Method and apparatus for predicting the fatigue limit of impact-corrosion bond damaged structures

Abstract

The present invention discloses a method and apparatus for predicting the fatigue limit of an impact-corrosion coupled damaged structure based on the critical distance method. The method calculates a three-dimensional fractal dimension based on a planar image of the impact-corrosion coupled damaged structure, calculates a theoretical stress concentration factor based on the damage situation of the damaged structure, establishes a stress gradient correction function for the root of the damaged notch based on the three-dimensional fractal dimension and the theoretical stress concentration factor, searches a pre-generated material-critical distance table to obtain the critical distance corresponding to the current material of the damaged structure to be predicted, and establishes a three-dimensional model of the damaged structure to be predicted. When the error between the corrected stress corresponding to the critical point and the fatigue limit of the smooth specimen is within a predetermined threshold, the external load on the three-dimensional model becomes the fatigue limit of the damaged component to be predicted. The prediction process of the present invention is relatively simple, requires only linear elasticity analysis, and has relatively high prediction accuracy.

Description

[Technical Field]

[0001] This invention relates to a technology for predicting the fatigue limit of damaged structures, and more particularly to a method and apparatus for predicting the fatigue limit of impact-corrosion bonded damaged structures. [Background technology]

[0002] During service, structures often face complex working environments and are subjected to different types of damage, significantly reducing their load capacity, fatigue life, and reliability, potentially leading to failure of structural integrity. Therefore, accurately assessing the fatigue limits of structures in complex service environments and ensuring they meet the requirements of their use, such as fatigue life and high reliability, is a critical issue during construction. Some critical structures during construction are difficult to avoid being subjected to external impacts, easily forming stress concentrations, residual stresses, and microstructural damage at the impact sites. Simultaneously, the structure is affected by factors such as humidity and acidity in the working environment, leading to further corrosion, and generally forming microscopic etch pits on the material surface. The combined effect of impact and corrosion creates crack sources in these damaged notches, which rapidly expand under fatigue load, greatly reducing the structure's fatigue performance and potentially leading to high-cycle failures.

[0003] Scholars both domestically and internationally have proposed several mathematical models for predicting the fatigue limit of notches, such as the mean stress model proposed by Neuber, the Peterson formula corrected by Peterson based on it, the critical distance theory proposed by Taylor, the worst-case notch model proposed by Hudak, and the weakest loop theory proposed by Weibull based on statistical data. Each of these models has its own advantages and disadvantages in predicting the fatigue of notched parts, and when applied to notches with specific damage types, it is also necessary to analyze the characteristics of the notch, obtain characteristic parameters of the notch characteristics, and incorporate them into the model. The damage morphology and microscopic characteristics of bonded damage notches are the main factors that affect their fatigue strength, and these are related to the type and size of the external object, the impact velocity and angle, the material of the structure, the corrosion environment, and the length of time. Currently, there are relatively few fatigue performance studies that comprehensively consider impact-corrosion bonded damage notches. For such joint damage notches, it is common practice to predict the fatigue limit by calculating the theoretical stress concentration factor based on the macro-notch morphology. However, this method cannot consider the effect of the notch stress gradient, resulting in low prediction accuracy, and it also fails to consider the effect of joint damage. Therefore, there is currently no simple and accurate method for predicting the fatigue limit of joint damage notches in construction projects. [Overview of the Initiative]

[0004] Objective of the Invention: The present invention aims to provide a method and apparatus for predicting the fatigue limit of impact-corrosion bond damage structures with higher prediction accuracy, in order to address the problems that exist in the prior art.

[0005] Technical proposal: According to a first aspect, the present invention provides a method for predicting the fatigue limit of an impact-corrosion bonded damaged structure based on critical distance, and this method for predicting the fatigue limit of an impact-corrosion bonded damaged structure is This involves calculating the three-dimensional fractal dimension of the damage structure to be predicted based on a planar image of the damage structure to be predicted for impact-corrosion bonding, and Calculating the theoretical stress concentration factor of the damaged notch based on the damage status of the damaged structure to be predicted, Establishing a stress gradient correction function for the root part of the damage notch of the damage structure to be predicted based on the three-dimensional fractal dimension and the theoretical stress concentration factor; Searching a pre-generated material - critical distance table to obtain the critical distance corresponding to the material of the damage structure to be predicted currently; Establishing a three-dimensional model of the damage structure to be predicted, and when the error between the corrected stress corresponding to the critical point and the fatigue limit of the smooth sample is a preset threshold value, setting the external load on the three-dimensional model as the fatigue limit of the damaged member to be predicted. This includes:

[0006] Furthermore, calculating the three-dimensional fractal dimension of the damage structure based on the planar image of the damage structure to be predicted for impact - corrosion combination specifically includes: Obtaining a planar image of the damage area of the damage structure to be predicted for impact - corrosion combination and converting it into a grayscale image; Establishing a three-dimensional grayscale surface with the coordinates of the located pixel as the planar coordinates and the grayscale value of the located pixel as the z - axis coordinate for the grayscale image; Calculating the three-dimensional fractal dimension of the three-dimensional grayscale surface as the three-dimensional fractal dimension of the damage structure to be predicted. This includes:

[0007] Furthermore, calculating the theoretical stress concentration factor of the damage notch based on the damage condition of the damage structure to be predicted specifically includes: Calculating the radius of curvature of the root part of the notch according to the following formula based on the damage depth and damage width of the damage structure to be predicted:

Equation

Equation

[0010] , includes representing the theoretical stress concentration factor.

[0008] Furthermore, the stress gradient correction function specifically is [Number] In the formula, φ(r) is the stress gradient correction function, K T represents the theoretical stress concentration factor, D is the three-dimensional fractal dimension, r is the distance from any point on the bisector of the notch root to the notch root, and a is a constant.

[0009] Optionally, the critical distance is Randomly select a plurality of impact-corrosion combined damage structures with any damage situation that is the same as the damage structure material to be predicted, Obtain the fatigue limit σ0 of the smooth sample that is the same as the damage structure material to be predicted and the fatigue limits σ1, σ2,... of the selected plurality of damage structures through tests, Establish a three-dimensional model for each selected damage structure, and obtain the stress distributions σ s,1 (r), σ s,2 (r),... on the bisector of the notch root of each damage structure through finite element analysis, For the stress distributions σs ,1 (r), σ s,2 (r),... of each damage structure, correct them with the stress gradient correction function to obtain the corrected stress distributions σ e,1 (r), σ e,2 (r),..., σ e,1 (r) = σ0, σ e,2 (r) = σ0,... and solve the values of r as r1, r2, ··· respectively, It is obtained by a method of calculating twice the average value of r1, r2, ··· as the critical distance L0.

[0010] Furthermore, establishing the three-dimensional model of the damage structure to be predicted and setting the external load on the three-dimensional model as the fatigue limit of the damage member to be predicted when the error between the corrected stress at the critical point and the fatigue limit of the smooth sample is a preset threshold specifically is Based on the damage width and depth of the damaged structure to be predicted, a three-dimensional finite element model is established. Initial external load values ​​are added to the three-dimensional model, and the stress distribution σ along the bisector of the notch root is determined by finite element analysis. s The objective is to obtain (r), where r is the distance from any point on the bisector of the notch base to the notch base, Stress distribution σ s (r) is corrected with the stress gradient correction function, and the corrected stress σ at the critical point is obtained. e (L0), L0 is obtained as the critical distance, Corrected stress σ at the aforementioned critical point e (L0) and determining whether the error in the fatigue limit of a smooth sample of the same material is within a predetermined threshold, In that case, the currently applied external load will be used as the fatigue limit of the damaged member being predicted, Otherwise, the method includes adjusting the value of the applied external load until the error between the corrected stress at the critical point and the fatigue limit of the smooth sample reaches a predetermined threshold, and then setting this external load as the fatigue limit of the damaged member being predicted.

[0011] According to a second aspect, the present invention further provides a fatigue limit prediction device for impact-corrosion bonded damaged structures based on critical distance, the fatigue limit prediction device for impact-corrosion bonded damaged structures, A three-dimensional fractal dimension verification module for calculating the three-dimensional fractal dimension of a damage structure to be predicted based on a planar image of the damage structure to be predicted for impact-corrosion bonding, A theoretical stress concentration coefficient verification module for calculating the theoretical stress concentration coefficient of a damaged notch based on the damage status of the damaged structure to be predicted, A stress gradient correction function verification module for establishing a stress gradient correction function at the root of a damaged notch in a damaged structure to be predicted, based on the three-dimensional fractal dimension and the theoretical stress concentration coefficient, A material-critical distance table for storing the critical distance of each material, wherein the critical distance is the distance from a point on the bisector of the notch root to the notch root when the stress in any damaged structure is the fatigue limit of a smooth sample of the material, A search module for obtaining the critical distance corresponding to the material of the currently predicted damage structure by searching a material-critical distance table, A three-dimensional model of the damage structure to be predicted is established, and the error between the corrected stress at the critical point and the fatigue limit of the smooth sample is a predetermined threshold. The external load of the three-dimensional model is a fatigue limit confirmation module that becomes the fatigue limit of the damaged member to be predicted, and the corrected stress is a fatigue limit confirmation module in which the stress distribution calculated in the three-dimensional model is corrected using the stress gradient correction function.

[0012] According to a third aspect, the present invention further provides a fatigue limit prediction device for impact-corrosion bond damage structures based on critical distance, comprising a processor and an executable program stored in memory and operable on the processor, wherein the processor, upon executing the executable program, realizes the method according to the first aspect.

[0013] According to a fourth aspect, the present invention further provides a storage medium including a computer-executable program, which, when executed by a computer processor, is used to perform the method described in the first aspect.

[0014] Compared to conventional techniques, the beneficial effect of this invention is that it predicts the fatigue limit of a bonded damage notch based on the critical distance method by linking bonded damage parameters and damage notch gradients, the prediction process is relatively simple, requires only linear elasticity analysis, and has relatively high prediction accuracy. [Brief explanation of the drawing]

[0015] [Figure 1] This is a flowchart of the fatigue limit prediction method for impact-corrosion bond damage structures based on critical distance according to the present invention. [Figure 2] This is a schematic diagram of the structure of a fatigue limit prediction device for impact-corrosion bond damage structures based on critical distance according to the present invention. [Figure 3]This is a schematic diagram of the structure of a fatigue limit prediction device for impact-corrosion bond damage structures based on critical distance according to the present invention. [Figure 4] This is a diagram illustrating the damage morphology of impact-corrosion bond damage structure sample 2-2. [Figure 5] This is a three-dimensional grayscale surface view of impact-corrosion bond damage structure sample 2-2. [Modes for carrying out the invention]

[0016] The following clearly and completely describes the technical concepts in the embodiments of the present invention, linking them to the accompanying drawings. Clearly, the described embodiments represent only a portion of the embodiments of the present invention, not all of them. All other embodiments obtained by those skilled in the art without any creative effort based on the embodiments of the present invention are all within the scope of protection of the present invention.

[0017] The terms "first," "second," etc., used in the specification, claims, and accompanying drawings of this invention are not intended to describe a specific order, but rather to distinguish different subjects. Where the term "examples" is used herein, it means that certain features, structures, or properties described in conjunction with the examples may be included in at least one example of the invention. This phrase appearing in various places in the specification does not necessarily refer to the same example, nor are they mutually exclusive, independent, or alternative examples. Those skilled in the art will understand, both explicitly and implicitly, that the examples described herein can be combined with other examples.

[0018] Example 1 An embodiment of the present invention provides a method for predicting the fatigue limit of an impact-corrosion bond damage structure based on critical distance, and includes the following steps, as shown in Figure 1.

[0019] S101 calculates the three-dimensional fractal dimension of the damage structure to be predicted based on a planar image of the damage structure to be predicted for impact-corrosion bonding.

[0020] The three-dimensional fractal dimension is a mathematical tool for describing the complexity of a three-dimensional fractal set. The dimension value, i.e., the three-dimensional fractal dimension, is obtained by recursively partitioning the three-dimensional fractal set and then calculating the size proportions of the partitions at each level.

[0021] In some embodiments, step S101 may be implemented in the following steps.

[0022] S1011, a planar image of the damaged area of ​​the damaged structure to be predicted for impact-corrosion bonding is acquired and converted into a grayscale image. The planar image pixel size may be set to 256 × 256, or it may be divided into 256 × 256 meshes, and the grayscale average value of each mesh may be used as the mesh grayscale value.

[0023] S1012, a three-dimensional grayscale surface is established using the grayscale image, with the coordinates of the pixels being located as planar coordinates and the grayscale value of the pixels being located as the z-axis coordinate.

[0024] S1013, the three-dimensional fractal dimension of the three-dimensional grayscale surface is calculated as the three-dimensional fractal dimension of the damage structure to be predicted. The three-dimensional fractal dimension may be calculated using the box-counting method and fractal software, or it may be calculated using other methods. The box-counting method is a commonly used method for calculating the three-dimensional fractal dimension. The pixel space on which the three-dimensional grayscale surface is located is a large cube of 256 × 256 × 256. The large cube is divided into boxes of small cubes with side length k, and it is important to note that 256 / k is an integer. Thus, the cube is (256 / k) 3 The image is divided into boxes, and a MATLAB program is built to calculate the number of boxes that cover the grayscale image surface, which is Nr(k). A set of Nr(k) is obtained by changing the size of the box's side length k, and then pair the points.

number

number

[0025] S102 calculates the theoretical stress concentration factor of the damaged notch based on the damage status of the damaged structure to be predicted.

[0026] The theoretical stress concentration factor is the ratio of the maximum actual stress to the nominal stress at the root of the notch, obtained from elastic theory under ideal elastic conditions. In some embodiments, step S102 may be obtained by the following method.

[0027] S1021, Based on the damage depth and damage width of the damage structure to be predicted, the radius of curvature of the notch root is calculated according to the following formula:

number

number

[0028] S103. Based on the three-dimensional fractal dimension and the theoretical stress concentration coefficient, a stress gradient correction function is established for the root of the damaged notch of the damaged structure to be predicted.

[0029] Of these, the stress gradient correction function is, specifically,

number

[0030] S104, the pre-generated material-critical distance table is searched to obtain the critical distance corresponding to the material of the currently predicted damaged structure.

[0031] Of these, the critical distance is twice the distance from the root of the notch to the point on the bisector of any damaged notch, provided that the maximum principal stress at a point on the bisector of the notch is the fatigue limit of a smooth member of the same material. The critical point is a point on the bisector of the root of the notch, at a distance of L0 / 2 from the root of the notch. A material-critical distance table has been generated in advance, and the critical distance is related only to the material and is ideally a single constant, meaning that the critical distances for any damaged structure of the same material are all equal. When generating critical distances, ideally, any damaged structure experiment can be used to calculate the critical distance. However, in reality, due to various error conditions such as simulation errors, the critical distance calculated for different damage structures fluctuates within a small range. Therefore, to improve prediction accuracy, multiple impact-corrosion bond damage structures with arbitrary damage conditions identical to the damage structure material to be predicted are randomly selected. The fatigue limit σ0 of a smooth sample identical to the damage structure material to be predicted and the fatigue limits σ1, σ2, ... of the selected multiple damage structures are obtained by testing. A three-dimensional model is established for each selected damage structure, mesh division is performed, mesh refinement is performed near the notch, material attributes are given to the finite element model, edge conditions are added to the model, and the load conditions in the real environment are simulated. The stress distribution σ on the bisector of the notch root of each damage structure is obtained by finite element analysis. s,1 (r), σ s,2 (r),... obtain the stress distribution σ of each damaged structure s,1 (r), σ s,2 (r),... are corrected with a stress gradient correction function, and the corrected stress distribution σ e,1 (r) = σ s,1 (r)φ(r),σ e,2 (r) = σ s,2(r)φ(r),... obtained, σ e,1 (r) = σ0, σ e,2 Let (r) = σ0, ... Solve for the values ​​of r, r1, r2, ... and find the critical distance to be twice the average value of r1, r2, ...

number

[0032] In S105, a three-dimensional model of the damage structure to be predicted is established. If the error between the corrected stress at the critical point and the fatigue limit of the smooth sample is a predetermined threshold, the external load on the three-dimensional model becomes the fatigue limit of the damaged member to be predicted.

[0033] In some embodiments, step S105 specifically includes the following steps:

[0034] S1051, Based on the damage width and damage depth of the predicted damaged structure, a three-dimensional finite element model is established, the mesh is divided, the mesh is subdivided at the root of the notch, initial external load values ​​are added to the three-dimensional model, and the stress distribution σ on the bisector of the root of the notch is determined by finite element analysis. s We obtain (r), where r is the distance from any point on the bisector of the notch base to the notch base.

[0035] S1052, stress distribution σ s (r) is corrected with the stress gradient correction function, and the corrected stress σ at the critical point is obtained. e We obtain (L0 / 2), where L0 is the critical distance.

[0036] S1053, Correction stress σ of the critical point e It is determined whether the error between (L0) and the fatigue limit σ0 of the same material smooth sample is within a predetermined threshold.

[0037] S1054, if so, the currently applied external load is taken as the fatigue limit of the damaged member being predicted.

[0038] S1055, otherwise, the value of the applied external load is adjusted until the error between the corrected stress at the critical point and the fatigue limit of the smooth sample reaches a predetermined threshold, and this external load is taken as the fatigue limit of the damaged member being predicted.

[0039] Example 2 Figure 2 is a schematic diagram of a fatigue limit prediction device for impact-corrosion bond damage structures based on critical distance according to an embodiment of the present invention. This system may be implemented in software and / or hardware form, and the device may be installed in terminal equipment. This device is A three-dimensional fractal dimension verification module 201 for calculating the three-dimensional fractal dimension of a damage structure to be predicted based on a planar image of the damage structure to be predicted for impact-corrosion bonding, A theoretical stress concentration coefficient verification module 202 for calculating the theoretical stress concentration coefficient of a damaged notch based on the damage status of the damaged structure to be predicted, A stress gradient correction function verification module 203 for establishing a stress gradient correction function at the root of a damaged notch in a damaged structure to be predicted, based on the three-dimensional fractal dimension and the theoretical stress concentration coefficient, A material-critical distance table 204 for storing the critical distance L0 of each material, A search module 205 for searching a material-critical distance table to obtain the critical distance corresponding to the material of the currently predicted damage structure, A fatigue limit confirmation module 206 is provided for establishing a three-dimensional model of the damaged structure to be predicted, and for the external load of the three-dimensional model to become the fatigue limit of the damaged member to be predicted, provided that the error between the corrected stress at the critical point and the fatigue limit of the smooth sample is a predetermined threshold, wherein the corrected stress is the stress obtained by correcting the stress distribution calculated in the three-dimensional model using the stress gradient correction function.

[0040] Of these, the three-dimensional fractal dimension verification module 201 specifically, An image conversion unit for acquiring a planar image of the damaged area of ​​a damaged structure targeted for impact-corrosion bonding and converting it to a grayscale image, A grayscale surface establishment unit for establishing a three-dimensional grayscale surface using the grayscale image, with the coordinates of the pixels being located as planar coordinates and the grayscale value of the pixels being the z-axis coordinate, The system includes a three-dimensional fractal dimension calculation unit for calculating the three-dimensional fractal dimension of the three-dimensional grayscale surface as the three-dimensional fractal dimension of the damage structure to be predicted.

[0041] The aforementioned theoretical stress concentration coefficient verification module 202 is, specifically, Based on the damage depth and damage width of the damage structure to be predicted, the radius of curvature of the notch root is calculated according to the following formula:

number

number

[0042] The critical distance is obtained by the critical distance calculation module, and the critical distance calculation module, Randomly select multiple impact-corrosion bond damage structures of arbitrary damage conditions that are the same as the damaged structural material to be predicted. The tests obtained the fatigue limit σ0 of a smooth sample, which is the same as the material of the damaged structure being predicted, and the fatigue limits σ1, σ2, ... of several selected damaged structures. A three-dimensional model of each selected damage structure was established, and the stress distribution σ along the bisector of the notch root of each damage structure was determined by finite element analysis. s,1 (r), σ s,2 (r),... obtain and Each damaged structural stress distribution σ s,1 (r), σs,2 (r),... are corrected with a stress gradient correction function, and the corrected stress distribution σ e,1 (r), σ e,2 (r), ... obtained, σ e,1 (r) = σ0, σ e,2 Let (r) = σ0, ... and solve for the values ​​of r, r1, r2, ... r1, r2, ... twice the average value is the critical distance

number

[0043] The fatigue limit confirmation module 206, specifically, Based on the damage width and depth of the damaged structure to be predicted, a three-dimensional finite element model is established. Initial external load values ​​are added to the three-dimensional model, and the stress distribution σ along the bisector of the notch root is determined by finite element analysis. s A model establishment unit for obtaining (r), where r is the distance from any point on the bisector of the notch root to the notch root, Stress distribution σ s (r) is corrected with the stress gradient correction function, and the corrected stress σ at the critical point is obtained. e A stress correction unit for obtaining (L0), where L0 is the critical distance of the stress correction unit, Corrected stress σ at the aforementioned critical point e A determination unit for determining whether the error in the fatigue limit of a smooth sample of the same material as (L0) is within a predetermined threshold, If the judgment unit result is so, a first judgment unit is used to determine the fatigue limit of the damaged member to be predicted based on the currently applied external load, If the judgment unit result is otherwise, the value of the applied external load is adjusted, and the execution model establishment unit returns to the judgment unit until the error between the corrected stress at the critical point and the fatigue limit of the smooth sample is within a preset threshold. This includes a second judgment unit that sets the external load at this point as the fatigue limit of the damaged member to be predicted.

[0044] The apparatus according to an embodiment of the present invention may be used to carry out the method according to Embodiment 1 of the present invention, and will have the functions and beneficial effects corresponding to the method of carrying out the method. For details that are not described, please refer to Embodiment 1, and no further description will be given.

[0045] It should be noted that, in the above-described embodiment of the decision-making device, the included units and modules are merely distinguished based on functional logic, and are not limited to the above distinctions; they only need to be able to realize the corresponding function. Furthermore, the specific names of each functional unit are for the purpose of facilitating their distinction from one another and are not intended to limit the scope of protection of the present invention.

[0046] The embodiments described above are illustrative only, and modules described as separate components may or may not be physically separate, and components shown as modules may or may not be physical modules, that is, they may be located in one place or distributed across multiple network modules. Some or all of these modules may be selected as needed to achieve the objectives of this embodiment. As will be clearly evident to those skilled in the art, each embodiment may be implemented in the form of software and a necessary general-purpose hardware platform, or of course, in hardware alone, as long as it can perform the function or role.

[0047] Example 3 Figure 3 is a schematic diagram of the structure of a device according to Embodiment 3 of the present invention, and this embodiment of the present invention provides a service for realizing the method of Embodiment 1 of the present invention. As shown in Figure 3, this device may include a memory 301 in which a computer-executable program is stored, and a processor 302 coupled to the memory 301, the processor 302 being used to call the computer-executable program stored in the memory 301 and to perform the steps in the method described in Embodiment 1.

[0048] Memory 301 may include a computer system-readable medium in the form of volatile memory, such as random access memory (RAM) and / or high-speed cache memory. The device may further include other removable / non-removable, volatile / non-volatile computer system storage media. For example, memory 301 may be used to read and write to a non-removable, non-volatile magnetic medium (commonly called a hard disk drive). A program / utility having a set (at least one) program module may be stored in memory 301, for example, such a program module may include, but is not limited to, an operating system, one or more application programs, other program modules and program data, and each of these examples or some kind of combination may include the implementation of a network environment. The computer-executable program of the program module generally performs the functions and / or methods in the embodiments described in the present invention.

[0049] Code for a computer-executable program to perform the operations of the present invention may be written in one or more programming languages ​​or a combination thereof, and the programming languages ​​include object-oriented programming languages ​​such as Java, Smalltalk, and C++, and further include general-purpose process-oriented programming languages ​​such as the "C" language or similar programming languages.

[0050] The processor 302 executes various functional applications and data processing by running the program stored in the memory 301, thereby realizing, for example, the method according to Embodiment 1 of the present invention.

[0051] Example 4 Embodiments of the present invention provide a storage medium containing a computer-executable program, which is used to perform the method of Embodiment 1 when executed by a computer processor.

[0052] The storage medium in the embodiments of the present invention may employ any combination of one or more computer-readable media. The computer-readable media may be a computer-readable signal medium or a computer-readable storage medium. The computer-readable storage medium may be, but is not limited to, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any combination thereof. More specific examples (not exhaustive) of computer-readable storage media include electrical connections having one or more wires, portable computer magnetic disks, disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fibers, portable compact magnetic disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination thereof. In this specification, the computer-readable storage medium may be any tangible medium containing or storing a program, which may be used by or in conjunction with an instruction execution system, apparatus, or device.

[0053] Code for a computer-executable program to perform the operations of the present invention may be written in one or more programming languages ​​or a combination thereof, and the programming languages ​​include object-oriented programming languages, such as Java, Smalltalk, and C++, and further include general-purpose process-oriented programming languages, such as the "C" language or similar programming languages. The program code may run entirely on the user's computer, partially on the user's computer, run as a single standalone software package, run partially on the user's computer, partially on a remote computer, or run entirely on a remote computer or server. If a remote computer is involved, the remote computer may be connected to the user's computer or to an external computer (for example, connected via the Internet using an Internet Service Provider) on any type of network, including a local area network (LAN) or a wide area network (WAN).

[0054] Of course, a storage medium containing a computer-executable program according to an embodiment of the present invention may not be limited to the operations of the above-described method, but may also perform related operations in any embodiment of the present invention.

[0055] The present invention will be experimentally verified below.

[0056] The material used in the experiment was a 13Cr stainless steel structure, and precast damage experiments were conducted under different impact and corrosion environments. The external damage parameters were steel balls with diameters of 2 mm and 3 mm, made of GGr15 material. Two impact velocities were used: 200 m / s and 300 m / s. Corrosion damage parameters: The corrosive solution was a 5% NaCl solution by mass fraction, with dilute H2SO4 added to adjust the solution's pH to 4 ± 0.2. Corrosion times included 24 h, 48 h, and 96 h, and the corrosion temperature was a constant 40 degrees Celsius. Corrosion interval: the solution was replaced once every 48 hours.

[0057] The experiment includes three types: impact only, corrosion followed by impact, and impact followed by corrosion. Using sample 2-2 as an example, the bond damage cutout image is as shown in Figure 4, the grayscale surface of the image is as shown in Figure 5, and the three-dimensional fractal dimension of the image is calculated to be 2.2276.

[0058] Using sample 2-2 as an example, when calculating the damage width l = 1.097 mm, damage depth d = 0.553 mm, and radius of curvature ρ = 0.544 at the base of the notch, the theoretical stress concentration factor K is calculated. T = 3.016. The stress gradient correction function is,

number

number

[0059] [Table 1] Using this invention, the fatigue limit of bond damage notches was predicted, and the overall trend of the prediction results was consistent with the experimental results, all within a ±20% error range.

Claims

1. A method for predicting the fatigue limit of an impact-corrosion bond damage structure based on critical distance, This involves calculating the three-dimensional fractal dimension of the damage structure to be predicted based on a planar image of the damage structure to be predicted for impact-corrosion bonding, and Calculating the theoretical stress concentration factor of the damaged notch based on the damage status of the damaged structure to be predicted, Based on the three-dimensional fractal dimension and the theoretical stress concentration coefficient, a stress gradient correction function is established for the root of the damaged notch of the damaged structure to be predicted. Search the pre-generated material-critical distance table to find the critical distance L corresponding to the material of the currently predicted damage structure. ０ To obtain, A three-dimensional model of the damage structure to be predicted is established, and the error between the corrected stress corresponding to the critical point and the fatigue limit of the smooth sample is a predetermined threshold. In this case, the external load on the three-dimensional model becomes the fatigue limit of the damage structure to be predicted, and the critical point is located at the base of the notch, on the bisector of the base of the notch, from the base of the notch to L. ０ A method for predicting the fatigue limit of an impact-corrosion bond damaged structure, characterized in that the points are 2 / 2 apart, and the corrected stress is the stress obtained by correcting the stress distribution calculated in the three-dimensional model with the stress gradient correction function.

2. Specifically, calculating the three-dimensional fractal dimension of a damaged structure based on a planar image of the damaged structure to be predicted for impact-corrosion bonding involves the following: This involves obtaining a planar image of the damaged area of ​​the damaged structure targeted for impact-corrosion bonding prediction, and converting it to a grayscale image. The grayscale image is used to establish a three-dimensional grayscale surface, where the coordinates of the pixels within the image are planar coordinates, and the grayscale values ​​of the pixels within the image are the z-axis coordinates. A method for predicting the fatigue limit of an impact-corrosion bonded damage structure based on critical distance, as described in claim 1, comprising calculating the three-dimensional fractal dimension of the three-dimensional grayscale surface as the three-dimensional fractal dimension of the damage structure to be predicted.

3. Specifically, calculating the theoretical stress concentration factor of a damaged notch based on the damage status of the damaged structure to be predicted involves: Based on the damage depth and damage width of the damage structure to be predicted, the radius of curvature of the notch root is calculated according to the following formula: [Number 15] In the formula, ρ represents the radius of curvature at the base of the notch, l represents the width of the damage, and d represents the depth of the damage. Based on the radius of curvature of the notch root, the theoretical stress concentration coefficient of the damaged structure to be predicted is calculated according to the following formula: [Number 16] In the formula, K Ｔ The method for predicting the fatigue limit of an impact-corrosion bond damage structure based on critical distance according to claim 1, characterized in that it includes representing a theoretical stress concentration factor.

4. The stress gradient correction function is, specifically, [Number 17] And, In the equation, φ(r) is the stress gradient correction function, and K Ｔ The method for predicting the fatigue limit of an impact-corrosion bond damage structure based on a critical distance according to claim 1, characterized in that represents the theoretical stress concentration factor, D is the three-dimensional fractal dimension, r is the distance from any point on the bisector of the notch root to the notch root, and a is a constant.

5. The aforementioned critical distance is, Randomly select multiple impact-corrosion bond damage structures of arbitrary damage conditions that are the same as the damaged structural material to be predicted. The test showed that the fatigue limit σ of the smooth sample is the same as that of the damaged structural material being predicted. ０ and the fatigue limit σ of multiple selected damaged structures １ , σ ２ , . . . obtain, Establish a three-dimensional model of each selected damaged structure, and use finite element analysis to obtain the stress distributions σ ｓ，１ (r), σ ｓ，２ (r) , . . . obtain, Stress distribution σ of each damaged structure ｓ，１ (r), σ ｓ，２ (r) The stress gradient correction function is used to correct the stress distribution σ. ｅ，１ (r), σ ｅ，２ (r) , . . . obtained, s ｅ，１ (r) = s ０ ,s ｅ，２ (r) = s ０ , . . . The value of r １ ,r ２ Solve each of the following: r １ ,r ２ The critical distance L is twice the average value of ... ０ A method for predicting the fatigue limit of an impact-corrosion bond damage structure based on the critical distance described in claim 1, obtained by a method of calculation as follows.

6. In the above-mentioned case, where a three-dimensional model of the damage structure to be predicted is established, and the error between the corrected stress corresponding to the critical point and the fatigue limit of the smooth sample is a predetermined threshold, setting the external load on the three-dimensional model as the fatigue limit of the damaged member to be predicted means, specifically, Based on the damage width and depth of the damaged structure to be predicted, a three-dimensional finite element model is established. Initial external load values ​​are added to the three-dimensional model, and the stress distribution σ along the bisector of the notch root is determined by finite element analysis. ｓ The objective is to obtain (r), where r is the distance from any point on the bisector of the notch base to the notch base, Stress distribution σ ｓ (r) is corrected with a stress gradient correction function, and the corrected stress σ at the critical point is obtained. ｅ (L ０ To obtain (2), Correction stress σ at the critical point ｅ (L ０ / 2) To determine whether the error between the fatigue limit of a smooth sample of the same material and the error is within a predetermined threshold, In that case, the currently applied external load will be used as the fatigue limit of the damaged member being predicted, Otherwise, the method for predicting the fatigue limit of an impact-corrosion bonded damaged structure based on critical distance, characterized in that it includes adjusting the value of the applied external load until the error between the corrected stress at the critical point and the fatigue limit of the smooth sample becomes a predetermined threshold, and setting this external load as the fatigue limit of the damaged member to be predicted.

7. A fatigue limit prediction device for impact-corrosion bond damage structures based on critical distance, A three-dimensional fractal dimension verification module for calculating the three-dimensional fractal dimension of a damage structure to be predicted based on a planar image of the damage structure to be predicted for impact-corrosion bonding, A theoretical stress concentration coefficient verification module for calculating the theoretical stress concentration coefficient of a damaged notch based on the damage status of the damaged structure to be predicted, A stress gradient correction function verification module for establishing a stress gradient correction function at the root of a damaged notch in a damaged structure to be predicted, based on the three-dimensional fractal dimension and the theoretical stress concentration coefficient, Critical distance L for each material ０ Materials for memorizing - critical distance table and A search module for obtaining the critical distance corresponding to the material of the currently predicted damage structure by searching a material-critical distance table, A fatigue limit verification module for establishing a three-dimensional model of the damage structure to be predicted, and for setting the external load of the three-dimensional model as the fatigue limit of the damage structure to be predicted when the error between the corrected stress at the critical point and the fatigue limit of a smooth sample is a predetermined threshold, wherein the critical point is on the bisector of the root of the notch from the root of the notch to L ０ A fatigue limit prediction device for an impact-corrosion bond damage structure, characterized by including a fatigue limit confirmation module, which is a point 2 / 2 away from the object, and the corrected stress is the stress obtained by correcting the stress distribution calculated in the three-dimensional model with the stress gradient correction function.

8. The stress gradient correction function is, specifically, [Number 18] And, In the equation, φ(r) is the stress gradient correction function, and K Ｔ The fatigue limit prediction device for impact-corrosion bond damage structure based on critical distance according to claim 7, characterized in that represents the theoretical stress concentration factor, D is the three-dimensional fractal dimension, r is the distance from any point on the bisector of the notch root to the notch root, and a is a constant.

9. A fatigue limit prediction device for an impact-corrosion bond damaged structure based on critical distance, comprising a processor and an executable program stored in memory and operable on the processor, wherein the processor, upon executing the executable program, implements the method according to any one of claims 1 to 6.

10. A storage medium containing a program that can be executed on a computer, A storage medium characterized in that the computer-executable program, when executed by a computer processor, is used to perform the method described in any one of claims 1 to 6.

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