Structure life extension method, and structure life extension system

Abstract

To provide a structure life extension method capable of simply extending the life of a structure in a short time.SOLUTION: According to one aspect of the present invention, a method for extending the life of a structure made of steel includes the steps of: searching for target fatigue cracks that occur in the structure; acquiring information on the target fatigue cracks for the target fatigue cracks extracted in a step for searching for the target fatigue cracks; and determining the amount of an injection agent to be injected into the target fatigue cracks on the basis of the acquired information on the target fatigue cracks and information representing the relation between information on fatigue cracks acquired in advance and the amount of the injection agent.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present disclosure relates to a method for extending the life of a structure and a system for extending the life of a structure. [Background technology]

[0002] As structural design methods shift from those that aim to prevent fatigue damage to those that are damage-tolerant, development of methods to extend fatigue crack life is underway. Examples of methods for extending fatigue life include injecting a paste containing alumina particles into the fatigue crack surface, or injecting a corrosion accelerator to forcibly deposit corrosion products. These methods are known to promote fatigue crack closure, but no design method based on detailed mechanisms has been established.

[0003] For example, Patent Document 1 discloses a method for predicting the behavior of fatigue cracks at opening and closing by analysis using the finite element method. Specifically, it describes that in the process of simulating crack opening and closing, contact pressure is generated between opposing elements when the gap between the elements becomes equal to or less than a critical gap, which is a value greater than 0. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-135275 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the prediction method described in Patent Document 1, the behavior of fatigue cracks when they close differs in some respects from the actual phenomenon, and the behavior when repeated loads are applied has not been verified. Therefore, when the prediction method described in Patent Document 1 is applied to a method for extending the life of a structure, there are problems such as the time required for analysis that takes into account the actual phenomenon.

[0006] Therefore, it is desirable to provide a method for extending the life of a structure that can easily extend the life of the structure in a short period of time. [Means for solving the problem]

[0007] One aspect of the present disclosure is a method for extending the life of a structure made of steel, comprising the steps of: searching for a target fatigue crack that has occurred in the structure; acquiring information about the target fatigue crack for the target fatigue crack extracted in the step of searching for the target fatigue crack; and determining the amount of injection agent to be injected into the target fatigue crack based on the acquired information about the target fatigue crack and information representing the relationship between the previously acquired information about the fatigue crack and the amount of injection agent. [Effects of the Invention]

[0008] A method for extending the lifespan of a structure according to one aspect of the present disclosure can easily extend the lifespan of a structure in a short period of time. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a schematic diagram of an analysis model according to an embodiment. [Figure 2] FIG. 1 is a schematic diagram illustrating the properties of an orthotropic material implemented in an analysis model according to an embodiment. [Figure 3] 1 is a flowchart showing the procedure of a fatigue crack propagation life prediction method according to an embodiment. [Figure 4] 1 is a flowchart showing the steps of a method for extending a life span of a structure according to an embodiment. [Figure 5] 10 is a flowchart showing the steps of a method for extending the life of a structure according to another embodiment. [Figure 6] FIG. 10 is a diagram for explaining information showing the relationship between previously acquired information about fatigue cracks and the amount of injection agent in a method for extending the life of a structure according to another embodiment. [Figure 7] 1 is a schematic diagram of a terminal in a life extension system for a structure according to one embodiment. FIG. [Figure 8] FIG. 2 is a front view of an analytical model in the embodiment. [Figure 9] FIG. 2 is a side view of an analytical model in the embodiment. [Figure 10] 1 is a graph showing the relationship between crack length and fatigue crack propagation life in Example 1. [Figure 11] 10 is a graph showing the relationship between crack length and fatigue crack propagation life in Example 2. [Figure 12] 10 is a graph showing the relationship between crack length and fatigue crack propagation life in Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0010] Non-limiting embodiments of the present invention will be described below with reference to the drawings. In the drawings, identical or corresponding members or components are designated by identical or corresponding reference symbols. Further, duplicate descriptions of identical or corresponding members or components will be omitted below. Furthermore, in the drawings, members or components are not necessarily drawn to scale. Therefore, those skilled in the art can arbitrarily determine specific dimensions by referring to the following non-limiting embodiments. Furthermore, the following embodiments are illustrative and do not limit the invention. Furthermore, features and combinations thereof in the embodiments are not necessarily essential to the invention.

[0011] <Fatigue crack propagation life prediction method> Fig. 1 is a schematic diagram of an analytical model according to one embodiment, Fig. 2 is a schematic diagram illustrating the properties of an orthotropic material implemented in the analytical model according to one embodiment, and Fig. 3 is a flowchart showing the steps of a fatigue crack propagation life prediction method according to one embodiment. The fatigue crack propagation life prediction method of this embodiment is a method for predicting fatigue crack propagation life when fatigue crack closure treatment is performed using numerical analysis. Examples of fatigue crack closure treatment include injecting a paste containing particles such as alumina particles into the fatigue crack surface, or injecting a corrosion accelerator such as nitric acid to forcibly deposit corrosion products (rust).

[0012] 1 to 3, the fatigue crack propagation life prediction method of this embodiment includes the steps of: preparing an analytical model 1 having a notch 11; applying a load to the analytical model 1 multiple times using elastic-plastic analysis to simulate a process of propagating a crack 12 by a predetermined length (step S1); simulating a process of increasing the load to open the crack 12 and expand the crack surface 13 so that opposing crack surfaces 13 of the analytical model 1 are more likely to come into contact with each other (step S2); and simulating a process of applying a load to the analytical model 1 multiple times using elastic-plastic analysis after the process of expanding the crack surface 13 to simulate a process of propagating the crack 12 again (step S3). Furthermore, in the fatigue crack propagation life prediction method of this embodiment, the crack surface elements of the analytical model 1 are made of an orthotropic material only in the process of simulating the process of expanding the crack surface 13, as shown in FIG.

[0013] When a fatigue crack is closed, materials such as rust deposited by a paste or corrosion accelerator injected into the fatigue crack come into contact with the crack surface. In the fatigue crack propagation life prediction method of this embodiment, the crack surface elements of the analysis model 1 are made of orthotropic material only in the process simulating the process of expanding the crack surface 13. Therefore, unlike the contact between crack surface elements and rigid surfaces that occurs when the analysis model is symmetrical, for example, the crack surface elements come into contact with each other. Therefore, the fatigue crack propagation life prediction method of this embodiment can reproduce actual phenomena with high accuracy and predict the fatigue crack propagation life.

[0014] Each step will be described in detail below. In the fatigue crack propagation life prediction method of this embodiment, for example, analysis by the finite element method (FEM) can be used.

[0015] (Process to simulate the crack propagation process) The fatigue crack propagation life prediction method of this embodiment includes the steps of preparing an analytical model 1 having a notch 11 as shown in FIG. 1 and applying a load to the analytical model 1 multiple times using elastic-plastic analysis to simulate the process of propagating a crack 12 by a predetermined length. The analytical model 1 corresponds to the object of analysis, and the notch 11 corresponds to the generated fatigue crack. In the step of simulating the process of propagating the crack 12, examples of material models implemented in the analytical model 1 include material models of steel, aluminum alloy, etc. The analytical model 1 is prepared by setting the shape, dimensions, mechanical properties of the material, etc. of the object of analysis. In addition, the load and stress ratio, for example, are set as loading conditions. The number of times a load is applied to the analytical model 1 can be set depending on the material model, etc. implemented in the analytical model.

[0016] In this step, it is assumed that the crack 12 propagates in a direction perpendicular to the load application direction F, and a cubic element of about 50 μm is placed as the smallest element near the crack propagation region on the crack surface 13.

[0017] (Process to simulate the process of expanding the crack surface) The fatigue crack propagation life prediction method of this embodiment includes a step of simulating a process of increasing the load, opening the crack 12, and expanding the crack surfaces 13 so that the opposing crack surfaces 13 of the analysis model 1 are more likely to come into contact with each other. Moreover, only in the step of simulating the process of expanding the crack surfaces 13, the crack surface elements of the analysis model 1 are made of an orthotropic material. This step corresponds to the behavior when a fatigue crack is closed.

[0018] As shown in Figure 2, the orthotropic elastic modulus Eyy of the orthotropic material in a direction perpendicular to the crack surface 13 is smaller than the orthotropic elastic modulus Exx of the orthotropic material in one direction parallel to the crack surface 13 and the orthotropic elastic modulus Ezz of the orthotropic material in a direction perpendicular to that direction. Because the orthotropic material has the property of being easily deformed in the direction perpendicular to the crack surface 13, the effect of changes in the stress and strain state around the crack tip can be reduced compared to expanding a crack surface element with an isotropic elastic modulus that has high omnidirectional rigidity without introducing an orthotropic material. Therefore, the fatigue crack propagation life prediction method of this embodiment can reproduce actual phenomena with higher accuracy and predict fatigue crack propagation life.

[0019] In the process of simulating the process of expanding the crack surface 13, the crack surface elements can be made expandable by heat or plastic deformation. This allows the orthotropic material to easily deform in directions perpendicular to the crack surface 13, thereby reducing the effects of changes in the stress and strain states around the crack tip compared to a case where an orthotropic material is not used and a crack surface element with an isotropic elastic modulus with high omnidirectional rigidity is deformed by heat input or plastic deformation. Therefore, the fatigue crack propagation life prediction method of this embodiment can reproduce actual phenomena with higher accuracy and predict the fatigue crack propagation life.

[0020] In the process simulating the process of expanding the crack surface, for example, a load and a stress ratio are set as the load conditions for opening the crack 12. The load in this process is set to the maximum load of the load set in the process simulating the process of propagating the crack.

[0021] (Process to simulate the process of crack re-propagation) The fatigue crack propagation life prediction method of this embodiment includes a step of simulating the process of expanding the crack surface 13, followed by a step of applying a load to the analysis model 1 multiple times using elastic-plastic analysis to simulate the process of re-propagating the crack 12. This step corresponds to the behavior of a fatigue crack propagating after a fatigue crack closure treatment has been applied to the fatigue crack. In this step, the same material model as that used in the step of simulating the crack propagation process described above is implemented in the analysis model 1. In other words, in this step, the crack surface elements of the analysis model 1 are not made of orthotropic material.

[0022] The load and stress ratio set in the process of simulating the crack propagation process are the same as those set in the process of simulating the crack re-propagation process, which allows the fatigue crack propagation life prediction method of this embodiment to reproduce actual phenomena with higher accuracy and predict the fatigue crack propagation life.

[0023] <Methods for extending the life of structures> 4 is a flowchart showing the steps of a method for extending the life of a structure according to one embodiment. The method for extending the life of a structure according to this embodiment is a method for extending the life of a structure made of steel. As shown in FIG. 4, the method for extending the life of a structure according to this embodiment includes the steps of: searching for fatigue cracks that have occurred in the structure (step S11); measuring the length of the fatigue crack and the load imposed by the structure and calculating an estimated remaining life of the structure based on the measurement results (step S12); calculating the volume of the grout to be injected into the fatigue crack based on the estimated remaining life (step S13); injecting the grout into the fatigue crack (step S14); and verifying the life extension effect using the fatigue crack propagation life prediction method according to this embodiment (step S15).

[0024] In the method for extending the life of a structure according to this embodiment, the fatigue crack propagation life prediction method according to this embodiment can accurately reproduce actual phenomena and predict the fatigue crack propagation life in order to verify the life extension effect. Furthermore, based on the prediction results, it is possible to select the optimal mass and type of grout to be injected into the fatigue crack, thereby extending the life of the structure.

[0025] Each step will be described in detail below.

[0026] (process for detecting fatigue cracks) The method for extending the life of a structure according to this embodiment includes a step of detecting fatigue cracks that have occurred in the structure. Examples of the structure include components such as the boom of a shovel. Methods for detecting fatigue cracks that have occurred in the structure include visual inspection, ultrasonic flaw detection, non-destructive testing using radiation, and the like.

[0027] (Process for calculating the estimated remaining life of a structure) The method for extending the life of a structure according to this embodiment includes measuring the length of a fatigue crack and the load imposed by the structure, and calculating the estimated remaining life of the structure based on the measurement results. The length of the fatigue crack can be measured, for example, by ultrasonic testing or non-destructive testing using radiation. The load imposed by the structure can be measured, for example, by measurements using strain gauges or digital image correlation (DIC). The estimated remaining life of the structure can be calculated by elastic-plastic analysis based on the measured length of the fatigue crack and the load imposed by the structure.

[0028] In this step, it is not necessary to measure the length of the fatigue crack and the load due to the structure. That is, the method for extending the life of a structure according to this embodiment may include a step of measuring the length of the fatigue crack and a step of measuring the load due to the structure, separate from this step. Furthermore, instead of the step of measuring the load due to the structure, it may include a step of obtaining the load in advance by analysis based on the design data, CAD data, etc. of the structure.

[0029] (Step of calculating the volume of the injectate) The method for extending the life of a structure according to this embodiment includes a step of calculating the volume of the injection agent to be injected into the fatigue crack based on the estimated remaining life. The calculation of the mass of the injection agent can be performed by setting the desired life based on the estimated remaining life, changing the set value of the expansion amount of the crack surface of the analytical model according to the set life, and simulating the process of expanding the crack surface.

[0030] Here, the ideal injection amount (ideal value) that maximizes the lifespan of the analytical model is obtained. However, in this process, a volume of the injection agent less than the ideal value may be calculated to slightly extend the lifespan, taking into account the cost of the injected material. This reduces material costs. If the actual injection amount is greater than the ideal value, the injection agent may overflow from the cracks. However, considering the standardization of the injection process, a volume of the injection agent greater than the ideal value may be calculated in this process so that the injection agent does not overflow from the cracks. This reduces the required skill level when the injection process is performed manually and shortens the operation time. Furthermore, even when the injection process is performed semi-automatically or automatically by a work robot or the like, fine adjustment of the injection amount is not required, simplifying the work robot.

[0031] (Step of injecting injection agent) The method for extending the life of a structure according to this embodiment includes a step of injecting a filler into a fatigue crack. The filler may be a paste containing a solid component and a liquid oil component, or an oxidizing agent. This reduces the amount of shape displacement at the opening or closure of the crack due to the rust or other substances deposited by the paste or oxidizing agent in the fatigue crack. Therefore, the method for extending the life of a structure according to this embodiment can suppress the occurrence of further fatigue cracks in the structure after use, thereby further extending the life of the structure.

[0032] The solid content of the paste is preferably fine particles, and the hardness of the fine particles is preferably greater than the hardness of the structure.

[0033] Examples of the fine particles contained in the paste 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. One or more of these may be used as the fine particles contained in the paste.

[0034] The particle size of the fine particles contained in the paste is preferably smaller than the distance between the opposing surfaces of the fatigue crack, so that the space between the opposing surfaces of the fatigue crack can be sufficiently filled with paste 6.

[0035] Examples of the liquid oil contained in the paste include salad oil and industrial oil.

[0036] Examples of oxidizing agents include nitric acid, hydrochloric acid, sulfuric acid, and other rust-generation accelerators. In the step of injecting the grout, the surface facing the fatigue crack may be oxidized with the oxidizing agent, and then rust conversion may be performed with a rust converter. This converts the red rust generated by the oxidizing agent into black rust, thereby suppressing excessive rust growth.

[0037] Each step may be performed discontinuously. In particular, the step of searching for fatigue cracks may be performed discontinuously with the steps of calculating the estimated remaining life of the structure, calculating the volume of the grout, and injecting the grout. By dividing the steps into smaller steps and reducing the continuous work time per cycle of the method for extending the life of a structure of this embodiment, it is possible to utilize the time when the structure, such as a work machine, is not performing work.

[0038] In the method for extending the life of a structure according to this embodiment, in the step of injecting a filler, a load greater than the load applied during use may be applied to the structure in the direction in which a fatigue crack that has occurred in the structure opens, and the filler is then injected into the opened fatigue crack, followed by removing the load greater than the load applied during use. This allows the method for extending the life of a structure according to this embodiment to generate compressive stress in the fatigue crack, and to reduce the amount of shape displacement at the opening or closure of the crack by the filler applied to the fatigue crack or by a substance such as rust deposited by the filler. Therefore, the method for extending the life of a structure according to this embodiment can suppress further fatigue crack occurrence in the structure after use, thereby further extending the life of the structure.

[0039] When the structure is a component such as a boom of a shovel, the method for extending the life span of a structure according to this embodiment can be applied to the maintenance of the shovel.

[0040] Next, another example of the method for extending the life of a structure will be described. Fig. 5 is a flowchart showing the steps of the method for extending the life of a structure according to another embodiment, and Fig. 6 is a diagram for explaining information representing the relationship between previously acquired information about a fatigue crack and the amount of injection agent in the method for extending the life of a structure according to another embodiment. The method for extending the life of a structure according to the other embodiment is a method for extending the life of a structure made of steel. The method for extending the life of a structure according to the other embodiment includes a step of searching for a target fatigue crack that has occurred in the structure (step S21), a step of acquiring information about the target fatigue crack for the target fatigue crack extracted in the step of searching for the target fatigue crack (step S22), and a step of determining the amount of injection agent to be injected into the target fatigue crack based on the acquired information about the target fatigue crack and information representing the relationship between the previously acquired information about the fatigue crack and the amount of injection agent (step S23).

[0041] As a result, in another embodiment of the method for extending the life of a structure, the amount of injection agent to be injected into the target fatigue crack is determined based on information representing the relationship between the fatigue crack and the amount of injection agent obtained in advance, thereby making it possible to easily extend the life of the structure in a short period of time.

[0042] Each step will be described in detail below. The step of searching for a target fatigue crack is the same as the step of searching for a fatigue crack in the method for extending the life of a structure according to one embodiment, and therefore a description thereof will be omitted.

[0043] (Process for acquiring information about the target fatigue crack) Another embodiment of the method for extending the life of a structure includes a step of acquiring information about the target fatigue crack extracted in the step of searching for the target fatigue crack. Details of this step will be described later.

[0044] (Step of determining the amount of injectable agent) Another embodiment of a method for extending the life of a structure includes a step of determining the amount of injection agent to be injected into the target fatigue crack based on the acquired information about the target fatigue crack and information representing the relationship between the previously acquired information about the fatigue crack and the amount of injection agent.

[0045] First, the information representing the relationship between previously acquired information about fatigue cracks and the amount of filler will be described with reference to FIG. 6. The information representing the relationship between previously acquired information about fatigue cracks and the amount of filler may be a relational expression (FIG. 6) derived by performing a numerical analysis calculation evaluation using data such as the overall and local shapes of the welded joint, crack information, load information, life extension effect, and environmental factors, i.e., previously acquired information about fatigue cracks. This relational expression can be used to calculate the optimal amount of filler to be injected into the fatigue crack. This relational expression may be created using the fatigue crack propagation life prediction method described above.

[0046] The data used in the numerical analysis calculation evaluation, such as the overall and local shapes of the welded joint, crack information, load information, life extension effect, and environmental factors, were acquired in advance for fatigue cracks that occurred in a sample structure other than the target structure for the life extension method. Note that the example shown in Figure 6 assumes that crack B occurs in weld A of welded joint 10.

[0047] As the overall shape of the welded joint, the example shown in Fig. 6 shows the overall shapes of three types of welded joints 10. The overall shape of the welded joint 10 is, for example, B , medium plate thickness t m , main plate width W, gusset thickness t g , gusset length L, etc. In FIG. 6, the corresponding local shapes are shown below the overall shapes of the three welded joints 10. The local shapes of the welded joints 10 refer to the cross-sectional shape of the welded portion A of the welded joint 10. The local shapes of the welded joints 10 include elements such as throat thickness D, weld fillet angle θ, toe radius ρ, weld leg length l, weld fillet height h, and weld fillet width WB, for example.

[0048] The data of the overall shape of the weld joint 10 is, for example, visually confirmed, and the above-mentioned main plate thickness t BThe data on the local shape of the weld joint 10 can be obtained by measuring the shape of the weld joint 10, or by analyzing an image acquired by a camera. The data on the local shape of the weld joint 10 can be obtained by measuring the shape of the weld joint 10, or by analyzing an image acquired by a camera.

[0049] The crack information includes, for example, elements such as the crack extension direction (vertical upward, vertical downward, horizontal, etc.), crack depth a, crack opening width b, and crack length, as shown in Fig. 6. Crack information data can be obtained using a crack shape measuring instrument such as the RMG4015 crack depth meter manufactured by Nihon Matec Co., Ltd., or by analyzing images taken with a camera.

[0050] The load information is information about the load acting on the structure, and includes, for example, the direction of the load applied to the crack in the welded joint 10. The load information includes, for example, elements such as the axial load p, the shear force Q, and the bending load M. The load information data can be obtained by structural calculations using CAD shapes, etc.

[0051] The life extension effect of a structure means the life extension period, such as the number of years or months the structure's life is extended. For example, according to the above-mentioned formula, if the life extension effect is M years (for example, 5 years for a bridge), the amount of grout required is Ng.

[0052] The environmental factors include, for example, the temperature and humidity of the environment in which the structure is placed, the temperature of the structure, and the like.

[0053] The information about the target fatigue crack in this process and in the process of acquiring information about the target fatigue crack includes, for example, the overall and local shapes of the weld joint in the structure, crack information, load information, and environmental factors, and indicates actual measured values. Details of each piece of information are similar to the information about the previously acquired fatigue crack described above, so explanations are omitted. Furthermore, the method for acquiring information about the target fatigue crack in the process of acquiring information about the target fatigue crack is similar to the method for acquiring information about the previously acquired fatigue crack described above, so explanations are omitted.

[0054] It should be noted that when determining the amount of grout to be injected from crack information, it is not necessary to obtain all crack information. It is possible to set the amount of grout to be injected as long as crack information and load information can be obtained. Of course, if the overall shape and local shape of the welded joint can be understood, it is possible to determine the amount of grout to be injected that will have an effect on extending the lifespan with even greater precision.

[0055] The information about the target fatigue crack preferably includes the crack extension direction, crack opening width, or crack depth, among the above. Thus, in another embodiment of the method for extending the life of a structure, if data on at least the crack extension direction, crack opening width, or crack depth is acquired as information about the target fatigue crack, the amount of injection agent to be injected into the target fatigue crack can be determined based on previously acquired information indicating the relationship between the fatigue crack and the amount of injection agent, thereby making it possible to extend the life of the structure more easily and in a shorter time.

[0056] Among the above, the information about the target fatigue crack preferably includes information about the load acting on the structure. As a result, in the method for extending the life of a structure according to another embodiment, if at least load information data is acquired as information about the target fatigue crack, the amount of injection agent to be injected into the target fatigue crack can be determined based on previously acquired information expressing the relationship between the fatigue crack and the amount of injection agent, thereby making it possible to extend the life of the structure more easily and in a shorter time.

[0057] The data on the overall and local shapes of the welded joint, as well as the crack information, in the information on the target fatigue crack may be compared with the respective images in the information on the fatigue crack acquired in advance as described above, and data with a similar shape may be selected as each data related to the fatigue crack.

[0058] The information about the target fatigue crack may include the desired life extension effect of the structure. That is, in the step of determining the amount of injection agent, the amount of injection agent to be injected into the target fatigue crack may be determined based on the acquired information about the target fatigue crack and the previously acquired information representing the relationship between the information about the fatigue crack and the amount of injection agent, as well as the desired life extension effect of the structure. Here, the desired life extension effect of the structure means the desired life extension period, such as the number of years or months of life extension.

[0059] Thus, according to the method for extending the life of a structure of another embodiment, by substituting information about the target fatigue crack and data on the desired life extension effect of the structure into the above-mentioned relational equation (FIG. 6) for calculating the amount of injection agent created in advance, it is possible to calculate the amount of injection agent corresponding to the desired life extension effect of the structure. That is, in the method for extending the life of a structure of another embodiment, information about the target fatigue crack as measurement results and the desired life extension effect of the structure are input, and the amount of injection agent to be injected into the target fatigue crack can be obtained as output.

[0060] The information representing the relationship between the previously acquired information on fatigue cracks and the amount of grout can be a functional model, a lookup table, or a machine learning model trained using training data such as the overall and local shapes of the welded joint, crack information, load information, life extension effect, environmental factors, etc. The calculated value may be corrected or modified as necessary and then used as the output (amount of grout injected).

[0061] When the previously acquired information representing the relationship between the fatigue crack information and the amount of injectant is the above-mentioned machine learning model, the accuracy of the injectant injection amount (output) relative to the measurement results (input) can be improved by progressively increasing or correcting parameters through learning using actual data. Furthermore, the results of improvements and additions to the simulation model can be used to correct the database. This can improve the accuracy of the injectant injection amount (output) relative to the measurement results (input).

[0062] In the step of determining the amount of injectant, the estimated remaining life of the structure may be calculated based on information about the target fatigue crack, the desired structural life extension effect, and previously acquired information about the fatigue crack, and the amount of injectant to be injected into the target fatigue crack may be calculated based on the calculated estimated remaining life of the structure. The method for calculating the estimated remaining life of the structure is similar to the step of calculating the estimated remaining life of the structure in the structural life extension method according to one embodiment, and therefore a description thereof will be omitted. In this way, the amount of injectant to be injected into the target fatigue crack can be calculated by comparing the desired structural life extension effect with the estimated remaining life of the structure.

[0063] The information about the target fatigue crack includes the crack extension direction and the crack opening width. In the step of determining the amount of grout, the amount of grout may be determined based on the crack extension direction and the crack opening width without any calculation process. As a result, for example, when the crack extension direction is vertically upward, it tends to be difficult to inject grout. In this case, the structure life extension method of another embodiment can increase the amount of grout in such a case compared to when the crack extension direction is vertically downward. Furthermore, for example, when the crack opening width is relatively small, it tends to be difficult to inject grout. In this case, the structure life extension method of another embodiment can increase the amount of grout in such a case compared to when the crack opening width is relatively large. Therefore, in the structure life extension method of another embodiment, in such a case, the maximum possible amount of grout can be injected (taking into account the possibility of leakage as a result of attempted injection) without any calculation process, thereby more easily extending the life of the structure.

[0064] The information about the target fatigue crack may include crack location information, and the amount of grout may be determined based on the crack location information without any calculation process in the step of determining the amount of grout. This allows the amount of grout to be increased, for example, when a crack occurs in a location that requires work in a narrow space or at a relatively high position relative to the worker, compared to when the crack occurs at a location other than these. Therefore, in the method for extending the life of a structure according to another embodiment, in the above-mentioned cases, the maximum possible amount of grout can be injected to complete the work without any calculation process, thereby more easily extending the life of the structure.

[0065] In the step of determining the amount of injectant, the amount of injectant may be determined from among at least a first injection amount and a second injection amount greater than the first injection amount. This allows the method for extending the lifespan of a structure of another embodiment to extend the lifespan of the structure more easily and in a shorter time.

[0066] The grout is preferably any one selected from the group consisting of a paste containing a solid component and a liquid oil component, an oxidizing agent, a resin, a metal adhesive, and a metal plating. This allows the method for extending the lifespan of a structure according to another embodiment to extend the lifespan of the structure more easily and in a shorter time.

[0067] The paste containing the solid content and the liquid oil content and the oxidizing agent may be the same as those used in the method for extending the life of a structure according to an embodiment. The resin may be, for example, an epoxy resin.

[0068] When the grout is an oxidizing agent, the grout amount may be set to a value greater than the predetermined value if the temperature of the structure is lower than the reaction temperature of the oxidizing agent, thereby allowing the oxidizing agent to sufficiently form corrosion products even at a temperature where the chemical reaction of the oxidizing agent is difficult to occur.

[0069] <Structure life extension system> FIG. 7 is a schematic diagram of a terminal in a structure life extension system according to one embodiment. The structure life extension system of this embodiment is a system for extending the life of a steel structure. The structure life extension system of this embodiment includes a search unit that searches for a target fatigue crack that has occurred in the structure, and an acquisition unit that acquires information about the target fatigue crack for the target fatigue crack extracted by the search unit. The structure life extension system also includes an injection amount determination unit that determines the amount of injection agent to be injected into the target fatigue crack based on the information about the target fatigue crack acquired by the acquisition unit and previously acquired information representing the relationship between the fatigue crack and the amount of injection agent. With this configuration, the structure life extension system of this embodiment determines the amount of injection agent to be injected into the target fatigue crack based on previously acquired information representing the relationship between the fatigue crack and the amount of injection agent, thereby enabling the structure's life to be extended easily and quickly.

[0070] The search unit performs the step of searching for the target fatigue crack in the method for extending the life of a structure according to the other embodiment described above. The search unit may include an ultrasonic flaw detector or a non-destructive inspection device using radiation.

[0071] The acquisition unit performs the step of acquiring information about the target fatigue crack in the method for extending the life of a structure according to the other embodiment described above.

[0072] The injection amount determination unit performs the step of determining the amount of injection agent in the life extension method for a structure according to the other embodiment described above. The injection amount determination unit may include a calculation unit that calculates the amount of injection agent to be injected into the target fatigue crack based on the information about the target fatigue crack acquired by the acquisition unit and information indicating the relationship between the fatigue crack and the amount of injection agent acquired in advance.

[0073] The structure life extension system may include a terminal 30, as shown in Fig. 7. The terminal 30 is a terminal device used at any location by a user in charge of maintenance of the structure. The terminal 30 is not particularly limited, but may be, for example, a tablet terminal, a smartphone, or a personal computer. The terminal 30 may include a display unit, an input unit, a communication unit, a control unit, and a storage unit.

[0074] The display unit may display a screen 31 including input fields for information about the generated target fatigue crack, such as the overall and local shapes of the weld joint, crack information, load information, etc. (information about the target fatigue crack), and information about the desired life extension effect of the structure. The input unit may have a touch panel that also serves as the display of the display unit. The user can input this information into the input fields. Note that the input unit is not limited to a touch panel, and may also have a mouse, keyboard, operation buttons, etc. The display unit may also display the amount of injectant to be injected into the determined target fatigue crack. The memory unit may store the amount of injectant to be injected into the determined target fatigue crack. This makes it possible to instruct a serviceman, manager, work machine user, etc., about the amount of injectant to be injected into the determined target fatigue crack.

[0075] The system for extending the lifespan of a structure may include means for injecting the injectant. The injecting means may be an automated machine, a remote-controlled robot, etc. Alternatively, the injecting work may be performed by a human. [Example]

[0076] FIG. 8 is a front view of the analytical model in the example, and FIG. 9 is a side view of the analytical model in the example.

[0077] (Example 1) As shown in Figures 8 and 9, an analytical model 2 simulating a CT test piece with a notch 21 was prepared. The dimensions of the analytical model were 120 mm in length, 125 mm in width, and 6 mm in thickness. The minimum element size was 0.05 mm x 0.05 mm x 0.05 mm, and the element type was a hexahedral primary element. The general-purpose finite element analysis software "ADVENTURE Cluster 2022" was used for the analysis.

[0078] Using elastic-plastic analysis, a load of 10 kN at a stress ratio of 0.048 was applied 10 times to analytical model 2, and an analysis simulating the process of crack propagation (elastic-plastic fatigue crack propagation analysis) was performed (Step 1). The load was applied above the upper opening 22 in the loading direction F, which is perpendicular to the notch 21. The crack length was set to 0 mm at the test piece loading point, and was allowed to propagate to 39.8 mm.

[0079] Next, an analysis was performed to simulate the process of increasing the load, opening the crack, and expanding the crack surfaces so that the opposing crack surfaces of the analytical model could come into contact with each other (Step 2). At this time, the crack surface elements of the analytical model were made of orthotropic material with Eyy = 10 MPa and Exx = Ezz = 206000 MPa.

[0080] Finally, the crack surface elements of the analytical model were returned to their original state, and a load of 10 kN and a stress ratio of 0.048 was applied 10 times while the crack was allowed to propagate little by little, and an elastic-plastic fatigue crack propagation analysis was performed (Step 3). After the first elastic-plastic fatigue crack propagation analysis, all deformation, stress, strain, and internal variables were retained in the analysis. The fatigue crack propagation life was calculated based on the obtained analysis results.

[0081] (Example 2) In step 1, the analysis was carried out in the same manner as in Example 1, except that the crack length was allowed to grow to 29.4 mm, and the fatigue crack propagation life was calculated.

[0082] (Example 3) The analysis was performed in the same manner as in Example 1, except that in step 1, the applied load was set to 7.5 kN and the crack length was allowed to grow to 38.9 mm, and in step 3, the applied load was set to 7.5 kN, and the fatigue crack propagation life was calculated.

[0083] For each of Examples 1 to 3, graphs were quoted from the reference (Cut Atika PUTRI et al., "Retardation of Fatigue Crack Growth by Injection of Corrosion Accelerator," Proceedings of the Steel Construction Research Society, 2021, Vol. 28, No. 112, pp. 111-116, Fig. 9 (SP-2, SP-3, SP-4)) as experimental results for the same process as the one carried out and estimated results for the displacement range of the crack opening, and graphs were created by overlaying them on the calculation results (analysis results) for Examples 1 to 3.

[0084] Fig. 10 is a graph showing the relationship between crack length and fatigue crack propagation life in Example 1, Fig. 11 is a graph showing the relationship between crack length and fatigue crack propagation life in Example 2, and Fig. 12 is a graph showing the relationship between crack length and fatigue crack propagation life in Example 3. As shown in Figs. 10 to 12, it was confirmed that the fatigue crack propagation behavior can be reproduced with high accuracy by using the fatigue crack propagation life prediction method of this embodiment, taking into account the contact between crack surfaces when the fatigue crack is closed when a fatigue crack closure treatment is performed. [Explanation of symbols]

[0085] 1, 2 Analysis model 11, 21 Notch 12 Crack 13 Crack surface 22 Opening

Claims

1. A method for extending the life of a steel structure, comprising: a step of searching for a target fatigue crack that has occurred in the structure; a step of acquiring information about the target fatigue crack extracted in the step of searching for the target fatigue crack; A method for extending the life of a structure, comprising a step of determining the amount of injection agent to be injected into the target fatigue crack based on the acquired information about the target fatigue crack and information representing the relationship between the previously acquired information about the fatigue crack and the amount of injection agent.

2. 2. The method for extending the life of a structure according to claim 1, wherein the step of determining the amount of injection agent further determines the amount of injection agent to be injected into the target fatigue crack based on the desired effect of extending the life of the structure.

3. The life extension method according to claim 1 , wherein the information about the target fatigue crack includes the extension direction of the crack, the opening width of the crack, or the depth of the crack.

4. The life extension method according to claim 1 , wherein the information about the target fatigue crack includes information about a load acting on the structure.

5. The method for extending the lifespan of a structure according to claim 1 , wherein in the step of determining the amount of injection agent, the amount of injection agent is determined from among at least a first injection amount and a second injection amount greater than the first injection amount.

6. 2. The method for extending the life of a structure according to claim 1, wherein the injection agent is any one selected from the group consisting of a paste containing solids and liquid oil, an oxidizing agent, a resin, a metal adhesive, and metal plating.

7. the injectant is an oxidizing agent; 6. The method for extending the life of a structure according to claim 5, wherein in the step of determining the amount of injection agent, if the temperature of the structure is lower than the reaction temperature of the oxidizer, the amount of injection agent is set to a value greater than a specified value.

8. A system for extending the life of a steel structure, comprising: a search unit that searches for a target fatigue crack that has occurred in the structure; an acquisition unit that acquires information about the target fatigue crack extracted by the search unit; A life extension system for a structure having an injection amount determination unit that determines the amount of injection agent to be injected into the target fatigue crack based on information about the target fatigue crack acquired by the acquisition unit and information representing the relationship between the fatigue crack and the amount of injection agent acquired in advance.

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