position β of the end of the bent portion located at the boundary between the first wall portion 12 and the first main surface portion 11 to the position γ of the end of the bent portion located at the boundary between the second wall portion 22 and the second main surface portion 21. Therefore, H usually satisfies the relationship H=H1+H2. The maximum value H of the wall portion height H MAX is, for example, 200 mm or less, and may be 150 mm or less. The dimensions of H1 and H2 can be adjusted by the dimensions of the second wall constituent portion 22 disposed on the outside.

[0054] In the present disclosure, H1 (height of the first wall component in the wall) at any position belonging to the concave curved portion is defined as H 1X In the present disclosure, H1 at any position belonging to the non-concave curved portion is defined as H 1Y In this disclosure, H 1X and H 1Y is at least partially H 1X <H 1Y That is, it is preferable that H at any position belonging to the concave curved portion is satisfied. 1x is H at any position that belongs to the non-concave curved part. 1YIt is preferable that the height H1 is smaller than . Conventionally, it has not been known to change the height H1 (the height of the first wall constituent part in the wall part) in a concavely curved part and a non-concavely curved part. In the present disclosure, by relatively reducing the height H1 of the first wall constituent part in a concavely curved part, it is possible to suppress the occurrence of tensile residual stress and improve the fatigue strength of the weld.

[0055] In addition, the minimum value of H1 in the concave curved part is H 1X-MIN For example, if a structural member has a first concave curved portion, a non-concave curved portion, and a second concave curved portion, H 1X-MIN The concave curved portion for which H1 is to be calculated may be the first concave curved portion or the second concave curved portion. 1Y-MIN For example, if a structural member has a first non-concave curved portion, a concave curved portion, and a second non-concave curved portion, H 1Y-MIN The non-concave curved portion for which H is to be determined may be the first non-concave curved portion or the second non-concave curved portion. 1X-MIN The concave curved part for which H is to be calculated 1Y-MIN The non-concave curved portion for which the value of the curved portion is to be determined may be disposed adjacent to the non-concave curved portion.

[0056] H 1X-MIN and H 1Y-MIN is H 1X-MIN <H 1Y-MIN It is preferable that H 1Y-MIN H against 1X-MIN The ratio (H 1X-MIN / H 1Y-MIN ) may be 0 or greater than 0. In the latter case, H 1X-MIN / H 1Y-MIN is, for example, 0.1 or more. 1X-MIN / H 1Y-MIN is usually less than 1, and may be 0.75 or less, or may be 0.5 or less. 1X-MIN / H 1Y-MIN If the value is large, it may not be possible to sufficiently suppress out-of-plane deformation of the wall portion during welding.

[0057] As shown in FIG. 4(a), H1 (height of the first wall component in the wall) at any position belonging to the concave curved portion is defined as H 1X And H 1X H2 (height of the second wall component in the wall) at the position 2X In this disclosure, H 1X and H 2X is at least partially H 1X ≦H 2X It is preferable to satisfy H 1X / (H 1X +H 2X ) may be 0 or greater than 0. In the latter case, H 1X / (H 1X +H 2X ) is, for example, 0.1 or more. 1X / (H 1X +H 2X ) is, for example, 0.5 or less, may be 0.4 or less, or may be 0.3 or less. 1X / (H 1X +H 2X ) is large, it may not be possible to sufficiently suppress out-of-plane deformation of the wall portion during welding.

[0058] In addition, when the structural member is viewed from above in the height direction of the wall, H 1X and H 2X H 1X ≦H 2X It is preferable to satisfy the following: where H 1X ≦H 2X and the above-mentioned H 1X / (H 1X +H 2X ) is referred to as the "predetermined height relationship." 1X and H 2X The height relationship may be satisfied in 70% or more of the concave curved portion, or in 90% or more of the concave curved portion, or in 100% of the concave curved portion. In addition, when a structural member has a plurality of concave curved portions, H 1X and H 2XHowever, it is preferable that the above-mentioned predetermined height relationship be satisfied.

[0059] Also, as shown in Figure 12, H 1X-MIN H2 (height of the second wall component in the wall) at the position where 2XA Let's say. H 2XA For example, when the height of the wall of the concave curved portion is constant, the maximum value H2 of the concave curved portion is 2X-MAX H 1X-MIN and H 2XA is usually 0≦H 1X-MIN / (H 1X-MIN +H 2XA )<1. Here, as shown in Figure 12, H 1X-MIN and H 2XA The sum of H 1X-MIN The height H of the wall at the position X Therefore, H 1X-MIN / (H 1X-MIN +H 2XA ) is H 1X-MIN / H X is equivalent to H 1X-MIN / H X may be 0 or may be greater than 0. In the latter case, H 1X-MIN / H X is, for example, 0.1 or more. 1X-MIN / H X is usually less than 1, and may be 0.75 or less, or may be 0.5 or less. 1X-MIN / H X If the value is large, it may not be possible to sufficiently suppress out-of-plane deformation of the wall portion during welding.

[0060] In addition, the average value of H1 in the concave curved part is H 1X-AVE The average value of H1 in the non-concave curved part is H 1Y-AVE The average value of H1 in a concavely curved portion is calculated by measuring H1 at each position at equal intervals (for example, 1 mm intervals) in the welding direction and calculating the average value. The same applies to the average value of H1 in a non-concavely curved portion. When a structural member has multiple concavely curved portions, the average value of H1 in each concavely curved portion is calculated. 1X-AVESimilarly, if the structural member has multiple non-concave curved portions, it is preferable to determine H at each non-concave curved portion. 1Y-AVE It is preferable to find H 1X-AVE and H 1Y-AVE is H 1X-AVE <H 1Y-AVE It is preferable that H 1Y-AVE H against 1X-AVE The ratio (H 1X-AVE / H 1Y-AVE ) may be 0 or greater than 0. In the latter case, H 1X-AVE / H 1Y-AVE is, for example, 0.1 or more. 1X-AVE / H 1Y-AVE is usually less than 1, and may be 0.75 or less, or may be 0.5 or less. 1X-AVE / H 1Y-AVE If the value is large, it may not be possible to sufficiently suppress out-of-plane deformation of the wall portion during welding.

[0061] In addition, the average value of H2 in the concave curved part is H 2X-AVE If a structural member has multiple concave curved portions, the H 2X-AVE It is preferable to find H 1X-AVE and H 2X-AVE is usually 0≦H 1X-AVE / (H 1X-AVE +H 2X-AVE )<1, where H 1X-AVE and H 2X-AVE The sum of these is the average height H of the wall at the concave curve. X-AVE Therefore, H 1X-AVE / (H 1X-AVE +H 2X-AVE ) is H 1X-AVE / H X-AVE is equivalent to H 1X-AVE / H X-AVE may be 0 or may be greater than 0. In the latter case, H 1X-AVE / H X-AVE is, for example, 0.1 or more. 1X-AVE / H X-AVE is usually less than 1, and may be 0.75 or less, or may be 0.5 or less.1X-AVE / H X-AVE If the value is large, it may not be possible to sufficiently suppress out-of-plane deformation of the wall portion during welding.

[0062] A structural member according to the present disclosure has a first main surface, a second main surface, and a wall connecting the first and second main surfaces. The structural member may have only one wall, or may have multiple walls. For example, the structural member shown in FIG. 2 has wall 31 and wall 32.

[0063] The structural member may have a closed cross section having a first main surface portion 11, a second main surface portion 21, and a wall portion 31. For example, in FIG. 2, the first main surface portion 11, the second main surface portion 21, the wall portion 31, and the wall portion 32 form a closed cross section. A "closed cross section" refers to a cross section in which the outer edge is closed (the outer edge is endless and has no ends in the circumferential direction of the cross section). The shape of the outer edge of the closed cross section is not particularly limited, but examples include polygons such as rectangles. Note that a polygon in the present disclosure includes not only a strict polygon but also a shape in which the portions corresponding to the corners of a polygon are formed in an arc shape.

[0064] A structural member may be composed of multiple members. For example, the structural member shown in FIG. 2 is composed of a first member 1 and a second member 2. The first member 1 has a first main surface portion 11, a first wall-forming portion 12 extending from one end of the first main surface portion 11, and a first wall-forming portion 13 extending from the other end of the first main surface portion 11. Meanwhile, the second member 2 has a second main surface portion 21, a second wall-forming portion 22 extending from one end of the second main surface portion 21, and a second wall-forming portion 23 extending from the other end of the second main surface portion 21. The first member 1 and the second member 2 are joined to each other by two welds 3.

[0065] For example, the structural member shown in FIG. 13(a) is also composed of a first member 1 and a second member 2, similar to the structural member shown in FIG. 2. The first member 1 has a first main surface portion 11, a first wall-forming portion 12 extending from one end of the first main surface portion 11, and a first wall-forming portion 13 extending from the other end of the first main surface portion 11. On the other hand, the second member 2 has a second main surface portion 21, a second wall-forming portion 22 extending from one end of the second main surface portion 21, and a second wall-forming portion 23 extending from the other end of the second main surface portion 21. The first wall-forming portion 12 is positioned more inward than the second wall-forming portion 22, and a welded portion 3 is positioned at an end of the second wall-forming portion 22. On the other hand, the first wall-forming portion 13 is positioned more outward than the second wall-forming portion 23, and a welded portion 3 is positioned at an end of the first wall-forming portion 13. In this way, when a structural member according to the present disclosure has a plurality of first wall-forming portions, it is sufficient that at least one of the first wall-forming portions is disposed more inward than the corresponding second wall-forming portion.

[0066] A structural member may be composed of a single member. For example, the structural member shown in Fig. 13(b) is composed of a single member having a first wall-forming portion 12, a first main surface portion 11, a wall portion 32, a second main surface portion 21, and a second wall-forming portion 22. The wall portion 31 is composed of the first wall-forming portion 12 and the second wall-forming portion 22, and a weld portion 3 is disposed at the end of the second wall-forming portion 22.

[0067] In a structural member, the first and second main surfaces are preferably positioned opposite each other. "Positioned opposite each other" means that at least a portion of the first and second main surfaces overlap when observed from a certain direction. When the first and second main surfaces are planar, they may be parallel in a cross section including the first and second main surfaces and the wall. For example, in FIG. 2, the first and second main surfaces 11 and 12 are parallel. "Parallel" means that the angle between the extension direction of the first and second main surfaces 11 and 12 is 10° or less. On the other hand, as shown in FIG. 13(c), the first and second main surfaces 11 and 12 do not have to be parallel.

[0068] One of the components constituting the structural member may be made using a tailored blank (TB). For example, the structural member shown in FIG. 14(a) is composed of a single member, similar to the structural member shown in FIG. 13(b). This single member is formed by joining components of different types, thicknesses, and other properties using a tailored blank joint 4. For example, the structural member shown in FIG. 14(b) has a first main surface 11 with one tailored blank joint 4 and a second main surface 21 with multiple tailored blank joints 4. The tailored blank joints 4 are welded joints formed by, for example, laser welding, arc welding, mushroom welding, or the like. A tailored blank with a welded joint is also called a tailored welded blank (TWB).

[0069] Examples of materials constituting the structural member (particularly the first principal surface portion, the second principal surface portion, and the wall portion) include metal materials such as steel, aluminum alloy, and magnesium alloy. In particular, the structural member is preferably made of a metal plate such as a steel plate. The tensile strength of the metal plate is not particularly limited, but is, for example, 780 MPa or more, or may be 980 MPa or more, or may be 1180 MPa or more. The higher the tensile strength of a material used, the higher the fatigue strength required of the welded portion. The structural member of the present disclosure is particularly effective when a material with high tensile strength is used, since the fatigue strength of the welded portion is high. Furthermore, the thickness of the metal plate is, for example, 1 mm or more and 3.5 mm or less, or 1.5 mm or more and 3.2 mm or less, or 1.5 mm or more and 2.9 mm or less. A thin metal plate may not provide sufficient strength, and a thick metal plate may not achieve sufficient weight reduction.

[0070] The use of the structural member in the present disclosure is not particularly limited, but examples thereof include automotive applications. That is, the structural member may be a structural member for an automobile. Examples of structural members for an automobile include suspension members such as a front lower arm, a rear lower arm, a front suspension member, and a rear suspension member. The structural member in the present disclosure may also be an automobile frame. Furthermore, the structural member in the present disclosure may be used in vehicles other than automobiles, such as motorcycles, ships, and aircraft, as well as architectural structures.

[0071] The manufacturing method of the structural member according to the present disclosure is not particularly limited. FIG. 15 is a schematic cross-sectional view illustrating an example of the manufacturing method of the structural member according to the present disclosure. First, as shown in FIG. 15(a), a first member 1 and a second member 2 are prepared. The first member 1 has a first main surface portion 11, a first wall-forming portion 12 extending from one end of the first main surface portion 11, and a first wall-forming portion 13 extending from the other end of the first main surface portion 11. Meanwhile, the second member 2 has a second main surface portion 21, a second wall-forming portion 22 extending from one end of the second main surface portion 21, and a second wall-forming portion 23 extending from the other end of the second main surface portion 21. The first member 1 and the second member 2 are obtained, for example, by pressing a metal plate.

[0072] Next, as shown in FIG. 15(b), the first member 1 and the second member 2 are placed in predetermined positions. Specifically, the first wall constituent portion 12 is placed inside the second wall constituent portion 22, and the first wall constituent portion 13 is placed inside the second wall constituent portion 23. Next, as shown in FIG. 15(c), welds 3 are formed to secure the first member 1 and the second member 2 together. Specifically, welds 3 are formed at the end of the second wall constituent portion 22 and the end of the second wall constituent portion 23. Arc welding, for example, can be used as a method for forming the welds 3. A structural member is obtained by performing the steps described above.

[0073] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any configuration that is substantially identical to the technical idea described in the claims of the present disclosure and that provides similar effects is included within the technical scope of the present disclosure. [Example]

[0074] The geometric model of the structural member shown in Figure 1 was created on a computer using CAD (Computer Aided Design) software. Specifically, the height H of the wall near line BB (concave curved part) shown in Figure 1 was calculated. X is fixed at 22.5 mm, and the height H of the first wall component is 1X Shape models were created with the dimensions changed to 6.5 mm, 10.5 mm, and 13.0 mm.

[0075] The geometric model of the structural member that was created was subjected to CAE analysis to determine the maximum tensile residual stress. The material properties of the structural member were those of a 2.6 mm thick, 980 MPa-class steel plate. The results are shown in Table 1 and Figure 16. The "reduction rate of maximum tensile residual stress" in Table 1 is calculated by the H 1X The reduction rate is based on the case where the value is 13.0 mm.

[0076] [Table 1]

[0077] As shown in Table 1 and Figure 16, H 1X It was confirmed that the tensile residual stress was reduced by reducing [Explanation of symbols]

[0078] 1 ... First member 2 ... Second member 3... Welded section 10... Structural members 11 … First main surface part 12, 13 … 1st wall component 21 … Second main surface part 22, 23 … 2nd wall component 31, 32 … Wall part

Claims

1. A first main surface portion; A second main surface portion; a wall portion connecting the first main surface portion and the second main surface portion; A structural member having the wall portion has a first wall component extending from the first main surface portion and a second wall component extending from the second main surface portion, In the wall portion, the first wall-constituting portion is disposed inside the second wall-constituting portion, a welded portion for fixing the first wall constituent portion and the second wall constituent portion is disposed at an end portion of the second wall constituent portion; When the structural member is viewed in a plan view from a height direction of the wall portion, the structural member has a concavely curved portion and a non-concavely curved portion, The height of the first wall component in the wall portion is H １ and the H at any position belonging to the concave curved portion １ H １Ｘ and the H at any position belonging to the non-concave curved portion １ H １Ｙ In this case, the H １Ｘ and the H １Ｙ is at least partially H １Ｘ <H １Ｙ Structural members that meet the above requirements.

2. The H in the concave curved portion １ The minimum value of H １Ｘ－ＭＩＮ and the H １ The minimum value of H １Ｙ－ＭＩＮ In this case, the H １Ｘ－ＭＩＮ and the H １Ｙ－ＭＩＮ Is, H １Ｘ－ＭＩＮ <H １Ｙ－ＭＩＮ The structural member according to claim 1 , which satisfies the following:

3. The H １Ｘ－ＭＩＮ and the H １Ｙ－ＭＩＮ is 0≦H １Ｘ－ＭＩＮ / H １Ｙ－ＭＩＮ 3. The structural member of claim 2, wherein the structural member satisfies ≦0.

75.

4. The height of the second wall component in the wall portion is H ２ and the H １Ｘ－ＭＩＮ The H at the position ２ H ２ＸＡ In this case, the H １Ｘ－ＭＩＮ and the H ２ＸＡ is 0≦H １Ｘ－ＭＩＮ / (H １Ｘ－ＭＩＮ +H ２ＸＡ 4. The structural member according to claim 2 or 3, wherein the structural member satisfies the following: )≦0.

5.

5. The H in the concave curved portion １ The average value of H １Ｘ－ＡＶＥ and the H １ The average value of H １Ｙ－ＡＶＥ In this case, the H １Ｘ－ＡＶＥ and the H １Ｙ－ＡＶＥ Is, H １Ｘ－ＡＶＥ <H １Ｙ－ＡＶＥ The structural member according to any one of claims 1 to 4, wherein the above formula (1) is satisfied.

6. The H １Ｘ－ＡＶＥ and the H １Ｙ－ＡＶＥ is 0≦H １Ｘ－ＡＶＥ / H １Ｙ－ＡＶＥ 6. The structural member of claim 5, wherein the structural member satisfies ≦0.

75.

7. The height of the second wall component in the wall portion is H ２ and the H ２ The average value of H ２Ｘ－ＡＶＥ In this case, the H １Ｘ－ＡＶＥ and the H ２Ｘ－ＡＶＥ is 0≦H １Ｘ－ＡＶＥ / (H １Ｘ－ＡＶＥ +H ２Ｘ－ＡＶＥ 7. The structural member according to claim 5 or claim 6, wherein the structural member satisfies the following: )≦0.

5.

8. A first main surface portion; A second main surface portion; a wall portion connecting the first main surface portion and the second main surface portion; A structural member having the wall portion has a first wall component extending from the first main surface portion and a second wall component extending from the second main surface portion, In the wall portion, the first wall-constituting portion is disposed inside the second wall-constituting portion, a welded portion for fixing the first wall constituent portion and the second wall constituent portion is disposed at an end portion of the second wall constituent portion; When the structural member is viewed in a plan view from a height direction of the wall portion, the structural member has a concavely curved portion and a non-concavely curved portion, The height of the first wall component in the wall portion is H １ and the H at any position belonging to the concave curved portion １ H １Ｘ and the height of the second wall component in the wall portion is H ２ and the H １Ｘ The H at the position ２ H ２Ｘ In this case, The H １Ｘ and the H ２Ｘ is at least partially H １Ｘ ≦H ２Ｘ Fulfilling A structural member, wherein when the minimum value of H 1 in the concave curved portion is H 1X-MIN and H 2 at the position where H 1X-MIN is reached is H 2XA , ​​H 1X-MIN and H 2XA satisfy 0≦H 1X-MIN / (H 1X-MIN +H 2XA )≦0.

5.

9. A first main surface portion; A second main surface portion; a wall portion connecting the first main surface portion and the second main surface portion; A structural member having the wall portion has a first wall component extending from the first main surface portion and a second wall component extending from the second main surface portion, In the wall portion, the first wall-constituting portion is disposed inside the second wall-constituting portion, a welded portion for fixing the first wall constituent portion and the second wall constituent portion is disposed at an end portion of the second wall constituent portion; When the structural member is viewed in a plan view from a height direction of the wall portion, the structural member has a concavely curved portion and a non-concavely curved portion, The height of the first wall component in the wall portion is H １ and the H at any position belonging to the concave curved portion １ H １Ｘ and the height of the second wall component in the wall portion is H ２ and the H １Ｘ The H at the position ２ H ２Ｘ In this case, The H １Ｘ and the H ２Ｘ is at least partially H １Ｘ ≦H ２Ｘ Fulfilling A structural member, wherein when the average value of H 1 in the concave curved portion is H 1X-AVE and the average value of H 2 in the concave curved portion is H 2X-AVE, H 1X-AVE and H 2X-AVE satisfy 0≦H 1X-AVE / (H 1X-AVE +H 2X-AVE)≦0.

5.

10. When the structural member is viewed in a plan view from the height direction of the wall portion, the H １Ｘ and the H ２Ｘ Is H １Ｘ ≦H ２Ｘ The structural member according to claim 8 or claim 9, which satisfies the above.

11. A structural member according to any one of claims 1 to 10, wherein when the structural member is viewed in a plane from the height direction of the wall portion, the concave curved portion and the non-concave curved portion are arranged adjacent to each other.

12. The maximum height H of the wall ＭＡＸ The structural member according to any one of claims 1 to 11, wherein is 200 mm or less.

13. 13. The structural member according to claim 1, wherein the structural member is made of a steel plate, and the tensile strength of the steel plate is 780 MPa or more.

14. 14. The structural member according to claim 13, wherein the steel plate has a tensile strength of 980 MPa or more.

15. 15. The structural member according to claim 13 or claim 14, wherein the steel plate has a thickness of 3.5 mm or less.

16. 16. The structural member of claim 15, wherein the steel plate has a thickness of 2.9 mm or less.

17. 17. A structural member according to any one of claims 1 to 16, wherein the structural member is a structural member for an automobile.

18. 18. The structural member according to claim 1, wherein the structural member is a front lower arm.

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