JP5252112B1 - Peening construction method - Google Patents

Abstract

A method for peening a welded structure capable of significantly improving the fatigue strength of a welded joint by introducing a compressive residual stress by peening the welded structure after welding with a simple tool. To provide.
A peening method for improving the fatigue characteristics of a welded joint by hitting a surface of a base material by using a peening tool 2 having a hitting tool 1 having a flat part at a tip, and hitting by the hitting tool 1 The peening method is characterized in that the impact is made by inclining the direction of 5 degrees or more and 20 degrees or less to the opposite side of the welded portion with respect to the vertical direction of the base material surface.
[Selection] Figure 2

Description

  The present invention relates to a method for improving the fatigue performance of welded joints in large steel structures such as bridges, ships and offshore structures subjected to repeated loads, and machine products such as automobiles and construction machinery, and repair of steel structures and machine products. -It relates to a method for prolonging life.

Steel structures such as bridges, ships, marine structures, automobiles, etc. are constructed by joining many steel members by welding, but in recent years, stress or heat applied to steel structures and mechanical parts repeatedly acts. Many damage accidents due to metal fatigue have occurred.
This is because in the design of steel structures such as bridges, the strength of steel materials used has been increased for the purpose of increasing the size and accompanying weight reduction, but the fatigue strength of the steel body itself is increased. On the other hand, the fatigue strength does not improve even if the tensile strength of the steel material is increased in the welded joint, and this is because metal fatigue occurs in the welded joint.
For this reason, when a large-sized welded structure receives a repeated load, it is necessary to sufficiently consider the safety against the fatigue strength of the welded portion.

The fatigue strength of the welded portion is affected by the shape of the welded joint, residual stress, weld defects, and the like.
FIG. 15 is a view showing a state in which a weld bead (welded joint) 13 is formed by fillet welding the metal plate 11 and the metal plate 12 that are superimposed. A weld bead toe 14 is formed at the boundary between the metal plate 12 and the weld bead 13. The vicinity of the weld toe portion 14 is a portion where a tensile residual stress is likely to be present due to rapid solidification during welding, and is also a portion where stress concentration is likely to occur when an external force is applied to the metal member. When a repeated load is applied to this welded joint, even a small weld defect can lead to a crack or crack, and this crack or crack has a significant impact on the reliability of the entire structure. Become.
For this reason, in order to improve the fatigue characteristics of the welded joint portion, various methods have been proposed as a method for reducing the tensile residual stress in the welded joint portion and a method for reducing the stress concentration.

  As a method for reducing the tensile residual stress in the welded portion, a method of performing decorative welding with a welding material having higher tensile strength than the base material after welding (see Patent Document 1), a method of applying plastic deformation after welding (Patent Document 2). See), a method of hammering (hammer peening) the weld toe with a hammer hitting device (see Patent Document 3), a method of performing laser peening (Patent Document 4), and a method of performing peening by hitting an ultrasonic transducer (Patent Document 5), a method of performing arc welding using a welding material whose martensitic transformation expansion ends at or near the room temperature at which welding is completed, and utilizing the transformation expansion of the weld metal (see Patent Document 6). .

  Moreover, as a method of relieving the stress concentration of the welded portion, a technique of grinding a weld bead (see Patent Document 7), a weld toe radius and a contact angle are increased by adjusting a weld metal component, and the stress concentration is relieved. A technique (see Patent Document 8) has been proposed.

Of the methods for reducing the tensile residual stress in the weld after welding, the peening method is a cost effective method because it is easy to operate, but laser peening has a problem that it is inferior in handling properties because the device becomes large. In addition, peening using an ultrasonic vibrator has a problem that the apparatus is expensive and difficult to obtain.
On the other hand, hammer peening has a better handling property than other peening apparatuses and is a preferable method in terms of cost.

In Patent Document 9, in order to improve the fatigue durability of a welded portion, a striking tool 1 having a flat portion 3 at the tip as shown in FIG. The fatigue strength is improved by introducing a compressive strain into the welded portion by hitting.
Further, in Patent Document 10, a hitting tool as shown in FIG. 17 is attached to a mounting portion 15 for mounting on a chuck 17 of a peening tool, and a hitting portion 16 fixed to the mounting portion by being eccentric from the axis of the mounting portion. A method of using a striking tool composed of

JP 52-98642 A JP-A-5-253673 JP-A-4-21717 Japanese Patent Application Laid-Open No. 7-246483 JP 2004-130313 A JP-A-12-84670 JP-A 61-186611 Japanese Patent Laid-Open No. 4-361766 Japanese Patent No. 4895407 Japanese Patent No. 495856

In the method of striking the base material in the vertical direction using the striking tool 1 having the flat portion 3 at the tip shown in FIG. 1, it is necessary to introduce compressive strain close to both sides of the striking mark, that is, the welded portion. Efficient compression strain is introduced into the base metal on the side where there is and the base metal on the side far from the weld where it is not necessary to introduce the compressive strain, and it is efficient on the side where the compression strain needs to be introduced near the weld There is a problem that compression strain cannot be introduced.
Then, in view of the said subject, this invention aims at providing the peening processing method which can introduce | transduce a compressive strain efficiently to the position which needs to introduce a compressive strain by the impact | damage with a striking tool.

The inventors of the present invention have applied a direction to the distribution of compressive strain by hitting a peening tool having a flat portion at the tip with an inclination with respect to the vertical direction of the base material surface, and the opposite side to the inclined side. As a result, it was found that compressive strain can be more efficiently applied to the base material.
That is, the present invention relates to a peening method as described below.

(1) A peening method for improving the fatigue characteristics of a welded joint by striking the surface of a base material using a peening tool having a striking tool having a flat part at the tip, wherein the direction of striking by the striking tool is determined by the mother A peening construction method characterized in that an impact is made by inclining 10 degrees or more and 20 degrees or less to the opposite side of the welded portion with respect to the vertical direction of the material surface.
(2) The peening method according to (1), wherein the peening tool has a striking frequency of 1 kHz or less.
(3) The flat portion of the impact tool is rectangular, one side of the rectangle is 2 mm or more and 5 mm or less, and the area is 4 mm ² or more and 25 mm ² or less (1) or (2) The peening construction method described in 1.
(4) The peening tool is tilted 10 degrees or more and 20 degrees or less to the opposite side of the welded portion with respect to the vertical direction of the hit surface and fixed to the hand tool to perform peening (1) to (3) ) The peening construction method according to any one of the above.
(5) The peening tool is tilted 10 degrees or more and 20 degrees or less to the opposite side of the welded portion with respect to the vertical direction of the hit surface and fixed to the feeding device, and the feeding device is run manually or automatically running The peening method according to any one of (1) to (3), wherein peening is performed.
(6) The peening method according to any one of (1) to (5), wherein the hitting surface is hit twice or more by the hitting tool.
(7) The peening method according to any one of (1) to (6), wherein the feeding speed of the peening tool is set to 60 cm / min or more.

  By tilting the peening tool provided with a striking tool having a flat part at the tip as in the present invention, the fatigue durability of the welded part can be improved more than the construction method by striking in the vertical direction, Moreover, the application range is broader than the construction conditions premised on hitting the base material surface in the vertical direction.

It is a figure which shows the peening tool which enforces the peening construction method of this invention. It is a figure explaining the peening construction method of the present invention. It is a figure which shows the surface state of the base material at the time of implementing the peening construction method of this invention. It is a figure explaining the effect of the peening construction method of the present invention. It is a figure explaining the peening construction method of the present invention. It is a figure explaining the peening construction method of the present invention. It is a figure explaining the test method in the Example of this invention. It is a figure explaining the effect of the peening construction method of the present invention. It is a figure explaining the effect of the peening construction method of the present invention. It is a figure explaining the effect of the peening construction method of the present invention. It is a figure explaining the effect of the peening construction method of the present invention. It is a figure which shows the shape of the test body used in the Example. It is a figure which shows notionally the surface state of the test body used in the Example. It is a figure which shows the relationship between the frequency | count of fracture of a test body, and a stress range (MPa). It is a figure which shows the state which joined the metal plate with the welded joint. It is a figure explaining the example of the conventional peening tool. It is a figure explaining the example of the conventional peening tool.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows an example of a peening apparatus used for the peening work of the present invention.
Fig.1 (a) is a figure which shows the chisel-shaped hitting tool 1 by which the flat hitting surface 3 whose hardness is higher than a welding base material was provided in the front-end | tip part, The upper end part is a tool shown in FIG.1 (b). 2 so that it can be fixed to 2.
FIG. 1B is a view showing a peening tool (blow tool) 2 to which a hitting tool 1 is attached and for causing the hitting tool 1 to reciprocate up and down to hit the base material.
When carrying out the peening method of the present invention, the impact tool 1 is repeatedly impacted at a low frequency of 1 kHz or less, preferably 100 Hz or less (in the present invention, “frequency” means “strike frequency”), and the mother A peening apparatus capable of giving an impact force to the material is used.

The illustrated peening tool 2 is an air hammer, which is supplied with compressed air 4 from above and reciprocates a piston in the air hammer body to strike the impact tool 1 disposed at the tip.
As this air hammer, a flux chipper used for removing welding flux or the like can be used. If the air hammer is large, it will be difficult to handle and it will be difficult to adjust so that it hits a position of 0 to 3 mm from the toe.

The impact tool 1 has a flat tip. As the tip shape, one that can easily give plastic deformation to the surface of the base material, such as a circle, ellipse, or rectangle, can be selected as appropriate, and if the optimum tip shape is determined by the air pressure of the compressor and the performance of the tool that gives impact Good. If the power of the air hammer is large, the area of the tip of the impact tool may be increased, but increasing the impact mark width will not change the effect on the weld bead side, so it is necessary to increase the impact scar width too much. There is no. In addition, when the power of the air hammer is small, if the area of the tip is increased, an appropriate plastic deformation cannot be applied to the base material.
The area of the flat part is preferably 4 mm ² or more and 25 mm ² or less. Further, the tip shape is preferably rectangular, and one side of the rectangle is preferably 2 mm or more and 5 mm or less. Moreover, it is preferable to chamfer the tip portion.

FIG. 2 is a view showing a state in which the peening tool 2 with the striking tool 1 is tilted with respect to the base material by an angle θ from the vertical direction to hit the base material. In the following description, hitting the peening tool with an inclination may be referred to as “oblique hitting”.
However, it is difficult to manually maintain the peening tool at a constant inclination angle.
For this reason, in order to keep the inclination angle of the peening tool constant, the peening tool is used, for example, as a hand tool or a feeding device used in the hitting processing apparatus described in Patent Document 10 (Patent No. 4958666). It is preferable to wear and perform peening. The feeding device may be advanced along a guide. The guide may be separately installed like a rail, or a guide member parallel to the peening location may be provided. The feeding device may be a general-purpose robot such as an articulated robot, and the peening tool may be attached to a manipulator at the tip of the general-purpose robot.

FIG. 3 is a diagram schematically showing a cross-sectional profile of the surface of the base material 7 when the surface of the base material 7 is struck by the peening method of the present invention to form a band-shaped hitting mark 21 on the surface of the base material. . When the peening tool 2 is tilted at an angle (θ degrees) opposite to the welded portion with respect to the vertical direction of the surface of the base material 7 and the base material surface 7 is hit with the striking tool 1, the hitting mark 21 is the base material surface before hitting. In the front portion, a hitting mark rising peak (front) 22 is formed in the front part, and a hitting mark rising peak (rear) 23 is formed in the rear part.
In FIG. 3, Lf represents a distance (separated) from the hitting trace rising peak (front), and Lb represents a distance (separated) from the hitting trace rising peak (rear).

FIG. 4 shows the estimation of the distance Lf (mm) and Lb (mm) from the peak of the rising of the impact mark and the compressive strain when the peening tool is fixed to the automatic feeder so that the inclination angle is 15 degrees. It is a figure which shows the relationship with a value (micro).
As shown in FIG. 4, the front compression strain becomes larger than the rear compression strain when slanted with a striking tool. That is, even when the same striking force is applied, oblique compression can give a larger compressive strain in the forward direction.

By tilting the peening tool equipped with a hitting tool having a flat part at the tip to the opposite side to the welded part, the effect of expanding the applicable range of the welded object to be hit apart from the effects described above is obtained. It is done.
For example, when a peening operation is performed with a striking tool 1 on a welded portion in which a rib 6 is vertically installed on the surface of a base material 7 as shown in FIG. By inclining and striking in the direction opposite to the weld bead 5 with respect to the direction, it becomes possible to strike closer to the welded portion, and the compressive strain introduced into the welded portion is larger than hitting in the vertical direction. Thus, fatigue resistance can be further improved.

  Moreover, FIG. 6 showed a mode that the welding part of the welding thing which erected the rib 6 which has the overhang | projection part 8 which the upper part overhang | projected with respect to the base material 7 by the direction of the peening tool 2 was welded. FIG. In the construction method in which the conventional base material surface as shown in FIG. 6 (a) is struck in the vertical direction by the striking tool, this overhanging portion 8 interferes with the peening tool 2 to prevent the striking, but FIG. 6 (b) According to the construction method of the present invention shown in the figure, the peening tool 2 is tilted and hit, so that the peening tool 2 does not interfere with the overhanging portion 8 and can be hit well.

[Example 1]
A hammer tool (G.1.1: manufactured by Fuji Aircraft) was processed into a flat rectangular shape with a tip of about 3 mm x 3 mm, and the outer periphery of the tip was chamfered with a radius of about 0.5 mm Was used.
As a peening tool, a hammer tool (flux chipper: FCH-20 manufactured by Fuji Aircraft Co., Ltd .: hitting frequency: 90 Hz) as shown in FIG. 1 was used, and the hitting tool was attached to the peening tool.
As the test body, an iron plate as shown in FIG. 7 was used, and five gauges were attached to both sides of the surface of the iron plate with the striking position interposed therebetween.
The peening tool is fixed to the automatic feeding device, and the peening tool tilt angle θ is changed to 0 degree, 10 degrees, 15 degrees, and 20 degrees, and the peening construction is performed once (two times) at a feeding speed of 60 cm / min. Blow marks were formed.
The test was conducted for 2 test specimens at 0 °, 3 test specimens at 10 °, and 2 test specimens at 15 °, and an approximate curve of compression strain was obtained from the data. Estimated compressive strain at 3mm position

FIG. 8 shows the results obtained by obtaining the distance Lf (mm) from the striking peak (front) and the estimated value (μ) of the compressive strain based on the data obtained by the above test.
From the results shown in FIG. 8, it can be seen that the compression strain is improved at a position 2 mm forward from the peak of the rising of the hitting mark as compared with the case of hitting in the vertical direction, and the same effect can be obtained even at 3 mm.

Furthermore, based on the obtained data, the relationship between the impact angle θ (degrees) and the estimated compression strain is shown in FIG. Here, the numerical value of the negative impact angle is a compression strain estimated value at a distance Lb from the impact trace rising peak (backward) in FIG.
According to FIG. 9, it is estimated that there is an effect of improving the compressive strain at the positions where Lf is 2 mm and 3 mm even when the impact angle θ is 5 degrees as compared with the case where the impact angle θ is 0 degrees. The effect is more remarkable when the hitting angle θ is 10 to 20 degrees.
However, at a negative impact angle θ, not only is there no effect of “oblique strike”, but conversely, the amount of compression strain introduced is lower than when the impact angle θ is 0 degree, which is the prior art.

[Example 2]
Using the same striking device as in Example 1, the first impact and the second impact were performed at an impact angle of 15 degrees and a feed rate of 60 cm / min, and the value of compression strain was measured.
The result is shown in FIG.
FIG. 10 shows the distance (separated) from the hitting peak (front).
From the results shown in FIG. 10, it can be seen that when the impact is made twice, the compressive strain is approximately doubled, and it is preferable that the impact is performed a plurality of times. The surface pattern of the hit mark is slightly uneven when it is hit once, but is not seen when hit more than once.

[Example 3]
Using a striking device similar to that in Example 1, striking was performed at a striking angle of 15 degrees, a feed rate of 30 cm / min, 60 cm / min, and 90 cm / min. The result is shown in FIG.
From this result, it can be seen that compressive strain can be effectively applied even when the feed rate of the peening tool is set to 60 cm / min or more, which is more advantageous in terms of processing cost.

[Example 4]
In this example, using the same striking device as in Example 1, the fatigue strength of the test specimen was measured when the specimen was hit with an inclination angle of 10 degrees and a feed rate of 100 cm / min.
A “load non-transmission type cross joint” having the shape shown in FIG. 12 was used as a test body.
Table 1 below shows the conditions (stress range, separation (Lf), depth (h), width (w)) of the impact test performed on the test bodies 1 to 4. Here, the separation (Lf) is the distance from the peak of rising of the hitting mark (front) to the weld toe, and the depth (h) is the depth of the hitting mark measured from the surface of the base material.
In addition, Table 1 shows the number of times of rupture (times), the number of times of rupture as welded (times), and the number of times (number of times of rupture (times) / number of times of rupture as welded (times)).
FIG. 13 is a diagram conceptually showing the surface state of the specimen.

Moreover, FIG. 14 is the figure which plotted the relationship between the frequency | count of a fracture | rupture and the stress range (MPa) of the test bodies 1-4. In the figure, □ is a plot for specimens 1, 2, 3, and 4 subjected to the impact test in order from the left, and ● is a plot for three specimens as welded.
The curves A to E in the figure indicate the grades of the road bridge specifications / comments (March 2012).
The A grade in the figure indicates the fatigue strength corresponding to the base material.
FIG. 14 shows that, for example, the test body 2 was fractured at about 500,000 times when the stress of 5 to 255 MPa was repeatedly applied, and the test body 4 was 2 million when the stress of 5 to 205 MPa was repeatedly applied. It shows that it did not break even after the first time.
According to this test result, it shows that it is about E grade if it is welded, and it turns out that the fatigue strength more than B grade is substantially obtained with the test bodies 1-4 of this invention.

  The peening method of the present invention can greatly improve the fatigue strength of welded joints using a simple tool, so that large steel structures such as bridges, ships, offshore structures, automobiles, construction, etc. that are subjected to repeated loads It is suitable for repairing and extending the life of machine products such as machines.

1 Blow tool 2 Peening tool (blow tool)
3 Blow tool tip 4 Compressed air 5 Weld bead (welded joint)
6 Rib 7 Base material 8 Overhang 9 Weld toe 11, 12 Metal plate 13 Weld bead (welded joint)
14 Weld bead toe 15 Impact tool mounting 16 Impact tool impact 17 Peening tool chuck

Claims (7)

A peening method for improving the fatigue characteristics of a welded joint by striking a base metal surface using a peening tool having a striking tool having a flat portion at the tip, wherein the direction of striking by the striking tool is determined on the surface of the base material. A peening method, wherein the impact is made by tilting at an angle of 10 degrees or more and 20 degrees or less to the opposite side of the welded portion with respect to the vertical direction.   The peening method according to claim 1, wherein an impact frequency of the peening tool is 1 kHz or less. 3. The peening construction according to claim 1, wherein the flat portion of the impact tool is rectangular, one side of the rectangle is 2 mm or more and 5 mm or less, and the area is 4 mm ² or more and 25 mm ² or less. Method. 4. The peening is performed by tilting the peening tool 10 degrees or more and 20 degrees or less to the opposite side of the welded portion with respect to the vertical direction of the hit surface and fixing the peening tool to the hand tool. The peening construction method described. By tilting the peening tool 10 degrees or more and 20 degrees or less to the opposite side of the welded portion with respect to the vertical direction of the hit surface, and fixing the peening tool to the feeding device and running the feeding device manually or automatically. Peening is performed, The peening construction method in any one of Claims 1-3 characterized by the above-mentioned.   6. The peening method according to claim 1, wherein the hitting surface is hit twice or more by the hitting tool.   The peening method according to any one of claims 1 to 6, wherein the feeding speed of the peening tool is set to 60 cm / min or more.