Repair method for fatigue cracks, and repair kit.

Abstract

This invention provides a fatigue crack repair method and repair kit that can reduce the time and effort required for repair work when multiple cracks occur simultaneously, and is also effective against potential microcracks that are not visible from the outside of the structure. [Solution] For a metal base material or welded joint, a location where the occurrence of fatigue cracks 5 is estimated or has already occurred is selected. If the selected location is inside a closed cross-section structure 4 having an internal space S, an electrolyte aerosol 17 is supplied to fill the internal space S of the closed cross-section structure 4. If the selected location is a structure other than a closed cross-section structure, a three-dimensional cover 18 that covers the fatigue cracks 5 is installed on the surface of the structure, and an electrolyte aerosol 17 is supplied to fill the internal space S' of the installed three-dimensional cover 18. The propagation of fatigue cracks 5 is suppressed by the wedge effect of electrodeposited deposits or corrosion products generated when the electrolyte aerosol 17, or the electrolyte produced when it condenses, adheres to the crack surface of the fatigue crack, etc.

Description

[Technical Field]

[0001] This invention relates to a method for repairing fatigue cracks occurring in various structures such as ships, offshore structures, bridges, vehicles, aircraft, or machine tools, and to a repair kit. [Background technology]

[0002] Various structures such as ships, offshore structures, bridges, vehicles, aircraft, and machine tools are mainly composed of structural members made of metals such as iron and aluminum, or their alloys (steel, aluminum alloy, etc.). When repeated loads are applied to these metal structural members, metal fatigue can cause cracks, especially at stress concentration points. Such fatigue cracks in structures gradually propagate as time passes and the number of load cycles increases. If the crack length exceeds the structural limit, it can lead to serious damage or accidents. Therefore, it is necessary to detect cracks while they are still short and take measures to effectively suppress or stop their propagation. As one such measure, Patent Document 1 and Non-Patent Document 2 describe that when the base material is a corrosive metal such as steel, covering the area around the crack opening with a crack propagation suppression sheet using a highly water-containing gel creates a moderately moist environment within the crack, promoting the formation of corrosion products on the crack surface. This significantly suppresses crack propagation due to the wedge effect of the corrosion products deposited within the crack. Furthermore, Patent Document 2 describes that when the base material is a metal, covering the area around the crack opening with a crack propagation suppression sheet using a highly water-containing gel creates a moderately moist environment within the crack, promoting the formation of electrodeposited deposits on the crack surface. This significantly suppresses crack propagation due to the wedge effect of the electrodeposited deposits accumulated within the crack.

[0003] Furthermore, Non-Patent Document 1 describes that deck-propagating cracks and two types of bead-propagating cracks occur and propagate from the weld root area between the U-ribs and deck plates of a steel bridge deck. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2021-103167 [Patent Document 2] Japanese Patent Publication No. 2023-8893 [Non-patent literature]

[0005] [Non-Patent Document 1] Masashi Hattori, Kazuo Tateishi, Tsuyoshi Hanji, and Yu Shimizu, "Fatigue Evaluation of Root Cracks in Steel Deck U-Rib and Deck Plate Welds," Journal of Japan Society of Civil Engineers, Series A1 (Structural and Earthquake Engineering), Vol. 77, No. 2, pp. 255-270, 2021. [Non-Patent Document 2] Kazuhiko Takahashi, Prototype and Performance Evaluation of Fatigue Crack Propagation Inhibiting Sheet Using High-Water-Content Gel - Utilizing the Wedge Effect of Corrosion Products -, Transactions of the Japan Welding Society, Vol. 41, No. 4, pp. 289-301 (2023) [Overview of the project] [Problems that the invention aims to solve]

[0006] In the methods described in Patent Documents 1 and 2 above, it is necessary to apply (attach) at least one crack propagation suppression sheet to each crack, and if multiple cracks occur simultaneously in the same structural member, the on-site repair work requires a considerable amount of time and effort. Furthermore, in order to properly determine the area to which crack propagation suppression sheets should be applied during repair work, it is generally necessary for cracks to appear on the surface of the member and for their location to be identified. Therefore, it is difficult to apply them to fatigue cracks that are difficult to see, such as non-penetrating cracks that are propagating from the inside of a closed cross-section structure. The deck-propagating cracks and the two types of bead-propagating cracks disclosed in Non-Patent Literature 1 both correspond to non-penetrating cracks that propagate from the inside of the closed cross-section structure in the initial stages of propagation, and it is quite possible that multiple cracks continue to propagate without being detected within the closed cross-section structure.

[0007] Therefore, the present invention aims to provide a fatigue crack repair method and repair kit that can reduce the time and effort required for repair work when multiple cracks occur simultaneously in the same structural member, and that is also effective against potential microcracks that are not visible from the outside of the structure. [Means for solving the problem]

[0008] A fatigue crack repair method corresponding to claim 1 is characterized by selecting a location in a metal base material or welded joint of a structure where the occurrence of a fatigue crack is suspected or where a fatigue crack has occurred; if the selected location is inside a closed cross-sectional structure having an internal space, an opening is made in a part of the closed cross-sectional structure and an electrolyte aerosol, which is a mixture of electrolyte and gas, is supplied to fill the internal space; if the selected location is a structure other than a closed cross-sectional structure, a three-dimensional cover having an opening to cover the fatigue crack, or capable of forming an opening, is installed on the surface of the structure, an electrolyte aerosol is supplied to fill the internal space formed inside the installed three-dimensional cover, and the electrolyte aerosol supplied to the internal space, and / or the electrolyte produced by the condensation of the electrolyte aerosol, adheres to the base material or welded joint and the crack surface of the fatigue crack, thereby suppressing the propagation of the fatigue crack by the wedge effect of electrodeposited deposits or corrosion products. According to the present invention as described in claim 1, by filling the internal space inside the closed cross-sectional structure at a selected location, or the internal space inside the three-dimensional cover covering the selected location, it is possible to repair multiple cracks at once, thereby reducing the time and effort required for repair work. Furthermore, even when the location of fatigue cracks cannot be identified or seen, repair work can be performed on the location where their occurrence is suspected.

[0009] The present invention as described in claim 2 is characterized in that the particle size of the electrolyte aerosol is 10 μm or less in terms of the median mass diameter (MMD). According to the present invention as described in claim 2, the electrolyte fine particles contained in the electrolyte aerosol supplied to the internal space remain there for a long time and diffuse evenly, making it easier for an electrochemical circuit to form. Furthermore, even if the fatigue crack is only a micron-order opening even under maximum tensile load, the electrolyte fine particles can smoothly enter through the opening, promoting the formation of electrodeposited deposits or corrosion products on the crack surface.

[0010] The present invention as described in claim 3 is characterized in that, when attempting to generate electrodeposited deposits or corrosion products within a fatigue crack, carbon dioxide or oxygen is mixed with the electrolyte aerosol and supplied to the internal space, or, if the fatigue crack is a crack that penetrates the thickness of the plate, air is introduced into the fatigue crack from the crack opening of the crack that penetrates the thickness of the plate along with the supply of the electrolyte aerosol. According to the present invention as described in claim 3, since carbon dioxide, oxygen, or air is supplied together with the electrolyte aerosol into the internal space or fatigue crack, electrodeposited deposits or corrosion products can be formed in the fatigue crack without a shortage of CO2 or O2 necessary for the electrochemical reaction.

[0011] The present invention as described in claim 4 is characterized in that, when attempting to generate corrosion products within a fatigue crack, a corrosive gas is mixed with an electrolyte aerosol and supplied to the internal space. According to the present invention as described in claim 4, the corrosion reaction can be accelerated, and corrosion products can be generated early within fatigue cracks.

[0012] The present invention as described in claim 5 is characterized in that, while maintaining an electrolyte aerosol inside the internal space, a galvanic anode with a lower potential than the base metal of the base material or the weld metal of the weld at the selected location, or a galvanic cathode with a higher potential than the base metal of the weld at the selected location, or an external DC power supply, is used to continuously flow a current in a direction that promotes the electrodeposition reaction or corrosion reaction to the base material or weld at the selected location. According to the present invention as described in claim 5, by passing an electric current in a direction that promotes the electrodeposition reaction or corrosion reaction through the electrolyte aerosol or condensed electrolyte, electrodeposited deposits or corrosion products can be generated early within the fatigue crack.

[0013] In the case of passing an electric current in a direction that promotes an electrodeposition reaction, an electric current anode is provided in the vicinity of the base metal or the weld metal at a selected location of a structure having as a base metal at least any one of iron, steel, aluminum alloy, magnesium alloy, and titanium alloy, and a cathode potential is applied to the base metal or the weld metal. This is the gist of the invention. According to the present invention described in claim 6, electrodeposition deposits can be locally and selectively generated within a fatigue crack in a relatively short period of time, and the wedge effect of the electrodeposition deposits deposited inside the crack promotes crack closure, thereby suppressing the stress intensity factor range at the crack tip.

[0014] In the case of passing an electric current in a direction that promotes a corrosion reaction, an electric current cathode is provided in the vicinity of the base metal or the weld metal at a selected location, and an anode potential is applied to the base metal or the weld metal. This is the gist of the invention. According to the present invention described in claim 7, corrosion products can be locally and selectively generated within a fatigue crack in a relatively short period of time, and the wedge effect of the corrosion products deposited inside the crack promotes crack closure, thereby suppressing the stress intensity factor range at the crack tip.

[0015] An electrode is provided in the vicinity of the base material or the welded part at a selected location. When passing an electric current in a direction that promotes an electrodeposition reaction, the negative electrode of an external DC power source is connected to the base metal or the weld metal side. When passing an electric current in a direction that promotes a corrosion reaction, the positive electrode of an external DC power source is connected to the base metal or the weld metal side. In either case, the opposite electrode is installed in an electrolytic solution aerosol. This is the gist of the invention. According to the present invention described in claim 8, electrodeposition deposits or corrosion products can be locally and selectively generated within a fatigue crack in a relatively short period of time, and the wedge effect of the electrodeposition deposits or corrosion products deposited inside the crack promotes crack closure, thereby suppressing the stress intensity factor range at the crack tip.

[0016] The invention according to claim 9 is characterized in that when the selected location is inside the closed cross-section structure, a sealing means for preventing the passage of the electrolytic solution aerosol is installed in the internal space of the closed cross-section structure, thereby limiting the section where the electrolytic solution aerosol is supplied. According to the invention of claim 9, the region filled with the electrolytic solution aerosol, that is, the region to be repaired for fatigue cracks, can be limited to a specific section within the internal space.

[0017] The invention according to claim 10 is characterized in that when there are a plurality of fatigue cracks, a three-dimensional cover having a size that covers all the fatigue cracks is used. According to the invention of claim 10, even when there are a plurality of fatigue cracks, only one three-dimensional cover is required, and the basic configuration can be the same as in the case of a single fatigue crack.

[0018] The invention according to claim 11 is characterized in that the three-dimensional cover is attached to the surface of the structure using cover attachment means. According to the invention of claim 11, the cover attachment means facilitates the attachment of the three-dimensional cover to the surface, and when it is likely that a gap will occur between the three-dimensional cover and the structure, the use of the cover attachment means for joining the two can improve workability.

[0019] The invention according to claim 12 is characterized in that the electrolytic solution particles in the electrolytic solution aerosol filled in the internal space are adsorbed and / or removed, and the gas is released to the outside. If the electrolytic solution aerosol leaks outside the internal space, it may have an adverse effect on other devices, structures, etc. However, according to the invention of claim twelve, since the electrolytic solution aerosol is adsorbed and / or removed and then the gas is released to the outside, adverse effects on the working environment and the surroundings can be prevented.

[0020] The invention according to claim 13 is characterized in that the location where fatigue cracks occur in the structure is identified by the white-colored electrodeposits that exhibit a color due to the wedging effect of the electrodeposits and suppress the progression of the fatigue cracks. According to the present invention as described in claim 13, since the electrodeposited material exhibits a white color, visibility can be improved, and even minute cracks that are difficult to detect by normal visual inspection can be identified.

[0021] A fatigue crack repair set corresponding to claim 14 is a repair set used in a fatigue crack repair method, characterized by comprising: an aerosol generator that mixes an electrolyte and a gas to generate an electrolyte aerosol; and an electrolyte aerosol supply means that supplies the electrolyte aerosol generated by the aerosol generator into an internal space. According to the present invention as described in claim 14, the fatigue crack repair method of the present invention can be carried out using a repair set.

[0022] The present invention as described in claim 15 is characterized in that the aerosol generator generates an electrolyte aerosol using artificial seawater containing calcium and magnesium or seawater as an electrolyte. According to the present invention as described in claim 15, an electrolyte aerosol containing a sufficient amount of electrolyte to form an electrochemical circuit can be supplied to the internal space. Furthermore, even if the electrolyte aerosol leaks or diffuses into the surroundings, it can be ensured that there is no adverse effect on humans because its components are artificial seawater or seawater.

[0023] The present invention as described in claim 16 further comprises a three-dimensional cover for covering fatigue cracks used when the selected location has a structure other than a closed cross-section structure, characterized in that the internal state of the three-dimensional cover is visible from the outside. According to the present invention as described in claim 16, it is possible to confirm whether or not electrodeposited precipitates or corrosion products as wedge material have been formed in the fatigue crack without removing the three-dimensional cover.

[0024] The present invention as described in claim 17 is further characterized by comprising a cover mounting means having a magnet for joining a three-dimensional cover to the surface of a structure. According to the present invention as described in claim 17, the cover mounting means has a magnet, which makes it possible to easily attach and detach the three-dimensional cover when the metal of the structure is a magnetic material.

[0025] The present invention as described in claim 18 further comprises a sealing means installed in the internal space of a closed cross-sectional structure, wherein the sealing means is flexible. According to the present invention as described in claim 18, it is possible to limit the area filled with the electrolyte aerosol to only the internal space where fatigue cracks are repaired, and it is also possible to easily install or remove the sealing means from the internal space.

[0026] The present invention as described in claim 19 is further characterized by comprising an aerosol treatment means for treating the generated electrolyte aerosol and discharging it to the outside. According to the present invention as described in claim 19, leakage of electrolyte aerosol to the outside can be prevented, and adverse effects on the equipment and the environment can be avoided. The aerosol treatment means includes filters, air purifiers, air vacuum devices, and the like. [Effects of the Invention]

[0027] According to the present invention, it is possible to effectively generate wedge-shaped materials consisting of electrodeposited deposits or corrosion products in fatigue cracks within the internal space, enabling effective repair of potential microcracks that cannot be located or seen from the outside of the structure, thereby suppressing crack propagation. Furthermore, even when multiple cracks exist within the same structural member, the effort and time required for repair work are not significantly different from that for a single crack, enabling efficient, simultaneous repair of multiple cracks. [Brief explanation of the drawing]

[0028] [Figure 1] Sectional cross-sectional view of a structure used in steel bridge decks, ship hatch covers, etc. [Figure 2] Perspective view diagram of a structure with four U-ribs arranged on a single main plate. [Figure 3]This figure shows the state in which the fixtures and piping included in the repair kit according to the first embodiment of the present invention are installed. [Figure 4] A diagram illustrating the principle and reaction process by which electrodeposited deposits are formed as wedge-shaped materials. [Figure 5] This figure shows a state in which a sealing means is installed inside the U-rib in the first embodiment of the present invention. [Figure 6] This figure shows the state in which the fixtures and piping included in the repair kit of the second embodiment of the present invention are installed. [Figure 7] This figure shows a modified example of the state in which the fixtures and piping included in the repair kit of the first embodiment of the present invention are installed. [Figure 8] This figure shows a modified example of the repair kit included in the second embodiment of the present invention, with the fixtures and piping installed. [Figure 9] Diagram showing the shape and dimensions of a notched flat plate test specimen. [Figure 10] Table showing the conditions and results of comparative examples and examples. [Figure 11] A photograph showing an overview of the back side of the flat test specimen in the example. [Figure 12] A photograph showing an overview of the test system in the example. [Figure 13] Graph showing crack propagation curves in comparative examples and examples. [Figure 14] Photographs showing the fracture surface of the comparative example (a) and the fracture surface of the example (b). [Figure 15] Observation photograph of the front side of the flat plate test specimen at the number of load cycles N = 1.92 × 10⁵ in the example. [Modes for carrying out the invention]

[0029] A first embodiment of the fatigue crack repair method and repair set according to the present invention will be described. The first embodiment is applicable when fatigue cracks occur inside the closed cross-section structure of a structure. Figure 1 is a partial cross-sectional view of a structure used in steel bridge decks and ship hatch covers, etc. A closed cross-sectional structure 4 with an internal space S is formed by joining metal U-ribs 2, which act as stiffeners, to a metal main plate 1 from the outside with two fillet welds 3. In terms of structural form, it is common for multiple U-ribs 2 to be arranged in parallel at regular intervals on a single main plate 1, and when multiple cross-sectional structures like the one shown in Figure 1 are lined up (lined up horizontally in the figure), the structure extends over a long length in the longitudinal direction of the U-ribs 2 (perpendicular to the plane of the paper in the figure). For example, Figure 2 is a perspective view of a structure in which four U-ribs 2 are arranged on a single main plate 1. In the interior of the U-rib 2 (internal space S), a sealing partition perpendicular to the longitudinal direction may be provided at an appropriate position in the longitudinal direction for rust prevention. In this case, a completely sealed structure is formed in three dimensions by the main plate 1, the U-rib 2, and the two partitions.

[0030] In a closed cross-section structure 4 as shown in Figure 1, repeated loads such as plate bending, tension, and shear are applied to the main plate 1, causing a large stress concentration at the root R of the fillet weld 3, which can lead to the occurrence of fatigue cracks 5 originating from the root R. The cracks can take two forms: main plate side cracks 5a that originate at the root R on the main plate 1 side and propagate toward the main plate 1 side, and weld bead side cracks 5b that originate at the root R on either the main plate 1 side or the U-rib 2 side and propagate through the weld bead. If left untreated, either type of crack can eventually penetrate the main plate 1 or the weld bead, potentially leading to serious damage as described in Non-Patent Literature 1. However, since both the main plate crack 5a and the weld bead crack 5b originate from the inner root portion R in the closed section structure 4, it is impossible to visually inspect them from the outside of the closed section structure 4 until they penetrate the main plate 1 or the weld bead. Furthermore, in the case of steel deck plates, the outer surface of the main plate 1 is covered with paving material, so even if the main plate crack 5a penetrates the main plate 1, it cannot be visually inspected unless the paving material is removed. Therefore, it is extremely difficult to detect the main plate crack 5a and the weld bead crack 5b by visual inspection. Furthermore, as mentioned above, steel bridge decks and ship hatch covers generally have multiple long U-ribs 2 arranged in parallel, so there are numerous locations where the occurrence and propagation of cracks 5a on the main plate side or cracks 5b on the weld bead side is a concern. Finding or predicting each of these and repairing them individually would be an extremely complicated and difficult task.

[0031] Therefore, in the fatigue crack repair method according to this embodiment, an electrochemical circuit is formed in the internal space S of the closed cross-sectional structure 4 including the crack surface, and electrodeposited precipitates or corrosion products are generated inside the fatigue crack (crack surface of the fatigue crack) that has occurred on the inside of the closed cross-sectional structure 4, and the propagation of the fatigue crack 5 is suppressed by the wedge effect of the electrodeposited precipitates or corrosive organisms. This makes it possible to repair multiple cracks simultaneously, even if the location of individual cracks cannot be identified, when fatigue cracks 5 are suspected to occur inside a structure, thereby efficiently suppressing crack propagation.

[0032] Figure 3 shows the equipment and piping included in the repair kit installed. As a means of forming an electrochemical circuit that generates electrodeposited deposits or corrosion products on the crack surface of fatigue cracks that originate and propagate from the inside of the closed cross-sectional structure 4, an electrolyte aerosol 17, which is a mixture of fine particles of the electrolyte 16 and gas (mainly air) that fills the internal space S of the closed cross-sectional structure 4, and an electrolyte formed by the localized condensation of the fine particles of the electrolyte 16 are used. Here, the fine particles of the electrolyte 16 (hereinafter referred to as "electrolyte particles") contain charged particles and precipitated components, and it is preferable that their particle size is 10 μm or less in terms of mass median diameter (MMD). Furthermore, if there is concern about a shortage of CO2 or O2 in the electrochemical reaction in the internal space S, it is preferable to supply CO2 or O2 to the internal space S via a ventilation means. This ensures that a sufficient amount of CO2 or O2 is supplied into the fatigue crack. An example of a ventilation means is a device that mixes carbon dioxide or oxygen with the electrolyte aerosol 17. In addition, if the fatigue crack 5 is a crack that penetrates the thickness of the plate, a ventilation means can also be configured to allow air to flow into the fatigue crack from the crack opening on the outside.

[0033] Furthermore, if it is desirable to generate electrodeposited deposits or corrosion products more quickly, it is preferable to pass a weak current through the electrolyte aerosol 17 or the condensed electrolyte in a direction that promotes the electrodeposition or corrosion reaction. As a means of passing a weak current, a galvanic anode metal (galvanic anode) 14 with a lower potential than the main plate 1 (base metal) and weld metal of the closed cross-section structure 4, a galvanic cathode metal (galvanic cathode) with a higher potential, or an external DC power supply can be used. Here, the galvanic anode 14 may be a zinc-rich primer coating for steel rust prevention, and the galvanic cathode metal may be copper for steel, for example. To generate electrodeposited deposits, a galvanic anode 14 is placed in the internal space S at the selected location to apply a cathode potential to the base metal or weld metal, or an electrode is placed near the fatigue crack 5, with the negative electrode of an external DC power supply connected to the fatigue crack 5 side and the positive electrode placed in the electrolyte aerosol 17. To generate corrosion products, a galvanic cathode is placed in the internal space S at the selected location to apply an anode potential to the base metal or weld metal, or an electrode is placed near the fatigue crack 5, with the positive electrode of an external DC power supply connected to the fatigue crack 5 side and the negative electrode placed in the electrolyte aerosol 17.

[0034] In order to suppress the propagation of fatigue cracks 5 by generating electrodeposited deposits as wedge material, in structures where metals such as iron, steel, aluminum alloy, magnesium alloy, and titanium alloy are used as the base material (main plate 1) or weld metal, in the closed cross-section structure 4, at locations where fatigue cracks 5 are detected or where the occurrence of fatigue cracks 5 is a concern, an electrochemical circuit is formed in the internal space S including the crack surface of the fatigue crack by filling the internal space S with an electrolyte aerosol 17 and simultaneously condensing a portion of the electrolyte aerosol 17 around the crack opening. Then, while maintaining this electrochemical circuit, a cathode potential is applied to the crack surface of the fatigue crack, and at the same time, CO2 supply to the fatigue crack is ensured by a ventilation means. As a result, electrodeposited deposits are generated locally, selectively and in a relatively short period of time on the newly formed and electrochemically active crack surface of the fatigue crack, and the wedge effect of the electrodeposited deposits deposited inside the crack promotes crack closure and suppresses the stress intensity coefficient range at the crack tip. Figure 4 illustrates an example of the principle and reaction process by which electrodeposited deposits are formed as wedge-shaped materials. It schematically shows the principle and reaction process by which electrodeposited deposits such as calcium carbonate and magnesium hydroxide are formed as wedge-shaped materials inside fatigue cracks 5 that have formed in a steel member coated with a zinc-rich primer, using an electrolyte aerosol 17 containing components of seawater. In this example, the zinc-rich primer coating acts as a galvanic anode 14 that imparts a cathode potential to the crack surface.

[0035] On the other hand, when attempting to suppress the propagation of fatigue cracks 5 by generating corrosion products as wedge material, in structures where easily corroded metals such as iron and steel are used as the base material (main plate 1) or weld metal, in the closed section structure 4, at locations where fatigue cracks 5 are detected or where the occurrence of fatigue cracks 5 is a concern, an electrochemical circuit is formed in the internal space S including the crack surface of the fatigue crack by filling the internal space S with an electrolyte aerosol 17 and simultaneously condensing a portion of the electrolyte aerosol 17 around the crack opening. Then, while maintaining this electrochemical circuit, an anodic potential is applied to the crack surface, and at the same time, the supply of O2 into the crack is ensured by a ventilation means. As a result, corrosion products are generated locally, selectively and in a relatively short period of time on the newly formed crack surface of the fatigue crack, which is rich in electrochemical activity, and the wedge effect of the corrosion products deposited inside the crack promotes crack closure and suppresses the range of the stress intensity factor at the crack tip.

[0036] The specific steps for the repair method of fatigue crack 5 according to the first embodiment are as follows. In the following, it is assumed that electrodeposited deposits are generated as the wedge material. [Step 1-1] For the main plate 1 constituting a closed cross-section structure 4 with an internal space S within a metal structure, locations where cracks are presumed to be propagating internally are selected based on information about cracks found to have progressed to the outside of the weld bead, as well as inspection results from non-destructive testing such as ultrasonic testing and infrared thermography. For example, in this embodiment, as described above, it is presumed that a crack 5a on the main plate side and a crack 5b on the weld bead side occurred at the joint (welded area) between the main plate 1 and the U-rib 2.

[0037] [Steps 1-2] As shown in Figure 3, the repair kit is installed at the area to be repaired. The repair set used in the method for repairing fatigue cracks 5 in the first embodiment includes an aerosol generator 10 (generation mechanism omitted) that generates electrolyte aerosol 17 and has a chemical tank 11 for storing electrolyte 16, an electrolyte aerosol supply means for supplying the generated electrolyte aerosol 17 to an internal space S, an electrolyte aerosol discharge means for discharging the electrolyte aerosol 17 from the internal space S, a galvanic anode 14, and a sealing means 15 installed in the internal space S. The electrolyte aerosol supply means includes an air supply fan 12A and an air supply pipe 12B, and the electrolyte aerosol discharge means includes an exhaust fan 13A and an exhaust pipe 13B. The air supply piping 12B includes an outlet air supply piping 12Ba that connects to the outlet side of the air supply fan 12A, and an inlet air supply piping 12Bb that connects to the inlet side of the air supply fan 12A. The exhaust piping 13B includes an inlet exhaust piping 13Ba that connects to the inlet side of the exhaust fan 13A, and an outlet exhaust piping 13Bb that connects to the outlet side of the exhaust fan 13A.

[0038] In step 1-2, two through-holes 19 are made as openings using a tool such as a drill in a suitable location on the bottom surface or flange portion of the U-rib 2, where the structural stress is not particularly severe. When using a galvanic anode 14, it is inserted through the through-hole 19 into the internal space S (within the U-rib 2) and installed at an appropriate location. If the location of a crack is known in advance, it is preferable to place the galvanic anode 14 as close to the crack as possible. The galvanic anode 14 does not necessarily need to be long in the longitudinal direction of the U-rib 2; it should be of a shape and size that allows it to be installed using the through-hole 19. If it is absolutely necessary to use a long galvanic anode, one can make arrangements such as providing multiple through-holes 19 in the longitudinal direction of the U-rib 2 and installing a wire-shaped galvanic anode 14. Note that when using a zinc-rich primer coating as the galvanic anode, as shown in Figure 4, installation of the galvanic anode 14 is unnecessary.

[0039] Figure 5 shows the state in which a sealing means is installed inside the U-rib, with Figure 5(a) being a cross-sectional view and Figure 5(b) being a cross-sectional view taken along line X-X'. Although a large portion of the structure is a closed cross-section structure 4 due to the length of the U-rib 2, if the area where fatigue cracks 5 are suspected to have occurred is limited to only a part of it, even if the internal space S is divided into multiple sections by watertight partitions (sealing partitions), it is more efficient to further limit the area to be repaired to the area around where fatigue cracks 5 are suspected to have occurred. Therefore, in such cases, it is preferable in step 1-2 to insert the sealing means 15 through the through hole 19 and install it in the internal space S so that the electrolyte aerosol 17 does not diffuse outside the section partitioned by the sealing means 15. This makes it possible to limit the area to which the electrolyte aerosol 17 is filled, that is, the area to be repaired for fatigue cracks 5, to a specific section within the internal space S.

[0040] In step 1-2, the outlet-side air supply pipe 12Ba is routed through one through-hole 19, and the inlet-side exhaust pipe 13Ba is routed through the other through-hole 19. In this case, one end of the outlet-side air supply pipe 12Ba protrudes into the internal space S, and the other end is connected to the air supply fan 12A. One end of the inlet-side exhaust pipe 13Ba protrudes into the internal space S, and the other end is connected to the exhaust fan 13A. In some cases, an on / off valve may be provided instead of the exhaust fan 13A. Furthermore, although Figure 3 shows two through-holes 19 at the same cross-sectional position, if the closed cross-sectional structure 4 is elongated in the longitudinal direction of the U-rib (perpendicular to the plane of the paper in the figure), it is preferable to place each through-hole 19 near both ends of the U-rib 2. For example, in the structure shown in Figure 2, if there is no sealing partition in the middle of the U-rib 2, one through-hole 19 is made near one end 2A of the U-rib 2, and the other through-hole 19 is made near the other end 2B of the U-rib 2. The aerosol generator 10 is connected to the inlet side of the air supply fan 12A via the inlet side air supply piping 12Bb. The chemical solution tank 11 of the aerosol generator 10 is filled with the selected electrolyte 16. The outlet side exhaust piping 13Bb is connected to the outlet side of the exhaust fan 13A.

[0041] [Steps 1-3] An external load is applied to the structure such that the fatigue crack 5 that has formed at the selected location opens and closes dynamically, or opens statically. In this case, if the normal working load is used as the external load to dynamically open and close the fatigue crack 5, there is no need to apply a separate external load, and the repair can be carried out while the structure is in operation. For example, in the case of a steel bridge, it can be carried out without blocking vehicle traffic, and in the case of a ship or aircraft, it can be carried out under normal operating conditions. On the other hand, external loads that can be used to statically open fatigue cracks 5 include internal pressure loads on pressure vessels (including pressurized loads on aircraft), the placement of heavy vehicles on steel bridges, changes in cargo arrangement or ballast loading on ships, and heavy loads on machine tools (large cranes, etc.).

[0042] [Steps 1-4] The aerosol generator 10 is started, and the intake fan 12A and exhaust fan 13A are operated (or stopped) as appropriate to supply and fill the internal space S with electrolyte aerosol 17.

[0043] [Steps 1-5] The concentration of electrolyte aerosol 17 in the exhaust gas coming out of the exhaust piping 13Bb on the outlet side of the exhaust fan 13A is checked, and the supply fan 12A and exhaust fan 13A are adjusted as appropriate to maintain the electrolyte aerosol concentration in the internal space S at an appropriate level.

[0044] [Steps 1-6] While continuing to apply the external load to the structure in Steps 1-3, the electrolyte aerosol concentration in the internal space S is maintained at a predetermined level for a certain period in Steps 1-5 (standing period). This period lasts until electrodeposited deposits are formed and accumulated on the crack surface of the fatigue crack, reaching a thickness that is effective as a wedge material within the fatigue crack. The expected completion time should be determined in advance through experiments using the same repair procedure.

[0045] [Steps 1-7] After a certain period of time has elapsed since steps 1-6, the aerosol generator 10 is stopped and removed, and the supply fan 12A and exhaust fan 13A are operated as appropriate to circulate only dry air into the internal space S, thereby thoroughly drying the internal space S.

[0046] [Steps 1-8] The intake fan 12A, exhaust fan 13A, intake piping 12B, and exhaust piping 13B are removed, and if possible, an industrial endoscope or a robot with a camera is inserted through the through-hole 19 to observe the internal space S and confirm that a sufficient amount of electrodeposited material has been generated at the target repair location (weld root section R). In this way, the electrolyte aerosol 17 supplied to the internal space S, or the electrolyte formed by the condensation of the electrolyte aerosol 17, adheres to the main plate 1 near the fatigue crack, the welded area, and the crack surface of the fatigue crack, thereby generating electrodeposited deposits. The wedge effect of these electrodeposited deposits can suppress the propagation of the fatigue crack 5.

[0047] <<<Modification 1>>> In the configuration shown in Figure 3, it is conceivable that if aerosols diffuse outside the closed cross-section structure 4, they may adversely affect other equipment and the surrounding environment. For this reason, as shown in Figure 7, a filter 21 may be provided in the outlet exhaust piping 13Bb as an aerosol treatment means. In Figure 7, components similar to those in Figure 3 are denoted by the same reference numerals.

[0048] By adsorbing electrolyte particles in the aerosol onto the filter 21, the electrolyte particles can be removed before being discharged to the outside of the closed cross-section structure 4. The type and method of the filter 21 can be appropriately determined according to the type and amount of aerosol. The filter 21 should be selected to reliably adsorb and remove electrolyte particles in the aerosol with a particle size on the order of microns. Although Figure 7 shows an example where the filter 21 is installed on the outlet exhaust piping 13Bb side, the filter 21 may also be installed on the inlet exhaust piping 13Ba side. The order in which the exhaust fan 13A and the filter 21 are arranged can be appropriately determined.

[0049] Next, a second embodiment of the fatigue crack repair method and repair kit according to the present invention will be described. Figure 6 shows the state in which the equipment and piping included in the repair kit of the second embodiment are installed. Parts that overlap with those of the first embodiment described above are denoted by the same reference numerals and their descriptions are omitted. In the first embodiment, a method for repairing fatigue cracks 5 that may occur inside a closed cross-section structure 4 having an internal space S was described. However, the repair method in the second embodiment is applicable to structures other than the closed cross-section structure 4. Note that structures other than the closed cross-section structure 4 also include the outer portion of the closed cross-section structure 4. That is, the repair method in the second embodiment can be applied to single or multiple fatigue cracks 5 appearing on the surface of the main plate 1 or its welded portion that does not constitute the closed cross-section structure 4, as well as to single or multiple fatigue cracks 5 appearing on the outer surface of the main plate 1 or its welded portion that constitutes a closed cross-section structure 4 having an internal space S, as shown in Figure 1. The specific steps for the repair method of fatigue crack 5 according to the second embodiment are as follows. Note that in the following, electrodeposited deposits are assumed to be generated as the wedge material.

[0050] [Step 2-1] Visual inspection or non-destructive testing will be used to inspect the surface of the main plate 1 or welded joint of the structure for the presence or absence of fatigue cracks 5. Note that fatigue cracks 5 can be either penetrating the plate thickness or not.

[0051] [Step 2-2] If fatigue cracks 5 are found on the surface of the main plate 1 or welded joint of a structure other than a closed cross-section structure, a repair kit will be installed at the repair site to suppress the propagation of the fatigue cracks 5. The repair kit used in the fatigue crack repair method in the second embodiment includes the same aerosol generator 10, chemical tank 11, electrolyte aerosol supply means, and galvanic anode 14 as in the first embodiment, as well as a three-dimensional cover 18 for covering the fatigue crack 5. On the other hand, the electrolyte aerosol discharge means and sealing means 15 are not included. When using a galvanic anode 14, it should be installed in a suitable location near the fatigue crack 5, inside the three-dimensional cover (funnel-shaped casing) 18 that will be attached later. Note that if the zinc-rich primer coating pre-applied to the main plate 1 is used as the galvanic anode, the installation of the galvanic anode 14 is unnecessary. Furthermore, a three-dimensional cover 18 is attached to the main plate 1 (the surface of the structure) so as to cover the fatigue crack 5. When there is a single fatigue crack 5, it is preferable to use a three-dimensional cover 18 large enough to enclose the entire fatigue crack. When there are multiple fatigue cracks 5, as shown in Figure 6, it is preferable to use a three-dimensional cover 18 large enough to enclose all of the fatigue cracks 5. This allows the basic configuration to be the same whether there is a single or multiple fatigue cracks 5. The outlet-side air supply pipe 12Ba is connected at one end to the internal space S' through the opening of the three-dimensional cover 18, and the other end is connected to the air supply fan 12A. The aerosol generator 10 is connected to the inlet side of the air supply fan 12A via the inlet side air supply piping 12Bb. The chemical solution tank 11 of the aerosol generator 10 is filled with the selected electrolyte 16.

[0052] [Steps 2-3] Similar to the first embodiment, an external load is applied to the structure such that the fatigue crack 5 opens and closes dynamically or opens statically.

[0053] [Steps 2-4] By activating the aerosol generator 10 and operating the air supply fan 12A as needed, the electrolyte aerosol 17 is supplied to and fills the internal space S' of the three-dimensional cover 18.

[0054] [Steps 2-5] The concentration of the electrolyte aerosol 17 in the gas leaking from between the three-dimensional cover 18 and the main plate 1 (or welded joint) is checked, and the supply fan 12A (or, in the case of the modified example 2 described later, both the supply fan 12A and the exhaust fan 13A) is adjusted as appropriate to maintain the electrolyte aerosol concentration in the internal space S' at an appropriate level.

[0055] [Steps 2-6] While continuing to apply the external load to the structure in Step 2-3, the electrolyte aerosol concentration in the internal space S' is maintained at a predetermined level for a certain period in Step 2-5 (standing period). This period is until electrodeposited deposits are formed and accumulated on the crack surface of the fatigue crack, reaching a thickness that is effective as a wedge material within the fatigue crack. The expected completion time should be determined in advance through experiments using the same repair procedure.

[0056] [Steps 2-7] After a certain period of time has elapsed since step 2-6, the aerosol generator 10 is stopped and removed, and the air supply fan 12A (or, in the case of modification 2 described later, both the air supply fan 12A and the exhaust fan 13A) is operated as appropriate to circulate only dry air into the internal space S' and to thoroughly dry the internal space S'.

[0057] [Steps 2-8] Remove the three-dimensional cover 18 and observe the fatigue crack 5 and its vicinity to confirm that a sufficient amount of electrodeposited material has been generated. In this way, the electrolyte aerosol 17 supplied to the internal space S', or the electrolyte formed by the condensation of the electrolyte aerosol 17, adheres to the main plate 1, the welded area, and the crack surface of the fatigue crack, thereby generating electrodeposited deposits. The wedge effect of these electrodeposited deposits can suppress the propagation of the fatigue crack 5.

[0058] <<<Modification 2>>> In the configuration shown in Figure 6, it is conceivable that if aerosols diffuse outside the three-dimensional cover 18, they may adversely affect other equipment and the surrounding environment. For this reason, as shown in Figure 8, an inlet exhaust pipe 13Ba, an outlet exhaust pipe 13Bb, an exhaust fan 13A, and a filter 21 as an aerosol treatment means may be provided on the outside of the three-dimensional cover 18. In Figure 8, components similar to those in Figure 6 are denoted by the same reference numerals.

[0059] By adsorbing electrolyte particles in the aerosol onto the filter 21, the electrolyte particles can be removed before being discharged to the outside of the three-dimensional cover 18. In some cases, the exhaust fan 13A can be omitted and replaced with an on / off valve. The type and method of the filter 21 should be determined appropriately according to the type and amount of aerosol. The filter 21 should be selected to reliably adsorb and remove electrolyte particles in the aerosol with a particle size on the order of microns. In Figure 8, an example is shown in which the filter 21 is installed on the outlet exhaust piping 13Bb side, but the filter 21 may also be installed on the inlet exhaust piping 13Ba side. The order in which the exhaust fan 13A and the filter 21 are arranged should be determined appropriately.

[0060] Alternatively, instead of directly connecting the inlet exhaust piping 13Ba to the three-dimensional cover 18 as shown in Figure 8, the inlet exhaust piping 13Ba may be positioned near (outside) the boundary between the three-dimensional cover 18 and the main plate 1, and aerosols leaking from this boundary may be sucked in. In this case, commercially available air purifiers or air vacuum devices can also be used.

[0061] In the specific procedures of the first and second embodiments described above, electrodeposited deposits produced by applying a cathode potential to the fatigue crack 5 side (main plate 1 or weld side) are used as wedge material to be generated inside the fatigue crack 5 in order to suppress the propagation of the fatigue crack 5. However, if the main plate 1 or weld metal is made of a corrosive material such as steel, it is also possible to use corrosion products generated and deposited inside the fatigue crack 5 by applying an anode potential, and use these as wedge material. In this case, in addition to corrosive electrolytes such as artificial seawater and saltwater, it is also possible to use water containing trace amounts of impurities as the electrolyte used in the aerosol when it is desired to minimize the impact on the outside of the internal space S'. Furthermore, if corrosion products are to be generated as wedge material, a mechanism may be provided to mix a corrosive gas that promotes the corrosion reaction of the metal into the electrolyte aerosol 17. This accelerates the corrosion reaction and allows corrosion products to be generated earlier. Possible corrosive gases include chlorine gas and hydrogen sulfide gas, but since both are harmful and dangerous to the human body, strict control is necessary regarding their concentration and leakage prevention measures. Table 1 below compares and summarizes the basic composition of the wedge material when electrodeposition precipitates are used and when corrosion products are used. [Table 1]

[0062] Next, the components and requirements of the repair kit used in the first and second embodiments described above will be listed and explained below.

[0063] 1. Aerosol generator The type of aerosol generator 10 can be arbitrarily selected from ultrasonic, jet, or mesh types used in medical nebulizers and humidifiers, but it is preferable to use an ultrasonic type, which can easily generate aerosols on the order of microns continuously for a long period of time.

[0064] The basic requirements for the aerosol generator 10 are as follows: 1-1. Aerosol particle size The diameter of the electrolyte particles contained in the aerosol is preferably MMD ≤ 10 μm in terms of the median mass diameter (MMD), as described above, but it is even more preferable that MMD ≤ 5 μm. When the electrolyte particles meet this requirement, they remain in the air for a long time after spraying, facilitating even diffusion into the internal spaces S and S' to form an electrochemical circuit. Furthermore, the electrolyte particles can smoothly enter even through minute fatigue crack openings 5 ​​that only open on the order of microns even under maximum tensile load, promoting the formation of electrodeposited deposits or corrosion products on the crack surface. 1-2. Spraying ability The spraying capacity of the aerosol generator 10 is preferably 0.5 mL / min or more. This allows the electrolyte aerosol concentration in the internal space S,S' to be increased in a relatively short time in steps 1-5 or 2-5 described above, and to maintain a concentration above a certain level even during the standing period in the subsequent steps 1-6 or 2-6. 1-3. Capacity of the chemical tank The capacity of the chemical tank 11 depends on how many hours the electrolyte aerosol 17 is generated during the repair work, but it is preferably 20 mL or more, and more preferably 100 mL or more, so that replenishment of the electrolyte 16 during the repair is not necessary.

[0065] The following two additional mechanisms are envisioned for the aerosol generator 10. 1-4. Additional Mechanism 1 If there is concern about a shortage of CO2 or O2 in the electrochemical reaction within the internal spaces S and S', it is preferable to provide a separate mechanism (the ventilation means described above) that sprays and mixes carbon dioxide or oxygen into the electrolyte 16 or electrolyte aerosol 17. 1-5. Additional Mechanisms Part 2 If there is a concern that the electrolyte 16 may run out during the repair process due to the nature of the work or the waiting period, it is preferable to provide a separate mechanism to automatically replenish the electrolyte 16 from outside the chemical tank 11.

[0066] 1-6. Electrolyte Aerosol Concentration Regarding the electrolyte aerosol concentration within the internal spaces S and S', in steps 1-4 or 2-4 described above, the electrolyte aerosol concentration to be maintained within the internal spaces S and S' is a mass concentration of 10 g / m³. 3 Preferably, the mass concentration is 15 g / m³ or higher. 3 It is even more preferable that the above conditions are met.

[0067] 2. Electrolyte The type of electrolyte 16 used in the aerosol generator 10 is arbitrary, but considering various requirements such as i) dissolving a sufficient amount of electrolyte to form an electrochemical circuit in the internal spaces S,S', ii) dissolving components to generate electrodeposited deposits or corrosion products as wedge materials on the crack surface, and iii) ensuring safe construction without adverse effects on people even if the electrolyte aerosol 17 leaks and diffuses into the surroundings, it is preferable to use an electrolyte 16 based on seawater components as shown in Figure 4. For example, in the case of artificial seawater prepared using a commercially available metal corrosion test kit ("Aquamarine" (registered trademark) manufactured by Yashima Pharmaceutical Co., Ltd.), the weight concentrations of the main components are sodium chloride 2.35%, magnesium chloride 1.07%, sodium sulfate 0.39%, calcium chloride 0.15%, and potassium chloride 0.07%.

[0068] 3. Sealing means In the first embodiment described above, the sealing means 15 included in the repair set preferably consists of an airbag 15A that inflates when air is introduced, a hose 15B connected to the airbag, and an air pump (not shown) that supplies air to the airbag 15A through the hose 15B, as shown in Figure 5. The shape and dimensions of the airbag 15A are preferably such that when it is inflated to its maximum capacity under internal pressure, it fits almost seamlessly inside the closed cross-sectional structure 4. However, as shown in Figure 5(a) where a gap is present between the airbag 15A and the U-rib 2 at the top, it is permissible for a small gap to occur at the corners of the airbag 15A. The material of the airbag 15A is arbitrary, but it is preferable to use a highly flexible material such as resin, cloth, or rubber in order to facilitate insertion and removal through the through-hole 19. The material and shape of the hose 15B are arbitrary, but it is preferable to use a material (for example, resin or rubber) and shape that has a certain degree of rigidity in order to adjust it so that when the deflated airbag 15A is inserted through the hole 19, it will later inflate under internal pressure and be in contact with the closed cross-sectional structure 4 with almost no gaps. The airbag 15A or hose 15B shall be appropriately equipped with a sealing plug or sealing valve to maintain the airbag 15A inflated during repairs, or to deflate and fold it after the repairs are completed.

[0069] 4. Air supply piping, exhaust piping With regard to the outlet side air supply piping 12Ba, the inlet side air supply piping 12Bb, the inlet side exhaust piping 13Ba, and the outlet side exhaust piping 13Bb, the type of piping is arbitrary, but considering ease of installation on site, it is preferable to use resin hoses with appropriate flexibility.

[0070] 5. Current electrode When using galvanic electrodes (galvanic anode or galvanic cathode) as a means of applying a potential to promote electrochemical reactions in cracked areas, the potential and material are as shown in Table 1 above.

[0071] 6.External DC power supply When an external DC power supply is used as a means of applying a potential to promote electrochemical reactions in the crack, the electrodes connected to the crack side are as shown in Table 1 above. In both cases, whether a current is applied to promote the electrodeposition reaction or to promote the corrosion reaction, the electrode opposite to the electrode connected to the crack side is placed in the electrolyte aerosol 17, that is, in an appropriate position in the internal space S, S' filled with the electrolyte aerosol 17 (near the fatigue crack 5 if possible).

[0072] 7. 3D cover The shape and dimensions of the three-dimensional cover 18 in the second embodiment described above can be arbitrary, such as funnel-shaped or dome-shaped, but it is preferable to use the most suitable shape depending on the surface shape and extent of the structure to be repaired. The material can also be arbitrary, but considering the ease of installation on site, it is preferable to use a resin or rubber material that has a shape that conforms to the surface shape of the structure, or a shape that matches the surface shape of the structure, and it is preferable that the material be transparent or translucent so that the condition inside the three-dimensional cover 18 can be seen from the outside.

[0073] 8. Cover mounting means The cover mounting means 20 facilitates the attachment of the three-dimensional cover 18 to the surface of the structure. In the second embodiment described above, if a gap is likely to occur between the cracked main plate 1 or welded area and the three-dimensional cover 18, workability can be improved by joining the two using the cover mounting means 20. In particular, if the main plate 1 or welded area is made of a magnetic material such as steel, the three-dimensional cover 18 can be easily attached and detached by using the cover mounting means 20 which has magnets for joining to their surfaces. The opening of the three-dimensional cover 18 may be provided in the three-dimensional cover 18 itself or in the cover mounting means 20. Alternatively, a small gap formed between the three-dimensional cover 18 or the cover mounting means 20 and the surface of the structure when the three-dimensional cover 18 is attached to the surface of the structure may be used as the opening.

[0074] 9. Filter 21 The type and configuration of the filter 21 should be determined appropriately according to the type and amount of aerosol. The filter 21 should be selected to reliably adsorb and remove electrolyte particles in aerosols with a particle size on the order of microns. If it is difficult to directly connect the inlet exhaust piping 13Ba to the closed cross-section structure 4 or the three-dimensional cover 18, a configuration may be used in which aerosols leaking to the outside of the closed cross-section structure 4 or the three-dimensional cover 18 are sucked in and filtered or adsorbed. In that case, commercially available air purifiers or air vacuum devices can also be used.

[0075] <<<Comparative Examples and Examples>>> <Comparative Examples and Examples Using Notched Flat Test Specimens> To verify the effectiveness of the fatigue crack repair method and repair kit according to the present invention, a crack propagation test was conducted using a notched steel plate test specimen. Details of the test, including the test specimen, testing machine, and test conditions, are as follows. • Test specimen: A 5mm thick flat plate made of JIS SM490A steel was used, with a 10mm long x 0.3mm wide notch machined into the center (see Figure 9). • Testing machine: Electro-hydraulic servo-type fatigue testing machine (manufactured by Shimadzu Corporation, dynamic capacity 98kN) • Test conditions: (a) During normal testing: Nominal stress range Δσ in the cross section without notches n The load was set to 104 MPa, stress ratio R=0 (perfectly unidirectional on the tensile side), and load frequency f=5.1 Hz. (b) During beach mark formation: While keeping the maximum stress the same as in (a), the minimum stress was increased, reducing the stress range to about 1 / 4 of that in (a), and the load frequency f = 13 Hz. The timing of beach mark formation and the number of loading cycles were set appropriately while measuring the surface crack length.

[0076] Figure 10 summarizes the conditions and results of the comparative example and the example in which crack propagation tests were conducted. First, the comparative example was tested in air with the metal base material as is, without using an electrolyte aerosol. On the other hand, the example embodies the second embodiment shown in Table 1 and Figure 6, focusing on two cracks that originate and propagate from both ends of a notch. Conductive zinc foil tape was attached as a galvanic anode 14 to the top and bottom of the notch on the back side (the side where the repair work was performed) of the flat plate test specimen. A general view photograph of the back side of the test specimen immediately after the tape was attached is shown in Figure 11.

[0077] In the crack propagation test of this embodiment, a load was first applied 96,000 times in an atmosphere without spraying the electrolyte aerosol 17 to propagate the fatigue crack 5 to a crack length of 0.31 mm, resulting in the state shown in Figure 6. Subsequently, a three-dimensional cover 18 was attached to cover the crack opening on the back side. The three-dimensional cover 18 was made of a transparent resin mask attached to a medical nebulizer, which will be described later. For attaching the three-dimensional cover 18, a magnetic hook and neodymium magnets were used as the cover attachment means 20. The aerosol generator 10 was connected to the three-dimensional cover 18 via the air supply piping 12B (outlet side air supply piping 12Ba and inlet side air supply piping 12Bb). The crack propagation test was conducted while filling the inside of the three-dimensional cover 18 with the electrolyte aerosol 17. As the air supply piping 12B, a bellows-type flexible hose attached to a medical nebulizer, which will be described later, was used. Here, an overview photograph of the test system in this embodiment is shown in Figure 12.

[0078] The aerosol generator 10 used was the Comfort 3000 KU-500, a medical nebulizer manufactured by Shin-ei Kogyo Co., Ltd., which is commercially available. The main specifications are as follows. ·Atomization method: Ultrasonic method • Spray particle size: MMAD (Aerodynamic Median Mass Diameter) approximately 5.5 μm Furthermore, since artificial seawater aerosol was used as the electrolyte aerosol, its density ρ ≈ 1 g / cm³ 3 Therefore, we assumed that MMAD = ρMMD ≈ MMD (see below). • Chemical solution tank 11: The capacity of the main chemical solution cup is 100 mL, but as shown in Figure 12, an external tank with a capacity of 2 L was added and used. • Atomization rate: The average atomization rate during the test, calculated from the change in the liquid volume in the external tank, was 0.93 mL / min. Furthermore, artificial seawater (prepared using "Aquamarine" for metal corrosion testing, manufactured by Yashima Pharmaceutical Co., Ltd.) was used as the electrolyte for atomization. As mentioned above, artificial seawater is a liquid that readily forms electrochemical circuits and readily deposits hard electrodeposited materials on crack surfaces. · Air supply fan 12A: As the air supply fan 12A, the one built in the above aerosol generator 10 was used with the minimum air volume set.

[0079] The crack propagation test curves in the comparative example and the example are shown in Fig. 13. In the comparative example with the metal base material as it is, it broke at the number of load cycles N = 529296 as shown in Fig. 10, whereas in the example where the second embodiment of the present invention was realized using artificial seawater as the electrolytic solution, after N = 3.84×10 6 cycles, the crack did not progress at all and completely stopped. Even after continuing the test, no change was observed, so this test ended once at N = 8.448×10 6 cycles, the instruments for spraying the electrolytic solution aerosol were removed, and the nominal stress range Δσ n was increased from 104 MPa to 119 MPa and repeated loading was performed. However, since there was no change even at N = 9.216×10 6 cycles, the nominal stress range Δσ n was further increased from 119 MPa to 126 MPa and repeated loading was performed. As a result, it finally broke at N = 9.5186×10 6 cycles.

[0080] Here, magnified photographs of the fracture surfaces of the comparative example and the example are shown in Fig. 14(a) and Fig. 14(b) respectively. In both cases, the thickness of the test piece was 5 mm, the crack occurred from the notch end on the right side of the photograph, and then progressed in the left direction of the photograph with the repeated load.

[0081] The fracture surface of the comparative example (Figure 14(a)) is a typical fatigue fracture surface, with clearly visible elliptical beach marks formed at intervals on the textured metal matrix fracture surface. On the other hand, in the fracture surface of the example (Figure 14(b)), a prominent wedge layer (the dark-looking area) is continuously formed over a range of approximately 3.6 mm from the notch end. This is presumed to be due to the effect of an electrolyte aerosol using artificial seawater as the electrolyte, which caused a significant electrodeposition reaction (and some corrosion reaction) within the crack. The hard precipitates formed on the crack surface act as wedges, continuously and strongly compressing the crack surface of the matrix that attempts to close during unloading, resulting in the dark discoloration of the matrix fracture surface. Note that the textured metal matrix fracture surface extending to the left of the wedge layer in Figure 14(b) is a fatigue fracture surface formed when repeated loading was performed with the nominal stress range Δσn increased to 126 MPa in order to force fracture.

[0082] Figure 15 shows the number of load cycles N = 1.92 × 10⁻¹⁰ in the example. 5 This is an observation photograph of the area near the notch on the front side of the flat plate test specimen. At this point, the crack lengths are short in both cases: a1 = 1.45 mm on the left side of the notch and a2 = 2.19 mm on the right side of the notch. These cracks are extremely difficult to detect by normal visual inspection. However, by applying the artificial seawater aerosol described in the example, a significant amount of whitish electrodeposited deposits are formed in the crack area, as shown in the photograph, making it possible to easily detect the cracks by visual inspection. [Industrial applicability]

[0083] This invention can be used in any structure where fatigue cracks are a concern and require immediate on-site repair, including ships, offshore structures, bridges, vehicles, aircraft, and machine tools. Furthermore, by using an electrolyte aerosol, it can be used in any structure where it is necessary to repair a large number of fatigue cracks in a confined space all at once. [Explanation of Symbols]

[0084] 1 Main plate (base material) 3. Fillet welding (welded area) 4 Closed section structure 5. Fatigue cracks 10 Aerosol generator 12A Air intake fan (electrolyte aerosol supply means) 12B Air supply piping (electrolyte aerosol supply means) 13A Exhaust Fan 13B Exhaust piping 14. Anode 15 Sealing means 16 Electrolyte 17 Electrolyte Aerosol 18 3D cover 19. Opening (through hole) 21. Filter (aerosol processing means) S-shaped closed cross-sectional structure interior space S' Internal space of the 3D cover

Claims

1. Select locations in the metal base material or welded joints of a structure where fatigue cracks are suspected to occur, or where such fatigue cracks have occurred. If the selected location is inside a closed cross-sectional structure having an internal space, an opening is made in a part of the closed cross-sectional structure and an electrolyte aerosol, which is a mixture of electrolyte and gas, is supplied to fill the internal space. If the selected location is a structure other than the closed cross-section structure, a three-dimensional cover having an opening to cover the fatigue crack, or capable of forming an opening, is installed on the surface of the structure, and the electrolyte aerosol is supplied to fill the internal space formed inside the installed three-dimensional cover. A method for repairing fatigue cracks, characterized in that the propagation of fatigue cracks is suppressed by the wedge effect of electrodeposited deposits or corrosion products generated when the electrolyte aerosol supplied to the internal space and / or the electrolyte formed by the condensation of the electrolyte aerosol adheres to the base material or the welded part and the crack surface of the fatigue crack.

2. The method for repairing fatigue cracks according to claim 1, characterized in that the particle size of the electrolyte aerosol is 10 μm or less in terms of median mass diameter (MMD).

3. The method for repairing a fatigue crack according to claim 1, characterized in that, when attempting to generate the electrodeposited deposit or corrosion product within the fatigue crack, carbon dioxide or oxygen is mixed with the electrolyte aerosol and supplied to the internal space, or, if the fatigue crack is a plate-thickness crack, air is introduced into the fatigue crack from the crack opening of the plate-thickness crack along with the supply of the electrolyte aerosol.

4. The method for repairing a fatigue crack according to claim 1, characterized in that, when attempting to generate the corrosion products within the fatigue crack, a corrosive gas is mixed with the electrolyte aerosol and supplied to the internal space.

5. The method for repairing fatigue cracks according to claim 1, characterized in that, while the state in which the electrolyte aerosol is contained in the internal space is maintained, a galvanic anode having a lower potential than the base metal of the base material at the selected location or the weld metal of the weld, or a galvanic cathode having a higher potential than the base metal of the weld, or an external DC power supply, is used to continuously apply a current in a direction that promotes the electrodeposition reaction or corrosion reaction to the base material or the weld at the selected location.

6. The method for repairing fatigue cracks according to claim 5, characterized in that, when a current is passed in a direction that promotes the electrodeposition reaction, the galvanic anode is provided near the base metal or the weld metal at a selected location of the structure, which has a base metal containing at least one of iron, steel, aluminum alloy, magnesium alloy, and titanium alloy, and a cathode potential is applied to the base metal or the weld metal.

7. The method for repairing fatigue cracks according to claim 5, characterized in that, when applying a current in a direction that promotes the corrosion reaction, the galvanic cathode is provided near the base metal or the weld metal at a selected location, and an anode potential is applied to the base metal or the weld metal.

8. The method for repairing fatigue cracks according to claim 5, characterized in that electrodes are provided near the base material or the weld at the selected location, the negative electrode of the external DC power supply is connected to the base material metal or the weld metal side when a current is passed in the direction that promotes the electrodeposition reaction, and the positive electrode of the external DC power supply is connected to the base material metal or the weld metal side when a current is passed in the direction that promotes the corrosion reaction, and in either case the opposite electrode is placed in the electrolyte aerosol.

9. The method for repairing a fatigue crack according to claim 1, characterized in that, when the selected location is inside the closed cross-sectional structure, a sealing means is installed in the internal space of the closed cross-sectional structure to prevent the passage of the electrolyte aerosol, thereby limiting the section to which the electrolyte aerosol is supplied.

10. The method for repairing fatigue cracks according to claim 1, characterized in that, if there are multiple fatigue cracks, the three-dimensional cover used is of a size that covers all of the fatigue cracks.

11. The method for repairing fatigue cracks according to claim 1, characterized in that the three-dimensional cover is attached to the surface of the structure using a cover attachment means.

12. The method for repairing fatigue cracks according to claim 1, characterized in that electrolyte particles in the electrolyte aerosol filling the internal space are adsorbed and / or removed, and the gas is released to the outside.

13. The method for repairing a fatigue crack according to claim 1, characterized in that the location of the fatigue crack in the structure is identified by the electrodeposited deposit, which exhibits a white color due to the wedge effect of the electrodeposited deposit, thereby suppressing the propagation of the fatigue crack.

14. A repair set for use in a fatigue crack repair method according to any one of claims 1 to 13, An aerosol generator that mixes an electrolyte and a gas to generate an electrolyte aerosol, A fatigue crack repair kit characterized by comprising an electrolyte aerosol supply means for supplying the electrolyte aerosol generated by the aerosol generator into the internal space.

15. The fatigue crack repair set according to claim 14, characterized in that the aerosol generator generates the electrolyte aerosol using artificial seawater or seawater containing calcium and magnesium as the electrolyte.

16. The fatigue crack repair set according to claim 14, further comprising a three-dimensional cover to cover fatigue cracks used when the selected area has a structure other than a closed cross-section structure, wherein the three-dimensional cover allows the internal condition to be visually inspected from the outside.

17. A repair set used in the method for repairing fatigue cracks described in claim 11, The fatigue crack repair set according to claim 16, further comprising a cover mounting means having a magnet for joining the three-dimensional cover to the surface of the structure.

18. A repair set used in the fatigue crack repair method described in claim 9, The structure further comprises sealing means installed in the internal space of the closed cross-section structure, The sealing means is characterized by being flexible, as described in claim 14, for repairing fatigue cracks.

19. A repair set used in the fatigue crack repair method described in claim 12, The fatigue crack repair set according to claim 14, further comprising an aerosol treatment means for treating the generated electrolyte aerosol and discharging it to the outside.

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