Method and system for determining critical inelastic strain rate in creep-fatigue damage process

Abstract

The invention discloses a method and a system for determining a critical inelastic strain rate in a creep-fatigue damage process, and relates to the technical field of life prediction of high-temperature equipment, and the method comprises the following steps: obtaining a plurality of high-temperature equipment materials; based on the same temperature working condition, respectively carrying out creep, fatigue and creep-fatigue interaction tests on the high-temperature equipment material to obtain a creep test result, a fatigue test result and a creep-fatigue interaction test result; establishing a stress relaxation formula according to a creep test result; according to a fatigue test result, establishing a failure inelastic strain energy density fitting equation; establishing a net tensile hysteresis energy fatigue damage equation according to a creep-fatigue interaction test result; and determining the creep-fatigue life of the high-temperature equipment material based on a stress relaxation formula, a failure inelastic strain energy density fitting equation and a net tensile hysteresis energy fatigue damage equation according to a linear cumulative damage rule. According to the method, the creep-fatigue life of the high-temperature equipment material can be predicted more accurately.

Description

Technical Field

[0001] The present application relates to the technical field of high-temperature equipment life prediction, and in particular to a method and system for determining a critical inelastic strain rate in a creep-fatigue damage process. Background Art

[0002] In the fields of new energy batteries, aerospace, mechanical chemicals, etc., a large number of mechanical equipment such as gas engines, aircraft engines, heat exchangers, lithium batteries and fuel cells, etc., work in high temperature and high pressure extreme environments for a long time. During the working process, they must not only withstand the thermal stress generated during steady-state operation and the creep damage caused by it, but also withstand the fatigue damage caused by the alternating stress during start-stop. This creep-fatigue interaction is one of the main reasons for the failure of high-temperature equipment. Therefore, mastering the creep-fatigue failure behavior of high-temperature equipment materials during the working process and understanding the law of change of their lifespan are of great practical significance for their long-term reliability design and safe operation. Summary of the invention

[0003] The purpose of this application is to provide a method and system for determining the critical inelastic strain rate in the creep-fatigue damage process, which can more accurately predict the creep-fatigue life of high-temperature equipment materials.

[0004] To achieve the above objectives, this application provides the following solutions:

[0005] In a first aspect, the present application provides a method for determining a critical inelastic strain rate in a creep-fatigue damage process, comprising:

[0006] Obtain several identical high-temperature equipment materials;

[0007] Based on the same temperature conditions, creep test, fatigue test and creep-fatigue interaction test are carried out on high temperature equipment materials respectively, and creep test results, fatigue test results and creep-fatigue interaction test results are obtained;

[0008] According to the creep test results, a stress relaxation formula is established; the stress relaxation formula is used to calculate the critical stress after the strain maintains the initial corrected critical inelastic strain rate;

[0009] According to the fatigue test results, a failure inelastic strain energy density fitting equation is established; the failure inelastic strain energy density fitting equation is used to calculate the corrected inelastic strain energy density dissipation rate and the creep damage under each cycle;

[0010] According to the creep-fatigue interaction test results, a net tensile hysteresis energy fatigue damage equation is established; the net tensile hysteresis energy fatigue damage equation is used to calculate cycle-by-cycle fatigue damage;

[0011] According to the linear cumulative damage law, based on the stress relaxation formula, the failure inelastic strain energy density fitting equation and the net tensile hysteresis energy fatigue damage equation, the creep-fatigue life of high-temperature equipment materials under creep-fatigue interaction is determined.

[0012] In a second aspect, the present application provides a system for determining a critical inelastic strain rate in a creep-fatigue damage process, comprising:

[0013] Material acquisition module, used to obtain several identical high-temperature equipment materials;

[0014] The test module is used to perform creep test, fatigue test and creep-fatigue interaction test on high-temperature equipment materials under the same temperature conditions to obtain creep test results, fatigue test results and creep-fatigue interaction test results;

[0015] A stress relaxation formula building module is used to establish a stress relaxation formula according to the creep test results; the stress relaxation formula is used to calculate the critical stress after the strain maintains the initial corrected critical inelastic strain rate;

[0016] A failure inelastic strain energy density fitting equation construction module is used to establish a failure inelastic strain energy density fitting equation according to the fatigue test results; the failure inelastic strain energy density fitting equation is used to calculate the corrected inelastic strain energy density dissipation rate and the creep damage under cycle by cycle;

[0017] A net tensile hysteresis energy fatigue damage equation building module is used to establish a net tensile hysteresis energy fatigue damage equation according to the creep-fatigue interaction test results; the net tensile hysteresis energy fatigue damage equation is used to calculate cycle-by-cycle fatigue damage;

[0018] The life calculation module is used to determine the creep-fatigue life of high-temperature equipment materials under creep-fatigue interaction according to the linear cumulative damage law, based on the stress relaxation formula, the failure inelastic strain energy density fitting equation and the net tensile hysteresis energy fatigue damage equation.

[0019] According to the specific embodiments provided in this application, this application discloses the following technical effects:

[0020] The present application provides a method and system for determining the critical inelastic strain rate in a creep-fatigue damage process, the method comprising: obtaining a plurality of groups of completely identical high-temperature equipment material samples; performing creep tests, fatigue tests and creep-fatigue interaction tests on the high-temperature equipment material samples under the same temperature conditions to obtain corresponding creep test data, fatigue test data and creep-fatigue interaction test data; constructing a stress relaxation formula based on the obtained creep test data; the stress relaxation formula is used to calculate the critical stress value after the initial correction of the critical inelastic strain rate; constructing a failure inelastic strain energy density fitting equation based on the fatigue test data; the fitting equation is used to calculate the corrected inelastic strain energy density dissipation rate and the creep damage on a cycle-by-cycle basis; constructing a net tensile hysteresis energy fatigue damage equation based on the creep-fatigue interaction test data; the equation is used to calculate the fatigue damage on a cycle-by-cycle basis; based on the linear cumulative damage law, combining the stress relaxation formula, the failure inelastic strain energy density fitting equation and the net tensile hysteresis energy fatigue damage equation, the creep-fatigue life of the high-temperature equipment material under creep-fatigue interaction is determined. The present application modifies the method for determining the critical inelastic strain rate in the creep-fatigue damage process to more accurately distinguish between the ineffective creep damage stage and the effective creep damage stage. Through the modified cycle-by-cycle creep-fatigue damage accumulation, the defect of the existing creep-fatigue life prediction method that the creep-fatigue life prediction results of high-temperature equipment materials are too conservative is further reduced, thereby more accurately predicting the creep-fatigue life of high-temperature equipment materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0022] Figure 1 A flowchart of a method for determining a critical inelastic strain rate in a creep-fatigue damage process provided in one embodiment of the present application.

[0023] Figure 2 A schematic diagram of a loading condition provided in accordance with an embodiment of the present application.

[0024] Figure 3 This is a fitting curve diagram of a material stress relaxation test provided in one embodiment of the present application.

[0025] Figure 4 A graph showing the variation of the inelastic strain rate of a material over time provided in one embodiment of the present application.

[0026] Figure 5A schematic diagram of strain energy density without critical failure provided in an embodiment of the present application.

[0027] Figure 6 A schematic diagram of critical failure strain energy density provided in one embodiment of the present application.

[0028] Figure 7 This is a fitting curve diagram of fatigue damage parameters of a material fatigue test provided in an embodiment of the present application.

[0029] Figure 8 A comparison chart of the life prediction of P92 martensitic steel material provided in one embodiment of the present application.

[0030] Fig. 9 This is a comparison chart of the life prediction of the GH4169 nickel-based alloy material provided in one embodiment of the present application.

[0031] Fig.10 This is a life prediction comparison chart of 304SS stainless steel material provided in one embodiment of the present application.

[0032] Fig.11 This is a life prediction comparison chart of Crofer 22APU stainless steel material provided in one embodiment of the present application.

[0033] Fig.12 This is a life prediction comparison chart of Inconel 625Inconel625 diffusion welded joints provided in one embodiment of the present application. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0035] Since the 20th century, domestic and foreign scholars have proposed many constitutive models to predict the creep-fatigue life of high-temperature equipment materials. With the development of fatigue theory and fracture mechanics and the failure analysis of high-temperature equipment, people have gradually discovered that its damage mechanism not only has independent creep damage and fatigue damage, but also has fatigue and creep damage interaction mechanisms. The high-temperature fatigue damage mechanism is not only related to time-independent plastic deformation, but also to time-dependent creep and oxidation. The complex creep-fatigue load conditions pose a severe challenge to the life prediction of high-temperature equipment materials. At present, according to the theoretical system, the creep-fatigue life prediction models of high-temperature components are mainly divided into three categories, namely, creep-fatigue life prediction methods based on the Manson-Coffin equation, based on the differentiation method, and based on the linear damage accumulation criterion. The life prediction model based on the Manson-Coffin equation is mainly represented by the frequency separation model proposed by Coffin. It considers the cycle frequencies of tension and compression separately for the first time, making the model more adaptable to different creep fatigue loading conditions. However, this model ignores the stress welding effect of compression loading and the average stress effect during asymmetric loading. The life prediction model based on the differentiation method is mainly represented by the strain range differentiation method. This method considers that creep-fatigue failure is caused by the inelastic strain of the material. By distinguishing four inelastic strain range components with different properties, the Manson-Coffin equation is used to calculate the damage corresponding to the components with different properties, and the creep-fatigue life is obtained by superimposing them according to specific criteria. However, this method has defects and limitations in predicting creep-fatigue life in low strain control range and long life. In the theoretical system of linear damage accumulation criterion, the creep-fatigue life prediction model considering anelastic recovery based on strain energy density dissipation method is widely adopted due to its clear physical meaning, strong operability, fewer parameters and simple acquisition. However, it does not consider the influence of different anelastic recovery rates in the initial stage of load holding in different strain ranges under cyclic softening / hardening of high-temperature equipment materials, and approximates the creep damage per half-life cycle to the creep damage per week, making the life prediction results too conservative.

[0036] The purpose of this application is to provide a method and system for determining the critical inelastic strain rate in the creep-fatigue damage process, which can more accurately predict the creep-fatigue life of high-temperature equipment materials.

[0037] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0038] Embodiment 1

[0039] like Figure 1 As shown, this embodiment provides a method for determining the critical inelastic strain rate in a creep-fatigue damage process, comprising:

[0040] Step 101: Obtain a number of identical high-temperature equipment materials;

[0041] Step 102: Based on the same temperature conditions, creep test, fatigue test and creep-fatigue interaction test are respectively performed on the high temperature equipment material to obtain creep test results, fatigue test results and creep-fatigue interaction test results;

[0042] Step 103: establishing a stress relaxation formula according to the creep test results; the stress relaxation formula is used to calculate the critical stress after the strain maintains the initial corrected critical inelastic strain rate;

[0043] Step 104: establishing a failure inelastic strain energy density fitting equation according to the fatigue test results; the failure inelastic strain energy density fitting equation is used to calculate the corrected inelastic strain energy density dissipation rate and the creep damage under each cycle;

[0044] Step 105: establishing a net tensile hysteresis energy fatigue damage equation according to the creep-fatigue interaction test results; the net tensile hysteresis energy fatigue damage equation is used to calculate cycle-by-cycle fatigue damage;

[0045] Step 106: According to the linear cumulative damage law, based on the stress relaxation formula, the failure inelastic strain energy density fitting equation and the net tensile hysteresis energy fatigue damage equation, the creep-fatigue life of the high temperature equipment material under the creep-fatigue interaction is determined.

[0046] In some embodiments, when executing step 101, the specific steps may be as follows:

[0047] Among the several identical high-temperature equipment materials obtained, the high-temperature equipment materials may be P92 martensitic steel material, GH4169 nickel-based alloy material, 304SS stainless steel material, Crofer 22APU stainless steel material and Inconel625Inconel625 diffusion welding joint.

[0048] In some embodiments, when executing step 102, the specific steps may be as follows:

[0049] Under the same temperature conditions, creep test, fatigue test and creep-fatigue interaction test of high temperature equipment materials are carried out respectively. The implementation methods of creep test, fatigue test and creep-fatigue interaction test are not described in detail here. Figure 2 shows an actual loading condition, such as Figure 2 As shown in Figure 2, the loading amplitude and loading rate of the fatigue test and the creep-fatigue interaction test are the same.

[0050] In some embodiments, when executing step 103, the specific steps may be as follows:

[0051] Based on the creep test results, a stress relaxation formula is established. The stress relaxation formula describes the functional relationship between the stress of high-temperature equipment materials under maximum tensile load and time, and the relationship is as follows:

[0052] σ(t)=σ0-(A·lgΔε pp +B)·lg(1+t) (1).

[0053] Where σ0 represents the instantaneous (maximum) stress at the maximum tensile strain under half-life cycles, Δε pp represents the plastic strain range, t represents the half-maximum tensile holding time, and A and B are the parameters for fitting the Jeong stress relaxation formula.

[0054] For example, Figure 3 The stress relaxation test fitting curve of Crofer22APU stainless steel material in 750℃ high temperature equipment is shown. The fitting curve is obtained by fitting the stress relaxation curve parameters of the half-life cycle strain holding stage. During the fitting, constant A is set to 0.031, constant B is set to 2.755, and the strain condition is set to 0.5%. Figure 3 It can be seen that the stress decreases continuously with the increase of time.

[0055] Specifically, the critical stress after the strain maintains the initial corrected critical inelastic strain rate is calculated. The specific process is as follows:

[0056] 1) According to the stress relaxation formula, calculate the critical inelastic strain rate of the material within the maximum tensile load. First, differentiate formula (1) to calculate the stress relaxation rate, and the formula is as follows:

[0057]

[0058] In the formula, represents the inelastic strain rate; represents the derivative of formula (1); E represents the elastic modulus of the material at the creep-fatigue test temperature.

[0059] Based on the effective creep damage theory during stress relaxation, the critical inelastic strain rate is determined by the stress relaxation rate curve calculated by formula (2), and then substituted into formula (1) to obtain the corrected critical strain rate, as follows:

[0060]

[0061] α=(aΔεp+b)(4).

[0062] In the formula, represents the critical inelastic strain rate, Indicates the maximum inelastic strain rate at the initial stage of stress relaxation, Δε p is the strain control range, α, a and b are material parameters that are independent of the number of cycles, and the specific calculation method is as follows: Figure 4 shown.

[0063] For example, Figure 4 Among them, 0.65%, 0.75%, and 0.85% are creep-fatigue test strain conditions, t Xre is the time taken by the high temperature equipment material to reach the critical inelastic strain rate during the strain holding period, and (0,1.4-4) is the maximum inelastic strain rate corresponding to zero holding time. (t Xre , 1.4-5) is the critical inelastic strain rate corresponding to creep damage-free in the hysteresis recovery stage At this time, the hysteresis elastic recovery period under different strain conditions Decrease one order of magnitude to The required parameter α is different, according to three different strain conditions Δε p The sum of α can be calculated by formula (4), a is set to -0.33, b is set to 0.35, and α and α under other strain conditions are calculated by formula (4) The value of . Figure 4 It can be seen that the critical inelastic strain rate in the cyclic softening material anelastic recovery stage varies with the strain condition.

[0064] 2) Calculate the time taken by the high temperature equipment material to reach the critical inelastic strain rate during the strain holding period by formula (5) express:

[0065]

[0066] 3) The stress relaxation formula of formula (1) is corrected. The corrected stress relaxation formula σ Xnew (t) means:

[0067] σ Xnew (t) = σ0-(A·lgΔε pp +B)·lg(1+t+t Xre ) (6).

[0068] 4) The t calculated by formula (5) Xre Substituting into equation (1), we can obtain the modified critical stress σ considering the material anelastic recovery: Xre , expressed as:

[0069]

[0070] In some embodiments, when executing step 104, the specific steps may be as follows:

[0071] According to the results of creep test, the failure inelastic strain energy density fitting equation is established. This equation reflects the failure inelastic strain energy density w of high temperature equipment materials in double logarithmic coordinates. f and the inelastic strain energy density dissipation rate The functional relationship between them is as follows:

[0072]

[0073] in, represents, T represents temperature, n1 and are temperature and material related model parameters, respectively.

[0074] Specifically, the failure inelastic strain energy density w f and the inelastic strain energy density dissipation rate The calculation formulas are as follows:

[0075] w f =σ·ln(1+ε f )(9).

[0076]

[0077] Specifically, the corrected inelastic strain energy density dissipation rate is calculated. The specific process is as follows:

[0078] According to the hysteresis loop under half-life cycles, the inelastic strain energy density w after correction considering creep-fatigue hysteresis recovery is calculated. in,Xnew , the calculation formula is:

[0079]

[0080] Among them, σ m It represents the average stress of the material under half life cycles.

[0081] By taking the derivative of equation (11), we can obtain the corrected inelastic strain energy density dissipation rate w: in,Xnew , the formula for the modified inelastic strain energy density dissipation rate is:

[0082]

[0083] in, It is the stress relaxation rate of high temperature equipment materials corrected cycle by cycle under the maximum tensile load. The calculation formula is:

[0084]

[0085] Substituting equation (7) and equation (13) into equation (12), we obtain:

[0086]

[0087] Among them, M and N are intermediate variables defined for the convenience of writing formula (14), which are as follows:

[0088]

[0089] The steps for calculating the creep damage under cycle-by-cycle conditions are as follows:

[0090] First, the creep test is used to determine whether there is a critical failure inelastic strain energy density, and then different equations are used to calculate the creep damage based on the determination results. The specific steps are:

[0091] When there is no critical failure strain energy density w in the creep test f0 When , the creep damage of each cycle is calculated by formula (17);

[0092]

[0093] in, represents the cycle-by-cycle creep damage when there is no critical failure inelastic strain energy density; t h Indicates the maximum strain holding time;

[0094] In the fitting equation (8) of the parameters, if w f The value of increases with the increase of, indicating that the w of the material at this temperature f There is no upper plateau value, that is, there is no critical failure strain energy density w f0 .For example, Figure 5 For the case where there is no critical failure inelastic strain energy density, it is not difficult to find that the failure inelastic strain energy density w based on creep test is f and the inelastic strain energy density dissipation rate Is positively correlated.

[0095] Substituting equations (8) and (14) into equation (17), we can obtain the strain energy density w that does not exist in the creep test: f0 Creep damage

[0096]

[0097] When there is a critical failure strain energy density w in the creep test f0 When , the creep damage under each cycle is calculated by formula (20):

[0098]

[0099] in, Represents the cycle-by-cycle creep damage in the presence of a critical failure inelastic strain energy density.

[0100] In the process of fitting the parameters of equation (8), if w f The first becomes larger with the increase of After exceeding a certain value, w f The value remains unchanged, indicating that the w of the material at this temperature f There is an upper plateau value, that is, there is a critical failure inelastic strain energy density w f0 .For example, Figure 6 In the case of a critical failure inelastic strain energy density, it is not difficult to find that the failure inelastic strain energy density w based on creep test is f First, the inelastic strain energy density dissipation rate becomes larger with the increase of When it continues to increase beyond a certain value, w f The value remains unchanged.

[0101] Substituting equations (8) and (14) into equation (19), we can obtain the critical failure strain energy density w in the creep test: f0 Creep damage

[0102]

[0103] in, represents the cumulative creep damage of the first i cycles, represents the single-cycle creep damage of the jth cycle. min(·) is the minimum value, It represents the minimum failure strain energy density of the material. The specific calculation formula is as follows:

[0104]

[0105] In some embodiments, when executing step 105, the specific steps may be as follows:

[0106] The half-life net tensile hysteresis of high-temperature equipment materials obtained through fatigue tests can fit the parameters a2 and b2, and establish the cycle-by-cycle fatigue damage formula as follows:

[0107]

[0108] in, is the superimposed fatigue damage superimposed to the i-th cycle, is the fatigue damage of the jth week, is the peak stress of the jth week, is the plastic strain range of the jth cycle, and a2 and b2 are material parameters that are independent of the cycle number.

[0109] For example, Figure 7 The half-life net tensile hysteresis energy fitting curve of the pure fatigue test of the 750℃ high-temperature equipment Crofer22APU is shown. The fatigue test uses three different strain control ranges of ±1%, ±0.5% and ±0.25%. The fitting curve is obtained by fitting the fatigue test half-life cycle curve parameters. The constant a2 is set to 87.67 and the constant b2 is set to -0.92.

[0110] In some embodiments, when executing step 106, the specific steps may be as follows:

[0111] According to the linear cumulative damage law, based on the stress relaxation formula, the failure inelastic strain energy density fitting equation and the net tensile hysteresis energy fatigue damage equation, the creep-fatigue life of high-temperature equipment materials under creep-fatigue interaction is determined, and the creep-fatigue life equation is used in different situations;

[0112] When there is no critical failure strain energy density, the creep-fatigue life can be calculated as follows:

[0113]

[0114] According to the failure criterion, when The i value at this time is the predicted value of creep-fatigue life under the corresponding working condition.

[0115] When there is a critical failure strain energy density, the creep-fatigue life can be calculated as follows:

[0116]

[0117] According to the failure criterion, when The i value at this time is the predicted value of creep-fatigue life under the corresponding working condition.

[0118] In some embodiments, the present application predicts the life under creep-fatigue interaction for P92 martensitic steel material, GH4169 nickel-based alloy material, 304SS stainless steel material, Crofer 22APU stainless steel material and Inconel 625Inconel625 diffusion welded joint, which can be specifically as follows:

[0119] Example 1: Life prediction of martensitic steel material (P92) under creep-fatigue interaction in 630℃ high temperature equipment.

[0120] Because only the life of martensitic steel at 630℃ is studied, the constant is obtained by using formula (8) The relationship between the failure inelastic strain energy density and the dissipation rate of the inelastic strain energy density at 630°C was studied, and it was found that there is a critical failure inelastic strain energy density w f0 =52; In the creep-fatigue test at 630°C, the constants A=-0.69 and B=10.95 depending on the material characteristics were calculated by controlling the strain range of ±0.2% and ±0.3%, and the stress relaxation curve was established, namely, formula (1); combined with ABAQUS finite element simulation and subroutine, formulas (2), (3), (4), and (5) were used to calculate According to literature research, the elastic modulus of the material at 630°C is E=94GPa. All material constants required for the creep-fatigue life prediction model of P92 material at 630°C are obtained.

[0121] This application calculates the fatigue damage per week in a certain total strain range according to formula (22). Due to the existence of critical failure strain energy density, the creep damage per week is calculated by formula (20) in combination with ABAQUS finite element simulation and subroutine. Finally, the linear cumulative damage law is used to calculate the predicted life under different total strain ranges and holding times through formula (24), which is compared with the actual experimental results. The results are as follows: Figure 8 shown.

[0122] Depend on Figure 8 It can be seen from the results that all the predicted lifespans calculated by this application are not only within the 1.5 times error band, but also the experimental results are closer to the predicted results. It is not difficult to find that compared with the existing creep-fatigue life prediction model, the life prediction ability of this application is greatly improved. It can be seen that the method of determining the critical inelastic strain rate in the creep-fatigue damage process shown in this application can better predict the creep-fatigue life of P92 at 630°C.

[0123] Example 2: Life prediction of GH4169 nickel-based alloy material under creep-fatigue interaction in 650℃ high-temperature equipment.

[0124] Since only the lifetime of GH4169 at 650°C is studied, the constant is obtained by using formula (8): The relationship between the failure inelastic strain energy density and the dissipation rate of the inelastic strain energy density at 650°C was studied, and it was found that there is a critical failure inelastic strain energy density w f0 =46; In the creep-fatigue test at 650°C, the constants A=13.3 and B=17.4 depending on the material characteristics are calculated through the strain control range of ±1.0%, ±1.2%, ±1.6%, and ±2.0%, and the stress relaxation curve is established, that is, formula (1); combined with ABAQUS finite element simulation and subroutine, formulas (2), (3), (4), and (5) are used to calculate According to literature research, the elastic modulus of the material at 650°C is E=171GPa. All material constants required for the creep-fatigue life prediction model of GH4169 material at 650°C are obtained.

[0125] This application calculates the fatigue damage per week in a certain total strain range according to formula (22). Due to the existence of critical failure strain energy density, the creep damage per week is calculated by formula (20) in combination with ABAQUS finite element simulation and subroutine. Finally, the linear cumulative damage law is used to calculate the predicted life under different total strain ranges and holding times through formula (24), which is compared with the actual experimental results. The results are as follows: Fig. 9 shown.

[0126] Depend on Fig. 9 It can be seen from the results that all the predicted lifespans calculated by this application are not only within the 1.5 times error band, but also the experimental results are closer to the predicted results, while the existing model prediction results are only around the 1.5 times error band. Therefore, compared with the existing creep-fatigue life prediction model, the life prediction ability of this application is greatly improved. It is not difficult to find that a method for determining the critical inelastic strain rate in the creep-fatigue damage process shown in this application can better predict the creep-fatigue life of GH4169 at 650°C.

[0127] Example 3: Life prediction of 304SS stainless steel under creep-fatigue interaction in 650℃ high temperature equipment.

[0128] Since only the life of 304SS at 650°C is studied, the constant is obtained by using formula (8) The relationship between the failure inelastic strain energy density and the inelastic strain energy density dissipation rate at 650℃ was studied, and it was found that there was no critical failure inelastic strain energy density. In the creep-fatigue test at 650℃, the constants A=45.55 and B=129.19 depending on the material characteristics were calculated through the strain control range of ±0.5% and ±2.0%, and the stress relaxation curve was established, that is, formula (1). Combined with ABAQUS finite element simulation and subroutine, formulas (2), (3), (4), and (5) were used to calculate According to literature research, the elastic modulus of the material at 650°C is E=193GPa. All material constants required for the creep-fatigue life prediction model of 304SS material at 650°C are obtained.

[0129] This application calculates the fatigue damage per week in a certain total strain range according to formula (22). Due to the existence of critical failure strain energy density, the creep damage per week is calculated by formula (18) in combination with ABAQUS finite element simulation and subroutine. Finally, the linear cumulative damage law is used to calculate the predicted life under different total strain ranges and holding times through formula (23), which is compared with the actual experimental results. The results are as follows: Fig.10 shown.

[0130] Depend on Fig.10 It can be seen from the results that all the predicted lifespans calculated by this application are not only within the 1.5 times error band, but also the experimental results are closer to the predicted results, while the existing model prediction results are only around the 1.5 times error band. Therefore, compared with the existing creep-fatigue life prediction model, the life prediction ability of this application is greatly improved. It is not difficult to find that a method for determining the critical inelastic strain rate in the creep-fatigue damage process shown in this application can better predict the creep-fatigue life of 304SS at 650°C.

[0131] Example 4: Life prediction of Crofer22APU stainless steel under creep-fatigue interaction in 750℃ high temperature equipment.

[0132] Since we only study the life of Crofer22APU at 750℃, we use formula (8) to obtain the constant The relationship between the failure inelastic strain energy density and the inelastic strain energy density dissipation rate at 750℃ was studied, and it was found that there was no critical failure inelastic strain energy density. In the creep-fatigue test at 750℃, the constants A=0.031 and B=2.77 depending on the material characteristics were calculated through the strain control range of ±0.25% and ±0.5%, and the stress relaxation curve was established, namely formula (1). Combined with ABAQUS finite element simulation and subroutine, formulas (2), (3), (4), and (5) were used to calculate The elastic modulus of the material at 750°C tested is E=0.239 GPa. All material constants required for the creep-fatigue life prediction model of Crofer22APU material at 750°C are obtained.

[0133] This application calculates the fatigue damage per week in a certain total strain range according to formula (22). Due to the existence of critical failure strain energy density, the creep damage per week is calculated by formula (18) in combination with Crofer22APU finite element simulation and subroutine. Finally, the linear cumulative damage law is used to calculate the predicted life under different total strain ranges and holding times through formula (23), which is compared with the actual experimental results. The results are as follows: Fig.11 shown.

[0134] Depend on Fig.11 It can be seen from the results that all the predicted lifespans calculated by this application are not only within the 1.5 times error band, but also the experimental results are closer to the predicted results, while the existing model prediction results are only around the 1.5 times error band. Therefore, compared with the existing creep-fatigue life prediction model, the life prediction ability of this application is greatly improved. It is not difficult to find that a method for determining the critical inelastic strain rate in the creep-fatigue damage process shown in this application can better predict the creep-fatigue life of Crofer22APU at 750°C.

[0135] Example 5: Life prediction of Inconel625 diffusion welded joint under creep-fatigue interaction in 650℃ high temperature equipment.

[0136] Since only the life of Inconel625 diffusion welded joints at 650°C is studied, the constant is obtained by using formula (8): The relationship between the failure inelastic strain energy density and the inelastic strain energy density dissipation rate at 650℃ was studied, and it was found that there was no critical failure inelastic strain energy density. In the creep-fatigue test at 650℃, the constants A=6.08 and B=19.5 depending on the material characteristics were calculated through the strain control range of ±0.25% and ±0.3%, and the stress relaxation curve was established, namely formula (1). Combined with ABAQUS finite element simulation and subroutine, formulas (2), (3), (4), and (5) were used to calculate According to literature research, the elastic modulus of the material at 650°C is E=179417GPa. All material constants required for the creep-fatigue life prediction model of Inconel625 diffusion welded joints at 650°C are obtained.

[0137] This application calculates the fatigue damage per week in a certain total strain range according to formula (22). Due to the existence of critical failure strain energy density, the creep damage per week is calculated by formula (18) in combination with ABAQUS finite element simulation and subroutine. Finally, the linear cumulative damage law is used to calculate the predicted life under different total strain ranges and holding times through formula (23), which is compared with the actual experimental results. The results are as follows: Fig.12 shown.

[0138] Depend on Fig.12It can be seen from the results that all the predicted lifespans calculated by this application are not only within the 1.5 times error band, but also the experimental results are closer to the predicted results, while the existing model prediction results are only around the 1.5 times error band. Therefore, compared with the current creep-fatigue life prediction model, the life prediction ability of this application is improved, especially the life prediction ability under different loading conditions of cyclic softening / hardening materials is greatly improved. It can be seen that a method for determining the critical inelastic strain rate in the creep-fatigue damage process shown in this application can well predict the creep-fatigue life of Inconel625 at 650°C.

[0139] Embodiment 2

[0140] This embodiment provides a system for determining a critical inelastic strain rate in a creep-fatigue damage process, comprising:

[0141] Material acquisition module, used to obtain several identical high-temperature equipment materials;

[0142] The test module is used to perform creep test, fatigue test and creep-fatigue interaction test on high-temperature equipment materials under the same temperature conditions to obtain creep test results, fatigue test results and creep-fatigue interaction test results;

[0143] A stress relaxation formula building module is used to establish a stress relaxation formula according to the creep test results; the stress relaxation formula is used to calculate the critical stress after the strain maintains the initial corrected critical inelastic strain rate;

[0144] A failure inelastic strain energy density fitting equation construction module is used to establish a failure inelastic strain energy density fitting equation according to the fatigue test results; the failure inelastic strain energy density fitting equation is used to calculate the corrected inelastic strain energy density dissipation rate and the creep damage under cycle by cycle;

[0145] A net tensile hysteresis energy fatigue damage equation building module is used to establish a net tensile hysteresis energy fatigue damage equation according to the creep-fatigue interaction test results; the net tensile hysteresis energy fatigue damage equation is used to calculate cycle-by-cycle fatigue damage;

[0146] The life calculation module is used to determine the creep-fatigue life of high-temperature equipment materials under creep-fatigue interaction according to the linear cumulative damage law, based on the stress relaxation formula, the failure inelastic strain energy density fitting equation and the net tensile hysteresis energy fatigue damage equation.

[0147] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0148] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A method for determining the critical inelastic strain rate in a creep-fatigue damage process, characterized in that: The method for determining the critical inelastic strain rate in a creep-fatigue damage process comprises: Obtain several identical high-temperature equipment materials; Based on the same temperature conditions, creep test, fatigue test and creep-fatigue interaction test are carried out on high temperature equipment materials respectively, and creep test results, fatigue test results and creep-fatigue interaction test results are obtained; According to the creep test results, a stress relaxation formula is established; the stress relaxation formula is used to calculate the critical stress after the strain maintains the initial corrected critical inelastic strain rate; According to the fatigue test results, a failure inelastic strain energy density fitting equation is established; the failure inelastic strain energy density fitting equation is used to calculate the corrected inelastic strain energy density dissipation rate and the creep damage under each cycle; According to the creep-fatigue interaction test results, a net tensile hysteresis energy fatigue damage equation is established; the net tensile hysteresis energy fatigue damage equation is used to calculate cycle-by-cycle fatigue damage; According to the linear cumulative damage law, based on the stress relaxation formula, the failure inelastic strain energy density fitting equation and the net tensile hysteresis energy fatigue damage equation, the creep-fatigue life of high-temperature equipment materials under creep-fatigue interaction is determined.

2. The method for determining the critical inelastic strain rate in the creep-fatigue damage process according to claim 1, characterized in that: The stress relaxation formula is specifically: σ(t)=σ0-(A·lgΔεpp+B)·lg(1+t); Where σ0 represents the instantaneous stress at the maximum tensile strain under half-life cycles, Δε pp represents the plastic strain range, t represents the half-maximum tensile holding time, and A and B are the parameters for fitting the Jeong stress relaxation formula.

3. The method for determining the critical inelastic strain rate in the creep-fatigue damage process according to claim 2, characterized in that: The calculation formula of the critical stress after the strain maintains the initial corrected critical inelastic strain rate is specifically: in, represents the plastic strain range of the jth cycle, It represents the time taken for the jth cycle to reach the critical inelastic strain rate during the strain holding period.

4. The method for determining the critical inelastic strain rate in the creep-fatigue damage process according to claim 3, characterized in that: The failure inelastic strain energy density fitting equation is specifically: Among them, w f represents the failure inelastic strain energy density, represents the inelastic strain energy density dissipation rate, T represents the temperature, n1 and are temperature and material related model parameters, respectively.

5. The method for determining the critical inelastic strain rate in the creep-fatigue damage process according to claim 4, characterized in that: The calculation formula for calculating the modified inelastic strain energy density dissipation rate and the creep damage under cycle by cycle specifically includes: According to the formula Calculate the corrected inelastic strain energy density dissipation rate; According to the formula Japanese formula Calculate creep damage on a cycle-by-cycle basis; Among them, M (j) 、N (j) are all intermediate variables. σ m is the average stress under half-life cycles, represents the time taken to reach the critical inelastic strain rate during the strain holding period of the jth cycle, E represents the elastic modulus of the material at this temperature, represents the critical stress of the jth cycle, is the cumulative creep damage of the first i cycles when there is no critical failure strain energy density, is the single-cycle creep damage of the jth cycle when there is no critical failure strain energy density. Both are creep damage when there is no critical failure strain energy density. h Indicates the tensile holding time, is the cumulative creep damage of the first i cycles when there is a critical failure strain energy density, is the single-cycle creep damage of the jth cycle when there is no critical failure strain energy density.

6. The method for determining the critical inelastic strain rate in the creep-fatigue damage process according to claim 1, characterized in that: The calculation formula of the cycle-by-cycle fatigue damage is specifically: in, is the superimposed fatigue damage superimposed to the i-th cycle, is the fatigue damage of the jth week, is the peak stress of the jth week, is the plastic strain range of the jth cycle, a2 and b2 represent material parameters that are independent of the cycle number.

7. A method for determining the critical inelastic strain rate in a creep-fatigue damage process according to claim 6, characterized in that: According to the linear cumulative damage law, based on the stress relaxation formula, the failure inelastic strain energy density fitting equation and the net tensile hysteresis energy fatigue damage equation, the creep-fatigue life of high-temperature equipment materials under creep-fatigue interaction is determined, including: When there is no critical failure strain energy density, according to the formula Calculate creep-fatigue life; When there is a critical failure strain energy density, according to the formula Calculate creep-fatigue life; in, is the cumulative creep damage of the first i cycles when there is no critical failure strain energy density, is the cumulative creep damage of the first i cycles when there is a critical failure strain energy density.

8. The method for determining the critical inelastic strain rate in the creep-fatigue damage process according to claim 1, characterized in that: The high-temperature equipment materials include P92 martensitic steel material, GH4169 nickel-based alloy material, 304SS stainless steel material, Crofer 22APU stainless steel material and Inconel 625Inconel625 diffusion welding joint.

9. The method for determining the critical inelastic strain rate in the creep-fatigue damage process according to claim 1, characterized in that: The loading amplitude and loading rate of the fatigue test and the creep-fatigue interaction test are the same.

10. A system for determining critical inelastic strain rate in a creep-fatigue damage process, characterized in that: include: Material acquisition module, used to obtain several identical high-temperature equipment materials; The test module is used to perform creep test, fatigue test and creep-fatigue interaction test on high-temperature equipment materials under the same temperature conditions to obtain creep test results, fatigue test results and creep-fatigue interaction test results; A stress relaxation formula building module is used to build a stress relaxation formula according to the creep test results; The stress relaxation formula is used to calculate the critical stress after the strain maintains the initial corrected critical inelastic strain rate; A failure inelastic strain energy density fitting equation building module is used to establish a failure inelastic strain energy density fitting equation according to the fatigue test results; The failure inelastic strain energy density fitting equation is used to calculate the corrected inelastic strain energy density dissipation rate and the creep damage under cycle by cycle; A net tensile hysteresis energy fatigue damage equation building module is used to establish a net tensile hysteresis energy fatigue damage equation according to the creep-fatigue interaction test results; the net tensile hysteresis energy fatigue damage equation is used to calculate cycle-by-cycle fatigue damage; The life calculation module is used to determine the creep-fatigue life of high-temperature equipment materials under creep-fatigue interaction according to the linear cumulative damage law, based on the stress relaxation formula, the failure inelastic strain energy density fitting equation and the net tensile hysteresis energy fatigue damage equation.

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