Corrosion fatigue crack propagation life prediction method based on environmental damage model

Abstract

The invention provides a corrosion fatigue crack propagation life prediction method based on an environmental damage model, and the method comprises the steps: building a corrosion fatigue damage model according to a fatigue damage model considering the effects of maximum stress and plastic strain and the influence of an environmental factor Cenv; carrying out a low-cycle fatigue test and a corrosion fatigue crack propagation test by utilizing the low-cycle fatigue sample and the compact tensile sample to respectively obtain low-cycle fatigue data and corrosion fatigue crack propagation rates under different stress ratios; the damage model is written into a subprogram in a USDFLD user subprogram interface provided by finite element software ABAQUS, corrosion fatigue crack propagation simulation is carried out, and the corrosion fatigue crack propagation rate of the standard compact tensile sample under different stress ratios is predicted. The influence of a fatigue damage model and an environmental factor Cenv is taken into consideration, finite element simulation is carried out in combination with a USDFLD subprogram of finite element software ABAQUS, and corrosion fatigue crack propagation simulation of the structure is achieved. The method is high in universality and easy to master and implement.

Description

Technical Field

[0001] This patent relates to the field of corrosion fatigue crack prediction and simulation technology, and specifically to a corrosion fatigue crack extension life prediction method based on an environmental damage model. Background Art

[0002] Power station structural materials have been in service for a long time in a high-temperature and high-pressure circulating water environment. Corrosion fatigue is one of their potential failure forms. The increase in parameters such as steam temperature and pressure leads to a very harsh service environment for the key high-temperature pipelines of the unit. In particular, when there are various defects such as cracks in the pipelines, the safe operation of the unit is seriously threatened, and a scientific and accurate life assessment is required.

[0003] The Key Laboratory of Nuclear Materials and Safety Assessment of the Chinese Academy of Sciences has carried out a lot of work on the corrosion fatigue behavior of domestic power plant structural materials and proposed the IMR model. Compared with low-cycle fatigue tests, fatigue crack growth data in high-temperature and high-pressure water environments need to be further enriched, and the crack growth law, mechanism and model of nuclear power structural materials in high-temperature and high-pressure water environments need to be further improved. After cracks appear in in-service equipment, determining the number of cycles or time required for crack growth to a critical size is crucial for fatigue design based on damage tolerance method and determining the remaining life of components. Fatigue crack growth data of power plant structural materials is one of the basic data for power plant design and service safety evaluation. Since the service environment of key power plant components such as power plant pressure vessels, main pipelines, and steam generators is a high-temperature and high-pressure water environment, studying the fatigue crack growth behavior of power plant structural materials in a high-temperature and high-pressure water environment is crucial for nuclear power plant design, safe operation, and aging management. Therefore, establishing a corrosion fatigue crack growth life prediction method based on a coupled environmental factor fatigue damage model suitable for water environments is of great significance to the corrosion fatigue safety assessment of domestic power plant structural materials in my country. Summary of the invention

[0004] The purpose of the present invention is to provide a corrosion fatigue crack growth life prediction method based on an environmental damage model for the corrosion fatigue crack growth behavior of a structure under the combined action of corrosion and fatigue loads. env The corrosion fatigue damage model was established based on the influence of the stress ratio. Low-cycle fatigue tests and corrosion fatigue crack growth tests were carried out using low-cycle fatigue specimens and compact tensile specimens, and the low-cycle fatigue data and corrosion fatigue crack growth rates under different stress ratios were obtained respectively. The damage model was written as a subroutine in the USDFLD user subroutine interface provided by the finite element software ABAQUS, and corrosion fatigue crack growth simulation was carried out to predict the corrosion fatigue crack growth rates of standard compact tensile specimens under different stress ratios.

[0005] The technical solution of the present invention is as follows: A method for predicting corrosion fatigue crack growth life based on an environmental damage model, comprising the following steps:

[0006] S1: Establishing the corrosion fatigue damage model includes the following steps:

[0007] S1.1: Calculate the cyclic stress-strain relationship using the formula:

[0008]

[0009] where σ max , σ min and Δσ are the maximum stress, minimum stress and stress range respectively; K′ and n′ are the cyclic strength coefficient and cyclic strain hardening exponent respectively, Δε p is the cyclic plastic strain;

[0010] S1.2: Calculate the cyclic plastic strain using the formula:

[0011]

[0012] Where R is the stress ratio;

[0013] S1.3: Calculate the low cycle fatigue life using the following formula:

[0014]

[0015] Where N f is the low cycle fatigue life, C 1 and β are the low cycle fatigue life coefficient and low cycle fatigue life index respectively;

[0016] S1.4: Calculate fatigue damage using the following formula:

[0017]

[0018] where ω f is fatigue damage, N is the number of cycles;

[0019] Where R v is the stress multiaxiality coefficient, and the formula is:

[0020]

[0021] Where ν is Poisson's ratio, is the stress triaxiality;

[0022] S1.6: Calculate corrosion fatigue damage using the following formula:

[0023]

[0024] Among them C env It is an environmental factor;

[0025] S2: Carry out low cycle fatigue test on low cycle fatigue specimens to obtain low cycle fatigue test data;

[0026] S3: Perform fitting regression based on low-cycle fatigue test data to obtain various characteristic parameters of the corrosion fatigue damage model;

[0027] S4: Write the corrosion fatigue damage model established in S1 into a Fortran language subroutine based on the USDFLD interface;

[0028] S5: Using the standard compact tensile specimen CT specimen as the fatigue crack growth research object, fatigue crack growth tests were carried out in air environment and water environment respectively to obtain the corresponding average fatigue crack growth rate data;

[0029] S6: For standard compact tensile specimens, corrosion fatigue crack growth simulation is carried out using ABAQUS.

[0030] In S2, the low cycle fatigue sample is 316LN stainless steel.

[0031] Low cycle fatigue tests were carried out at 330°C with a stress ratio of R=-1 and strain amplitudes of 0.3%, 0.4%, 0.6%, 0.8% and 1.0% respectively, and low cycle fatigue test data under different conditions were obtained.

[0032] The S3 includes:

[0033] S3.1: First, according to formula (1), and through the maximum stress σ used in S2 max , minimum stress σ min and the cyclic plastic strain Δε p , the fitting results show that the cyclic strength coefficient K′=349.87686MPa and the cyclic strain hardening exponent n′=0.30469;

[0034] S3.2: Then, according to the low-cycle fatigue life calculation formula (3), the low-cycle fatigue life N f , and the maximum stress σ used in S2 max , cyclic plastic strain Δε p , the low cycle fatigue life coefficient C is obtained by fitting 1 =6277396 and low cycle fatigue life index β = -0.71099.

[0035] In S4, the corrosion fatigue damage ω is obtained by formula (6): cf , if corrosion fatigue damage ω cfIf it is greater than 0.995, the fatigue crack begins to expand; otherwise, it means that the crack has not reached the critical expansion point.

[0036] In S5, 316LN stainless steel was selected, and the CT specimen at a high temperature of 330°C was used as the fatigue crack growth research object, with the initial stress intensity factor K = 10 MPa·m 0.5 As the research load, the stress ratio R=0.1, the loading and unloading time is 30s, and the fatigue crack growth tests in air environment and water environment are carried out respectively to obtain the corresponding fatigue crack growth rate.

[0037] The S6 comprises,

[0038] S6.1: Based on the fatigue damage formula (4) and the fatigue crack growth test data in the air environment in S5, a finite element simulation of the standard compact tensile specimen CT specimen is performed. At this time, the environmental factor C env =0, take the initial damage index q=0.1; extract the corresponding average crack growth rate according to the simulation results, compare the simulation results with the fatigue crack growth test results in the air environment in S5, and debug to obtain the damage index q when the error between the two is less than 10%;

[0039] S6.2: Then, according to the corrosion fatigue damage formula (6) and the corrosion fatigue crack growth test in the water environment in S5, the finite element simulation of the standard compact tensile specimen CT specimen is carried out. At this time, the damage index q = 0.5, and the initial environmental factor C is taken env =-0.1; extract the corresponding average crack growth rate according to the simulation results, compare the simulation results with the fatigue crack growth test results in the air environment in S5, and debug to obtain the environmental factor C when the error between the two is less than 10% env .

[0040] Damage index q = 0.5, environmental factor C env =-0.55.

[0041] The S6 finite element simulation was performed using ABAQUS2020.

[0042] Finite element simulation includes:

[0043] Establish the finite element model of the CT specimen with main load tensile loading. In order to improve the calculation efficiency, the 1 / 4 model is used for modeling. In the material property module, the elastic plastic parameters at high temperature, the user-defined field USDFLD, and the number of custom variables DEPVAR are set to 7. The mesh is divided in the mesh module. The binding coupling between the reference point and the pin hole center is set in the contact module. The output custom parameter SDV is set in the analysis step module, where SDV6 is the damage value. Set the tensile load in the load module, as well as the constraint conditions: including symmetry conditions and fixed conditions;

[0044] Submit the task calculation in the job module to obtain the calculation results containing corrosion fatigue damage. In the result file, the damage SDV6 can be obtained from the field variables to determine the failure time of the node or unit, and the corrosion fatigue crack extension length can be determined and extracted based on the distance between the failure node and the initial crack.

[0045] The remarkable effects of the present invention are:

[0046] (1) The method provided by the present invention takes into account the maximum stress and plastic strain in the structure and the environmental factor C env The influence of corrosion on fatigue crack growth rate was studied, and a fatigue damage model was established to achieve the rationality and accuracy of the simulation results of corrosion fatigue crack growth rate.

[0047] (2) The present invention establishes a calculation framework and implementation method based on the finite element software ABAQUS combined with the USDFLD subroutine, which effectively realizes the corrosion fatigue crack propagation simulation of the structure. The method is simple and easy to implement and has strong scalability. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 Detailed flow chart of the corrosion fatigue crack growth life prediction method based on the coupled environmental factor fatigue damage model

[0049] Figure 2 Fitting of cyclic stress-strain data of 316LN at 330℃

[0050] Figure 3 Fitting of low cycle fatigue life data of 316LN at 330℃

[0051] Figure 4 Compact Tension Specimen (CT Specimen) Finite Element Model

[0052] Figure 5 Schematic diagram of fatigue crack damage growth DETAILED DESCRIPTION

[0053] Many specific details are described in the following description to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways than those described herein, and those skilled in the art can make similar generalizations without violating the connotation of the present application, so the present application is not limited by the specific implementation disclosed below.

[0054] The terms used in one or more embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit one or more embodiments of the present application. The singular forms of "a", "said" and "the" used in one or more embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings. It should also be understood that the term "and / or" used in one or more embodiments of the present application refers to and includes any or all possible combinations of one or more associated listed items.

[0055] It should be understood that, although the terms first, second, etc. may be used to describe various information in one or more embodiments of the present application, such information should not be limited to these terms. These terms are only used to distinguish the same type of information from each other. For example, without departing from the scope of one or more embodiments of the present application, the first may also be referred to as the second, and similarly, the second may also be referred to as the first.

[0056] The corrosion fatigue crack growth life prediction method based on the coupled environmental factor fatigue damage model provided by the present invention includes considering the effects of maximum stress and plastic strain as well as the environmental factor C env Influence, establish fatigue damage model; fit damage model parameters based on low cycle fatigue test data; write corrosion fatigue damage model subroutine based on USDFLD in ABAQUS software; establish compact tensile specimen finite element model, realize finite element simulation and extract corrosion fatigue damage and crack extension results. It is characterized by including the following steps:

[0057] S1: Based on the fatigue damage model considering the effects of maximum stress and plastic strain and the environmental factor C env The influence of corrosion fatigue damage model is established. The establishment of corrosion fatigue damage model mainly includes the following steps:

[0058] (1) First, calculate the cyclic stress-strain relationship, and the calculation formula is:

[0059]

[0060] where σ max , σ min and Δσ are the maximum stress, minimum stress and stress range respectively; K′ and n′ are the cyclic strength coefficient and cyclic strain hardening exponent respectively, Δε p is the cyclic plastic strain.

[0061] (2) Then calculate the cyclic plastic strain, and its calculation formula is:

[0062]

[0063] Where R is the stress ratio.

[0064] (3) Then calculate the low cycle fatigue life, the calculation formula is:

[0065]

[0066] Where N f is the low cycle fatigue life, C 1 and β are the low cycle fatigue life coefficient and low cycle fatigue life index respectively.

[0067] (4) Secondly, fatigue damage is calculated using the following formula:

[0068]

[0069] where ω f is fatigue damage, and N is the number of cycles.

[0070] Where R v is the stress multiaxiality coefficient, and the formula is:

[0071]

[0072] Where ν is Poisson's ratio, is the stress triaxiality.

[0073] (5) Finally, the corrosion fatigue damage is calculated using the following formula:

[0074]

[0075] Among them C env is an environmental factor. env When =0, it is considered that the environment has no effect on fatigue damage.

[0076] S2: Carry out low cycle fatigue test on low cycle fatigue specimens to obtain low cycle fatigue test data;

[0077] S3: Perform fitting regression based on low-cycle fatigue test data to obtain various characteristic parameters of the corrosion fatigue damage model;

[0078] S4: Write a corrosion fatigue damage subroutine. Use the established coupled environmental factor fatigue damage model to write a Fortran language subroutine based on the USDFLD interface. The critical value of corrosion fatigue damage is 0.995, that is, nodes with damage values ​​greater than 0.995 will fail. At this time, there are still two important parameters in the corrosion fatigue damage subroutine (damage index q and environmental factor C env ) is not determined, the following steps are required to determine the specific value;

[0079] S5: Using the standard compact tensile specimen CT specimen as the fatigue crack growth research object, fatigue crack growth tests were carried out in air environment and water environment respectively to obtain the corresponding average fatigue crack growth rate data;

[0080] S6: Finally, for the standard compact tensile specimen CT specimen, ABAQUS is used to carry out corrosion fatigue crack propagation simulation. The damage value of the crack front unit is greater than or equal to 0.995 as the basis for judging the unit failure. The unit that reaches the critical value of damage is identified as the location of the crack, thereby realizing the corrosion fatigue crack propagation of the simulated crack. The parameters in the corrosion fatigue damage formula are fitted in combination with the finite element simulation results. The specific steps include:

[0081] (1) First, according to the fatigue damage formula (4), the finite element simulation of the standard compact tensile specimen is carried out according to the fatigue crack growth in the air environment. At this time, the environmental factor C env =0, and the initial damage index q = 0.1. The corresponding average crack growth rate is extracted according to the simulation results, and the simulation results and test results are compared so that the error between the two is less than 10%. Finally, the damage index q is obtained by debugging;

[0082] (2) Then, according to the corrosion fatigue damage formula (6), the corrosion fatigue crack growth test in the water environment is carried out by finite element simulation of the standard compact tensile specimen. At this time, the damage index q has been determined, and the initial environmental factor C is taken env =-0.1. The corresponding average crack growth rate is extracted according to the simulation results, and the error between the simulation results and the test results is made less than 10%. Finally, the environmental factor C is obtained by debugging. env .

[0083] The finite element simulation is performed using ABAQUS2020, and the corrosion fatigue crack propagation simulation process includes the following steps:

[0084] (1) First, establish the finite element model of the CT specimen under the main load tensile loading. In order to improve the calculation efficiency, the 1 / 4 model is used for modeling. In the material property module, the elastic plastic parameters at high temperature, the user-defined field USDFLD, and the number of custom variables DEPVAR are set to 7. The mesh is divided in the mesh module. The binding coupling between the reference point and the pin hole center is set in the contact module. The output custom parameter SDV is set in the analysis step module, where SDV6 is the damage value. Set the tensile load in the load module, as well as the constraint conditions: including symmetry conditions and fixed conditions;

[0085] (2) Submit the task calculation in the job module to obtain the calculation results containing corrosion fatigue damage. In the result file, the damage SDV6 can be obtained from the field variables to determine the failure time of the node or unit, and the corrosion fatigue crack extension length can be determined and extracted based on the distance between the failure node and the initial crack.

[0086] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Figure 1 As shown, the following steps are included:

[0087] S1: Building the model

[0088] S2: 316LN stainless steel was selected, and low cycle fatigue tests were carried out at 330°C with a stress ratio of R = -1 and strain amplitudes of 0.3%, 0.4%, 0.6%, 0.8%, and 1.0% using low cycle fatigue specimens, to obtain low cycle fatigue test data under different conditions;

[0089] S3: Perform fitting regression based on low-cycle fatigue test data to obtain various characteristic parameters of the corrosion fatigue damage model. The fitting of various characteristic parameters of the corrosion fatigue damage model mainly includes the following steps:

[0090] S3.1: First, according to formula (1), and through the maximum stress σ used in S2 max , minimum stress σ min and the cyclic plastic strain Δε p , the fitting results show that the cyclic strength coefficient K′=349.87686MPa and the cyclic strain hardening exponent n′=0.30469 (such as Figure 2 shown):

[0091]

[0092] S3.2: Then, according to the low-cycle fatigue life calculation formula (3), the low-cycle fatigue life N f , and the maximum stress σ used in S2 max , cyclic plastic strain Δε p , the low cycle fatigue life coefficient C is obtained by fitting 1 = 6277396 and low cycle fatigue life index β = -0.71099 (such as Figure 3 shown):

[0093]

[0094] S4: Write a corrosion fatigue damage subroutine. Write a Fortran language subroutine based on the USDFLD interface using the corrosion fatigue damage model established in S1, i.e., formula (6). The corrosion fatigue damage ω is obtained through (6). cf , corrosion fatigue damageω cf The critical value of is 0.995, that is, if the corrosion fatigue damage ω cf If it is greater than 0.995, the fatigue crack begins to expand; otherwise, it means that the crack has not reached the critical expansion;

[0095] At this time, the corrosion fatigue damage subroutine still has two important parameters: damage index q and environmental factor C env If not determined, the following steps are required to determine the specific value;

[0096] S5: 316LN stainless steel was selected and the CT specimens at 330℃ were used as the fatigue crack growth research object. The initial stress intensity factor was K = 10 (MPa·m 0.5 ) as the research load, the stress ratio R = 0.1, the loading and unloading time is 30s, and the fatigue crack growth tests in air environment and water environment are carried out respectively to obtain the corresponding fatigue crack growth rate;

[0097] S6: For the CT specimen in S5, ABAQUS is used to carry out corrosion fatigue crack growth simulation. The CT specimen model is as follows: Figure 4 According to formula (4) or (6) and the test data of S5, fatigue damage ω is obtained f or corrosion fatigue damageω cf , if fatigue damage ω f or corrosion fatigue damageω cf If it is greater than or equal to 0.995, it means that the fatigue crack begins to expand; otherwise, it means that the crack has not reached the critical expansion; the parameters in the corrosion fatigue damage formula are fitted based on the finite element simulation results. The specific steps include:

[0098] S6.1: First, according to the fatigue damage formula (4) and the fatigue crack growth test data in the air environment in S5, the finite element simulation of the standard compact tensile specimen CT specimen is carried out. At this time, the environmental factor C env =0, and the initial damage index q=0.1. The corresponding average crack growth rate is extracted according to the simulation results, and the simulation results are compared with the fatigue crack growth test results in the air environment in S5, so that the error between the two is less than 10%. Finally, the damage index q=0.5 is obtained by debugging:

[0099]

[0100] S6.2: Then, according to the corrosion fatigue damage formula (6) and the corrosion fatigue crack growth test data in the water environment in S5, the finite element simulation of the standard compact tensile specimen CT specimen is carried out. At this time, the damage index q = 0.5, and the initial environmental factor C is taken env =-0.1. The corresponding average crack growth rate is extracted according to the simulation results, and the simulation results are compared with the fatigue crack growth test results in the air environment in S5, so that the error between the two is less than 10%. Finally, the environmental factor C is obtained by debugging. env =-0.55:

[0101]

[0102] The finite element simulation is performed using ABAQUS2020, and the corrosion fatigue crack propagation simulation process includes the following steps:

[0103] (1) First, establish the finite element model of the CT specimen under the main load tensile loading. In order to improve the calculation efficiency, the 1 / 4 model is used for modeling. In the material property module, the elastic plastic parameters at high temperature, the user-defined field USDFLD, and the number of custom variables DEPVAR are set to 7. The mesh is divided in the mesh module. The binding coupling between the reference point and the pin hole center is set in the contact module. The output custom parameter SDV is set in the analysis step module, where SDV6 is the damage value. Set the tensile load in the load module, as well as the constraint conditions: including symmetry conditions and fixed conditions;

[0104] (2) Submit the task calculation in the job module to obtain the calculation results containing corrosion fatigue damage. In the result file, the damage SDV6 can be obtained from the field variables to determine the failure time of the node or unit, and the corrosion fatigue crack extension length can be determined and extracted based on the distance between the failure node and the initial crack.

[0105] The above description is only a preferred embodiment of this patent and is not intended to limit this patent. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of this patent should be included in the scope of protection of this patent.

[0106] It should be noted that, for the above-mentioned method embodiments, for the sake of simplicity of description, they are all expressed as a series of action combinations, but those skilled in the art should be aware that the present application is not limited by the described action sequence, because according to the present application, certain steps can be performed in other sequences or simultaneously. Secondly, those skilled in the art should also be aware that the embodiments described in the specification are all preferred embodiments, and the actions and modules involved are not necessarily required by the present application.

[0107] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0108] The preferred embodiments of the present application disclosed above are only used to help explain the present application. The optional embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation methods described. Obviously, many modifications and changes can be made according to the content of the present application. The present application selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present application, so that those skilled in the art can understand and use the present application well.

Claims

1. A corrosion fatigue crack growth life prediction method based on an environmental damage model, characterized in that: The following steps are involved: S1: Establishing the corrosion fatigue damage model includes the following steps: S1.1: Calculate the cyclic stress-strain relationship using the formula: where σ max , σ min and Δσ are the maximum stress, minimum stress and stress range respectively; K′ and n′ are the cyclic strength coefficient and cyclic strain hardening exponent respectively, Δε p is the cyclic plastic strain; S1.2: Calculate the cyclic plastic strain using the formula: Where R is the stress ratio; S1.3: Calculate the low cycle fatigue life using the following formula: Where N f is the low cycle fatigue life, C1 and β are the low cycle fatigue life coefficient and low cycle fatigue life index respectively; S1.4: Calculate fatigue damage using the following formula: where ω f is fatigue damage, N is the number of cycles; Where R v is the stress multiaxiality coefficient, and the formula is: Where ν is Poisson's ratio, is the stress triaxiality; S1.6: Calculate corrosion fatigue damage using the following formula: Among them C env It is an environmental factor; S2: Carry out low cycle fatigue test on low cycle fatigue specimens to obtain low cycle fatigue test data; S3: Perform fitting regression based on low-cycle fatigue test data to obtain various characteristic parameters of the corrosion fatigue damage model; S4: Write the corrosion fatigue damage model established in S1 into a Fortran language subroutine based on the USDFLD interface; S5: Using the standard compact tensile specimen CT specimen as the fatigue crack growth research object, fatigue crack growth tests were carried out in air environment and water environment respectively to obtain the corresponding average fatigue crack growth rate data; S6: For standard compact tensile specimens, corrosion fatigue crack growth simulation is carried out using ABAQUS.

2. The method for predicting corrosion fatigue crack growth life based on an environmental damage model according to claim 1, characterized in that: In S2, the low cycle fatigue sample is 316LN stainless steel.

3. The method for predicting corrosion fatigue crack growth life based on an environmental damage model according to claim 2, characterized in that: Low cycle fatigue tests were carried out at 330°C with a stress ratio of R=-1 and strain amplitudes of 0.3%, 0.4%, 0.6%, 0.8% and 1.0% respectively, and low cycle fatigue test data under different conditions were obtained.

4. The method for predicting corrosion fatigue crack growth life based on an environmental damage model according to claim 1, characterized in that: The S3 includes: S3.1: First, according to formula (1), and through the maximum stress σ used in S2 max , minimum stress σ min and the cyclic plastic strain Δε p , the fitting results show that the cyclic strength coefficient K′=349.87686MPa and the cyclic strain hardening exponent n′=0.30469; S3.2: Then, according to the low-cycle fatigue life calculation formula (3), the low-cycle fatigue life N f , and the maximum stress σ used in S2 max , cyclic plastic strain Δε p The fitting results show that the low-cycle fatigue life coefficient C1=6277396 and the low-cycle fatigue life exponent β=-0.71099.

5. The method for predicting corrosion fatigue crack growth life based on an environmental damage model according to claim 1, characterized in that: In S4, the corrosion fatigue damage ω is obtained by formula (6): cf , if corrosion fatigue damage ω cf If it is greater than 0.995, the fatigue crack begins to expand; otherwise, it means that the crack has not reached the critical expansion point.

6. The method for predicting corrosion fatigue crack growth life based on an environmental damage model according to claim 1, characterized in that: In S5, 316LN stainless steel was selected, and the CT specimen at a high temperature of 330°C was used as the fatigue crack growth research object, with the initial stress intensity factor K = 10 MPa·m 0.5 As the research load, the stress ratio R=0.1, the loading and unloading time is 30s, and the fatigue crack growth tests in air environment and water environment are carried out respectively to obtain the corresponding fatigue crack growth rate.

7. The method for predicting corrosion fatigue crack growth life based on an environmental damage model according to claim 1, characterized in that: The S6 comprises, S6.1: Based on the fatigue damage formula (4) and the fatigue crack growth test data in the air environment in S5, a finite element simulation of the standard compact tensile specimen CT specimen is performed. At this time, the environmental factor C env =0, take the initial damage index q=0.1; extract the corresponding average crack growth rate according to the simulation results, compare the simulation results with the fatigue crack growth test results in the air environment in S5, and debug to obtain the damage index q when the error between the two is less than 10%; S6.2: Then, according to the corrosion fatigue damage formula (6) and the corrosion fatigue crack growth test in the water environment in S5, the finite element simulation of the standard compact tensile specimen CT specimen is carried out. At this time, the damage index q = 0.5, and the initial environmental factor C is taken env =-0.1; extract the corresponding average crack growth rate according to the simulation results, compare the simulation results with the fatigue crack growth test results in the air environment in S5, and debug the environmental factor C when the error between the two is less than 10% env .

8. The method for predicting corrosion fatigue crack growth life based on an environmental damage model according to claim 7, characterized in that: Damage index q = 0.5, environmental factor C env =-0.

55.

9. The method for predicting corrosion fatigue crack growth life based on an environmental damage model according to claim 7, characterized in that: The S6 finite element simulation was performed using ABAQUS2020.

10. The method for predicting corrosion fatigue crack growth life based on an environmental damage model according to claim 7, characterized in that: Finite element simulation includes: Establish the finite element model of the CT specimen with main load tensile loading. In order to improve the calculation efficiency, the 1 / 4 model is used for modeling. In the material property module, the elastic plastic parameters at high temperature, the user-defined field USDFLD, and the number of custom variables DEPVAR are set to 7. The mesh is divided in the mesh module. The binding coupling between the reference point and the pin hole center is set in the contact module. The output custom parameter SDV is set in the analysis step module, where SDV6 is the damage value. Set the tensile load in the load module, as well as the constraint conditions: including symmetry conditions and fixed conditions; Submit the task calculation in the job module to obtain the calculation results containing corrosion fatigue damage. In the result file, the damage SDV6 can be obtained from the field variables to determine the failure time of the node or unit, and the corrosion fatigue crack extension length can be determined and extracted based on the distance between the failure node and the initial crack.

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