Method and equipment for predicting fatigue limits of impact-corrosion coupled 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] The present invention relates to a fatigue limit prediction technique for damaged structures, and more particularly to a method and apparatus for predicting the fatigue limit of impact-corrosion coupled damaged structures. [Background technology]

[0002] During service, structures often face complex working environments and are subject to various damage patterns, significantly reducing their load-bearing capacity, fatigue life, and reliability, potentially resulting in the destruction of structural integrity. Therefore, accurately assessing the fatigue limit of structures in complex working environments and ensuring that the structures meet the fatigue life and high reliability requirements of their intended use is a key issue during construction. Some key structures in construction are unavoidably subjected to external impacts during operation, which can easily lead to stress concentrations, residual stresses, and microstructural damage at the impact sites. At the same time, the humidity, acidity, and baseness of the working environment can further corrode the structures, typically resulting in the formation of microscopic etch pits on the material surface. The combined effects of impact and corrosion can cause cracks to form at the damaged notches, which rapidly expand under fatigue loading, significantly reducing the fatigue performance of the structure and potentially resulting in high-cycle failures.

[0003] Scholars at home and abroad have proposed several mathematical models for predicting the fatigue limit of notches, including the mean stress model proposed by Neuber, the modified Peterson formula by Peterson, 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 merits and demerits in predicting the fatigue limit of notched components. When applying these models to specific notches with different damage types, it is necessary to analyze the notch characteristics and obtain their characteristic parameters for incorporation into the model. The damage morphology and microscopic characteristics of a bonded damage notch are key factors affecting its fatigue strength, and these are related to the type, size, impact velocity and angle of the object, the material of construction, the corrosive environment, and the duration of the corrosion. Currently, there are relatively few studies that comprehensively consider the fatigue performance of impact-corrosion bonded damage notches. For such bond damage notches, the fatigue limit is typically predicted by calculating the theoretical stress concentration factor based on the macroscopic notch shape. However, this method does not take into account the influence of the notch stress gradient, resulting in low prediction accuracy, and also does not take into account the influence of bond damage. Therefore, there is currently no simple and accurate method for predicting the fatigue limit of bond damage notches in engineering. Summary of the Invention

[0004] Object of the invention: The object of the present invention is to provide a method and apparatus for predicting the fatigue limit of impact-corrosion coupled damaged structures with higher prediction accuracy, in contrast to the problems existing in the prior art.

[0005] Technical solution: According to a first aspect, the present invention provides a fatigue limit prediction method for impact-corrosion coupled damaged structures based on critical distance, the fatigue limit prediction method for impact-corrosion coupled damaged structures includes: Calculating a three-dimensional fractal dimension of the damage structure of the impact-corrosion coupling prediction target based on a planar image of the damage structure of the prediction target; Calculating a theoretical stress concentration factor of the damaged notch based on the damage state of the damaged structure to be predicted; Establishing a stress gradient correction function at the root of the damaged notch of the damaged 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 a critical distance corresponding to the material of the currently predicted damaged structure; The method includes establishing a three-dimensional model of the damaged structure to be predicted, and when the error between the corrected stress corresponding to the critical point and the fatigue limit of the smooth specimen is a predetermined threshold, setting the external load on the three-dimensional model as the fatigue limit of the damaged component to be predicted.

[0006] Furthermore, the calculation of the three-dimensional fractal dimension of the damage structure based on the planar image of the damage structure of the impact-corrosion coupling prediction target specifically includes: obtaining a planar image of a damaged region of a damaged structure for which impact-corrosion coupling is to be predicted and converting the image into a grayscale image; Establishing a three-dimensional grayscale surface using the grayscale image with coordinates of the pixel located as plane coordinates and the grayscale value of the pixel located as z-axis coordinates; and calculating a three-dimensional fractal dimension of the three-dimensional grayscale surface as the three-dimensional fractal dimension of the damage structure to be predicted.

[0007] Furthermore, the calculation of the theoretical stress concentration factor of the damaged notch based on the damage state of the damaged structure to be predicted can be specifically performed as follows: Based on the damage depth and damage width of the damage structure to be predicted, calculate the curvature radius of the notch root according to the following formula:

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[0008] Furthermore, the stress gradient correction function is specifically expressed as follows:

number

[0009] Optionally, the critical distance is: Randomly select multiple impact-corrosion coupled damaged structures with any damage situation that is the same as the damaged structural material to be predicted; The fatigue limit of the smooth specimen σ0, which is the same as the damaged structure material to be predicted, and the fatigue limits σ1, σ2, ... of the selected damaged structures are obtained through the test. A three-dimensional model of each selected damaged structure was established, and the stress distribution σ on the bisector of the notch root of each damaged structure was calculated by finite element analysis. s,1 (r),σ s,2 (r),...and Each damaged structure stress distribution σs ,1 (r),σ s,2 (r),... are corrected using the stress gradient correction function, and the corrected stress distribution σ e,1 (r),σ e,2 (r),...and σ e,1 (r)=σ0,σ e,2 Let (r) = σ0,... and solve for the values ​​of r, r1, r2,... respectively. It is obtained by calculating twice the average value of r1, r2, etc. as the critical distance L0.

[0010] Furthermore, when the above-mentioned 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 specimen is a preset threshold, the external load on the three-dimensional model is set as the fatigue limit of the damage component to be predicted, specifically, Based on the damage width and damage depth of the damaged structure to be predicted, a three-dimensional finite element model is established, and an initial external load value is added to the three-dimensional model. The stress distribution σ on the bisector of the notch root is calculated by finite element analysis. s (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 by the stress gradient correction function, and the corrected stress σ at the critical point is calculated. e (L0), where L0 is the critical distance, The corrected stress σ at the critical point e (L0) and determining whether the error in the fatigue limit of a smooth specimen of the same material is within a predetermined threshold; If so, the currently applied external load is set as the fatigue limit of the damaged component to be predicted; If not, 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 specimen reaches a predetermined threshold, and the external load at this time is set as the fatigue limit of the damaged component to be predicted.

[0011] According to a second aspect, the present invention further provides a fatigue limit prediction device for an impact-corrosion coupled damaged structure based on a critical distance, the fatigue limit prediction device for an impact-corrosion coupled damaged structure comprising: a three-dimensional fractal dimension confirmation module for calculating a three-dimensional fractal dimension of the damage structure of the impact-corrosion coupling prediction target based on a planar image of the damage structure of the prediction target; a theoretical stress concentration coefficient confirmation module for calculating a theoretical stress concentration coefficient of the damaged notch based on the damage status of the damaged structure to be predicted; a stress gradient correction function confirmation module for establishing a stress gradient correction function at the root of the damaged notch of the damaged structure to be predicted based on the three-dimensional fractal dimension and the theoretical stress concentration factor; a material-critical distance table for storing the critical distance of each material, the critical distance being the distance from a point on the bisector of the notch root to the notch root when the stress in an arbitrary damaged structure is the fatigue limit of a smooth specimen of the same material; a search module for searching a material-critical distance table to obtain a critical distance corresponding to the material of the currently predicted damaged structure; The present invention also includes a fatigue limit confirmation module that establishes a three-dimensional model of the damaged structure to be predicted, and when the error between the corrected stress at the critical point and the fatigue limit of the smooth specimen is a preset threshold, the external load of the three-dimensional model becomes the fatigue limit of the damaged component to be predicted, and the corrected stress is a stress obtained by correcting the stress distribution calculated in the three-dimensional model using the stress gradient correction function.

[0012] According to a third aspect, the present invention further provides a fatigue limit prediction device for an impact-corrosion coupled damaged structure based on a critical distance, comprising a processor and an executable program stored in a memory and operable to run on the processor, wherein the processor, when executing the executable program, implements the method according to the first aspect.

[0013] According to a fourth aspect, the present invention further provides a storage medium containing a computer-executable program, the computer-executable program being used to perform the method of the first aspect when executed by a computer processor.

[0014] Compared with the prior art, the advantageous effect of the present invention is that the present invention combines the bond damage parameters and the damage notch gradient to predict the fatigue limit of the bond damage notch based on the critical distance method, the prediction process is relatively simple, only requires linear elastic analysis, and the prediction accuracy is relatively high. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a flowchart of a method for predicting fatigue limits of impact-corrosion coupled damaged structures based on critical distance according to the present invention. [Figure 2] 1 is a structural schematic diagram of a fatigue limit prediction device for impact-corrosion coupled damaged structures based on critical distance according to the present invention; FIG. [Figure 3]1 is a structural schematic diagram of a fatigue limit prediction device for impact-corrosion coupled damaged structures based on critical distance according to the present invention; FIG. [Figure 4] FIG. 1 is a diagram showing the damage morphology of impact-corrosion bond damaged structure sample 2-2. [Figure 5] FIG. 1 is a three-dimensional grayscale surface diagram of impact-corrosion bond damaged structure specimen 2-2. DETAILED DESCRIPTION OF THE INVENTION

[0016] The following clearly and completely describes the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only some embodiments of the present invention, and not all embodiments, and all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without any creative efforts are all within the protection scope of the present invention.

[0017] The terms "first," "second," and the like in the specification and claims of the present invention and the accompanying drawings are intended to distinguish between different objects, not to describe a particular order. The term "embodiment" used in this specification means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the present invention. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it refer to an independent or alternative embodiment that is mutually exclusive with other embodiments. Those skilled in the art can explicitly and implicitly understand that the embodiments described in this specification can be combined with other embodiments.

[0018] Example 1 An embodiment of the present invention provides a method for predicting fatigue limit of impact-corrosion coupled damaged structure based on critical distance, which includes the following steps, as shown in FIG.

[0019] S101, calculate the three-dimensional fractal dimension of the damage structure of the impact-corrosion coupling prediction target based on a planar image of the damage structure of the prediction target.

[0020] The 3D fractal dimension is a mathematical tool to describe the complexity of a 3D fractal set object. By recursively dividing the 3D fractal object and then calculating the size ratio after each division level, the final dimension value, i.e., the 3D fractal dimension, is obtained.

[0021] In some embodiments, step S101 may be realized by the following steps.

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

[0023] S1012, a three-dimensional grayscale surface is established from the grayscale image by taking the coordinates of the pixel located on the plane as the coordinates and the grayscale value of the pixel located on the z-axis as the coordinates.

[0024] S1013: Calculate the three-dimensional fractal dimension of the three-dimensional grayscale surface as the three-dimensional fractal dimension of the damage structure to be predicted. The three-dimensional fractal dimension can be calculated using a box-counting method and fractal software, or can be calculated using other methods. The box-counting method is a commonly used method for calculating three-dimensional fractal dimension. The pixel space where the three-dimensional grayscale surface is located is a large cube of 256 × 256 × 256. The large cube is divided into small cubes with side lengths of k. It should be noted that 256 / k is an integer, so the cube is divided into (256 / k) 3 The image is divided into boxes, and a matlab program is constructed to calculate the number of boxes covering the image grayscale surface as Nr(k). The size of the box side length k is changed to obtain a set of Nr(k), and the point pair

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[0025] S102, calculate 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 notch root, determined from elastic theory under ideal elastic conditions. In some embodiments, step S102 may be obtained in the following manner.

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

number

number

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

[0029] Specifically, the stress gradient correction function is:

number

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

[0031] The critical distance is twice the distance from a point on the bisector of any damaged notch to the notch root when the maximum principal stress at this point is the fatigue limit of a smooth component of the same material. The critical point is a point on the bisector of the notch root that is L0 / 2 away from the notch root. The material-critical distance table is pre-generated, and the critical distance is related only to the material and is ideally a constant, i.e., the critical distances for any damaged structure of the same material are all the same. Ideally, the critical distances can be calculated using any damaged structure experiment. However, in reality, due to various error conditions such as simulation error, the calculated critical distance for different damage structures fluctuates within a small range. Therefore, to improve the prediction accuracy, multiple impact-corrosion coupled damage structures with arbitrary damage conditions that are the same as the target damage structure material are randomly selected, and through testing, the fatigue limit σ0 of a smooth specimen that is the same as the target damage structure material and the fatigue limits σ1, σ2, ... of the selected multiple damage structures are obtained. A three-dimensional model of each selected damage structure is then established, mesh division is performed, mesh refinement is performed near the notch, material attributes are assigned to the finite element model, and edge conditions are added to the model, which simulates the loading conditions in the real environment. The stress distribution σ on the bisector of the notch root of each damage structure is then calculated through finite element analysis. s,1 (r),σ s,2 (r),... and obtain the stress distribution σ s,1 (r),σ s,2 (r),... are corrected using the 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),..., and σ e,1 (r)=σ0,σ e,2 Let (r) = σ0,..., and solve for the values ​​r1 and r2... respectively. Then, twice the average value of r1 and r2... is the critical distance.

number

[0032] S105: Establish a three-dimensional model of the damaged structure to be predicted, and when the error between the corrected stress at the critical point and the fatigue limit of the smooth specimen is a preset threshold, the external load on the three-dimensional model becomes the fatigue limit of the damaged component 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 damage structure to be predicted, establish a three-dimensional finite element model, divide the mesh, refine the mesh at the root of the notch, add the initial value of the external load to the three-dimensional model, and use finite element analysis to calculate the stress distribution σ on the bisector of the root of the notch. s (r) is obtained, where r is the distance from any point on the bisector of the notch root to the notch root.

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

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

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

[0038] S1055: If not, adjust 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 preset threshold, and use the external load at this time as the fatigue limit of the damaged component to be predicted.

[0039] Example 2 2 is a schematic diagram of a fatigue limit prediction device for impact-corrosion coupled damaged structures based on critical distance according to an embodiment of the present invention. The system may be implemented in software and / or hardware, and the device may be located in a terminal device. The device includes: a three-dimensional fractal dimension confirmation module 201 for calculating a three-dimensional fractal dimension of the damage structure of the impact-corrosion coupling prediction target based on a planar image of the damage structure of the prediction target; a theoretical stress concentration coefficient confirmation module 202 for calculating a theoretical stress concentration coefficient of the damaged notch based on the damage status of the damaged structure to be predicted; a stress gradient correction function confirmation module 203 for establishing a stress gradient correction function at the root of the damaged notch of the damaged structure to be predicted based on the three-dimensional fractal dimension and the theoretical stress concentration factor; 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 a critical distance corresponding to the material of the currently predicted damaged structure; and a fatigue limit confirmation module 206 for establishing a three-dimensional model of the damaged structure to be predicted, and for determining the fatigue limit of the damaged component to be predicted when the error between the corrected stress at the critical point and the fatigue limit of the smooth specimen is a preset threshold, wherein the external load of the three-dimensional model becomes the fatigue limit of the damaged component to be predicted, and the corrected stress is a stress obtained by correcting the stress distribution calculated in the three-dimensional model using the stress gradient correction function.

[0040] Among them, the three-dimensional fractal dimension confirmation module 201 specifically includes: an image conversion unit for obtaining a planar image of a damaged region of the damaged structure for which impact-corrosion coupling is predicted and converting it into a grayscale image; a grayscale surface establishment unit for establishing a three-dimensional grayscale surface from the grayscale image, with coordinates of the pixels located on the grayscale image as plane coordinates and the grayscale values ​​of the pixels located on the grayscale image as z-axis coordinates; and 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 theoretical stress concentration factor confirmation module 202 specifically includes: Based on the damage depth and damage width of the damage structure to be predicted, calculate the curvature radius of the notch root according to the following formula:

number

number

[0042] The critical distance is obtained by a critical distance calculation module, which includes: Randomly select multiple impact-corrosion coupled damaged structures with any damage situation that is the same as the damaged structural material to be predicted; The fatigue limit of the smooth specimen σ0, which is the same as the damaged structure material to be predicted, and the fatigue limits σ1, σ2, ... of the selected damaged structures are obtained through the test. A three-dimensional model of each selected damaged structure was established, and the stress distribution σ on the bisector of the notch root of each damaged structure was calculated by finite element analysis. s,1 (r),σ s,2 (r),...and Stress distribution σ of each damaged structure s,1 (r),σs,2 (r),... are corrected using the stress gradient correction function, and the corrected stress distribution σ e,1 (r),σ e,2 (r),...and σ e,1 (r)=σ0,σ e,2 Let (r) = σ0,..., and solve for the values ​​of r, r1, r2,..., respectively. r1, r2, ... twice the average value is the critical distance

number

[0043] Specifically, the fatigue limit confirmation module 206: Based on the damage width and damage depth of the damaged structure to be predicted, a three-dimensional finite element model is established, and an initial external load value is added to the three-dimensional model. The stress distribution σ on the bisector of the notch root is calculated 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 by the stress gradient correction function, and the corrected stress σ at the critical point is calculated. e a stress correction unit for obtaining (L0), where L0 is a critical distance; The corrected stress σ at the critical point e A judgment unit for judging whether the error of the fatigue limit of (L0) and a smooth specimen of the same material is within a preset threshold value; a first judgment unit for determining the currently applied external load as the fatigue limit of the damaged member to be predicted if the judgment unit result is yes; If the judgment unit result is not the case, 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 reaches a preset threshold, and the second judgment unit is used to determine the external load at this time as the fatigue limit of the damaged component to be predicted.

[0044] The device according to the embodiment of the present invention may be used to perform the method according to the first embodiment of the present invention, and has the functions and beneficial effects corresponding to the method. For details, please refer to the first embodiment and will not be described further.

[0045] It should be noted that in the above embodiment of the determination device, the included units and modules are simply divided based on functional logic, and are not limited to the above divisions as long as they can achieve the corresponding functions. Furthermore, the specific names of the functional units are used only to facilitate mutual distinction, and are not intended to limit the scope of protection of the present invention.

[0046] The above-described embodiments are merely illustrative, and modules described as separate components may or may not be physically separated, and components shown as modules may or may not be physical modules, i.e., they may be located in a single location or distributed across multiple network modules. Depending on actual needs, some or all of the modules may be selected to achieve the objectives of the solutions of the present embodiments. As will be apparent to those skilled in the art, each embodiment may be realized in the form of software and a required general-purpose hardware platform, or may be realized solely in hardware, as long as the functions or roles can be realized.

[0047] Example 3 3 is a structural schematic diagram of an apparatus according to a third embodiment of the present invention, which provides services for implementing the method of the first embodiment of the present invention. As shown in FIG. 3, the apparatus may include a memory 301 in which a computer-executable program is stored, and a processor 302 coupled to the memory 301, where the processor 302 is used to call the computer-executable program stored in the memory 301 and perform the steps of the method described in the first embodiment.

[0048] Memory 301 may include computer system-readable media in the form of volatile memory, such as random access memory (RAM) and / or high-speed cache memory. The device may also include other removable / non-removable, volatile / non-volatile computer system storage media. By way of example only, memory 301 may be used to read from and write to non-removable, non-volatile magnetic media (commonly referred to as a hard disk drive). A set of (at least one) program / utility modules may be stored in memory 301, for example. Such program modules may include, but are not limited to, an operating system, one or more application programs, other program modules, and program data, each of which may include, but is not limited to, a network environment. The computer-executable programs of the program modules generally perform the functions and / or methods of the described embodiments of the present invention.

[0049] Computer-executable program code for performing operations of the present invention may be written in one or more programming languages ​​or a combination thereof, including object-oriented programming languages ​​such as Java, Smalltalk, C++, and also general process-based programming languages ​​such as "C" or similar programming languages.

[0050] The processor 302 executes the programs stored in the memory 301 to perform various functional applications and data processing, for example, to realize the method according to the first embodiment of the present invention.

[0051] Example 4 An embodiment of the present invention provides 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 of an embodiment of the present invention may employ any combination of one or more computer-readable media. The computer-readable medium may be a computer-readable signal medium or a computer-readable storage medium. The computer-readable storage medium may be, for example, but not limited to, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any combination thereof. More specific examples (a non-exhaustive list) of computer-readable storage media include an electrical connection having one or more wires, a portable computer magnetic disk, a disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact magnetic disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the above. As used herein, a computer-readable storage medium may be any tangible medium that contains or stores a program, which may be used by or in connection with an instruction execution system, apparatus, or device.

[0053] Computer-executable program code for performing the operations of the present invention may be written in one or more programming languages, or a combination thereof, including object-oriented programming languages ​​such as Java, Smalltalk, C++, and general process-based programming languages ​​such as "C" or similar. The program code may run entirely on the user's computer, partially on the user's computer, as a separate software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. When referring to a remote computer, the remote computer may be connected to the user's computer by any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., connected to the Internet using an Internet Service Provider).

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

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

[0056] The materials used in the experiments were 13Cr stainless steel structures, and precast damage experiments were conducted under different impact and corrosion environments. The external damage parameters were 2mm and 3mm diameter steel balls, made of GGr15. The impact velocities were 200m / s and 300m / s. Corrosion damage parameters: The corrosive solution was a 5% NaCl solution, with dilute H2SO4 added to adjust the solution pH to 4±0.2. The corrosion times included 24h, 48h, and 96h. The corrosion temperature was kept constant at 40°C, and the solution was replaced every 48h.

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

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

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[0059] [Table 1] The present invention was used to predict the fatigue limit of the bond damage notch, and the overall trend of the predicted results was consistent with the experimental results, all within the ±20% error range.

Claims

1. A method for predicting fatigue limit of an impact-corrosion coupled damaged structure based on critical distance, comprising: Calculating a three-dimensional fractal dimension of a damage structure of a predicted target based on a planar image of the damage structure of a predicted target of impact-corrosion coupling; Calculating a theoretical stress concentration factor of the damaged notch based on the damage state of the damaged structure to be predicted; Establishing a stress gradient correction function at the root of the damaged notch of the damaged structure to be predicted based on the three-dimensional fractal dimension and the theoretical stress concentration factor; A previously generated material-critical distance table is searched to find the critical distance L corresponding to the material of the currently predicted damaged structure. ０ and A three-dimensional model of the damage structure to be predicted is established, and when the error between the corrected stress corresponding to the critical point and the fatigue limit of the smooth specimen is a preset threshold, 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 on the bisector of the notch root, L ０ and the corrected stress is a stress obtained by correcting the stress distribution calculated using a three-dimensional model with the stress gradient correction function.

2. Specifically, the calculation of the three-dimensional fractal dimension of the damage structure based on the planar image of the damage structure of the impact-corrosion coupling prediction target includes: obtaining a planar image of a damaged region of a damaged structure for which impact-corrosion coupling is to be predicted and converting the image into a grayscale image; establishing a three-dimensional grayscale surface using the grayscale image with coordinates of pixels in the image as plane coordinates and grayscale values ​​of pixels in the image as z-axis coordinates; and calculating the three-dimensional fractal dimension of the three-dimensional grayscale surface as the three-dimensional fractal dimension of the damaged structure to be predicted.

3. The calculation of the theoretical stress concentration factor of the damaged notch based on the damage state of the damaged structure to be predicted specifically includes the following steps: Based on the damage depth and damage width of the damage structure to be predicted, calculate the curvature radius of the notch root according to the following formula: [Equation 15] In the formula, ρ represents the radius of curvature of the notch root, l represents the damage width, and d represents the damage depth. Calculate a theoretical stress concentration factor of the damaged structure to be predicted based on the radius of curvature of the notch root portion according to the following formula: [0016] In the formula, K Ｔ The method for predicting fatigue limit of impact-corrosion coupled damaged structure based on critical distance according to claim 1, characterized in that:

4. Specifically, the stress gradient correction function is [Equation 17] and In the equation, φ(r) is the stress gradient correction function, and K Ｔ 2. The method for predicting the fatigue limit of an impact-corrosion coupled damaged structure based on the critical distance according to claim 1, characterized in that: √{square root over ( ...

5. The critical distance is Randomly selecting a plurality of impact-corrosion coupled damaged structures with any damage situation that is the same as the damaged structure material to be predicted; The fatigue limit σ of a smooth specimen is the same as that of the structural material for which damage is predicted by the test. ０ and the fatigue limit σ of the selected multiple damaged structures １ , σ ２ ,....., and A three-dimensional model of each selected damaged structure was established, and the stress distribution σ on the bisector of the notch root of each damaged structure was calculated by finite element analysis. ｓ，１ (r), σ ｓ，２ (r) ,....., and Stress distribution σ of each damaged structure ｓ，１ (r), σ ｓ，２ (r) ,.... are corrected using the stress gradient correction function, and the corrected stress distribution σ ｅ，１ (r), σ ｅ，２ (r) ,..... and s ｅ，１ (r) = s ０ ,s ｅ，２ (r) = s ０ ,..., the value of r is １ , r ２ , ... respectively, r １ , r ２ , ...Twice the average value is the critical distance L ０ The method for predicting the fatigue limit of an impact-corrosion coupled damaged structure based on the critical distance according to claim 1, wherein the critical distance is obtained by calculating the following:

6. Establishing the 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 specimen is a preset threshold, setting the external load on the three-dimensional model as the fatigue limit of the damage component to be predicted can be specifically performed as follows: Based on the damage width and damage depth of the damaged structure to be predicted, a three-dimensional finite element model is established, and an initial external load value is added to the three-dimensional model. The stress distribution σ on the bisector of the notch root is calculated by finite element analysis. ｓ (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 by the stress gradient correction function, and the corrected stress σ at the critical point is ｅ (L ０ / 2) and Corrected stress σ at the critical point ｅ (L ０ / 2) and determining whether the error between the fatigue limit of a smooth specimen of the same material is within a preset threshold value; If so, the currently applied external load is set as the fatigue limit of the damaged component to be predicted; If not, the method for predicting the fatigue limit of an impact-corrosion coupled damaged structure based on the critical distance as claimed in claim 1 further comprises: 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 specimen reaches a predetermined threshold, and setting the external load at this time as the fatigue limit of the damaged component to be predicted.

7. A fatigue limit prediction device for impact-corrosion coupled damaged structures based on critical distance, comprising: a three-dimensional fractal dimension confirmation module for calculating a three-dimensional fractal dimension of the damage structure of the impact-corrosion coupling prediction target based on a planar image of the damage structure of the prediction target; a theoretical stress concentration coefficient confirmation module for calculating a theoretical stress concentration coefficient of the damaged notch based on the damage status of the damaged structure to be predicted; a stress gradient correction function confirmation module for establishing a stress gradient correction function at the root of the damaged notch of the damaged structure to be predicted based on the three-dimensional fractal dimension and the theoretical stress concentration factor; Critical distance L for each material ０ a material-critical distance table for storing a search module for searching a material-critical distance table to obtain a critical distance corresponding to the material of the currently predicted damaged structure; A fatigue limit confirmation module for establishing a three-dimensional model of a damage structure to be predicted, and determining the external load of the three-dimensional model when the error between the corrected stress at the critical point and the fatigue limit of a smooth specimen is a preset threshold value as the fatigue limit of the damage structure to be predicted, wherein the critical point is located at a distance L from the notch root on the bisector of the notch root. ０ and a fatigue limit confirmation module for correcting the stress distribution calculated by a three-dimensional model by the stress gradient correction function, wherein the corrected stress is a point 1 / 2 away from the impact-corrosion coupled damaged structure.

8. Specifically, the stress gradient correction function is [Equation 18] and In the equation, φ(r) is the stress gradient correction function, and K Ｔ 8. The fatigue limit prediction device for impact-corrosion coupled damaged structures based on critical distance according to claim 7, characterized in that: √{square root over ( ...

9. 1. A fatigue limit prediction device for an impact-corrosion coupled damaged structure based on a critical distance, the device comprising: a processor; and an executable program stored in a memory and operable to run on the processor, 7. A fatigue limit prediction device for impact-corrosion coupled damaged structures based on critical distance, characterized in that, when the processor executes the executable program, the device realizes the method according to any one of claims 1 to 6.

10. A storage medium containing a computer-executable program, 7. A storage medium, comprising a computer-executable program, the computer-executable program being used to perform the method of any one of claims 1 to 6 when executed by a computer processor.

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