TECHNICAL FIELD
[0001] The present invention relates to a method of
forming a fillet arc welded joint and a fillet arc
I
welded joint, and is preferred to be used
particularly for fillet arc welding plural metal
members. .
BACKGROUND ART
[0002] In the automotive field, for example,
improvement in collision safety is required together
with improvement in fuel consumption by weight
reduction of vehicle bodies for environmental
conservation. Thus, use of high-strength steel
sheets for thickness reduction and optimization of
vehicle body structures have been practiced hitherto
in various ways, so as to achieve weight reduction of
vehicle bodies and improvement in collision safety.
[0003] Large fatigue strength is also required in
the high-strength steel sheets for weight reduction
of vehicle bodies. In general, the fatigue strength
of a parent material to be used for a welded member
increases in proportion to steel sheet strength, but
it is known that the fatigue strength of a welded
joint barely increases even when the steel sheet
strength is increased. This hinders the weight
reduction of vehicle bodies by use of the highstrength
steel sheets.
[0004] For underbody members such as suspension arms
and sub-frames in particular, the fatigue strength of
welded portions becomes more important. Fillet arc
welding is often used for welding of these underbody
members. Thus, in order to achieve the weight
reduction of underbody members, an lncrease in
fatigue strength of fillet arc welded joints becomes
an issue.
[0005] Fig. 1 shows a cross-sectional shape of a
typical lap fillet welded joint formed by overlapping
an upper steel product 1 and a lower steel product 2
and welding only a corner portion of one side of
corner portions formed on both sides of an abutted
portion of the upper steel product 1 and the lower
steel product 2. In such a lap fillet welded joint,
stress is concentrated in a toe portion 4 and a root
portion 5 of a fillet weld bead 3 and a fatigue crack
progresses in a direction vertical to a load, and
thereby the welded joint is broken. Therefore, for
improvement in fatigue strength, decreasing the
stress concentration in the toe portion 4 and the
root portion 5 becomes important. Incidentally, in
the following explanation, the fillet weld bead is
referred to as a fillet bead as necessary.
[00061 Conventionally, as a means of improving
fatigue strength of a fillet welded joint, welding a
reinforcing member such as a rib into/to a proper
shapeeposition, finishing a toe portion of a weld
bead by a grinder operation, decorative build-up
welding, and the like, and the like are performed.
However, welding an additional member leads to an
increase in cost. Further, additional work is
required for the finishing of the toe portion. Thus,
these means are not techniques applicable to
manufacture of mass-produced goods such as automobile
parts.
[0007] Further, in terms of a welding method, a
technique of decreasing stress concentration to a toe
portion is proposed in Patent Literatures 1 and 2.
In Patent Literature 1, there is disclosed a
method of decreasing stress concentration to a toe
portion and improving fatigue strength by optimizing
chemical components of a weld metal to increase a
curvature radius of the toe portion.
In Patent Literature 2, there is disclosed a weld
bead structure in which a weld bead is extended when
an end surface of another steel sheet is butted
against one surface of a steel sheet to have a Tshaped
cross section and a fillet bead is formed on
both sides of the butted portion.
[0008] In Patent Literature 3, there is disclosed
that when a sheet surface of a plate-shaped me~ber
and a square member are butted and fillet welding is
performed with respect to all the portions of edges
of the square member in contact with the plate-shaped
member, linear welded portions intersecting crosswise
each other are formed on corner portions of the
square member.
[0009] However, even with the techniques disclosed
in Patent Literatures 1 to 3, it is not possible to
expect the effect of decreasing the stress
concentration to the root portion 5 of the typified
lap fillet welded joint formed by welding only one
side of the overlapped portion of the steel sheets 1
and 2 shown in Fig. I.
Further, in the technique disclosed in Patent
Literature 2, the weld bead is extended, and thereby
fatigue strengths at a welding start point (start
1 edge portion) of the weld bead and at a welding end
!
point (end edge portion) of the weld bead improve.
However, there is little effect for improvement in
fatigue strength of an intermediate portion of the
weld bead.
[0010] Further, in the technique disclosed in Pat-ent
Literature 3, the number of welding start points to
remain independently near a fillet bead is increased.
The shape of a toe portion at a welding start point
projects and this projected angle is steep, so that
stress is easily concentrated at the welding start
point if the welding start point exists independently.
[0011] As above, in the techniques disclosed in
Patent Literatures 1 to 3, it is not easy to suppress
occurrence of fatigue fracture when a welded
structure member to which a cyclic load is applied
such as an automobile underbody member is formed by
fillet welding metal sheets having a thin sheet
thickness.
CITATION LIST
PATENT LITERATURE
[0012] Patent Literature 1: Japanese Lald-open
Patent Publication No. 06-340947
Patent Literature 2: Japanese Lald-open Patent
Publication No. 09-253843
Patent Literature 3: Japanese Lald-open Patent
Publication No. 51-14844
SUMMARY OF. INVENTION
TECHNICAL PROBLEM
[0013] Thus, the present invention has an object to
make it possible to suppress occurrence of a crack
caused by fatigue of a welded structure member formed
by fillet welding metal members having a thin sheet
thickness.
SOLUTION TO PROBLEM
[0014] A method of forming a fillet arc welded joint
of the present invention is a method of forming a
fillet arc welded joint by fillet arc welding at
least a partial region of corner portions that are
edge regions of an abutted portion of at least one of
a sheet surface portion and a sheet thickness portion
of one metal member and a sheet surface portior. of
the other metal member and have at least one turned
portion at at least one portion thereof, the method
including: forming a fillet bead with respect to a
region containing the turned portion of the corner
portion by the fillet arc welding; and forming a
stiffening bead on one place or plural places of at
least the one turned portion by arc welding different
from the fillet arc welding so that a welding start
point or a welding end point of the stiffening bead
overlaps with the fillet bead, in which the
stiffening bead is formed in a direction of, of the
one metal member and the other metal member, the
metal memberin which a larger tensile stress occurs
when, to a fillet arc welded joint formed under the
same condition as that of the fillet arc welded joint
except for the polnt that the stiffening bead is not
formed, a cyclic load expected to be applied to the
fillet arc welded joint is applied, and at least one
metal member of the one metal member and the other
metal member is formed of a metal sheet having a
sheet thickness of 3.2 mm or less.
[0015] A fillet arc welded joint of the present
invention is a fillet arc welded joint formed by
fillet arc welding at least a partial region of
corner portions that are edge regions of an abutted
portion of at least one of a sheet surface portion
and a sheet thickness portion of one metal member and
a sheet surface portion of the other metal member and
have at least one turned portion at at least oce
portion thereof, the fillet arc welded joint
including: a fillet bead formed with respect to a
region containing the turned portion of the corner
portion by the fillet arc welding; and a stiffening
bead formed on one place or plural places of at least
the one turned portion by arc welding different from
the flllet arc welding, in which the stiffening bead
is formed so that a welding start polnt or a welding
end point of the stiffening bead overlaps with the
fillet bead, and is formed in a direction of, of the
one metal member and the other metal member, the
metal member in which a larger tensile stress occurs
when, to a fillet arc welded joint formed under the
same condition as that of the fillet arc welded joint
except for the point that the stiffening bead is not
formed, a cyclic load expected to be applied to the
fillet arc welded joint is applied, and at least one
metal member of the one metal member and the other
metal member is formed of a metal sheet having a
sheet thickness of 3.2 mm or less.
ADVANTAGEOUS EFFECTS OF INVENTION
[0016] According to the present invention, it is
possible to suppress occurrence of a crack caused by
fatigue of a welded structure member formed by fillet
welding metal members having a thin sheet thickness.
BRIEF DESCRIPTTON OF DRAWINGS
[0017] [Fig. 11 Fig. 1 is a view showing a crosssectional
shape of a lap fillet welded joint;
[Fig. 21 Fig. 2 is a view showing a test piece
on which a lap fillet welded joint is formed;
[Fig. 31 Fig. 3 is a view showing fatigue lives
(times) of the case when no stiffening bead is
disposed and the case when a stiffening bead is
disposed;
[Fig. 41 Fig. 4 is a view showing fatigue lives
(times) according to a difference between a hardness
of a stiffening bead and a steel member maximum
hardness;
[Fig. 51 .Fiy. 5 is a view showing a first
example of a welded structure member;
[Flg. 61 Flg. 6 is a view showing a second
example of the welded structure member;
[Fig. 71 Fig. 7 is a view showing a third
example of the welded structure member;
[Fig. 8 1 Fig. 8 is a view showing a fourth
example of the welded structure member;
[Fig. 91 Fig. 9 is a view showing a fifth
example of the welded structure member; and
[Fig. 101 Fig. 10 is a view showlng a fifth
example of the welded structure member
DESCRIPTION OF EMBODIMENTS
[0018] There will be explained embodiments of a
fillet arc welded joint and a method of forming the
same of the present invention in detail by using the
drawings.
When thin steel sheets for automobile are fillet
welded, for example, a fillet bead is sometimes
placed only (not on front and rear sides) but on one
side of the thin steel sheets in terms of
productivity.
[0019] When a sheet thickness portion of one thin
steel sheet is abutted on a sheet surface portion of
the other thin steel sheet to be fillet welded, for
example, it is common that fillet arc welding is
designed to be performed only on a corner portion of
one side of corner portions formed on both sides of 'I ! the abutted portion of the one thin steel sheet and
the other thin'steel sheet (see Fig. 5 to Fig. 8 that
will be described later).
[0020] Further, even when a sheet surface portion of
one thin steel sheet is abutted on a sheet surface
portion of the other thin steel sheet to be lap
fillet welded, it is common that fillet arc welding
is designed to be performed only on a corner portion
of one side of corner portions formed on both sides
of the abutted portion of the one thin steel sheet
and the other thin steel sheet (see Fig. 9 and Fig.
10 that will be described later).
[0021] This is because there is a problem that when
!
the one side (front side) of the corner portion (a
joined portion) is fillet welded and then the
opposite side (rear side) of the sheets is soon
fillet welded, the steel sheet itself melts down
because the steel sheets are not cooled down due to
thin sheet thickness.
Incidentally, the corner portion (joined portion)
is an edge region of an abutted portion of at least
one of a sheet surface portion and a sheet thickness
portion of one metal member and a sheet surface
portion of the other metal member. The fillet arc
welding is performed with respect to at least a
partial region of such a corner portion (joined
portion) .
[0022] Thus, the present inventors conducted a
fatigue test on a welded structure member in which of
corner portions (joined portions) formed on both
sides of an abutted portion of two steel members, at
least one of the steel members set to a thin steel
sheet having a sheet thickness of 3.2 mm or less,
only the corner portion (joined portion) of one side
is fillet welded. As a result, it was turned out
that a fatigue crack sometimes occurs in a fillet
bead of such a welded structure member. In the
following explanation, the corner portion (joined
portion) of one side of the corner portions (joined
portions) formed on both sides of the abutted portion
of the two steel members will be referred to as a
"corner portj.on (joined portion) of one side"
according to need.
[0023] As described above, the welded structure
member such as an underbody member has a welded place
where not corner portions (joined portions) of both
sides but a corner portion (joined portion) of one
side is fillet welded due to the structure of the
member. It is expected that the fatigue crack is
likely to occur in such a welded place. Thus, the
present inventors examined a cause of occurrence of a
fatigue crack and a means of suppressing occurrence
of a fatigue crack by taking a basic lap fillet
welded joint as an example.
[0024] Here, a lap fillet welded joint in which only
a corner portion of one side of an overlapped portion
of steel sheets 1 and 2 shown in Fig. 1 is fillet arc
welded was set as an object of the examination. The
present inventors analyzed how the steel sheets 1 and
2 are deformed by using a three-dimensional finite
element method when on a fillet bead 3 formed by
fillet arc welding, a tensile force El acts along the
upper steel sheet 1 and a tensile force F2 acts along
the lower steel sheet 2.
I00251 As. a result, it was found that a large
bending moment occurs by a displacement between a
center axis of the upper steel sheet 1 (a line
passing through the centers of the thickness and the
width of the steel sheet and parallel to the
longitudinal direction of the steel sheet) and a
center axis of the lower steel sheet 2, and the lower
steel sheet 2 bends in the vicinity of the fillet
bead 3, and thus a root portion 5 opens. This
conceivably increases a stress concentration to the
root portion 5 and causes the occurrence of a fatigue
crack.
[0026] Thus, the present inventors further examined
a means of suppressing the bending of the lower steel
sheet 2.
As a result, it was confirmed that the occurrence
of a fatlgue crack can be suppressed as long as
welding is performed as shown in Fig. 2. That is, in
addition to the fillet arc welding, another arc
welding is performed in such a manner that the
position of a welding start point overlaps with the
- 11 -
fillet bead 3 and the position of a welding end point
is positioned on the front surface of the lower steel
sheet 2, and in addition to the fillet bead 3,
another arc weld bead (a stiffening bead 3A) is
formed. A s long as this is applied, the stiffening
bead 3A functions as a member of increasing
stiffnesses of the steel sheet and a weld metal
against the direction in which the above-described
bending moment is applied, to thereby be able to
suppress the bending of the lower steel sheet 2.
Thus, it is possible to suppress the occurrence of a
fatigue crack. This is because the bead shape of a
start edge portion of the weld bead becomes a
projecting shape, whereas the bead shape of an end
edge portion becomes flat and the stress
concentration in the end edge portion decreases, as
described above.
100271 Further, the reason why the welding end point
of the stiffening bead 3A is positioned on the lower
steel sheet 2 is because a compression stress acts on
the front surface of the upper steel sheet 1, and a
tensile stress acts on the front surface of the lower
steel sheet 2. That is, the stiffening bead 3h is
formed in the direction of, of the steel sheets 1 and
2, the steel sheet in which a larger tensile stress
acts when to a welded structure member without the
stiffening bead 3A formed thereon, a cyclic load to
be expected in the welded structure member is applied
Incidentally, in each of the drawings, a place
where a reglon of an entire ellipse is seen is shown
1 as the welding end point ~ [0028] Next, actual test pleces were made to examlne
1 effects of the stiffening bead.
As the test pieces, there was fabricated a test
piece A, in which an upper steel sheet 1 having a
sheet thickness of 2.3 mm and having a sheet width of
35 mm was overlapped on a lower steel sheet 2 having
a sheet thickness of 2.3 mm and having a sheet width
of 60 mm wlth an overlapping portlon of 20 mm Erom
above, the overlapped portion was fillet arc welded,
and then a fillet bead 3 having a width of 7 mm and
havlng a length of 40 mm was formed on an end portion
of the upper steel sheet 1.
Next, there was fabricated a test piece B, in
which in addition to the fillet bead 3, a stiffening
bead 3A having a length of 10 mm and having a width
of 6 mm was further formed by bead-on welding so as
to partially overlap with a center portion of the
fillet bead 3 with the fillet bead 3 being a welding
start point (see Fig. 2).
A fatigue test of these test pieces A and B was
conducted.
As a result, as shown in Fig. 3, it was confirmed
that fatigue strength of a joint improves when the
stiffening bead is formed in the middle of the fillet
bead.
[0029] Further, changes of a fatigue life according
to a magnitude relation between hardnesses (Vickers
hardnesses) of the stiffening bead and the steel
sheet were examined.
Steel sheets 1 and 2 each having a hardness of
182 Hv were used,and a weld metal having a hardness
Hw of 150 Hv was used, to thereby form a test piece C
similar to the above-described test piece A, and a
fatigue test was conducted.
Further, steel sheets 1 and 2 each having a
hardness of 192 Hv were used and weld metals having
the hardnesses Hw of 150, 183, and 270 respectively
were used, to thereby form test pieces D, E, and F
similar to the above-described test piece R, and a
fatigue test was conducted.
[0030] As a result, as shown in Fig. 4, it was found
that by providing the stiffening bead, the fatigue
life improves, and further when the hardness Hw of
the stiffening bead is larger than a steel member
maximum hardness Hb, the fatigue life further
improves.
Incidentally, in Fig. 4, "-36", "I", and " 8 8 "
each indicate a value obtained by subtracting the
steel member maximum hardness Hb from the hardness Hw
of the stiffening bead. Further, the steel shcet
maximum hardness Hb and the hardness Hw of the
stiffening bead will be described later.
[0031] Further, as is a welded joint having a Tshaped
cross section, one obtained by welding corner
portions of a fillet arc welded joint formed by a
sheet thickness portion and a sheet surface portion
being joined is common. In this case as well,
depending on the shape of a steel member, there may
be a case where only a corner portion of one side can
be welded. The present inventors confirmed that
fillet arc welding can be treated similarly to lap
fillet arc welding even when fillet arc welding is
performed only on a corner portion of one slde of
such a fillet arc welded joint.
[0032] The effects obtained by the stiffening bead
were confirmed as above, and thus they subsequently
examined application of this means of increasing
stiffness of a steel member by the stiffening bead to
fillet welding of welded structure members.
[ 0 0 3 3 ] With regard to welded structure members for
automobile, particularly welded structure members for
underbody, the ones in which a sheet and a sheet are
simply overlapped to be fillet welded, such as the
above-described test pieces, and the like are not
many, there are members having various shapes, and
further there are various directions in which a
cyclic load is applied. As a result that they
examined a forming method of a stiffening bead
effective for such welded structure members, it was
turned out that it is effective to form a stiffening
bead on one place or plural places of a region of a
turned portion, being a portion having a bent weld
line, (first region) of a region of a fillet bead
formed in a single stroke manner.
LO0341 Particularly, it was turned out that it is
effective to form a stiffening bead on one place or
plural places of at least one region of a bent
portion and a curved portion of the weld line (second
region) of theregion of the fillet bead formed in a
single stroke manner.
[ 0 0 3 5 ] Further, it was turned out that when a
welding start point and a welding end point of the
fillet bead are not connected and the welding start
point of the fillet bead is positioned at a position
different from the welding end polnt, it is effective
to form a stiffening bead on one place or plural
places of a region where magnitude of a maximum
principal stress (tensile stress) is larger than at
the welding start point of the fillet bead (third
region) of the above-described first region or second
region.
[ 0 0 3 6 ] Particularly, it was turned out that when the
welding start point side of the fillet bead is
extended from a corner portion of steel products, it
is effective to form a stiffening bead on one place
or plural places of such a third region.
Further, it was turned out that it is effective
to form a stiffening bead in a region where a fatigue
crack first occurs when a cyclic stress expected to
be applied to a welded structure member with no
stiffening bead formed thereon is applied to the
welded structure member (fourth region) of the abovedescribed
first region, second region, or third
region. The place where a fatigue crack first occurs
corresponds to the place where magnitude of a maximum
principal stress becomes maximum (a tensile stress
becomes maximum).
Particularly, when the curvature of the weld line
of the fillet bead is constant, it is effective to
form a stiffening bead in such a fourth region.
[0037] The stress in the fillet bead can be obtained
by finding distribution of stress to occur when a
cyclic load is applied to the welded structure member
by a FEM stress analysis with the use of threedimensional
CAD, for example. Further, the stress in
the fillet bead can also be obtained by conducting a
stress application test with the use of an actual
welded structure member to examine distribution of
strain by using a strain gauge or the like on this
occasion.
[0038] Hereinafter, there will be explained concrete
examples of the case where the stiffening bead is
applied to a fillet weld bead by using welded
structure members shown in Fig. 5 to Fig. 10.
Incidentally, it is set in these examples that a
cyclic load is applied in the outline arrow direction
shown in each drawing.
Fig. 5 is a view showing a first example of the
welded structure member.
A welded structure member 50 shown in Fig. 5 is
formed in a manner that one end portion of a channel
product (channel steel) 51 is abutted on one side
surface (front surface) of a box product 52 using a
- 17 -
square-shaped steel pipe, and of the abutted portion,
only the portion positioned outside a sheet surface
of the channel product 51 is fillet welded.
[0039] As shown -in Fig. 5, when a fillet bead 53 is
formed, an extended bead 54 is formed in a manner
that a region of one end of the abutted portion
positioned outside the sheet surface of the channel
product 51 of the abutted portion of the channel
product 51. and the box product 52 is riot set to its
welding start point, but a position only a constant
distance away from the region along the abutted
portion is set to its welding start point rather than
the region, and then the fillet bead 53 is formed
continuously. In the same manner, the fillet bead 53
is formed in a manner that a region of the other end
of the abutted portion is not set to its welding end
point, but a position only a constant distance away
from the region along the abutted portion is set to
its welding end point rather than the region, and
then an extended bead is formed continuously.
[0040] There are two bent portions in the fillet
bead 53 formed on the welded structure member 5 0 .
Here, it is set that when a cyclic load expected to
be applied to the welded structure member 50 is
applied to the welded structure member 50 with no
stiffening bead formed thereon, magnitude of the
maximum principal stress becomes larger in the bent
portions (corner portions of the channel product
(channel steel) 51) than at the welding start
position of the fillet bead 53 (extended bead).
[0041] Further, here, it is set that the place where
a fatigue crack first occurs when a cyclic load
expected to be applied to the welded structure member
50 is applied to the welded structure member 50 with
no stiffening bead formed thereon is the bent
portions.
Thus, here, stiffening beads 55A and 55B are
formed respectively so that the two bent portions of
the fillet bead 53 become their welding start point
and the front surface of the box product 52 becomes
their welding end point. Forming the single
stiffening bead in each place is sufficient.
[0042] Fig. 6 is a view showing a second example of
the welded structure member.
A welded structure member 60 shown in Fig. 6 is
formed in a manner that on the front surface of a
pipe-shaped box product 62 using a circular steel
pipe, one end portion of a channel product (channel
steel having one end processed in accordance with the
shape of the pipe product) 61 is abutted, and of the
abutted portion, only the portlon positioned outside
a sheet surface of the channel product 61 is fillet
welded.
[0043] As shown in Flg. 6, when a fillet bead 63 is
formed, an extended bead 64 is formed in a manner
that a region of one end of the abutted portion
positioned outside the sheet surface of the channel
product 61 of the abutted portion of the channel
product 61 and the box product 62 is not set to its
welding start point, but a position only a constant
distance away from the region along the abutted
portion is set to its welding start point rather than
the region, and then the fillet bead 63 is formed
continuously. In the same manner, the fillet bead 63
is formed in a manner that a region of the other end
of the abutted portion is not set to its welding end
point, but a position only a constant distance away
from the region along the abutted portion is set to
its welding end point rather than the region, and
then an extended bead is formed continuously.
[0044] There are two bent portions also in the
fillet bead 63 formed on the welded structure member
60 similarly in the weld bead 53 shown in Fig. 5.
Thus, here, stiffening beads 65A and 65B are formed
respectively so that the positions of the two bent
portions of the fillet bead 63 become their welding
start point and the front surface of the box product
62 becomes their welding end point. Forming the
single stiffening bead in each place is sufficient.
Further, the fillet bead 63 has a region having the
same curvature as that of the box product 62
(constant curvature over 0). It is set in the welded
structure member 60 that magnitude of the maximum
principal stress becomes larger in the bent portions
than in this region, and no stiffening bead is formed
in this region here.
[0045] Fig. 7 is a view showing a third example of
the welded structure member.
A welded structure member 70 shown in Fig. 7 is
formed in a manner that one end portion of a pipeshaped
channel product 71 using a circular steel pipe
is abutted on one side surface (front surface) of a
box product 72 using a square-shaped steel pipe, and
of the abutted portion, only the portion positioned
outside a sheet surface of the channel product 71 is
fillet welded.
As shown in Fig. 7, a welding start point and a
welding end point of a fillet bead 73 are connected,
and a start edge portion and an end edge portion do
not exist (independently) in the fillet bead 73.
[0046] The fillet bead 73 formed on the welded
structure member 70 has substantially the same
curvature as that of the channel product 71 (constant
curvature over 0). Thus, a stiffening bead 74 is
formed so that the place where a fatigue crack first
occurs when a cyclic load expected to be applied to
the welded structure member 70 is applied to the
welded structure member 70 with no stiffening bead
formed thereon becomes its welding start point and
the front surface of the box product 72 becomes its
welding end point. Concretely, here, the place
directly opposite the side where the load is applied
is set to the welding start point of the stiffening
bead 74. Forming the single stiffening bead in each
place is sufficient.
[0047] Further, in Fig. 7, the single stiffening
bead 74 is disposed in the fillet bead 73. However,
in order to further increase strength, for example,
each one stiffening bead, two in total, may also be
disposed on both sides of the stiffening bead 74 at a
constant distance apart from the stiffening bead 74.
[0048] Fig. 8 is a view showing a fourth example of
the welded structure member.
A welded structure member 80 shown in Fig. 8 is
formed in a manner that one end portion of a channel
product 81 in which a thin steel sheet is formed into
a hollow rectangular parallelepiped shape with an
open top surface and an open bottom surface is
abutted on one side surface (front surface) of a box
product 82 using a square-shaped steel pipe, and of
the abutted portion, only the portion positioned
outside a steel surface of the channel product 81 is
fillet welded.
As shown in Fig. 8, a welding start point and a
welding end point of a fillet bead 83 are connected,
and a start edge portion and an end edge portion do
not exist (independently) in the fillet bead 83.
[0049] There are four bent portions in the fillet
bead 83 formed on the welded structure member CO.
Here, it is set that the place where a fatigue crack
first occurs when a cyclic load expected to be
applied to the welded structure member 80 is applied
to the welded structure member 80 with no stiffening
bead formed thereon becomes the bent portions.
Thus, here, stiffening beads 84A, 84B, and 84C
are formed respectively so that the positions of the
four bent portions of the fillet bead 83 become their
welding start point and the front surface of the box
product 82 becomes their welding end point. Forming
the single stiffening bead in each place is
sufficient.
[0050] Here, from results of later-described
examples (TEST PIECE SYMBOLS C9, D12, C10, and the
like in Table 2), the present inventors found that
when on the welded structure member in which at least
one steel member of steel members to be welded by
performing fillet arc welding is formed of a steel
sheet having a sheet thickness of 3.2 mm or less, the
welding start position of the stiffening bead is not
positioned on the fillet bead side but on the box
product side, in spite of the stiffening bead being
formed, a fatigue life does not improve and sometimes
decreases instead. That is, the present inventors
found that when the welding start position of the
stiffening bead is positioned in a region near the
fillet bead and exists independently without mixing
with other weld beads, in spite of the stiffening
bead being formed, a fatigue life does not improve
and sometimes decreases instead.
[0051] Thus, in this embodiment, as described above,
the welding start position of the stiffening bead is
positioned in a region near the fillet bead and does
not exist independently without mixing with other
weld beads, and the stiffening bead is formed so that
the welding start point or the welding end point is
positioned in a region overlapping with the fillet
bead and in a bent region (turned portion) of a
corner portion, which is set as an original
understanding.
[ 0 0 5 2 ] Further, in the technique described in Patent
Literature 3, a weld bead extended from a corner
portion and a weld bead in the corner portion are
formed in a single stroke manner (namely, these weld
beads are formed by the same arc welding). Therefore,
the number of welding start points positioned near
the fillet bead and existing independently without
mixing with other weld beads is increased more than
necessary.
[0053] In contrast to this, in this embodiment, the
stiffening bead is formed in a bent region (turned
portion) of a corner portion of a region between the
welding start point and the welding end point of the
fillet bead formed in a single stroke manner by a
single welding operation.
Further, a weldlng operation of the fillet bead
and a welding operation of the stiffening bead are
performed separately. That is, it is designed that
the fillet bead and the stiffening bead are formed by
different arc welding, and the welding start point or
the welding end point of the stiffening bead formed
to overlap with the fillet bead remains ln a state to
be distinguished from the fillet bead.
By setting as above, the degree of freedom of the
positions of the welding start point and the welding
end point of the stiffening bead improves. Thus, it
is possible to prevent the number of welding start
points positioned near the fillet bead and existing
independently wlthout mixing with other weld beads
from increasing more than necessary.
Fig. 5 to Fig. 8 above each show an example of
the fillet arc welded joint in which a sheet
thickness portion ~f one steel member and a sheet
surface portion of the other stee1,member are joined
to each other.
[0054] Fig. 9 is a view showing a fifth example of
the welded structure member.
A welded structure member 90 shown in Fig. 9 is
formed in a manner that rear surfaces of flange
portions on both sides of a channel product (channel
steel processed in such a manner that tips of flange
portions on both sides are each curved with a certain
curvature) 91 are attached to side surfaces facing
each other of a box product 92, and the tips of the
flange portions are lap fillet welded. As shown in
Fig. 9, when a fillet bead 93 is formed, an extended
bead 94A is formed in a manner that one edge region
of a boundary between the tip and a base end portion
of the flange portion (boundary between the curved
region and the other region) is not set to its
welding start point, but a position, only a constant
distance away from the region along the curvature of
the curved region is set to its welding start point
rather than the region, and then the fillet bead 93
is formed continuously. Similarly, the fillet bead
93 is formed in a manner that the other edge region
of the boundary between the tip and the base end
portion of the flange portion is not set to its
welding end point, but a position only a constant
distance away from the region along the curvature of
the curved region is set to its welding end point
rather tha.n the region, and then an extended bead 94B
is formed continuously.
[0055] The fillet bead 93 formed on the welded
structure member 90 has substantially the same
curvature as that of the tip of the flange portion of
' ! the channel product 91 (constant curvature over 0).
I
i Thus, a stiffening bead 95 is formed so that the
I
!
place where a fatigue crack first occurs when a
cyclic load expected to be applied to the welded
structure member 90 is applied to the welded
structure member 90 with no stiffening bead formed
thereon becomes its welding start point and the front
surface of the box product 92 becomes its welding end
point. Concretely, here, the center portion (deepest
portion) in a direction along a weld line of tlie
fillet bead 93 is set to the welding start point of
the stiffening bead 95. Forming the single
stiffening bead in each place is sufficient.
LO0561 Further, in Fig. 9, the single stiffening
bead 95 is disposed in the deepest portion of the
fillet bead 93. However, in order to further
increase strength, each one stiffening bead, two in
total, may also be disposed in the vicinity of the
1/3 length position and the 2/3 length position of
the entire length of the fillet bead 95, for example.
As described above, also on the side opposite the
flange portion of the channel product 91, a lap
fillet bead, extended beads, and a stiffening bead
are formed in the same manner as that of the fillet
bead 93, the extended beads 94A and 948, and the
stiffening bead 95.
Fig. 9 shows an example of the fillet arc welded
joint (lap flllet arc welded joint) in which sheet
surface portions of one steel member and the other
i steel member are joined to each other.
LO0571 Fig. 10 is a view showing a sixth example of
the welded structure member.
A welded structure member 100 shown in Fig. 10 is
constituted by using a box product 52 using a squareshaped
steel pipe and a flange product 51 in which
one pair of surfaces of two pairs of surfaces facing
each other of a tip portion of a square-shaped steel
pipe is cut off to fit the shape of the box product
52. The box product 52 and the flange product 51 are
combined so that a rear surface of an uncut portion
of the tip portion of the flange product 51 is
abutted on the front surface of the box product 52
and a sheet thickness portion of the portion from
which the tip portion has been cut off of the flange
product 51 is abutted on the front surface of the box
product 52 and the abutted portlon is fillet welded,
and thereby the welded structure member 100 is formed.
I
I
I [0058] There are bent portions in a flllet bead 103
I
formed on the welded structure member 100. It is set
that the place where a fatlgue crack flrst occurs
when a cyclic load expected Lo be applied to the
welded structure member 100 is applied to the welded
structure member 100 with no stiffening bead formed
thereon is the bent portions in a corner portion of
the abutted portion of the sheet thickness portion of
the portion from which the tip portlon has been cut
off of the flange product 51 and the front surface of
the box product 52.
I00591 Thus, here, stiffening beads 104 A and 104B
are formed respectively so that the positions of
these two bent portions of the fillet bead 103 become
their welding start point and the front surface of
the box product 102 becomes their welding end point.
Forming the single stiffening bead in each place is
sufficient.
Fig. 10 shows an example of the fillet arc welded
joint in which a sheet surface portion and a sheet
thickness portlon of one steel product are both
joined to a sheet surface portlon of the other steel
product. Further, as shown in Fig. 10, it is not
necessary to form the stiffening bead with respect to
all the bent portions of the corner portion.
[0060] In the foregoing, the baslc items of this
embodiment have been explained, and further
respective requirements and preferable requirements
for constituting this embodiment will be explained in
detail.
(Welded structure member)
In this embodiment, a welded structure member
(fillet arc welded joint) in which at least one steel
member of steel members to be welded by performing
fillet arc welding is formed of a steel sheet having
a sheet thickness 3f 3.2 mm or less is targeted.
Further, a welded structure member.(fillet arc welded
joint) to which a cyclic load such as vibration load
is applied is targeted.
This is because such a welded structure member is
required to improve fatigue strength by a simple
means because a fatigue crack is likely to occur in a
toe portion or a root portion of a fillet weld bead.
[0061] Further, a welded structure member with a
corner portion including at least one turned portion
is targeted. Further, a welded structure member in
which a fillet bead is formed in a single stroke
manner so as to contain at least one of turned
portions is targeted. The turned portion may be a
bent portion or a curved portion. Further, thc
curvature of the turned portion may be constant, or
may also vary. Further, as long as there is at least
one fillet bead formed in a single stroke manner, the
number of fillet beads to be formed on a single
welded structure member may be one, or may also be
plural.
As long as such welded structure members are used, ~ it is possible to easily improve the fatigue strength
I of the welded structure member by subsequently to
(
fillet weldlng, performing weldlng for a stiffening
bead with the use of a welder and welding materials
used for formation of a fillet bead.
100621 (Mode of disposition of the stiffening bead)
The welding start position or the welding end
position of the stiffening bead needs to be formed to
overlap with the fillet bead. This is because when
the stlffen~ng bead is formed separately from the
fillet bead, it does not function as a member to
increase stiffness of the steel sheet.
In this embodiment, the stiffening bead is formed
in a manner that the position overlapping with the
fillet bead is set to its welding start point, and of
steel members constituting a corner portion (joined
portion), the front surface of the steel member
having a larger tensile stress act thereon is set to
its welding end point, which is set as an original
understanding. As described above, this is because
at the welding start point, the shape of the toe
portion projects and a projected angle is steep, and
thus a stress concentration occurs easily.
[ 0 0 6 3 ] However, when a stiffening bead is used in
common for two independent fillet beads, of the
stiffening bead, the welding start point overlaps
with the one flllet bead and the welding end point
overlaps with the other fillet bead. That is, it is
- 30 -
only necessary to set in such a manner that either
the welding start point or the welding end point of
the stiffening bead overlaps with the fillet bead and
the welding start'point of the stiffening bead does
not exist independently without mixing with other
weld beads. This is because if the above is applied,
it is possible to suppress projection of the shape of
the bead at the position of the welding start point
of the stiffening bead.
[ 0 0 6 4 ] Further, when the welded structure member has
a place where a stress hardly occurs even though a
cyclic load is applied, or a place where fracture is
unlikely to occur even though a cyclic load is
applied and a stress occurs, the place may also be
set to the welding start point of the stiffening bead.
When the above is applied, the welding start point of
the stiffening bead results in existing independently
without mixing with other weld beads. This is
because if such a place is set to the welding start
point of the stiffening bead, fatigue strength of the
fillet arc welded joint is not largely affected even
though the shape of the bead at the place projects.
( 0 0 6 5 1 Further, the stiffening bead may be formed on
the fillet weld bead, or it is also possible to
dispose a weld bead corresponding to the stiffening
bead in advance before fillet welding and to dispose
the fillet bead thereon. That is, as long as the
welding start position or the welding end position of
the stiffening bead overlaps with the fillet bead,
- 31 -
the stiffening head may be on or under the fillet
bead
On the other hand, in this embodiment, as
described above,, 'the welding end point of the
stiffening bead is a region of, of steel members
constituting a corner portion (joined portion), the
steel sheet where a larger tensile stress acts when a
cyclic load is applied to the welded structure member,
which is set as an original understanding. This is
because at the welding end point, rhe shape of the
bead becomes flat, and thus a stress concentration
does not occur easily.
[ 0 0 6 6 ] The disposition position of the stiffening
bead with respect to the fillet bead is one place or
plural places in at least one region of the second
region, the third region, and the fourth region on
the condition that the above-described first region
exists. Further, as long as the stiffening bead is
disposed in such a region, the stiffening bead may
also be disposed in the other regions.
[ 0 0 6 7 ] (Length La of the stiffening bead)
A length La of the stiffening bead preferably
satisfies the following condition (A).
(A) Length La of stiffening bead 1 width W of
fillet bead x 2
Here, the length La of the stiffening bead is a
length to a melting end of the stiffening bead with a
contact point of the fillet bead and the stiffening
bead being a starting point.
[0068] When the length La of the stiffening bead is
short, it is not possible to sufficiently increase
stiffness of the steel member and to exhibit the
function of improving fatigue strength of the welded
joint. If the length La of the stiffening bead
projecting from the toe portion of the fillet bead is
the width W of the fillet bead or more, the function
of improving fatigue strength can be exhibited
depending on the dzgree of a load to be applied to
the welded structure member, but in order to further
increase stiffness, the length of the stiffening bead
is preferably set to two times or more of the width W
of the fillet bead.
[00691 Further, the upper limit of the length La of
the stiffening bead is restricted by the shape.
structure of a steel product manufacture by welding.
When the length of the fillet,bead is set to L, for
example, the length La of the stiffening bead can be
less than 0.5 x L.
[0070] (Height H a of the stiffening bead)
A height Ha of the stiffening bead from the front
surface of the steel member preferably satisfies the
following condition ( B ) with respect to a thickness t
(mm) of the steel member on which the stiffening bead
is formed.
(B) Height Ha of stiffening bead zthickness t of
steel member x 0.5
When the height Ha of the stiffening bead is less
than 0.5 times (= t/2) of the thickness t of the
steel member on which the stiffening bead is formed,
it does not sufficiently exhibit the function as the
stiffening bead. The larger the height Ha of the
stiffening bead, the larger its effect, but naturally
there is a limit to avoid strike through or melt down
of the steel sheet. Thus, the height Ha of the
stiffening bead is, realistically, equal to or less
than the thickness t of the steel member on which the
stiffening bead is formed.
100711 (Width Wa of the stiffening bead)
Further, a width Wa of the stiffening bead
preferably satisfies the following condition ( C ) .
(C) Width Wa of stiffening bead 2 width W of
fillet bead x 0.5
When the width Wa of the stiffening bead is less
than 0.5 times (W/2) of the width W of the fillet
bead, it does not sufficiently exhibit the function
as the stiffening bead. The upper limit of the width
Wa of the stiffening bead is not defined particularly,
but similarly to the height Ha of the stiffening bead,
it is necessary to form the stiffening bead within
the range that strike through or melt down does not
occur, and thus it is determined naturally in this
view point.
[0072] Incidentally, welding of a welded structure
member for automobile is performed by automatic
welding by a robot, so that it is efficient to form
the stiffening bead by using a welder to form the
fillet bead and welding materials as they are, and
under the condit-ion, it is possible to obtain an
effect of sufficiently improving a fatigue property.
However, the fatigue strength to be obtained also
varies depending 'on the welded structure member, so
that the length, the width, and the height of the
stiffening bead are preferably selected within the
above-described ranges.
[ 0 0 7 3 ] (Hardness Hw of the stiffening bead)
A hardness of the stiffening bead, namely a
hardness Hw of a weld metal of the stiffening bead
preferably satisfies the following condition (D) with
respect to the steel sheet maximum hardness Hb of the
steel member on which the stiffening bead is placed.
(D) Hardness Hw of weld metal of stiffening bead
> steel sheet maximum hardness Hb
When the hardness Hw of the weld metal of the
stiffening bead is larger than the steel sheet
maximum hardness Hb, a strain concentration to a weld
toe portion is suppressed, resulting in that it is
possible to improve a fatigue life (times).
LO0741 The hardness Hw of the weld metal of the
stiffening bead is measured as follows. First, the
stiffening bead-formed portion of the welded
structure member is cut vertically to the weld line
at the center, of the stiffening bead, in the
longitudinal direction, and a cut surface is polished.
Then, a hardness is measured in a direction parallel
to the front surface of the steel sheet (base metal)
at a position, of the cut surface, 0.2 mm deep in the
sheet thickness direction from the front surface of
the steel sheet (base metal). Concretely, Vickers
hardness of five points is measured by a Vickers
hardness tester at intervals of 0.2 mm in a weld
metal direction with one point of a melting boundary
at the position being a starting point, and an
arithmetic mean value of measured values is
calculated. Incidentally, the mean value is
calculated with five points excluding the hardness of
the melting boundary. A load to be applied at the
measurement is preferably 1 kgf.
[0075] The steel sheet maximum hardness Hb is
measured as follows. First, the stiffening beadformed
portion of the welded structure member is cut
vertically to the weld line at the center, of the
stiffening bead, in the longitudinal direction, and a
cut surface is polished. Then, a hardness is
measured in a direction parallel to the front surface
of the steel sheet (base metal) at a position, of the
cut surface, 0.2 mm deep in the sheet thickness
direction from the front surface of the steel sheet
(base metal). Concretely, Vickers hardness is
measured up to a position 10 mm away from a melting
boundary by a Vickers hardness tester at intervals of
0.2 mm in a base metal direction with one point of
the melting boundary at the position being a starting
point, and the maximum value of them is set to the
steel sheet maximum hardness Hb. Incidentally, the
hardness of the melting boundary is excluded when the
steel sheet maximum hardness Hb is found. A load to
be applied at the measurement is preferably 1 kgf.
Further, the starting point when the hardness Hw of
the weld metal.of the stiffening bead (Vickers
hardness' is measured and the starting point when the
steel sheet maximum hardness Hb (Vickers hardness) is
measured are made to agree with each other, and the
direction in which the hardness Hw of the weld metal
of the stiffening bead (Vickers hardness) is measured
and the direction in which the steel sheet maximum
hardness Hb (Vickers hardness) is measured are made
opposite to each other (an angle formed between these
directions is made 180").
[0076] (Angle of the stiffening bead)
An angle y of the stiffening bead preferably
satisfies the following condition ( E ) .
(E) 45' 5 angle y of stiffening bead 5 135"
In order for the stiffening bead to exhibit the
function of increasing stiffness of the steel sheet
to suppress bending, the angle y of the stiffening
bead is preferably 45 to 135". When the angle y is
less than 45" or greater than 13S0, the
aforementioned function of the stiffening bead
decreases.
I00771 Here, when the stiffening bead is formed as
shown in Fig. 5 to Fig. 9 (the turned portion in the
corner portion (joined portion) is formed on one
surface of each of the box products 52, 62, 72, 82,
and 9 2 ) , the angle y of the stiffening bead i s an
- 37 -
angle to a tangent at a point of the fillet bead
overlapping with the stiffening bead.
On the other hand, when the stiffening bead is
formed as shown in Fig. 10 (the turned portlon ln the
;: corner portion (joined portion) is formed on two
continuing surfaces of the box product 102), the
angle of the stiffening bead is an angle formed by
the fillet bead and the stiffening bead on, of the
two surfaces, the surface where the stlffenlng bead
1s formed.
[0078] (Other requirements)
The arc welding conditions for forming the fillet
bead and forming the stiffening bead and the
composition of a welding wire used may be in
I
accordance with ordinary methods, and are not limlted
to specific ones. However, it is preferred that, in
terms of production, formation of the fillet bead and
formation of the stiffening bead should be performed
continuously using the same weldxng equipment.
However, as long as the function of increasing
stxffness of the steel sheet of the stiffening bead
is secured, the welding conditions of the both and
the composition of a welding wire used may be
dxfferent.
[0079] Further, in the welded joint, in order to
form the stiffening bead so as to overlap with the
fillet bead, it is necessary that there should be an
area where the stiffening bead can be formed with a
required angle and a required length, height, and
- 38 -
width in the vicinity of the welded joint.
[0080] As above, in this embodiment, it is possible
to significantly suppress occurrence of fatigue
fracture by a simple means of providing the
stiffening bead even when the welded structure member
is subjected to a cyclic vibration stress.
[0081] As above, it is possible to largely improve
fatlgue strength of the steel member only with the
provision of the stiffening bead. However, by
combining an operation of decreasing stress
concentrations at the start point and the end point
of welding and formation of the stiffening bead, a
joint whose fatigue strength is improved can be
obtained. For example, as shown in Fig. 5, Fig. 6,
and Fig. 9, on the premise that the fillet bead is
extended from the corner portion and the welding
start point and the welding end point of the fillet
bead are each disposed at a position away from the
corner portion (namely, on the premise that the
above-described extended bead is formed), the
stiffening bead can be provided. However, such
extension of the fillet bead is not necessarily
needed.
[0082] Further, the present inventors confirmed that
the method of thls embodiment can be applied also to
metal members other than the steel member. For
example, it is possible to apply the method of this
embodiment to aluminum members or stainless members
instead of the steel member. Further, the present
inventors confirmed that the method of this
i
embodiment can be applied also to metal members of
different types.
LO0831 It shouid be noted that all of the abovedescribed
embodiments of the present invention merely
illustrate examples of implementing the present
invention, and the technical scope of the present
invention is not to be construed in a restrictive
manner bythese embodiments. That is, the present
invention may be implemented in various forms without
departing from the technical spirit or main features
thereof.
EXAMPLES
[ 0 0 8 4 ] Next, examples of the present invention will
be described. The conditions in the examples are one
conditional example employed for confirming
applicability and effects of the present invention,
and the present invention is not limited to this one
conditional example. The present invention can
employ various conditions as long as the object of
the present invention can be achieved without
departing from the gist of the present invention.
[ 0 0 8 5 1 Welded structure members 5 0 , 60, 7 0 , 8 0 , 90,
and 1 0 0 having the shapes shown in Fig. 5 to Fig. 1 0
were fabricated. Further, there were fabricated
welded structure members that were the same as the
welded structure members 5 0 , 6 0 , 7 0 , 8 0 , 90, and 1 0 0
having the shapes shown in Fig. 5 to Fig. 1 0 except
for the point that the welding start point and the
welding end point of the stiffening bead were
replaced with each other. Further, there were
fabricated welded structure members that were the
same as the welded structure members 50, 60, 70, 80,
90, and 100 havlng the shapes shown in Fig. 5 to Fig
10 except for the point that the stiffening bead was
not formed
Then, these welded structure members were each
subjected to a fatigue test
COO861 Steel members and welding materials used for
the welded structure members are shown in Table 1
In Table 1, two types of steel members, Steel product
A and Steel product B, were used. Incidentally, two
ones having sheet thicknesses (2.3 mm and 2.6 mm)
were prepared for Steel sheet A and Steel sheet B
each. Further, two types of welding materials, Wlre
A and Wire B, were used. Wire A and Wire B each have
a diameter of 1.2 mm.
l00881 In this example, the box product 52 shown in
[0087] [Table 11
Flg. 5 has a size of 300 mm x 150 mm x 50 mm. The
SHEET
THICKNESS
-
(mm)
2.3, 2.6
2.3, 2.6
-
-
STEEL
PRODUCT
A
STELL
PRODUCT
B
WIRE A
WTKE D
STATIONARY CHEMICAL COMPOSITTON
STRENGTH
YP
(MPa)
370
740
--
C SI Mn
-
-
TS
(MPa)
480
780
(mass*)
EL P S I A1
( 8 )
25
20
N
0.12
0.04
0.08
0.08
0.03
0.04
-
-
0.003
0.003
-
-
0.02
0.9
-
0.35
0.31
0.02
0.007
0.011
0.002
0.51
1.27
0.85
1.3
0.004
0.001
--
0.005
0.002
channel product 51 has a size of 80 mm in flange
width x 75 mm in web width x 80 mm in height.
1
In this example, the box product 62 shown in Fig.
6 has a size of'150 mm in diameter x 300 mm in height
(length in axial direction). The channel product 61
has a size of 80 mm in flange width x 75 mm in web
width of a corner portion (joined portion) x 80 mm in
height (maximum value).
[0089] In this example, the box product 72 shown in
Fig. 7 has a size of 300 mm x 100 mm x 50 mm. The
channel product 71 has a size of 50 mm in diameter x
150 mm in height (length in axial direction).
In this example, the box product 82 shown in Fig.
8 has a size of 300 mm x 150 mm x 50 mm. The channel
product 81 has a size of 180 mm x 75 mm K 56 mm.
[00?0] In this example, the box product 92 shown in
Fig. 9 has a size of 300 mm x 100 mm x 50 mm. The
channel product 91 has a size of 75 mm in flange
width x 105 mm in web width x 80 mm in height. The
curvature radius of a tip of a flange of the channel
product 81 is 50 mm.
In this example, the box product 102 shown in Fig
10 has a size of 300 mm x 100 mm x 50 mm. The
channel product 101 is one in which 30 mm of a
portion having a length of 56 mm of a square-shaped
steel pipe having a size of 180 mm x 75 mm x 56 mm is
cut off from the tip.
[0091] Stiffening beads were each formed for the
case where the welding start point of the stiffening
bead (start position of the stiffening bead in Table
2) is on the fillet bead and the case where it is on
the box product
Further, stitfeninq beads were each formed for
the casewhere the welding start point of the
stiffening bead is on the fillet bead and the welding
end point of the stiffening bead (end position of the
stiffening bead in Table 2 to Table 12) is on the box
product and for the case where the welding start
point of the stiffening bead is on the fillet bead
and the welding end point of the stiffening bead is
on the channel product.
[0092] Further, stiffening beads were each formed
for the case where the stiffening bead is formed at
the turned portion in the corner portion (joined
portion) and for the case where it is formed at the
straight portion in the corner portion.
Further, stiffening beads were formed while
changing the length La of the stiffening bead, the
helght Ha of the stiffening bead, and the width Wa of
the stiffening bead.
[0093] The welding conditions are as follows.

Welding method: consumable electrode welding
Welding power supply: DP350 (made by DAIHEN
Corporation)
Welding mode: DC-Pulse
Welding posture: downward, horizontal
Distance between chip steel sheets (projecting
length): 15 mm
Shielding gas type: Ar + 20% C02
Shielding gas flow rate: 20 L/min

Torch angle: standing angle 60" from the lower
sheet, angle of advance 0"
Target position: corner of the overlapped portion
Welding rate: 80 cm/min
Welding current and voltage: a value that does
not cause an undercut is set
One example:
approximately 220 A, approximately 24 V in the case
of fillet arc welding with a sheet thickness of 2.3
mm )

Torch angle: standing angle 90' from the steel
sheet, angle of advance 0"
Target position and welding direction: welding on
the lower steel sheet in a direction perpendicular to
the fillet bead in the center in the width direction
of the test piece with a welded metal surface of the
fillet bead being a starting point
Welding rate: 50 cm/min
Welding current and voltage: a welding current
that is approximately 2/3 of the fillet bead is set
One example: 150 A, 21
V in the case where the stiffening bead is disposed
on the steel sheet having a sheet thickness of 2 . 3 mm
[0094] One steel member (box product) and the other
steel member (channel product) of each of the
fabricated test pieces were held in an
electrohydraulic fatigue test apparatus so that a
load direction became the direction indicated by the
outline arrow in each of Fig. 5 to Fig. 10, and they
were subjected to a fatigue test with a load range
being constant (constant stress range), a load ratio
being -1, and a repetition frequency being 5 Hz.
The hardness Hw of the stiffening bead and the
steel sheet maximum hardness Hb were measured by the
respective above-described methods.
Effects of the examples are explained based on
Table 2 to Table 12.
[0095]
[Table 21
TEST
'IECE
SYMBOL
MEMBER
SHAPE
STEEL
PRODUCT
C1
COMPARATIVE
A
.
A
A
CZ
C3
WELDING
MATERIAL
COMPARATIVE
WIDTH Wa
2 . 3
2 . 3
2 . 3
COMPARATIVE
EXAMPLE
COMPARATIVE
EXAMP1.E
CZ
-C 3
C 4
CHANNEL
pE:ii:T
(mm)
2 . 3
2 . 3
2 . 3
Fig.
Fig.
--
1 5 0
1 4 9
148
BOX
P ~ ~ ~ ~ ~ T
THICKNESS
(rnrnl
WELD TOE PORTION
ON BOX PRODUCT
S I D E OF F I L L E T
BEAD
WELD TOE PORTION
ON BOX PRODUCT
S I D E OF F I I I L E T
-BEAD
S T I F F E N I N G BEAD
START EDGE
PORTION
A
A
CRACK OCCURRENCE
P O S I T I O N
1 7 9 9 0 ° 3 2 1 9 0 0 0 -95 C 1
1 8 0
1 8 1
9 0 -
9 0 "
3
3
2 4 0 0 0 0
2 5 0 0 0 0
-1 0 4
-1-09
C 1
C1
[Table 31
POSITION
TEST PIECE
[Table 41
POSITION
TEST PIECE
[ 0 0 9 8 1
[ T a b l e 51
P O S I T I O N
ANGLE OF TEST PIECE
[Table 61
[Table 71
ANGLE OF
TEST
'IECE
SYMBOL
CRACK OCCURRENCE
POSITION
MEMBER I~ L O E , U "
SHAPE
PRODUCT I CHANNEL 1 BOX
vrc.-u~z-w I SHEET I SHEET
PHICKNESS
lrnrnl
. ,
f n v v v r i irxirnrr.u
WELD TOE PORTION
THICKNESS
(mm)
'
, . . . . . . , I
[ T a b l e 81
POSITION
ON BOX PRODUCT
TEST
PIECE
SYMBOL
C9.
Dl2
CIO
PRODUCT
MRXIMUM
HARDNESS
H b
150
149
152
BEAD WELD
METAL
HARDNESS
HW
179
182
178
ANGLE OF
STIFFENING
BEAD
-
90'
go9
TEtiNtFD
IkNI
5
5
5
FATIGUE
LIFE
(TIMES)
460000
760000
450000
LIFE
IMPROVING
PERCENTAGE
1%)
-
165
-9a
TEST PIECE
SYMBOL AS
REFERENCE
-
C 9
c 9
[Table 91
POSITION
~b HW
C 1 1
C1Z
C13
--
1 5 3
1 4 9
1 5 0
1 8 2
1 8 1
1 7 8
--
.
9 0 '
90"
1 5
1 5
1 5
3 4 0 0 0 0
3 5 0 0 0 0
3 2 0 0 0 0
-
-1 0 3
-9 4
.
C 1 1
C 1 1
[ T a b l e 101
TEST
P I E C E
SYMBOL -
D13
-
D14
STEEL
PRODUCT
A
A
CATEGORY
INVENTION
EXAMPLE
INVENTION
EXAMPLE
A 2 . 3 2 . 3
ON BOX PRODUCT
A
S I D E OF F I L L E T
ON BOX PRODUCT
S I D E O F F I L L E T
MEMBER
SHAPE
Fig.
Fig,
WELDING
MATERIAL
A
A
D l 5 151
CRACK OCCURRENCE
P O S I T I O N
WELD TOE PORTION
ON BOX PRODUCT
S I D E OF F I L L E T
--BE AD
WELD TOE PORTION
ON BOX PRODUCT
S I D E OF F I L L E T
BEAD
WELD T O E P O R T I O N
CHANNEL
SHEET
THICKNESS
Imml
2 . 3
2 . 3
BOX
PEiii;T
THICKNESS
(rnrn)
2 . 3
2 . 3
1 7 9
2 4 4 C 1 1
--
9 0 ' 1 5 4 3 0 0 0 0
D l 6 1 8 2 9 0 " 15 8 3 0 0 0 0
-1 2 6
1 5 2
C 1 1
[ T a b l e 111
[Table 121
POSITION
SIDE OF FILLET
WIDTH Wa
TEST PIECE
[OlOG] Test piece symbols C1, C5, C7, C9, C11, and
C14 indicate results of the welded structure members
each having no stiffening bead formed thereon with
respect to the welded structure members 50, 60, 70,
80, 90, and 100 shown in Fi.g. 5, Fig. 6, Fig. 7, Fig.
8, Fig. 9, and Fig. 10 respectively. Based on the
fatigue life of these welded structure members, the
effect of the stiffening bead was verified. Based on
the fatigue lives of the test piece symbols described
in "TEST PIECE SYMBOL AS REFERENCE" in Table 2 to
Table 12, "FATIGUE LIFE I M P R O V I N G PERCENTAGE" was
c a l c u l a t e d . I n t h i s example, it was d e t e r m i n e d t h a t
when "FATIGUE LIFE IMPROVING PERCENTAGE" e x c e e d s 120%,
t h e e f f e c t by t'he s t i f f e n i n g bead e x i s t s .
[ 0 1 0 7 ] D l t o D9 each i n d i c a t e an e v a l u a t i o n of t h e
e f f e c t of t h e s t i f f e n i n g bead t a r g e t e d a t t h e welded
s t r u c t u r e member 50 shown i n F i g . 5 . On t h e welded
s t r u c t u r e member 50, no s t i f f e n i n g beads were formed,
s o t h a t a c r a c k o c c u r r e d i n t h e weld t o e p o r t i o n s on
t h e box p r o d u c t 52 s i d e i n t h e b e n t p o r t i o n s of t h e
f i l l e t bead 5 3 ( s e e "CRACK OCCURRENCE POSITION" of
C l ) . T h e r e f o r e , it is n e c e s s a r y t o i n c r e a s e t h e
f a t i g u e l i f e i n t h e s e p l a c e s by t h e s t i f f e n i n g beads
55A and 55B. Thus, t h e s t i f f e n i n g beads 55A and 55B
were formed i n a manner t h a t t h e p o s i t i o n s of t h e
b e n t p o r t i o n s of t h e f i l l e t bead 5 3 were s e t t o t h e i r
welding s t a r t p o s i t i o n and t h e f r o n t s u r f a c e of t h e
box p r o d u c t 52 was s e t t o t h e i r welding end p o s i t i o n
( s e e "FILLET BEAD CORNER" of "START POSITION OF
STIFFENING BEAD" and "ON BOX PRODUCT" of "END
POSITION OF STIFFENING BEAD" of Dl t o D 9 ) .
[0108] A s i n d i c a t e d i n D l t o D9, t h e s t i f f e n i n g
beads 55A and 558 were formed a s above, and t h e i e b y
t h e f a t i g u e l i f e was i n c r e a s e d and t h e c r a c k
o c c u r r e n c e p o s i t i o n changed t o t h e end edge p o r t i o n s
of t h e s t i f f e n i n g beads 55A and 55B from t h e t o e
p o r t i o n s of t h e f i l l e t bead 53 ( s e e "STIFFENING BEAD
END EDGE PORTION" of "CRACK OCCURRENCE POSITION" of
D l t o D 9 ) .
[0109] Further, as indicated in Dl to D3, and D8,
unless the conditions of (A) to (E) described above
are satisfied, an improved margin of the fatigue life
tends to decrease.
Concretely, in Dl, the length La of the
stiffening bead is not two times or more of the width
W of the fillet bead ("La/W" of Dl does not become
200% or more, which does not satisfy the condition of
(A)). In D2, the angle y of the stiffening bead is
not in the range of 45" to 135' ("ANGLE OF STIFFENING
BEAD'' of 02 does not become 45" to 135", which does
not satisfy the condition of (E)). In D3, the hei.ght
Ha of the stiffening bead is not 0.5 times or more of
the thickness t of the steel member on which the
stiffening bead is formed, and the width Wa of the
stiffening bead is not 0.5 times or more of the wi-dth
W of the fillet bead ("Ha/tl' of D3 does not become
50% or more, which does not satisfy the condition of
(B), and "Wa/Wr' of D3 does not become 50% or more,
which does not satisfy the condition of ( C ) ) . In D8,
the maximum hardness of the box product where a crack
occurs (steel sheet maximum hardness Hb) does not
exceed the hardness Hw (of the weld metal) of the
stiffening bead ("STIFFENING BEAD WELD METAL HARDNESS
Hw" of D8 does not exceed 'BOX PRODUCT MAXIMUM
HARDNESS Hb," which does not satisfy the condition of
(D)). However, in all the cases, the fatigue life
improving percentage exceeded 120%.
[0110] Dl0 indicates an evaluation of the effect of
the stiffening bead targeted at the welded structure
member 60 shown in Fig. 6. On the welded structure
1 member 60, no stiffening beads were formed, so that a
;I crack occurred in the weld toe portions on the box
product 62 side in the bent portions of the fillet :
bead 63 (see "CRACK OCCURRENCE POSITION" of C5).
;;
Therefore, it is necessary to increase the fatigue
;I
i life in these places by the stiffening beads 65A and
65B. Thus, the stiffening beads 65A and 65B were
formed in a manner that the bent portions of the
fillet bead 63 were set to their welding start
position and the front surface of the box product 62
was set to their welding end position (see "FILLET
BEAD CORNER" of "START POSITION OF STIFFENING BEAD"
and "ON BOX PRODUCT" of "END POSITION OF STIFFENING
BEAD" of D10).
[Olll] As indicated in D10, the stiffening beads 65A
and 65B were formed as above, and thereby the fatigue
life was increased and the crack occurrence position
changed to the end edge portions of the stiffening
beads 65A and 65B from the toe portions of the fillet
bead 63 (see "STIFFENING BEAD END EDGE PORTION" of
"CRACK OCCURRENCE POSITION" of D10).
Incidentally, it was confirmed that unless the
conditions of (A) to (E) described above are
satisfied, an improved margin of the fatigue life
tends to decrease also in the welded structure member
60 shown in Fig. 6, which is not shown in the table.
[0112] Dl1 indicates an evaluation of the effect of
the stiffening bead targeted at the welded structure
i member 70 shown in Fig. 7. On the welded structure
I 1 member 70, no stiffening bead was formed, so that a
j crack occurred in the weld toe portion on the box
product 72 side at the point directly opposite the
point of the fillet bead 73 where a load is applied
(see "CRACK OCCURRENCE POSITION" of C7). Thus, the
stiffening bead 74 was formed in a manner that this
point of the fillet bead 73 was set to its welding
start position and the front surface of the box
product 62 was set to its welding end position (see
"ON FILLET BEAD" of "START POSITION OF STIFFENING
BEAD" and 'ON BOX PRODUCT" of "END POSITION OF
STIFFENING BEAD" of D11).
I [0113] As indicated in D11, the stiffening bead 74
I
was formed as above, and thereby the fatigue life was
increased and the crack occurrence position changed
to the end edge portion of the stiffening bead 74
from the toe portion of the fillet bead 73 (see
"STIFFENING BEAD END EDGE PORTION" of "CRACK
OCCURRENCE POSITION" of D11) .
Incidentally, it was confirmed that unless the
conditions of (A) to (E) described above are
satisfied, an improved margin of the fatigue life
tends to decrease also in the welded structure member
70 shown in Fig. 7, which is not shown in the table.
[@I141 Dl2 indicates an evaluation of the effect of
the stiffening bead targeted at the welded structure
member 80 shown in Fig. 8. On the welded structure
member 80, no stiffening beads were formed, so that a
crack occurred in the weld toe portions on the box
product 82 side in the bent portions of the fillet
bead 83 (see "CRACK OCCURRENCE POSITION" of C9)
Therefore, it is necessary to increase the fatigue
life in these places by the stiffening beads 84A, 48,
and 84C. Thus, the stiffening beads 84A, 848, and
84C were formed in a manner that the bent portions of
the fillet bead 83 were set to their welding start
position and the front surface of the box product 82
was set to their welding end position (see "FILLET
BEAD CORNER" of 'START POSITION OF STIFFENING BEAD"
and "ON BOX PRODUCT" of "END POSITION OF STIFFENING
BEAD" of 012). Incidentally, similarly to the other
stiffening beads, another stiffening bead was formed
also in the other invisible bent portion hidden in
Fig. 8.
[0115] As indicated in D12, the stiffening beads 84A,
84B, and 84C were formed as above, and thereby the
fatigue life was increased and the crack occurrence
position changed to the root portion of the fillet
bead 53 from the toe portion of the fillet bead 83
(see "STIFFENING BEAD END EDGE PORTION" of 'CRACK
OCCURRENCE POSITION" of D12) .
Incidentally, it was confirmed that unless the
conditions of (A) to (E) described above are
satisfied, an improved margin of the fatigue life
tends to decrease also in the welded structure member
80 shown in Fig. 8, which is not shown in the table.
[011.61 Dl3 to 020 each indicate an evaluation of the
effect of the stiffening bead targeted at the welded
structure member 90 shown in Fig. 9. On the welded
structure member '90, no stiffening bead was formed,
so that a crack occurred from the root portion in the
center portion in the direction along the weld line
of the fillet bead 93 (see "CRACK OCCURRENCE
POSITION" of Cll). Therefore, it is necessary to
increase the fatigue life in this place by the
stiffening bead 95. Thus, the stiffening bead 95 was
formed in a manner that the center portion in the
direction along the weld line of the fillet bead 93
was set to its welding start position and the front
surface of the box product 92 was set to its welding
end position (see "ON FILLET BEAD" of "START POSITION
OF STIFFENING BEAD" and "ON BOX PRODUCT" of "END
POSITION OF STIFFENING BEAD" of Dl3 to D20).
[0117] As indicated in Dl3 to D20, the stiffening
bead 95 was formed as above, and thereby the fatigue
life was increased and the crack occurrence posi.tion
changed to the end edge portion of the stiffening
bead 95 from the root portion side in the center
portion of the fillet bead 93 (see "STIFFENING BEAD
END EDGE PORTION" of "CRACK OCCURRENCE POSITION" of
Dl3 to D20).
[0118] Further, as indicated in Dl3 to D15, and D19,
unless the conditions of (A) to (E) described above
are satisfied, an improved margin of the fatigue life
tends to decrease..
Concretely, in Dl3, the length La of the
stiffening bead is not two times or more of the width
W of the fillet bead ("La/Wt' of Dl3 does not become
200% or more, which does not satisfy the condition of
(A)). In Dl4, the angle y of the stiffening bead is
not in the range of 45" to 135" ("La/Wf' of Dl4 does
not become 200% or more, which does not satisfy the
!
condition of (E)). In D15, the height Ha of the
stiffening bead is not 0.5 times or more of the
thickness t of the steel member on which the
stiffening bead is formed, and the width Wa of the
stiffening bead is not 0.5 times or more of the width
W of the fillet bead ("Ha/t" of Dl5 does not become
50% or more, which does not satisfy the condition of
(B), and "Wa/Wr' of Dl5 does not become 50% or more,
which does not satisfy the condition of ( C ) ) . In D19,
the maximum hardness of the box product where a crack
occurs (steel sheet maximum hardness Hb) does not
exceed the hardness Hw (of the weld metal) of the
stiffening bead ("STIFFENING BEAD WELD METAL HARDNESS
Hwn of Dl9 does not exceed "BOX PRODUCT MAXIMUM
HARDNESS Hb," which does not satisfy the condition of
(D)). However, in all the cases, the fatigue life
improving percentage exceeded 120%.
[0119] D21 indicates an evaluation of the effect of
the stiffening bead targeted at the welded structure
member 100 shown in Fig. 10. On the welded structure
member 100, no stiffening beads were formed, so that
a crack occurred in the weld toe portions on the box
product 102 side in the bent portions abutted on the
sheet surface portion of the channel product 101 of
the bent portions of the fillet bead 103 (see "CRACK
OCCURRENCE POSITION" of C14). Therefore, it is
necessary to increase the fatigue life in these
places by the stiffening beads 104A and 1048. Thus,
the stiffening beads 104A and 104B were formed in a
manner that the bent portions of the fillet bead 103
were set ko their eld ding start position and the
front surface of the box product 102 was set to their
welding end position (see "FILLET BEAD CORNER" of
"START POSITION OF STIFFENING BEAD" and "ON BOX
PRODUCT" of "END POSITION OF STIFFENING BEAD" of D21).
[01201 As indicated in D21, the stiffening beads
104A and 104B were formed as above, and thereby the
fatigue life was increased and the crack occurrence
position changed to the end edge portions of the
stiffening beads 104A and 104B from the toe portions
of the fillet bead 103 (see "STIFFENING BEAD END EDGE
PORTION" of "CRACK OCCURRENCE POSITION" of D21).
Incidentally, it was confirmed that unless the
conditions of (A) to (E) described above are
satisfied, an improved margin of the fatigue life
tends to decrease also in the welded structure member
100 shown in Fig. 10, which is not shown in the table.
[0121] C2 indicates results of the one in which the
welding end point of the stiffening bead was set not
to the box product 52 side where a crack occurs when
a load is applied to the welded structure member 50
with no stiffening beads formed thereon but to the
channel product 51 side with respect to the welded
structure member 50 shown in Fig. 5.
[0122] C3 Indicates results of the one in which the
welding start point and the welding end point of the
stiffening bead were replaced with each other with
respect to the welded structure member 50 shown in
Fig. 5.
C4 indicates results of the one in which the
stiffening bead was not formed in the bent portions
of the fillet bead 53, but the stiffening bead was
formed, of the region of the fillet bead 53, in the
center region in the width direction of the web of
the channel product 51 in a manner that a place in
the fillet bead 53 was set to its welding start
position and the front surface of the box product 52
was set to its welding end position with respect to
the welded structure member 50 shown in Fig. 5.
In all the cases of C2 to C4, the fatigue life
improving percentage fell below 120%.
[ 0 1 2 3 1 C6 indicates results of the one in which the
welding start point and the welding end point of the
stiffening bead were replaced with each other cith
respect to the welded structure member 60 shown in
Fig. 6. C8 indicates results of the one in which the
welding start point and the welding end point of the
stiffening bead were replaced with each other with
respect to the welded structure member 70 shown in
Fig. 7. C10 indicates results of the one in which
- 65 -
t h e welding s t a r t p o i n t and t h e welding end p o i n t of
1 t h e s t i f f e n i n g bead were r e p l a c e d w i t h each o t h e r
w i t h r e s p e c t t o t h e welded s t r u c t u r e member 80 shown
i n F i g . 8.
I n a l l t h e c a s e s of C 6 , C8, and C10, t h e f a t i g u e
l i f e improving p e r c e n t a g e f e l l below 120%.
[0124] C12 i n d i c a t - e s r e s u l t s of t h e one i n which t h e
w e l d i n g end p o i n t of t h e s t i f f e n i n g bead was s e t n o t
t o t h e box p r o d u c t 92 s i d e where a c r a c k o c c u r s when
a l o a d i s a p p l i e d t o t h e welded s t r u c t u r e member 90
w i t h no s t i f f e n i n g bead formed t h e r e o n b u t t o t h e
c h a n n e l p r o d u c t 91 s i d e w i t h r e s p e c t t o t h e welded
s t r u c t u r e member 90 shown i n F i g . 9.
C13 i n d i c a t e s r e s u l t s of t h e one i n which t h e
welding s t a r t p o i n t and t h e welding end p o i n t of t h e
s t i f f e n i n g bead were r e p l a c e d w i t h each o t h e r w i t h
r e s p e c t t o t h e welded s t r u c t u r e member 90 shown i n
F i g . 9.
I n b o t h t h e c a s e s of C12 and C13, t h e f a t i g u e
l i f e improving p e r c e n t a g e f e l l below 120%.
[0125] C15 i n d i c a t e s r e s u l t s of t h e one i n which t h e
w e l d i n g s t a r t p o i n t and t h e w e l d i n g end p o i n t of t h e
s t i f f e n i n g bead were r e p l a c e d w i t h each o t h e r w i t h
r e s p e c t t o t h e welded s t r u c t u r e member 100 shown i n
F i g . 10.
I n t h e c a s e of C15, t h e f a t i g u e l i f e improving
p e r c e n t a g e f e l l below 120%.
INDUSTRIAL APPLICABILITY
[OX261 The p r e s e n t i n v e n t i o n can be used i n an
industrial field using welding such as machine
industry, for example.

WE CLAIMS:-
A method of forming a fillet arc welded
joint by fillet arc welding at least a partial region
of corner portion's that. are edge regions of an
abutted portion of at least one of a sheet surface
portion and a sheet thickness portion of one metal
member and a sheet surface portion of the other metal
member and have at least one turned portion at at
least one portion thereof, the method comprising:
forming a fillet bead with respect to a region
containing the turned portion of the corner portion
by the fillet arc welding; and
forming a stiffening bead on one place or plural
places of at least the one turned portion by arc
welding different from the fillet arc welding so that
a welding start point or a welding end point of the
stiffening bead overlaps with the fillet bead,
wherein
the stiffening bead is formed in a direction of,
of the one metal member and the other metal member,
the metal member in which a larger tensile stress
occurs when, to a fillet arc welded joint formed
under the same condition as that of the fillet arc
welded joint except for the point that the stiffening
bead is not formed, a cyclic load expected to be
applied to the fillet arc welded joint is applied,
the fillet bead is formed with respect to the
corner portion of one side of the corner portions
formed on both sides of the abutted port.ion, and
at least one metal member of the one metal member
and the other metal member is formed of a metal sheet
having a sheet thickness of 3.2 mm or less.
[Claim 21 The method of forming the fillet arc
welded joint according to claim 1, wherein
the stiffening bead is formed so that the welding
start point of the stiffening bead overlaps with
another weld bead.
[Claim 31 The method of forming the fillet arc
welded joint according to claim 2, wherein
the stiffening bead is formed so that the welding
start point of the stiffening bead overlaps with the
fillet bead.
[Claim 41 The method of forming the fillet arc
welded joint according to any one of clalms 1 to 3,
wherein
the turned portion contains at least one of a
bent portion and a curved portion.
[Claim 51 The method of forming the fillet arc
welded joint according to any one of ciaims 1 to 4,
wherein
the stiffening bead is formed in a region that
constitutes the turned portion and where magnitude of
a maximum principal stress becomes larger than at a
welding start position of the fillet bead when the
cyclic load is applied to a fillet arc welded joint
formed under the same condition as that of the fillet
arc welded joint except for the point that the
stiffening bead is not formed.
- 69 -
[Claim 61 The method of forming the fillet arc
welded joint according to any one of claims 1 to 4,
wherein
the stiffening bead is formed in a reglon that
constitutes the turned portion and where the
magnitude of the maximum principal stress becomes
maximum when the cyclic load is applied to a fillet
arc welded joint formed under the same condition as
that of the fillet arc welded joint except for the
point that the stiffening bead is not formed.
[Claim 71 The method of forming the fillet arc
welded joint according to any one of claims 1 to 6,
wherein
a hardness Hw of the stiffening bead exceeds a
metal member maximum hardness Hb of, of the one metal
member and the other metal member, the metal member
on which the stiffening bead is formed.
[Claim 81 The method of forming the fillet arc
welded joint according to any one of claims 1 to 7,
wherein
a length La of the stiffening bead is two times
or more of a width W of the fillet bead,
a height Ha of the stiffening bead is 0.5 times
or more of a thickness t of, of the one metal member
and the other metal member, the metal member on which
the stiffening bead is formed,
a width Wa of the stiffening bead is 0.5 times or
more of the width W of the fillet bead, and
an angle y of the stiffening bead with respect to
- 70 -
the fillet bead is not less than 45' nor more than
135".
[Claim 91 A fillet arc welded jolnt formed by fillet
arc welding at least a partial reglon of corner
portionsthat are edge regions of an abutted portion
of at least one of a sheet surface portion and a
sheet thickness portion of one metal member and a
sheet surface portion of the other metal member and
have at least one turned portion at at least one
portion thereof, the fillet arc welded joint
comprising:
a fillet bead formed with respect to a region
containing the turned portion of the corner'portion
by the fillet arc welding; and
a stiffening bead formed on one place or plural
places of at least the one turned portion by arc
welding different from the fillet arc welding,
wherein
the stiffening bead is formed so that a welding
start point or a welding end point of the stiffening
bead overlaps with the fillet bead, and is formed in
a direction of, of the one metal member and the other
metal member, the metal member in which a larger
tensile stress occurs when, to a fillet arc welded
joint formed under the same condition as that of the
fillet arc welded joint except for the point that the
stiffening bead is not formed, a cyclic load expected
to be applied to the fillet arc welded joint is
applied,
the fillet bead is formed with respect to the
corner portion of one side of the corner portions
formed on both sides of the abutted portion, and
at least one metal member of the one metal member
and the other metal member is formed of a metal sheet
having a sheet thickness of 3.2 mm or less.
[Claim 101 The fillet arc welded joint according to
claim 9, wherein
the welding start point of the stiffening bead is
at a position overlapping with another weld bead.
[Claim 111 The fillet arc welded joint according to
claim 10, wherein
the welding start point of the stiffening bead is
at a position overlapping with the fillet bead.
[Claim 121 The fillet arc welded joint according to
any one of claims 9 to 11, wherein
the turned portion contains at least one of a
bent portion and a curved portion.
[Claim 131 The fillet arc welded joint according to
any one of claims 9 to 12, wherein
the stiffening bead is formed in a region that
constitutes the turned portion and where magnitude of
a maximum principal stress becomes l.arger than at a
welding start position of the fillet bead when the
cyclic load is applied to a fillet arc welded joint
formed under the same condition as that of the fillet
arc welded joint except for the point that the
stiffening bead is not formed.
[Claim 141 The fillet arc welded joint according to
any one of claims 9 to 12, whe.rein
the stiffening bead is formed in a region that
constitutes the turned portion and where the
magnitude of the maximum principal stress becomes
maximum when thd cyclic load is applied to a fillet
arc welded joint formed under the same condition as
that of the fillet arc welded joint except for the
point that the stiffening bead is not formed.
[Claim 151 The fillet arc welded joint according to
any one of claims 9 to 14, wherein
a hardness Hw of the stiffening bead exceeds a
metal member maximum hardness Hb of.,. of the one metal
member and the other metal member, the metal member
on which the stiffening bead is formed.
(Claim 161 The fillet arc welded joint according to
any one of claims 9 to 15, wherein
- a length La of the stiffening bead is two times
or more of a width W of the fillet bead,
a height Ha of the stiffening bead is 0'5 times
or more of a thickness t of, of the one metal 111i:mber
and the other metal member, the metal member on which
the stiffening bead is formed, a
a width Wa of the stiffening bead is 0.5 times or
more of the width W of the fillet bead, and
an angle y of the stiffening bead with respect to
the fillet bead is not less than 45" nor more than
135".