Calculation method of environmental fatigue correction factor based on average strain rate

Abstract

The invention discloses a method for calculating the conversion strain rate of an environmental fatigue correction factor, and the method comprises the steps: calculating an average strain rate and a strain range based on the peak stress and valley stress of a transient combination in fatigue calculation, and obtaining the environmental fatigue correction factor under each combination through weighting. According to the method, the peak value and the valley value in the stress change process are considered, the influence of the stress process of the structure on the environmental fatigue correction factor can be considered, the influence of transient stress fluctuation can be simplified and enveloped through the average effect of the peak value stress and the valley value stress, and the application range is wide.

Description

Technical Field

[0001] This patent relates to the technical field of reactor structural mechanics, and specifically to a method for calculating an environmental fatigue correction factor based on average strain rate. Background Art

[0002] Compared with the fatigue life in air environment, the fatigue life of carbon steel, low alloy steel, austenitic stainless steel and nickel-chromium-iron alloy will be significantly reduced in reactor coolant environment and metal low strain rate. It is clearly stated in the trial period criteria of the nuclear grade specification that if it cannot be proved that the impact of the pressurized water reactor water environment on the fatigue life of the components is small enough, it is necessary to use the environmental fatigue correction factor to analyze the environmental effect of the fatigue life of the structure. The environmental effect in the pressurized water reactor is expressed by the Fen factor, which is defined as the ratio of the life in air at ambient temperature to the life in pressurized water reactor water at operating temperature. In response to the impact of the coolant environment on the life of materials, some foreign nuclear power research institutions, nuclear safety regulatory authorities, industry regulatory agencies, etc. have conducted a large number of experimental studies, analyzed the various factors and laws that affect the life of materials, and summarized the impact evaluation methods.

[0003] Based on the data analysis of existing fatigue curves and the consideration of environmental fatigue effects, NUREG / CR-6909 determines that materials, loads and environmental parameters are the key factors affecting the fatigue life of carbon steel, low alloy steel and austenitic stainless steel, and gives the expression of environmental fatigue correction factor Fen for nickel-based alloys and austenitic stainless steel. The calculation of the conversion strain rate in the expression needs to be combined with the stress state of the structure. Summary of the invention

[0004] The purpose of the present invention is to provide a method for calculating an environmental fatigue correction factor, through which the strain rate considering the time history can be calculated based on the stress state of the structure under the transient action of temperature and pressure, thereby calculating the conversion strain rate and the environmental fatigue correction factor. The structural fatigue correction factor considering the environmental influence can be calculated, and this method has important guiding significance for fatigue analysis of engineering structure design.

[0005] The technical solution of the present invention is as follows: A method for calculating an environmental fatigue correction factor based on an average strain rate comprises the following steps:

[0006] Step 1: Consider only the transient loads and other mechanical external loads of the structure under the time-varying internal pressure and internal temperature, and calculate the result of the time-varying stress of each transient state of the structure in the air environment;

[0007] Step 2: Create transient combinations. Each transient combination includes two transients. The number of transients in all transient events is marked as n, and the number of transient combinations is marked as N.

[0008] Step 3: Combine the peaks and troughs of each transient in each transient combination. Each transient combination generates a stress amplitude. Combined with the fatigue curve characteristics of the material in the air environment, the fatigue service factor Ui of a single transient combination is calculated, i = 1, 2, 3...N;

[0009] Step 4: Add up the fatigue usage coefficient results of multiple transient combinations to get the total fatigue usage coefficient

[0010] Step 5: For the N transient combinations formed, calculate the environmental fatigue correction factor of each transient combination based on the average strain rate method;

[0011] Step 6: Multiply each transient combination by F en,m-k , calculate the cumulative fatigue usage factor CUF considering the environmental fatigue correction factor en , the calculation formula is as follows

[0012] CUF en =U 1 ×F en,1 +…+U n ×F en,n

[0013] Among them, CUF en Fatigue usage factor corrected to take into account environmental fatigue;

[0014] U 1 , U n is the fatigue service factor of the 1st and nth transient combination;

[0015] F en,1 and F en,n is the environmental fatigue correction factor for the 1st and nth transient combination.

[0016] In the Step 1, the process and method for fatigue calculation of nuclear-grade pressure equipment provided in the nuclear energy industry specification ASME Volume III NB3200 or RCC-M Volume I B3200 are adopted.

[0017] In the Step 1, finite element software is used to calculate the stress variation over time corresponding to each transient state of the structure in an air environment.

[0018] In Step 2, transient combination is performed according to the rain flow method provided by ASME and RCC-M.

[0019] In the Step 3, the fatigue usage coefficients of the four transient combinations in the air environment are calculated to be 0.72676, 0.16684, 0.0, and 0.0, respectively.

[0020] In Step 4, the total fatigue usage coefficient U=0.89361.

[0021] The Step 5 includes:

[0022] Step 5.1: Traverse the transient combinations from 1 to N, such as Figure 3 As shown, the transient numbers of the qth transient combination are: transient m and transient k, the trough of transient m is point A, the peak of transient k is point B, the trough of transient 2 is point C, and the peak of transient 2 is point D. The results of the stress or strain changes over time of this part are saved and screened.

[0023] Step 5.2: According to the time period in which the increment is positive during the stress or strain change process of the combination, the stress values ​​of the four points A, B, C, and D of the transient m and transient k are saved. The point B is the valley point of the transient m, recorded as: σ max，m，i , point A is the peak point of transient m, denoted as: σ min，m，i , point D is the valley point of transient k, denoted as: σ max，k，i , point C is the valley point of transient k, denoted as: σ min，k，i , each point has 6 stress components x, y, z, xy, xz, yz, so i represents x, y, z, xy, xz, yz;

[0024] Step 5.3: Based on the calculated σ of the six stress components of the four points A, B, C, and D i , the difference is calculated by subtracting the peak value from the valley value, that is, Δσ m , i =σ max，m，i -σ min，m，i , Δσ k , i =σ max，k，i -σ min，k，i , each point has 6 stress components x, y, z, xy, xz, yz, where i represents x, y, z, xy, xz, yz;

[0025] Step 5.4: Based on the calculated difference Δσ of the transient m m，i , Δσ m，y , Δσ m，z , Δσ m，xy , Δσ m，xz , Δσ m，yz , calculate the three difference principal stresses Δσ of the transient m m，1 , Δσ m，2 , Δσ m，3 , the difference intensity Δσ k，SI ; Similarly, based on the calculated transient k difference Δσ k，i, Δσ k，y , Δσ k，z , Δσ k，xy , Δσ k，xz , Δσ k，yz , calculate the three difference principal stresses Δσ of the transient k k，1 , Δσ k，2 , Δσ k，3 , the difference intensity Δσ k，SI ;

[0026] Step 5.5: Based on the calculated differential principal stress, divide it by the time difference between the peak and valley values ​​Δt m and Δt k , determine the average stress rate of the transient m Determine the mean stress rate for transient 2 Each point has 6 stress components x, y, z, xy, xz, yz, where i represents x, y, z, xy, xz, yz;

[0027] Step 5.6: Based on the calculated six stress rate components Calculate the transient rate principal stress of m and and rate stress intensity Similarly, based on the calculated six stress rate components Calculate the transient k rate principal stress and and rate stress intensity

[0028] Step 5.7: Calculate the strain range. The calculation formula for each transient strain range is as follows:

[0029]

[0030]

[0031] Among them, K e is the simplified elastic-plastic correction factor for load combination, corresponding to ASME NB-3228.5; E is the elastic modulus;

[0032] Step 5.8: Calculate the average strain rate. The formula for calculating the average strain rate of each transient state is as follows:

[0033]

[0034]

[0035] Step 5.9: Calculate the conversion strain rate based on the average strain rate

[0036] Step 5.10: Based on the calculated conversion strain rate, calculate the environmental fatigue correction factor F of transient m and transient k en,simp,m and F en,simp,k ;

[0037] Step 5.11: According to the calculated strain range Δε m and Δε k , environmental fatigue correction factor F for transient m and transient k en,simp,m and F en,simp,k , weighted calculation of transient combined environmental fatigue correction factor F en,n ;

[0038]

[0039] In the Step 5.1, the screening principle is: remove the section with negative stress increment and keep the section with positive stress increment, that is, only keep the stress results of the section from A to B and the section from C to D.

[0040] In Step 5, the environmental fatigue correction factor of each transient combination is calculated according to material mechanics.

[0041] In Step 5.9, the conversion strain rate is calculated using the formula provided by NUREG / CR-6909.

[0042] In Step 5.9, the environmental fatigue correction factor F of transient m and transient k is calculated using the formula provided by NUREG / CR-6909. en,simp,m and F en,simp,k .

[0043] In Step 6, the transient combined environmental fatigue correction factor F en,n The corresponding transient combination fatigue usage factor CUF after considering the environmental fatigue correction factor is 6.547, 4.847 and 3.542. en,i They are 4.758, 0.809, and 0.0 respectively. The total fatigue service life coefficient CUF considering the environmental fatigue correction factor is calculated. en It is 5.567.

[0044] The significant effect of the present invention is that: the method provided by the present invention for calculating the environmental fatigue correction factor conversion strain rate can consider the influence of the stress history of the structure on the environmental fatigue correction factor by considering the peak and valley values ​​in the stress change history, and can simplify and envelop the influence of transient stress fluctuations through the average effect of the peak and valley stresses, and has a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1A schematic diagram of a finite element model, loads, and boundary conditions provided in an embodiment of the present invention;

[0046] Figure 2 A schematic diagram of the time history of a transient stress component 1 provided in an embodiment of the present invention;

[0047] Figure 3 A transient combination schematic diagram is provided for an embodiment of the present invention;

[0048] Table 1 is a schematic table of transient data provided by an embodiment of the present invention;

[0049] Table 2 is a schematic table of fatigue calculation results in an air environment provided by an embodiment of the present invention;

[0050] Table 3 is a schematic diagram of the conversion strain rate calculation formula provided in an embodiment of the present invention.

[0051] Table 4 is a schematic table of environmental fatigue calculation results of section 1 provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0052] 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.

[0053] 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.

[0054] 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.

[0055] In the present invention, the instantaneous or transient state is understood as an event, or a process in which an event occurs.

[0056] A method for calculating the environmental fatigue correction factor based on the average strain rate, the steps are as follows:

[0057] Step 1: Consider only the instantaneous loads and other mechanical external loads of the structure under the time-varying internal pressure and internal temperature, and calculate the result of the time-varying stress of each transient state of the structure in the air environment.

[0058] 1. Preferably, in step 1, the process and method for fatigue calculation of nuclear-grade pressure equipment provided in the nuclear energy industry specification ASME Volume III NB3200 or RCC-M Volume I B3200 are adopted;

[0059] 2. As a preferred embodiment, in step Step 1, finite element software is used to calculate the stress variation with time corresponding to each transient state of the structure in an air environment. In this result, there will be a maximum stress value, called a peak, and a minimum stress value, called a trough. After calculating many transient states, many stress peaks and troughs can be obtained. Here, transient refers to the load of pressure and temperature varying with time.

[0060] Step 2: Perform transient combination according to the rain flow method provided by ASME and RCC-M. Each transient combination consists of 2 transients. Here, the number of transients in all transient events is marked as n, and the number of transient combinations is marked as N.

[0061] Step 3: Combine the peaks and troughs of each transient combination, and each transient combination will generate a stress amplitude. This stress amplitude is combined with the inherent fatigue curve characteristics of the material in the air environment to calculate the fatigue service coefficient Ui of a single transient combination, i = 1. . . N;

[0062] Step 4: Add up the fatigue usage coefficient results of multiple transient combinations to get the total fatigue usage coefficient

[0063] Step 5: For the N transient combinations formed, calculate the environmental fatigue correction factor of each transient combination based on the average strain rate method.

[0064] Step 5.1: Traverse the transient combinations from 1 to N. Assume that the transient numbers of the qth transient combination are: transient m and transient k. The trough (minimum value) of transient m is point A, the peak (maximum value) of transient k is point B, the trough (minimum value) of transient 2 is point C, and the peak (maximum value) of transient 2 is point D. Save the results of the stress or strain change over time of this part and screen it. The principle of screening is: remove the section with negative stress increment and keep the section with positive stress increment, that is, only keep the stress results of the section from A to B and the section from C to D.

[0065] Step 5.2: According to the time period in which the increment is positive in the process of stress or strain change in the combination, the stress values ​​of the four points A, B, C, and D of the transient m and transient k are saved. The point B is the valley point (i.e. the low point) of the transient m, recorded as: σ max，m，i , point A is the peak point of transient m (i.e. the high point), denoted as: σ min，m，i , point D is the valley point of transient k (i.e. the low point), recorded as: σ max，k，i , point C is the valley point of transient k (i.e. the low point), recorded as: and σ min，k，i ,According to material mechanics, each point has 6 stress components, so i represents,x,y,z,xy,xz,yz;

[0066] Step 5.3: Based on the calculated σ of the six stress components of the four points A, B, C, and D i , the difference is calculated by subtracting the peak value from the valley value, that is, Δσ m , i =σ max，m，i -σ min，m，i , Δσ k , i =σ max，k，i -σ min，k，i , ,According to material mechanics, each point has 6 stress components, where i represents ,x, y, z, xy, xz, yz;

[0067] Step 5.4: Based on the calculated difference Δσ of the transient m m，i , Δσ m，y , Δσ m，z , Δσ m，xy , Δσ m，xz , Δσ m，yz According to the method of calculating principal stress provided in material mechanics, the three differential principal stresses Δσ of transient m are calculated m，1 , Δσ m，2 , Δσ m，3 , the difference intensity Δσ k，SI Similarly, the difference Δσ of the transient k can also be calculated k，i , Δσ k，y , Δσ k，z , Δσ k，xy , Δσ k，xz , Δσ k，yz According to the method of calculating principal stress provided in material mechanics, the three differential principal stresses Δσ of transient k are calculated k，1 , Δσ k，2 , Δσ k，3 , the difference intensity Δσ k，SI ;

[0068] Step 5.5: Based on the calculated differential principal stress, divide it by the time difference between the peak and valley values ​​Δt m and Δt k , determine the average stress rate of the transient m Determine the mean stress rate for transient 2 According to material mechanics, each point has 6 stress components, where i represents x, y, z, xy, xz, yz;

[0069] Step 5.6: Based on the calculated six stress rate components According to the calculation method of material mechanics, the transient principal stress of m is deduced. and and rate stress intensity Similarly, based on the calculated six stress rate components According to the calculation method of material mechanics, the transient k rate principal stress is calculated and and rate stress intensity

[0070] Step 5.7: Calculate the strain range. The calculation formula for each transient strain range is as follows:

[0071]

[0072]

[0073] Among them, K e It is the simplified elastic-plastic correction factor for load combination, corresponding to ASME NB-3228.5; E is the elastic modulus.

[0074] Step 5.8: Calculate the average strain rate. The formula for calculating the average strain rate of each transient state is as follows:

[0075]

[0076]

[0077] Step 5.9: Based on the average strain rate, calculate the conversion strain rate using the formula provided by NUREG / CR-6909

[0078] Step 5.10: Based on the calculated conversion strain rate, use the formula provided by NUREG / CR-6909 to calculate the environmental fatigue correction factor F for transient m and transient k en,simp,m and F en,simp,k ;

[0079] Step 5.11: According to the calculated strain range Δε m and Δεk , environmental fatigue correction factor F for transient m and transient k en,simp,m and F en,simp,k , weighted calculation of transient combined environmental fatigue correction factor F en,m-k .

[0080]

[0081] Step 6: Multiply each transient combination by F en,m-k , calculate the cumulative fatigue usage factor CUF considering the environmental fatigue correction factor en , the calculation formula is as follows

[0082] CUF en =U 1 ×F en,1 +…+U n ×F en,n

[0083] Among them, CUF en U is the fatigue usage factor after correction for environmental fatigue; 1 , U n is the fatigue service factor of the first and nth transient combination; F en,1 and F en,n is the environmental fatigue correction factor for the 1st and nth transient combination.

[0084] Taking the reactor pressure vessel nozzle as an example, the method of calculating and using the present invention is as follows:

[0085] Step 1: Consider only the transient loads and other mechanical external loads of the reactor pressure vessel nozzle structure under the time-varying internal pressure and internal temperature, and calculate the time-varying results of each transient stress of the structure in the air environment. The transient loads used are shown in Table 1.

[0086] Among them, the number of transient state 1 is 20 times, the number of transient state 2 is 50 times, and the number of transient state 3 is 500 times.

[0087] 1. Preferably, in step 1, the process and method for fatigue calculation of nuclear-grade pressure equipment provided in the nuclear energy industry specification ASME Volume III NB3200 or RCC-M Volume I B3200 are adopted;

[0088] 2. As a preferred method, in step 1, finite element software is used to calculate the stress change over time corresponding to each transient state of the structure in an air environment. In this result, there will be a maximum stress value, called a peak, and a minimum stress value, called a trough. After calculating many transient states, many stress peaks and troughs can be obtained. Here, transient refers to the load of pressure and temperature changing over time. The finite element model of the reactor pressure vessel nozzle is as follows: Figure 1 The curve of the change of the axial stress component with time under transient 1 is shown in Figure 2 shown.

[0089] Step 2: According to the method provided by ASME and RCC-M, transient combinations are performed. Each transient combination consists of 2 transients. Here, the number of transients is 3, and the number of transient combinations is 3, as shown in Table 2. It should be noted that the transient combination can be a combination of the same transient itself or a combination of two different transients.

[0090] Step 3: Combine the peaks and troughs of each transient combination. Each transient combination generates a stress amplitude. This stress amplitude is combined with the inherent fatigue curve characteristics of the material in the air environment to calculate the fatigue service factor U of a single transient combination. i .U i Defined as the fatigue service factor of the ith transient combination.

[0091] As shown in Table 2, the fatigue usage coefficients of the four transient combinations in the air environment are calculated to be 0.72676, 0.16684, 0.0, and 0.0, respectively.

[0092] Step 4: Add up the fatigue usage coefficient results of multiple transient combinations to obtain the total fatigue usage coefficient U=0.89361 in the air environment, see Table 2.

[0093] Step 5: For the N transient combinations formed, calculate the environmental fatigue correction factor of each transient combination based on the average strain rate method.

[0094] Step 5.1: Traverse the transient combinations from 1 to N, such as Figure 3 As shown, the transient numbers of the qth transient combination are: transient m and transient k, the trough (minimum value) of transient m is point A, the peak (maximum value) of transient k is point B, the trough (minimum value) of transient 2 is point C, and the peak (maximum value) of transient 2 is point D. The results of the stress or strain change over time of this part are saved and screened. The principle of screening is: remove the section with a negative stress increment and retain the section with a positive stress increment, that is, only retain the stress results of the section from A to B and the section from C to D;

[0095] Step 5.2: According to the time period in which the increment is positive in the process of stress or strain change in the combination, the stress values ​​of the four points A, B, C, and D of the transient m and transient k are saved. The point B is the valley point (i.e. the low point) of the transient m, recorded as: σ max，m，i , point A is the peak point of transient m (i.e. the high point), denoted as: σ min，m，i , point D is the valley point of transient k (i.e. the low point), recorded as: σmax，k，i , point C is the valley point of transient k (i.e. the low point), denoted as: σ min，k，i ,According to material mechanics, each point has 6 stress components, so i represents,x,y,z,xy,xz,yz;

[0096] Step 5.3: Based on the calculated σ of the six stress components of the four points A, B, C, and D i , the difference is calculated by subtracting the peak value from the valley value, that is, Δσ m , i =σ max，m，i -σ min，m，i , Δσ k , i =σ max，k，i -σ min，k，i , ,According to material mechanics, each point has 6 stress components, where i represents ,x, y, z, xy, xz, yz;

[0097] Step 5.4: Based on the calculated difference Δσ of the transient m m，i , Δσ m，y , Δσ m，z , Δσ m，xy , Δσ m，xz , Δσ m，yz According to the method of calculating principal stress provided in material mechanics, the three differential principal stresses Δσ of transient m are calculated m，1 , Δσ m，2 , Δσ m，3 , the difference intensity Δσ k，SI Similarly, the difference Δσ of the transient k can also be calculated k，i , Δσ k，y , Δσ k，z , Δσ k，xy , Δσ k，xz , Δσ k，yz According to the method of calculating principal stress provided in material mechanics, the three differential principal stresses Δσ of transient k are calculated k，1 , Δσ k，2 , Δσ k，3 , the difference intensity Δσ k，SI ;

[0098] Step 5.5: Based on the calculated differential principal stress, divide it by the time difference between the peak and valley values ​​Δt m and Δt k , determine the average stress rate of the transient m Determine the mean stress rate for transient 2 According to material mechanics, each point has 6 stress components, where i represents x, y, z, xy, xz, yz;

[0099] Step 5.6: Based on the calculated six stress rate components According to the calculation method of material mechanics, the transient principal stress of m is deduced. and and rate stress intensity Similarly, based on the calculated six stress rate components According to the calculation method of material mechanics, the transient k rate principal stress is calculated and and rate stress intensity

[0100] Step 5.7: Calculate the strain range. The calculation formula for each transient strain range is as follows:

[0101]

[0102]

[0103] Among them, K e It is the simplified elastic-plastic correction factor for load combination, corresponding to ASME NB-3228.5; E is the elastic modulus.

[0104] Step 5.8: Calculate the average strain rate. The formula for calculating the average strain rate of each transient state is as follows:

[0105]

[0106]

[0107] Step 5.9: Based on the average strain rate, calculate the conversion strain rate using the formula provided by NUREG / CR-6909 The calculation formula is shown in Table 3.

[0108] Step 5.10: Based on the calculated conversion strain rate, use the formula provided by NUREG / CR-6909 to calculate the environmental fatigue correction factor F for transient m and transient k en,simp,m and F en,simp,k ;

[0109] Step 5.11: According to the calculated strain range Δε m and Δε k , environmental fatigue correction factor F for transient m and transient k en,simp,m and F en,simp,k , weighted calculation of transient combined environmental fatigue correction factor F en,n .

[0110]

[0111] Step 6: Multiply each transient combination by F en,n , calculate the cumulative fatigue usage factor CUF considering the environmental fatigue correction factor en , the calculation formula is as follows

[0112] CUF en =U 1 ×F en,1 +…+U n ×F en,n

[0113] Among them, CUF en U is the fatigue usage factor after correction for environmental fatigue; 1 , U n is the fatigue service factor of the first and nth transient combination; F en,1 and F en,n is the environmental fatigue correction factor for the 1st and nth transient combination.

[0114] As shown in Table 4, the environmental fatigue correction factors F of the three transient combinations are en,n They are 6.547, 4.847 and 3.542 respectively. The fatigue usage coefficients of the three transient combinations after considering the environmental fatigue correction factor are 4.758, 0.809 and 0.0 respectively. Therefore, the total fatigue service life coefficient considering the environmental fatigue correction factor is 5.567.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] 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.

[0119] Table 1

[0120]

[0121] Table 2

[0122]

[0123] Table 3

[0124]

[0125] Table 4

[0126]

Claims

1. A method for calculating an environmental fatigue correction factor based on average strain rate, characterized in that: The following steps are involved: Step 1: Consider only the transient loads and other mechanical external loads of the structure under the time-varying internal pressure and internal temperature, and calculate the result of the time-varying stress of each transient state of the structure in the air environment; Step 2: Create transient combinations. Each transient combination includes two transients. The number of transients in all transient events is marked as n, and the number of transient combinations is marked as N. Step 3: Combine the peaks and troughs of each transient in each transient combination. Each transient combination generates a stress amplitude. Combined with the fatigue curve characteristics of the material in the air environment, the fatigue service factor Ui of a single transient combination is calculated, i = 1, 2, 3...N; Step 4: Add up the fatigue usage coefficient results of multiple transient combinations to get the total fatigue usage coefficient Step 5: For the N transient combinations formed, calculate the environmental fatigue correction factor of each transient combination based on the average strain rate method; Step 6: Multiply each transient combination by F en,m-k , calculate the cumulative fatigue usage factor CUF considering the environmental fatigue correction factor en , the calculation formula is as follows CUF en =U1×F en,1 +…+U n ×F en,n Among them, CUF en Fatigue usage factor corrected to take into account environmental fatigue; U1,U n is the fatigue service factor of the 1st and nth transient combination; F en,1 and F en,n is the environmental fatigue correction factor for the 1st and nth transient combination.

2. The method for calculating the environmental fatigue correction factor based on the average strain rate according to claim 1 is characterized in that: In the Step 1, the process and method for fatigue calculation of nuclear-grade pressure equipment provided in the nuclear energy industry specification ASME Volume III NB3200 or RCC-M Volume I B3200 are adopted.

3. The method for calculating the environmental fatigue correction factor based on the average strain rate according to claim 1 is characterized in that: In the Step 1, finite element software is used to calculate the stress variation over time corresponding to each transient state of the structure in an air environment.

4. The method for calculating the environmental fatigue correction factor based on the average strain rate according to claim 1 is characterized in that: In Step 2, transient combination is performed according to the rain flow method provided by ASME and RCC-M.

5. The method for calculating the environmental fatigue correction factor based on the average strain rate according to claim 1 is characterized in that: In the Step 3, the fatigue usage coefficients of the four transient combinations in the air environment are calculated to be 0.72676, 0.16684, 0.0, and 0.0, respectively.

6. The method for calculating the environmental fatigue correction factor based on the average strain rate according to claim 1 is characterized in that: In Step 4, the total fatigue usage coefficient U=0.89361.

7. The method for calculating the environmental fatigue correction factor based on average strain rate according to claim 1 is characterized in that: The Step 5 includes: Step 5.1: Traverse the transient combinations from 1 to N. As shown in Figure 3, the transient numbers of the qth transient combination are: transient m and transient k. The trough of transient m is point A, the peak of transient k is point B, the trough of transient 2 is point C, and the peak of transient 2 is point D. Save the results of the stress or strain changes over time for this part and screen them. Step 5.2: According to the time period in which the increment is positive during the stress or strain change process of the combination, the stress values ​​of the four points A, B, C, and D of the transient m and transient k are saved. The point B is the valley point of the transient m, recorded as: σ max，m，i , point A is the peak point of transient m, denoted as: σ min，m，i , point D is the valley point of transient k, denoted as: σ max，k，i , point C is the valley point of transient k, denoted as: σ min，k，i , each point has 6 stress components x, y, z, xy, xz, yz, so i represents x, y, z, xy, xz, yz; Step 5.3: Based on the calculated σ of the six stress components of the four points A, B, C, and D i , the difference is calculated by subtracting the peak value from the valley value, that is, Δσ m，i =σ max，m，i -σ min，m，i , Δσ k，i =σ max，k，i -σ min，k，i , each point has 6 stress components x, y, z, xy, xz, yz, where i represents x, y, z, xy, xz, yz; Step 5.4: Based on the calculated difference Δσ of the transient m m，i , Δσ m，y , Δσ m，z , Δσ m，xy , Δσ m，xz , Δσ m，yz , calculate the three difference principal stresses Δσ of the transient m m，1 , Δσ m，2 , Δσ m，3 , the difference intensity Δσ k，SI ; Similarly, based on the calculated transient k difference Δσ k，i , Δσ k，y , Δσ k，z , Δσ k，xy , Δσ k，xz , Δσ k，yz , calculate the three difference principal stresses Δσ of the transient k k，1 , Δσ k，2 , Δσ k，3 , the difference intensity Δσ k，SI ; Step 5.5: Based on the calculated differential principal stress, divide it by the time difference between the peak and valley values ​​Δt m and Δt k , determine the average stress rate of the transient m Determine the mean stress rate for transient 2 Each point has 6 stress components x, y, z, xy, xz, yz, where i represents x, y, z, xy, xz, yz; Step 5.6: Based on the calculated six stress rate components Calculate the transient rate principal stress of m and and rate stress intensity Similarly, based on the calculated six stress rate components Calculate the transient k rate principal stress and and rate stress intensity Step 5.7: Calculate the strain range. The calculation formula for each transient strain range is as follows: Among them, K e is the simplified elastic-plastic correction factor for load combination, corresponding to ASME NB-3228.5; E is the elastic modulus; Step 5.8: Calculate the average strain rate. The formula for calculating the average strain rate of each transient state is as follows: Step 5.9: Calculate the conversion strain rate based on the average strain rate Step 5.10: Based on the calculated conversion strain rate, calculate the environmental fatigue correction factor F of transient m and transient k en,simp,m and F en,simp,k ; Step 5.11: According to the calculated strain range Δε m and Δε k , environmental fatigue correction factor F for transient m and transient k en,simp,m and F en,simp,k , weighted calculation of transient combined environmental fatigue correction factor F en，n ; 8. The method for calculating the environmental fatigue correction factor based on the average strain rate according to claim 7 is characterized in that: In the Step 5.1, the screening principle is: remove the section with negative stress increment and keep the section with positive stress increment, that is, only keep the stress results of the section from A to B and the section from C to D.

9. The method for calculating the environmental fatigue correction factor based on average strain rate according to claim 7, characterized in that: In Step 5, the environmental fatigue correction factor of each transient combination is calculated according to material mechanics.

10. The method for calculating the environmental fatigue correction factor based on the average strain rate according to claim 7, characterized in that: In Step 5.9, the conversion strain rate is calculated using the formula provided by NUREG / CR-6909.

11. The method for calculating the environmental fatigue correction factor based on the average strain rate according to claim 7, characterized in that: In Step 5.9, the environmental fatigue correction factor F of transient m and transient k is calculated using the formula provided by NUREG / CR-6909. en,simp,m and F en,simp,k .

12. The method for calculating the environmental fatigue correction factor based on average strain rate according to claim 1, characterized in that: In Step 6, the transient combined environmental fatigue correction factor F en，n The corresponding transient combination fatigue usage factor CUF after considering the environmental fatigue correction factor is 6.547, 4.847 and 3.

542. en,i They are 4.758, 0.809, and 0.0 respectively. The total fatigue service life coefficient CUF considering the environmental fatigue correction factor is calculated. en It is 5.567.

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