Long crack propagation residual life evaluation method

Abstract

The invention discloses a long crack propagation residual life evaluation method, which is applied to the field of component safety evaluation. In order to solve the problem that a traditional crack propagation model is poor in adaptability to a material subjected to surface treatment, dynamic treatment of fracture mechanical parameters of the crack propagation model and correction of a crack propagation threshold are carried out by introducing a hardness gradient and a residual stress gradient contained in a modified layer, and a brand new crack propagation model is obtained. And long crack propagation residual life evaluation is facilitated. According to the method, on the basis of a traditional crack propagation model Paris model, the basic rule of long crack propagation can be simulated, the hardness gradient and the residual stress gradient serve as two main contents introduced by the surface treatment technology and can reflect the gradient structure of a part subjected to surface treatment, the two factors are considered in the crack propagation model, and the precision of the part is improved. And meanwhile, the hardness gradient and the residual stress gradient appear in various surface treatment processes, and the application range is wide.

Description

Technical Field

[0001] This invention relates to the field of component safety assessment technology, and in particular to a method for assessing the remaining life of long crack propagation. Background Technology

[0002] In modern engineering structures, fatigue crack propagation is one of the main causes of failure in mechanical components and infrastructure. Especially when cracks reach the "long crack" stage (millimeters or larger), the propagation rate accelerates significantly, potentially leading to catastrophic accidents. Statistics show that approximately 80% of structural failures can be attributed to the initiation and propagation of fatigue cracks. While the long crack propagation stage accounts for only 10%-30% of fatigue life, it directly determines the final failure timing of the structure, becoming a critical window for safety assessment.

[0003] Surface modification techniques (such as shot peening, rolling, and induction hardening) significantly improve the fatigue resistance of material surfaces by introducing a residual compressive stress layer. For example, shot peening can reduce the crack depth of high-speed train axles by more than 50% and increase fatigue life by more than 250% when the crack depth is less than 4 mm. However, the presence of the modified layer also complicates crack propagation behavior and brings new scientific challenges. Although residual compressive stress can effectively delay the propagation of shallow cracks, its inhibitory effect weakens sharply as the crack extends deeper, and it may even induce secondary crack bifurcation due to stress gradient. At the same time, the increase in surface hardness caused by surface treatment may also lead to a decrease in material plasticity and a weakening of crack propagation resistance. Therefore, developing a long crack propagation life assessment method for surface modified layers is not only related to the safe operation of major equipment, but also a key technical support for realizing "damage-tolerant design" and "predictive maintenance".

[0004] To date, the engineering field has developed a multi-level methodology for assessing the remaining life of cracked structures, ranging from empirical formulas to numerical simulations. Current main methods include: the stress intensity factor (SIF) concept based on linear elastic fracture mechanics (LEFM); Paris and its improved methods, which describe the relationship between crack tip stress intensity and propagation rate; analytical methods that express the relationship between crack propagation rate and load conditions and geometric factors through simple empirical formulas; and the extended finite element method (XFEM), which decouples the geometric description of physical discontinuities from the topology of the finite element mesh based on the finite element method (FEM). XFEM enhances the expressive power of the approximation by locally and selectively adding special functions (called enrichment functions) to the standard FEM approximation space, thereby accurately capturing jumps across discontinuities and singularities near the crack tip and numerically simulating the crack propagation path. The former method, due to its use of coarse fracture mechanics parameters, is difficult to express the gradient change law of the material surface and has poor adaptability to the gradient structure of the surface modification layer. The latter method is difficult to determine the gradient structure and residual stress reconstruction of the material in finite modeling, and has high computational cost and requires a lot of computational resources.

[0005] Therefore, there is an urgent need for a computationally simple method for assessing the remaining lifetime of long crack propagation that can address the adaptability issues of modified layer gradient structures. Summary of the Invention In view of this, to address the problem of poor adaptability of traditional crack propagation models to surface-treated materials, this invention proposes a method for assessing the remaining life of long crack propagation in surface-modified layers. Based on the Paris crack propagation analytical model, by introducing the hardness gradient and residual stress gradient contained in the modified layer, the fracture mechanics parameters of the crack propagation model are dynamically processed and the crack propagation threshold is corrected, resulting in a novel crack propagation model that can better characterize the long crack propagation process under gradient structures, facilitating accurate assessment and prediction of the remaining life of long crack propagation.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, embodiments of the present invention provide a method for assessing the remaining life of long crack propagation. Based on the Paris crack propagation analytical model, a hardness gradient and a residual stress gradient are introduced to modify the crack propagation threshold and fracture mechanics parameters, thereby obtaining a long crack propagation model adapted to the influence of the gradient structure of the surface modification layer. Based on the long crack propagation model, the long crack propagation process under the gradient structure is characterized, and the remaining life of long crack propagation is assessed.

[0007] In one specific implementation, the method includes the following steps: S1. Perform basic analysis on the component to be solved to determine its geometric characteristics, load conditions, crack morphology, and obtain the surface gradient field; wherein the surface gradient field includes the hardness gradient field and the residual stress gradient field. S2. Obtain the crack propagation threshold of the core structure and surface hardened layer of the component material, as well as the fracture mechanics parameters in the Paris crack propagation analytical model, through experiments or reference value queries. S3. Using the parameters obtained in step S2 and the hardness gradient field and residual stress field obtained in step S1, construct a binary mapping of the crack propagation threshold of the component in the radial direction with stress ratio and hardness gradient, and construct a mapping of fracture mechanical parameters with hardness gradient. S4. Based on the fracture mechanics parameters and crack propagation threshold obtained in step S3, modify the Paris crack propagation analytical model to obtain the long crack propagation model; S5. Using the geometry, load conditions, and crack morphology obtained in S1, the crack propagation rate obtained from the long crack propagation model is integrally solved to obtain the remaining life.

[0008] In one specific embodiment, in step S2, at least the stress ratio is obtained. Crack propagation threshold and fracture mechanics parameters under two loading conditions.

[0009] In one specific implementation, step S3, establishing the mapping relationship, includes: ① The variation law of the core microstructure crack propagation threshold under the influence of stress ratio is determined as follows:

[0010] in, Indicates the crack propagation threshold, subscript co Indicates the core, R represents the stress ratio; The variation law of the crack propagation threshold of the surface hardened layer under the influence of stress ratio is determined as follows:

[0011] Among them, subscript su Indicates surface tissue; ② The residual stress is used to correct the nominal stress ratio to the actual stress ratio using the superposition theory; the actual stress ratio after correction by introducing residual stress is:

[0012] in, Indicates the actual stress ratio. The minimum stress intensity factor representing the external load. Indicates the maximum stress intensity factor under external load. This represents the stress intensity factor corresponding to the residual stress; ③ Combining the models obtained in ① and ②, establish the function of the crack propagation threshold changing on the surface gradient field, expressed as:

[0013]

[0014] in, This indicates the current hardness value. Indicates the Vickers hardness of the core structure. The Vickers hardness indicates the surface hardness of the hardened layer. This represents the crack propagation threshold that varies with depth. ④ Establish the empirical relationship between fracture mechanics parameters and hardening, expressed as:

[0015]

[0016] in, to These are the fitting parameters, , These are fracture mechanics parameters.

[0017] In one specific embodiment, the long crack propagation model obtained in step S4 is as follows:

[0018] in, This represents the crack propagation rate. , All of these are fracture mechanics parameters. This is the effective stress intensity factor.

[0019] In one specific embodiment, the necessary condition for crack propagation in the long crack propagation model is:

[0020] in, This represents the crack propagation threshold that varies with depth.

[0021] In one specific embodiment, the termination condition for crack propagation in the long crack propagation model is:

[0022]

[0023] in, Crack size The critical crack size. The maximum stress intensity factor, This refers to fracture toughness.

[0024] In a second aspect, the present invention also provides an electronic device, including a processor and a memory, wherein the memory stores machine-executable instructions that can be executed by the processor, and the processor executes the machine-executable instructions to implement the above-described method for assessing the remaining life of long crack propagation.

[0025] Compared with the prior art, the present invention has at least the following beneficial effects: This invention provides a method for assessing the remaining life of long crack propagation. Based on the Paris crack propagation analytical model, by introducing the hardness gradient and residual stress gradient contained in the modified layer, the fracture mechanics parameters of the crack propagation model are dynamically processed and the crack propagation threshold is corrected, resulting in a novel crack propagation model that can better characterize the long crack propagation process under gradient structures. This method is computationally simple and can solve the adaptation problem of the gradient structure of the modified layer, making it easy to accurately assess and predict the remaining life of long crack propagation.

[0026] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description and the accompanying drawings.

[0027] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0030] Figure 1 This is a schematic diagram of the basic characteristics of the sample provided in the embodiment of the present invention, wherein (a) is the basic dimensions of the sample and (b) is a cross-sectional view of the gradient modification layer on the surface of the sample after induction hardening.

[0031] Figure 2 This is a schematic diagram of the gradient information of the surface modification layer of the sample used in the embodiment of the present invention, wherein (a) is the microhardness test result and (b) is the residual stress test result.

[0032] Figure 3 This is a schematic flowchart of the method for assessing the remaining life of long crack propagation provided in an embodiment of the present invention.

[0033] Figure 4 This is a binary space representation of the crack propagation threshold correction relationship provided in the embodiments of the present invention.

[0034] Figure 5 This is a schematic diagram of the variation curves of fracture mechanics parameters in the gradient layer provided in an embodiment of the present invention, wherein (a) shows the variation trend of parameter C and (b) shows the variation trend of parameter m.

[0035] Figure 6 This is a schematic diagram comparing the prediction results of the remaining lifetime of the sample under different methods provided in the embodiments of the present invention.

[0036] Figure 7 This is a schematic diagram of the electronic device structure provided in an embodiment of the present invention. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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 some embodiments of the present invention, but not all embodiments.

[0038] In the description of this invention, it should be noted that some processes described in this application specification and drawings include multiple operations that appear in a specific order. However, it should be clearly understood that these operations may be performed in any order or in parallel. Furthermore, various numbers are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0039] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0040] To address the issue of poor adaptability of traditional crack propagation models to surface-treated materials, this invention introduces the hardness gradient and residual stress gradient contained in the modified layer. This allows for dynamic processing of the empirical constants (fracture mechanics parameters C and m) of the crack propagation model and correction of the crack propagation threshold, resulting in a novel crack propagation model that facilitates the assessment of remaining life for long crack propagation. Based on the traditional Paris model, this invention can simulate the fundamental laws of long crack propagation. The hardness gradient and residual stress gradient, as two major components introduced by the surface treatment process, reflect the gradient structure of the component after surface treatment. Incorporating these two factors into the crack propagation model does not excessively increase the computational load. Furthermore, the hardness gradient and residual stress gradient appear in various surface treatment processes, making it widely applicable.

[0041] The specific implementation of the method of the present invention will be described in detail below: This invention takes a high-speed train axle steel as an example. The material is AAR-CM steel, which undergoes induction hardening to form a surface modification layer. The axle is a solid cylinder with a diameter of 17mm, containing an initial semi-elliptical surface crack. The major axis 2c = 4mm, and the minor axis 2a = 2mm (i.e., a / c = 0.5, initial depth a0 = 1mm). The surface hardened layer is approximately 3mm deep, and the hardness and residual stress are distributed in a gradient along the depth. Its specific dimensions are as follows: Figure 1 As shown. Figure 2 The surface hardness gradient and residual stress gradient of the sample are shown; its material parameters and experimental results are detailed in Tables 1 to 3.

[0042] like Figure 3 The diagram shown is a flowchart of a method for assessing the remaining life of long crack propagation according to the present invention, which specifically includes the following steps: S1. Perform basic analysis on the component to be solved to determine its geometric characteristics, load conditions, crack morphology, and obtain the surface gradient field, including the hardness gradient field and the residual stress gradient field; Figure 1 Part (a) shows the basic geometry of the induction-hardened AAR-CM axle steel, and part (b) shows the cross-sectional distribution of the hardened layer. Its load conditions and initial crack are shown in Table 1, subjected to cyclic bending stress with an amplitude of... The stress ratio R=0.1, and the surface pre-crack is a semi-elliptical crack with a depth of 1mm.

[0043] Table 1 Initial Crack Conditions and Loading Conditions of the Specimens

[0044] Microhardness test results are as follows Figure 2 As shown in section (a), the residual stress test results are as follows: Figure 2 As shown in section (b).

[0045] S2. Obtain the crack propagation threshold of the core microstructure and the surface hardened layer of the material through experiments or by consulting reference values. The fracture mechanics parameters C and m in the conventional crack propagation model, the Paris model, were used. AAR-CM axle steel was induction hardened, and four-point bending specimens (SEBN) with a core hardness of 200 HV and a surface hardness of 700 HV were obtained by exfoliation while ensuring the release of residual stress. Crack propagation rates were detected, and the crack propagation threshold was fitted using the NASGRO model formula. The fracture mechanics parameters C and m were used. The experimental results are recorded as shown in Table 2.

[0046] Table 2 Summary of fracture mechanical parameters of the core and surface of the specimens

[0047] This operation can also obtain relevant parameters by searching professional databases, and for hardened layers caused by other process parameters, as long as their maximum hardness is within the tested hardness range, no additional testing is required. In other words, it will not incur excessive costs for this method.

[0048] S3. Using the parameters obtained in S2 and the hardness gradient field and residual stress field obtained in S1, construct a binary mapping of the crack propagation threshold of the component in the radial direction as a function of stress ratio and hardness gradient, and construct the mapping of fracture mechanics parameters C and m as a function of hardness gradient; the specific steps are as follows: A1. The variation law of the core crack propagation threshold under the influence of stress ratio R is described as follows:

[0049] In this context, the subscript "co" represents the core, and the subscript "R" represents the corresponding stress ratio. This represents the crack propagation threshold.

[0050] Similarly, the variation law of the crack propagation threshold of the surface hardened tissue under the influence of stress ratio R can be obtained as follows:

[0051] Among them, subscript su It represents the surface tissue.

[0052] A2. The residual stress is corrected to the nominal stress ratio R to the actual stress ratio R(a) using the superposition theory. It should be noted that the stress ratio should be constrained between (-5, 0.8), because an excessively high stress ratio R=1 approaches static load and is meaningless for studying fatigue life, while an excessively low stress ratio results in the effective stress intensity factor for crack initiation being far below the crack propagation threshold. The actual stress ratio after residual stress correction is described as follows:

[0053] Where R(a) represents the actual stress ratio, The minimum stress intensity factor representing the external load. Indicates the maximum stress intensity factor under external load. This represents the stress intensity factor corresponding to the residual stress.

[0054] A3. Combining the models obtained from A1 and A2, a function is established to describe the change of the crack propagation threshold in the surface gradient field. This function is described as the triangular region enclosed by the two straight lines from A1 and the line R=-5. First, the function is mapped to... and Scaling to the interval (0,1), and then describing the threshold at any point using linear interpolation, is specifically expressed as follows:

[0055]

[0056] in, This represents the crack propagation threshold that varies with depth. Indicates the Vickers hardness of the core structure. The Vickers hardness indicates the surface hardness of the hardened layer. HV This indicates the current hardness value. and These represent the variation patterns of the two crack propagation thresholds obtained in step A1.

[0057] like Figure 4 The image shows the experimental sample in... Figure 2 The binary interval between the residual stress gradient and the crack propagation threshold under the hardness gradient.

[0058] A4. Establish the empirical relationship between fracture mechanics parameters C and m and hardening, and combine it with the law of change of engineering empirical parameters with hardening, which is described by the following expression:

[0059]

[0060] in, k 1 to k 4 represents the fitting parameters. The hardened layer parameters C1 and m1 obtained in step S2 are fitted with the original core tissue C2 and m2 to obtain the fracture mechanics parameters of gradient change. , .

[0061] like Figure 5 The parameters are shown in section (a). The trend and pattern of changes with hardness Figure 5 Section (b) shows the parameters. The trend of changes in hardness.

[0062] S4. A novel crack propagation model adapted to the surface-modified layer is obtained. Combining the fracture mechanics parameters and crack propagation threshold obtained in step S3, and modifying the original Paris formula, a long crack propagation model incorporating the surface-hardened layer can be obtained; the long crack propagation model is described as follows:

[0063] in, This represents the crack propagation rate. , All of these are fracture mechanics parameters. The effective stress intensity factor range can be determined using the crack closure effect based on fundamental knowledge in this field.

[0064] The necessary condition for a long crack propagation model to determine whether the crack will propagate is described as follows:

[0065] The termination condition for crack propagation in the long crack propagation model is described as follows:

[0066] in, This represents the crack size during the propagation process. The critical crack size. The maximum stress intensity factor, This refers to fracture toughness.

[0067] S5. The remaining life is obtained by integrating the geometry, load conditions, and crack shape obtained in S1 with the crack propagation rate obtained in S4; the integral solution can be described as the following numerical calculation:

[0068]

[0069]

[0070]

[0071] in, For remaining lifespan, Crack size The critical crack size. , All of these are fracture mechanics parameters. The iteration step size, , These represent the crack lengths before and after one iteration step. The remaining lifetime corresponds to the iteration step size. , for The corresponding fracture mechanics parameters.

[0072] The crack propagation model obtained earlier was established using MATLAB, and the remaining life of the experimental specimen was calculated to be 1,320,000 cycles through integration. The crack propagation path was compared with that of the classical model. Figure 6 As shown in Table 3, the experimental results, calculation results of the remaining lifetime of the Paris, NASGRO, and methods of this invention, along with their errors, are presented. It can be seen that compared to classical models, the method of this invention has higher accuracy in the case of long crack propagation with a surface-modified layer.

[0073] Table 3 Comparison of Remaining Life Calculation Results

[0074] As described in the above embodiments, those skilled in the art will understand that the present invention proposes a method for assessing the remaining lifetime of long crack propagation that includes a surface-modified layer. Based on the Paris crack propagation analytical model, by introducing surface hardness gradient and residual stress gradient to correct model empirical parameters and update the crack propagation threshold, a completely new crack propagation model is obtained. This results in a long crack propagation remaining lifetime calculation model adapted to surface modification, which can better characterize the long crack propagation process under gradient structures and facilitates accurate assessment and prediction of the remaining lifetime of long crack propagation. Specific advantages are as follows: (1) A threshold for crack propagation in the hardened layer was proposed. A simplified approach to determining the crack propagation threshold under the influence of two parameters: stress ratio R and surface Vickers hardness. This method is different from traditional delamination tests for estimating the crack propagation threshold. This solves the problem of residual stress release during delamination and improves the accuracy of estimation.

[0075] (2) The mapping relationship between fracture mechanics parameters and hardness gradient was proposed, and the law of increased material brittleness due to hardening was simulated. Compared with the delamination experiment, it has higher accuracy and lower cost.

[0076] (3) The present invention utilizes the hardness gradient information contained in the modified layer, which has higher accuracy than conventional methods for homogenizing the entire hardened layer.

[0077] (4) This invention proposes a method for assessing the remaining life of long crack propagation with a surface-modified layer. Starting from the residual stress gradient and hardness gradient caused by surface treatment, it is applicable to common surface treatments of various steels such as shot peening, rolling, and induction hardening, and has high universality.

[0078] Furthermore, referring to Figure 7As shown, this embodiment of the invention also provides an electronic device, which may include a processor 10, a memory 11, a communication bus 12 and a communication interface 13, and may also include a computer program stored in the memory 11 and executable on the processor 10. The processor executes the computer program to implement the long crack propagation remaining life assessment method in the above embodiment.

[0079] In some embodiments, the processor 10 may be composed of integrated circuits, such as a single packaged integrated circuit or multiple integrated circuits packaged with the same or different functions, including combinations of one or more central processing units, microprocessors, digital processing chips, graphics processors, and various control chips. The processor 10 is the control core of the electronic device, connecting various components of the entire electronic device through various interfaces and lines. It executes programs or modules stored in the memory 11 and calls data stored in the memory 11 to perform various functions and process data within the electronic device.

[0080] Those skilled in the art will understand that embodiments of the present invention can be provided as methods or electronic products, etc. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media containing computer-usable program code.

[0081] It should be noted that the word "comprising" does not exclude the presence of components or steps not listed in the claims. The words "a" or "an" preceding a component do not exclude the presence of a plurality of such components. This invention can be implemented by means of hardware comprising several different components and by means of a suitably programmed computer.

[0082] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0083] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for assessing the remaining life of long crack propagation, characterized in that, Based on the Paris crack propagation analytical model, hardness gradient and residual stress gradient are introduced to modify the crack propagation threshold and fracture mechanics parameters, resulting in a long crack propagation model adapted to the influence of the gradient structure of the surface modification layer. The long crack propagation process under the gradient structure is characterized based on the long crack propagation model, and the remaining life of long crack propagation is evaluated.

2. The method for assessing the remaining life of long crack propagation according to claim 1, characterized in that, The method specifically includes the following steps: S1. Perform basic analysis on the component to be solved to determine its geometric characteristics, load conditions, crack morphology, and obtain the surface gradient field; wherein the surface gradient field includes the hardness gradient field and the residual stress gradient field. S2. Obtain the crack propagation threshold of the core structure and surface hardened layer of the component material, as well as the fracture mechanics parameters in the Paris crack propagation analytical model, through experiments or reference value queries. S3. Using the parameters obtained in step S2 and the hardness gradient field and residual stress field obtained in step S1, construct a binary mapping of the crack propagation threshold of the component in the radial direction with stress ratio and hardness gradient, and construct a mapping of fracture mechanical parameters with hardness gradient. S4. Based on the fracture mechanics parameters and crack propagation threshold obtained in step S3, modify the Paris crack propagation analytical model to obtain the long crack propagation model; S5. Using the geometry, load conditions, and crack morphology obtained in step S1, the crack propagation rate obtained from the long crack propagation model is integrally solved to obtain the remaining life.

3. The method for assessing the remaining life of long crack propagation according to claim 2, characterized in that, In step S2, at least the stress ratio is obtained. and Crack propagation threshold and fracture mechanics parameters under two loading conditions.

4. The method for assessing the remaining life of long crack propagation according to claim 3, characterized in that, In step S3, the establishment of the mapping relationship includes: ① The variation law of the core microstructure crack propagation threshold under the influence of stress ratio is determined as follows: in, Indicates the crack propagation threshold, subscript co Indicates the core, R represents the stress ratio; The variation law of the crack propagation threshold of the surface hardened layer under the influence of stress ratio is determined as follows: Among them, subscript su Indicates surface tissue; ② The residual stress is used to correct the nominal stress ratio to the actual stress ratio using the superposition theory; the actual stress ratio after correction by introducing residual stress is: in, Indicates the actual stress ratio. The minimum stress intensity factor representing the external load. Indicates the maximum stress intensity factor under external load. This represents the stress intensity factor corresponding to the residual stress; ③ Combining the models obtained in ① and ②, establish the function of the crack propagation threshold changing on the surface gradient field, expressed as: in, This indicates the current hardness value. Indicates the Vickers hardness of the core structure. The Vickers hardness indicates the surface hardness of the hardened layer. This represents the crack propagation threshold that varies with depth. ④ Establish the empirical relationship between fracture mechanics parameters and hardening, expressed as: in, to These are the fitting parameters, , These are fracture mechanics parameters.

5. The method for assessing the remaining life of long crack propagation according to claim 1, characterized in that, In step S4, the obtained long crack propagation model is as follows: in, This represents the crack propagation rate. , All of these are fracture mechanics parameters. This is the effective stress intensity factor.

6. The method for assessing the remaining life of long crack propagation according to claim 5, characterized in that, The necessary condition for crack propagation in the long crack propagation model is: in, This represents the crack propagation threshold that varies with depth.

7. The method for assessing the remaining life of long crack propagation according to claim 5, characterized in that, The termination condition for the long crack propagation model is as follows: in, Crack size The critical crack size. The maximum stress intensity factor, This refers to fracture toughness.

8. An electronic device, characterized in that, It includes a processor and a memory, the memory storing machine-executable instructions that can be executed by the processor, the processor executing the machine-executable instructions to implement a method for assessing the remaining life of long crack propagation as described in any one of claims 1-7.

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