Method and system for evaluating low-cycle fatigue life damage of steam turbine rotor in peak shaving state

Abstract

The invention provides a steam turbine rotor low-cycle fatigue life damage assessment method in a peak shaving state, and belongs to the field of life assessment. The method comprises the following steps: S1, obtaining a rotor low-cycle fatigue stress-strain formula and an SWT-based low-cycle fatigue life prediction model; s2, establishing a finite element geometric model of the rotor; s3, acquiring an equivalent stress distribution cloud picture; s4, obtaining an optimized SWT low-cycle fatigue life prediction model; s5, the maximum equivalent stress in the equivalent stress distribution cloud picture is substituted into the optimized SWT low-cycle fatigue life prediction model, and the allowable cycle times under different peak regulation working conditions are obtained; and S6, based on an accumulative damage theory, carrying out accumulative calculation on the low-cycle fatigue life loss amount of the rotor under peak regulation operation. According to the method, the optimized SWT low-cycle fatigue life prediction model is utilized, the equivalent stress distribution cloud picture is combined, the complexity of calculating the maximum stress is reduced, and it is guaranteed that the equivalent stress obtained through simulation can be directly substituted into the optimized model for calculation.

Description

Technical Field

[0001] The present invention relates to the field of life assessment, and in particular to a method and system for assessing the low-cycle fatigue life damage of a steam turbine rotor under peak load conditions. Background Art

[0002] In recent years, with the increasing proportion of photovoltaic power generation and wind power generation in my country's energy structure, the demand in the electricity market has fluctuated frequently and the amplitude has increased. The load adjustment of thermal power units, that is, peak-shaving operation, has become routine. However, compared with the basic load, peak-shaving of units means more frequent start-stop and load changes. The frequent changes in steam temperature and pressure cause the turbine rotor to be subjected to alternating stress, thereby causing low-cycle fatigue damage, resulting in accelerated failure of high-temperature load-bearing components of thermal power units. Therefore, conducting low-cycle fatigue life damage assessment of steam turbine rotor components of thermal power units during peak-shaving operation is of great significance and value to strengthen the supervision and maintenance of peak-shaving thermal power units and ensure their safe operation.

[0003] At present, the evaluation model of low-cycle fatigue life mainly relies on the Manson-Coffin model. However, this model is an empirical formula summarized based on a large amount of test data. Its form is too simple and cannot reflect the impact of stress on the fatigue life of components under operating conditions.

[0004] Many scholars have made modifications based on the Manson-Coffin model and obtained the Morrow model and the SWT model. There are many methods in the prior art that use the Morrow model or the SWT model to evaluate fatigue life damage, such as CN114970009A, which discloses a method for predicting the life of a turbine blade trapezoidal wave thermomechanical fatigue test. According to the damage mechanism of the material under thermomechanical load, the pure mechanical low-cycle fatigue damage and the persistent creep damage (including the loading stage, the load holding stage, and the unloading stage) are respectively calculated. The linear cumulative damage principle is used to calculate the thermomechanical fatigue damage of the low-cycle and creep interaction of a single cycle, and then the life of the turbine blade is predicted, which has the advantage of a wide range of applications. However, it still has the following problems: when using the SWT model for low-cycle fatigue life damage assessment, the calculation process of the maximum stress is relatively complicated, requiring a large amount of basic data resources, and the solution process is very cumbersome. Summary of the invention

[0005] The technical problem to be solved by the present invention is how to solve the problems of complex maximum stress calculation process, low solution efficiency and long time required when using the SWT model for low cycle fatigue life assessment.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions: a method for evaluating the low-cycle fatigue life damage of a steam turbine rotor under peak load state, comprising the following steps:

[0007] S1: Conduct mechanical property tests and high-temperature low-cycle fatigue tests on rotor materials to obtain the rotor's low-cycle fatigue stress-strain formula, strain amplitude formula, and SWT-based low-cycle fatigue life prediction model;

[0008] S2: Use the equivalent transformation method to simplify the rotor structure and establish the rotor finite element geometric model;

[0009] S3: Mesh the rotor 3D geometric model, input boundary conditions, perform finite element stress analysis on the rotor, and obtain an equivalent stress distribution cloud map;

[0010] S4: According to the strain amplitude formula and the SWT-based low-cycle fatigue life prediction model, the optimized SWT low-cycle fatigue life prediction model is obtained;

[0011] S5: Substitute the maximum equivalent stress in the equivalent stress distribution cloud diagram into the optimized SWT low-cycle fatigue life prediction model to obtain the allowable number of cycles N under different peak load conditions. f ;

[0012] S6: Based on Miner’s cumulative damage theory, the low-cycle fatigue life loss F of the rotor under peak operation is cumulatively calculated.

[0013] Preferably, in step S1, the low cycle fatigue stress-strain formula is: in, is the stress amplitude of low cycle fatigue, K' is the cyclic strength coefficient, n' is the strain hardening exponent, is the plastic strain amplitude;

[0014] The total strain amplitude formula is: in, is the stress amplitude of low cycle fatigue, K' is the cyclic strength coefficient, n' is the strain hardening exponent, and E is the elastic modulus;

[0015] The low cycle fatigue life prediction model based on SWT is: Among them, σ max is the maximum stress, is the total strain amplitude, E is the elastic modulus, σ' f is the fatigue strength coefficient, ε' f is the fatigue ductility coefficient, b is the fatigue strength index, c is the fatigue ductility coefficient, N f It is the total number of cycles to fatigue fracture, that is, the allowable number of cycles.

[0016] Preferably, the specific process of simplifying the rotor structure by using the equivalent conversion method described in step S2 is: treating the blade root of the rotor as a whole with the rotor, replacing the blades and shrouds of the rotor with blocks of equal mass, and replacing the centrifugal force generated by the rotor during operation with an annular disk of equal mass.

[0017] Preferably, the width of the annular disk is the same as the width of the root of the rotor blade, and the radial height of the annular disk is determined by the centrifugal force generated by the blades excluding the root of the blade and the shroud during rotation.

[0018] The present invention simplifies the turbine rotor model by using an equivalent conversion method, thereby reducing the complexity of the simulation while ensuring the overall accuracy of the simulation.

[0019] Preferably, the boundary conditions described in step S3 include steam temperature and heat release coefficient at different axial positions of the rotor.

[0020] Preferably, when obtaining the heat release coefficients at different axial positions of the rotor, the heat release coefficient of the edge of the rotor disc is taken as the average value of the heat release coefficients on both sides of the disc.

[0021] Preferably, in step S4, the specific process of obtaining the optimized SWT low cycle fatigue life prediction model is: Substitute into the low cycle fatigue life prediction model based on SWT The optimized SWT low cycle fatigue life prediction model is obtained:

[0022]

[0023] Preferably, in step S5, the number of cycles N allowed under different peak load conditions is obtained. f The specific process is: Substitute the maximum equivalent stress in the equivalent stress distribution cloud map into the optimized SWT low-cycle fatigue life prediction model, that is, Substitution In the formula: Then solve the allowed number of cycles N f .

[0024] The present invention makes corrections on the SWT model, and can directly substitute the maximum equivalent stress obtained by simulation into the formula for calculation, thereby reducing the complexity of calculation.

[0025] Preferably, in step S6, the calculation formula for the low cycle fatigue life loss F is: Among them, n1, n2, ..., n n is the actual number of operations of the turbine rotor under different operating conditions, N1, N2, ..., N n It is the allowable number of low cycle fatigue cycles of the turbine rotor under different operating conditions.

[0026] Corresponding to the above method, the present invention also provides a system for assessing the low-cycle fatigue life damage of a steam turbine rotor under peak load conditions, comprising the following modules:

[0027] Obtaining life prediction model module: used to perform mechanical property tests and high-temperature low-cycle fatigue tests on rotor materials, and obtain the rotor's low-cycle fatigue stress-strain formula, total strain amplitude formula, and SWT-based low-cycle fatigue life prediction model;

[0028] Modeling module: used to simplify the rotor structure using the equivalent transformation method and establish the rotor finite element geometric model;

[0029] Obtaining equivalent stress distribution cloud map module: used to mesh the rotor 3D geometric model, input boundary conditions, perform finite element stress analysis on the rotor, and obtain the equivalent stress distribution cloud map;

[0030] Obtain optimized life prediction model module: used to obtain the optimized SWT low-cycle fatigue life prediction model according to the total strain amplitude formula and the SWT-based low-cycle fatigue life prediction model;

[0031] The module for obtaining the number of cycles allowed is used to substitute the maximum equivalent stress in the equivalent stress distribution cloud map into the optimized SWT low-cycle fatigue life prediction model to obtain the number of cycles allowed N under different peak load conditions. f ;

[0032] Life loss calculation module: used to perform cumulative calculation of the low-cycle fatigue life loss F of the rotor under peak operation based on Miner cumulative damage theory.

[0033] Compared with the prior art, the advantages of the present invention are:

[0034] (1) The equivalent conversion method is used to treat the rotor blade root and the rotor as a whole, replace the rotor blades and shrouds with blocks of equal mass, and replace the centrifugal force generated by the rotor during operation with a circular disk of equal mass, thereby simplifying the rotor structure and reducing the complexity of the simulation while ensuring the accuracy of the simulation;

[0035] (2) The optimized SWT model obtained by modification while ensuring the accuracy of the SWT model is combined with the equivalent stress distribution cloud map to reduce the complexity of calculating the maximum stress and ensure that the maximum equivalent stress obtained by simulation can be directly substituted into the optimized model calculation;

[0036] (3) The Miner cumulative damage theory is used to accumulate the low-cycle fatigue damage under different peak load conditions, and the impact of peak load on the low-cycle fatigue life of the turbine rotor is comprehensively considered;

[0037] (4) The operation is simple and the calculation is convenient. It can obtain the damage assessment results of fatigue life in a short time and has high solution efficiency. It is suitable for low-cycle fatigue life damage assessment of turbine rotors under different peak-shaving conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a flow chart of Embodiment 1 of the present invention;

[0039] Figure 2 is the finite element model of the steam turbine rotor in Example 1 of the present invention;

[0040] Figure 3 This is a stress field cloud diagram of the maximum equivalent stress at -1000MW in cold start in Example 1 of the present invention;

[0041] Figure 4 This is a stress field cloud diagram of the peak load operation to 70% of the maximum equivalent stress in Example 1 of the present invention;

[0042] Figure 5 This is a stress field cloud diagram of the peak load operation to 40% of the maximum equivalent stress in Example 1 of the present invention;

[0043] Figure 6 This is a stress field cloud diagram of the maximum equivalent stress during accident shutdown in Example 1 of the present invention. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] Example 1

[0046] like Figure 1 The flowchart of this embodiment is shown. The embodiment of the present invention provides a method for evaluating the low-cycle fatigue damage of a steam turbine rotor under peak load state. Taking the high-pressure rotor of a supercritical unit of a coal-fired thermal power plant as an example, the material of the high-pressure rotor is 12Cr10Co3MoWVNbNB rotor steel, and the damage evaluation of low-cycle fatigue life is performed. The specific steps are as follows:

[0047] Step 1: Conduct mechanical property tests and high-temperature low-cycle fatigue tests on the rotor material to obtain the rotor's low-cycle fatigue stress-strain formula, strain amplitude formula, and SWT-based low-cycle fatigue life prediction model;

[0048] The mechanical property test complies with the requirements of GB / T 228.1-2021 "Metallic material tensile test Part 1 Room temperature test method", and the low cycle fatigue test complies with the requirements of GB / T 26077-2021 "Metallic material fatigue test axial strain control method";

[0049] The low cycle fatigue characteristics of the material were tested and analyzed. To ensure the accuracy of the test, each sample was tested twice or more and the average value was taken. The test temperature was determined according to the maximum temperature of the actual operation of the turbine rotor.

[0050] In this embodiment, the test temperature is set at 598°C, the test adopts axial strain control, the stress ratio R=-1, the loading waveform is a triangular wave, and the strain rate is 5×10 -3 s -1 ;

[0051] The total strain amplitude in this embodiment The values ​​were set to 0.27%, 0.35%, 0.45%, 0.50% and 0.55% respectively. The following fatigue parameters were obtained: cyclic strength coefficient K', strain hardening exponent n', fatigue strength coefficient σ' f , fatigue ductility coefficient ε' f , fatigue strength index b and fatigue ductility index c;

[0052] The low cycle fatigue stress-strain formula is: in, is the low cycle fatigue stress amplitude, is the plastic strain amplitude;

[0053] The total strain amplitude formula is: in, is the stress amplitude of low cycle fatigue, K' is the cyclic strength coefficient, n' is the strain hardening exponent, and E is the elastic modulus, which is determined by the high temperature tensile test at the same temperature as the low cycle fatigue test;

[0054] The low cycle fatigue life prediction model based on SWT is: Among them, σ max is the maximum stress, E is the elastic modulus, N f It is the total number of cycles to fatigue fracture, that is, the allowable number of cycles.

[0055] Step 2: Establish the high-pressure rotor finite element geometric model based on the turbine rotor size and actual assembly photos.

[0056] Before modeling and finite element simulation, the equivalent conversion method can be used to simplify the structure, specifically:

[0057] Since the blade root is embedded in the rotor, there is no need to consider the centrifugal force equivalence of the blade root. It is regarded as a whole with the rotor. Therefore, in the equivalent conversion process, only the blade and the shroud are replaced with equivalent mass blocks, and the centrifugal force generated during operation is replaced with a circular ring disk of equal mass, which not only ensures the calculation accuracy but also reduces the complexity of modeling.

[0058] In the above equivalent conversion process, it is assumed that the width of the equivalent annular disk is the same as the original blade root width, and the radial height of the annular disk is determined by the centrifugal force generated by the blades and shrouds other than the blade root during rotation; when modeling, the annular disk is superimposed on the corresponding blade root position and forms a whole with the rotor, and then the finite element geometric model of the high-pressure rotor is obtained, such as Figure 2 shown.

[0059] Step 3: Mesh the rotor 3D geometric model, input boundary conditions, perform finite element stress analysis on the rotor using the indirect thermal coupling method, and obtain the equivalent stress distribution cloud map. The specific process is as follows:

[0060] S301: Mesh the finite element geometric model of the high-pressure rotor. Considering the calculation accuracy and speed, adjust the size of the mesh, select a 10 mm mesh, and further refine the local mesh at the connection between the blade disk and the rotor.

[0061] S302: Input boundary conditions. The specific process is as follows:

[0062] (1) The two end faces of the running rotor are not in contact with high-temperature, high-pressure steam, and the heat flux density is much smaller than that of the high-pressure stage rotor, so the two ends of the rotor are treated as insulation surfaces;

[0063] (2) The outer surface of the rotor is in contact with high-temperature, high-pressure steam and exchanges heat, so the steam temperature and heat release coefficient at different axial positions of the rotor are taken as the third type of boundary conditions, namely, the convection boundary conditions, also known as the Robin conditions or mixed boundary conditions, which take into account the combined effects of convection and heat conduction on the boundary;

[0064] (3) The heat release coefficient of the edge of the rotor disc is the average of the heat release coefficients on both sides of the disc;

[0065] S303: Using the indirect thermal coupling method to perform stress and strain finite element simulation calculations on the rotor, and calculating the required physical property data of the rotor material. In this embodiment, the physical property data of 12Cr10Co3MoWVNbNB steel at 598°C are shown in the following table:

[0066]

[0067] And the equivalent stress distribution cloud diagram of the rotor under different working conditions is obtained:

[0068] like Figure 3 As shown, it is the stress field cloud diagram of the maximum equivalent stress at cold start-1000MW in this embodiment. At this time, the maximum equivalent stress of the rotor is 416.88MPa;

[0069] like Figure 4As shown, it is a stress field cloud diagram when the peak load operation reaches 70% of the maximum equivalent stress in this embodiment. At this time, the maximum equivalent stress of the rotor is 384.46MPa;

[0070] like Figure 5 As shown, it is a stress field cloud diagram when the peak load operation reaches 40% of the maximum equivalent stress in this embodiment, and the maximum equivalent stress of the rotor is 373.68MPa at this time;

[0071] like Figure 6 As shown in FIG. 1 , it is a stress field cloud diagram of the maximum equivalent stress during an accident shutdown in this embodiment. At this time, the maximum equivalent stress of the rotor is 446.84 MPa.

[0072] Step 4: According to the total strain amplitude formula and the SWT-based low-cycle fatigue life prediction model, the optimized SWT low-cycle fatigue life prediction model is obtained, which is:

[0073] The total strain amplitude Substitute into the low cycle fatigue life prediction model based on SWT The optimized SWT low cycle fatigue life prediction model is obtained:

[0074]

[0075] Step 5: Substitute the maximum equivalent stress in the equivalent stress distribution cloud diagram into the optimized SWT low-cycle fatigue life prediction model to obtain the allowable number of cycles N under different peak load conditions. f , specifically:

[0076] When other parameters remain unchanged, the larger the strain amplitude, the lower the low-cycle fatigue life of the material, that is, the lower the allowable number of cycles, so in a conservative calculation, the maximum stress in the equivalent stress distribution cloud map is equivalent to the stress amplitude, that is, Substitution In the formula: When the material coefficients in the formula are determined, enter the above formula using the formula editor and directly enter σ max The allowable number of low-cycle fatigue cycles of the material can be obtained.

[0077] The life loss of the high-temperature superheater tube of the boiler under different working conditions in this embodiment is calculated as follows: the number of adjustments from cold start to 1000MW is A, and the allowable number of cycles is N1=1.75×10 5 , the number of adjustments from 1000MW to 700MW (70% load) is B, and the number of cycles allowed is N2 = 3.64 × 10 6 , the adjustment times of load 700MW-400MW (40% load) is C, and the allowed number of cycles is N3=7.5×10 6, the adjustment times of 1000MW accident shutdown is D, and the allowable cycle times is N4=1.72×10 4 , …. The details are shown in the following table:

[0078]

[0079] Step 6: In this embodiment, the damage from cold start to 1000MW condition is The damage under the condition of 1000MW changing to 700MW (70% load) is The damage under the condition of 700MW changing to 400MW (40% load) is The damage under 1000MW accident shutdown condition is Based on Miner's cumulative damage theory, the low-cycle fatigue life loss F of the rotor under peak load operation is cumulatively calculated: The low cycle fatigue life loss F is obtained from this.

[0080] In this embodiment, the low cycle fatigue test temperature of the steam turbine rotor material is set according to the actual service temperature of the rotor. The settings of other test parameters are also set according to the actual operating conditions of the rotor, which greatly improves the accuracy of the model;

[0081] According to the total strain amplitude formula and the SWT-based low-cycle fatigue life prediction model, the optimized SWT low-cycle fatigue life prediction model was obtained to correct the SWT model; the rotor structure was simplified by the equivalent conversion method before finite element simulation, which ensured the accuracy of the simulation while reducing the complexity of the simulation; combined with the equivalent stress distribution cloud map, the complexity of calculating the maximum stress was reduced, ensuring that the equivalent stress obtained from the simulation could be directly substituted into the optimized model calculation, which greatly reduced the computational complexity of low-cycle fatigue life damage assessment using the SWT low-cycle fatigue life prediction model.

[0082] Example 2

[0083] Corresponding to Example 1, this embodiment provides a system for assessing the low-cycle fatigue life damage of a steam turbine rotor under peak load conditions, including the following modules:

[0084] Obtaining life prediction model module: used to perform mechanical property tests and high-temperature low-cycle fatigue tests on rotor materials, and obtain the rotor's low-cycle fatigue stress-strain formula, total strain amplitude formula, and SWT-based low-cycle fatigue life prediction model;

[0085] Modeling module: used to simplify the rotor structure using the equivalent transformation method and establish the rotor finite element geometric model;

[0086] Obtain equivalent stress distribution cloud map module: It is used to mesh the rotor three-dimensional geometric model, input boundary conditions, perform finite element stress analysis on the rotor, and obtain the equivalent stress distribution cloud map. It specifically includes the following units:

[0087] Meshing unit: used to mesh the high-pressure rotor finite element geometric model. Considering the calculation accuracy and speed, the mesh size is adjusted and a 10 mm mesh is selected. The local mesh at the connection between the blade disk and the rotor is further refined.

[0088] Input boundary condition unit: used to input boundary conditions;

[0089] Finite element simulation calculation unit: used to perform finite element simulation calculations on the rotor's stress and strain, calculate the rotor material's physical performance data, and obtain the equivalent stress distribution cloud map.

[0090] Get optimized SWT model module: used to convert the total strain amplitude Substitute into the low cycle fatigue life prediction model based on SWT The optimized SWT low cycle fatigue life prediction model is obtained:

[0091] Get the allowable number of cycles module: It is used to substitute the maximum equivalent stress in the equivalent stress distribution cloud map into the optimized SWT low-cycle fatigue life prediction model. Substitution In the formula: Then solve the allowed number of cycles N f .

[0092] Life loss calculation module: used to perform cumulative calculation of the low-cycle fatigue life loss F of the rotor under peak load operation based on Miner cumulative damage theory. The calculation formula of the low-cycle fatigue life loss F is: where n1, n2, ..., n n is the actual number of operations of the turbine rotor under different operating conditions, N1, N2, ..., N n It is the allowable number of low cycle fatigue cycles of the turbine rotor under different operating conditions.

[0093] In this embodiment, the low-cycle fatigue stress-strain formula, the total strain amplitude formula and the low-cycle fatigue life prediction model based on SWT of the rotor are first obtained by obtaining the life prediction model module; then the rotor finite element geometric model is established by using the modeling module; and then the equivalent stress distribution cloud map is obtained by using the equivalent stress distribution cloud map obtaining module;

[0094] By using the module for obtaining optimized SWT model, the optimized SWT low-cycle fatigue life prediction model is obtained according to the rotor's low-cycle fatigue stress-strain formula and the SWT-based low-cycle fatigue life prediction model; then, by using the module for obtaining the number of allowable cycles, the maximum equivalent stress in the equivalent stress distribution cloud map is substituted into the optimized SWT low-cycle fatigue life prediction model to obtain the allowable number of cycles N under different peak load conditions. f ; Finally, the life loss calculation module is used to cumulatively calculate the low-cycle fatigue life loss F of the rotor under peak operation based on Miner's cumulative damage theory.

[0095] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for assessing the low-cycle fatigue life damage of a steam turbine rotor under peak load conditions, characterized in that: The following steps are involved: S1: Mechanical property test and high temperature low cycle fatigue test are carried out on the rotor material to obtain the rotor low cycle fatigue stress-strain formula, total strain amplitude formula and low cycle fatigue life prediction model based on SWT; S2: Use the equivalent transformation method to simplify the rotor structure and establish the rotor finite element geometric model; S3: Mesh the rotor 3D geometric model, input boundary conditions, perform finite element stress analysis on the rotor, and obtain an equivalent stress distribution cloud map; S4: The optimized SWT low-cycle fatigue life prediction model is obtained according to the total strain amplitude formula and the SWT-based low-cycle fatigue life prediction model; S5: Substitute the maximum equivalent stress in the equivalent stress distribution cloud diagram into the optimized SWT low-cycle fatigue life prediction model to obtain the allowable number of cycles N under different peak load conditions. f ; S6: Based on Miner’s cumulative damage theory, the low-cycle fatigue life loss F of the rotor under peak operation is cumulatively calculated.

2. The method for evaluating the low-cycle fatigue life damage of a steam turbine rotor under peak load condition according to claim 1 is characterized in that: In step S1, the low cycle fatigue stress-strain formula is: in, is the stress amplitude of low cycle fatigue, K' is the cyclic strength coefficient, n' is the strain hardening exponent, is the plastic strain amplitude; The total strain amplitude formula is: in is the stress amplitude of low cycle fatigue, K' is the cyclic strength coefficient, n' is the strain hardening exponent, and E is the elastic modulus; The low cycle fatigue life prediction model based on SWT is: Among them, σ max is the maximum stress, is the total strain amplitude, E is the elastic modulus, σ' f is the fatigue strength coefficient, ε' f is the fatigue ductility coefficient, b is the fatigue strength index, c is the fatigue ductility coefficient, N f It is the total number of cycles to fatigue fracture, that is, the allowable number of cycles.

3. The method for evaluating the low-cycle fatigue life damage of a steam turbine rotor under peak load condition according to claim 1, characterized in that: The specific process of simplifying the rotor structure by using the equivalent conversion method described in step S2 is: treating the blade root of the rotor as a whole with the rotor, replacing the blades and shrouds of the rotor with blocks of equal mass, and replacing the centrifugal force generated by the rotor during operation with a circular ring disk of equal mass.

4. The method for assessing the low-cycle fatigue life damage of a steam turbine rotor under peak load condition according to claim 3 is characterized in that: The width of the annular disk is the same as the width of the root of the rotor blade, and the radial height of the annular disk is determined by the centrifugal force generated by the blades excluding the root of the blade and the shroud during the rotation process.

5. The method for evaluating the low-cycle fatigue life damage of a steam turbine rotor under peak load condition according to claim 1, characterized in that: The boundary conditions described in step S3 include the steam temperature and heat release coefficient at different axial positions of the rotor.

6. The method for evaluating the low-cycle fatigue life damage of a steam turbine rotor under peak load condition according to claim 5, characterized in that: When obtaining the heat release coefficients at different axial positions of the rotor, the heat release coefficient at the edge of the rotor disk is taken as the average value of the heat release coefficients on both sides of the disk.

7. The method for evaluating the low cycle fatigue life damage of a steam turbine rotor under peak load condition according to claim 2, characterized in that: In step S4, the specific process of obtaining the optimized SWT low cycle fatigue life prediction model is as follows: the total strain amplitude Substitute into the low cycle fatigue life prediction model based on SWT The optimized SWT low cycle fatigue life prediction model is obtained:

8. The method for evaluating the low cycle fatigue life damage of a steam turbine rotor under peak load condition according to claim 7, characterized in that: In step S5, the allowed number of cycles N under different peak load conditions is obtained. f The specific process is: Substitute the maximum equivalent stress in the equivalent stress distribution cloud map into the optimized SWT low-cycle fatigue life prediction model, that is, In the formula: Then solve the allowed number of cycles N f .

9. The method for evaluating the low-cycle fatigue life damage of a steam turbine rotor under peak load condition according to claim 1, characterized in that: In step S6, the calculation formula of the low cycle fatigue life loss F is: where n1, n2, ..., n n is the actual number of operations of the turbine rotor under different operating conditions, N1, N2, ..., N n It is the allowable number of low cycle fatigue cycles of the turbine rotor under different operating conditions.

10. A system for assessing the low-cycle fatigue life of a steam turbine rotor under peak load conditions, characterized in that: Includes the following modules: Obtaining life prediction model module: used to perform mechanical property tests and high-temperature low-cycle fatigue tests on rotor materials, and obtain the rotor's low-cycle fatigue stress-strain formula, total strain amplitude formula, and SWT-based low-cycle fatigue life prediction model; Modeling module: used to simplify the rotor structure using the equivalent transformation method and establish the rotor finite element geometric model; Obtaining equivalent stress distribution cloud map module: used to mesh the rotor 3D geometric model, input boundary conditions, perform finite element stress analysis on the rotor, and obtain the equivalent stress distribution cloud map; Obtain optimized life prediction model module: used to obtain the optimized SWT low-cycle fatigue life prediction model according to the total strain amplitude formula and the SWT-based low-cycle fatigue life prediction model; The module for obtaining the number of cycles allowed is used to substitute the maximum equivalent stress in the equivalent stress distribution cloud map into the optimized SWT low-cycle fatigue life prediction model to obtain the number of cycles allowed N under different peak load conditions. f ; Life loss calculation module: used to perform cumulative calculation of the low-cycle fatigue life loss F of the rotor under peak operation based on Miner cumulative damage theory.

Images