JP2007075826A - Welded joint structure for reducing fatigue damage - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a welded joint structure joined by fillet-welding a main plate and a rib plate, which welded joint structure can improve its fatigue strength by reducing the stress concentration produced at the toe portion of welding. <P>SOLUTION: Putty layers 4 are laminated on the whole surface of the welded metal 3 of the fillet welding and are stuck to the main plate 1 and the rib plate 2 so as to form concave cylindrical surfaces toward the welded portions. By this method, the putty layers can share the load applied to the fillet welded portion, and also can relax the stress concentration produced at the toe portion of welding. As a result, the fatigue strength of the welded joint structure can be improved. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a welded joint structure of a metal material such as a cruciform joint, a T joint, and a corner joint, and more particularly to a fatigue reduction type welded joint structure that improves the fatigue strength of a fillet joint.

  A joint structure using fillet welding is widely used for manufacturing structures using metal materials such as steel and aluminum alloys. However, in joint structures joined by conventional fillet welding, if tensile stress or bending stress is applied to the base metal, stress concentrates on the toe of the fillet weld, so that repeated stress is applied to the weld toe. Fatigue cracks are likely to occur, and the fatigue strength of the weld is significantly lower than that of the base material. For this reason, the fatigue strength of the entire structure is dominated by the welded joint, and the characteristics of the base material cannot be fully utilized.

  In order to improve the fatigue strength of the welded portion, it is necessary to increase the thickness of the base material to reduce the strain of the base material against the stress and to reduce the stress applied to the weld toe. However, it is necessary to use a base material whose strength is much higher than the design strength of the entire structure, which makes the material design very uneconomical.

  Therefore, conventionally, the weld toe is cut and ground with a grinder or the like, or remelted with TIG or plasma to rework the toe smoothly to reduce stress concentration on the toe, The fatigue strength was improved. However, these methods need to process the weld metal after the formation of the structure, and thus require a lot of labor and labor, and the cost load is high.

  Further, Patent Document 1 discloses a method for improving weld fatigue strength as a method for reducing stress concentration on the weld toe. A schematic cross-sectional view illustrating the disclosed invention is shown in FIG. In this disclosed invention, in a welded joint in which a main plate 90 and a rib plate 91 are joined by fillet welding, the elastic modulus is 5% to 150% and (elastic modulus) × (thickness) is 1% to the base material 90. 50% fiber reinforced plastic (FRP) 92 is fixed to the base material 90 and fillet weld 91 so as to cover the weld toe 93 of fillet weld, and the stress concentration applied to the weld toe 93 is FRP. It is dispersed by the action of.

  This method can disperse the stress concentration on the weld toe and improve the fatigue strength of the fillet welded joint. However, the disclosed invention is a technique invented focusing only on the stress concentration at the weld toe, and does not reduce the total amount of stress applied to the welded portion, and thus has a limited effect.

JP-A-8-243778

  The problem to be solved by the present invention is to provide a joint structure capable of improving the fatigue strength of a fillet weld in a joint structure of a metal material.

  In order to solve the above problems, the fatigue-reducing welded joint structure of the present invention is a welded joint structure in which a rib material is joined to a main plate by fillet welding, covers the fillet welded portion, and is fixed to the main plate and the rib plate. The putty layer is laminated, and the putty layer alleviates stress concentration on the weld toe of the fillet welded portion and shares and bears the stress applied to the fillet welded portion.

  According to the fatigue-reducing welded joint structure of the present invention, the stress flow concentrated on the toe portion of fillet weld is dispersed in the putty layer to alleviate the stress concentration, and related to the conventional fillet welded portion. Part of the stress is shared by the putty layer, and the fatigue strength of the welded joint can be improved by reducing the stress flowing through the fillet weld.

The putty layer is formed of a material having high adhesion and high rigidity to the main plate and the rib plate such as a plastic putty. If the Young's modulus of the putty layer is significantly lower than that of the main plate and rib plate, the putty layer cannot sufficiently bear the stress applied to the fillet welds. For example, an epoxy putty with relatively high rigidity is used. It is preferable to use a putty material in which reinforcing fibers are kneaded. In addition, glass fiber, carbon fiber, aramid fiber, iron fiber, etc. can be utilized as the reinforcing fiber.
Moreover, when a plastic metal putty such as an iron putty, for example, in which metal powder is mixed with a polymer putty material, the texture of the surface of the putty layer is close to the texture of the main plate or rib plate, and the finish is good. For example, a putty material (trade name Debcon A (ITW Industry Co., Ltd.) or the like) in which iron powder is kneaded with an epoxy type putty is suitable.

  The surface of the putty layer can be any shape such as a flat surface or curved surface, but if the surface is a concave cylindrical surface toward the fillet weld, the stress concentration at the end of the putty layer can be reduced. It is very preferable because there are advantages such as prevention of water accumulation at the welded portion and beautiful finish. Further, for example, a similar effect can be obtained even when a hyperboloid is used.

  The thickness of the putty layer laminated on the fillet weld is arbitrary. However, in order to reduce the stress applied to the fillet weld, it is necessary to bear the stress in the putty layer, so a thickness of a certain level or more is required. For example, when the surface is a cylindrical surface, the curvature radius of the surface must be at least one times the plate thickness of the main plate. In addition, it is preferable that the radius of curvature of the surface is about 20 times or less the plate thickness of the main plate because the fatigue reduction effect is saturated with respect to the thickness of the putty layer and the structure is unnecessarily enlarged.

In the fatigue-reducing welded joint structure of the present invention, when a reinforcing member having higher rigidity than the putty material forming the putty layer is embedded in the putty layer, a higher fatigue reduction effect is obtained.
Especially when the Young's value of the main plate or rib plate is high, when the putty layer is formed only with the putty material, the putty layer lacks rigidity, and the putty layer cannot sufficiently share the stress applied to the fillet weld. The predetermined fatigue reduction effect may not be obtained. Therefore, it is preferable to embed a highly rigid reinforcing member inside the putty layer so that the reinforcing member bears a stress in a supplemental manner.

For example, the reinforcing member can be a plate material such as a steel plate and can be installed in parallel to the surface of the fillet weld. Further, the reinforcing member may be a wire, and may be disposed in a direction against a compressive stress or a tensile stress applied between the main plate and the rib plate. When the reinforcing member is a wire, it is effective to arrange the wire in a direction that spans the opposing surfaces of the main plate and the rib plate. A large number of wires may be arranged side by side as necessary. However, if it is difficult to construct, embed multiple wires in close contact with the crossing line of the main plate and rib plate so that the wire and wire are in contact with each other, and generate resistance against the pressure in the diameter direction of the wire. It may be possible to resist compressive stress.
What is necessary is just to select suitably the material and arrangement | positioning attitude | position of a reinforcement member according to the direction of the stress concerning a main board and a rib board, intensity | strength, etc. FIG.

Further, the stress load of the putty layer may be assisted by covering the surface of the putty layer with a reinforcing plate to form a reinforcing layer. A reinforcing layer is laminated in close contact with the entire surface of the putty layer. In the welded joint structure of this embodiment, the reinforcing layer bears a part of the stress applied to the putty layer and relaxes the stress concentration applied to the fillet welded portion together with the putty layer.
As the reinforcing layer, a fiber reinforced plastic (FRP) sheet, a glass fiber reinforced plastic (GFRP) sheet, or the like can be used.

As described above, according to the fatigue-reducing welded joint structure of the present invention, the putty layer laminated on the upper surface of the fillet weld zone relieves stress concentration on the fillet weld portion, and stress fatigue of the weld toe portion is reduced. This can reduce the fatigue strength of the joint structure. Therefore, the fatigue design load of the welded portion can be increased, and the quality of the welded structure can be improved by reducing the weight and cost of the base material.
The fatigue-reducing welded joint structure of the present invention can be applied to welded structures in a wide range of fields from relatively small structures such as automobiles and motorcycles to large structures such as bridges.
In addition, the welded joint structure of the present invention can be easily constructed using a simple tool, particularly when applied to an existing structure or when on-site construction is required. Compared to other construction methods such as overlay welding, there are significant advantages.

  Hereinafter, the best mode of a fatigue reduction type welded joint structure of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a conceptual perspective view showing a construction example of the fatigue reduction type welded joint structure of the present embodiment. FIG. 1 shows an example of construction on a cross joint. The main plate 1 and the rib plate 2 are joined to each other by a weld metal 3. The fatigue reduction type welded joint structure of the present embodiment is formed by laminating a putty layer 4 on a fillet weld metal 3. The putty layer 4 covers the entire surface of the weld metal 3 and is adhered and laminated to the weld metal 3 and the main plate 1 and the rib plate 2. Although the upper surface of the putty layer 4 may have an arbitrary shape, in this embodiment, it is a concave cylindrical surface toward the weld.

The procedure for constructing the putty layer 4 is shown below. First, the surface of the weld metal 3 is degreased by wiping with acetone. Subsequently, a putty material obtained by kneading the main agent and the curing agent is placed on the weld metal 3. After that, as shown in FIG. 2, a cylindrical mold member 20 having a desired radius of curvature is pressed against the putty member, fixed for 24 hours, and then removed to complete.
As the mold material, a material obtained by attaching a fluororesin sheet 21 to the surface of wood was used. FIG. 2 shows a state in which two types of mold materials, a mold material 20 having a curvature radius of 20 mm and a mold material 22 having a curvature radius of 25 mm, are used as a reference.

  The conceptual perspective view showing the construction example of the fatigue reduction type welded joint structure of another form in FIG. 3 was shown. In the figure, only the welded joint structure in the upper right part is shown, and the others are omitted. In this embodiment, a steel plate 32 having both ends bent is embedded in a putty layer 31 stacked on the upper surface of the weld metal 30 in parallel with the surface of the weld metal 30. In the welded joint structure of the present embodiment, the surface of the weld metal 30 is degreased to deposit a small amount of putty material, and after placing the steel plate 32, the putty layer 31 is formed in the same manner as in the first embodiment. The curvature radius of the formed putty layer 31 is 25 mm.

  The conceptual perspective view showing the construction example of the fatigue reduction type welded joint structure of a 3rd form was shown in FIG. In the figure, only the welded joint structure in the upper right part is shown, and the others are omitted. A putty layer 41 is formed on the weld metal 40, and a glass fiber reinforced plastic sheet (GFRP sheet) 42 is further laminated. After putting the putty material on the weld metal 40 in the same manner as in Example 1, the mold material was pressed and temporarily molded, and the GFRP sheet 42 was placed and crimped with the mold material. In this embodiment, the radius of curvature of the putty layer 41 is 20 mm.

Below, the fatigue reduction effect of the fatigue reduction type welded joint structure of the said Example is shown. The fatigue reduction effect was measured by placing strain gauges at 12 points on the main plate, applying bending pressure with a 4-point bending jig, and measuring the strain gauge output.
FIG. 5 shows a layout diagram of strain gauges. A total of twelve strain gauges 52 are installed on the upper and lower surfaces of the main plate 50 on the center line of the main plate 50 and 10 mm from both ends of the main plate 50 and 10 mm from the intersecting line of both side surfaces of the rib plate 51 and the main plate 50. . Further, FIG. 6 shows a layout diagram of a four-point bending jig. A jig 62 is disposed on the lower surface of the main plate 60 at a position 50 mm from the center of the rib plate 61, and a jig 62 is disposed on the upper surface of the main plate 60 at a position of 110 mm from the center of the rib plate 61. Bending stress was applied to the.

FIG. 7 shows the test results measured using the above measuring tool. The load was applied by gradually increasing and decreasing the pressure of the 4-point bending jig up to a maximum load of 200 kgf for 2 cycles, and the average of the outputs measured by 12 strain gauges was used as an index of strain. A value obtained by dividing the strain value after construction by the strain value before construction was defined as the strain reduction rate, and the inverse of the cube of the strain reduction rate was defined as the predicted increase in life.
In this test, an iron putty (trade name: Devcon A) in which iron powder was kneaded with an epoxy-based putty was used as a putty material.

  As shown in FIG. 7, when the putty layer is R20 mm, the life of the joint structure is 1.6 times longer, and when the putty layer is R25 mm, the life is further increased. In addition, by embedding a steel plate in the R25mm putty layer, the life is 1.2 times longer than in the case of using only the putty material. Life is 1.4 times longer.

On the other hand, FIG. 8 shows the result of calculation regarding the effect of relieving the stress concentration related to the toe portion of fillet welding. In this test, the stress relaxation effect with respect to the plate bending load and the tensile load when the radius of curvature of the putty layer is changed is shown as a ratio of the generated stress with 1 before construction. In the figure, the plate bending load represents the bending moment applied when pressure is applied to the main plate in the plate thickness direction, and the tensile load represents the tensile force applied in the longitudinal direction of the main plate.
The plate thickness of the main plate and rib plate is 6 mm, Young's modulus is 200 GPa, the foot length of the weld metal is 6 mm for the main plate side and the rib plate side, the curvature radius of the weld metal toe is 0.3 mm, and the Young's modulus of the putty material is It was calculated by simulation as 6 GPa.

As shown in the figure, when the radius of curvature of the putty layer is 18 mm (three times the plate thickness t of the main plate), the stress is about 0.9 times for the tensile load and about 0.75 times for the plate bending load. Concentration relaxation effect. When the radius of curvature of the putty layer is increased to 4t and 5t, the stress concentration mitigating effect on the plate bending load is dramatically increased. When the radius of curvature is 5t, the stress concentration at the toe is half that before construction. It is as follows.
Although not shown, even in a test in which the putty layer thickness is constant and the Young's modulus of the putty material is changed, the stress concentration is increased for both tensile load and plate bending load by increasing the Young's modulus of the putty material. The result that the relaxation effect increases is obtained. Therefore, when the Young's modulus of the putty layer is increased by using, for example, a reinforcing fiber kneading putty kneaded with glass fiber, carbon fiber, aramid fiber, iron fiber, or by embedding a reinforcing member such as a steel plate or steel wire. It is effective.

As described above, according to the fatigue reduction type welded joint structure of this example, the putty layer laminated on the fillet weld part reduces the stress applied to the fillet weld part, and the stress concentration applied to the weld toe part is reduced. Since it relaxes, the fatigue crack of the fillet welded part due to repeated stress can be prevented, and the fatigue life of the welded joint can be improved.
Therefore, the fatigue design load of the welded joint structure can be increased, and the weight and cost of the structure can be reduced.
Since the fatigue reduction type welded joint structure of the present embodiment can obtain a fatigue reduction effect with an inexpensive material and simple construction, it can be introduced into a wide range of industrial fields.

It is a conceptual perspective view which shows the construction example of the fatigue reduction type welded joint structure concerning 1st Example of this invention. It is a perspective view explaining the construction method concerning the 1st example of the present invention. It is a conceptual perspective view showing the construction example of the fatigue reduction type welded joint structure concerning the 2nd form of this invention. It is a conceptual perspective view showing the construction example of the fatigue reduction type welded joint structure concerning the 3rd form of this invention. It is an arrangement view of strain gauges in a test for explaining the effect of the present invention. It is an arrangement view of a four-point bending jig in a test for explaining the effect of the present invention. It is a table | surface which shows the test result of the test explaining the effect of this invention. It is a graph which shows the effect which relieves stress concentration in the fatigue reduction type welded joint structure of a present Example. It is a schematic sectional drawing explaining the prior art.

Explanation of symbols

1, 50, 60, 90 Main plate 2, 51, 61, 91 Rib plate 3, 30, 40 Weld metal 4, 31, 41, Putty layer 20, 22 Mold material 21 Fluorine resin sheet 32 Steel plate 42 GFRP sheet 52 Strain gauge 62 Healing Tool 92 FRP
93 Weld toe

Claims (15)

  In a welded joint structure in which a main plate and a rib plate are joined by fillet welding, the fillet welded portion is covered and laminated to the main plate and the rib plate, and a putty layer is laminated. A fatigue-reducing welded joint structure characterized in that stress concentration on a weld toe is alleviated and stress applied to the fillet weld is shared and borne.   The fatigue-reducing welded joint structure according to claim 1, wherein the putty layer is formed of a plastic putty.   The fatigue-reducing welded joint structure according to claim 2, wherein the putty layer is formed of an epoxy putty.   4. The fatigue-reducing welded joint structure according to claim 2, wherein the putty layer is formed of a plastic steel putty in which metal powder is mixed with a plastic putty material.   5. The fatigue-reducing welded joint structure according to claim 1, wherein reinforcing fibers are kneaded in the putty material forming the putty layer.   6. The fatigue-reducing welded joint structure according to claim 5, wherein the reinforcing fiber is one of glass fiber, carbon fiber, aramid fiber, and iron fiber.   7. The fatigue-reducing welded joint structure according to claim 1, wherein a cross-sectional shape of the putty layer is a circular arc with a concave surface in a cross section cut perpendicular to the line of intersection of the main plate and the rib plate.   The fatigue reduction type welded joint structure according to claim 7, wherein a radius of curvature of a cross-sectional shape of the putty layer is 1 to 20 times a plate thickness of the main plate.   The fatigue-reducing welded joint structure according to any one of claims 1 to 8, wherein a reinforcing member having higher rigidity than the putty material forming the putty layer is embedded in the putty layer.   The fatigue-reducing welded joint structure according to claim 9, wherein the reinforcing member is a plate material.   The fatigue-reducing welded joint structure according to claim 9, wherein the reinforcing member is a wire, and the reinforcing member is arranged in a direction that spans the opposing surfaces of the main plate and the rib plate.   The fatigue-reducing welded joint structure according to claim 9, wherein the reinforcing member is a wire, and a plurality of the reinforcing members are arranged in parallel to the intersection line of the main plate and the rib plate.   The fatigue reduction type welded joint structure according to any one of claims 1 to 12, wherein a reinforcing layer is laminated on a surface of the putty layer.   The fatigue-reducing welded joint structure according to claim 13, wherein the reinforcing layer is a fiber reinforced plastic (FRP) sheet.   The fatigue-reducing welded joint structure according to claim 14, wherein the reinforcing layer is a glass fiber reinforced plastic (GFRP) sheet.

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