Method and apparatus for predicting fatigue limit of structure subjected to impact-corrosion coupling damage

Abstract

The application discloses a kind of based on critical distance method's impact-corrosion coupling damage structure fatigue limit prediction method and equipment, the present application is according to the plan image of impact-corrosion coupling predicted damage structure to calculate three-dimensional fractal dimension;According to the damage situation of predicted damage structure, the theoretical stress concentration coefficient is calculated;According to the three-dimensional fractal dimension and the theoretical stress concentration coefficient, the stress gradient correction function of damage notch root is established;Look up pre-generated material-critical distance table to obtain the critical distance corresponding to the material of current predicted damage structure;Establish the three-dimensional model of predicted damage structure, when the error of the correction stress corresponding to critical point and the fatigue limit of smooth sample is the preset threshold value, the external load on three-dimensional model is as the fatigue limit of predicted damage piece.The prediction process of the present application is relatively simple, only needs linear elastic analysis, and prediction accuracy is higher.

Description

Technical Field

[0001] This invention relates to fatigue limit prediction technology for damaged structures, and more particularly to a method and device for predicting fatigue limit of impact-corrosion coupled damaged structures. Background Technology

[0002] Structures often face complex operating environments and various forms of damage during service, resulting in significant reductions in their load-bearing capacity, fatigue life, and reliability, potentially leading to the loss of structural integrity. Therefore, accurately assessing the fatigue limit of structures under complex service environments to ensure they meet the required fatigue life and high reliability is a crucial engineering issue. Some critical structures in engineering projects are inevitably subjected to impacts from external objects during operation, easily leading to stress concentration, residual stress, and microstructural damage at the impact sites. Simultaneously, the humidity and pH levels of the operating environment further corrode the structure, typically forming micro-pits on the material surface. Under the coupled effects of impact and corrosion, these damage gaps can become crack initiation sites, rapidly propagating under fatigue loads, resulting in significantly reduced structural fatigue performance and high-cycle failure.

[0003] Scholars both domestically and internationally have proposed various mathematical models for predicting the fatigue limit of notched components, such as Neuber's average stress model, Peterson's modified Peterson formula, Taylor's critical distance theory, Hudak's worst-case notch model, and Weibull's weakest-loop theory based on statistical data. These models each have their advantages and disadvantages in predicting fatigue in notched components. When applied to notches with different damage forms, it is necessary to analyze the notch characteristics, obtain characterization parameters, and incorporate them into the model. The damage morphology and microstructure of coupled-damage notches are the main factors affecting their fatigue strength, and they are related to the type and size of the external object, impact velocity and angle, structural material, corrosion environment, and duration. Currently, there are relatively few studies comprehensively considering the fatigue performance of impact-corrosion coupled-damage notches. For such coupled-damage notches, the fatigue limit is generally predicted by calculating the theoretical stress concentration factor based on the macroscopic notch morphology. However, this method cannot consider the influence of the notch stress gradient, resulting in low prediction accuracy, and it also cannot account for the influence of coupled damage. Therefore, there is still no simple and accurate method for predicting the fatigue limit of coupled-damage notches in engineering. Summary of the Invention

[0004] Purpose of the invention: This invention addresses the problems existing in the prior art by providing a method and device for predicting the fatigue limit of structures with higher accuracy in predicting impact-corrosion coupled damage.

[0005] Technical solution: In a first aspect, the present invention provides a method for predicting the fatigue limit of structures with coupled impact-corrosion damage based on critical distance, comprising:

[0006] The three-dimensional fractal dimension of the damage structure to be predicted is calculated based on the planar image of the impact-corrosion coupled damage structure.

[0007] The theoretical stress concentration factor of the damage notch is calculated based on the damage condition of the structure to be damaged.

[0008] Based on the three-dimensional fractal dimension and the theoretical stress concentration factor, a stress gradient correction function is established at the root of the damage notch in the structure to be predicted.

[0009] Find the critical distance corresponding to the material of the current damage structure to be predicted by searching the pre-generated material-critical distance table;

[0010] A three-dimensional model of the damaged structure to be predicted is established. 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 is taken as the fatigue limit of the damaged part to be predicted.

[0011] Furthermore, the calculation of the three-dimensional fractal dimension of the damaged structure based on the planar image of the impact-corrosion coupled damaged structure specifically includes:

[0012] Acquire a planar image of the damage region of the structure to be predicted under impact-corrosion coupling, and convert it to a grayscale image;

[0013] A three-dimensional grayscale surface is established by using the coordinates of the pixels as planar coordinates and the grayscale value of the pixels as the z-axis coordinates.

[0014] The three-dimensional fractal dimension of the three-dimensional grayscale surface is calculated and used as the three-dimensional fractal dimension of the damaged structure to be predicted.

[0015] Furthermore, the calculation of the theoretical stress concentration factor of the damage notch based on the damage condition of the structure to be damaged specifically includes:

[0016] Based on the damage depth and damage width of the structure to be predicted, the radius of curvature at the notch root is calculated using the following formula:

[0017]

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

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

[0020]

[0021] In the formula, K T This represents the theoretical stress concentration factor.

[0022] Furthermore, the stress gradient correction function is specifically as follows:

[0023]

[0024] In the formula, K is the stress gradient correction function. T denoted by , D is the three-dimensional fractal dimension, r is the distance from any point on the bisecting line at the root of the notch to the root of the notch, and a is a constant.

[0025] Optionally, the critical distance is obtained by the following method:

[0026] Randomly select several impact-corrosion coupled damage structures with the same damage conditions as the material of the structure to be damaged;

[0027] The fatigue limit σ0 of a smooth specimen identical to the material of the damaged structure to be predicted and the fatigue limits σ1, σ2, ... of several selected damaged structures were obtained through experiments.

[0028] Establish a three-dimensional model for each selected damaged structure, and obtain the stress distribution σ on the bisecting line at the root of the notch in each damaged structure through finite element analysis. s，1 (r),σ s,2 (r),...;

[0029] For each damaged structure, the stress distribution σ s，1 (r),σ s,2 (r),... is corrected using the stress gradient correction function to obtain the corrected stress distribution σ. e，1 (r),σ e,2 (r),...;

[0030] Let σ e，1 (r)=σ0,σ e,2 (r) = σ0,..., and the values ​​of r1, r2,... are obtained by solving for r respectively;

[0031] Calculate twice the average value of r1, r2, ... as the critical distance L0.

[0032] Furthermore, the establishment of a three-dimensional model of the damaged structure to be predicted, where the error between the corrected stress at the critical point and the fatigue limit of the smooth specimen is a preset threshold, uses the external load on the three-dimensional model as the fatigue limit of the damaged component to be predicted, specifically includes:

[0033] Based on the damage width and depth of the structure to be damaged, a three-dimensional finite element model is established. Initial external load values ​​are applied to the three-dimensional model, and the stress distribution σ on the bisecting line at the root of the notch is obtained through finite element analysis. s (r), where r is the distance from any point on the bisection line at the root of the gap to the root of the gap;

[0034] Stress distribution σ s (r) The stress gradient correction function is used to correct the stress, and the corrected stress σ at the critical point is obtained. e (L0), where L0 is the critical distance;

[0035] Determine the corrected stress σ at the critical point e (L0) Whether the error between the fatigue limit of the smooth specimen of the same material and that of the L0 is within the preset threshold;

[0036] If so, the currently applied external load is taken as the fatigue limit of the component to be damaged;

[0037] If not, adjust the applied external load value until the error between the corrected stress at the critical point and the fatigue limit of the smooth specimen is equal to the preset threshold. Then, take the external load at this point as the fatigue limit of the damaged part to be predicted.

[0038] Secondly, the present invention also provides a fatigue limit prediction device for impact-corrosion coupled damage structures based on critical distance, comprising:

[0039] The 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 planar image of the damage structure to be predicted by the impact-corrosion coupling.

[0040] The theoretical stress concentration factor confirmation module is used to calculate the theoretical stress concentration factor of the damage notch based on the damage condition of the structure to be predicted.

[0041] The stress gradient correction function confirmation module is used to establish the stress gradient correction function at the root of the damage notch in the structure to be predicted based on the three-dimensional fractal dimension and the theoretical stress concentration factor.

[0042] A material-critical distance table is used to store the critical distances of various materials; wherein, the critical distance is the distance from the point on the bisection line of the notch root to the notch root when the stress is the fatigue limit of a smooth specimen of the same material in any damaged structure.

[0043] The lookup module is used to look up the material-critical distance table to obtain the critical distance corresponding to the material of the current damage structure to be predicted.

[0044] The fatigue limit confirmation module is used to establish a three-dimensional model of the damaged structure 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, 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 after correcting the stress distribution calculated by the three-dimensional model using the stress gradient correction function.

[0045] Thirdly, the present invention also provides a fatigue limit prediction device for impact-corrosion coupled damage structures based on critical distance, comprising a processor and an executable program stored in a memory and capable of running on the processor, characterized in that: when the processor executes the executable program, it implements the method described in the first aspect.

[0046] Fourthly, the present invention also provides a storage medium comprising a computer-executable program, which, when executed by a computer processor, is used to perform the method described in the first aspect.

[0047] Compared with the prior art, the beneficial effects of this invention are: this invention links the coupled damage parameters with the damage notch gradient, and predicts the fatigue limit of the coupled damage notch based on the critical distance method. The prediction process is relatively simple, requiring only linear elastic analysis, and the prediction accuracy is high. Attached Figure Description

[0048] Figure 1 This is a flowchart illustrating the fatigue limit prediction method for impact-corrosion coupled damage structures based on critical distance provided by the present invention.

[0049] Figure 2 This is a schematic diagram of the fatigue limit prediction device for impact-corrosion coupled damage structures based on critical distance provided by the present invention.

[0050] Figure 3 This is a schematic diagram of the structure of the impact-corrosion coupled damage structure fatigue limit prediction device based on critical distance provided by the present invention;

[0051] Figure 4 This is a damage morphology diagram of specimen 2-2 with impact-corrosion coupled damage structure;

[0052] Figure 5 This is a three-dimensional grayscale surface image of specimen 2-2, which shows the impact-corrosion coupled damage structure. Detailed Implementation

[0053] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0054] The terms "first," "second," etc., used in the specification, claims, and accompanying drawings of this invention are used to distinguish different objects, not to describe a specific order. The reference to "embodiment" herein means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0055] Example 1

[0056] This invention provides a method for predicting the fatigue limit of structures with impact-corrosion coupled damage based on critical distance, such as... Figure 1 As shown, it includes the following steps:

[0057] S101. Calculate the three-dimensional fractal dimension of the damage structure to be predicted based on the planar image of the damage structure to be predicted under impact-corrosion coupling.

[0058] The three-dimensional fractal dimension is a mathematical tool used to describe the complexity of a three-dimensional fractal object. It is obtained by recursively dividing the three-dimensional fractal object and then calculating the size ratio of each level of division, ultimately yielding a dimension value, i.e., the three-dimensional fractal dimension.

[0059] In some embodiments, step S101 can be implemented by the following steps:

[0060] S1011. Obtain a planar image of the damage region of the structure to be predicted under impact-corrosion coupling, and convert it into a grayscale image. The pixel size of the planar image can be set to 256×256, or divided into 256×256 grids, with the average grayscale value of each grid as the grid grayscale value.

[0061] S1012. Using the coordinates of the pixel in the grayscale image as the planar coordinates and the grayscale value of the pixel as the z-axis coordinate, a three-dimensional grayscale surface is established.

[0062] 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. Box-counting is a commonly used method for calculating the three-dimensional fractal dimension. The coordinate space of the three-dimensional grayscale surface is a large cube of 256×256×256. The large cube is divided into smaller cubes with side length k. Note that 256 / k is an integer, so the cube is divided into (256 / k) smaller cubes. 3 Given N boxes, build a MATLAB program to calculate the number of boxes that cover the grayscale surface of an image. r (k). Changing the side length k of the box yields a set of N. r (k), calculate the point pairs {ln(256 / k), ln(N)} r The linear regression of (k))} yields a straight line, the slope of which is the three-dimensional fractal dimension D. The expression for D is as follows:

[0063] S102. Calculate the theoretical stress concentration factor of the damage notch based on the damage condition of the structure to be damaged.

[0064] The theoretical stress concentration factor is the ratio of the maximum actual stress to the nominal stress at the root of the notch, obtained from elastic theory under ideal elastic conditions. In some embodiments, step S102 can be obtained by the following method:

[0065] S1021. Based on the damage depth and damage width of the structure to be predicted, calculate the radius of curvature at the notch root according to the following formula:

[0066]

[0067] In the formula, ρ represents the radius of curvature at the root of the notch, l represents the damage width, and d represents the damage depth;

[0068] S1022. Calculate the theoretical stress concentration factor of the damaged structure to be predicted based on the radius of curvature at the notch root using the following formula:

[0069]

[0070] In the formula, K T This represents the theoretical stress concentration factor.

[0071] S103. Establish the stress gradient correction function at the root of the damage gap in the structure to be predicted based on the three-dimensional fractal dimension and the theoretical stress concentration factor.

[0072] Specifically, the stress gradient correction function is:

[0073]

[0074] In the formula, K is the stress gradient correction function. T denoted by , D is the three-dimensional fractal dimension, r is the distance from any point on the bisecting line at the root of the notch to the root of the notch, and a is a constant.

[0075] S104. Find the critical distance corresponding to the material of the current damaged structure by searching the pre-generated material-critical distance table.

[0076] The critical distance is defined as twice the distance from the notch root to a point on the bisecting line of any damage notch when the maximum principal stress at that point is the fatigue limit of a smooth part made of the same material. The critical point is a point on the bisecting line of the notch root at a distance L0 / 2 from the notch root. A material-critical distance table is pre-generated, and the critical distance is only related to the material, ideally being a constant, meaning that the critical distance is equal for any damage structure made of the same material. Ideally, the critical distance can be calculated experimentally using any damage structure when generating the critical distance. However, in reality, due to various errors such as simulation errors, the calculated critical distance for different damaged structures fluctuates within a small range. Therefore, to improve prediction accuracy, the following method can be used to calculate the critical distance: Randomly select several impact-corrosion coupled damage structures with the same material as the damaged structure to be predicted; obtain the fatigue limit σ0 of a smooth specimen with the same material as the damaged structure to be predicted and the fatigue limits σ1, σ2,... of the selected damage structures through experiments; establish a three-dimensional model for each selected damage structure, perform mesh generation, refine the mesh near the notch, assign material properties to the finite element model, apply boundary conditions to the model, simulate its load condition in a real environment, and obtain the stress distribution σ on the bisecting line at the root of the notch of each damage structure through finite element analysis. s，1 (r),σ s,2 (r),...;For each damaged structure, the stress distribution σ s，1 (r),σ s,2 (r),... is corrected using a stress gradient correction function to obtain 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.

[0077] S105. Establish a three-dimensional model of the damaged structure 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, the external load on the three-dimensional model is taken as the fatigue limit of the damaged part to be predicted.

[0078] In some embodiments, step S105 specifically includes:

[0079] S1051. Based on the damage width and depth of the structure to be damaged, a three-dimensional finite element model is established. The model is meshed, with the mesh refined at the notch root. Initial external load values ​​are applied to the three-dimensional model. Through finite element analysis, the stress distribution σ along the bisecting line at the notch root is obtained. s (r), where r is the distance from any point on the bisection line at the root of the gap to the root of the gap;

[0080] S1052, Stress distribution σ s (r) The stress gradient correction function is used to correct the stress, and the corrected stress σ at the critical point is obtained. e (L0 / 2), where L0 is the critical distance;

[0081] S1053. Determine the corrected stress σ at the critical point. e (L0) Whether the error between the fatigue limit σ0 of the smooth specimen of the same material and (L0) is within the preset threshold;

[0082] S1054. If so, the currently applied external load shall be taken as the fatigue limit of the component to be damaged.

[0083] S1055. If not, adjust the applied external load value until the error between the corrected stress at the critical point and the fatigue limit of the smooth specimen is equal to the preset threshold. Then, take the external load at this point as the fatigue limit of the damaged part to be predicted.

[0084] Example 2

[0085] Figure 2 This is a schematic diagram of a fatigue limit prediction device for impact-corrosion coupled damage structures based on critical distance, provided in an embodiment of the present invention. The system can be implemented using software and / or hardware, and the device can be configured in a terminal device. The device includes:

[0086] The 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 planar image of the damage structure to be predicted by the impact-corrosion coupling.

[0087] Theoretical stress concentration factor confirmation module 202 is used to calculate the theoretical stress concentration factor of the damage notch based on the damage condition of the structure to be predicted.

[0088] The stress gradient correction function confirmation module 203 is used to establish the 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 factor.

[0089] Material-Critical Distance Table 204 is used to store the critical distance L0 of each material;

[0090] The lookup module 205 is used to look up the material-critical distance table to obtain the critical distance corresponding to the material of the current damage structure to be predicted.

[0091] The fatigue limit confirmation module 206 is used to establish a three-dimensional model of the damaged structure 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, 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 after correcting the stress distribution calculated by the three-dimensional model using the stress gradient correction function.

[0092] Specifically, the three-dimensional fractal dimension confirmation module 201 includes:

[0093] The image conversion unit is used to acquire a planar image of the damage region of the structure to be predicted under impact-corrosion coupling and convert it into a grayscale image;

[0094] The grayscale surface creation unit is used to create a three-dimensional grayscale surface from the grayscale image by using the coordinates of the pixel as the planar coordinates and the grayscale value of the pixel as the z-axis coordinate.

[0095] 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.

[0096] The theoretical stress concentration factor confirmation module 202 specifically includes:

[0097] The radius of curvature calculation unit is used to calculate the radius of curvature at the root of the notch according to the damage depth and damage width of the damage structure to be predicted, using the following formula:

[0098]

[0099] In the formula, ρ represents the radius of curvature at the root of the notch, l represents the damage width, and d represents the damage depth;

[0100] The coefficient calculation unit is used to calculate the theoretical stress concentration factor of the damaged structure to be predicted based on the radius of curvature at the notch root according to the following formula:

[0101]

[0102] In the formula, K T This represents the theoretical stress concentration factor.

[0103] The critical distance is obtained through a critical distance calculation module, which is used to implement the following methods:

[0104] Randomly select several impact-corrosion coupled damage structures with the same damage conditions as the material of the structure to be damaged;

[0105] The fatigue limit σ0 of a smooth specimen identical to the material of the damaged structure to be predicted and the fatigue limits σ1, σ2, ... of several selected damaged structures were obtained through experiments.

[0106] Establish a three-dimensional model for each selected damaged structure, and obtain the stress distribution σ on the bisecting line at the root of the notch in each damaged structure through finite element analysis. s，1 (r),σ s,2 (r),...;

[0107] For each damaged structure, the stress distribution σ s，1 (r),σ s,2 (r),... is corrected using the stress gradient correction function to obtain the corrected stress distribution σ. e，1 (r),σ e,2 (r),...;

[0108] Let σ e，1 (r)=σ0,σ e,2 (r) = σ0,..., and the values ​​of r1, r2,... are obtained by solving for r respectively;

[0109] Calculate twice the average value of r1, r2, ... as the critical distance. n is the number of randomly selected damaged structures.

[0110] The fatigue limit confirmation module 206 specifically includes:

[0111] The model building unit is used to establish a finite element three-dimensional model of the structure to be damaged based on the damage width and damage depth. Initial external load values ​​are applied to the three-dimensional model, and the stress distribution σ along the bisecting line at the root of the notch is obtained through finite element analysis. s (r), where r is the distance from any point on the bisection line at the root of the gap to the root of the gap;

[0112] Stress correction element, used to adjust stress distribution σ s (r) The stress gradient correction function is used to correct the stress, and the corrected stress σ at the critical point is obtained. e (L0), where L0 is the critical distance;

[0113] The judgment unit is used to determine the corrected stress σ at the critical point. e (L0) Whether the error between the fatigue limit of the smooth specimen of the same material and that of the L0 is within the preset threshold;

[0114] The first determination unit is used to take the currently applied external load as the fatigue limit of the damaged part if the result of the determination unit is yes.

[0115] The second determination unit is used to adjust the value of the applied external load if the result of the determination unit is negative, and return to the execution model establishment unit to the determination unit until the error between the corrected stress at the critical point and the fatigue limit of the smooth specimen is a preset threshold. At this point, the external load is taken as the fatigue limit of the damaged part to be predicted.

[0116] The apparatus provided in this embodiment of the invention can be used to execute the method provided in Embodiment 1 of the invention, and has the corresponding functions and beneficial effects of executing the method. Details not covered herein are as described in Embodiment 1 and will not be repeated here.

[0117] It is worth noting that in the embodiments of the above-mentioned determining device, the various units and modules included are only divided according to functional logic, but are not limited to the above division, as long as the corresponding functions can be realized; in addition, the specific names of each functional unit are only for easy differentiation and are not used to limit the scope of protection of the present invention.

[0118] The embodiments described above are merely illustrative. 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; that is, they may be located in one place or distributed across multiple network modules. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art will clearly understand that each implementation can be achieved using software plus necessary general-purpose hardware platforms, or it can be implemented solely through hardware, as long as the function or purpose can be achieved.

[0119] Example 3

[0120] Figure 3 This is a schematic diagram of the structure of a device provided in Embodiment 3 of the present invention. This embodiment provides services for implementing the method of Embodiment 1 of the present invention. Figure 3 As shown, the device may include: a memory 301 storing a computer-executable program; a processor 302 coupled to the memory 301; the processor 302 calls the computer-executable program stored in the memory 301 to perform the steps in the method described in Embodiment 1.

[0121] 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, memory 301 may be used to read and write non-removable, non-volatile magnetic media (commonly referred to as a "hard disk drive"). A program / utility having a set (at least one) of program modules may be stored, for example, in memory 301. Such program modules include, but are not limited to, an operating system, one or more application programs, other program modules, and program data. Each or some combination of these examples may include an implementation of a network environment. The computer-executable program of the program modules typically performs the functions and / or methods described in the embodiments of the present invention.

[0122] The code 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, and C++, as well as conventional procedural programming languages ​​such as the "C" language or similar programming languages.

[0123] The processor 302 executes various functional applications and data processing by running programs stored in the memory 301, such as implementing the method provided in Embodiment 1 of the present invention.

[0124] Example 4

[0125] This invention provides a storage medium containing a computer-executable program, which, when executed by a computer processor, is used to perform the method of Embodiment 1.

[0126] The storage medium of embodiments of the present invention may be any combination of one or more computer-readable media. A computer-readable medium may be a computer-readable signal medium or a computer-readable storage medium. A 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 of computer-readable storage media (a non-exhaustive list) include: an electrical connection having one or more wires, a portable computer disk, a hard disk, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, portable compact disk read-only memory (CD-ROM), optical storage device, magnetic storage device, or any suitable combination thereof. In this document, a computer-readable storage medium may be any tangible medium containing or storing a program that can be used by or in conjunction with an instruction execution system, apparatus, or device.

[0127] The code for a computer-executable program that performs the operations of this invention can be written in one or more programming languages ​​or a combination thereof. Programming languages ​​include object-oriented programming languages ​​such as Java, Smalltalk, and C++, as well as conventional procedural programming languages ​​such as C or similar languages. The program code can be executed entirely on the user's computer, partially on the user's computer, as a standalone 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 remote computers, the remote computer can be connected to the user's computer via any type of network, including a local area network (LAN) or a wide area network (WAN), or it can be connected to an external computer (e.g., via the Internet using an Internet service provider).

[0128] Of course, the computer-executable program provided in the embodiments of the present invention is not limited to the above-described method operations, but can also perform related operations in the methods provided in any embodiment of the present invention.

[0129] The present invention will now be experimentally verified.

[0130] The experiment used 13Cr stainless steel for the structure and conducted pre-damage experiments under different impact and corrosion environments. The external damage parameters were steel balls with diameters of 2mm and 3mm, made of GGr15 steel. Impact velocities included 200m / s and 300m / s. Corrosion damage parameters: the corrosive solution was a 5% (w / w) NaCl solution, with dilute H₂SO₄ added to adjust the pH to 4 ± 0.2; corrosion durations included 24h, 48h, and 96h; the corrosion temperature was maintained at a constant 40°C; and the solution was replaced every 48h.

[0131] 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 below. Figure 4 As shown, the grayscale surface of the image is as follows: Figure 5 As shown, the three-dimensional fractal dimension of the image is calculated to be 2.2276.

[0132] Taking specimen 2-2 as an example, the damage width of the specimen is l = 1.097 mm, the damage depth is d = 0.553 mm, and the radius of curvature at the notch root is calculated to be ρ = 0.544. Therefore, the theoretical stress concentration factor K... T =3.016. The stress gradient correction function is: The fatigue limit of the smooth specimen was obtained as 575.11 MPa, and the critical distance of the material was calculated to be 0.07 mm. A modified critical distance model was used to predict the fatigue limit of the coupled damage notch. The prediction results are shown in Table 1. In the table, σ... e To experimentally determine the fatigue limit, σ p The prediction result is given by the expression: `error` represents the relative error.

[0133] Experimental Results Table 1

[0134]

[0135] Using this invention to predict the fatigue limit of coupled damage notches, the overall trend of the prediction results is consistent with the experimental results, all within the ±20% error range.

Claims

1. A method for predicting the fatigue limit of structures subjected to impact-corrosion coupled damage based on critical distance, characterized in that, include: The three-dimensional fractal dimension of the damage structure to be predicted is calculated based on the planar image of the impact-corrosion coupled damage structure. The theoretical stress concentration factor of the damage notch is calculated based on the damage condition of the structure to be damaged. Based on the three-dimensional fractal dimension and the theoretical stress concentration factor, a stress gradient correction function is established at the root of the damage notch in the structure to be predicted. Find the critical distance L0 corresponding to the material of the current damage structure to be predicted by searching the pre-generated material-critical distance table; A three-dimensional model of the damaged structure to be predicted is established. 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 is taken as the fatigue limit of the damaged structure to be predicted. The critical point is the point on the bisection line of the notch root at a distance of L0 / 2 from the notch root. The corrected stress is the stress obtained after correcting the stress distribution calculated by the three-dimensional model using the stress gradient correction function. The calculation of the theoretical stress concentration factor of the damage notch based on the damage condition of the structure to be damaged specifically includes: Based on the damage depth and damage width of the structure to be predicted, the radius of curvature at the notch root is calculated using the following formula: , In the formula, Indicates the radius of curvature at the root of the notch. Indicates the width of the damage. Indicates the depth of damage; The theoretical stress concentration factor of the damaged structure to be predicted is calculated based on the radius of curvature at the root of the notch using the following formula: , In the formula, Indicates the theoretical stress concentration factor; The stress gradient correction function is specifically: , In the formula, This is the stress gradient correction function. denoted by , D is the three-dimensional fractal dimension, r is the distance from any point on the bisecting line at the root of the notch to the root of the notch, and a is a constant.

2. The method for predicting the fatigue limit of impact-corrosion coupled damage structures based on critical distance according to claim 1, characterized in that, The calculation of the three-dimensional fractal dimension of the damage structure based on the planar image of the impact-corrosion coupled damage structure specifically includes: Acquire a planar image of the damage region of the structure to be predicted under impact-corrosion coupling, and convert it to a grayscale image; A three-dimensional grayscale surface is established by using the coordinates of the pixels as planar coordinates and the grayscale value of the pixels as the z-axis coordinates. The three-dimensional fractal dimension of the three-dimensional grayscale surface is calculated and used as the three-dimensional fractal dimension of the damaged structure to be predicted.

3. The fatigue limit prediction method for impact-corrosion coupled damage structures based on critical distance according to claim 1, wherein the critical distance is obtained by the following method: Randomly select several impact-corrosion coupled damage structures with the same damage conditions as the material of the structure to be damaged; The fatigue limit of a smooth specimen identical to the material of the structure whose damage was to be predicted was obtained through experiments. and the fatigue limit of several selected damaged structures ; Establish a three-dimensional model for each selected damaged structure, and obtain the stress distribution along the bisecting line at the root of the notch in each damaged structure through finite element analysis. ; Stress distribution for each damaged structure The corrected stress distribution is obtained by using a stress gradient correction function. ; make The values ​​of r, r1, r2, ..., are obtained by solving for r respectively. Calculate twice the average value of r1, r2, ... as the critical distance. .

4. The method for predicting the fatigue limit of impact-corrosion coupled damage structures based on critical distance according to claim 1, characterized in that, The establishment of a three-dimensional model of the damaged structure to be predicted, wherein 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 is used as the fatigue limit of the damaged component to be predicted, specifically includes: Based on the damage width and depth of the structure to be damaged, a three-dimensional finite element model is established. Initial external load values ​​are applied to the three-dimensional model, and the stress distribution along the bisecting line at the root of the notch is obtained through finite element analysis. , where r is the distance from any point on the bisection line at the root of the gap to the root of the gap; Stress distribution The corrected stress at the critical point is obtained by using a stress gradient correction function. , ; Correction stress for determining the critical point Whether the error in fatigue limit compared to a smooth specimen of the same material is within a preset threshold; If so, the currently applied external load is taken as the fatigue limit of the component to be damaged; If not, adjust the applied external load value until the error between the corrected stress at the critical point and the fatigue limit of the smooth specimen is equal to the preset threshold. Then, take the external load at this point as the fatigue limit of the damaged part to be predicted.

5. A device for predicting the fatigue limit of impact-corrosion coupled damage structures based on critical distance, characterized in that, include: The 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 planar image of the damage structure to be predicted by the impact-corrosion coupling. The theoretical stress concentration factor confirmation module is used to calculate the theoretical stress concentration factor of the damage notch based on the damage condition of the structure to be predicted. The stress gradient correction function confirmation module is used to establish the stress gradient correction function at the root of the damage notch in the structure to be predicted based on the three-dimensional fractal dimension and the theoretical stress concentration factor. The material-critical distance table stores the critical distance L0 for each material. The lookup module is used to look up the material-critical distance table to obtain the critical distance corresponding to the material of the current damage structure to be predicted. The fatigue limit confirmation module is used to establish a three-dimensional model of the damaged structure 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, the external load of the three-dimensional model is taken as the fatigue limit of the damaged structure to be predicted. The critical point is the point on the bisecting line at the root of the notch, at a distance of L0 / 2 from the root of the notch. The corrected stress is the stress obtained after correcting the stress distribution calculated by the three-dimensional model using the stress gradient correction function. The theoretical stress concentration factor confirmation module specifically includes: The radius of curvature calculation unit is used to calculate the radius of curvature at the root of the notch according to the damage depth and damage width of the damage structure to be predicted, using the following formula: , In the formula, Indicates the radius of curvature at the root of the notch. Indicates the width of the damage. Indicates the depth of damage; The coefficient calculation unit is used to calculate the theoretical stress concentration factor of the damaged structure to be predicted based on the radius of curvature at the notch root according to the following formula: , In the formula, Indicates the theoretical stress concentration factor; The stress gradient correction function is specifically: , In the formula, This is the stress gradient correction function. denoted by , D is the three-dimensional fractal dimension, r is the distance from any point on the bisecting line at the root of the notch to the root of the notch, and a is a constant.

6. A fatigue limit prediction device for impact-corrosion coupled damage structures based on critical distance, comprising a processor and an executable program stored in a memory and capable of running on the processor, characterized in that: When the processor executes the executable program, it implements the method as described in any one of claims 1-4.

7. A storage medium containing a computer-executable program, characterized in that, The computer executable program, when executed by a computer processor, is used to perform the method as described in any one of claims 1-4.

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