Multi-axial creep-fatigue damage evaluation method based on internal stress plastic strain energy

Abstract

The invention discloses a multi-axis creep-fatigue damage evaluation method based on internal stress plastic strain energy, which comprises the following steps: acquiring related parameters of multi-axis creep-fatigue damage evaluation and life prediction, and acquiring fatigue damage and creep damage of a target material test per week based on the related parameters; calculating accumulated fatigue damage and accumulated creep damage according to the fatigue damage and the creep damage under different weeks; according to the accumulated fatigue damage, the accumulated creep damage and a bilinear damage accumulation criterion, a creep-fatigue damage interaction diagram is drawn, the damage state of the target material is obtained, the damage state is judged according to the creep-fatigue damage interaction diagram, and a target material failure evaluation result is obtained; a bilinear cumulative damage rule is adopted to calculate the number of weeks with the sum of cumulative fatigue damage and cumulative creep damage being 1, and the predicted life of the target material is obtained so as to achieve effective damage evaluation and life prediction of the target material under the multi-axis creep-fatigue interaction effect.

Description

Technical Field

[0001] The invention belongs to the technical field of material damage assessment and life prediction, and in particular relates to a multi-axial creep-fatigue damage assessment method based on internal stress plastic strain energy. Background Art

[0002] In the fields of nuclear power, aerospace, petrochemicals, etc., many key structural components operate under high temperature conditions for a long time. Due to frequent start-up and shutdown, operating condition fluctuations, etc., their high-temperature components are often subjected to creep-fatigue interactive damage. In addition, due to the complex geometry of the components, they are subjected to tangential loads while bearing axial loads, that is, multi-axial creep-fatigue loads. At present, the traditional uniaxial strain-controlled creep-fatigue tests or notched multi-axial creep-fatigue tests used in the laboratory are difficult to reflect the actual operating conditions of high-temperature complex components. Therefore, under the conditions of multi-axial creep-fatigue load interaction, the realization of multi-axial creep-fatigue damage evaluation and life prediction of materials is a key issue that needs to be broken through.

[0003] In recent decades, with the joint efforts of many domestic and foreign researchers, the research on multiaxial low-cycle fatigue damage evaluation and life prediction methods has made great progress. However, for multiaxial creep-fatigue loading conditions, especially under multiaxial non-proportional loading, the stress-strain relationship is very complex, making it difficult to predict the creep-fatigue life. Because there are many factors that affect the multiaxial creep-fatigue life and damage degree of materials, many damage evaluation and life prediction methods are limited by materials and test conditions. In the past, a large number of creep-fatigue life prediction models have been developed, such as linear damage accumulation method, strain range division method, frequency correction method, ductility exhaustion method, etc. However, these methods are usually suitable for uniaxial creep-fatigue damage evaluation and life prediction. When they are used for multiaxial creep-fatigue loads, especially under non-proportional multiaxial loads, large errors will occur. Therefore, it is urgent to study a new multiaxial creep-fatigue damage evaluation and life prediction method to meet the needs of damage evaluation and life prediction under different creep-fatigue loads. Summary of the invention

[0004] In order to solve the above technical problems, the present invention proposes a multi-axial creep-fatigue damage evaluation method based on internal stress plastic strain energy, so as to better realize the damage evaluation and life prediction of materials under multi-axial creep-fatigue interaction. At the same time, it can also more intuitively observe the cumulative damage of the material, and has good data readability, so as to guide the life design under complex loads, thereby solving the problems existing in the above-mentioned prior art.

[0005] To achieve the above object, the present invention provides a multiaxial creep-fatigue damage evaluation method based on internal stress plastic strain energy, comprising:

[0006] Obtain relevant parameters for multiaxial creep-fatigue damage evaluation and life prediction, including material constants, instantaneous inelastic strain energy density dissipation rate, failure inelastic strain energy density and failure strain energy density upper platform;

[0007] Based on relevant parameters, the fatigue damage and creep damage of the target material test per week are obtained;

[0008] According to the fatigue damage and creep damage under different cycles, the cumulative fatigue damage and cumulative creep damage are calculated;

[0009] According to the cumulative fatigue damage, cumulative creep damage and bilinear damage accumulation criterion, a creep-fatigue damage interaction diagram is drawn to obtain the damage state of the target material, and the damage state is judged according to the creep-fatigue damage interaction diagram to obtain the failure evaluation result of the target material;

[0010] The bilinear cumulative damage law is used to calculate the number of cycles at which the sum of cumulative fatigue damage and cumulative creep damage is 1, and the predicted life of the target material is obtained.

[0011] Optionally, by performing several groups of different strain-controlled pure fatigue tests and pure creep tests on the target material at the same temperature, relevant parameters for obtaining multi-axial creep-fatigue damage evaluation and life prediction are calculated, wherein the adjustment parameters of the pure fatigue test include strain amplitude and strain ratio, and the adjustment parameters of the pure creep test include stress level.

[0012] Optionally, the process of obtaining the material constants includes:

[0013] The functional relationship between fatigue life and equivalent friction stress and back stress plastic strain energy density under half-life cycles is fitted, and the material constant and functional relationship are:

[0014]

[0015] in, is the equivalent friction stress plastic strain energy density under half life cycles, is the equivalent back stress plastic strain energy density under half life cycles, N f is fatigue life, a and b are different material constants;

[0016] Among them, the equivalent friction stress plastic strain energy density under half-life cycles and the equivalent back stress plastic strain energy density under half-life cycles are:

[0017]

[0018] in, is the plastic strain energy density of axial friction stress, is the plastic strain energy density of torsional friction stress, is the plastic strain energy density of the axial back stress, is the plastic strain energy density of torsional back stress.

[0019] Optionally, the process of obtaining the failure strain energy density upper platform includes:

[0020] Obtain the instantaneous inelastic strain energy density dissipation rate and failure inelastic strain energy density:

[0021]

[0022] w f =σ·ln(1+ε f )

[0023] Where σ is the stress level, t R is the creep rupture time, ε f is creep ductility;

[0024] By performing nonlinear fitting on the instantaneous inelastic strain energy density dissipation rate and the failure inelastic strain energy density, a relationship diagram between the instantaneous inelastic strain energy density dissipation rate and the failure inelastic strain energy density is constructed, and the function expression of the relationship diagram is:

[0025]

[0026] in, is the first linear regression coefficient, n1 is the first linear regression power index;

[0027] According to the relationship diagram, the upper platform of failure strain energy density is obtained.

[0028] Optionally, at the same temperature, several groups of different strain-controlled multiaxial creep-fatigue tests are performed on the target material, wherein the adjustment parameters of the multiaxial creep-fatigue test include equivalent strain amplitude, strain ratio, load holding time, and load holding direction.

[0029] Optionally, the fatigue damage acquisition process includes:

[0030]

[0031] in, is the equivalent friction stress plastic strain energy density, is the equivalent back stress plastic strain energy density, a and b are material constants.

[0032] Optionally, the process of obtaining the creep damage includes:

[0033]

[0034] in, is the equivalent viscous stress plastic strain energy density rate, is the equation for the failure strain energy density determined by the equivalent viscous stress, plastic strain energy density rate and temperature, w f,crit (T) is the failure strain energy density upper platform, t h To maintain the loading time.

[0035] Optionally, the process of obtaining the cumulative fatigue damage and cumulative creep damage includes:

[0036] The fatigue damage and creep damage under different cycles are accumulated and summed separately to obtain the cumulative fatigue damage and cumulative creep damage.

[0037] Optionally, the bilinear damage accumulation criterion is:

[0038]

[0039] in, and is the cumulative fatigue damage value and cumulative creep damage value at the interactive turning point in the bilinear criterion, D f represents the cumulative fatigue damage of the target material, D c Represents the accumulated creep damage of the target material.

[0040] Compared with the prior art, the present invention has the following advantages and technical effects:

[0041] The invention discloses a multiaxial creep-fatigue damage evaluation method based on internal stress plastic strain energy. The method is based on established fatigue and creep damage equations and adopts a bilinear damage accumulation criterion based on competition and coupling of creep and fatigue damage that is widely used in domestic and foreign standards. The method establishes a high-temperature axial-torsion multiaxial creep-fatigue damage evaluation method applicable to different multiaxial stress states and different fatigue and creep loads. The method has a clear physical meaning and strong flexibility according to the macro failure criterion based on equivalent internal stress plastic strain energy density that has been obtained through research. The method can evaluate the damage state of target materials under uniaxial and multiaxial creep-fatigue loads in real time and accurately predict the life of the materials. The method can be used to guide the life design and damage evaluation of complex components under multiaxial loads. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0043] Figure 1 This is a flow chart of a multiaxial creep-fatigue damage evaluation method based on internal stress plastic strain energy according to an embodiment of the present invention;

[0044] Figure 2 A loading waveform diagram of a multiaxial creep-fatigue test according to an embodiment of the present invention;

[0045] Figure 3 It is a schematic diagram of the decomposition of the plastic strain energy density of creep-fatigue internal stress in an embodiment of the present invention;

[0046] Figure 4 A graph showing the relationship between the failure inelastic strain energy density and the instantaneous inelastic strain energy density dissipation rate according to an embodiment of the present invention;

[0047] Figure 5 It is a multiaxial creep-fatigue damage interaction diagram of a 316L stainless steel material at 550° C. and a P92 martensitic heat-resistant steel material at 600° C. according to a multiaxial creep-fatigue damage evaluation method based on internal stress plastic strain energy according to an embodiment of the present invention;

[0048] Figure 6 This is a graph showing the multiaxial creep-fatigue life prediction results of 316L stainless steel material at 550°C and P92 martensitic heat-resistant steel material at 600°C according to the multiaxial creep-fatigue damage evaluation method based on internal stress plastic strain energy of an embodiment of the present invention. DETAILED DESCRIPTION

[0049] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0050] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0051] The present invention proposes a multiaxial creep-fatigue life damage evaluation method based on internal stress plastic strain energy, including: performing multiple groups of different strain-controlled pure fatigue tests and creep tests on the target material at the same temperature to obtain the parameters required for multiaxial creep-fatigue damage evaluation and life prediction; performing multiple groups of different strain-controlled multiaxial creep-fatigue tests on the target material at the same temperature to obtain fatigue damage and creep damage of the target material per week; and then determining the cumulative fatigue damage and cumulative creep damage of the target material; judging the damage state of the sample at any time according to the cumulative damage of the sample and the bilinear damage accumulation criterion; and finally predicting the life of the material under multiaxial creep-fatigue load based on the obtained cumulative damage. The present invention has clear physical meaning and strong flexibility, can evaluate the damage state of the target material under uniaxial and multiaxial creep-fatigue loads in real time, and accurately predict the life of the material, and can be used to guide the life design and damage evaluation of complex components under multiaxial loads.

[0052] The technical solution of the present invention is described in detail with reference to the accompanying drawings:

[0053] like Figure 1 As shown, the multiaxial creep-fatigue damage evaluation method based on internal stress plastic strain energy of the present invention comprises the following steps:

[0054] Step S1, performing multiple sets of different strain-controlled pure fatigue tests and creep tests on the target material at the same temperature to obtain the parameters required for multi-axial creep-fatigue damage evaluation and life prediction. Specifically including:

[0055] Step S11, keeping the temperature constant, performing multiaxial low-cycle fatigue tests on the target material under different strain amplitudes ε and strain ratios λ, obtaining stress-strain data under different cycles, and obtaining material constants a and b of the target material according to the relationship between the equivalent friction stress and the equivalent back stress plastic strain energy density under the fatigue life and half-life cycles;

[0056] The method for calculating the material constants a and b of the target material is as follows: first, according to the creep-fatigue internal stress plastic strain energy density decomposition diagram (such as Figure 3 The equivalent friction stress and back stress plastic strain energy density of the target material under multiaxial low-cycle fatigue test conditions are extracted per cycle. Then, the functional relationship between fatigue life and equivalent friction stress and back stress plastic strain energy density under half-life cycles is established according to formula (1):

[0057]

[0058] In the formula, is the equivalent friction stress plastic strain energy density under half life cycles, is the equivalent back stress plastic strain energy density under half life cycles, N f is the fatigue life. The equivalent formula is:

[0059]

[0060] In the formula, is the plastic strain energy density of axial friction stress, is the plastic strain energy density of torsional friction stress, is the plastic strain energy density of the axial back stress, is the plastic strain energy density of torsional back stress.

[0061] Then, the material constants a and b of the target material are obtained through nonlinear fitting.

[0062] Step S12, a pure creep test is performed on the target material at the same temperature and different stress levels, and the creep ductility ε of the target material is determined. f, creep rupture time t R And the stress level σ is calculated to obtain the instantaneous inelastic strain energy density dissipation rate Failure inelastic strain energy density w f and failure strain energy density upper platform w f,crit (T);

[0063] First, calculate the instantaneous inelastic strain energy density dissipation rate according to formula (4) (5): Failure inelastic strain energy density w f :

[0064]

[0065] w f =σ·ln(1+ε f ) (5)

[0066] Where σ is the stress level, t R is the creep rupture time, ε f Creep ductility.

[0067] Then, the relationship between the failure inelastic strain energy density and the instantaneous inelastic strain energy density dissipation rate of the 316L stainless steel material at 550°C and the P92 martensitic heat-resistant steel material at 600°C is obtained, as shown in Figure 4 As shown, according to formula (6), the first linear regression coefficient can be obtained by nonlinear fitting and the first linear regression power index n1, and the failure strain energy density upper platform w is obtained from the relationship diagram f,crit (T).

[0068]

[0069] Step S2: at the same temperature, the target material is subjected to different equivalent strain amplitudes ε, strain ratios λ, and holding times t h , strain-controlled multiaxial creep-fatigue test in the load direction (such as Figure 2 According to the parameters obtained in steps S11-S12, the fatigue damage and creep damage of the target material per week are obtained.

[0070] For fatigue damage (d f ), the changing strain amplitude and multiaxial strain ratio are reflected in the functional expression of the equivalent back stress and equivalent friction stress plastic strain energy density, and a multiaxial fatigue damage equation with the equivalent back stress and equivalent friction stress plastic strain energy density as the core parameters is established, that is, the fatigue damage d of the target material per week is f Calculate according to formula (7):

[0071]

[0072] In the formula, is the equivalent friction stress plastic strain energy density, is the equivalent back stress plastic strain energy density, a and b are material constants.

[0073] For creep damage (d c ), which mainly occurs in the load-keeping stage, the energy dissipation method is used to describe the energy dissipation method in the form of equivalent viscous stress-plastic strain energy density, so as to establish a multiaxial creep damage equation considering the microscopic damage mechanism, that is, the creep damage d of the target material per week c Calculate according to formula (8):

[0074]

[0075] In the formula, is the equivalent viscous stress plastic strain energy density rate, is the equation for the failure strain energy density determined by the equivalent viscous stress, plastic strain energy density rate and temperature, w f,crit (T) is the failure strain energy density upper platform, t h is the load holding time. The equivalent formula of viscous stress plastic strain energy density is:

[0076]

[0077] In the formula, is the axial viscous stress plastic strain energy density, is the torsional viscous stress plastic strain energy density.

[0078] Step S3, according to the fatigue damage d per week f and creep damage per week d c Calculate the cumulative damage of the i-th week, where i is the cumulative week corresponding to the cumulative total damage.

[0079] Specifically, the cumulative fatigue damage D of the i-th week is calculated according to formula (10) (11): f , cumulative creep damage D c :

[0080]

[0081] In the formula, is the fatigue damage in the ith week, is the creep damage of the i-th cycle, where i is a natural number greater than zero.

[0082] Step S4, based on the cumulative damage of the sample and the bilinear damage accumulation criterion, draw a creep-fatigue damage interaction diagram of the target material to determine the damage state of the sample at any time. If the damage state point is outside the bilinear envelope, it is determined that the material has failed, otherwise it is not failed. Figure 5 As shown in the figure, the damage accumulation law in the figure is a simplified bilinear cumulative damage law, and its mathematical expression is:

[0083]

[0084] In the formula, and Defined as the interaction turning point in the bilinear criterion, D f represents the cumulative fatigue damage of the target material, D c represents the cumulative creep damage of the target material. In this embodiment,

[0085] Step S5, predicting the life of the material under multiaxial creep-fatigue load based on the obtained cumulative damage. The specific method is to use the simplified bilinear cumulative damage law mentioned above, and in each gradually increasing cycle, after calculating different cumulative damages using formulas (10) and (11), calculate the cumulative fatigue damage D f , cumulative creep damage D c Substitute into formula (12) to determine whether formula (12) is valid. If it is valid, it means that the sum of the cumulative fatigue damage and the cumulative creep damage is 1. The cycle i at which the sum of the cumulative fatigue damage and the cumulative creep damage is 1 is recorded, which is the predicted life of the target material.

[0086] The invention discloses a multiaxial creep-fatigue damage evaluation method based on internal stress plastic strain energy. The method is based on established fatigue and creep damage equations and adopts a bilinear damage accumulation criterion based on competition and coupling of creep and fatigue damage that is widely used in domestic and foreign standards. The method establishes a high-temperature axial-torsion multiaxial creep-fatigue damage evaluation method applicable to different multiaxial stress states and different fatigue and creep loads. The method has a clear physical meaning and strong flexibility according to the macro failure criterion based on equivalent internal stress plastic strain energy density that has been obtained through research. The method can evaluate the damage state of target materials under uniaxial and multiaxial creep-fatigue loads in real time and accurately predict the life of the materials. The method can be used to guide the life design and damage evaluation of complex components under multiaxial loads.

[0087] The multiaxial creep-fatigue life prediction method and damage assessment method of the present invention are used to verify 316L stainless steel at 550°C and P92 martensitic heat-resistant steel at 600°C.

[0088] 1. Verification of 316L stainless steel material at 550℃

[0089] First, based on the multiaxial creep-fatigue test data and the results of the fatigue test and creep-fatigue test, it can be concluded that the strain range of 316L stainless steel at 550°C is 0.3% to 0.6%, and the creep-fatigue failure cycles are 637 to 6500 cycles. The material constants a = 2163.799 and b = -0.743 are calculated by nonlinear fitting. Figure 4 , the first linear regression coefficient is calculated by least squares fitting The first linear regression power index n1 = 0.22, the failure strain energy density upper platform w f,crit (T)=200MJ / m 3 Thus, all material parameters for evaluating the multiaxial creep-fatigue damage of 316L stainless steel under multiaxial creep-fatigue conditions at 550°C were obtained.

[0090] According to the above formula (7) and formula (8), the fatigue damage per week d is calculated f , creep damage per week d c , and then calculate the cumulative damage of a cycle i according to formula (10) (11). The cumulative creep damage D of the i-th cycle is c As the horizontal axis, the cumulative fatigue damage D of the ith week f As the ordinate, a creep-fatigue damage interaction diagram is constructed. According to the bilinear cumulative damage law, that is, formula (12), the damage is evaluated in real time. The results are as follows Figure 5 As shown in the figure, it can be seen that almost all the test data points fall outside the bilinear envelope, showing the good feasibility of the damage assessment method.

[0091] The life of the material under multiaxial creep-fatigue loading is predicted based on the accumulated damage obtained. The results are as follows: Figure 6 As shown in the figure, it can be seen that the lifespan predicted by the present invention is within a 2-fold error band. Therefore, the multiaxial creep-fatigue damage evaluation method based on internal stress plastic strain energy of the present invention is universal for multiaxial creep-fatigue loads, test materials, and test temperatures.

[0092] 2. Verification of P92 martensitic heat-resistant steel material at 600°C

[0093] First, according to the multiaxial creep-fatigue test data and the results of fatigue test and creep-fatigue test, it can be concluded that the strain range of P92 martensitic heat-resistant steel at 600°C is 0.3% to 0.6%, and the creep-fatigue failure cycles are 285 to 865 cycles. The material constants a=848.306 and b=-0.938 are calculated by nonlinear fitting. Figure 4 , the first linear regression coefficient is calculated by least squares fitting The first linear regression power index n1 = 0.15, the failure strain energy density upper platform w f,crit (T)=18MJ / m 3 Thus, all material parameters for evaluating the multiaxial creep-fatigue damage of P92 martensitic heat-resistant steel under multiaxial creep-fatigue conditions at 600℃ were obtained.

[0094] According to the above formula (7) and formula (8), the fatigue damage per week d is calculated f , creep damage per week d c , and then calculate the cumulative damage of a cycle i according to formula (10) (11). The cumulative creep damage D of the i-th cycle is c As the horizontal axis, the cumulative fatigue damage D of the ith week f As the ordinate, a creep-fatigue damage interaction diagram is constructed. According to the bilinear cumulative damage law, that is, formula (12), the damage is evaluated in real time. The results are as follows Figure 5 As shown in the figure, it can be seen that almost all the test data points fall outside the bilinear envelope, showing the good feasibility of the damage assessment method.

[0095] The life of the material under multiaxial creep-fatigue loading is predicted based on the accumulated damage obtained. The results are as follows: Figure 6 As shown in the figure, it can be seen that the lifespan predicted by the present invention is within a 2-fold error band. Therefore, the multiaxial creep-fatigue damage evaluation method based on internal stress plastic strain energy of the present invention is universal for multiaxial creep-fatigue loads, test materials, and test temperatures.

[0096] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A multiaxial creep-fatigue damage evaluation method based on internal stress plastic strain energy, characterized in that: include: Obtain relevant parameters for multiaxial creep-fatigue damage evaluation and life prediction, including material constants, instantaneous inelastic strain energy density dissipation rate, failure inelastic strain energy density and failure strain energy density upper platform; Based on relevant parameters, the fatigue damage and creep damage of the target material test per week are obtained; According to the fatigue damage and creep damage under different cycles, the cumulative fatigue damage and cumulative creep damage are calculated; According to the cumulative fatigue damage, cumulative creep damage and bilinear damage accumulation criterion, a creep-fatigue damage interaction diagram is drawn to obtain the damage state of the target material, and the damage state is judged according to the creep-fatigue damage interaction diagram to obtain the failure evaluation result of the target material; The bilinear cumulative damage law is used to calculate the number of cycles at which the sum of cumulative fatigue damage and cumulative creep damage is 1, and the predicted life of the target material is obtained.

2. The method according to claim 1, characterized in that By performing several groups of different strain-controlled pure fatigue tests and pure creep tests on the target material at the same temperature, relevant parameters for obtaining multi-axial creep-fatigue damage evaluation and life prediction are calculated, wherein the adjustment parameters of the pure fatigue test include strain amplitude and strain ratio, and the adjustment parameters of the pure creep test include stress level.

3. The method according to claim 2, characterized in that The process of obtaining the material constants includes: The functional relationship between fatigue life and equivalent friction stress and back stress plastic strain energy density under half-life cycles is fitted, and the material constant and functional relationship are: in, is the equivalent friction stress plastic strain energy density under half life cycles, is the equivalent back stress plastic strain energy density under half life cycles, N f is fatigue life, a and b are different material constants; Among them, the equivalent friction stress plastic strain energy density under half-life cycles and the equivalent back stress plastic strain energy density under half-life cycles are: in, is the plastic strain energy density of axial friction stress, is the plastic strain energy density of torsional friction stress, is the plastic strain energy density of the axial back stress, is the plastic strain energy density of torsional back stress.

4. The method according to claim 2, characterized in that: The process of obtaining the failure strain energy density upper platform includes: Obtain the instantaneous inelastic strain energy density dissipation rate and failure inelastic strain energy density: w f =σ·ln(1+ε f ) Where σ is the stress level, t R is the creep rupture time, ε f is creep ductility; By performing nonlinear fitting on the instantaneous inelastic strain energy density dissipation rate and the failure inelastic strain energy density, a relationship diagram between the instantaneous inelastic strain energy density dissipation rate and the failure inelastic strain energy density is constructed, and the function expression of the relationship diagram is: in, is the first linear regression coefficient, n1 is the first linear regression power index; According to the relationship diagram, the upper platform of failure strain energy density is obtained.

5. The method according to claim 1, characterized in that At the same temperature, several groups of different strain-controlled multiaxial creep-fatigue tests are carried out on the target material, wherein the adjustment parameters of the multiaxial creep-fatigue test include equivalent strain amplitude, strain ratio, holding time and holding direction.

6. The method according to claim 1, characterized in that The process of obtaining fatigue damage includes: in, is the equivalent friction stress plastic strain energy density, is the equivalent back stress plastic strain energy density, a and b are material constants.

7. The method according to claim 1, characterized in that The process of obtaining the creep damage includes: in, is the equivalent viscous stress plastic strain energy density rate, is the equation for the failure strain energy density determined by the equivalent viscous stress, plastic strain energy density rate and temperature, w f,crit (T) is the failure strain energy density upper platform, t h To maintain the loading time.

8. The method according to claim 1, characterized in that The process of obtaining cumulative fatigue damage and cumulative creep damage includes: The fatigue damage and creep damage under different cycles are accumulated and summed separately to obtain the cumulative fatigue damage and cumulative creep damage.

9. The method according to claim 1, characterized in that: The bilinear damage accumulation criterion is: in, and is the cumulative fatigue damage value and cumulative creep damage value at the interactive turning point in the bilinear criterion, D f represents the cumulative fatigue damage of the target material, D c Represents the accumulated creep damage of the target material.

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