Failure probability evaluation method of stress intensity limit value St

Abstract

The invention relates to a failure probability evaluation method of a stress intensity limit value St, which comprises the following steps: acquiring creep fracture test data of a sample under different working conditions, including creep fracture life and a creep strain-time curve; determining a logarithmic creep fracture life standard error; determining an average stress required for the total strain to reach 1% under each working condition, a minimum stress at the beginning of a third creep stage and a minimum stress causing creep fracture, and respectively taking the average stress, the minimum stress and the minimum stress as a first criterion stress, a second criterion stress and a third criterion stress; creep life models corresponding to the first criterion stress, the second criterion stress and the third criterion stress are determined; determining creep life models which correspond to the first criterion stress, the second criterion stress and the third criterion stress and consider safety coefficients; determining probability parameters corresponding to the first, second and third criterion stresses respectively based on the creep life model with the introduced probability parameters in combination with the creep life model with each criterion considering the safety coefficient; and respectively calculating the failure probabilities of the first, second and third criterion stresses under different working conditions.

Description

Technical Field

[0001] The present invention relates to the field of high temperature structural integrity, and more specifically to a stress intensity limit S t Failure probability assessment method. Background Art

[0002] In order to improve the conversion efficiency of energy systems, many components must operate at high temperatures. For example, the operating temperature of the main pressure vessel of a fast neutron breeder reactor is around 550°C, and the operating temperature of a new generation of thermal power plant turbines is as high as 700°C. It can be foreseen that creep is an important damage mode for these components at high temperatures, and creep assessment is crucial to the structural integrity of the components and the long-term safe operation of the system.

[0003] In the prior art, the linear elastic analysis process based on the non-damage mechanics method in the ASME (American Society of Mechanical Engineers) specification is usually used to evaluate the creep of service components under high temperature. t To evaluate the creep of components, the stress intensity limit S t It is mainly related to temperature and time and is defined as the minimum of the following three criteria: (1) 100% of the average stress required to reach a total strain of 1%; (2) 80% of the minimum stress that causes the beginning of the third stage of creep; (3) 67% of the minimum stress that causes creep rupture.

[0004] However, most of the existing creep life assessment methods are deterministic assessments, which can only assess the stress strength limit S of the material. t (Also known as allowable stress), it is rare to evaluate the stress intensity limit S of the material under different working conditions. t In practical applications, the failure probability of a material is crucial to evaluating its reliability and safety. Summary of the invention

[0005] The object of the present invention is to provide a stress intensity limit S t The failure probability assessment method is used to evaluate the stress intensity limit S of the material under different working conditions. t failure probability.

[0006] Based on the above purpose, the present invention provides a stress intensity limit S t The failure probability assessment method comprises the following steps:

[0007] S100: Perform creep rupture tests on the specimens under different working conditions to obtain creep rupture test data of the specimens under different working conditions, including creep rupture life and creep strain-time curve;

[0008] S200: Determine the logarithmic creep rupture life standard error based on the creep rupture test data under various working conditions;

[0009] S300: according to the creep rupture test data under each working condition, determine the average stress required for the total strain to reach 1%, the minimum stress at the beginning of the third stage of creep, and the minimum stress causing creep rupture under the working condition, and use them as the first criterion stress, the second criterion stress, and the third criterion stress respectively;

[0010] S400: determining a creep life model corresponding to the first criterion stress, a creep life model corresponding to the second criterion stress, and a creep life model corresponding to the third criterion stress according to creep rupture test data under various working conditions and the first criterion stress, the second criterion stress, and the third criterion stress under various working conditions;

[0011] S500: determining a creep life model considering a safety factor corresponding to the first criterion stress, a creep life model considering a safety factor corresponding to the second criterion stress, and a creep life model considering a safety factor corresponding to the third criterion stress according to the creep life model corresponding to the first criterion stress, the creep life model corresponding to the second criterion stress, and the creep life model corresponding to the third criterion stress, respectively;

[0012] S600: Determine a creep life model after the probability parameters are introduced, and determine the probability parameters corresponding to the first criterion stress, the probability parameters corresponding to the second criterion stress, and the probability parameters corresponding to the third criterion stress based on the creep life model after the probability parameters are introduced and the creep life model considering the safety factor corresponding to the first criterion stress, the creep life model considering the safety factor corresponding to the second criterion stress, and the creep life model considering the safety factor corresponding to the third criterion stress;

[0013] S700: determining the failure probability of the first criterion stress, the failure probability of the second criterion stress and the failure probability of the third criterion stress under different working conditions according to the probability parameter corresponding to the first criterion stress, the probability parameter corresponding to the second criterion stress and the probability parameter corresponding to the third criterion stress respectively.

[0014] Furthermore, the creep life model corresponding to the first criterion stress is:

[0015]

[0016] Among them, S 1％ is the first criterion stress, t1 is the creep life based on the first criterion stress, a 0,1 、a 1,1 、a 2,1 and C1 are the material parameters obtained by fitting the first criterion stress and creep life of each working condition.

[0017] Furthermore, the creep life model corresponding to the second criterion stress is:

[0018]

[0019] Among them, S t3 is the second criterion stress, t2 is the creep life based on the second criterion stress, a 0,2 、a 1,2 、a 2,2 , C2 and A1 are the material parameters obtained by fitting the second criterion stress and creep life of each working condition.

[0020] Furthermore, the creep life model corresponding to the third criterion stress is:

[0021]

[0022] Among them, S r is the third criterion stress, t3 is the creep life based on the third criterion stress, a 0,3 、a 1,3 、a 2,3 , C3 are the material parameters obtained by fitting the third criterion stress and creep life of each working condition.

[0023] Furthermore, the creep life model considering the safety factor corresponding to the first criterion stress is:

[0024]

[0025] Among them, SF S1％ is the safety factor of the first criterion stress.

[0026] Furthermore, the creep life model considering the safety factor corresponding to the second criterion stress is:

[0027]

[0028] Among them, SF St3 is the safety factor of the second criterion stress.

[0029] Furthermore, the creep life model considering the safety factor corresponding to the third criterion stress is:

[0030]

[0031] Among them, SF Sr is the safety factor of the third criterion stress.

[0032] Furthermore, the probability parameter corresponding to the first criterion stress is:

[0033]

[0034] Among them, k S1％ is the probability parameter corresponding to the first criterion stress, and σ is the stress.

[0035] Furthermore, the probability parameter corresponding to the second criterion stress is:

[0036]

[0037] Among them, k St3 is the probability parameter corresponding to the second criterion stress, and σ is the stress.

[0038] Furthermore, the probability parameter corresponding to the third criterion stress is:

[0039]

[0040] Among them, k Sr is the probability parameter corresponding to the third criterion stress, and σ is the stress.

[0041] The stress intensity limit S of the present invention t The failure probability assessment method can evaluate the stress intensity limit S of the material under different working conditions. t The failure probability can be calculated, which can more accurately evaluate the reliability and safety of materials and provide more reliable evaluation results for engineering practice. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 is the stress intensity limit S according to the embodiment of the present invention t Flow chart of the failure probability assessment method;

[0043] Figure 2 is a relationship curve between various criterion stresses and creep rupture life of 316 stainless steel according to an embodiment of the present invention;

[0044] Figure 3 : failure probability curves of various criterion stresses of 316 stainless steel at different temperatures and safety factors according to an embodiment of the present invention;

[0045] Figure 4 316 stainless steel according to an embodiment of the present invention under a specific temperature and failure probability of each criterion safety factor and stress relationship curve. DETAILED DESCRIPTION

[0046] The preferred embodiments of the present invention are given below in conjunction with the accompanying drawings and described in detail.

[0047] like Figure 1 As shown, the embodiment of the present invention provides a stress intensity limit S tThe failure probability assessment method comprises the following steps:

[0048] S100: performing creep rupture tests on the sample under different working conditions to obtain creep rupture test data of the sample under different working conditions, wherein the creep rupture test data includes creep rupture life and creep strain-time curve.

[0049] The specimen can be a standard specimen specified in the ASME specification, which can be made of any material you want to evaluate to evaluate the creep performance of the material. Each working condition includes temperature and load (i.e. stress). When any one of the temperature and load is different, it belongs to a different working condition. Under the same working condition, multiple groups of parallel tests are generally carried out, that is, creep rupture tests are carried out on multiple specimens separately to make the test results more accurate. Based on the creep rupture test data, the creep rupture life of the specimen and the creep strain-time curve during the test can be obtained.

[0050] S200: Determine the logarithmic creep rupture life standard error based on the creep rupture test data under various working conditions.

[0051] By taking the logarithmic value of the creep rupture life under each working condition, the logarithmic creep rupture life under each working condition can be obtained, and then the standard error of the logarithmic creep rupture life is calculated based on each logarithmic creep rupture life.

[0052] S300: According to the creep rupture test data under each working condition, the average stress required for the total strain to reach 1%, the minimum stress at the beginning of the third stage of creep, and the minimum stress causing creep rupture under the working condition are determined, and they are used as the first criterion stress, the second criterion stress, and the third criterion stress, respectively.

[0053] According to the creep rupture life and creep strain-time curve under each working condition, the average stress required for the total strain to reach 1%, the minimum stress at the beginning of the third stage of creep, and the minimum stress causing creep rupture can be obtained. Since these three stresses correspond to the stress intensity limit S in the ASME specification, t The three criteria for determining the value can therefore be called the first criterion stress, the second criterion stress, and the third criterion stress, respectively.

[0054] S400: Determine a creep life model corresponding to the first criterion stress, a creep life model corresponding to the second criterion stress, and a creep life model corresponding to the third criterion stress according to the creep life under each working condition and the first criterion stress, the second criterion stress, and the third criterion stress under each working condition.

[0055] In some embodiments, the Larson-Miller equation may be used to describe the creep life corresponding to each criterion stress. The Larson-Miller equation is:

[0056] LMP=T×(logt+C)=a0+a1×log(σ)+a2×(log(σ)) 2 (1)

[0057] Wherein, LMP is the Larson-Miller parameter; T is the temperature; t is the creep life; σ is the stress; a0, a1, a2 and C are all material parameters.

[0058] The creep life corresponding to the first criterion stress can be described by the following formula:

[0059]

[0060] Among them, a0, a1, a2 and C are all unknown material parameters, which can be obtained by fitting the creep life and the first criterion stress under each working condition. Specifically, the creep life, the first criterion stress and the temperature under all working conditions are fitted to formula (2), and the values ​​of a0, a1, a2 and C can be obtained. Assume that the obtained value is a 0,1 、a 1,1 、a 2,1 and C1, then the creep life model corresponding to the first criterion can be expressed as:

[0061]

[0062] Among them, S S1％ is the first criterion stress, and t1 is the creep life obtained based on the first criterion stress.

[0063] The creep life corresponding to the second criterion stress can be described by the following formula:

[0064]

[0065] Among them, SEE is the standard error of the logarithmic creep rupture life. Similarly, a0, a1, a2, C and A are all unknown material parameters, which can be obtained by fitting the creep life and the second criterion stress under each working condition. Specifically, the creep life, the second criterion stress and the temperature under all working conditions are fitted to formula (4), and the values ​​of a0, a1, a2, C and A can be obtained. Assume that the obtained value is a 0,2 、a 1,2 、a 2,2 , C2 and A1, then the creep life model corresponding to the second criterion stress is:

[0066]

[0067] Among them, S St3 is the second criterion stress, and t2 is the creep life obtained based on the second criterion stress.

[0068] The creep life corresponding to the third criterion stress can be described by the following formula:

[0069]

[0070] Among them, a0, a1, a2, and C are all undetermined material parameters, which can be obtained by fitting the creep life and the third criterion stress under each working condition. Specifically, the creep life, the first criterion stress, and the temperature under all working conditions are fitted to formula (6), and the values ​​of a0, a1, a2, C, and A can be obtained. Assume that the obtained value is a 0,3 、a 1,3 、a 2,3 , C3, then the creep life model corresponding to the third criterion stress can be expressed as:

[0071]

[0072] Among them, S r is the third criterion stress, and t3 is the creep life obtained based on the third criterion stress.

[0073] The average creep life model is:

[0074]

[0075] Among them, t4 is the average creep life.

[0076] In some embodiments, a 0,3 、a 1,3 、a 2,3 , C3 can be combined with a 0,2 、a 1,2 、a 2,2 , C2 are the same, that is, a 0,3 =a 0,2 , a 1,3 =a 1,2 , a 2,3 =a 2,2 , C3=C2.

[0077] S500: Determine a creep life model considering safety factor corresponding to the first criterion stress, a creep life model considering safety factor corresponding to the second criterion stress, and a creep life model considering safety factor corresponding to the third criterion stress according to the creep life model corresponding to the first criterion stress, the creep life model corresponding to the second criterion stress, and the creep life model corresponding to the third criterion stress, respectively.

[0078] The creep life model in step S400 directly uses the first, second and third criterion stresses to evaluate the creep life without considering the safety factor. Therefore, the first, second and third criterion stresses can be multiplied by their respective safety factors and then substituted into the above formulas (3), (5) and (7) respectively. Thus, the creep life models considering the safety factor corresponding to the first, second and third criterion stresses can be obtained respectively:

[0079]

[0080]

[0081]

[0082] Among them, SF S1％ is the first criterion stress S 1％ Safety factor, SF St3 is the second criterion stress S t3 Safety factor, SF Sr is the third criterion stress S r The safety factor is a number greater than or equal to 1. For example, in the ASME specification, SF S1％ =1, SF St3 =1.25, SF Sr =1.5.

[0083] S600: Determine the creep life model after the probability parameters are introduced, and determine the probability parameters corresponding to the first criterion stress, the probability parameters corresponding to the second criterion stress, and the probability parameters corresponding to the third criterion stress based on the creep life model after the probability parameters are introduced and the creep life model considering the safety factor corresponding to the first criterion stress, the creep life model considering the safety factor corresponding to the second criterion stress, and the creep life model considering the safety factor corresponding to the third criterion stress.

[0084] In some embodiments, the creep life model after introducing the probability parameter is:

[0085]

[0086] Among them, k is the probability parameter.

[0087] Combine equation (11) and equation (8) and let t = t1, σ = S 1％ , the probability parameter k corresponding to the first criterion stress can be obtained S1％ :

[0088]

[0089] Similarly, combine formula (11) and formula (9) and let t = t2, σ = S t3, the probability parameter k corresponding to the second criterion stress can be obtained St3 :

[0090]

[0091] If a 0,3 =a 0,2 , a 1,3 =a 1,2 , a 2,3 =a 2,2 , C3=C2, then:

[0092]

[0093] Combine equation (11) and equation (10) and let t = t3, σ = S r , the probability parameter k corresponding to the third criterion stress can be obtained Sr :

[0094]

[0095] S700: determining the failure probability of the first criterion stress, the failure probability of the second criterion stress, and the failure probability of the third criterion stress according to the probability parameter corresponding to the first criterion stress, the probability parameter corresponding to the second criterion stress, and the probability parameter corresponding to the third criterion stress, respectively.

[0096] The creep life obeys the log-normal distribution, and the probability parameter is the probability density function. Under a specific temperature and safety factor, the probability parameter changes with the stress σ. By integrating it, the failure probability function can be obtained. The specific calculation formula is as follows:

[0097]

[0098] Where F(k) is the failure probability and f(t) is the probability density function.

[0099] Thus, the failure probability curves corresponding to the three criterion stresses can be obtained as a function of stress. When conducting creep assessment, the safety factors of the first criterion stress, the second criterion stress, and the third criterion stress can be determined first, and then the minimum value obtained by multiplying each criterion stress by its respective safety factor can be used as the stress intensity limit S. t For example, the safety factor of the first criterion stress can be 1, the safety factor of the second criterion stress can be 1.25, and the safety factor of the third criterion stress can be 1.5. Then the stress intensity limit S t Substituting the creep life model considering the safety factor corresponding to the criterion stress, the creep life can be obtained, and the stress intensity limit S t Substituting into the failure probability function corresponding to the criterion stress, the corresponding failure probability can be obtained, and the reliability of the creep life can be obtained based on the failure probability.

[0100] The method of the present invention is used to determine the stress strength limit S of 316 stainless steel material in nuclear power equipment. t The failure probability assessment is carried out with a service temperature of 550°C and a load range of 20MPa-169MPa.

[0101] During the evaluation process, the material parameters of stainless steel are shown in Table 1:

[0102] Table 1 Material parameters of stainless steel

[0103] After obtaining the material parameters, various creep life models can be obtained. Using these creep life models, a deterministic creep assessment of stainless steel materials can be performed. The results are as follows: Figure 2 As shown, Figure 2 Medium S ave is the average creep life curve. Figure 2 It can be seen that:

[0104] (1) When the safety factor is not considered and the stress level is low, the stress intensity of the three criteria is: S 1％ >S r >S t3 , indicating that the minimum stress that causes the beginning of the third stage of creep is the stress intensity limit S t The master control criteria;

[0105] (2) When the safety factor is not considered and the stress level is high, the average stress required for the total strain to reach 1% is the stress intensity limit S t The main control criteria are in the order of S r >S t3 >S 1％ ;

[0106] (3) Taking the safety factor into account, the minimum stress that causes creep rupture is the stress intensity limit S t However, the order of the three criteria is different at low and high stress levels. To be precise, at low stress levels, the order is S 1％ >S t3 >S r , while at high stress levels close to the upper limit (i.e. 169 MPa), the order is S t3 >S 1％ >S r .

[0107] Then, the failure probability corresponding to each criterion stress was evaluated when the temperature was 550℃, 650℃ and 750℃, and the safety factors of the first criterion stress, the second criterion stress and the third criterion stress were 1, 1.25 and 1.5, respectively, and multiple failure probability curves were obtained. The results are as follows: Figure 3 As shown. Figure 3 It can be seen that the minimum stress that causes creep rupture of 316 stainless steel at 550℃, 650℃ and 750℃ is the stress intensity limit S t The minimum stress failure probability values ​​that lead to creep rupture when the safety factor is 1.5 are 10 -8 ~10 -5 , 10 -7 ~10 -4 and 10 -6 ~10 -4 about.

[0108] The ASME code stipulates the failure probability of composite core components as follows: At 550°C, for SRC-1 and SRC-3 composite cores, the failure probability of the allowable stress is 10 -4 and 10 -2 In the above failure probability assessment of 316 stainless steel, the failure probability is 10 -8 ~10 -5 , which is 1-4 and 3-6 orders of magnitude lower than the failure probability of SRC-1 and SRC-3 components, respectively, and is very conservative. For 316 stainless steel at 550℃, if the failure probability of SRC-3 components (i.e. 10 -2 ), then the stress intensity limit S t The conservatism included can be significantly reduced. However, when the failure probability of SRC-1 components (i.e., 10 -4 ) when designing, the conservatism of 316 stainless steel can also be reduced at 550°C.

[0109] Under the conditions of temperature 550℃ and failure probability 0.1%, the curve of safety factor corresponding to each criterion stress and its change with each criterion stress can be obtained, such as Figure 4 As shown. Figure 4 It can be seen that:

[0110] The safety factors of the three criterion stresses all decrease with the increase of stress level. This means that under a given failure probability value, the safety factor at a small stress level is higher than the safety factor at a high stress level. r The safety factor is higher than S t3 This is because under the same stress level and safety factor, S r The failure probability is higher than S t3 , the same conclusion can be drawn from the k expressions of the two. Therefore, when the same failure probability is achieved, S r The corresponding safety factor is higher than S t3 .

[0111] The stress intensity limit S of the embodiment of the present invention t The failure probability assessment method can evaluate the material under the stress intensity limit S t The failure probability under certain conditions can be calculated, which can more accurately evaluate the reliability and safety of materials and provide more reliable evaluation results for engineering practice.

[0112] It should be noted that the present invention (e.g., the inventive concept, etc.) has been described in the specification of this patent document and / or illustrated in the drawings according to the exemplary embodiments; the embodiments of the present invention are presented only by way of example and are not intended to limit the scope of the present invention. The structure and / or arrangement of the elements of the inventive concept embodied in the present invention as described in the specification and / or illustrated in the drawings is merely illustrative. Although the exemplary embodiments of the present invention have been described in detail in this patent document, it is readily understood by those of ordinary skill in the art that equivalents, modifications, variations, etc. of the subject matter of the exemplary embodiments and alternative embodiments are possible and are considered to be within the scope of the present invention; all of these subject matters (e.g., modifications, variations, embodiments, combinations, equivalents, etc.) are intended to be included within the scope of the present invention. It should also be noted that various / other modifications, changes, substitutions, equivalents, alterations, omissions, etc. may be made in the configuration and / or arrangement of the exemplary embodiments (e.g., in terms of concepts, designs, structures, devices, forms, assemblies, constructions, means, functions, systems, processes / methods, steps, the order of process / method steps, operations, operating conditions, performances, materials, compositions, combinations, etc.) without departing from the scope of the present invention; all of these subjects (e.g., modifications, changes, embodiments, combinations, equivalents, etc.) are intended to be included within the scope of the present invention. The scope of the present invention is not intended to be limited to the subject matter (e.g., details, structures, functions, materials, behaviors, steps, sequences, systems, results, etc.) described in the specification and / or drawings of this patent document. Considering that the claims of this patent document will be appropriately interpreted as covering the full scope of the subject matter of the present invention (e.g., including any and all such modifications, changes, embodiments, combinations, equivalents, etc.); it should be understood that the terms used in this patent document are intended to provide a description of the subject matter of the exemplary embodiments, rather than as a limitation on the scope of the present invention.

[0113] It should also be noted that, depending on the exemplary embodiment, the present invention may include conventional technologies (such as technologies implemented and / or integrated in the exemplary embodiment, modifications, changes, combinations, equivalents), or may include any other applicable technologies (now and / or in the future) with the ability to perform the functions and processes / operations described in the specification and / or illustrated in the figures. All of these technologies (such as technologies implemented in embodiments, modifications, changes, combinations, equivalents, etc.) are considered to be within the scope of the present invention of this patent document.

Claims

1. A stress intensity limit S t The failure probability assessment method is characterized by: The following steps are involved: S100: Perform creep rupture tests on the specimens under different working conditions to obtain creep rupture test data of the specimens under different working conditions, including creep rupture life and creep strain-time curve; S200: Determine the logarithmic creep rupture life standard error based on the creep rupture test data under various working conditions; S300: according to the creep rupture test data under each working condition, determine the average stress required for the total strain to reach 1%, the minimum stress at the beginning of the third stage of creep, and the minimum stress causing creep rupture under the working condition, and use them as the first criterion stress, the second criterion stress, and the third criterion stress respectively; S400: determining a creep life model corresponding to the first criterion stress, a creep life model corresponding to the second criterion stress, and a creep life model corresponding to the third criterion stress according to creep rupture test data under various working conditions and the first criterion stress, the second criterion stress, and the third criterion stress under various working conditions; S500: determining a creep life model considering a safety factor corresponding to the first criterion stress, a creep life model considering a safety factor corresponding to the second criterion stress, and a creep life model considering a safety factor corresponding to the third criterion stress according to the creep life model corresponding to the first criterion stress, the creep life model corresponding to the second criterion stress, and the creep life model corresponding to the third criterion stress, respectively; S600: Determine a creep life model after the probability parameters are introduced, and determine the probability parameters corresponding to the first criterion stress, the probability parameters corresponding to the second criterion stress, and the probability parameters corresponding to the third criterion stress based on the creep life model after the probability parameters are introduced and the creep life model considering the safety factor corresponding to the first criterion stress, the creep life model considering the safety factor corresponding to the second criterion stress, and the creep life model considering the safety factor corresponding to the third criterion stress; S700: determining the failure probability of the first criterion stress, the failure probability of the second criterion stress and the failure probability of the third criterion stress under different working conditions according to the probability parameter corresponding to the first criterion stress, the probability parameter corresponding to the second criterion stress and the probability parameter corresponding to the third criterion stress respectively.

2. The stress intensity limit S according to claim 1 t The failure probability assessment method is characterized by: The creep life model corresponding to the first criterion stress is: Among them, S 1％ is the first criterion stress, t1 is the creep life based on the first criterion stress, a 0,1 、a 1,1 、a 2,1 and C1 are the material parameters obtained by fitting the first criterion stress and creep life of each working condition.

3. The stress intensity limit S according to claim 1 t The failure probability assessment method is characterized by: The creep life model corresponding to the second criterion stress is: Among them, S t3 is the second criterion stress, t2 is the creep life based on the second criterion stress, a 0,2 、a 1,2 、a 2,2 , C2 and A1 are the material parameters obtained by fitting the second criterion stress and creep life of each working condition.

4. The stress intensity limit S according to claim 1 t The failure probability assessment method is characterized by: The creep life model corresponding to the third criterion stress is: Among them, S r is the third criterion stress, t3 is the creep life based on the third criterion stress, a 0,3 、a 1,3 、a 2,3 , C3 are the material parameters obtained by fitting the third criterion stress and creep life of each working condition.

5. The stress intensity limit S according to claim 2 t The failure probability assessment method is characterized by: The creep life model considering the safety factor corresponding to the first criterion stress is: Among them, SF S1％ is the safety factor of the first criterion stress.

6. The stress intensity limit S according to claim 3 t The failure probability assessment method is characterized by: The creep life model considering the safety factor corresponding to the second criterion stress is: Among them, SF St3 is the safety factor of the second criterion stress.

7. The stress intensity limit S according to claim 4 t The failure probability assessment method is characterized by: The creep life model considering the safety factor corresponding to the third criterion stress is: Among them, SF Sr is the safety factor of the third criterion stress.

8. The stress intensity limit S according to claim 5 t The failure probability assessment method is characterized by: The probability parameter corresponding to the first criterion stress is: Among them, k S1％ is the probability parameter corresponding to the first criterion stress, and σ is the stress.

9. The stress intensity limit S according to claim 6 t The failure probability assessment method is characterized by: The probability parameter corresponding to the second criterion stress is: Among them, k St3 is the probability parameter corresponding to the second criterion stress, and σ is the stress.

10. The stress intensity limit S according to claim 7 t The failure probability assessment method is characterized by: The probability parameter corresponding to the third criterion stress is: Among them, k Sr is the probability parameter corresponding to the third criterion stress, and σ is the stress.

Images