Creep-fatigue life prediction method for high-temperature equipment materials considering anelastic recovery

Abstract

The present invention discloses a method for predicting the creep-fatigue life of high-temperature equipment materials that takes into account anelastic recovery. This method, which belongs to the field of high-temperature equipment life prediction, includes the following steps: conducting creep tests, fatigue tests, and creep-fatigue interaction tests on the high-temperature equipment materials under the same temperature conditions; establishing a failure strain energy density fitting equation based on the creep test results; calculating the fatigue damage per cycle of the high-temperature equipment materials based on the fatigue cycle life of the high-temperature equipment materials obtained in the fatigue tests; establishing a stress relaxation formula; calculating the critical stress at the initial stage of strain retention that takes into account anelastic recovery of the high-temperature equipment materials; calculating the corrected inelastic strain energy density dissipation rate; calculating the creep damage at half-life cycles; and calculating the creep-fatigue life of the high-temperature equipment materials under creep-fatigue interaction according to the linear cumulative damage law. This method can meet the requirements for accurate creep-fatigue life prediction of high-temperature equipment materials.

Description

Technical Field

[0001] The present invention belongs to the field of high-temperature equipment life prediction, and in particular relates to a method for predicting the creep-fatigue life of high-temperature equipment materials taking into account anelastic recovery. Background Art

[0002] In industries such as energy and chemical engineering, nuclear power, and aerospace, a large number of mechanical equipment, such as petrochemical smelting furnaces, aircraft engines, heat exchangers, steam pipelines, and core nuclear power equipment, are subjected to long-term service in extreme environments of high temperature and pressure. The creep deformation caused by these environments, combined with the fatigue deformation caused by dynamic loads, accelerates the damage and destruction of equipment components, seriously threatening the safety and reliability of high-temperature equipment. This creep-fatigue interaction is a common failure mode for many high-temperature equipment, making research on creep-fatigue life prediction of high-temperature equipment materials extremely valuable.

[0003] Since the 1950s, scholars at home and abroad have proposed nearly one hundred mathematical models to predict the creep-fatigue life of high-temperature equipment materials. However, the fatigue damage mechanism of materials at high temperatures is related not only to time-independent plastic deformation, but also to time-dependent creep and environmental effects. Under the operating conditions of components, not only do these independent damage mechanisms coexist, but they also interact with each other, which places high demands on creep-fatigue life prediction models. Currently, there are three widely accepted theoretical systems for predicting the creep-fatigue life of high-temperature equipment: those based on the Manson-Coffin equation, those based on the differentiation method, and those based on the linear damage accumulation criterion. Among theoretical systems based on the Manson-Coffin equation, the most widely used is the frequency correction model proposed by Coffin in 1969. This was the first attempt to introduce a time-dependent term into the total strain range form of the Manson-Coffin equation. However, this model ignores the varying degrees of influence of cyclic waveforms on life for different materials. Among the creep-fatigue life prediction models based on differentiation methods, the most common is the strain range differentiation method. This method considers the material's inelastic strain as the primary cause of creep-fatigue failure and distinguishes different inelastic strain components for differential calculation and damage superposition. While this method mechanistically explains the influence of creep effects on creep-fatigue life, it has difficulties and limitations in distinguishing smaller inelastic strain ranges under low-load conditions. Theoretical systems based on the linear damage accumulation criterion have developed to date, and the derived creep-fatigue life prediction model based on the strain energy density dissipation method has been widely praised for its high accuracy, simple parameter acquisition, and clear physical meaning. However, it does not consider the influence of anelastic recovery of strain in the initial stage of strain holding on creep damage calculation for high-temperature equipment materials, nor does it clearly distinguish between matrix damage and crystal damage, resulting in overly conservative life prediction results. Summary of the Invention

[0004] In order to solve the above problems, the present invention proposes a creep-fatigue life prediction method for high-temperature equipment materials considering anelastic recovery to meet the creep-fatigue life prediction accuracy of high-temperature equipment materials.

[0005] The technical solutions of the present invention are as follows:

[0006] A method for predicting creep-fatigue life of high-temperature equipment materials considering anelastic recovery comprises the following steps:

[0007] Step 1: Conduct creep test, fatigue test and creep-fatigue interaction test of high temperature equipment materials under the same temperature conditions;

[0008] Step 2: Based on the results of the creep test, establish a failure strain energy density fitting equation;

[0009] Step 3: Calculate the fatigue damage of the high-temperature equipment material per week based on the fatigue cycle life of the high-temperature equipment material obtained from the fatigue test;

[0010] Step 4: Establish a stress relaxation formula;

[0011] Step 5: Calculate the critical stress of the high-temperature equipment material considering the anelastic recovery at the initial stage of strain maintenance;

[0012] Step 6, calculating the corrected inelastic strain energy density dissipation rate;

[0013] Step 7: Calculate the creep damage under half-life cycles;

[0014] Step 8: Calculate the creep-fatigue life of high-temperature equipment materials under creep-fatigue interaction according to the linear cumulative damage law.

[0015] Furthermore, in step 2, the failure strain energy density fitting equation reflects the failure strain energy density w of the high-temperature equipment material under double logarithmic coordinates. f and inelastic strain energy density dissipation rate The functional relationship between them is as follows:

[0016]

[0017] Among them, w f is the failure strain energy density; B1 and n1 are constants that are independent of temperature; T represents the test temperature of the creep test, Q represents the thermal activation energy at the test temperature, and R represents the universal gas constant; exp(·) represents the exponential function; is the inelastic strain energy density dissipation rate;

[0018] Failure strain energy density wf and inelastic strain energy density dissipation rate The calculation formulas are as follows:

[0019] w f =σ·ln(1+ε f ) (2);

[0020]

[0021] Where σ represents the stress level applied in the creep test; ε f represents the creep rupture strain time obtained in the creep test; t R represents the rupture time obtained in the creep test;

[0022] When studying the creep-fatigue properties of high-temperature equipment materials at a constant temperature, formula (1) degenerates into the following formula:

[0023]

[0024] in, Represents the linear regression constant related to high temperature equipment material and temperature.

[0025] Furthermore, in step 3, the calculation formula for the fatigue damage of high-temperature equipment materials per week is as follows:

[0026] d f =1 / N fo (5);

[0027] Among them, N fo Indicates the fatigue cycle life of high-temperature equipment materials obtained in fatigue tests; d f Indicates fatigue damage of high-temperature equipment materials per week.

[0028] Furthermore, in step 4, the stress relaxation formula reflects the functional relationship between the stress of the high-temperature equipment material at half-life cycles during the holding time of the maximum tensile strain and time. The specific functional relationship is as follows:

[0029] σ(t)=σ0-(A·lgΔε P +B)·lg(1+t) (6);

[0030] Where σ represents the stress level applied in the creep test; σ0 represents the maximum stress at half-life cycles; A and B are constants that depend on the material; Δε P It represents the plastic strain range under half-life cycles; t represents the holding time of the maximum tensile strain under half-life cycles.

[0031] Furthermore, in step 5, the critical stress σ of the high-temperature equipment material anelastic recovery is considered at the initial stage of strain maintenancere The calculation formula is as follows:

[0032] σ re =σ0-(A·lgΔε P +B)·lg(1+t re ) (11);

[0033] Among them, t re It is the time taken by the high-temperature equipment material to reach the critical inelastic strain rate during the strain holding period. The calculation formula is as follows:

[0034]

[0035] Where E represents the elastic modulus of the high-temperature equipment material at the test temperature of the creep-fatigue interaction test; represents the critical inelastic strain rate, which is calculated as follows:

[0036]

[0037] in, Indicates the maximum inelastic strain rate at the initial stage of stress relaxation.

[0038] Furthermore, in step 6, the corrected inelastic strain energy density dissipation rate The calculation formula is as follows:

[0039]

[0040] Among them, M and N are intermediate variables, respectively expressed as:

[0041]

[0042]

[0043] Among them, σ m Indicates the average stress of high-temperature equipment materials under half-life cycles.

[0044] Furthermore, in step 7, firstly, it is determined whether there is a critical failure strain energy density in the creep test, and then the creep damage under half-life cycles is calculated according to the determination result;

[0045] In the process of fitting the parameters of formula (1), if w f The value of increases with the increase of , indicating that there is no critical failure strain energy density w f0 , the creep damage calculation formula is as follows:

[0046]

[0047] in, represents the creep damage when there is no critical failure strain energy density; t h Indicates the total time the maximum strain is maintained;

[0048] In the process of fitting the parameters of formula (1), if w f The value of increases with the increase of When it continues to increase beyond a certain value, w f The value remains unchanged, indicating that there is a critical failure strain energy density w f0 , the creep damage calculation formula is as follows:

[0049]

[0050] in, represents the creep damage when there is a critical failure strain energy density; min(·) represents the minimum value, It represents the minimum failure strain energy density of the material. The specific calculation formula is as follows:

[0051]

[0052] Furthermore, in step 8, the creep-fatigue life is calculated according to the judgment result of step 7;

[0053] When there is no critical failure strain energy density, the creep-fatigue life can be calculated as follows:

[0054]

[0055] in, represents the creep-fatigue life when there is no critical failure strain energy density;

[0056] When there is a critical failure strain energy density, the creep-fatigue life can be calculated as follows:

[0057]

[0058] in, Represents the creep-fatigue life when a critical failure strain energy density exists.

[0059] The beneficial technical effects brought about by the present invention are as follows: the method of the present invention fully considers the influence of anelastic recovery on creep damage calculation, more reasonably distinguishes the effective creep damage stage and the invalid creep damage stage, reduces the shortcoming of the existing creep-fatigue life prediction method in predicting the creep-fatigue life of high-temperature equipment materials being too conservative, and can accurately predict the creep-fatigue life of high-temperature equipment materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 The figure is a flow chart of the creep-fatigue life prediction method of high-temperature equipment materials considering anelastic recovery according to the present invention.

[0061] Figure 2 Schematic diagram of the loading condition in the present invention.

[0062] Figure 3 This is a fitting curve diagram of the stress relaxation test of the material in the present invention.

[0063] Figure 4 This is a graph showing the change of the inelastic strain rate of the material over time in the present invention.

[0064] Figure 5 Schematic diagram of the non-existence of critical failure strain energy density in the present invention.

[0065] Figure 6 Schematic diagram of critical failure strain energy density in the present invention.

[0066] Figure 7 This is a comparison chart of the life prediction of P92 martensitic steel material in Example 1 of the present invention.

[0067] Figure 8 This is a comparison chart of the life prediction of the GH4169 nickel-based alloy material in Example 2 of the present invention.

[0068] Figure 9 This is a comparison chart of the life prediction of 304SS stainless steel material in Example 3 of the present invention. DETAILED DESCRIPTION

[0069] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0070] like Figure 1 As shown, a creep-fatigue life prediction method for high-temperature equipment materials considering anelastic recovery includes the following steps:

[0071] Step 1: Conduct creep test, fatigue test and creep-fatigue interaction test of high temperature equipment materials under the same temperature conditions. For example, Figure 2 An actual loading condition is shown, such as Figure 2 As shown in Figure 3, the loading amplitude and loading rate are the same for the fatigue test and the creep-fatigue interaction test.

[0072] Step 2: Based on the results of the creep test, establish a failure strain energy density fitting equation. This equation reflects the failure strain energy density w of high-temperature equipment materials in double logarithmic coordinates. f and inelastic strain energy density dissipation rate The functional relationship between them is as follows:

[0073]

[0074] Wherein, B1 and n1 are constants that are independent of temperature; T represents the test temperature of the creep test, Q represents the thermal activation energy at the test temperature, R represents the universal gas constant, which is a constant value of 8.314×10-3 kJ / (K·mol); exp(·) represents the exponential function; the failure strain energy density w f and inelastic strain energy density dissipation rate The calculation formulas are as follows:

[0075] w f =σ·ln(1+ε f ) (2);

[0076]

[0077] Wherein, σ represents the stress level value applied in the creep test; ε f represents the creep rupture strain time obtained in the creep test; t R represents the rupture time obtained in the creep test;

[0078] When studying the creep-fatigue properties of a material at a constant temperature, equation (1) can be degenerated into the following formula:

[0079]

[0080] in, Represents the linear regression constant related to high temperature equipment material and temperature.

[0081] Step 3: Based on the fatigue cycle life N of the high temperature equipment material obtained from the fatigue test fo , calculate the fatigue damage d of high temperature equipment materials per week by formula (5) f The calculation formula is as follows:

[0082] d f =1 / N fo (5);

[0083] Step 4: Establish a stress relaxation formula. This stress relaxation formula reflects the functional relationship between the stress of high-temperature equipment materials and time changes in half-life cycles during the holding time of maximum tensile strain. The specific functional relationship is as follows:

[0084] σ(t)=σ0-(A·lgΔε P +B)·lg(1+t) (6);

[0085] Where σ0 represents the maximum stress under half-life cycles; A and B are constants; Δε PIt represents the plastic strain range under half-life cycles; t represents the holding time of the maximum tensile strain under half-life cycles.

[0086] For example, Figure 3 The stress relaxation test fitting curve of 304SS stainless steel material in 650℃ high temperature equipment is shown. The fitting curve is obtained by fitting the stress relaxation curve parameters in the half-life cycle strain holding stage. During the fitting, the constant A is set to 45.55 and the constant B is set to 129.19. Figure 3 It can be seen that the stress decreases with time.

[0087] Step 5: Calculate the critical stress of the high-temperature equipment material considering the anelastic recovery during the initial stage of strain maintenance. The specific process is as follows:

[0088] Step 5.1: Calculate the critical inelastic strain rate of the material during the maximum tensile strain holding time according to the functional relationship in step 4. First, differentiate equation (6) to calculate the stress relaxation rate, which is expressed as:

[0089]

[0090] in, represents the inelastic strain rate; represents the derivative of formula (6); E represents the elastic modulus of high-temperature equipment material at the test temperature of creep-fatigue interaction test;

[0091] Then, 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 (7);

[0092]

[0093] in, represents the critical inelastic strain rate, Indicates the maximum inelastic strain rate at the initial stage of stress relaxation.

[0094] For example, Figure 4 Shows the stress relaxation rate curve, reflecting the inelastic strain rate Changes in the holding time t of the maximum tensile strain at half-life cycles. Figure 4 In, t re It is the time taken by the high temperature equipment material to reach the critical inelastic strain rate during the strain holding period. represents the maximum inelastic strain rate at the initial stage of stress relaxation, represents the critical inelastic strain rate, (0,1.3 -4 ) is the maximum inelastic strain rate corresponding to the holding time of zero, (9,1.3 -5 ) is the critical inelastic strain rate corresponding to the holding time of 9 seconds.

[0095] Step 5.2: Calculate the time t taken by the high-temperature equipment material to reach the critical inelastic strain rate during the strain holding period using formula (9): re , expressed as:

[0096]

[0097] Step 5.3: Modify the stress relaxation formula of formula (6). The modified stress relaxation formula σ new (t) is expressed as:

[0098] σ new (t) = σ0-(A·lgΔε P +B)·lg(1+t+t re ) (10);

[0099] Step 5.4: Substitute the t calculated by formula (9) into re Substituting into equation (6) we can obtain the critical stress σ considering the material's anelastic recovery at the initial stage of strain retention: re , expressed as:

[0100] σ re =σ0-(A·lgΔε P +B)·lg(1+t re ) (11).

[0101] Step 6: Calculate the corrected inelastic strain energy density dissipation rate. The specific process is as follows:

[0102] According to the hysteresis loop under half-life cycles, the inelastic strain energy density w after correction considering creep-fatigue anelastic recovery is calculated. in,new , the calculation formula is:

[0103]

[0104] Among them, σ m It represents the average stress of the material under half life cycles.

[0105] By taking the derivative of Equation (12), we can obtain the corrected inelastic strain energy density dissipation rate:

[0106]

[0107] in, It indicates the stress relaxation rate of high temperature equipment materials corrected under half life cycles within the maximum tensile strain holding time. The calculation formula is:

[0108]

[0109] Substituting equations (10) and (14) into equation (13), we obtain:

[0110]

[0111] Among them, M and N are intermediate variables defined for the convenience of writing formula (15), which are as follows:

[0112]

[0113]

[0114] Step 7: Calculate creep damage under half-life cycles. First, determine whether there is a critical failure strain energy density in the creep test, and then calculate the creep damage under half-life cycles according to the determination results. The specific process is as follows:

[0115] Step 7.1: When there is no critical failure strain energy density w in the creep test f0 When , the creep damage under half-life cycles is calculated by formula (18);

[0116]

[0117] in, represents the creep damage corresponding to the absence of critical failure strain energy density; t h Indicates the total time the maximum strain is maintained;

[0118] In the process of fitting the parameters of formula (1), if w f The value of The increase of w increases with the increase of , indicating that the w of high temperature equipment materials 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 What is shown is a situation where there is no critical failure strain energy density. It can be clearly seen from the figure that the failure strain energy density w based on the creep test is f The value of always varies with the inelastic strain energy density dissipation rate increases with the increase of .

[0119] Substituting equations (1) and (15) into equation (18), we can obtain the strain energy density w that does not exist in the creep test. f0 Creep damage

[0120]

[0121] Step 7.2: When there is a critical failure strain energy density w in the creep test f0 When , the creep damage under half-life cycles is calculated by formula (20):

[0122]

[0123] in, Indicates creep damage when there is a critical failure strain energy density;

[0124] In the process of fitting the parameters of formula (1), if w f The value of increases with the increase of When it continues to increase beyond 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 strain energy density w f0 .For example, Figure 6 What is shown is a situation where there is a critical failure strain energy density. Figure 6 It is obvious that the failure strain energy density w based on creep test is f The value of the first decreases with the inelastic strain energy density dissipation rate increases with the increase of When it continues to increase beyond a certain value, w f The value remains unchanged.

[0125] Substituting equations (1) and (15) into equation (20), we can obtain the critical failure strain energy density w in the creep test: f0 Creep damage

[0126]

[0127] Among them, min(·) means finding the minimum value, It represents the minimum failure strain energy density of the material. The specific calculation formula is as follows:

[0128]

[0129] Step 8. Calculate the creep-fatigue life of high-temperature equipment materials under creep-fatigue interaction based on the linear cumulative damage law. The general calculation formula for creep-fatigue life is as follows:

[0130] N c-f =1 / (d f +d c ) (twenty three);

[0131] Among them, N c-f Indicates the creep-fatigue life calculated using the general calculation formula; d c Indicates creep damage.

[0132] The present invention calculates creep-fatigue life according to the judgment result of step 7;

[0133] When there is no critical failure strain energy density, substitute equations (1) and (19) into equation (23) to obtain the critical failure strain energy density w in the creep test. f0 The corresponding creep-fatigue life is:

[0134]

[0135] in, represents the creep-fatigue life corresponding to the absence of critical failure strain energy density;

[0136] When there is a critical failure strain energy density, substitute equations (1) and (21) into equation (23) to obtain the critical failure strain energy density w in the creep test. f0 The corresponding creep-fatigue life is:

[0137] in, It represents the creep-fatigue life when there is no critical failure strain energy density.

[0138] To demonstrate the feasibility of the present invention, the following three examples are presented. They respectively predict the lifespan of a martensitic steel (P92) in a 630°C high-temperature device, a nickel-based alloy (GH4169) in a 650°C high-temperature device, and a stainless steel (304SS) in a 650°C high-temperature device under creep-fatigue interaction.

[0139] Example 1: Life prediction of martensitic steel material (P92) under creep-fatigue interaction in 630°C high-temperature equipment.

[0140] First, since only the life of martensitic steel at a temperature of 630°C is studied, the linear regression constant related to material and temperature can be obtained by using the degradation formula (4). By analyzing the functional relationship between the failure strain energy density and the inelastic strain energy density dissipation rate at 630℃, it is found that there is a critical failure strain energy density w f0 =52; In the creep-fatigue test at 630°C, constants A=-0.69 and B=10.95 depending on the material characteristics were calculated through the total strain range of ±0.2% and ±0.3%, thereby obtaining the stress relaxation curve normalized by the plastic strain range, i.e., formula (6); t was then calculated through formulas (7), (8), and (9) re =9.7s. According to existing literature, the elastic modulus at 630°C is E = 94 GPa. Therefore, all the material constants required for the creep-fatigue life prediction model of P92 material at 630°C are obtained.

[0141] The present invention calculates the fatigue damage per week in a certain total strain range according to formula (5). Due to the existence of critical failure strain energy density, formula (21) is combined with the above material constants to calculate the creep damage of half life cycles under the total strain range, and it is approximately considered to represent the creep damage per week. Finally, the linear cumulative damage method is used to calculate the predicted life under different total strain ranges and holding times through formulas (23) and (25). It is compared with the actual experimental results. The results are as follows: Figure 7 shown.

[0142] Depend on Figure 7 The results show that all predicted lifespans calculated using the present invention are within a 1.5-fold error band, and the experimental results are very close to the predicted results, while the existing model's predictions sometimes exceed a 2-fold error band. Therefore, compared to existing creep-fatigue life prediction models, the present invention significantly improves its lifespan prediction capabilities. This shows that the creep-fatigue life prediction model shown in the present invention can effectively predict the creep-fatigue life of P92 at 630°C.

[0143] Example 2: Life prediction of nickel-based alloy material (GH4169) under creep-fatigue interaction in 650°C high-temperature equipment.

[0144] First, since only the material life at 650℃ is studied, the linear regression constant related to material and temperature can be obtained by using the degradation formula (4). By analyzing the functional relationship between the failure strain energy density and the inelastic strain energy density dissipation rate at 650℃, it is found that there is a critical failure strain energy density w f0 =46; In the creep-fatigue test at 650°C, constants A = 13.3 and B = 17.4, which depend on the material characteristics, were calculated over the total strain ranges of 1.0%, 1.2%, 1.6%, and 2.0%, thereby obtaining the stress relaxation curve normalized for the plastic strain range, i.e., formula (6); t was then calculated using formulas (7), (8), and (9). re =8.9s. According to existing literature, the elastic modulus at 650°C is E = 171 GPa. Therefore, all the material constants required for the creep-fatigue life prediction model of GH4169 material at 650°C are obtained.

[0145] The present invention calculates the fatigue damage per week of a certain total strain range according to formula (5). Due to the existence of critical failure strain energy density, formula (21) is combined with the above material constants to calculate the creep damage of half life cycles under the total strain range, and it is approximately considered to represent the creep damage per week. Finally, using the linear cumulative damage method, the predicted life under different total strain ranges and holding times is calculated by formula (23) and formula (25). It is compared with the actual experimental results. The results are as follows: Figure 8 shown.

[0146] Depend on Figure 8 The results show that all predicted lifespans calculated using the present invention are within a 1.5-fold error band, closely matching the experimental results. However, existing models sometimes exceed this error band by a factor of 2. Therefore, compared to existing creep-fatigue life prediction models, the present invention improves lifespan prediction capabilities, particularly under low-strain, short-hold-load conditions. This demonstrates that the creep-fatigue life prediction model presented in the present invention can effectively predict the creep-fatigue life of GH4169 at 650°C.

[0147] Example 3: Life prediction of stainless steel material (304SS) under creep-fatigue interaction in 650°C high-temperature equipment.

[0148] First, since only the material life at 650℃ is studied, the linear regression constant related to material and temperature can be obtained by using the degradation formula (4). The functional relationship between the failure strain energy density and the inelastic strain energy density dissipation rate at 650℃ was analyzed, and it was found that there was no critical failure 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 total strain range of 0.5% and 2.0%, and the stress relaxation curve normalized by the plastic strain range was obtained, namely formula (6). Then, t was calculated by formula (7), formula (8), and formula (9). re =9s, and according to existing literature, the elastic modulus at 650°C is E = 193 GPa. Therefore, all the material constants required for the creep-fatigue life prediction model of 304SS material at 650°C are obtained.

[0149] The present invention calculates the fatigue damage per week of a certain total strain range according to formula (5). Due to the existence of critical failure strain energy density, formula (21) is combined with the above material constants to calculate the creep damage of half life cycles under the total strain range, and it is approximately considered to represent the creep damage per week. Finally, using the linear cumulative damage method, the predicted life under different total strain ranges and holding times is calculated by formula (23) and formula (25). It is compared with the actual experimental results. The results are as follows: Figure 9 shown.

[0150] Depend on Figure 9 The results show that all predicted lifespans calculated using the present invention are within a 1.5-fold error band, with experimental results very close to the predicted results. However, existing models sometimes exceed this error band. Therefore, compared to existing creep-fatigue life prediction models, the present invention improves lifespan prediction capabilities, particularly under low-strain, short-hold-load conditions. This demonstrates that the creep-fatigue life prediction model presented in the present invention can effectively predict the creep-fatigue life of 304SS at 650°C.

[0151] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the scope of protection of the present invention.

Claims

1. A method for predicting creep-fatigue life of high-temperature equipment materials considering anelastic recovery, characterized in that: The steps include: Step 1: Conduct creep test, fatigue test and creep-fatigue interaction test of high temperature equipment materials under the same temperature conditions; Step 2: Based on the results of the creep test, establish a failure strain energy density fitting equation; Step 3: Calculate the fatigue damage of the high-temperature equipment material per week based on the fatigue cycle life of the high-temperature equipment material obtained from the fatigue test; Step 4: Establish a stress relaxation formula; Step 5: Calculate the critical stress of the high-temperature equipment material considering the anelastic recovery at the initial stage of strain maintenance; Step 6, calculating the corrected inelastic strain energy density dissipation rate; Step 7: Calculate the creep damage under half-life cycles; Step 8: Calculate the creep-fatigue life of high-temperature equipment materials under creep-fatigue interaction according to the linear cumulative damage law.

2. The creep-fatigue life prediction method for high-temperature equipment materials considering anelastic recovery according to claim 1 is characterized in that: In step 2, the failure strain energy density fitting equation reflects the failure strain energy density w of the high temperature equipment material under double logarithmic coordinates. f and inelastic strain energy density dissipation rate The functional relationship between them is as follows: Among them, w f is the failure strain energy density; B1 and n1 are constants that are independent of temperature; T represents the test temperature of the creep test, Q represents the thermal activation energy at the test temperature, and R represents the universal gas constant; exp(·) represents the exponential function; is the inelastic strain energy density dissipation rate; Failure strain energy density w f and inelastic strain energy density dissipation rate The calculation formulas are as follows: w f =σ·ln(1+ε f ) (2); Where σ represents the stress level applied in the creep test; ε f represents the creep rupture strain time obtained in the creep test; t R represents the rupture time obtained in the creep test; When studying the creep-fatigue properties of high-temperature equipment materials at a constant temperature, formula (1) degenerates into the following formula: in, Represents the linear regression constant related to high temperature equipment material and temperature.

3. The creep-fatigue life prediction method for high-temperature equipment materials considering anelastic recovery according to claim 1 is characterized in that: In step 3, the calculation formula for the fatigue damage of high-temperature equipment materials per week is as follows: d f =1 / N fo (5); Among them, N fo Indicates the fatigue cycle life of high-temperature equipment materials obtained in fatigue tests; d f Indicates fatigue damage of high-temperature equipment materials per week.

4. The creep-fatigue life prediction method for high-temperature equipment materials considering anelastic recovery according to claim 1 is characterized in that: In step 4, the stress relaxation formula reflects the functional relationship between the stress of the high-temperature equipment material at half-life cycles during the holding time of the maximum tensile strain and the time change. The specific functional relationship is as follows: σ(t)=σ0-(A·lgΔε P +B)·lg(1+t) (6); Where σ represents the stress level applied in the creep test; σ0 represents the maximum stress at half-life cycles; A and B are constants that depend on the material; Δε P It represents the plastic strain range under half-life cycles; t represents the holding time of the maximum tensile strain under half-life cycles.

5. The creep-fatigue life prediction method for high-temperature equipment materials considering anelastic recovery according to claim 1 is characterized in that: In step 5, the strain is maintained at the initial stage, considering the critical stress σ of the high temperature equipment material anelastic recovery re The calculation formula is as follows: s re =σ0-(A·lgΔε P +B)·lg(1+t re ) (11); Among them, t re It is the time taken by the high-temperature equipment material to reach the critical inelastic strain rate during the strain holding period. The calculation formula is as follows: Where E represents the elastic modulus of the high-temperature equipment material at the test temperature of the creep-fatigue interaction test; represents the critical inelastic strain rate, which is calculated as follows: in, Indicates the maximum inelastic strain rate at the initial stage of stress relaxation.

6. The creep-fatigue life prediction method for high-temperature equipment materials considering anelastic recovery according to claim 1, characterized in that: In step 6, the corrected inelastic strain energy density dissipation rate The calculation formula is as follows: Among them, M and N are intermediate variables, respectively expressed as: Among them, σ m Indicates the average stress of high-temperature equipment materials under half-life cycles.

7. The creep-fatigue life prediction method for high-temperature equipment materials considering anelastic recovery according to claim 1, characterized in that: In step 7, first determine whether there is a critical failure strain energy density in the creep test, and then calculate the creep damage under half-life cycles according to the determination result; In the process of fitting the parameters of formula (1), if w f The value of increases with the increase of , indicating that there is no critical failure strain energy density w f0 , the creep damage calculation formula is as follows: in, represents the creep damage when there is no critical failure strain energy density; t h Indicates the total time the maximum strain is maintained; In the process of fitting the parameters of formula (1), if w f The value of increases with the increase of When it continues to increase beyond a certain value, w f The value remains unchanged, indicating that there is a critical failure strain energy density w f0 , the creep damage calculation formula is as follows: in, represents the creep damage when there is a critical failure strain energy density; min(·) represents the minimum value, It represents the minimum failure strain energy density of the material. The specific calculation formula is as follows:

8. The method for predicting creep-fatigue life of high-temperature equipment materials considering anelastic recovery according to claim 7, characterized in that: In step 8, the creep-fatigue life is calculated according to the judgment result of step 7; When there is no critical failure strain energy density, the creep-fatigue life can be calculated as follows: in, represents the creep-fatigue life when there is no critical failure strain energy density; When there is a critical failure strain energy density, the creep-fatigue life can be calculated as follows: in, Represents the creep-fatigue life when a critical failure strain energy density exists.

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