Metal composite material and production method thereof

Abstract

To provide a metal composite material that has an excellent rigidity in comparison with conventional technologies even including an adhesive layer.SOLUTION: According to a metal composite material 10 of the present invention, a thickness h1 of a thin steel sheet 1 and a thickness h2 of a low specific gravity sheet 2 are set so as to satisfy a formula that represents a preset bending rigidity [D] of the metal composite material 10. Moreover, a method for producing a metal composite material includes: a step for preparing the thin steel sheet and the low specific gravity sheet; and a step for joining the thin steel sheet and the low specific gravity sheet with each other via an adhesive layer 3 therebetween. The step for joining the thin steel sheet and the low specific gravity sheet with each other is carried out in such a way that a neutral axis when the metal composite material is bent and deformed is set to be within the adhesive layer that has a lower strength than those of the thin steel sheet and the low specific gravity sheet.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a metal composite material and a method for producing the same. [Background technology]

[0002] In recent years, efforts to provide access to sustainable transport systems that take into consideration vulnerable transport participants such as the elderly, people with disabilities and children have been gaining momentum. To achieve this, we are focusing on research and development to further improve transport safety and convenience through development of improved reinforcement effects for vehicles. Conventionally, a side sill structure is known that includes a plate member that divides the closed cross section of the side sill in the vehicle width direction, and a pair of reinforcing members that are arranged in the closed cross section of the side sill so as to sandwich the plate member from both sides in the vehicle width direction (see, for example, Patent Document 1). Each of the reinforcing members of this side sill structure is generally hat-shaped in cross section, and has a bulge that is bonded to the plate member and a flange that is bonded to the inner wall surface of the side sill. According to this side sill structure, the plate member and the reinforcing member ensure the rigidity of the side sill, thereby making it possible to ensure a larger crash stroke of the side sill during a side collision. This allows the side sill to efficiently absorb energy during a side collision. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2010-143461 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in conventional side sill structures (see, for example, Patent Document 1), an adhesive layer is interposed between the reinforcing member and the plate member. Therefore, in the event of a side collision, the adhesive layer may peel off before the reinforcing member or the plate member, and the side sill structure may not be able to exert a sufficient reinforcing effect. Therefore, there is a demand for a metal composite material that is applied to a vehicle body structure such as this side sill structure and that contributes to collision load transmission while including an adhesive layer and exerts a better reinforcing effect.

[0005] The object of the present invention is to provide a metal composite material that includes an adhesive layer but has an excellent reinforcing effect without being broken at the adhesive, and a manufacturing method thereof, which will contribute to reducing the vehicle weight required for collision safety. [Means for solving the problem]

[0006] The present invention, which achieves the above-mentioned object, is a metal composite material having a thin steel plate, a low-specific-gravity plate material having a lower specific gravity and strength than the thin steel plate, and an adhesive layer which joins the thin steel plate and the low-specific-gravity plate material and has a lower strength than the thin steel plate and the low-specific-gravity plate material, wherein the thickness of the thin steel plate and the thickness of the low-specific-gravity plate material are set so as to satisfy the following equations (1) and (2), which represent a preset bending rigidity [D] of the metal composite material.

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[0007] The present invention, which has achieved the object, is a manufacturing method for a metal composite material, comprising the steps of preparing a thin steel plate and a low-specific-gravity plate material having a lower specific gravity and strength than the thin steel plate, and joining the thin steel plate and the low-specific-gravity plate material via an adhesive layer, wherein the joining step of the thin steel plate and the low-specific-gravity plate material is performed such that a neutral axis during bending deformation of the metal composite material is set within the adhesive layer, which has a lower strength than the thin steel plate and the low-specific-gravity plate material. Effect of the Invention

[0008] According to the present invention, it is possible to provide a metal composite material and a manufacturing method thereof that includes an adhesive layer but has an excellent reinforcing effect without being broken down at the adhesive, and that contributes to reducing the vehicle weight necessary for collision safety. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram illustrating the configuration of a metal composite material according to an embodiment of the present invention. [Diagram 2] 1 is a schematic diagram showing the relationship between the thickness of a thin steel plate, a low-specific-gravity plate material, and an adhesive layer in a metal composite material and stress distribution. FIG. [Diagram 3] 1 is a perspective view showing a side sill structure to which a metal composite material according to an embodiment of the present invention is applied, viewed from the inside of a vehicle. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV of FIG. [Diagram 5] 5A to 5C are schematic explanatory diagrams showing deformation behavior of a side sill structure during a side collision. [Figure 6] FIG. 2 is a schematic diagram of a test piece of a metal composite material used in the examples of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Next, a mode (embodiment) for carrying out the metal composite material of the present invention will be described in detail with reference to the drawings as appropriate. The metal composite material of this embodiment has an asymmetric sandwich structure made of a plurality of plate members, as will be described in detail later. The metal composite material of this embodiment is assumed to be a composite material in which a predetermined plate-like member is layered on a thin steel plate via an adhesive layer. Specifically, when a buckling stress occurs in the metal composite material due to a load input in a direction along the joint surface of the metal composite material, the neutral axis of the metal composite material is set in the adhesive layer. Preferably, the neutral axis is set at the joint interface between the adhesive layer and the thin steel plate, or the joint interface between the adhesive layer and the plate-like member. The neutral axis in the metal composite material of this embodiment is set based on a relational expression that will be described in detail later.

[0011] FIG. 1 is a diagram illustrating the configuration of a metal composite material 10 according to an embodiment of the present invention. As shown in FIG. 1, the metal composite material 10 of this embodiment is composed of a thin steel plate 1, a low-specific-gravity plate material 2 having a lower specific gravity than the thin steel plate 1, and an adhesive layer 3 that bonds the thin steel plate 1 and the low-specific-gravity plate material 2.

[0012] The thin steel plate 1 in this embodiment may be a known one, and a commercially available product may be used. The thin steel plate 1 in this embodiment is assumed to be a high-tensile steel plate having a plate thickness of 1.0 mm or more and 2.0 mm or less and a tensile strength of 340 MPa or more, but is not limited thereto. As shown in FIG. 1, the thickness h2 of the low specific gravity plate material 2 is greater than the thickness h1 of the thin steel plate 1 (h1 <h2)。 Specific examples of the low specific gravity plate material 2 include, but are not limited to, aluminum alloy plates (including duralumin plates), magnesium alloy plates, CFRP (Carbon Fiber Reinforced Plastics) plates, GFRP (Glass Fiber-Reinforced Plastics) plates, etc. Therefore, the low specific gravity plate material 2 can be appropriately selected according to the required bending strength of the metal composite material 10, which is determined in advance according to the type of vehicle body structure to which the metal composite material 10 is applied (for example, a side sill structure, a center pillar structure, etc.).

[0013] The adhesive layer 3 is assumed to be made of, for example, an epoxy-based or urethane-based structural adhesive, but is not limited to this. The adhesive layer 3 can also be made of an injection molding resin (thermoplastic resin) that is injected between the thin steel plate 1 and the low specific gravity plate material 2 that are placed in a predetermined mold. The Young's modulus of such an adhesive layer 3 is significantly lower than that of the thin steel plate 1 . Furthermore, the strength of the adhesive layer 3 is significantly lower than that of the thin steel plate 1. Furthermore, the strength of the adhesive layer 3 is significantly lower than that of the low specific gravity plate material 2 . The thickness h3 of the adhesive layer 3 is equal to or greater than the thickness h1 of the thin steel plate 1 (h1≦h3), as shown in Fig. 1. Also, it is preferable that the thickness h3 of the adhesive layer 3 is smaller than the thickness h2 of the low-specific-gravity plate material 2 (h2>h3), as shown in Fig. 1.

[0014] 1, in the metal composite material 10 of the present embodiment, the neutral axis Ax is set in the adhesive layer 3. In addition, although not shown, the neutral axis Ax is preferably set at the bonding interface between the adhesive layer 3 and the thin steel plate 1, or at the bonding interface between the adhesive layer 3 and the low-specific-gravity plate material 2. Specifically, in the metal composite material 10, the plate thickness h1 of the thin steel plate 1 and the plate thickness h2 of the low-specific-gravity plate material 2 are set so as to satisfy the following formula (1) and the following formula (2), so that the neutral axis Ax is set within the adhesive layer 3, and preferably at the joint interface between the adhesive layer 3 and the thin steel plate 1, or the joint interface between the adhesive layer 3 and the low-specific-gravity plate material 2.

[0015]

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[0016]

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[0017] However, in Formula (1), b is the width of the metal composite material 10 (see FIG. 1). E1 is the longitudinal elastic modulus of the thin steel plate 1 (see FIG. 1), and E2 is the longitudinal elastic modulus of the low specific gravity plate material 2 (see FIG. 1). ν1 is the Poisson's ratio of the thin steel plate 1 (see FIG. 1), and ν2 is the Poisson's ratio of the low specific gravity plate material 2 (see FIG. 1). h1 is the plate thickness of the thin steel plate 1 (see FIG. 1), h2 is the plate thickness of the low specific gravity plate material 2 (see FIG. 1), and h3 is the thickness of the adhesive layer 3 (see FIG. 1). And, as shown in FIG. 1, h0 is the thickness of the adhesive layer 3 from the bonding interface between the low specific gravity plate material 2 and the adhesive layer 3 to the neutral axis Ax. Also, in Formula (2), h1 and h2 have the same meanings as h1 and h2 in the said Formula (1).

[0018] Next, the invention principle of the metal composite material 10 according to the present embodiment will be described. FIG. 2 is a schematic diagram showing the relationship between the thicknesses h1, h2, h3 of the thin steel plate 1, the low specific gravity plate material 2, and the adhesive layer 3 in the metal composite material 10 and the stress distribution. As shown in FIG. 2, in the present embodiment, it is assumed that a bending moment M acts on the metal composite material 10 so as to be compressed on the low specific gravity plate material 2 side by the load L input in the direction along the bonding surface in the metal composite material 10. That is, in the present embodiment, it is assumed that buckling stress occurs in the metal composite material 10. At this time, the vertical stress generated in the thin steel plate 1 exhibits elastic behavior until the metal composite material 10 reaches fracture. Also, the longitudinal elastic modulus E3 of the adhesive layer 3 is smaller than the longitudinal elastic modulus E1 of the thin steel plate 1 and the longitudinal elastic modulus E2 of the low specific gravity plate material 2 (E3 < E1, E3 < E2). Thereby, the share of the bending moment in the adhesive layer 3 can be omitted.

[0019] By the way, in the metal composite material 10 of the present embodiment, which is an asymmetric sandwich structure with different longitudinal elastic moduli E1 and E2 and different fracture strengths of the thin steel plate 1 and the low specific gravity plate material 2, as shown in FIG. 2, the neutral axis Ax is set so as not to coincide with the centroid. Specifically, as shown in FIG. 2, the neutral axis Ax is set at the position of the thickness h0 of the adhesive layer 3 from the bonding interface between the low specific gravity plate material 2 and the adhesive layer 3. That is, h0 can be defined as shown in the following formula (3) based on the so-called "beam theory."

[0020]

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[0021] In the formula (3), E1 is the modulus of longitudinal elasticity of the thin steel plate 1 (see FIG. 2). E2 is the modulus of longitudinal elasticity of the low-specific-gravity plate material 2 (see FIG. 2). h1 is the thickness of the thin steel plate 1 (see FIG. 2), h2 is the thickness of the low-specific-gravity plate material 2 (see FIG. 2), and h3 is the thickness of the adhesive layer 3 (see FIG. 2). The thickness h3 of the adhesive layer 3 is equal to or greater than the thickness h1 of the thin steel plate 1 and is thinner than the thickness h2 of the low-specific-gravity plate material 2 (h1≦h3, h2>h3).

[0022] In addition, the maximum bending stress σ1 generated in the thin steel plate 1 by the bending moment M shown in FIG. 2 is defined by the following formula (α), and the maximum bending stress σ2 generated in the low-specific-gravity plate material 2 by the bending moment M shown in FIG. 2 is defined by the following formula (β).

[0023]

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[0024]

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[0025] Here, E1, h0, h1, and h3 in formula (α) and E2, h0, and h2 in formula (β) have the same meanings as E1, E2, h0, h1, h2, and h3 in formula (3). Furthermore, D in the formulas (α) and (β) is the bending rigidity of the metal composite material 10 (see FIG. 2). As described above, since the sharing of the bending moment M (see FIG. 2) in the adhesive layer 3 (see FIG. 2) can be omitted, the bending rigidity D of the metal composite material 10 (see FIG. 2) can be expressed by the following formula (γ).

[0026]

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[0027] However, in formula (γ), E1 has the same meaning as E1 in the above formula (α). E2 has the same meaning as E2 in the above formula (β). And, since I1 is the second moment of area of the thin steel plate 1 and I2 is the second moment of area of the low specific gravity plate material 2, formula (γ) becomes formula (1).

[0028]

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[0029] The metal composite material 10 (see FIG. 2) of the present embodiment satisfies formula (1) on the condition that the plate thickness h2 of the low specific gravity plate material 2 (see FIG. 2) is thicker than the plate thickness h1 of the thin steel plate 1 (see FIG. 2) shown in formula (2) (h1 < h2). The plate thickness h1 of the thin steel plate 1 (see FIG. 2) and the plate thickness h2 of the low specific gravity plate material 2 (see FIG. 2) are set so that the neutral axis Ax (position of h0) is set within the adhesive layer 3. Preferably, although not shown, the neutral axis Ax (position of h0) is set at the joint interface between the adhesive layer 3 (see FIG. 2) and the thin steel plate 1 (see FIG. 2), or at the joint interface between the adhesive layer 3 (see FIG. 2) and the low specific gravity plate material 2 (see FIG. 2). That is, the metal composite material 10 (see FIG. 2) of the present embodiment is configured such that when the bending moment M (see FIG. 2) is applied as described above, the neutral axis Ax (position of h0) is set in the adhesive layer 3 (see FIG. 2) with the lowest strength.

[0030] As a manufacturing method of such a metal composite material 10, it has a first step of preparing a thin steel plate 1 (see FIG. 1) and a low specific gravity plate material 2 (see FIG. 1), and a second step of joining the thin steel plate 1 and the low specific gravity plate material 2 via an adhesive layer 3 (see FIG. 1). In this manufacturing method, the plate thickness h1 of the thin steel plate 1 and the plate thickness h2 of the low specific gravity plate material 2 of the metal composite material 10 are set so as to satisfy the above-mentioned formula (1) which expresses the bending rigidity D which is set in advance according to the type of a specific structure such as a side sill structure or a center pillar structure. As a result, the neutral axis Ax of the metal composite material 10 is set at a predetermined position. That is, the neutral axis Ax is set within the adhesive layer 3, and preferably at the joint interface between the adhesive layer 3 and the thin steel plate 1, or the joint interface between the adhesive layer 3 and the low specific gravity plate material 2.

[0031] Next, a vehicle structure using the metal composite material 10 according to this embodiment (see FIG. 1) will be described. Here, a side sill structure will be taken as an example of the vehicle structure to specifically describe how the metal composite material 10 is used. Fig. 3 is a perspective view showing the side sill structure 20 as viewed from inside the vehicle. Note that the up-down, front-rear, left-right directions indicated by the arrows in Fig. 3 correspond to the up-down, front-rear, left-right directions of a vehicle equipped with this side sill structure 20. In the following description, the left-right direction of the vehicle may be referred to as the vehicle width direction.

[0032] As shown in FIG. 3, the side sill S constituting the side sill structure 20 is a vehicle frame member extending in the front-rear direction of the vehicle on the side of the lower part of the vehicle. The outer edge of the floor panel 8a in the vehicle width direction is joined to the inner side of the side sill S in the vehicle width direction by spot welding or the like.

[0033] A floor cross member 8c extending in the vehicle width direction is disposed on the floor panel 8a. The floor cross member 8c has a hat shape that opens downward in a cross section intersecting the extending direction. A flange F10 of the floor cross member 8c that corresponds to a brim of the hat shape is joined to the floor panel 8a by spot welding or the like. An outer end portion of the floor cross member 8c in the vehicle width direction is welded to an inner side of the side sill S in the vehicle width direction.

[0034] The side sill S constituting the side sill structure 20 includes a side sill inner S2, a side sill outer S1, a plate member S4, a reinforcement S3, and a bulkhead 5. The side sill inner S2 is disposed on the inner side in the vehicle width direction (left side in FIG. 3) of the side sill outer S1, and has a hat shape that opens outward in the vehicle width direction in a cross section intersecting the longitudinal direction (front-rear direction in FIG. 2). Specifically, the side sill inner S2 is configured to have a bulging portion 24, an upper flange F6, and a lower flange F7.

[0035] The side sill outer S1 is disposed on the outer side of the side sill inner S2 in the vehicle width direction (right side in FIG. 3). The side sill outer S1 has a hat shape that opens inward in the vehicle width direction in a cross section intersecting the longitudinal direction (front-rear direction in FIG. 3). Specifically, the side sill outer S1 is configured to have a bulging portion 14, an upper flange F4, and a lower flange F5.

[0036] The plate member S4 is formed of a long, substantially flat plate extending along the longitudinal direction of the side sill S (the front-rear direction in FIG. 3) with its plate surface facing in the vehicle width direction. The plate member S4 is sandwiched between the flanges F6, F7 of the side sill inner S2 and the flanges F4, F5 of the side sill outer S1 and joined by triple welding.

[0037] 3, the bulkheads 5 shown by hidden lines (dotted lines) are disposed spaced apart from each other in the longitudinal direction (front-rear direction) of the side sill S so as to correspond to each of the pair of floor cross members 8c. The bulkheads 5 are disposed within the bulging portion 24 of the side sill inner panel S2 so as to be located on the inner side in the vehicle width direction relative to the plate member S4. The position of the bulkhead 5 within the bulging portion 24 coincides in the front-rear direction with the joint between the floor cross member 8c and the side sill inner panel S2. In this embodiment, the bulkhead 5 has a hat shape that opens inward in the vehicle width direction (to the left in FIG. 2) in cross section. The bulkhead 5 is joined to the inner wall of the side sill inner S2 by spot welding or the like.

[0038] The reinforcement S3 is a long resin member made of fiber reinforced resin or the like, having a substantially M-shaped cross section extending along the extension direction of the side sill S (the front-rear direction in FIG. 3). The reinforcement S3 is disposed inside the bulging portion 14 of the side sill outer S1.

[0039] As shown in Fig. 4, which is a cross-sectional view taken along the line IV-IV in Fig. 3, the reinforcement S3 has a pair of upper and lower outer convex portions 31, and an inner convex portion 32 that protrudes toward the plate member S4 between the outer convex portions 31. The protruding tip portion of the inner convex portion 32 is engaged with the plate member S4 by fitting or the like. The upper outer protrusion 31 is formed on the corner side between the upper wall 11 and the outer wall 12 of the side sill outer panel S1 so as to be in close contact with the upper wall 11 and the outer wall 12. The upper outer protrusion 31 is bonded with a structural adhesive A from the upper wall 11 to the outer wall 12 so as to be integrated with the side sill outer panel S1.

[0040] The lower outer protrusion 31 is formed on the corner side between the lower wall 13 and the outer wall 12 of the side sill outer panel S1 so as to be in close contact with the lower wall 13 and the outer wall 12. The lower outer protrusion 31 is bonded with a structural adhesive A from the lower wall 13 to the outer wall 12 so as to be integrated with the side sill outer panel S1.

[0041] In such a side sill structure 20, as shown in FIG. 4, a pair of upper and lower metal composite materials 10 are provided in portions corresponding to the upper wall 11 and the lower wall 13 of the side sill outer panel S1. That is, the metal composite material 10 of the side sill structure 20 is composed of a thin steel plate 1 (see Figure 1) that forms the upper wall 11 or the lower wall 13 of the side sill outer S1, a low-density plate material 2 (see Figure 1) made of fiber-reinforced resin of the reinforcement S3, and an adhesive layer 19 (see Figure 1) made of structural adhesive A.

[0042] <Action and effect> Next, the effects of the metal composite material 10 according to this embodiment will be described. In the metal composite material 10 of this embodiment, the plate thickness h1 of the thin steel plate 1 and the plate thickness h2 of the low-specific-gravity plate material 2 are set so as to satisfy the formula (1) and the formula (2) which represent the bending rigidity D of the metal composite material 10 which is set in advance.

[0043] According to such a metal composite material 10, the neutral axis Ax is set in the adhesive layer 3, and preferably at the joint interface between the adhesive layer 3 and the thin steel plate 1, or at the joint interface between the adhesive layer 3 and the low-specific-gravity plate material 2. As a result, when a bending moment M is applied to the metal composite material 10, the neutral axis Ax is set in the adhesive layer 3, which has the lowest strength. In the metal composite material 10, no stress is applied to the adhesive layer 3 having the neutral plane (neutral axis Ax), and this prevents the low-specific-gravity plate material 2 from peeling off from the thin steel plate 1. The metal composite material 10 can exhibit high bending rigidity when compared with conventional metal composite materials of the same weight.

[0044] Moreover, the metal composite material 10 has an asymmetric sandwich structure by satisfying the formula (1) and the formula (2). This, together with the adjustment of the position of the neutral axis Ax as described above, allows the metal composite material 10 to suppress out-of-plane deformation. The metal composite material 10 can fully utilize material properties that could not be fully utilized by conventional thin steel plates alone, and can improve the buckling strength of the thin steel plate 1.

[0045] 5A, 5B, and 5C are schematic explanatory diagrams showing, in chronological order, deformation behavior of a side sill structure 20 (see FIG. 4) having a metal composite material 10 (see FIG. 4) during a side collision. Note that reference numeral 50 in FIG. 5 denotes an object relatively approaching the side sill S. As shown in Fig. 5(a), an object 50 approaching the side sill S first comes into contact with the vehicle exterior surface of the side sill outer panel S1. At this time, a compressive load (load L in Fig. 2) acts in the vehicle width direction (left-right direction in Fig. 4) on the upper wall 11 and the lower wall 13 of the side sill outer panel S1 shown in Fig. 4.

[0046] As shown in FIG. 4, the portions of the side sill outer S1 made of the metal composite material 10 corresponding to the upper wall 11 and the lower wall 13 transmit the side collision load to the side sill inner S2 while exhibiting the guaranteed high rigidity. Next, as shown in Fig. 5(b), the bulkhead 5 provided in the side sill inner S2 so as to correspond to the floor cross member 8c starts to be crushed and deformed by the transmitted side impact load. The side sill outer S1 having the reinforcement S3 on the inside thereof causes the side sill inner S2 together with the bulkhead 5 to be crushed and deformed preferentially over the side sill outer S1.

[0047] 5(c), when the load input from the object 50 progresses further and the side sill outer S1 starts to bend, the reaction force of the side sill outer S1 increases as the displacement progresses. The increase in the reaction force of the side sill outer S1 continues until the input load reaches the maximum load capacity of the side sill outer S1.

[0048] According to the side sill structure 20 (see FIG. 4) having the metal composite material 10 (see FIG. 4) as described above, the side sill outer S1 deforms in stages after the side sill inner S2 having the bulkhead 5 is crushed and deformed during a side collision. This makes it possible for the side sill structure 20 (see FIG. 4) having the metal composite material 10 (see FIG. 4) to prevent the side sill outer S1 from being excessively bent and deformed in the early stage of a side collision. The side sill structure 20 can obtain a large energy absorption effect from the early stage to the later stage of a side collision.

[0049] In the metal composite material 10, h0 in formula (1) is expressed by formula (3), and the thickness h3 of the adhesive layer 3 is equal to or greater than the plate thickness h1 of the thin steel plate 1 (h1≦h3). According to such a metal composite material 10, by setting the neutral axis Ax within the range of the thickness h3 of the adhesive layer 3, it is possible to reduce the stress applied to the bonding interface with the low-specific-gravity plate material 2 and the thin steel plate 1. The metal composite material 10 can more effectively prevent the low-specific-gravity plate material 2 from peeling off from the thin steel plate 1. Further, it is desirable that the thickness h3 of the adhesive layer 3 is thinner than the thickness h2 of the low specific gravity plate material 2 (h2 > h3). Thereby, the metal composite material 10 can more effectively suppress the peeling of the low specific gravity plate material 2 from the thin steel plate 1.

[0050] Further, in the metal composite material 10, it is desirable that the thickness h3 of the adhesive layer 3 is thicker than the thickness h1 of the thin steel plate 1 (h1 < h3). According to such a metal composite material 10, by increasing the thickness of the adhesive layer 3, the neutral axis Ax can be more reliably set within the adhesive layer 3.

[0051] Further, in the metal composite material 10, the longitudinal elastic modulus E1 of the adhesive layer 3 is smaller than the longitudinal elastic modulus E3 of the thin steel plate 1 and also smaller than the longitudinal elastic modulus E3 of the low specific gravity plate material 2. According to such a metal composite material 10, the neutral axis Ax can be more reliably set within the adhesive layer 3.

[0052] Further, in the metal composite material 10, the low specific gravity plate material 2 is selected from an aluminum alloy plate (including a duralumin plate), a magnesium alloy plate, a CFRP plate, and a GFRP plate. According to such a metal composite material 10, by expanding the range of selection of the low specific gravity plate material 2, the range of selection of the bending rigidity D of the metal composite material 10 set in advance is also expanded. Thereby, the range of the vehicle body structure to which the metal composite material 10 is applied is also expanded.

[0053] Further, the metal composite material 10 can be applied to a vehicle body structure member. According to such a metal composite material 10, a vehicle body structure member excellent in the transmission performance of a collision load can be provided. Specifically, the metal composite material 10 can be applied to, for example, a side sill structure, a roof side rail structure, a front pillar structure, a center pillar structure, a bumper structure, a door beam structure, etc. Further, in addition to such vehicle structure members, the metal composite material 10 can also be applied to moving bodies such as airplanes and ships where both improvement of rigidity and weight reduction are desired.

[0054] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and can be embodied in various forms. EXAMPLES

[0055] Next, examples in which the effects of the metal composite material 10 of this embodiment were verified will be described. Example 1 In this embodiment, assuming the metal composite material 10 in the side sill structure 20 shown in Figure 4, a cold-rolled high-tensile steel plate [980 material] (unit width b: 1, modulus of elasticity E1: 210 GPa, Poisson's ratio v1: 0.3, plate thickness h1: 1.0 mm) was prepared as the thin steel plate 1 (see Figure 1) and a CFRP plate (unit width b: 1, modulus of elasticity E2: 70 GPa, Poisson's ratio v2: 0.3, plate thickness h2: 3.0 mm) was prepared as the low-density plate material 2 (see Figure 1). The plate thickness h2 of the FRP plate is greater than the plate thickness h1 of the thin steel plate 1.

[0056] Next, the cold-rolled high-tensile steel plate and an FRP plate were joined together with an epoxy structural adhesive to produce a metal composite material 10. The thickness h3 of the adhesive layer 3 (see FIG. 1) made of the cured product of this epoxy structural adhesive was set to satisfy the above formula (1) in order to bring the neutral axis Ax (see FIG. 1) of the metal composite material 10 close to the joint interface (h0=h3) between the thin steel plate 1 and the adhesive layer 3. The bending rigidity of the metal composite material 10 assuming the side sill structure 20 is 1,180,000 Nm 2 The thickness h3 of the adhesive layer 3 was 0.2 mm.

[0057] Next, in this example, a test piece made of the metal composite material 10 was produced. FIG. 6 is a schematic diagram of the test piece TP. As shown in FIG. 6, the test piece TP was made of four metal composite materials 10 of predetermined dimensions, and was formed into a rectangular tube with a square cross section with the thin steel plates facing outwards. In this example, a compression test was conducted on the test piece TP with a load L0 applied in the axial direction. In this compression test, the displacement of the thin steel plate in the measurement range A (see FIG. 6) in the direction perpendicular to the surface of the test piece TP when the load L0 was applied, the axial strain of the CFRP plate measured by the strain gauge, and the maximum load (maximum reaction force) of the test piece TP when the load L0 was applied in the axial direction were measured.

[0058] The displacement of the test piece TP in the direction perpendicular to the surface was measured by digital image correlation (DIC). In this embodiment, it was determined whether the fracture in the metal composite material 10 occurred in the FRP plate (low specific gravity plate material 2 (see FIG. 1)) or in the adhesive layer 3 (see FIG. 1) based on the displacement in the direction perpendicular to the surface and the axial strain measured by the strain gauge. The maximum load (maximum reaction force) of the test piece TP when a load L0 was applied in the axial direction was 506.6 kN. Furthermore, the fracture in the metal composite material 10 occurred in the FRP plate (low specific gravity plate material 2).

[0059] Example 2 In this embodiment, a test piece TP was prepared in the same manner as in Example 1, except that the thickness h3 of the adhesive layer 3 (see Figure 1) was set to 5.6 mm so that the neutral axis Ax (see Figure 1) of the metal composite material 10 was brought closer to the joint interface (h0 = h3) between the thin steel plate 1 and the adhesive layer 3 compared to Example 1, and a compression test was performed on the test piece TP. As a result, the maximum load (maximum reaction force) of the test piece TP when a load L0 was applied in the axial direction was 966.95 kN. Furthermore, the fracture in the metal composite material 10 occurred in the FRP plate (low specific gravity plate material 2).

[0060] Comparative Example 1 In Comparative Example 1, a test piece TP was prepared in the same manner as in Example 1, except that the plate thickness h2 of the FRP plate (low specific gravity plate material 2) was set to 1.0 mm, the same as the plate thickness h1 of the thin steel plate 1: 1.0 mm, and a compression test was performed thereon. As a result, the maximum load (maximum reaction force) of the test piece TP when a load L0 was applied in the axial direction was 186.93 kN. Furthermore, the fracture in the metal composite material 10 occurred at the adhesive layer 3.

[0061] Comparative Example 2 In Comparative Example 2, a test piece TP was prepared using only the cold-rolled high-tensile steel plate having a thickness of 1.0 mm that constitutes the metal composite material 10, and a compression test was performed on the test piece TP. As a result, the maximum load (maximum reaction force) of the test piece TP when a load L0 was applied in the axial direction was 74.36 kN.

[0062] (Evaluation Results) The maximum load of the metal composite material of Comparative Example 1 (186.93 kN) is about 2.5 times the maximum load of the cold-rolled high-tensile steel plate alone of Comparative Example 2 (74.36 kN). In contrast, the maximum load (506.6 kN) of the metal composite material 10 in Example 1 is 6.8 times the maximum load (74.36 kN) of the single cold-rolled high-tensile steel plate in Comparative Example 2. Moreover, the maximum load (966.95 kN) of the metal composite material 10 in Example 2 is 13.0 times the maximum load (74.36 kN) of the single cold-rolled high-tensile steel plate in Comparative Example 2. That is, in conventional thin steel plates, the material strength cannot be fully utilized due to insufficient deflection (rigidity) of the plate, and the plate deforms in the out-of-plane direction and buckles. In contrast, the metal composite material of the present invention is made by joining an FRP material with excellent specific rigidity to a thin steel plate via an adhesive layer, and setting the neutral axis in the adhesive layer, preferably at the bonding interface between the thin steel plate and the adhesive layer. This makes it possible for the metal composite material of the present invention to fully utilize the strength of the thin steel plate and to further improve the "rigidity" of the entire plate. Furthermore, even though this metal composite material contains an adhesive layer, it has an excellent reinforcing effect without causing destruction starting from the adhesive, and can also contribute to reducing the vehicle weight, which is necessary for collision safety. [Explanation of symbols]

[0063] 1 Thin steel plate 2 Low specific gravity board material 3 Adhesive layer 10 Metal composites

Claims

1. A metal composite material comprising a thin steel plate, a low-specific-gravity plate material having a lower specific gravity and strength than the thin steel plate, and an adhesive layer bonding the thin steel plate and the low-specific-gravity plate material and having a strength lower than the thin steel plate and the low-specific-gravity plate material, A metal composite material, characterized in that the thickness of the thin steel plate and the thickness of the low-specific-gravity plate material are set so as to satisfy the following formula (1) and the following formula (2), which represent the bending rigidity [D] of the metal composite material that is preset. [0010] (In the formula (1), b is the width of the metal composite material. １ is the modulus of longitudinal elasticity of the thin steel plate, and E ２ is the modulus of longitudinal elasticity of the low specific gravity plate material. １ is the Poisson's ratio of the thin steel plate, and ν ２ is the Poisson's ratio of the low specific gravity plate material. １ is the thickness of the thin steel plate, and h ２ is the thickness of the low specific gravity plate material, and h ３ is the thickness of the adhesive layer. ０ is the thickness of the adhesive layer from the bonding interface between the low specific gravity plate material and the adhesive layer to the neutral axis. [0025] (In the formula (2), h １ and h ２ is the h in the formula (1). １ and h ２ (Synonymous with

2. The above h ０ is expressed by the following formula (3), and the plate thickness of the thin steel plate and the plate thickness of the low specific gravity plate material are set so as to satisfy the following formula (4). [0030] (In the formula (3), h ０ , h １ , h ２ and h ３ is the h in the formula (1). ０ , h １ , h ２ and h ３ (Synonymous with [0045] (In the formula (4), h １ and h 3 is the h in the formula (1). １ and h ３ (Synonymous with

3. The metal composite material according to claim 1, characterized in that the neutral axis of the metal composite material during bending deformation is set within the adhesive layer, which has a lower strength than the thin steel plate and the low-specific-gravity plate material, or at the joint interface between the adhesive layer and the thin steel plate or the low-specific-gravity plate material.

4. 2. The metal composite material according to claim 1, wherein the adhesive layer has a thickness greater than a thickness of the thin steel plate.

5. 2. The metal composite material according to claim 1, wherein the adhesive layer has a modulus of Young's modulus smaller than that of the thin steel plate and smaller than that of the low-specific-gravity plate material.

6. 2. The metal composite material according to claim 1, wherein the low specific gravity plate material is selected from an aluminum alloy plate, a magnesium alloy plate, a CFRP plate, and a GFRP plate.

7. The metallic composite material according to claim 1 , which is a vehicle body structural member.

8. A step of preparing a thin steel plate and a low-specific-gravity plate material having a lower specific gravity and strength than the thin steel plate; a step of joining the thin steel plate and the low specific gravity plate material via an adhesive layer; A method for producing a metal composite material comprising the steps of: A manufacturing method for a metal composite material, characterized in that the joining process between the thin steel plate and the low-specific-gravity plate material is performed so that the neutral axis during bending deformation of the metal composite material is set within the adhesive layer, which has a lower strength than the thin steel plate and the low-specific-gravity plate material, or at the joining interface between the adhesive layer and the thin steel plate or the low-specific-gravity plate material.

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