[Name of Document] DESCRIPTION
[Title of the Invention] STRUCTURAL MEMBER FOR AUTOMOTIVE BODY
[Technical Field]
[0001]
The present invention relates to a structural member for an automotive body,
and more particularly to a structural member for an automotive body obtained by
press forming a forming material made of a steel sheet.
[Background Att]
[0002]
10 An automotive body includes major structural members such as vehicle
longitudinal members that are disposed along a vehicle fi·ont -back direction and
vehicle widthwise members that are disposed along a vehicle widthwise direction.
The vehicle longitudinal members and the vehicle widthwise members are joined, in
the way that one type of members have flanges formed at the ends and are joined to
15 the other type of members via the flanges, to ensure rigidity required for the
automotive body and bear the load in case of a collision event.
[0003]
The structural members such as the vehicle lengthwise members and the
vehicle widthwise members are required to have properties such as high load transfer
20 capability in the axial direction, high flexural rigidity, and high torsional rigidity.
High load transfer capability in the axial direction means that deformation is small
when the load acts in the axial direction. High flexural rigidity means that
deformation is small against the bending moment when the longitudinal axis of the
member is bent, and high torsional rigidity means that the angle of torsion is small
25 against the torsional moment when the member is twisted around the longitudinal
axis of the member. In recent years, a high tension steel sheet having a tensile
5
2
strength of390 MPa or more (a high-strength steel sheet or a high-tensile steel sheet)
has tended to be used as a material for the structural member in an aim to reduce
vehicle weight and improve collision safety.
[0004]
For example, a floor cross member, which is used to reinforce the floor of
an automotive body, has a cross section substantially shaped like a gutter and is
joined to vehicle longitudinal members such as side sills via outward flanges formed
at both ends of the floor cross member. It is impotiant for the floor cross member to
have an increased joining strength to other members and an increased rigidity to
10 ensure the rigidity of an automotive body and better load transfer capability when an
impact load is applied. Accordingly, it is necessaty not only to increase the material
strength but to modify the shape of the member so as to improve the load transfer
capability and the rigidity when an impact load is applied.
[0005]
15 Patent Literature 1 discloses a structural member for an automotive body
manufactured by press forming. The stmctural member has a substantially guttershaped
cross section as a whole and a groove-like depression in the hat top that is a
pati corresponding to the bottom in the gutter-shaped cross section.
[Prior Art Literature(s)]
20 [Patent Literature(s)]
[0006]
[Patent Literature 1] JP 2004-181502A
[Sununary of the Invention]
[Problem(s) to Be Solved by the Invention]
25 [0007]
When a groove-like depression (hereinafter referred to as simply "groove")
>I
J
3
is provided in the hat top as in the structural member for an automotive body
disclosed in Patent Literature 1, it is likely that the number of load-bearing ridgelines
increases, and thus the amount of energy absorption by the press-formed product is
increased. However, there have been cases in which energy absorption efficiency
5 has not been improved by simply forming the groove in a top plate in the structural
member having a substantially gutter-shaped cross section.
[0008]
FIG. 24 shows a state in which a structural member having a substantially
gutter-shaped cross section with a groove formed in a top plate deforms by receiving
10 an impact load in the axial direction. FIG. 24 shows that the structural member
deforms at each displacement stroke. This structural member has the groove in the
top plate but does not have an outward flange in the region along each ridge in the
longitudinal end, as illustrated in FIG. 15 (c). As illus.trated in FIG. 24, even though
the structural member had the groove, there were cases in which the structural
15 member buckled downward, in other words, buckled toward the opening of the
substantially gutter-shaped cross section where the rigidity of shape was relatively
small, as the displacement stroke became larger due to receiving a higher impact load.
If the structural member is buckled, the energy absorption stops increasing.
[0009]
20 An object of the present invention is to provide a stmctural member for an
automotive body that is excellent in load transfer capability and rigidity by
effectively enhancing energy absorption efficiency provided by disposing a groove in
a top plate in the structural member having a substantially gutter-shaped cross
section.
25 [Means for Solving the Problem(s)]
[0010]
4
To solve the problem, according to an aspect of the present invention, there
IS provided a stmctural member for an automotive body, the structural member
consisting of a press-formed product made of a steel sheet, the press-formed product
extending in a predetermined direction, including a top plate, a ridge continuing to
5 the top plate, and a vertical wall continuing to the ridge, and having a substantially
gutter-shaped cross section intersecting the predetermined direction, the structural
member including: at least one groove formed in the top plate, and extending in the
predetermined direction; and an outward flange formed at least in a region of the
ridge in an end in the predetermined direction. The groove having a depth set
10 according to a width of the groove and a sheet thickness of the steel sheet.
[0011]
The depth (h) of the groove, the width (w) of the groove, and the sheet
thickness (t) of.the.~l sheet in the end in the predetermined direction may satisfY a
relation: 0.2 x Ho :<: h :<: 3.0 x H0, where Ho = (0.037 t- 0.25) x w- 5.7 t + 29.2.
15 [0012]
The steel sheet may be a high-tensile steel sheet having a tensile strength of
390 MPa or more.
[0013]
The steel sheet may be a high-tensile steel sheet having a tensile strength of
20 590 MPa or more.
[0014]
The steel sheet may be a high-tensile steel sheet having a tensile strength of
980 MPa or more.
[0015]
25 The outward flange may be an outward continuous flange continuously
formed in a region over the ridge and at least a part of each of the top plate and the
5
vertical wall, in the end in the predetermined direction.
[0016]
The structural member may include the outward flange in a region of the
groove in the end in the predetermined direction.
5 [0017]
The structural member for an automotive body may be joined to another
member via the outward flange by resistance spot welding, penetration laser welding,
arc fillet welding, adhesion with an adhesive, or a combination thereof.
[Effect(s) of the Invention]
10 [0018]
According to the present invention, the structural member having the
outward flange in at least the end of the ridge enhances energy absorption in the
initial stage of collision. In addition, the structural member having the groove in
the top plate and the outward flange at least in the end of the ridge restrains buckling
15 of the structural member in the middle and later stage of collision, and thus enhances
the energy absorption effect provided by disposing the groove.
[0019]
In addition, the structural member according to the present invention having
the outward flange at least in the end of the ridge can provide a groove having an
20 effective depth according to the groove width and the sheet thickness. Accordingly,
it becomes easier to form a groove having a desired depth that allows the energy
absorption efficiency to improve, even in press forming the high-tensile steel sheet
that is relatively difficult for press forming. As a result, a structural member having
excellent load transfer capability and rigidity can be obtained with a high production
25 yield.
[0020]
6
Moreover, the structural member according to the present invention, which
has the outward flange at least in the region of the ridge in the end, enables joining to
other members via the outward flange or the flange in the vicinity thereof.
Consequently, this further improves load transfer capability and rigidity.
5 [Brief Description of the Drawing(s)]
[0021]
[FIG. I] FIG. I is a perspective view illustrating a shape of a structural
member according to an embodiment of the present invention.
[FIG. 2] FIG. 2 (a) is a view in the axial direction illustrating a structural
10 member according to the present embodiment, and FIG. 2 (b) is a view illustrating
another structural example of a stmctural member.
[FIG. 3] FIG. 3 is a cross sectional view illustrating a press-forming
apparatus for manufacturing a stmctural member.
[FIG. 4] FIG. 4 (a) is a perspective view illustrating a die, and FIG. 4 (b) is a
15 perspective view illustrating a ridge pad. FIG. 4 (c) is a perspective view
illustrating a punch.
[FIG. 5] FIG. 5 (a) is a cross sectional view illustrating a press-forming
apparatus including a pad known in the art, and FIG. 5 (b) is a schematic view
illustrating a state in which a forming material is restrained by a pad known in the art.
20 [FIG. 6] FIG. 6 is a schematic view illustrating a state in which a forming
material is restrained by a ridge pad.
[FIG. 7] FIG. 7 (a) is an overall plan view illustrating a shape of a developed
blank used in Analysis I, and FIG. 7 (b) is an enlarged plan view illustrating a
longitudinal end of a developed blank.
25 [FIG. 8] FIGs. 8 (a) and 8 (b) are a plan view and a view from above in the
axial direction of a structural member used in Analysis I, respectively.
7
[FIG. 9] FIG. 9 is a schematic view showing dimensions of a structural
member used in Analysis 1.
[FIG. 10] FIG. 10 IS a perspective view illustrating a press-forming
apparatus used in first press forming in Analysis 1.
5 [FIG. 11] FIG. II is a schematic view illustrating first press forming in
Analysis 1.
[FIG. 12] FIG. 12 is a perspective view illustrating a press-forming
apparatus used in a second press forming in Analysis 1.
[FIG. 13] FIG. l3 is a schematic view illustrating second press forming in
10 Analysis 1.
[FIG. 14] FIGs. 14 (a) and 14 (b) are schematic views illustrating an
intermediate product and a structural member, respectively, which show a maximum
decrease rate of sheet thickness in the vicinity of the edge of a ridge flange and a
minimum decrease rate of sheet thickness near the base of a ridge flange.
15 [FIG. 15] FIG. 15 (a) is a front elevational view illustrating an analytical
model for a struch1ral member according to the present embodiment, used in
Analysis 2, and FIG. 15 (b) is a front elevational view illustrating an analytical model
for Comparative Example 1. FIG. 15 (c) is a front elevational view illustrating an
analytical model for Comparative Example 2.
20 [FIG. I6] is a side view illustrating a shape of each analytical model used in
Analysis 2.
[FIG. 17] FIG. 17 is a graph showing axial load vs. stroke characteristics
obtained fi·om Analysis 2.
[FIG. 18] FIG. 18 is a graph showing amount of energy absorption vs. stroke
25 characteristics obtained from Analysis 2.
[FIG. 19] FIG. 19 (a) is a graph showing amount of energy absorption vs.
8
stroke characteristics for an analytical model of Comparative Example 2, obtained
from Analysis 3 using a steel sheet of 340HR, and FIG. 19 (b) is a graph showing
amount of energy absorption vs. stroke characteristics for an analytical model of a
structural member according to the present embodiment, obtained from Analysis 3
5 using a steel sheet of 340HR.
[FIG. 20] FIG. 20 is a graph showing amount of energy absmption vs.
groove depth characteristics obtained from Analysis 3 using a steel sheet of 340HR.
[FIG. 21] FIG. 21 (a) is a graph showing amount of energy absorption vs.
stroke characteristics for an analytical model of Comparative Example 2, obtained
10 from Analysis 3 using a steel sheet of 980Y, and FIG. 21 (b) is a graph showing
amount of energy absorption vs. stroke characteristics for an analytical model of a
structural member according to the present embodiment, obtained fi·om Analysis 3
using a steel sheet of 980Y.
[FIG. 22] FIG. 22 is a graph showing amount of energy absorption vs.
15 groove depth characteristics obtained fi·om Analysis 3 using a steel sheet of 980Y.
[FIG. 23] FIG. 23 is a graph showing normalized amount of energy
absorption vs. groove depth characteristics obtained from Analysis 3.
[FIG. 24] FIGs. 24 (a) to 24 (e) are schematic views illustrating deformation
of an analytical model of Comparative Example 2.
20 [FIG. 25] FIGs. 25 (a) to 25 (e) are schematic views illustrating defmmation
of an analytical model of a stmcturalmember according to the present embodiment.
[Mode(s) for Carrying out the Invention]
[0022]
Hereinafter, (a) preferred embodiment(s) of the present disclosure will be
25 described in detail with reference to the appended drawings. In this specification
and the appended drawings, structural elements that have substantially the same
9
fimction and structure are denoted with the same reference numerals, and repeated
explanation of these structural elements is omitted.
[0023]
<1. Structural Member for Automotive Body>
5 (1-1. Structural Example)
FIG. 1 is a schematic view illustrating an exemplary structural member (first
member) 2 for an automotive body according to the present embodiment. FIG. 2 (a)
is a view on the arrow A in FIG. 1, which is the view in the axial direction of the
structural member (first member) 2 according to the present embodiment.
10 [0024]
A first member 2 is joined to a second member 3 to constitute a joined
structure 1. The first member 2 is a press-formed product made of a steel sheet and
extends in a predetermined direction (or refened to as an axial direction) as
designated by the arrow X in FIG. 1. The first member 2 is joined at the axial end
15 to, for example, a second member 3 that is also a press-formed product made of steel
sheet, via outward continuous flanges 9a, 9b by, for example, spot welding. For
example, the first member 2 is joined to the second member 3 by using resistance
spot welding, penetration laser welding, arc fillet welding, or the combination thereof.
Joining the first member 1 to the second member 3 may be achieved by adhesion
20 using an adhesive or by the combination of welding and adhesion. The first
member 2 is a long member having a longitudinal length of, for example, 100 mm or
more, preferably 200 mm or more, and more preferably 300 nrm or more. The first
member 2 illustrated in FIG. 1 has the predetermined direction that corresponds to
the longitudinal direction, but the predetermined direction is not limited to the
25 longitudinal direction of the first member 2.
[0025]
10
As a forming material for the first member 2, a high-tensile steel sheet
having, for example, a thickness ranging from 0.5 to 6.0 mm and a tensile strength of
3 90 MPa or more measured by tensile testing in accordance with JIS Z 2241 can be
used. Preferably, a 2.0 mm or less thick high-tensile steel sheet having a tensile
5 strength of 440 MPa or more can be used as the forming material for the first
member 2. Incidentally, an upper limit of tensile strength, which is not pmiicularly
specified here, is, for example, about 1770 MPa and typically about 1470 MPa. For
a material and sheet thickness for the second member 3, which are not particularly
specified here, a steel sheet having, for example, a thickness of 0.5 to 6.0 mm and a
10 tensile strength of 390 MPa or more can be used.
[0026]
The first member 2 illustrated in FIG. 1 can be used as a member
constituting a joined . .structure 1 of an automotive bodyshell. Examples of the
joined structure 1 include a floor cross member, a side sill, a front side member, and
15 a floor tunnel brace. When the joined structure 1 is used as the floor cross member,
the side sill, the fmnt side member, the floor tunnel, or the like, it is preferable to use
a high tensile strength steel sheet having a tensile strength of 590 MPa or more, and
more preferably 780 MPa or more as the forming material.
20
[0027]
The first member 2 has a substantially hat -shaped cross section that includes
a top plate 4, ridges 4a, 4b continuing to the top plate 4, vertical walls Sa, Sb
continuing to the ridges 4a, 4b, curved sections 6a, 6b continuing to the vertical walls
Sa, Sb, and flanges 7a, 7b continuing to the curved sections 6a, 6b. The
substantially hat-shaped cross section is one mode of a substantially gutter-shaped
25 cross section. It is sufficient that the structural member (first member) 2 according
to the present embodiment has the substantially gutter-shaped cross section including
11
at least the top plate 4, the ridges 4a, 4b, and the vertical walls Sa, Sb, so that the
curved sections 6a, 6b and the flanges 7a, 7b may be omitted. For example, a Ushapcd
cross section is included in the substantially gutter-shaped cross section.
[0028]
5 In the perimeter of an axial end of the first member 2, outward continuous
flanges 9a, 9b are formed in the region along the top plate 4, the ridges 4a, 4b, and
the ve1iical walls Sa, Sb. The outward continuous flanges 9a, 9b are outward
flanges without having notches, which are formed continuously in the region along
the part of the top plate 4 that excludes the region along the groove 8, and in the
10 region along the ridges 4a, 4b and the vertical walls Sa, Sb. The first member 2 is a
member that has a ridge flange SOa or SOb at least in the region along each ridge 4a,
4b, which makes the first member 2 different from a known stmctural member that
does not have the outward flange in the region along the ridges 4a, 4b in the axial
end.
15 [0029]
Thanks to the outward continuous flanges 9a, 9b of the first member 2, the
ridges 4a, 4b, which receive the axial load, continues to contact surfaces with second
member 3. Because of this, the load that the ridges 4a, 4b bear in the initial stage
when an impact load is applied in the axial direction (for example, an amount of
20 displacement stroke of 0 to 40 mm) becomes larger. Accordingly, the first member
2 is advantageous in load transfer capability.
[0030]
It is sufficient that the width of the outward continuous flange 9a or 9b is at
least 1 mm or more to allow for enhancing energy absorption efficiency by forming a
25 groove 8, which will be described later. The width of the outward continuous
flange 9a or 9b, however, is preferably 3 mm or more in view of allowing for a
12
welding margin for laser welding, arc fillet welding, or the like, or preferably 10 mm
or more in view of allowing for a welding margin for spot welding. The width of
the outward continuous flange 9a or 9b is not necessarily constant along all the
regions. In view of making press forming easier, for example, the width of the
5. ridge flange 50a or SOb may be made smaller than that of the other pmt of the
outward flange. The width of the outward continuous flange 9a or 9b is adjustable
by modifying the shape of a blank into which the first member 2 is developed on a
flat plane (a developed blank).
[0031]
10 Incidentally, the term "outward flange" as used herein refers to a flange
formed in the way that an end of a press formed product having a substantially
gutter-shaped cross section is bent outwardly from the gutter. Further, the term
"ridge flange" as used herein refers to a flange formed along the ridge region in an
end of the press-formed product. Fmther, the term "outward continuous flange"
15 refers to an outward flange continuously formed over the ridge and at least a part of
each of a gutter bottom and the vertical wall.
[0032]
Fmthermore, the phrase "provide a notch in a flange" as used herein is
meant to provide a notch formed in the whole width of a flange, which makes the
20 flange discontinuous. The term "flange width" is used to have the same meaning as
the height of a flange. Accordingly, when the flange width is made partially small
but a pmt of the flange still remains, the notch is not meant to be provided in the
flange.
[0033]
25 Furthermore, the term "flange width" as used herein refers to the width of a
raised flat pottion of the flange that does not include the curved rising surface that
13
connects the outward continuous flanges 9a, 9b to the top plate 4, the ridges 4a, 4b,
and the vetiical walls 5a, 5b .
•
[0034]
As described above, the first member 2 according to the present
5 embodiment has the outward continuous flanges 9a, 9b in the perimeter of the axial
end thereof, or more particularly, in the region of the top plate 4 that excludes the
region along the groove 8, and also in the region along the ridges 4a, 4b and the
vertical walls 5a, 5b. It is sufficient, however, that the first member 2 has the ridge
flange 50a or 50b at least in the region along each ridge 4a, 4b. In addition, the first
10 member 2 may have an outward flange that has notches in the regions along the top
plate 4 and the vertical walls Sa, Sb so that the notches make the outward flange
discontinuous from the ridge flanges 50a, SOb.
[0035]
Further, as illustrated in Fl G. 2 (b), the outward continuous flange 9c may be
15 formed including the region along the groove 8 in the top plate 4. If the outward
continuous flange 9c is also formed in the region along the groove 8, the axial load is
transferred more easily to the ridges of the groove 8 so that such ridges will be also
able to bear the load efficiently.
[0036]
20 The top plate 4 of the first member 2 has the groove 8 disposed along the
axial direction. The shape of the groove 8 can be, for example, a substantially
trapezoidal shape or a V-letter shape. The first member 2 illustrated in FIG. I has
the substantially-trapezoidal groove 8. The first member 2 having the groove 8
increases the number of load-bearing ridgelines so that the amount of impact energy
25 absorption increases. Accordingly, this leads to, for example, weight reduction by
reducing sheet thickness without sacrificing collision safety.
14
[0037]
The upper width w of the groove 8 can be, for example, about 50 nun or less.
In view of formability in press forming, however, the upper width w of the groove 8
is preferably 5 mm or more. In addition, the depth h of the groove 8 is set
5 according to the width w of the groove 8 and also to the thickness t of the steel sheet
according to the present embodiment. More specifically, the depth h of the groove
8 is set such that the depth h and the width w of the groove 8 and the thickness t of
the steel sheet satisfy the following relation:
0.2 xHo:Sh:S3.0 xHo ... (!)
10 H0 = (0.037 t- 0.25) x w- 5.7 t + 29.2 ... (2)
[0038]
The formula (2) above represents a groove depth Ho when the amount of
energy absorption per unit area (kJ/mm2
) in the cross section of the first member 2
becomes around the maximum value at a displacement stroke of 100 mm in the case
15 that the first member 2 has the outward continuous flanges 9a, 9b. The cross
section of the first member 2 as used above refers to the cross section in the end of
the first member 2 that includes cross sections of the ends of the top plate 4, ridges
4a, 4b, and the vertical walls 5a, 5b, in which the cross sections are taken along the
border with the curved rising surface that continues to the outward continuous flange
20 9a or 9b.
[0039]
As indicated in the formula (!) above, if the groove depth h is within the
range of 20 to 300% of Ho that is the groove depth when the amount of energy
absorption per unit area becomes around the maximum value, the energy absorption
25 efficiency improves as compared to the shuctural member that has the outward
flanges but does not have the ridge flanges 50a, 50b.
u
" lS
[0040]
For example, when the sheet thickness t is 1.4 mm and the width w of the
groove 8 is 1 0 mm, the groove depth H0, in which the amount of energy absorption
per unit area becomes around its maximum, is 20 mm. In this case, the depth h of
5 the groove 8 is set from 4 nun to 60 mm. As another example, when the sheet
thickness tis 1.4 mm and the width w of the groove 8 is 40 mm, the groove depth H0,
in which the amount of energy absorption per unit area becomes around its maximum,
is 12 mm. In this case, the depth h of the groove 8 is set from 2.4 mm to 36 nun.
[0041]
10 As still another example, when the sheet thickness t is 2.0 mm and the width
w of the groove 8 is I 0 mm, the groove depth Ho, in which the amount of energy
absorption per unit area becomes around its maximum, is 17 mm. In this case, the
depth h of the groove 8 is set from 3.4 mm to 51 mm. As still another example,
when the sheet thickness tis 2.0 mm and the width w of the groove 8 is 40 mm, the
15 groove depth H0, in which the amount of energy absorption per unit area becomes
around its maximum, is I 0 mm. In this case, the depth h of the groove 8 is set fi·mu
2.0 mm to 30 mm.
[0042]
The first member 2 having the above-described structure is joined to the
20 second member"S· by welding via the outward continuous flanges 9a, 9b that include
the ridge flanges SOa, SOb. Thereby, the amount of energy absorption increases in
the initial stage of collision (at a displacement stroke of, for example, 40nml or less)
after receiving an impact load. In addition, the first member 2 has the groove 8 in
the top plate 4 and the outward continuous flanges 9a, 9b that include the ridge
25 flanges SOa, SOb in the axial end. Thereby, the buckling behavior of the first
member 2 becomes stable in the middle and later stage of collision (at a displacement
16
stroke of, for example, more than 40 mm) so that the amount of energy absorption is
increased.
[0043]
Moreover, even if an impact load applies to the first member 2 slantwise
5 relative to the axial direction, for example, the buckling behavior of the first member
2 during collision is still stable, and thus robustness against the load input is
improved for the first member 2 according to the present embodiment.
Consequently, the structural member (first member) 2 according to the present
embodiment has excellent load transfer capability.
10 [0044]
It should be noted that the above-described first member 2 has an open cross
section but the structural member according to the present embodiment is not limited
to this mode .... F:or,.example, the structural member may be shaped to have a closed
cross section in which another member is joined via flanges 7a, 7b. Moreover, the
15 first member 2, which has one groove 8 in the top plate 4, may have a plurality of
grooves.
[0045]
<2. Example of Method for Manufacturing Structural Member for Automotive
Body>
20 An example" of the method for manufacturing the structural member (first
member) 2 for an automotive body according to the present embodiment will now be
described. The . structural member 2 according to the present embodiment is
manufactured by press forming a high-tensile steel sheet having, for example, a sheet
thickness within the range of 0.5 mm to 6.0nun and a tensile strength of 390 MPa or
25 more, and thus forming defects such as wrinkling and cracking generally tend to
occur.
17
[0046]
For example, when attempting to form the outward continuous flanges 9a,
9b having a ce1iain degree of flange width along the whole perimeter of the axial end
of the stmctural member 2, forming defects such as cracking of stretched flange in
5 the edge of each ridge flange SOa, SOb and wrinkling near the base of each ridge
flange SOa, SOb tend to occur during press forming. In general, as the material
strength becomes higher, cracking in the edge and wrinkling near the base of each
ridge flange SOa, SOb are more likely to occur.
[0047]
10 Accordingly, when using a high-tensile steel sheet as the forming material, it
is difficult for press forming methods known in the art to manufacture the structural
member having the outward continuous flanges including ridge flanges because of
constraints in press forming. Consequently, a notch has hithe1io had to be provided
in the region along the ridge in the outward flange to compensate such difficulty in
15 press forming. Providing the notch is a cause to lower performance in terms of load
transfer capability, flexural rigidity, and torsional rigidity.
[0048]
In contrast, the structural member 2 according to the present embodiment
can be manufactured by a manufacturing method as described below even though it
20 has the outward continuous flanges 9a, 9b that include the ridge flanges SOa, SOb.
An example of the press-forming apparatus that can be used for manufacturing the
structural member 2 according to the present embodiment will be described hereafter,
and then a manufacturing method will be explained more specifically.
[0049]
25 (2-1. Press-forming Apparatus)
FIG. 3 and FIG. 4 are schematic views illustrating a press-forming apparatus
18
1 0 to be used for manufacturing the structural member 2. FIG. 3 is a cross sectional
view illustrating a part of the press forming apparatus 10, which corresponds to an
end of the structural member 2. FIG. 4 (a) is a perspective view illustrating a die I2,
and FIG. 4 (b) is a perspective view illustrating a pad 13. FIG. 4 (c) is also a
5 perspective view illustrating a punch 11. FIG. 4 (a) to 4 (c) are respective
perspective views illustrating the die 12, the pad 13, and the punch 11, as viewed
slantwise fi"om upper left, and the parts to form the outward continuous flanges 9a,
9b are shown on the deep side of the paper surface.
10
[0050]
The press-forming apparatus 10 includes the punch II and the die I2, and
the pad 13 that presses the forming material 14 against the punch II and restrains the
forming material 14. The punch II has a groove-forming part II b that is formed in
an upper surface 11 a of the punch 11 and extends in the longitudinal direction, and
has a side wall 11 c formed in the longitudinal end. The rising angle 0 of the side
15 wall II c is, for example, 50° to 90°.
[0051]
The shape of the groove-forming pmt II b corresponds to the shape of the
groove 8 to be formed in the structural member 2. For example, the grooveforming
part II b has a cross section of a trapezoidal shape or a V-letter shape (FIG. 3
20 (b) illustrates the trapezoidal shape). The width in the direction perpendicular to the
axial direction in the top opening of the groove-forming part lib is approximately 50
mm or less. The depth of the groove-forming part 11 b is designed to correspond to
the shape of the groove 8 of the structural member 2, which is determined by
satisfying the above-described formulas (I) and (2).
25 [0052]
The pad 13 has a top plate pressing part 13 b including a bump part 13a, a
19
ridge-pressing part 13c, and a side wall 13d. The bump part 13a faces the grooveforming
part 11 b that is formed in the punch 11 and extends in the longitudinal
direction. The top plate pressing part 13b having the bump pmi 13a presses, and
restrains, a portion to be formed into the top plate 4 in the forming material 14
5 against the upper surface 11 a of the punch 11. The top plate 4 having the groove 8
is formed by the pad 13 that presses the forming material· 14 against the upper
surface 11 a of the punch 11.
[0053]
The ridge-pressing pmi 13c presses against the punch 11, and restrains, the
10 ends of portions to be formed into ridges 4a, 4b in the vicinity of pmiions to be
formed into outward continuous flanges 9a, 9b in the forming material 14. The pad
13 is hereinafter referred to as the ridge pad.
[0054)
More specifically, the ridge pad 13 restrains the portion to be formed into
15 the top plate 4 and also the end of the portion to be formed into each ridge 4a, 4b in
the vicinity of the pmiion to be formed into each outward continuous flange 9a, 9b in
the forming material 14. It is sufficient, however, that the ridge pad 13 restrains at
least the end of the portion to be formed into each ridge 4a, 4b. The other parts of
the portions to be formed into ridges 4a, 4b, the portion to be formed into the top
20 plate 4, and "the portions to be formed into vertical walls Sa, Sb may leave
umestrained.
[0055]
FIG. 5 is a schematic view illustrating the shape of a pad 15 known in the art.
FIG. 5 (a) is a cross sectional view illustrating a press-forming apparatus 10' having
25 the pad 15 known in the ati, and FIG. 5 (b) is a perspective view illustrating a state in
which the forming material 14 is pressed by the known pad 15. FIG. 5 (a) is a cross
20
sectional view illustrating the same portion of the press-forming apparatus 10 as
illustrated in FIG. 3. As illustrated, the known pad 15 restrains the portion to be
formed into the top plate 4 in the forming material 14 but does not restrain the
portion to be formed into each ridge 4a, 4b.
5 [0056]
The press-forming apparatus 10 presses the end of the portion to be formed
into each ridge 4a, 4b using the ridge pad 13, and project outward approximately
only the steel sheet material nearby. Thereby, the ridges 4a, 4b in the vicinity of the
outward continuous flanges 9a, 9b are formed. Accordingly, this reduces the
10 movement of the material in the region that the ridge pad 13 contacts, and thus
reduces the generation of cracking of stretched flange in the end of the edge of each
ridge flange 50 a, SOb and wrinkling near the base of each ridge flange 50 a, 50 b.
[0057]
The ridge pad 13 is aimed at reducing the movement of the smmunding
15 material by projecting outward the material in the end of the pmiion to be formed
into each ridge 4a, 4b to form the end of each ridge 4a, 4b. Accordingly, the extent
of the pmiion to be formed into each ridge 4a, 4b that is restrained by the ridge pad
13 in the vicinity of the portion to be formed into each outward continuous flange 9a,
9b is preferably at least 1/3 or more of the perimeter length of the cross section of the
20 portion to be ·formed into each ridge 4a, 4b starting from the border between each
ridge 4a, 4b and the top plate 4.
[0058]
In addition, the extent in the axial direction in the portion to be formed into
each ridge 4a, 4b that is restrained by the ridge pad 13 in the vicinity of the portion to
25 be formed into each outward continuous flange 9a, 9b can be, for example, 5 mm to
100 mm along the axial direction from the base of the outward continuous flanges 9a,
il
'l
21
9b. If this restrained extent is less than 5 mm, there arises a concern that it may
become difficult to prevent distortion or scratches that may occur during press
forming. In addition, the portion to be formed into each ridge 4a, 4b may be
restrained over the whole length in the axial direction. However, if the above-
5 described restrained extent exceeds I 00 mm, the load that the ridge pad 13 requires
to press the forming material 14 may increase.
[0059]
The die 12, which has a rising surface 12a formed in the longitudinal end, is
disposed facing the punch II. The die 12, which does not have a pressing surface
10 corresponding to the portion to be formed into the top plate 4 in the structural
member 2, is disposed such that it does not overlap the pad 13 in the pressing
direction. The die 12 bends the forming materia114 along the portion to be formed
into each ridge 4a, 4b while the portion to be formed into the top plate 4 and the end
of the portion to be fmmed into each ridge 4a, 4b in the forming material 14 are
15 restrained by the ridge pad 13.
[0060]
Incidentally, the bending of the forming material 14 by the die 12 may be
bending forming in which the die 12 presses and bends the forming material 14, or
may be deep drawing in which a blank holder (not shown) and the die 12 clamp and
20 bend the forming material 14.
[0061]
(2-2. Manufacturing Method)
Now, a method for manufacturing the structural member 2 using the pressforming
apparatus I 0 will be described with reference to FIG. 6 together with FIG. 3
25 and FIG. 4. FIG. 6 is a perspective view illustrating a state in which the forming
material 14 is restrained by the ridge pad 13.
22
[0062]
The forming material 14, which is a developed blank having a shape into
which the structural member 2 to be formed is developed on a flat plane, is first
placed on the punch 11 in the press-forming apparatus 10. Subsequently, the ridge
5 pad 13 thrusts and presses the forming material 14 against the punch II, as illustrated
in FIG. 3 and FIG. 6. At this time, a part of the portion to be formed into each
outward continuous flange 9a, 9b in the forming material 14 is bent opposite to the
pressing direction by the side wall II c of the punch 11 and the side wall !3d of the
ridge pad 13.
10 [0063]
The end of the portion to be formed into each ridge 4a, 4b in the vicinity of
the potiion to be formed into each outward continuous flange 9a, 9b in the forming
material 14 is bent in the pressing direction by the ridge-pressing part 13c of the
ridge pad 13, and then restrained by the ridge-pressing pati 13c and the punch 11.
15 The top plate pressing pati 13b of the ridge pad 13 subsequently presses the portion
to be formed into the top plate 4 in the forming material 14 to cause the bump pati
13a to push a pati of the forming material 14 into the groove-forming part 11 b of the
punch 11, and then to cause the top plate pressing pmi 13b and the punch 11 to
restrain the forming material 14.
20 [0064]
While the forming material 14 is restrained by the ridge pad 13 and the
punch II as described above, the die 12 and the punch 11 carry out first press
forming. In the first press forming, a decrease or an increase in sheet thickness is
reduced, which otherwise causes cracking in the edge of the ridge flange SOa or SOb
25 or \Winkling near the base of the ridge flange SOa or SOb. The first press forming
provides an intermediate product having the substantially gutter-shaped cross section
23
and having the ridges 4a, 4b, the vertical walls Sa, Sb, and the top plate 4 including
the groove 8 that extends in the longitudinal direction. The intermediate product
has the outward continuous flanges 9a, 9b formed in the regions along the ridges 4a,
4b, a patt of the top plate 4, and the vertical walls Sa, Sb, in the longitudinal end of
5 the intermediate product.
[006S]
Incidentally, FIG. 6 illustrates a state in which the outward continuous
flanges 9a, 9b is formed in the regions along the ridges 4a, 4b, a part of the top plate
4 excluding the region along the groove 8, and the vertical walls Sa, Sb. It is
10 sufficient, however, that the outward flange is formed at least in the region along the
ridges 4a, 4b. In addition, the outward flange may be an outward continuous flange
9c that includes the region along the groove 8 (see FIG. 2 (b)). The shape and width
of the outward flange can be adjusted by modifying the shape of the developed blank
to be formed into the forming material 14.
15 [0066]
In addition, press forming of the intermediate product is described in the
above example in which the end of the portion to be formed into each ridge 4a, 4b
and the end of the portion to be formed into the top plate 4, in the forming material
14, are restrained by the ridge pad 13. However, the method for manufacturing the
20 structural member 2 is not limited to this example. The extent restrained by the
ridge-pressing part 13c of the ridge pad 13 may be a region of at least 1/3 or more of
the perimeter length of the cross section of each ridge 4a, 4b stm·ting from the border
between each ridge 4a, 4b and the top plate 4, in the portion to be formed into each
ridge 4a, 4b. If the extent of the forming material 14 restrained by the ridge pad 13
25 is smaller than the above-described extent, the ridge pad 13 may not achieve the
effect to reduce the generation of cracking and wrinkling sufficiently.
24
[0067]
After the first press forming is carried out as described above, the
intermediate product is then subjected to second press forming to form the pmis that
are left unformed in the first press forming. The second press forming presses the
5 portion that has not been formed by the ridge pad 13 and the die 12 and forms the
structural member 2 having the final shape. More specifically, a part of the pmtion
in each ve1tical wall Sa, Sb, which is located underneath the ridge pad 13 in the
pressing direction, is not completely press formed by the ridge pad 13 in the first
press forming. Accordingly, the pmi of the portion is press formed in the second
10 press forming by employing a different press-forming apparatus.
[0068]
Incidentally, the outward continuous flanges 9a, 9b may not be raised to the
angle in the final product in the first press forming due to the shape of the outward
continuous flanges 9a, 9b or the rising angle of flange. In this case, the outward
15 continuous flanges 9a, 9b may be raised approximately to a predetermined angle, for
example, to 60°, in the first press forming, and then further raised to the angle of the
final product in the second press forming or subsequent press forming.
[0069]
The press-forming apparatus to be used in the second press forming may be
20 an apparatus that can form what is not formed in the first press forming. Tllis pressforming
apparatus can be constituted by using a known press-forming apparatus
having a die and punch. If the second press forming does not complete forming
into the final shape of the structural member 2, another forming process may be
further carried out.
25 [0070]
Incidentally, although an example in which the groove 8 in the top plate 4 is
25
formed by the ridge pad 13 in the first press forming has been described as the
present embodiment, the groove 8 may be formed by die 12. In addition, although
an example in which the groove 8 is formed in the top plate 4 in the first press
forming has been described as the present embodiment, the groove 8 may be formed
5 in the second press forming.
[0071]
As described above, the structural member 2 is formed, with reduced
cracking in the edge and reduced wrinkling near the base of each ridge flange 50a,
SOb, by carrying out press forming using the ridge pad 13 including the ridge-
10 pressing pmi 13c and the top plate pressing pmi 13b that has the bump pmi 13a.
15
The stmctural member (first member) 2 is joined to the second member 3 via the
outward continuous flanges 9a, 9b formed in the longitudinal end to provide the
joined structure 1 including the first member 2 and the second member 3.
[0072]
It should be noted that the structural member having the outward flange
formed also in the region along the groove 8 in the longitudinal end, as illustrated in
FIG. 2 (b), can be manufactured, for example, in a sequence described below. That
is to say, a pad that has the ridge-pressing part 13c but does not have the bump part
13a forms an intermediate product having the outward continuous flange including
20 the outward flange formed also in the whole perimeter region along the top plate, in
the first stage. Subsequently, the intermediate product is pressed to form the groove
8 in the top plate 4 by using a pad or a punch having the bump pmi 13a for forming
the groove 8 in the second stage. Thereby, the structural member, which has the
outward flange in the region of the groove 8, can be obtained.
25 [0073]
In pmiicular, thanks to the outward continuous flanges 9a, 9b that are also
26
formed in the regions of the ridges 4a, 4b, the structural member according to the
present embodiment improves energy absorption efficiency even though the depth of
the groove 8 is relatively small. Consequently, a desired outward flange can be
provided also in the region along the groove 8 for the structural member by the
5 above-described press forming in the second stage.
[0074]
As described in the foregoing, the structural member 2 according to the
present embodiment is made to increase the amount of energy absorption in the
initial stage of collision, thanks to having the outward continuous flanges 9a, 9b,
10 which include the ridge flanges SOa, SOb, in the longitudinal end of the structural
member 2. Moreover, the stmctural member 2 according to the present
embodiment has the outward continuous flanges 9a, 9b as well as the groove 8 in the
top plate 4 that is configured in a predetermined range so that the energy absorption
efficiency in the middle and later stage of collision is increased. Consequently, the
15 structural member 2 according to the present embodiment is excellent in load transfer
capability, flexural rigidity, and torsional rigidity, which makes the structural member
suitable for structural members for an automotive body.
[007S]
Moreovet~ the structural member 2 according to the present embodiment has
20 the outward continuous flanges 9a, 9b that include the ridge flanges SOa, SOb, which
allows a groove 8 having an effective depth h determined according to the width w of
the groove 8 and the sheet thickness t to be provided in the structural member 2.
Consequently, it becomes easier to form the groove 8 having a desired depth that can
improve the energy absorption efficiency, even in press forming a high-tensile steel
25 sheet that is relatively difficult to form, so that the structural member having
excellent load transfer capability and rigidity can be obtained with a high production
yield.
[0076]
27
A preferable embodiment has been described so far with reference to the
accompanied drawings. The present invention, however, is not limited to the
5 above-described example. It will be evident that those skilled in the art to which
the present invention pertains may conceive various alternatives and modifications
while remaining within the scope of the technical idea as described in the claims. It
should be understood that such alternatives and modifications apparently fall within
the technical scope of the present invention.
10 [Example(s)]
[0077]
Examples of the present invention will now be described.
[0078]
(Analysis 1)
15 In Analysis 1, decrease rates of sheet thickness (or increase rates of sheet
thickness) in the edge and the base of ridge flanges SOa, SOb in a stmctural member 2
according to Example was first evaluated. FIG. 7 is a plan view illustrating a shape
of a developed blank as a forming material 14 for a stmctural member 2 used in
Analysis 1. FIG. 7 (a) is an overall plan view illustrating the shape of the forming
20 material 14 in:cluding an end in the longitudinal direction, and FIG. 7 (b) is an
enlarged plan view illustrating the longitudinal end.
[0079]
The forming material 14 is made of a dual-phase (DP) steel sheet having a
sheet thickness of 1.4 mm and a tensile strength of 980 MPa class measured by
25 tensile testing in accordance with JIS Z 2241. In the forming material 14, a portion
G to be formed into each ridge flange SOa, SOb has such a shape as to intend the
28
dispersion of deformation (a curvature radius of 60 mm). In addition, a notch 59 is
provided in the end of each ridgeline within a region along a groove 8, while an
outward flange 50c is also formed in a region along the portion to be formed into the
groove 8 in the end.
5 [0080]
FIG. 8 and FIG. 9 illustrate a structural member (first member) 2 to be
formed from the forming material14 that is illustrated in FIG. 7. FIG. 8 (a) is a top
plan view illustrating the structural member 2 as viewed from the top plate 4 side,
and FIG. 8 (b) a diagrammatic view of the structural member 2 as viewed slantwise
10 from above in the longitudinal direction. In addition, FIG. 9 is a cross sectional
view of the structural member 2. The height of the structural member 2 is 100 mm.
The curvature radius of the cross section of a ridge 4a or 4b is 12mm and the depth
of the groove 8 is 7.5mm. Other dimensions are as shown in FIG. 8 (b) and FIG. 9.
[0081]
15 FIG. 10 and FIG. 11 are schematic views illustrating a press-forming
apparatus 10 used in the first press forming in manufacturing the shuctural member 2
of Example. FIG. 10 is a perspective view of the press-forming apparatus 10, and
FIGs. 11 (a) to 11 (c) are schematic views illustrating Cross Section!, Cross Section
2, and Longitudinal Section in FIG. 10, respectively. In addition, FIG. 12 and FIG.
20 13 are schematic views illustrating a press-forming apparatus 20 used in the second
press forming in manufacturing the stmctural member 2 of Example. FIG. 12 is a
perspective view of the press-forming apparatus 20, and FIG. 13 (a) and FIG. 13 (b)
are schematic views illustrating Cross Section and Longitudinal Section in FIG. 12,
respectively. Each of FIG. 10 and FIG. 12 illustrates only a part for forming one end
25 of the structural member 2.
[0082]
il
J
29
When the structural member 2 was press formed from the forming material
14 by using the first and second press-forming apparatuses 10, 20, the deformation
behavior of the forming material 14 was analyzed by the finite element method. In
the first press forming, a ridge pad 13 according to Example was used to form an
5 intermediate product with the intention to reduce cracking in the edge and wrinkling
near the base of ridge flanges SOa or SOb to be fmmed in the region along ridges 4a,
4b in the longitudinal end. In the first press forming, a descending die 12 and a
punch II carried out press forming after the forming material 14 was pressed by the
ridge pad 13.
10 [0083]
The first press forming does not form the shape of a portion located, in the
pressing direction, under the region in each ridge 4a, 4b that is pressed by the ridge
pad 13, as illustrated in FIG. II (a). Accordingly, the pot1ion that was not formed in
the first press forming was formed by the second press forming. In the second press
15 forming, re-striking was carried out using bending forming, while forming what was
not formed in the first press forming. In the second press forming, a top portion 41
of an intermediate product 40 was first restrained by a pad 23 that had a bump part
23a corresponding to the groove 8 in shape. Subsequently, bending forming was
carried out by lowering a die 22 toward a punch 21 to form the structural member 2.
20 [0084]
FIGs. 14 (a) and 14 (b) respectively illustrate the obtained intermediate
product 40 and structural member 2 in which the analytical results on decrease rates
of sheet thickness in the edge and near the base of each ridge flange SOa, SOb are
shown. FIG. I 4 shows a maximum decrease rate of sheet thickness in the vicinity
25 of a region A, which is vulnerable to cracking in the edge of the ridge flange SO a or
SOb, and a minimum decrease rate of sheet thickness in the vicinity of a region B,
30
which is vulnerable to wrinkling near the base of the ridge flange SOa or SOb. A
negative value in decrease rate of sheet thickness means increase rate of sheet
thickness.
[008S]
5 As the press forming proceeds from the first press forming to the second,
the decrease rate of sheet thickness becomes larger in the region vulnerable to
cracking, in other words, in the vicinity of the edge of each ridge flange SOa, SOb
(region A), as shown in FIG. 14. It should be noted that, in the obtained structural
member 2, the decrease rate of sheet thickness, in the region vulnerable to cracking,
10 in other words, in the vicinity of the edge of each ridge flange SOa, SOb (region A),
was about 14%, with which cracking is avoidable.
[0086]
As the press forming proceeds from the first press forming to the second,
the increase rate of sheet thickness becomes larger in the region vulnerable to
15 wrinkling, in other words, in the vicinity of the base of each ridge flange SOa, SOb
(region B), as shown in FIG. 14. It should be noted that, in the obtained structural
member 2, the increase rate of sheet thickness, in the region vulnerable to wrinkling
or near the base of each ridge flange SOa, SOb (region B), was about 12%, with which
wrinkling is reduced.
20 [0087]
(Analysis 2)
Subsequently, energy absorption efficiency for the structural me11,1ber 2
according to Example, which had both the outward continuous flanges 9a, 9b
including the ridge flanges and the groove 8 in the top plate 4, was evaluated in
25 Analysis 2. In Analysis 2, the joined structure I in which the structural member
(first member) 2 was joined to a second member 3 by spot welding was assumed (see
31
FIG. l ), and the axial load and the amount of energy absorption were evaluated when
the structural member 2 was pressed along the axial direction :li'01n the side where the
second member 3 was joined. In Analysis 2, the displacement stroke was set up to
40 mm, which corresponded to the initial stage of collision, with the intention to
5 evaluate collision-safety capability from a deformation prevention point of view.
[0088]
FIG. 15 is schematic views illustrating analytical models used in Analysis 2.
FIG. 15 (a) illustrates an analyticalmodel30 of the structural member 2 according to
Example, and FIG. 15 (b) illustrates an analytical model 31 of Comparative Example
10 I, which does not have either the ridge flanges or the groove. FIG. 15 (c) illustrates
an analytical model 32 of Comparative Example 2, which has the groove 8 but does
not have the ridge flanges. FIG. 15 (a) to 15 (c) are diagra1111l1atic views of each
analytical model 30, 31, 32 as viewed slantwise from above in the longitudinal
direction. In addition, FIG. 16 is an overall view of the analytical models 30, 31, 32
15 as viewed from the lateral direction relative to the longitudinal direction.
[0089]
The analytical model 31 of Comparative Example 1 has the same shape as
the analytical model 30 of the structural member 2 according to Example, except that
a groove is not provided in the top plate 4 of the first member 2, and a notch 55 is
20 provided in the outward flange in the longitudinal end of each ridge 4a, 4b in the
analytical model 31. In addition, the analytical mode! 32 of Comparative Example
2 has the same shape as the analytical model 30 of the structural member 2 according
to Example, except that a notch 55 is provided in the outward flange in the
longitudinal end of each ridge 4a, 4b in the analytical model 32.
25 [0090]
In Analysis 2, each analytical model 30, 31, 32 was spot welded, via flanges
32
7a, 7b, to a closing plate 45 made of a 0.6 mm thick steel sheet having a tensile
strength of 270 MPa class. Each analytical model 30, 31, 32 had the same shape as
the above described structural member 2 illustrated in FIG. 8 and FIG. 9, except for
the presence of the closing plate 45 joined thereto and the presence or non-presence
5 of the groove or the ridge flange. Each analytical model 30, 31, 32 used the same
forming material14 as in Analysis 1, which was a 1.4 rmn thick steel sheet having a
tensile strength of 980 MPa class. This analysis assumed the second member 3 as a
rigid-body wall with the intention to study the influence of the shape of the joint
pmiion and the influence of the structure of the structural member 2 on collision-
10 safety capability.
[0091]
FIG. 17 is a graph showing the analytical results on axial load vs. stroke
characteristics, and FIG. 18 is a graph showing the analytical results on amount of
energy absorption vs. stroke characteristics. As shown in FIG. 17, the analytical
15 model 30 of the structural member 2 according to Example exhibits a higher peak
value in the axial load (kN) as compared to the analytical model 31 of Comparative
Example l. In addition, in the analytical model 30 of the structural member 2
according to Example, a peak value in the axial load (kN) in the initial stage of
collision has appeared on the smaller-stroke side of the graph, in other words, in an
20 earlier timing, ·as compared to the analytical model 31, 32 of Comparative Examples
1, 2.
[0092]
Moreover, in association with the peak difference in the axial load, the
amount of energy absorption (kJ) is also higher for the analytical model 30 of the
25 structural member 2 according to Example than that for the analytical model 31 of
Comparative Example 1. The structural member 2 according to Example also
5
33
exhibits a higher amount of energy absorption (kJ) than that of the analytical mode!
32 of Comparative Example 2 that has the groove 8 and the notches formed in the
outward flange.
[0093]
These results are likely due to the fact that the analytical model 30 of the
structural member 2 according to Example has more ridges that serve to transfer the
load than those of the analytical model 3! of Comparative Example I. It is also
likely that, in the analytical model 30 of the structural member 2 according to
Example, the outward continuous flanges 9a, 9b that include the ridge flanges SOa,
10 SOb cause the ridges to produce a high axial stress fi·om the initial stage of collision
and to be able to make the axial load confined and transferable with a high efficiency.
The above-described results from Analysis 2 show that the structural member 2
according to Example has an excellent ability as a deformation prevention member
as compared to Comparative Examples I, 2.
15 [0094]
(Analysis 3)
In Analysis 3, the energy absorption efficiency of the stmctural member 2
according to Example was evaluated in the middle and later stage of collision. In
Analysis 3, the analytical model 30 of the structural member 2 according to Example
20 illustrated in FIG. IS (a) and the analytical model 32 according to Comparative
Example 2 illustrated in FIG. 15 (c) were used among the analytical models used in
Analysis 2. In pmticular, the only difference between the shapes of two analytical
models 30, 32 is whether or not the notches 55 are provided in the outward flange.
The basic features of the shape and structure of the analytical models 30 and 32,
25 including having the closing plate 45 joined, are the same as in Analysis 2.
[0095]
34
In Analysis 3, however, each type of the analytical models 30, 32 was
formed using two different types of steel sheets, in other words, a 1.4 mm thick steel
sheet of 340 MPa class in tensile strength and a 1.4 mm thick steel sheet of 980 MPa
class in tensile strength. Fmther in Analysis 3, four different type of depths of the
5 groove 8, such as depths of 7.5mm, 15mm, 30mm, and 40nun, were provided and
then analyzed per each type of the steel sheet per each analytical model 30, 32. The
displacement stroke for Analysis 3 was set up to I 00 mm to cover the middle and
later stage of collision.
10
[0096]
FIG. 19 and FIG. 20 show the analytical results for the analytical models 30,
32 in which the 1.4 nm1 thick steel sheet of 340 MPa class in tensile strength was
used. FIG. 19 (a) is a graph showing the analytical results on amount of energy
absorption vs. stroke characteristics for the analytical model 32 according to
Comparative Example 2, and FIG. 19 (b) is a graph showing the analytical results on
15 amount of energy absorption vs. stroke characteristics for the analytical model 30 of
the structural member 2 according to Example. In addition, FIG. 20 is a graph
showing the analytical results on amount of energy absorption vs. groove depth
characteristics at a displacement stroke of I 00 mm for each of the analytical model
30 of the structural member 2 according to Example and the analytical model 32 of
20 Comparative Example 2.
[0097]
As shown in FIG. 19, when the 1.4 nun thick steel sheet of 340 MPa class in
tensile strength is used, the analytical model 30 of the structural member 2 according
to Example exhibits higher amounts of energy absorption (kJ) than those of the
25 analytical model 32 of Comparative Example 2 over the period until the
displacement stroke reaches I OOnun. However, an increase effect on the amount of
[j
'l
35
energy absorption is limited. In addition, as shown in FIG. 20, the analyticalmodcl
30 of the structural member 2 according to Example exhibits a higher amount of
energy absorption for every groove depth h at a displacement stroke of 100 mm (kJ)
than that of the analytical model 32 of Comparative Example 2.
5 [0098]
FIGs. 21 to 23 show the analytical results on the analytical models 30, 32 in
which the 1.4 mm thick steel sheet of 980 MPa class in tensile strength was used.
FIG. 21 (a) is a graph showing the analytical results on amount of energy absorption
vs. stroke characteristics for the analytical model 32 according to Comparative
10 Example 2, and FIG. 21 (b) is a graph showing the analytical results on amount of
energy absorption vs. stroke characteristics for the analytical model 30 of the
structural member 2 according to Example. In addition, FIG. 22 is a graph showing
the analytical results on amount of energy absorption vs. groove depth characteristics
at a displacement stroke of 100 mm for each of the analytical model 30 of the
15 structural member 2 according to Example and the analytical model 32 of
Comparative Example 2.
[0099]
In addition, FIG. 23 is a graph showing the analytical results on normalized
amount of energy absorption per unit cross sectional area vs. groove depth
20 characteristics at a displacement stroke of 100 mm for each of the analytical model
30 of the structural member 2 according to Example and the analytical model 32 of
Comparative Example 2. The normalized amount of energy absorption per unit
cross sectional area represents the value that is obtained as follows: an amount of
energy absorption per unit cross sectional area at a displacement stroke of I 00 mm is
25 divided by the amount of energy absorption per unit cross sectional area for the
analytical model 32 of Comparative Example 2 at a groove depth of7.5 mm and at a
36
displacement stroke of 100 nnn, and then the obtained result is multiplied by I 00.
Further, FIG. 24 and FIG. 25 are schematic views showing deformation, with respect
to displacement stroke (10 to 50mm), of the analytical model 32 of Comparative
Example 2 and the analytical model 30 of the structural member 2 according to
5 Example.
[0100]
As shown in FIG. 21, when the 1.4mm thick steel sheet of980 MPa class in
. tensile strength is used, the analytical model 30 of the structural member 2 according
to Example also exhibits higher amounts of energy absorption (kJ) than those of the
10 analytical model 32 of Comparative Example 2 over the period until the
displacement stroke reaches 1 OOmm. Moreover, an increase effect on the amount of
energy absorption is conspicuously shown as compared to the case using the 1.4 mm
thick steel sheet of 340 MPa class in tensile strength. Consequently, the structural
member 2 according to Example provides a higher improvement effect on the energy
15 absorption efficiency as the strength of the forming materiall4 increase.
[0101]
In addition, as shown in FIG. 22, the analytical model 30 of the structural
member 2 according to Example exhibits a higher amount of energy absorption (kJ)
at every groove depth h at a displacement stroke of 1 00 mm than that of the
20 analytical model 32 of Comparative Example 2. Further, the analytical model 30 of
the structural member 2 according to Example exhibits higher amounts of energy
absorption at a displacement stroke of 100 mm (kJ) fi·om the state in which the
groove depth h is smaller.
25
[0102]
Moreover, as shown in the graph in FIG. 23 in which the influence of the
perimeter length of each analytical model 30, 32 is eliminated, the analytical model
37
32 of Comparative Example 2 does not exhibit an increase in the energy absorption
efficiency (%) at a displacement stroke of 100 mm when the depth h of the groove 8
is small. Furthermore, the analytical model 32 of Comparative Example 2 does not
show a marked increase in the energy absorption efficiency when the depth h of the
5 groove 8 is made larger. This is due to the fact that the analytical model 32 of
Comparative Example 2 does not have the ridge flanges SOa, SOb so that when the
ridges of the groove 8 is stressed hard in the middle stage of collision in which the
displacement stroke exceeds 40 mm, the restraint at the ridge ends becomes loose
and the strncturalmember buckles, as shown in FIG. 24.
10 [01 03]
In contrast, the energy absorption efficiency (%) at a displacement stroke of
I 00 mm is increased, regardless of the groove depth h, in the analytical model 30 of
the structnral member 2 according to Example. In addition, when the energy
absorption efficiency at a displacement stroke of I 00 mm is a maximum, the groove
15 depth his smaller for the analyticalmodel30 of the structural member 2 according to
Example than that for the analytical model 32 of Comparative Example 2. This is
due to the fact that the analytical model 30 of the structnralmember 2 according to
Example has the ridge flanges SOa, SOb so that the buckling behavior of the structural
member 2 becomes stable in the middle stage of collision in which the displacement
20 stroke exceeds 40 mm, as shown in FIG. 2S.
[0104]
Incidentally, the groove depth Ho in FIG. 23, with which the energy
absorption efficiency at a displacement stroke of I 00 mm becomes a maximmn, can
be expressed in the above described formula (2). In addition, when the groove
25 depth h is in the range of 0.2 x H0 to 3.0 x Ho in terms of above Ho as shown in the
above described formula (I), the energy absorption efficiency at a displacement
fl
'l
5
10
15
20
25
38
stroke of I 00 mm becomes large as compared to the analytical model 32 according to
Comparative Example 2.
[Reference Signs List]
[OJ 05]
1 joined structure
2 structural member (first member)
3 second member
4 top plate
4a, 4b ridge
5a, 5b vertical wall
6a, 6b curved section
7a, 7b flange
8 groove
9a, 9b, 9c outward continuous flange
I 0 press-forming apparatus
11 punch
11 b groove-forming part
12 die
13 pad (ridge pad)
13a bump part
13 b top plate pressing part
13c ridge-pressing part
14 forming material
15 pad known in the att
20 press-forming apparatus
30, 31, 32 analytical model
5
40 intermediate product
45 closing plate
50a, 50b ridge flange
39
50c outward flange (groove bottom flange)
55 notch
h groove depth
w groove width

[Name of Document] CLAIMS
[Claim I]
A structural member for an automotive body, the structural member
consisting of a press-formed product made of a steel sheet, the press-formed product
5 extending in a predetermined direction, including a top plate, a ridge continuing to
the top plate, and a vertical wall continuing to the ridge, and having a substantially
gutter-shaped cross section intersecting the predetermined direction, the structural
member comprising:
at least one groove formed m the top plate, and extending m the
10 predetermined direction; and
an outward flange formed at least in a region of the ridge in an end in the
predetermined direction,
the groove having a depth set according to a width of the groove and a sheet
thickness of the steel sheet.
15 [Claim 2]
The structural member for an automotive body according to claim I,
wherein the depth (h) of the groove, the width (w) of the groove, and the sheet
thickness (t) of the steel sheet in the end in the predetermined direction satisfy a
relation: 0.2 x Ho::; h::; 3.0 x H0, where Ho = (0.037 t- 0.25) x w- 5.7 t + 29.2.
20 [Claim 3]
The structural member for an automotive body according to claim I or 2,
wherein the steel sheet is a high-tensile steel sheet having a tensile strength of 390
MPaormore.
[Claim 4]
25 The structural member for an automotive body according to claim I or 2,
wherein the steel sheet is a high-tensile steel sheet having a tensile strength of 590
41
MPaormore.
[Claim 5]
The structural member for an automotive body according to claim I or 2,
wherein the steel sheet is a high-tensile steel sheet having a tensile strength of 980
5 MPa or more.
[Claim 6]
The structural member for an automotive body according to any one of
claims I to 5, wherein the outward flange is an outward continuous flange
continuously formed in a region over the ridge and at least a part of each of the top
10 plate and the vetiical wall, in the end in the predetermined direction.
[Claim 7]
The structural member for an automotive body according to any one of
claims I to 6, wherein the structural member includes the outward flange in a region
of the groove in the end in the predetermined direction.
15 [Claim 8]
The structural member for an automotive body according to any one of
claims I to 7, wherein the structural member for an automotive body is joined to
another member via the outward flange by resistance spot welding, penetration laser
welding, arc fillet welding, adhesion with an adhesive, or a combination thereof.