Structure, manufacturing method of structure, and life lengthening method of structure

Abstract

To provide a structure which can suppress occurrence of fatigue crack.SOLUTION: A structure made of steel comprises: a first component; and a second component which is partially joined with the first component. Paste containing solid content and liquid oil is provided between facing surfaces at a non-joint portion of the first component and the second component.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a structure, a method for manufacturing the structure, and a method for extending the life of the structure.

Background Art

[0002] Structures such as box-shaped structures including the attachment structure of a hydraulic excavator are welded from the outside by single-sided fillet welding or the like because it is difficult to weld from the inside. In such a structure, there is a non-welded portion in a state where the base materials are in contact without being welded to each other. The non-welded portion has a relatively large stress concentration coefficient, and tensile residual stress is generated in the vicinity of the welded portion. Therefore, the non-welded portion and the welded portion often become the starting points of fatigue cracks. Thus, techniques for suppressing the occurrence of fatigue cracks have been proposed.

[0003] For example, Patent Document 1 discloses a technique for suppressing the occurrence of fatigue cracks in a steel floor slab having a configuration in which the tip portions of a pair of side wall portions of a trough rib are welded to the back surface of a deck plate. Specifically, it is disclosed that pressure is applied to the pair of side wall portions from the inside of the trough rib so that the pair of side wall portions are deformed toward the outside of the trough rib, and by removing the pressure applied to the pair of side wall portions, fatigue crack generation and fatigue crack propagation in the root portion of the weld bead are prevented.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in structures such as steel floor plates described in Patent Document 1, during use, repeated loads are applied, causing stress to concentrate at the non-joint portions. Therefore, there is a problem that the occurrence of fatigue cracks starting from the non-joint portions cannot be sufficiently suppressed.

[0006] Therefore, it is desirable to provide a structure capable of suppressing the occurrence of fatigue cracks.

Means for Solving the Problems

[0007] A structure according to one aspect of the present disclosure is a structure made of steel, having a first member and a second member partially joined to the first member, and a paste containing a solid component and a liquid oil component is provided between opposing surfaces of the non-joint portion of the first member and the second member.

Effects of the Invention

[0008] A structure according to one aspect of the present disclosure can suppress the occurrence of fatigue cracks.

Brief Description of the Drawings

[0009]

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Embodiments for Carrying Out the Invention

[0010] Hereinafter, non-limiting embodiments of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding members or parts are given the same or corresponding reference numerals. Also, hereinafter, duplicate descriptions of the same or corresponding members or parts will be omitted. Also, in the drawings, the members or parts are not necessarily drawn to scale. Therefore, those skilled in the art can arbitrarily determine specific dimensions with reference to the following non-limiting embodiments. Also, the following embodiments are illustrative rather than limiting the invention. Also, the features in the embodiments and their combinations are not necessarily essential to the invention.

[0011] <Structure> FIG. 1 is a side view of a structure according to an embodiment, and FIG. 2 is an enlarged view of a main part of FIG. 1. As shown in FIGS. 1 and 2, the structure 1 is made of steel and has a first member 2 and a second member 3 partially joined to the first member 2. That is, the structure 1 has a joint 4 between the first member 2 and the second member 3. Also, a paste 6 containing a solid component and a liquid oil component is provided between the opposing surfaces of the non-joint part 5 of the first member 2 and the second member 3. With this configuration, compared with the case where the paste 6 is not provided between the opposing surfaces of the first member 2 and the second member 3, the positive stress range when a load is applied during use and the total strain range when the load during use is removed at the boundary between the joint 4 and the non-joint part 5 can be reduced. Therefore, the structure 1 can suppress the occurrence of fatigue cracks.

[0012] Specifically, the structure 1 has a corner formed by one surface (front surface) 21 of the first member 2 and one surface (back surface) 32 of the second member 3, and a welded portion as a joint portion 4 provided at the corner (hereinafter referred to as the welded portion 4). The non-joint portion 5 is a non-welded portion (hereinafter referred to as the non-welded portion 5) of the end face 23 of the first member and the one surface 32 of the second member 3. The welded portion 4 is, for example, a welded portion formed by single-sided fillet welding. The non-welded portion 5 is a non-welded portion on the opposing surfaces of the end face 23 of the first member and the one surface 32 of the second member 3. The structure 1 of the present embodiment can reduce the positive stress range when a load is applied during use and the total strain range when the load during use is removed, compared with the case where no paste 6 is provided between the opposing surfaces of the first member 2 and the second member 3. Therefore, the structure 1 can suppress the occurrence of fatigue cracks.

[0013] The structure 1 may have a first member 2, a second member 3 whose one end is partially joined to one end of the first member 2, a third member 7 whose one end is partially joined to the other end of the first member 2, and a fourth member 8 whose one end is partially joined to the other end of the second member 3 and whose other end is partially joined to the other end of the third member 7. That is, the structure 1 may have a hollow structure. The cross-sectional shape of the structure 1 may be rectangular. That is, the first member 2, the second member 3, the third member 7, and the fourth member 8 are joined perpendicular to each other. The first member 2, the second member 3, the third member 7, and the fourth member 8 can be made of, for example, steel.

[0014] Each of the first member 2 and the second member 3 is flat, and the end face 23 of the first member 2 and the back face 32 of the second member 3 may be abutted and welded together. Further, the paste 6 may be provided between the end face 23 of the first member 2 and the back face 32 of the second member 3, and may be in a compressed state by being sandwiched between the end face 23 of the first member 2 and the back face 32 of the second member 3. With this configuration, since the paste 6 fills the entire non-welded portion 5, when a load is applied to the structure 1 during use, it is possible to promote the closing of the non-welded portion 5, and the positive stress range when a load is applied during use and the total strain range when the load during use is removed at the boundary between the welded portion 4 and the non-welded portion 5 can be made smaller. Therefore, the structure 1 can further suppress the occurrence of fatigue cracks.

[0015] The solid content contained in the paste 6 is fine particles, and it is preferable that the hardness of the fine particles is greater than the hardness of each of the first member 2 and the second member 3. Thereby, the positive stress range when a load is applied during use and the total strain range when the load during use is removed at the boundary between the welded portion 4 and the non-welded portion 5 can be made smaller. Therefore, the structure 1 can further suppress the occurrence of fatigue cracks.

[0016] Examples of the fine particles contained in the paste 6 include alumina, silica, silicon nitride, silicon carbide, zirconia, zirconium carbide, boron carbide, boron nitride, titanium carbide, tungsten carbide, cemented carbide, iron, steel, yttria, magnesium, magnesium alloy, titanium, titanium alloy, titanium oxide, copper, copper alloy, diamond, carbon, and carbon fiber. As the fine particles contained in the paste 6, one or more of these can be used.

[0017] It is preferable that the particle size of the fine particles contained in the paste 6 is smaller than the distance between the opposing surfaces of the first member 2 and the second member 3 in the non-jointed portion 5. Thereby, the space between the opposing surfaces of the first member 2 and the second member 3 in the non-jointed portion 5 can be sufficiently filled with the paste 6.

[0018] Examples of the liquid oil content included in the paste 6 include salad oil, industrial oil, and the like.

[0019] FIG. 3 is a side view of an excavator according to an embodiment. The excavator 100 includes a lower traveling body 101, an upper swing body 102 rotatably mounted on the lower traveling body 101, and a cab 103 provided at the front left side of the upper swing body 102. A boom 104 is rotatably connected to the front central portion of the upper swing body 102, and an arm 105 is rotatably connected to the tip of the boom 104. The boom 104 may be formed by connecting two hollow structures at a connecting portion 141.

[0020] Furthermore, a bucket 106 is rotatably connected to the tip of the arm 105. The structure 1 may be the boom 104 of the excavator 100. Since the boom 104 is a structure that is relatively likely to be loaded in the excavator 100, by applying the configuration of the structure 1 to the boom 104, the boom 104 can more effectively suppress the occurrence of fatigue cracks.

[0021] <Manufacturing method of the structure> FIG. 4 is a flowchart showing the procedure of the manufacturing method of the structure 1 according to an embodiment, and FIGS. 5 to 8 are diagrams for explaining the manufacturing method of the structure 1 according to an embodiment. With reference to FIGS. 4 to 8, an example of the manufacturing method of the structure 1 of the present embodiment will be described.

[0022] The manufacturing method of the structure 1 of the present embodiment is a method for manufacturing a hollow structure 1 made of steel. As shown in FIGS. 4 to 6, the manufacturing method of the structure 1 includes joining a first member 2 and a second member 3 by single-sided fillet welding to form a welded portion 4 formed on one surface 21 side (front surface side) and a non-welded portion 5 formed on the other surface 22 side (back surface side) with respect to the first member 2, and producing a hollow structure intermediate body 10 (step S1). Further, as shown in FIGS. 4 and 7, a step of applying a load (overload) greater than the load applied during use in the direction in which the non-welded portion 5 opens to the structure intermediate body 10 (step S2), and as shown in FIGS. 4 and 8, a step of injecting a paste 6 containing a solid component and a liquid oil component into the opened non-welded portion 5 (step S3), and a step of removing the load applied in the step of applying the load (step S4).

[0023] In the manufacturing method of the structure 1 described above, by the steps of applying a load and removing the load, it is possible to generate a compressive residual stress with respect to the tensile residual stress field in the vicinity of the welded portion 4 generated when the welded portion 4 is provided. Further, in the step of injecting the paste 6, by injecting the paste 6 into the opened non-welded portion 5, the positive stress range when the load during use is applied and the total strain range when the load during use is removed at the boundary between the welded portion 4 and the non-welded portion 5 can be made smaller than when the paste 6 is not injected. Therefore, according to the manufacturing method of the structure 1 of the present embodiment, it is possible to manufacture the structure 1 that suppresses the occurrence of fatigue cracks.

[0024] (Step of producing a structure intermediate body) As shown in FIGS. 5 and 6, the manufacturing method of the structure 1 of the present embodiment includes a step of joining a first member 2 and a second member 3 by single-sided fillet welding to produce a hollow structure intermediate body 10 having a welded portion 4 formed on one surface 21 side and a non-welded portion 5 formed on the other surface 22 side with respect to the first member 2. Since the first member 2, the second member 3, the welded portion 4, and the non-welded portion 5 are the same as the respective members in the structure 1 described above, the description thereof is omitted here. Hereinafter, for the members common to the structure 1, the description may be omitted because they are the same as those of the structure 1.

[0025] In the step of manufacturing the structure intermediate body 10, the cross-sectional shape of the structure intermediate body 10 is rectangular, and a welded portion 4 and a non-welded portion 5 may be formed at each of the four corners of the structure intermediate body 10. Thereby, the manufacturing method of the structure 1 of the present embodiment can manufacture the structure 1 that suppresses the occurrence of fatigue cracks at each of the four corners.

[0026] Specifically, the structure intermediate body 10 may include a first member 2, a second member 3 having one end partially joined to one end of the first member 2, a third member 7 having one end partially joined to the other end of the first member 2, and a fourth member 8 having one end partially joined to the other end of the second member 3 and the other end partially joined to the other end of the third member 7. Each of the first member 2, the second member 3, the third member 7, and the fourth member 8 has a front surface 21, 31, 71, 81 and a back surface 22, 32, 72, 82.

[0027] Further, the first member 2, the second member 3, the third member 7, and the fourth member 8 are joined perpendicular to each other. That is, one end face 23 of the first member 2 and the back surface 32 of the second member 3 are butted and welded, the other end face 24 of the first member 2 and the back surface 72 of the third member 7 are butted and welded, one end face 83 of the fourth member 8 and the back surface 32 of the second member 3 are butted and welded, and the other end face 84 of the fourth member 8 and the back surface 72 of the third member 7 are butted and welded. In this case, the structure intermediate body 10 has a welded portion 4 provided at each of the corners formed by the front surface 21 of the first member 2 and the back surface 32 of the second member 3, the corner formed by the front surface 21 of the first member 2 and the back surface 72 of the third member 7, the corner formed by the front surface 81 of the fourth member 8 and the back surface 72 of the third member 7, and the corner formed by the front surface 81 of the fourth member 8 and the back surface 32 of the second member 3. Further, the structure intermediate body 10 has a non-welded portion 5 formed on the back surface 22 side of the first member 2 rather than the welded portion 4 provided on the front surface 21 side of the first member 2 at both ends of the first member 2, and a non-welded portion 5 formed on the back surface 82 side of the third member 7 rather than the welded portion 4 provided on the front surface 81 side of the third member 7 at both ends of the third member 7.

[0028] (Step of applying a load) As shown in FIG. 7, the method for manufacturing the structure 1 of the present embodiment includes a step of applying a load greater than the load applied during use to the structure intermediate body 10 in the direction in which the non-welded portion 5 opens. Here, the load greater than the load applied during use means a load greater than the maximum value of the load applied during use at the load application portion. For example, a load can be applied to the structure intermediate body 10 by pressing the structure intermediate body 10 using a pressing member 9 such as a hydraulic jack. In the example shown in FIG. 7, the pressing member 9 is installed in the hollow portion of the structure intermediate body 10, and a load is applied from the inside to the outside of the structure intermediate body 10 (in the direction indicated by the arrow). Specifically, a load is applied from the back surfaces 22, 82 sides of the first member 2 and the fourth member 8 toward the front surfaces 21, 81 sides. In the step of applying a load, a load may be applied to the structure intermediate body 10 by pulling the structure intermediate body 10 outward from the outside of the structure intermediate body 10. Specifically, a load may be applied to the structure intermediate body 10 by pulling the first member 2 and the fourth member 8 from the front surfaces 21, 81 sides of the first member 2 and the fourth member 8 toward the front surfaces 21, 81 sides. When the structure intermediate body 10 has the first member 2, the second member 3, the third member 7, and the fourth member 8, the back surfaces 22, 82 of the opposing first member 2 and fourth member 8 may be pressed simultaneously, or the back surfaces 32, 72 of the opposing second member 3 and third member 7 may be pressed simultaneously.

[0029] In the example shown in FIG. 7, the central portion of the length of the opposing first member 2 and fourth member 8 in one direction is pressed, but a portion closer to the non-welded portion 5 than the central portion may be pressed.

[0030] (Step of injecting paste) As shown in Fig. 8, the manufacturing method of the structure 1 of the present embodiment includes a step of injecting a paste 6 containing a solid component and a liquid oil component into the open non-welded portion 5. In the step of injecting the paste 6, specifically, the paste 6 is injected into the gap formed between the opposing surfaces of the first member 2 and the second member 3. That is, the paste 6 is injected into the gap formed between the end face 23 of the first member 2 and the back face 32 of the second member 3. As a result, in the step of removing the load, the paste 6 is compressed on the opposing surfaces of the first member 2 and the second member 3, and the non-welded portion 5 is filled with the paste 6. Therefore, when a load is applied to the structure 1 during use, the closing of the non-welded portion 5 can be promoted, and the positive stress range when a load is applied during use and the total strain range when the load during use is removed at the boundary between the welded portion 4 and the non-welded portion 5 can be made smaller. Thus, according to the manufacturing method of the structure 1 of the present embodiment, a structure 1 that suppresses the occurrence of fatigue cracks can be manufactured. Since the paste 6 is the same as the paste 6 in the above-described structure 1, the description thereof is omitted here.

[0031] (Step of removing the load) The manufacturing method of the structure 1 of the present embodiment includes a step of removing the load applied in the step of applying the load. For example, the load can be removed by releasing the pressing from the state where the structure intermediate body 10 is pressed using a pressing member 9 such as a hydraulic jack.

[0032] When the structure 1 is the boom 104 of the excavator 100, the manufacturing method of the structure 1 of the present embodiment includes installing a pressing member 9 in each hollow portion of the two hollow structure intermediate bodies 10, applying a load greater than the load applied during use to the structure intermediate body 10 in the direction in which the non-welded portion 5 opens, injecting a paste 6 containing a solid component and a liquid oil component into the open non-welded portion 5, removing the load applied in the step of applying the load, and joining the two structure intermediate bodies 10.

[0033] <Method for extending the life of the structure> Figs. 9 to 11 are diagrams for explaining a method for extending the life of a structure according to an embodiment. With reference to Figs. 9 to 11, an example of the method for extending the life of the structure of the present embodiment will be described. In Figs. 10 and 11, illustration of the liquid oil component in the paste is omitted, and only the solid component is illustrated.

[0034] The method for extending the life of the structure 40 of the present embodiment is a method for extending the life of a structure 40 made of steel. The structure 40 is a structure after use, and as shown in Fig. 9, a fatigue crack 41 has occurred. As shown in Fig. 10, the method for extending the life of the structure 40 of the present embodiment applies a load greater than the load applied during use to the structure 40 in the direction in which the fatigue crack 41 generated in the structure 40 opens. After injecting the paste 6 containing the solid component and the liquid oil component into the opened fatigue crack 41, as shown in Fig. 11, the load greater than the load applied during use is removed. According to the method for extending the life of the structure 40 of the present embodiment, a compressive stress is generated in the fatigue crack 41, and as shown in Figs. 10 and 11, the solid component 61 of the paste 6 provided in the fatigue crack 41 promotes the closing of the fatigue crack 41. Therefore, the positive stress range when the load during use is applied and the total strain range when the load during use is removed at the tip of the fatigue crack 41 can be reduced. As described above, according to the method for extending the life of the structure 40 of the present embodiment, the occurrence of further fatigue cracks in the structure 40 after use can be suppressed, and the life of the structure 40 can be extended.

[0035] The load greater than the load applied during use and the paste 6 are the same as the load and the paste 6 in the manufacturing method of the above-described structure 1, and thus the description thereof is omitted here.

[0036] When the structure 40 is a component such as the boom 104 of the excavator 100, the method for extending the life of the structure 40 of the present embodiment can be applied to the maintenance of the excavator 100. When the structure 40 is the boom 104 of the excavator 100, the boom 104 is disassembled into two structures 40, the pressing member 9 is installed in each hollow portion of the structure 40, and a load larger than the load applied during use is applied to the structure 40 in the direction in which the fatigue crack 41 generated in the structure 40 opens. After injecting the paste 6 containing the solid component and the liquid oil component into the opened fatigue crack 41, as shown in FIG. 11, except for the load larger than the load applied during use, the two structures 40 may be joined.

[0037] Next, based on the results of the simulation by numerical analysis, the effects of the structure 1 of the present embodiment, the manufacturing method of the structure 1, and the method for extending the life of the structure 40 will be described.

[0038] First, a model was created in which a 3.0 mm slit was formed in a direction perpendicular to the major axis from the edge of a plate member on a flat plate made of steel with a length of 115.2 mm, a width of 21.0 mm, and a thickness of 1.5 mm. The slit corresponds to the non-joint portion 5 in the structure 1 or the fatigue crack 41 of the structure 40.

[0039] (Experimental Example 1) For the created model, an analysis was performed to simulate the influence when a paste was injected into the slit after loading a tensile load of 150 MPa as a load (overload) larger than the load applied during use. Then, the applied tensile load of 150 MPa was removed, and further, an analysis was performed under the condition of loading a tensile load of 100 MPa as a load (normal load) applied during use and then removing the 100 MPa tensile load, and the stress and strain values at the nodes at the tip of the slit were calculated.

[0040] (Experimental Example 2) For the created model, an analysis was performed under the same conditions as in Experimental Example 1 except that no paste was injected into the slit, and the stress and strain values at the nodes at the tip of the slit were calculated.

[0041] (Experimental Example 3) After applying a tensile load of 100 MPa as the normal load to the created model, analysis was performed under the condition of removing the 100 MPa tensile load, and the stress and strain values at the nodes at the tip of the slit were calculated.

[0042] For each of Experimental Examples 1 to 3, a graph was created based on the calculated stress and strain values. Fig. 12 is a graph showing the relationship between the stress and strain at the nodes at the tip of the slit. As shown in Fig. 12, the positive stress range when the normal load was applied was A1 MPa in Experimental Example 1, A2 MPa which is greater than A1 MPa in Experimental Example 2, and A3 MPa which is greater than A2 MPa in Experimental Example 3. Also, the total strain range after removing the normal load was B1 in Experimental Example 1, B2 which is greater than B1 in Experimental Example 2, and B3 which is greater than B2 in Experimental Example 3. That is, in Experimental Example 1, the positive stress range when the normal load was applied and the total strain range after removing the normal load were smaller values compared to Experimental Examples 2 and 3. From the above, it was confirmed that by applying an overload in the direction in which the slit opens, injecting paste into the slit, and then removing the overload, the generation or propagation of fatigue cracks can be suppressed.

Explanation of Signs

[0043] 1, 40 Structure 2 First member 21 One surface (front surface) 22 The other surface (back surface) 23 One end face 24 The other end face 3 Second member 31 The other surface (front surface) 32 One surface (back surface) 4 Joint part (weld part) 5 Non - joint part (non - weld part) 6 Paste 61 Solid content 9 Pressing member 10 Structure intermediate body 41 Fatigue crack 100 Excavator 104 Boom

Claims

1. A structure made of steel, having a first member and a second member partially joined to the first member, wherein a paste containing a solid component and a liquid oil component is provided between opposing surfaces of the non-joined portions of the first member and the second member. Structure.

2. A corner formed by one surface of the first member and one surface of the second member, and a welded portion provided at the corner, wherein the non-joined portion is a non-welded portion of the end face of the first member and the one surface of the second member. The structure according to claim 1.

3. The solid component is fine particles, and the hardness of the fine particles is greater than the hardness of each of the first member and the second member. The structure according to claim 2.

4. Each of the first member and the second member is in a flat plate shape, the first member and the second member are butt-welded with the end face of the first member and the back surface of the second member butted against each other, the paste is provided between the end face of the first member and the back surface of the second member, and is in a compressed state by being sandwiched between the end face of the first member and the back surface of the second member. The structure according to claim 3.

5. The structure is a boom of an excavator. The structure according to any one of claims 1 to 4.

6. A method for manufacturing a hollow structure made of steel, comprising a step of producing a hollow structure intermediate having a welded portion formed on one surface side and a non-welded portion formed on the other surface side with respect to the first member by joining the first member and the second member by single-sided fillet welding, a step of applying a load greater than the load applied during use to the structure intermediate in the direction in which the non-welded portion opens, a step of injecting a paste containing a solid component and a liquid oil component into the opened non-welded portion, and a step of removing the load applied in the step of applying the load. Method for manufacturing a structure.

7. In the step of injecting the paste, the paste is injected into a gap formed between opposing surfaces of the first member and the second member. The method for manufacturing a structure according to claim 6.

8. In the step of producing the structure intermediate, the cross-sectional shape of the structure intermediate is rectangular, and the welded portion and the non-welded portion are formed at each of the four corners of the structure intermediate. The method for manufacturing a structure according to claim 7.

9. A method for extending the life of a structure made of steel, In the direction in which the fatigue crack generated in the structure opens, apply a load greater than the load applied during use to the structure, inject a paste containing a solid component and a liquid oil component into the opened fatigue crack, and then remove the load greater than the load applied during use, Method for extending the life of a structure.

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