Impact-corrosion coupled damage structure fatigue limit prediction method and device

Abstract

Disclosed are an impact-corrosion coupled damage structure fatigue limit prediction method and device based on a critical distance method. The method of the present invention comprises: calculating a three-dimensional fractal dimension on the basis of a planar image of a damage structure to be predicted that has undergone impact-corrosion coupling; calculating a theoretical stress concentration factor on the basis of the damage situation of said damage structure; establishing a stress gradient correction function for the root of a damage notch on the basis of the three-dimensional fractal dimension and the theoretical stress concentration factor; looking up a pre-generated material-critical distance table to obtain a critical distance corresponding to the material of the current damage structure to be predicted; and establishing a three-dimensional model of the damage structure to be predicted, and when the error between the corrected stress corresponding to a critical point and the fatigue limit of a smooth specimen is a preset threshold value, using an external load on the three-dimensional model as the fatigue limit of a damage component to be predicted. According to the present invention, the prediction process is relatively simple, only linear elasticity analysis is needed, and the prediction precision is high.

Description

Fatigue limit prediction method and equipment for impact-corrosion coupled damaged structures Technical Field

[0001] The present invention relates to a fatigue limit prediction technology for a damaged structure, and in particular to a fatigue limit prediction method and equipment for an impact-corrosion coupled damaged structure. Background Art

[0002] During their service, structures often face complex working environments and suffer from different forms of damage, which greatly reduces their bearing capacity, fatigue life and reliability, which may lead to the destruction of structural integrity. Therefore, accurately assessing the fatigue limit of structures in complex service environments and ensuring that the structures meet the requirements of fatigue life and high reliability required for use are important issues in engineering. Some key structures in engineering are inevitably subjected to impact from external objects during operation, which easily leads to stress concentration, residual stress and microstructural damage at the impact site. At the same time, affected by the humidity, pH value and other factors of the working environment, further corrosion occurs to the structure, usually forming tiny pits on the surface of the material. Under the coupled effect of impact and corrosion, the damaged notch may become a source of crack initiation, which rapidly expands under fatigue load, resulting in a significant reduction in the fatigue performance of the structure and high-cycle failure.

[0003] Scholars at home and abroad have proposed various mathematical models for predicting the fatigue limit of notches, including Neuber's mean stress model, Peterson's modified Peterson formula, Taylor's critical distance theory, Hudak's worst-case notch model, and Weibull's weakest-link theory based on statistical data. Each of these models has its own advantages and disadvantages for fatigue prediction of notched components. When applied to notches with different damage forms, it is necessary to analyze the notch characteristics, obtain characterizing parameters, and incorporate them into the model. The damage morphology and microscopic features of coupled-damage notches are the primary factors affecting their fatigue strength. These factors are related to the type and size of the foreign object, the impact velocity and angle, the structural material, the corrosion environment, and the duration. Currently, relatively few studies have comprehensively considered the fatigue properties of notches damaged by impact-corrosion coupling. For such coupled-damage notches, fatigue limits are typically predicted by calculating the theoretical stress concentration factor based on the macroscopic notch morphology. However, this method fails to account for the influence of the notch stress gradient, resulting in low prediction accuracy. It also fails to account for the effects of coupled damage. Therefore, a simple and accurate method for predicting the fatigue limit of coupled-damage notches remains unavailable in engineering.

[0004] Summary of the Invention

[0005] Purpose of the invention: To address the problems existing in the prior art, the present invention provides a method and device for predicting the fatigue limit of impact-corrosion coupled damaged structures with higher prediction accuracy.

[0006] Technical solution: In the first aspect, the present invention provides a method for predicting the fatigue limit of a structure damaged by impact-corrosion coupling damage based on a critical distance, comprising:

[0007] Calculating the three-dimensional fractal dimension of the damage structure to be predicted based on the plane image of the damage structure to be predicted by impact-corrosion coupling;

[0008] Calculate the theoretical stress concentration factor of the damage notch according to the damage condition of the structure to be predicted;

[0009] Establishing a stress gradient correction function at the root of the damage notch of the damage structure to be predicted based on the three-dimensional fractal dimension and the theoretical stress concentration coefficient;

[0010] Search the pre-generated material-critical distance table to obtain the critical distance corresponding to the material of the current damage structure to be predicted;

[0011] A three-dimensional model of the structure to be damaged is established. When the error between the corrected stress corresponding to the critical point and the fatigue limit of the smooth specimen reaches a preset threshold, the external load on the three-dimensional model is used as the fatigue limit of the damaged part to be predicted.

[0012] Furthermore, the calculation of the three-dimensional fractal dimension of the damaged structure based on the plane image of the damage structure to be predicted due to impact-corrosion coupling specifically includes:

[0013] Obtain a plane image of the damaged area of ​​the structure to be predicted under impact-corrosion coupling and convert it into a grayscale image;

[0014] The grayscale image is used to establish a three-dimensional grayscale surface by taking the coordinates of the pixels as plane coordinates and the grayscale values ​​of the pixels as z-axis coordinates;

[0015] 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.

[0016] Furthermore, the calculation of the theoretical stress concentration factor of the damage notch according to the damage condition of the damage structure to be predicted specifically includes:

[0017] According to the damage depth and damage width of the damage structure to be predicted, the curvature radius of the notch root is calculated according to the following formula:

[0018] Where, ρ represents the curvature radius of the notch root, l represents the damage width, and d represents the damage depth;

[0019] The theoretical stress concentration factor of the damage structure to be predicted is calculated according to the curvature radius of the notch root using the following formula:

[0020] Where K TRepresents the theoretical stress concentration factor.

[0021] Furthermore, the stress gradient correction function is specifically:

[0022] Where, is the stress gradient correction function, K T represents the theoretical stress concentration coefficient, 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.

[0023] Optionally, the critical distance is obtained by the following method:

[0024] Randomly select several impact-corrosion coupled damage structures with the same damage conditions as the damage structure to be predicted;

[0025] Obtain the fatigue limit σ0 of a smooth specimen of the same material as the damaged structure to be predicted and the fatigue limits σ1, σ2, ... of several selected damaged structures through experiments;

[0026] Establish a three-dimensional model of each selected damaged structure, and obtain the stress distribution σ on the bisection line of the notch root of each damaged structure through finite element analysis s，1 (r),σ s,2 (r),...;

[0027] For each damaged structure stress distribution σ s，1 (r),σ s,2 (r),...Use the stress gradient correction function to correct and get the corrected stress distribution σ e，1 (r),σ e,2 (r),...;

[0028] Let σ e，1 (r)=σ0,σ e,2 (r) = σ0, ..., solve for the values ​​of r1, r2, ... respectively;

[0029] Calculate twice the average value of r1, r2, ... as the critical distance L0.

[0030] Furthermore, the three-dimensional model of the structure to be predicted for damage is established, 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 is used as the fatigue limit of the damaged part to be predicted, specifically including:

[0031] According to the damage width and damage depth of the damaged structure to be predicted, a finite element three-dimensional model is established, and the initial value of the external load is applied to the three-dimensional model. Through finite element analysis, the stress distribution σ on the bisection line of the notch root is obtained. s (r), r is the distance from any point on the bisector of the notch root to the notch root;

[0032] The stress distribution σ s (r) Using the stress gradient correction function to correct, we get the corrected stress σ at the critical point. e (L0), L0 is the critical distance;

[0033] Determine the modified stress σ of the critical point e (L0) Whether the error of fatigue limit of smooth specimen of the same material is within the preset threshold;

[0034] If so, the currently applied external load is taken as the fatigue limit of the damaged part to be predicted;

[0035] 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 preset threshold, and the external load at this time is used as the fatigue limit of the damaged part to be predicted.

[0036] In a second aspect, the present invention further provides a device for predicting fatigue limit of impact-corrosion coupled damaged structures based on critical distance, comprising:

[0037] A three-dimensional fractal dimension confirmation module is used to calculate the three-dimensional fractal dimension of the damage structure to be predicted based on the plane image of the damage structure to be predicted by impact-corrosion coupling;

[0038] Theoretical stress concentration factor confirmation module, used to calculate the theoretical stress concentration factor of the damage notch according to the damage condition of the damage structure to be predicted;

[0039] A stress gradient correction function confirmation module is used to establish a stress gradient correction function at the root of the damage notch of the damage structure to be predicted based on the three-dimensional fractal dimension and the theoretical stress concentration factor;

[0040] A material-critical distance table is used to store the critical distance of each material; wherein the critical distance is the distance from a point on the notch root bisector to the notch root in any damaged structure when the stress is at the fatigue limit of a smooth specimen of the same material;

[0041] A search module is used to search the material-critical distance table to obtain the critical distance corresponding to the material of the current damage structure to be predicted;

[0042] The fatigue limit confirmation module is used to establish a three-dimensional model of the structure to be predicted for damage. 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 is used as the fatigue limit of the damaged part to be predicted. The corrected stress is the stress obtained by correcting the stress distribution calculated by the three-dimensional model using the stress gradient correction function.

[0043] In a third aspect, the present invention also provides a fatigue limit prediction device for impact-corrosion coupled damaged structures based on critical distance, comprising a processor and an executable program stored in a memory and runnable on the processor, characterized in that the method described in the first aspect is implemented when the processor executes the executable program.

[0044] In a fourth aspect, the present invention further provides a storage medium comprising a computer executable program, wherein the computer executable program is used to execute the method described in the first aspect when executed by a computer processor.

[0045] Compared with the prior art, the present invention has the following advantages: the present invention links the coupling damage parameter with the damage notch gradient, and predicts the fatigue limit of the coupling damage notch based on the critical distance method. The prediction process is relatively simple, requiring only linear elastic analysis, and has high prediction accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] FIG1 is a schematic flow chart of a method for predicting fatigue limit of a structure damaged by impact-corrosion coupling based on critical distance provided by the present invention;

[0047] FIG2 is a schematic structural diagram of a device for predicting fatigue limit of a structure damaged by impact-corrosion coupling based on critical distance provided by the present invention;

[0048] FIG3 is a schematic structural diagram of a device for predicting fatigue limit of a structure damaged by impact-corrosion coupling based on critical distance provided by the present invention;

[0049] FIG4 is a damage morphology diagram of the impact-corrosion coupled damage structure sample 2-2;

[0050] FIG5 is a three-dimensional grayscale surface diagram of the impact-corrosion coupled damage structure sample 2-2. DETAILED DESCRIPTION

[0051] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0052] The terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish different objects, rather than to describe a specific order. Reference to "embodiment" in this article means that the specific features, structures or characteristics described in conjunction with the 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 is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0053] Example 1

[0054] An embodiment of the present invention provides a method for predicting the fatigue limit of a structure damaged by impact-corrosion coupling damage based on a critical distance, as shown in FIG1 , comprising the following steps:

[0055] S101. Calculating a three-dimensional fractal dimension of a damage structure to be predicted based on a plane image of the damage structure to be predicted due to impact-corrosion coupling.

[0056] The three-dimensional fractal dimension is a mathematical tool used to describe the complexity of a three-dimensional fractal object. By recursively partitioning a three-dimensional fractal object and calculating the size ratio at each level of partitioning, a dimensional value, the three-dimensional fractal dimension, is obtained.

[0057] In some embodiments, step S101 may be implemented by the following steps:

[0058] S1011. Obtain a plane image of the damaged area of ​​the structure to be predicted for impact-corrosion coupling damage, and convert it into a grayscale image. The pixel size of the plane image can be set to 256×256, or divided into 256×256 grids, and the average grayscale value of each grid is used as the grid grayscale value.

[0059] S1012, using the coordinates of the pixels in the grayscale image as plane coordinates and the grayscale values ​​of the pixels as z-axis coordinates to create a three-dimensional grayscale surface;

[0060] S1013. Calculate the three-dimensional fractal dimension of the three-dimensional grayscale surface as the three-dimensional fractal dimension of the damaged structure to be predicted. The three-dimensional fractal dimension can be calculated using box counting and fractal software or other methods. The box counting method is a commonly used three-dimensional fractal dimension calculation method. The coordinate space where the three-dimensional grayscale surface is located is a large cube of 256×256×256. The large cube is divided into small cube boxes with a side length of k. Note that 256 / k is an integer, so the cube is divided into (256 / k) 3 Boxes, build a matlab program to calculate the number of boxes covering the grayscale surface of the image is Nr (k). Change the size of the box side length k to get a set of N r (k), calculate the point pair {ln(256 / k), ln(N r (k))}, a straight line is obtained, whose slope is the three-dimensional fractal dimension D, and the expression of D is as follows:

[0061] S102. Calculate the theoretical stress concentration factor of the damage notch based on the damage condition of the structure to be predicted.

[0062] The theoretical stress concentration factor is the ratio of the maximum actual stress at the notch root to the nominal stress, calculated from elasticity theory under ideal elastic conditions. In some embodiments, step S102 can be obtained by the following method:

[0063] S1021. Calculate the notch root curvature radius according to the following formula based on the damage depth and damage width of the damage structure to be predicted:

[0064] Where, ρ represents the curvature radius of the notch root, l represents the damage width, and d represents the damage depth;

[0065] S1022. Calculate the theoretical stress concentration factor of the damage structure to be predicted according to the curvature radius of the notch root according to the following formula:

[0066] Where K T Represents the theoretical stress concentration factor.

[0067] S103 , establishing a stress gradient correction function at the root of the damage notch of the structure to be predicted based on the three-dimensional fractal dimension and the theoretical stress concentration coefficient.

[0068] The stress gradient correction function is specifically:

[0069] Where, is the stress gradient correction function, K T represents the theoretical stress concentration coefficient, 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.

[0070] S104 , searching a pre-generated material-critical distance table to obtain a critical distance corresponding to the material of the current damage-predicted structure.

[0071] The critical distance is defined as twice the distance from any point on the bisector of the damaged notch to the notch root when the maximum principal stress at that point reaches the fatigue limit of a smooth part made of the same material. The critical point is the point on the bisector of the notch root at a distance of L0 / 2 from the notch root. A pre-generated material-critical distance table describes this critical distance. The critical distance is material-dependent and ideally a constant, meaning that the critical distance is the same for any damaged structure made of the same material. Ideally, the critical distance can be calculated experimentally using any damaged structure. However, in reality, due to various errors such as simulation errors, the critical distances calculated for different damaged structures will fluctuate within a small range. Therefore, in order to improve the prediction accuracy, the following method can be used to calculate the critical distance: randomly select several impact-corrosion coupled damaged structures with arbitrary damage conditions and the same material as the damaged structure to be predicted; obtain the fatigue limit σ0 of the smooth specimen with the same material as the damaged structure to be predicted and the fatigue limits σ1, σ2,... of several selected damaged structures through experiments; establish a three-dimensional model of each selected damaged structure, divide the mesh, refine the mesh near the notch, assign material properties to the finite element model, impose boundary conditions on the model, simulate its load conditions in the real environment, and obtain the stress distribution σ on the bisector of the notch root of each damaged structure through finite element analysis. s，1 (r),σ s,2 (r),...; for each damaged structure stress distribution σ s，1 (r),σ s,2 (r),...Use the stress gradient correction function to correct and get the corrected stress distribution Let σ e，1 (r)=σ0,σ e,2 (r)=σ0,..., solve for the values ​​of r1,r2,... respectively; calculate twice the average value of r1,r2,... as the critical distance

[0072] S105. Establish a three-dimensional model of the structure to be damaged 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 is used as the fatigue limit of the damaged part to be predicted.

[0073] In some embodiments, step S105 specifically includes:

[0074] S1051. Based on the damage width and damage depth of the damaged structure to be predicted, a finite element three-dimensional model is established, meshing is performed, and the mesh is refined at the root of the notch. An initial external load is applied to the three-dimensional model, and the stress distribution σ on the bisecting line of the notch root is obtained through finite element analysis. s (r), r is the distance from any point on the bisector of the notch root to the notch root;

[0075] S1052, the stress distribution σs (r) Using the stress gradient correction function to correct, we get the corrected stress σ at the critical point. e (L0 / 2), L0 is the critical distance;

[0076] S1053, determining the modified stress σ of the critical point e (L0) Whether the error with the fatigue limit σ0 of the smooth specimen of the same material is within the preset threshold;

[0077] S1054: If yes, use the currently applied external load as the fatigue limit of the damaged part to be predicted;

[0078] 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 specimen reaches a preset threshold, and use the external load at this time as the fatigue limit of the damaged part to be predicted.

[0079] Example 2

[0080] FIG2 is a schematic diagram of a fatigue limit prediction device for a structure damaged by impact-corrosion coupling based on critical distance according to an embodiment of the present invention. The system can be implemented in software and / or hardware, and the device can be configured in a terminal device. The device includes:

[0081] A three-dimensional fractal dimension confirmation module 201 is used to calculate the three-dimensional fractal dimension of the damage structure to be predicted based on the plane image of the damage structure to be predicted due to impact-corrosion coupling;

[0082] Theoretical stress concentration coefficient confirmation module 202 is used to calculate the theoretical stress concentration coefficient of the damage notch according to the damage condition of the damage structure to be predicted;

[0083] A stress gradient correction function confirmation module 203 is used to establish a stress gradient correction function at the root of the damage notch of the damage structure to be predicted based on the three-dimensional fractal dimension and the theoretical stress concentration factor;

[0084] Material-critical distance table 204, used to store the critical distance L0 of each material;

[0085] A search module 205 is used to search the material-critical distance table to obtain the critical distance corresponding to the material of the current damage structure to be predicted;

[0086] The fatigue limit confirmation module 206 is used to establish a three-dimensional model of the structure to be predicted for damage. 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 is used as the fatigue limit of the damaged part to be predicted. The corrected stress is the stress obtained by correcting the stress distribution calculated by the three-dimensional model using the stress gradient correction function.

[0087] The three-dimensional fractal dimension confirmation module 201 specifically includes:

[0088] An image conversion unit is used to obtain a plane image of a damaged area of ​​a structure to be predicted due to impact-corrosion coupling and convert it into a grayscale image;

[0089] A grayscale surface establishment unit, configured to establish a three-dimensional grayscale surface by using the coordinates of the pixels of the grayscale image as plane coordinates and the grayscale values ​​of the pixels as z-axis coordinates;

[0090] The three-dimensional fractal dimension calculation unit is used to 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.

[0091] The theoretical stress concentration factor confirmation module 202 specifically includes:

[0092] The curvature radius calculation unit is used to calculate the curvature radius of the notch root according to the damage depth and damage width of the damage structure to be predicted according to the following formula:

[0093] Where, ρ represents the curvature radius of the notch root, l represents the damage width, and d represents the damage depth;

[0094] The coefficient calculation unit is used to calculate the theoretical stress concentration coefficient of the damage structure to be predicted according to the curvature radius of the notch root according to the following formula:

[0095] Where K T Represents the theoretical stress concentration factor.

[0096] The critical distance is obtained by a critical distance calculation module, which is used to implement the following method:

[0097] Randomly select several impact-corrosion coupled damage structures with the same damage conditions as the damage structure to be predicted;

[0098] Obtain the fatigue limit σ0 of a smooth specimen of the same material as the damaged structure to be predicted and the fatigue limits σ1, σ2, ... of several selected damaged structures through experiments;

[0099] Establish a three-dimensional model of each selected damaged structure, and obtain the stress distribution σ on the bisection line of the notch root of each damaged structure through finite element analysis s，1 (r),σ s,2 (r),...;

[0100] For each damaged structure stress distribution σ s，1 (r),σ s,2 (r),...Use the stress gradient correction function to correct and get the corrected stress distribution σe，1 (r),σ e,2 (r),...;

[0101] Let σ e，1 (r)=σ0,σ e,2 (r) = σ0, ..., solve for the values ​​of r1, r2, ... respectively;

[0102] Calculate twice the average value of r1, r2, ... as the critical distance n is the number of randomly selected damaged structures.

[0103] The fatigue limit confirmation module 206 specifically includes:

[0104] The model building unit is used to build a finite element three-dimensional model according to the damage width and damage depth of the damaged structure to be predicted, and to apply the initial value of the external load to the three-dimensional model. Through finite element analysis, the stress distribution σ on the bisection line of the notch root is obtained. s (r), r is the distance from any point on the bisector of the notch root to the notch root;

[0105] Stress correction unit is used to convert stress distribution σ s (r) Using the stress gradient correction function to correct, we get the corrected stress σ at the critical point. e (L0), L0 is the critical distance;

[0106] A judgment unit, used to judge the modified stress σ of the critical point e (L0) Whether the error of fatigue limit of smooth specimen of the same material is within the preset threshold;

[0107] a first determination unit, configured to use the currently applied external load as the fatigue limit of the damaged component to be predicted if the determination result is yes;

[0108] The second judgment unit is used to adjust the value of the applied external load if the result of the judgment unit is no, and return the execution model establishment unit to the judgment unit until the error between the corrected stress at the critical point and the fatigue limit of the smooth specimen reaches a preset threshold, and the external load at this time is used as the fatigue limit of the damaged part to be predicted.

[0109] The device provided in the embodiment of the present invention can be used to execute the method provided in the first embodiment of the present invention, and has the corresponding functions and beneficial effects of the execution method. For any details not provided in detail, please refer to the first embodiment and will not be repeated here.

[0110] It is worth noting that in the embodiment of the above-mentioned determination device, the various units and modules included are only divided according to functional logic, but are not limited to the above-mentioned division, as long as the corresponding functions can be achieved; in addition, the specific names of the functional units are only for the convenience of distinguishing each other, and are not used to limit the scope of protection of the present invention.

[0111] The embodiments described above are merely illustrative, wherein the modules described as separate components may or may not be physically separate, and the components shown as modules may or may not be physical modules, i.e., they may be located in one place or distributed across multiple network modules. Some or all of the modules may be selected based on actual needs to achieve the objectives of the present embodiment. Those skilled in the art will readily appreciate that each embodiment may be implemented using software plus a necessary general-purpose hardware platform, or may be implemented solely through hardware, as long as the functionality or effect can be achieved.

[0112] Example 3

[0113] Figure 3 is a schematic diagram of the structure of a device provided in Embodiment 3 of the present invention, which provides services for implementing the method described in Embodiment 1. As shown in Figure 3, the device may include: a memory 301 storing a computer-executable program; a processor 302 coupled to memory 301; processor 302 invokes the computer-executable program stored in memory 301 to execute the steps of the method described in Embodiment 1.

[0114] The memory 301 may include computer system readable media in the form of volatile memory, such as random access memory (RAM) and / or cache memory. The device may further include other removable / non-removable, volatile / non-volatile computer system storage media. By way of example only, the memory 301 may be used to read and write non-removable, non-volatile magnetic media (commonly referred to as "hard drives"). A program / utility having a set (at least one) of program modules may be stored in, for example, the memory 301, such program modules including but not limited to an operating system, one or more application programs, other program modules, and program data, each of which or some combination may include an implementation of a network environment. The computer executable program of the program module typically performs the functions and / or methods in the embodiments described herein.

[0115] The code for a computer executable program 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 conventional procedural programming languages ​​such as "C" or similar programming languages.

[0116] The processor 302 executes various functional applications and data processing by running the programs stored in the memory 301, such as implementing the method provided in the first embodiment of the present invention.

[0117] Example 4

[0118] An embodiment of the present invention provides a storage medium containing a computer executable program. When the computer executable program is executed by a computer processor, it is used to perform the method of the first embodiment.

[0119] The storage medium of the embodiment of the present invention can adopt any combination of one or more computer-readable media. Computer-readable media can be computer-readable signal media or computer-readable storage media. Computer-readable storage media can be, for example, but not limited to, electrical, magnetic, optical, electromagnetic, infrared, or semiconductor systems, devices or components, or any combination of the above. More specific examples (non-exhaustive list) of computer-readable storage media include: electrical connections with one or more wires, portable computer disks, hard disks, random access memories (RAM), read-only memories (ROM), erasable programmable read-only memories (EPROM or flash memory), optical fibers, portable compact disk read-only memories (CD-ROMs), optical storage devices, magnetic storage devices, or any suitable combination of the above. In this document, computer-readable storage media can be any tangible medium containing or storing a program that can be used by an instruction execution system, device or device or used in combination with it.

[0120] The code for a computer executable program for performing the operations of the present invention can be written in one or more programming languages, or a combination thereof, including object-oriented programming languages ​​such as Java, Smalltalk, C++, and conventional procedural programming languages ​​such as "C" or similar programming languages. The program code can be executed 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. In cases involving a remote computer, the remote computer can be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or can be connected to an external computer (e.g., through the Internet using an Internet service provider).

[0121] Of course, the storage medium containing a computer executable program provided by an embodiment of the present invention, the computer executable program of which is not limited to the above method operations, can also execute related operations in the method provided by any embodiment of the present invention.

[0122] The present invention is experimentally verified below.

[0123] The material used in the experiment was a 13Cr stainless steel structure, and prefabricated damage experiments were conducted under various impact and corrosion environments. The foreign object damage parameters were 2mm and 3mm diameter steel balls made of GGr15. The impact velocities were 200m / s and 300m / s. The corrosion damage parameters were: the corrosive solution was a 5% by mass NaCl solution with diluted H2SO4 added to a pH of 4±0.2; the corrosion durations were 24h, 48h, and 96h; the corrosion temperature was a constant 40°C; and the corrosion interval was: the solution was changed every 48h.

[0124] The experiments included three types: impact only, corrosion followed by impact, and impact followed by corrosion. Taking sample 2-2 as an example, the coupled 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 was calculated to be 2.2276.

[0125] Taking sample 2-2 as an example, the damage width of the sample is l = 1.097mm, the damage depth is d = 0.553mm, and the curvature radius of the notch root is calculated to be ρ = 0.544. The theoretical stress concentration factor K T =3.016. The stress gradient correction function is: The fatigue limit of the smooth specimen obtained in the experiment is 575.11MPa, and the critical distance of the material is calculated to be 0.07mm. The fatigue limit of the coupled damage notch is predicted using the modified critical distance model. The prediction results are shown in Table 1. In the table, σ e is the fatigue limit measured by the test, σ p is the prediction result, error is the relative error, and the expression is

[0126] Experimental results Table 1

[0127] The fatigue limit of the coupled damage notch is predicted using the present invention, and the overall trend of the prediction results is consistent with the experimental results, all within the error range of ±20%.

Claims

1. A fatigue limit prediction method for impact-corrosion coupling damaged structures based on the critical distance, characterized in that Including: Calculating the three-dimensional fractal dimension of the damage structure to be predicted according to the planar image of the damage structure to be predicted under impact-corrosion coupling; Calculating the theoretical stress concentration factor of the damage notch according to the damage condition of the damage structure to be predicted; Establishing a stress gradient correction function for the root of the damage notch of the damage structure to be predicted based on the three-dimensional fractal dimension and the theoretical stress concentration factor; Looking up the pre-generated material-critical distance table to obtain the critical distance L0 corresponding to the material of the current damage structure to be predicted; Establishing a three-dimensional model of the damage 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 the preset threshold, the external load on the three-dimensional model is used as the fatigue limit of the damage structure to be predicted, where the critical point is the point at a distance of L0 / 2 from the root of the notch on the bisector of the notch root, and the corrected stress is the stress obtained after correcting the stress distribution calculated by the three-dimensional model using the stress gradient correction function.

2. The method for predicting the fatigue limit of an impact-corrosion coupling damaged structure based on the critical distance according to claim 1, wherein The calculating the three-dimensional fractal dimension of the damage structure according to the planar image of the damage structure to be predicted under impact-corrosion coupling specifically includes: Obtaining the planar image of the damage area of the damage structure to be predicted under impact-corrosion coupling and converting it into a grayscale image; Taking the coordinates of the pixels in the grayscale image as the planar coordinates and the grayscale values of the pixels as the z-axis coordinates to establish a three-dimensional grayscale surface; 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. The fatigue limit prediction method for impact-corrosion coupling damage structure based on critical distance according to claim 1, characterized in that The calculating the theoretical stress concentration factor of the damage notch according to the damage condition of the damage structure to be predicted specifically includes: According to the damage depth and damage width of the damage structure to be predicted, calculate the notch root radius of curvature according to the following formula: where ρ represents the radius of curvature of the notch root, l represents the damage width, and d represents the damage depth; Calculate the theoretical stress concentration factor of the damage structure to be predicted according to the notch root curvature radius by the following formula: In the formula, K T represents the theoretical stress concentration factor.

4. The method for predicting the fatigue limit of an impact-corrosion coupling damaged structure based on the critical distance according to claim 1, wherein The specific stress gradient correction function is as follows: In the formula, 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 line at the notch root to the notch root, and a is a constant.

5. The method for predicting the fatigue limit of an impact-corrosion coupling damage structure based on the critical distance according to claim 1, wherein the critical distance is obtained by the following method: Randomly selecting a number of impact-corrosion coupling damage structures with arbitrary damage conditions and the same material as the damage structure to be predicted; Obtaining the fatigue limit σ0 of the smooth specimen with the same material as the damage structure to be predicted and the fatigue limits σ1, σ2,... of the selected number of damage structures through experiments; Establish a three-dimensional model of each selected damaged structure, and obtain the stress distributions σ s，1 (r), σ s,2 (r),...; For the stress distribution σ s，1 (r), σ s,2 (r),... of each damaged structure, it is corrected using a stress gradient correction function to obtain the corrected stress distributions σ e，1 (r), σ e,2 (r),...; Let σ e，1 (r) = σ0, σ e,2 (r) = σ0,... Solve respectively to obtain the values of r as r1, r2,...; Calculating twice the average value of r1, r2,... as the critical distance L0.

6. The method for predicting the fatigue limit of an impact-corrosion coupling damaged structure based on the critical distance according to claim 1, wherein The establishing a three-dimensional model of the damage 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 the preset threshold, the external load on the three-dimensional model is used as the fatigue limit of the damage part to be predicted specifically includes: According to the damage width and damage depth of the structure to be predicted for damage, a three-dimensional finite element model is established, and the initial value of the external load is applied to the three-dimensional model. Through finite element analysis, the stress distribution σ s (r) is obtained, where r is the distance from any point on the bisector line at the notch root to the notch root; The stress distribution σ s (r) is corrected using a stress gradient correction function to obtain the corrected stress σ e (L0 / 2); The corrected stress σ for judging the critical point e Whether the error between (L0 / 2) and the fatigue limit of a smooth specimen of the same material is within a preset threshold; If so, taking the currently applied external load as the fatigue limit of the damage part to be predicted; If not, 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 is the preset threshold, and taking the external load at this time as the fatigue limit of the damage part to be predicted.

7. A fatigue limit prediction device for impact-corrosion coupling damaged structures based on the critical distance, characterized in that, Including: A three-dimensional fractal dimension confirmation module for calculating the three-dimensional fractal dimension of the damage structure to be predicted according to the planar image of the damage structure to be predicted under impact-corrosion coupling; A theoretical stress concentration factor confirmation module for calculating the theoretical stress concentration factor of the damage notch according to the damage condition of the damage structure to be predicted; A stress gradient correction function confirmation module, configured to establish a stress gradient correction function for the damage notch root of the damage structure to be predicted according to the three-dimensional fractal dimension and the theoretical stress concentration factor; A material-critical distance table, configured to store the critical distance L0 of each material; A lookup module, configured to look up the critical distance corresponding to the material of the damage structure to be predicted currently from the material-critical distance table; A fatigue limit confirmation module, configured to establish a three-dimensional model of the damage structure to be predicted, and use the external load of the three-dimensional model when the error between the corrected stress at the critical point and the fatigue limit of the smooth specimen is a preset threshold as the fatigue limit of the damage structure to be predicted, wherein the critical point is the point at a distance of L0 / 2 from the notch root on the bisector of the notch root, and the corrected stress is the stress obtained after correcting the stress distribution calculated by the three-dimensional model using the stress gradient correction function.

8. The shock-corrosion coupling damage structure fatigue limit prediction device based on the critical distance according to claim 7, characterized in that, The specific stress gradient correction function is as follows: In the formula, 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 line of the notch root to the notch root, and a is a constant.

9. An impact-corrosion coupling damage structure fatigue limit prediction device based on critical distance, comprising a processor and an executable program stored in a memory and executable on the processor, characterized in that: When the processor executes the executable program, the method described in any one of claims 1-6 is implemented.

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

Images