Patent Application
20200164461
The present invention relates to a hollow structure.
The present application claims priority from Japanese Patent Application No. 2017-124639 filed on Jun. 26, 2017 and Japanese Patent Application No. 2017-224508 filed on Nov. 22, 2017, the entire contents of which are incorporated herein by reference.
One known hollow structure having a hollow closed cross-section portion is a cockpit support structure of a motor vehicle in PTL 1. This support structure includes a cross member having two tubular profiles (hollow closed cross-section portions) formed by extrusion. The tubular profiles arranged in their axial direction are welded together.
PTL 1: Japanese Unexamined Patent Application Publication No. 2013-28337
The hollow structure according to the present disclosure includes:
a main portion having an inner circumferential surface; and
a flange portion including a first overhanging portion and a second overhanging portion that protrude outward from an outer circumference of the main portion and face each other, wherein a first surface of the first overhanging portion and a second surface of the second overhanging portion are continuous with the inner circumferential surface, wherein the flange portion has a joint portion at which the first surface and the second surface are joined together,
wherein the main portion and the flange portion are formed of a metal material composed mainly of a light metal, and
wherein the formula ⅕<A/W1 is satisfied, where W1 is the width of the flange portion, and A is the width of the joint portion.
When a welded portion is formed at a longitudinal position that divides a hollow structure, like the hollow structure disclosed in PTL 1, the welded portion may be a mechanical weak point. Therefore, the flexural rigidity of the hollow structure may be low.
One object is to provide a hollow structure excellent in flexural rigidity.
The hollow structure of the present disclosure is excellent in flexural rigidity.
First, the details of embodiments of the present invention will be enumerated and described.
(1) A hollow structure according to one embodiment of the present invention includes:
a main portion having an inner circumferential surface; and
a flange portion including a first overhanging portion and a second overhanging portion that protrude outward from an outer circumference of the main portion and face each other,
wherein a first surface of the first overhanging portion and a second surface of the second overhanging portion are continuous with the inner circumferential surface,
wherein the flange portion has a joint portion at which the first surface and the second surface are joined together,
wherein the main portion and the flange portion are formed of a metal material composed mainly of a light metal, and
wherein the formula 1/5<A/W1 is satisfied, where W1 is the width of the flange portion, and A is the width of the joint portion.
The above configuration is excellent in flexural rigidity. This is because of the following reason. When the width ratio A/W1 satisfies the above range, the ratio of the joint portion in the flange portion can be increased, and the first overhanging portion and the second overhanging portion can be joined firmly together, so that the mechanical strength of the flange portion can be increased. Since the first overhanging portion and the second overhanging portion can be joined firmly together, the first overhanging portion and the second overhanging portion are unlikely to be separated due to application of external force.
(2) In one aspect of the hollow structure,
the flange portion may have a contact portion in which the first overhanging portion and the second overhanging portion are not joined together but are in contact with each other, and
the formula ¼<A/W2 may be satisfied, where W2 is the sum of the width A of the joint portion and the width of the contact portion.
In the above configuration, since the width of the joint portion is large, the first overhanging portion and the second overhanging portion can be joined more firmly together, so that higher flexural rigidity is obtained.
(3) In one aspect of the hollow structure having the contact portion,
the contact portion may include an inner contact portion formed closer to the main portion than the joint portion, and
the formula B/W2<⅗ may be satisfied, where B is the width of the inner contact portion.
In the above configuration, since the width of the contact portion is small, the ratio of the joint portion in the flange portion can be increased, so that higher flexural rigidity can be obtained.
(4) In one aspect of the hollow structure, the length of the joint portion may be 30% or more of the total length of the flange portion.
In the above configuration, since the length of the joint portion is large, the first overhanging portion and the second overhanging portion can be joined more firmly together over a wide area in the longitudinal direction of the flange portion.
(5) In one aspect of the hollow structure, the joint portion may include a friction stir welded portion at which the first overhanging portion and the second overhanging portion are joined together by friction stir welding.
In the above configuration, since the first overhanging portion and the second overhanging portion are joined firmly at the friction stir welded portion, excellent flexural rigidity is obtained.
(6) In one aspect of the hollow structure, the hollow structure may have at least one of an enlarged portion in which a space formed by the inner circumferential surface has a locally larger cross-sectional area and a reduced portion in which the space formed by the inner circumferential surface has a locally smaller cross sectional area.
When the enlarged portion is provided, the mechanical strength can be easily increased locally, and a peripheral member can be easily connected to the hollow structure using the enlarged portion. When the reduced portion is provided, a peripheral member can be disposed in the reduced portion, and therefore the hollow structure is unlikely to interfere with the peripheral member, so that space saving can be achieved easily.
(7) In one aspect of the hollow structure, the flange portion may include a wide portion in which the flange portion has a locally larger width.
In the above configuration, the mechanical strength of the flange portion can be easily increased locally.
(8) In one aspect of the hollow structure, the flange portion may have a notch.
In the above configuration, a peripheral member can be disposed in the notch, and therefore the hollow structure is unlikely to interfere with the peripheral member, so that space saving can be achieved easily.
(9) In one aspect of the hollow structure, the light metal may be magnesium or aluminum.
When the light metal is magnesium, the hollow structure is lightweight and is excellent not only in flexural rigidity but also in impact resistance.
When the light metal is aluminum, the hollow structure is lightweight and is excellent in mechanical strength, and its shape flexibility can be easily increased.
(10) In one aspect of the hollow structure, the light metal may be an AZ91 alloy.
When the light metal is a Mg alloy, i.e., a Mg-based alloy containing magnesium as a main component, the hollow structure has high specific strength, is excellent in corrosion resistance and mechanical properties, is lightweight, and is excellent in flexural rigidity and impact resistance.
Referring next to the drawings, embodiments of the present invention will be described in detail. In the drawings, the same numerals denote components with the same names.
Referring to
The hollow closed cross-section portion 2 forms a hollow space thereinside. The hollow closed cross-section portion 2 has a cross section with a closed inner side. The inner space of the hollow closed cross-section portion 2 is a space formed by its inner circumferential surface. The hollow closed cross-section portion 2 can have a shape appropriately selected according to its intended application. In the present example, the hollow closed cross-section portion 2 is an elongated tubular body (
The main portion 3 is part of the hollow closed cross-section portion 2 excluding the flange portions 4 and substantially forms the inner space of the hollow closed cross-section portion 2. The inner space of the main portion 3 is a space formed by the inner circumferential surface of the main portion 3. The cross section of the inner space of the main portion 3 has a circular annular shape (a circular shape (
The flange portions 4 included in the hollow closed cross-section portion 2 are portions protruding outward and increase the flexural rigidity of the hollow closed cross-section portion 2. The flange portions 4 include the respective first overhanging portions 41 and the respective second overhanging portions 42. The flange portions 4 include the respective joint portions 5 (
The flange portions 4 typically have a rectangular cross-sectional shape, and the shape of the flange portions 4 in plan view is typically rectangular. The dimensions (length, width W1, and thickness) of the flange portions 4 may be appropriately selected.
The larger the length of the flange portions 4 in the axial direction of the hollow closed cross-section portion 2, the more easily the flexural rigidity of the hollow closed cross-section portion 2 can be increased. In the present example, the formation regions (lengths) of the flange portions 4 that extend in the axial direction of the hollow closed cross-section portion 2 are axial regions (lengths) extending over the entire length of the hollow closed cross-section portion 2 in the axial direction (
The width W1 of each flange portion 4 (
In the present example, the thickness of each flange portion 4 is uniform in the longitudinal direction, but the flange portion 4 may have different thicknesses.
The number of flange portions 4 is two (plural) in the present example but may be three or more (four in
When the number of flange portions 4 is plural, the formation positions of the flange portions 4 that are arranged in the circumferential direction of the hollow closed cross-section portion 2 may be such that the clockwise circumferential distance between the flange portions 4 is equal to the counterclockwise circumferential distance between the flange portions 4 (
When the number of flange portions 4 is plural, the first overhanging portion 41 and the second overhanging portion 42 in each flange portion 4 may be composed of respective independent members. Specifically, the hollow closed cross-section portion 2 may be formed by combining the same number of split pieces (described later) as the number of flange portions 4.
When the number of flange portions 4 is one (
In this example, the hollow closed cross-section portion 2 includes the main portion 3 and the two flange portions 4 and is composed of a combination of two plate-shaped split pieces (a first split piece P1 and a second split piece P2) having the same shape and the same size. The first split piece P1 includes: a circumferential wall portion 31 having a semi-circular arcuate cross section and a pair of first overhanging portions 41 having a rectangular cross section and protruding radially outward from opposite ends of the circumferential wall portion 31. The circumferential wall portion 31 has an inner circumferential surface 391, and each of the first overhanging portions 41 has a first surface 471 continuous with the inner circumferential surface 391. The second split piece P2 includes a circumferential wall portion 32 and a pair of second overhanging portions 42 similar to those of the first split piece P1. The circumferential wall portion 32 has an inner circumferential surface 392, and each of the second overhanging portions 42 has a second surface 472 continuous with the inner circumferential surface 392. In the hollow closed cross-section portion 2, one of the first overhanging portions 41 and one of the second overhanging portions 42 are disposed so as to face each other, and the other one of the first overhanging portions 41 and the other one of the second overhanging portions 42 are disposed so as to face each other. In this case, the first overhanging portions 41 and the second overhanging portions 42 are disposed such that the side surfaces of the first split piece P1 are aligned with the respective side surfaces of the second split piece P2. Specifically, the main portion 3 of the hollow closed cross-section portion 2 is composed of the circumferential wall portions 31 and 32. One of the flange portions 4 includes one of the first overhanging portions 41 and one of the second overhanging portions 42, and the other one of the flange portions 4 includes the other one of the first overhanging portions 41 and the other one of the second overhanging portions 42. The flange portions 4 have their respective joint portions 5.
Each joint portion 5 is formed by joining the first surface 471 of the corresponding first overhanging portion 41 and the second surface 472 of the corresponding second overhanging portion 42. In the present example, the joint portion 5 has a friction stir welded portion 50 formed by friction-stir-welding the material forming the first overhanging portion 41 and the material forming the second overhanging portion 42. The friction stir welded portion 50 can be formed by subjecting the first overhanging portion 41 and the second overhanging portion 42 stacked one on another to friction stir welding. Alternatively, for example, the joint portion 5 may have a laser joined portion formed by laser welding. The joint portion 5 in the present example is formed from the friction stir welded portion 50. The larger the formation region of the joint portion 5, the higher the joint strength between the first overhanging portion 41 and the second overhanging portion 42, and the higher the flexural rigidity of the hollow closed cross-section portion 2.
The width A of each joint portion 5 satisfies ⅕<A/W1, where W1 is the width of the corresponding flange portion 4. In this case, the ratio of the joint portion 5 in the flange portion 4 can be increased, and the first overhanging portion 41 and the second overhanging portion 42 can be joined firmly together. Since the mechanical strength of the flange portion 4 can be increased, the flexural rigidity of the hollow closed cross-section portion 2 can be increased. The width A of the joint portion 5 (
Let the sum of the width A of the joint portion 5 and the width of a contact portion 6 described later be W2. Then it is preferable that the width of the joint portion 5 satisfies ¼<A/W2. In this case, the flexural rigidity of the hollow closed cross-section portion 2 can be further increased. The width of the contact portion 6 is the width of a portion in which the first overhanging portion 41 and the second overhanging portion 42 are not joined (friction-stir-welded in this case) but are in contact with each other. The width ratio A/W2 satisfies preferably ⅓≤A/W2 and particularly preferably ⅖≤A/W2.
Preferably, the length of the joint portion 5 is 30% or more of the length of the flange portion 4. In this case, the flexural rigidity of the hollow closed cross-section portion 2 can be further increased. The length of the joint portion 5 and the length of the flange portion 4 are their lengths in the axial direction of the hollow closed cross-section portion 2. The longer the length of the joint portion 5, the further the flexural rigidity of the hollow closed cross-section portion 2 can be increased. Therefore, the length of the joint portion 5 is preferably 40% or more of the length of the flange portion 4 and particularly preferably 50% of more of the length of the flange portion 4. The joint portion 5 may be formed continuously in the longitudinal direction of the flange portion 4 or may be formed intermittently. When the joint portion 5 is formed intermittently, the length of the joint portion 5 is the total length of the intermittently formed portions.
Each contact portion 6 is a portion in which the corresponding first overhanging portion 41 and the corresponding second overhanging portion 42 are not joined (friction-stir-welded in this case) but are in contact with each other. The contact portion 6 includes an inner contact portion 61 formed inward (on the main portion side) of the corresponding joint portion 5. Preferably, the width B of the inner contact portion 61 satisfies B/W2<⅗. In this case, the ratio of the joint portion 5 in the flange portion 4 can be increased, so that the flexural rigidity of the hollow closed cross-section portion 2 can be increased. The width ratio B/W2 satisfies preferably B/W2≤½ and particularly preferably B/W2≤⅖. The lower limit of the width ratio B/W2 is about 1/10. The contact portion 6 is allowed to include an outer contact portion 62 formed outward of the joint portion 5.
The material forming the hollow closed cross-section portion 2 may by a metal material containing a light metal as a main component. Specific examples of the metal material include Mg (magnesium)-based materials containing magnesium as a main component and Al (aluminum)-based materials containing aluminum as a main component. Examples of the Mg-based material include pure Mg and Mg alloys, and examples of the Al-based material include pure Al and Al alloys. The Mg-based materials are lightweight and excellent in flexural rigidity and impact resistance. The Al-based materials are lightweight and excellent in mechanical strength, and the shape flexibility of the hollow closed cross-section portion 2 can be easily increased.
Examples of the Mg alloy include alloys having various compositions including Mg and additive elements (the valance: Mg and unavoidable impurities). It is particularly preferable to use a Mg—Al-based alloy containing at least Al as an additive element. As the content of Al increases, the corrosion resistance is further improved, and the mechanical properties such as strength and plastic deformation resistance tend to be further improved. Therefore, in the present invention, the content of Al is preferably 3% by mass or more, more preferably 7.3% by mass or more, and still more preferably 8% by mass or more. However, since an Al content exceeding 12% by mass causes deterioration of plastic formability, the upper limit is set to 12% by mass. The Al content is particularly preferably 11% by mass or less and still more preferably 8.3% by mass or more and 9.5% by mass or less.
The additive elements other than Al may include at least one element selected from Zn, Mn, Si, Be, Ca, Sr, Y, Cu, Ag, Sn, Ni, Au, Li, Zr, Ce, and rare earth elements (except for Y and Ce). When such elements are contained, their total content may be 0.01% by mass or more and 10% by mass or less and preferably 0.1% by mass or more and 5% by mass or less. When at least one additive element selected from Si, Sn, Y, Ce, Ca, and rare earth elements (except for Y and Ce) is contained in a total amount of 0.001% by mass or more and preferably 0.1% by mass or more and 5% by mass or less, excellent thermal resistance and flame resistance are obtained. When rare earth elements are contained, their total content is preferably 0.1% by mass or more. In particular, when Y is contained, its content is preferably 0.5% by mass or more. Examples of the impurities include Fe.
Specific examples of the composition of the Mg—Al-based alloy include the following alloys specified in the American Society for Testing and Materials standards: AZ-based alloys (Mg—Al—Zn-based alloys, Zn: 0.2% by mass or more and 1.5% by mass or less); AM-based alloys (Mg—Al—Mn-based alloys, Mn: 0.05% by mass or more and 0.5% by mass or less); AS-based alloys (Mg—Al—Si-based alloys, Si: 0.3% by mass or more and 4.0% by mass or less); Mg—Al-RE (rare earth element)-based alloy; AX-based alloys (Mg—Al—Ca-based alloys, Ca: 0.2% by mass or more and 6.0% by mass or less); AZX-based alloys (Mg—Al—Zn—Ca-based alloys, Zn: 0.2% by mass or more and 1.5% by mass or less, Ca: 0.1% by mass or more and 4.0% by mass or less); and AJ-based alloys (Mg—Al—Sr-based alloys, Sr: 0.2% by mass or more and 7.0% by mass or less).
Of these, AZ-based alloys including AZ10, AZ31, AZ61, AZ63, AZ80, AZ81, and AZ91 are preferred. In particular, an AZ91 alloy (a Mg—Al-based alloy containing 8.3% by mass or more and 9.5% by mass or less of Al and 0.5% by mass or more and 1.5% by mass or less of Zn) is preferable to other AZ-based alloys because higher specific strength, higher corrosion resistance, and higher mechanical properties are obtained.
Examples of the Al alloy include A5052 alloy (5000-based alloy).
When the hollow closed cross-section portion 2 is produced by combining two (plural) split pieces P1 and P2 as in the present example, the two (all the) split pieces P1 and P2 may be formed of the same material, or the material forming one (at least one) of the split pieces, e.g., the split piece P1, may differ from the material forming the other one of the split pieces, i.e., the split piece P2. For example, the split piece P1 may be formed of a Mg-based material, and the split piece P2 may be formed of an Al-based material.
The two (all the) split pieces P1 and P2 may be each formed from a sheet. Alternatively, one (at least one) of the split pieces, e.g., the split piece P1, may be formed from a sheet, and the other one (one) of the split pieces, i.e., the split piece P2 may be formed from a block material (
To produce the hollow structure 1, a hollow structure production method is used, which includes: a preparation step of preparing the first split piece P1 and the second split piece P2; and a joining step of placing the first split piece P1 and the second split piece P2 such that their overhanging portions 41 and 42 face each other and then joining the overhanging portions 41 and 42 together. In the preparation step, the split pieces P1 and P2 having a prescribed shape may be produced by die casting or may be produced by subjecting sheets to press forming into a prescribed shape. In the joining step, each first overhanging portion 41 and the corresponding second overhanging portion 42 are disposed such that their side surfaces are aligned with each other. Then, in the present example, a friction stir welding tool (not shown) including a shoulder and a probe is rotated and moved in the longitudinal direction of the first overhanging portion 41 while pressure is applied to the surface of the first overhanging portion 41 to thereby friction-stir-weld the overhanging portions 41 and 42 together.
The hollow structure 1 according to the embodiment can be preferably used for beam materials for automobiles that require stiffness.
The hollow structure 1 according to embodiment 1 is excellent in flexural rigidity. Since the hollow closed cross-section portion 2 is formed by combining sheets, the shape flexibility is higher than that when extruded materials are used to form the hollow closed cross-section portion.
Modifications 1 to 16 of the hollow structure 1 according to embodiment 1 will be described. Hollow structures 1 in the modifications are the same as the hollow structure 1 in embodiment 1 in that the hollow closed cross-section portion 2 includes the main portion 3 and the flange portions 4 and that each flange portion 4 has the friction stir welded portion 50 (the joint portion 5). In each of the modifications, differences from embodiment 1 will be mainly described, and the description of the same structures will be omitted.
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The cross section of the inner space of the main portion 3 may have a triangular annular (triangular) or rectangular annular (triangular) shape. Specifically, the circumferential wall portion 31 of the first split piece P1 may have a V cross-sectional shape, as in modification 1, or a square U-shaped cross sectional shape including three surrounding sides, and the second split piece P2 may have a plate shape, as in the present example.
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As shown in
One of the second overhanging portions 42 (the left one in
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The first split piece P1 and the second split piece P2 have similar shapes and are formed from respective square U-shaped sheets each having three flat surrounding surfaces. The cross-sectional shape of the first split piece P1 is larger than the cross-sectional shape of the second split piece P2. The first split piece P1 includes: a square U-shaped circumferential wall portion 31 having three flat surrounding surfaces; and a pair of first overhanging portions 41 extending linearly from opposite ends of the circumferential wall portion 31. The number of bent portions of the circumferential wall portion 31 is two, and the circumferential wall portion 31 has two parallel flat surfaces and a flat surface that is orthogonal to the two flat surfaces and connects ends of the two parallel surfaces. The pair of first overhanging portions 41 are parallel to each other. The second split piece P2 includes: a circumferential wall portion 32; and a pair of second overhanging portions 42 protruding radially outward from opposite ends of the circumferential wall portion 32 so as to intersect the circumferential wall portion 32 (orthogonally, in the present example). The pair of second overhanging portions 42 are parallel to each other and also parallel to the pair of first overhanging portions 41. Since the overhanging portions 41 and 42 are flat and disposed parallel to each other, they can be in surface contact with each other, and the width A of joint portions 5 can be easily increased. The two flange portions 4 may not be parallel to each other.
An opening of the first split piece P1 and an opening of the second split piece P2 face the same direction, and the first split piece P1 and the second split piece P2 are combined such that the pair of second overhanging portions 42 are disposed on the inner side of the pair of the first overhanging portions 41. Specifically, among the four sides of a rectangular cross section of the main portion 3, three sides are formed from the circumferential wall portion 31 of the first split piece P1, and the remaining one side is formed from the circumferential wall portion 32 of the second split piece P2. One of the first overhanging portions 41 and one of the second overhanging portions 42 are disposed so as to face each other, and the other one of the first overhanging portions 41 and the other one of the second overhanging portions 42 are disposed so as to face each other. Preferably, the distance between the two flange portions 4 and the width W1 of the flange portions 4 are set such that a friction stir welding tool and a support member that faces the tool with one of the flange portions 4 therebetween can be disposed on the one of the flange portions 4 without interference with the other one of the flange portions 4. Since the flange portions 4 protrude in the same direction from the hollow structure 1, the joining operation can be performed on the flange portions 4 from the same direction. This is also the case for modifications 15 and 16 described later. In the present example, the side surfaces of the first split piece P1 and the side surfaces of the second split piece P2 are aligned with each other but may be displaced from each other in the width direction of the flange portions 4.
As shown in
The first split piece P1 and the second split piece P2 have different shapes. The second split piece P2 is the same as the second split piece P2 in modification 14. Specifically, the second split piece P2 is formed from a square U-shaped sheet having three flat surrounding surfaces and includes a circumferential wall portion 32 and a pair of second overhanging portions 42 having a rectangular cross-sectional shape and protruding radially outward from opposite ends of the circumferential wall portion 32 so as to intersect the circumferential wall portion 32 (orthogonally, in the present example). The first split piece P1 includes: a circumferential wall portion 31 having a C-shaped cross section with a plurality of bent portions; and a pair of first overhanging portions 41 protruding radially outward and each having a rectangular cross section. Although the number of bent portions of the circumferential wall portion 31 of the first split piece P1 in modification 14 is two, the number of bent portions of the circumferential wall portion 31 of the first split piece P1 in the present example is four. The pair of first overhanging portions 41 are parallel to each other and also parallel to the pair of the second overhanging portion 42. The two flange portions 4 may not be parallel to each other.
An opening of the first split piece P1 and an opening of the second split piece P2 face in the same direction, and the first split piece P1 and the second split piece P2 are combined such that the pair of second overhanging portions 42 are disposed on the inner side of the pair of the first overhanging portions 41, as in modification 14. In the present example, among the six sides of the hexagonal cross section of the main portion 3, five sides are formed from the circumferential wall portion 31 of the first split piece P1, and the remaining one side is formed from the circumferential wall portion 32 of the second split piece P2. One of the first overhanging portions 41 and one of the second overhanging portions 42 are disposed so as to face each other, and the other one of the first overhanging portions 41 and the other one of the second overhanging portions 42 are disposed so as to face each other. In the present example, the side surfaces of the first split piece P1 and the side surfaces of the second split piece P2 are aligned with each other but may be displaced from each other in the width direction of the flange portions 4. In the present example, the width β is shorter than the width α. Specifically, in the present example, the width W1 of the flange portions 4 is the width β.
Moreover, although not illustrated, the cross section of the inner space of the main portion 3 may have a polygonal annular (polygonal) shape other than the rectangular annular (rectangular) and hexagonal annular (hexagonal) shapes described above. Examples of the polygonal annular (polygonal) shape include a triangular annular (triangular) shape, a pentagonal annular (pentagonal) shape, and an octagonal annular (octagonal) shape. The number of bent portions in the circumferential wall portion 31 of the first split piece P1 is two when the cross section of the main portion 3 has a rectangular annular shape (four when cross section of the main portion 3 has a hexagonal annular shape). The cross section of the main portion 3 has a triangular shape (the circumferential wall portion 31 has a V shape) when the number of bent portions is one, has a pentagonal annular shape (the circumferential wall portion 31 has a C shape) when the number of bent portions is three, and has an octagonal annular shape (the circumferential wall portion 31 has a C shape) when the number of bent portions is six.
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The first split piece P1 and the second split piece P2 have different shapes. The second split piece P2 is the same as the second split piece P2 in modification 14. Specifically, the second split piece P2 is formed from a square U-shaped sheet having three flat surrounding surfaces and includes a circumferential wall portion 32 having a rectangular cross-sectional shape and a pair of second overhanging portions 42 having a rectangular cross-sectional shape and protruding radially outward from opposite ends of the circumferential wall portion 32 so as to intersect the circumferential wall portion 32 (orthogonally, in the present example). The first split piece P1 includes: a circumferential wall portion 31 having an arcuate cross-sectional shape (a C-shaped cross-sectional shape with no bent portion) with a longer arc length than a semi-circular arcuate shape; and a pair of first overhanging portions 41 having a rectangular cross-sectional shape and protruding radially outward from opposite ends of the circumferential wall portion 31. The pair of first overhanging portions 41 are parallel to each other and also parallel to the pair of second overhanging portions 42. The two flange portions 4 may not be parallel to each other.
An opening of the first split piece P1 and an opening of the second split piece P2 face in the same direction, and the first split piece P1 and the second split piece P2 are combined such that the pair of second overhanging portions 42 are disposed on the inner side of the pair of the first overhanging portions 41, as in modifications 14 and 15. In the present example, among the bowstring and the arc that form the bow-like cross section and also form the main portion 3, the bowstring is formed from the circumferential wall portion 32 of the second split piece P2, and the arc is formed from the circumferential wall portion 31 of the first split piece P1. One of the first overhanging portions 41 and one of the second overhanging portions 42 are disposed so as to face each other, and the other one of the first overhanging portions 41 and the other one of the second overhanging portions 42 are disposed so as to face each other. In the present example, the side surfaces of the first split piece P1 and the side surfaces of the second split piece P2 are aligned with each other but may be displaced from each other in the width direction of the flange portions 4. In the present example, the width β is shorter than the width α. Specifically, in the present example, the width W1 of the flange portions 4 is the width β.
Moreover, the cross section of the inner space of the main portion 3 may have, for example, a semi-circular annular (semi-circular) shape. When the first split piece P1 has a semi-circular shape, the main portion 3 can have a semi-circular annular cross-sectional shape.
The hollow structure described with reference to
For samples Nos. 1-1 to 1-3 and 1-101 to 1-103, the first and second split pieces having the same shape and the same size were prepared. Each of the split pieces includes: a circumferential wall portion having a semi-circular cross section; and a pair of overhanging portions having a rectangular cross section (see
The overhanging portions of the split pieces were disposed so as to face each other with their side surfaces aligned with each other and were joined together by friction stir welding, as shown in
The flexural rigidity of each sample was evaluated by a three-point bending test. Specifically, the joint state between the first overhanging portion and second overhanging portion of each flange portion was checked. The load was applied to the center of the main portion in its longitudinal direction so as to act in a direction orthogonal to the longitudinal direction and to the width direction of the flange portions. The load was 2,000 N. The test speed was 6 mm/min, and the length of the support span was 350 mm. The results are shown in Table 1. “Good” in the table means that the stiffness is 50% or more of the value of the stiffness computed based on the assumption that the flange portion is completely joined over the entire width W1. “Bad” means that the stiffness is less than 50% of the computational value.
As shown in Table 1, in the hollow structure samples Nos. 1-1 to 1-3, the flexural rigidity is better than that of the hollow structure samples Nos. 1-101 to 1-103.
The present invention is not limited to the above examples but is defined by the claims. The present invention is intended to cover any modifications within the scope of the claims and meaning equivalent to the scope of the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2017-124639 | Jun 2017 | JP | national |
| 2017-224508 | Nov 2017 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2018/023558 | 6/21/2018 | WO | 00 |
