Method for evaluating high-temperature high-cycle fatigue strength of material under multi-stress-ratio cyclic stress

Abstract

According to the high-temperature and high-cycle fatigue strength evaluation method of the material under the cyclic stress with the multiple stress ratios, a relational expression among the fatigue strength, the centigrade temperature, the number of fracture cycles and the stress ratios is established, and the fatigue strength of the material is evaluated through reasonable regression analysis of a limited number of fracture test data. A unified high-temperature and high-cycle fatigue strength fitting formula of two working types under a multi-temperature and multi-stress-ratio condition and a single-temperature and multi-stress-ratio condition is obtained, so that the evaluation accuracy of the fatigue strength of the material under the high-temperature and multi-stress-ratio cyclic load is improved; an accurate theoretical basis is provided for material selection, design and safety check of the component under the high-temperature and multi-stress-ratio cyclic load, and the method has important engineering significance.

Description

Technical Field

[0001] The invention belongs to the technical field of fatigue strength assessment, and in particular relates to a high temperature and high cycle fatigue strength assessment method for materials under multi-stress ratio cyclic stress. Background Art

[0002] In thermal machinery such as steam turbines, high-temperature fatigue damage is a common failure form of components. When the steam turbine is in different operating stages such as startup, peak load regulation, and shutdown, its components will not only be subjected to cyclic loads with different stress ratios, but also to different high-temperature loads, causing creep deformation and fatigue damage to the component materials at the same time, and affecting each other; since there is no obvious macroscopic deformation of the components before fatigue damage, fatigue damage is difficult to be discovered. Therefore, accurate assessment of the fatigue strength of component materials is of great significance for industrial production.

[0003] At present, although there are some models in the engineering field that can represent the fatigue strength of materials at different stress ratios, they have certain limitations. For example, the Goodman model is conservative for ductile materials, the Gerber model is inaccurate for brittle materials, and the Soderberg model is conservative for most metal materials. In addition, these models do not consider the effect of temperature on fatigue damage when evaluating fatigue strength, resulting in a large deviation between the estimated value of fatigue strength and the actual value, thereby reducing the accuracy of service component design and material verification. Summary of the invention

[0004] In view of the above shortcomings of the prior art, the purpose of the present invention is to provide a high-temperature high-cycle fatigue strength assessment method for materials under multi-stress ratio cyclic stress, which establishes the relationship between fatigue strength, Celsius temperature, stress ratio and number of fracture cycles through high-cycle fatigue test data, thereby realizing accurate assessment of fatigue strength under different service conditions.

[0005] To achieve the above-mentioned object and other related objects, the present invention provides a method for evaluating the high temperature and high cycle fatigue strength of a material under multi-stress ratio cyclic stress. The method comprises the following steps:

[0006] S1. Conduct high cycle fatigue tests on multiple specimens made of target materials under cyclic stress control at different temperatures, different stress ratios and different maximum stresses, and record the fracture test data of each fractured specimen; the fracture test data includes fatigue strength σ f , fracture cycle number N f , and the test temperature in degrees Celsius T f and stress ratio R f ;

[0007] S2. Set the fatigue-temperature-stress ratio parameter FTRP:

[0008]

[0009] Where: T K is the thermodynamic temperature, T K =T f +273.15;P F is the fatigue regression parameter. For the target material working at a single temperature, P F =0; For target materials working at multiple Celsius temperatures, their P at different stress ratios F It is determined by fitting the fracture test data of each fracture specimen at the corresponding stress ratio obtained in step S1.

[0010] S3. Establish fatigue strength σ f The relationship with the fatigue-temperature-stress ratio parameter FTRP is:

[0011]

[0012] Where: α, n are both positive integers; c j are polynomial fitting parameters;

[0013] S4, determining the working environment type of the target material, wherein the working environment type is a single Celsius temperature condition or a multi-Celsius temperature condition; calculating the fatigue-temperature-stress ratio parameter FTRP corresponding to each fracture specimen under the corresponding working environment type, and calculating the fatigue-temperature-stress ratio parameter FTRP and stress ratio R corresponding to each fracture specimen under the working environment type. f and fatigue strength σ f Input different α and n into formula (2) for regression analysis and calculation, and find the maximum goodness of fit value R 2 , select the corresponding α, n and c j ;

[0014] S5. Obtained α, n and c j Substituting into formula (2) and combining with formula (1), we can obtain the high temperature high cycle fatigue strength fitting formula under the corresponding working environment type:

[0015]

[0016] S6. Evaluate the fatigue strength corresponding to the service temperature, service stress ratio, and service cycle number according to formula (3).

[0017] Preferably, in step S2, the target material working at multiple temperatures has a P value at different stress ratios. F The method to obtain is:

[0018] S21, set the fatigue-temperature parameter FTP,

[0019] FTP = TK (P F +lgN f ) / 1000 Formula (1-1)

[0020] S22. Establish the relationship between fatigue-temperature parameter FTP and fatigue strength σ under the same stress ratio and multi-degree Celsius temperature conditions. f Relationship:

[0021]

[0022] Where: m is a positive integer, a i is the first fitting parameter;

[0023] S23, combine equation (1-1) and equation (1-2) to obtain lgN f and lgσ f The relationship is:

[0024]

[0025] S24, the Celsius temperature T corresponding to each fracture specimen that fractures under the same stress ratio f , fatigue strength σ f , fracture cycle number N f Input different m into formula (1-3) for regression analysis and calculation, and find the maximum goodness of fit value R 2 , select the corresponding P F , determine the stress ratio R f The corresponding fatigue-temperature regression parameter P F ;

[0026] S25, each fatigue-temperature regression parameter P F and the corresponding stress ratio R f Perform exponential function fitting to obtain the values ​​of fitting parameters A, B, and C, and determine the fatigue-temperature regression parameter P F and stress ratio R f The fitting formula is:

[0027]

[0028] Where A, B, and C are fitting parameters.

[0029] Preferably, α is 1 or 2, and n is 1 or 2.

[0030] Preferably, m is 1 or 2.

[0031] As described above, the high temperature and high cycle fatigue strength evaluation method of materials under multi-stress ratio cyclic stress of the present invention has the following beneficial effects:

[0032] The present invention combines stress ratio, Celsius temperature and fatigue life (i.e. fracture cycle coefficient) by performing reasonable regression analysis on high-temperature high-cycle fatigue test data under multiple stress ratios and a single Celsius temperature condition or multiple stress ratios and multiple Celsius temperature conditions, and obtains a unified high-temperature high-cycle fatigue strength fitting formula for two working types under multiple temperature and multiple stress ratio conditions and single temperature and multiple stress ratio conditions; data statistics show that the fatigue strength evaluation value calculated by the high-temperature high-cycle fatigue strength fitting formula is basically consistent with the fatigue strength test value under the same conditions (within a 2-fold dispersion band), thereby ensuring the accuracy and reliability of the fatigue strength evaluation value, providing an accurate theoretical basis for material selection, design and safety verification of components under high temperature and multiple stress ratio cyclic loads, and having important engineering significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is the fitting curve of formula (2) in Example 1 of the present invention.

[0034] Figure 2 A comparison chart of the fatigue strength evaluation value and the fatigue strength measured value in Example 1 of the present invention.

[0035] Figure 3 It is the fitting curve of formula (2) in the second embodiment of the present invention.

[0036] Figure 4 A comparison chart of the fatigue strength evaluation value and the fatigue strength measured value in the second embodiment of the present invention. DETAILED DESCRIPTION

[0037] The following is a description of the implementation of the present invention by means of specific embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification.

[0038] See also Figures 1 to 4 . It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings in this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention, so they have no substantial technical significance. Any modification of the structure, change in the proportional relationship, or adjustment of the size should still fall within the scope of the technical content disclosed by the present invention without affecting the effects and purposes that can be achieved by the present invention. At the same time, the terms such as "upper", "lower", "left", "right", "middle" and "one" quoted in this specification are only for the convenience of description, and are not used to limit the scope of the implementation of the present invention. Changes or adjustments in their relative relationships should also be regarded as the scope of the implementation of the present invention without substantially changing the technical content.

[0039] The present invention provides a method for evaluating the high temperature and high cycle fatigue strength of a material under multi-stress ratio cyclic stress, comprising the following steps:

[0040] S1. Conduct high cycle fatigue tests on multiple specimens made of target materials under cyclic stress control at different temperatures, stress ratios and maximum stresses, and record the fatigue strength σ of each fractured specimen. f , fracture cycle number N f , and the test temperature in degrees Celsius T f and stress ratio R f ; Among them, the fatigue strength σ of each fracture specimen f is the maximum stress corresponding to the fracture specimen test loading;

[0041] S2. Set the fatigue-temperature-stress ratio parameter FTRP:

[0042]

[0043] Where: T K is the thermodynamic temperature, T K =T f +273.15;P F is the fatigue regression parameter. For the target material working at a single temperature, P F =0; For target materials working at multiple Celsius temperatures, their P at different stress ratios F It is determined by fitting the fracture test data of each fracture specimen at the corresponding stress ratio obtained in step S1.

[0044] Specifically, the P values ​​of target materials working at multiple temperatures are F The method to determine is:

[0045] S21, set the fatigue-temperature parameter FTP,

[0046] FTP = T K (P F +lgN f ) / 1000 Formula (1-1)

[0047] S22. Establish the relationship between fatigue-temperature parameter FTP and fatigue strength σ under the same stress ratio and multi-degree Celsius temperature conditions. f Relationship:

[0048]

[0049] Where: m is a positive integer, a i is the first fitting parameter;

[0050] S23, combine equation (1-1) and equation (1-2) to obtain lgN f and lgσ f The relationship is:

[0051]

[0052] S24, the Celsius temperature T corresponding to each fracture specimen that fractures under the same stress ratio f , fatigue strength σ f , fracture cycle number N f Input different m into formula (1-3) for regression analysis and calculation, and find the maximum goodness of fit value R 2 , select the corresponding P F , determine the stress ratio R f The corresponding fatigue-temperature regression parameter P F ;

[0053] According to the cyclic characteristics of the fracture data, the highest order m of the equation is generally 1, 2 or 3; let the highest order m in equation (1-3) = 1, and the Celsius temperature T corresponding to each fracture specimen fractured under the same stress ratio f , fatigue strength σ f , fracture cycle number N f Input formula (1-3) to perform regression analysis and calculation, obtain the fitting equation corresponding to the stress ratio and calculate its goodness of fit value R 2 ; Then, let the highest degree of the equation in (1-3) be m = 2, and the Celsius temperature T and fatigue strength σ corresponding to each fracture specimen fractured under the same stress ratio f , fracture cycle number N f Input formula (1-3) to perform regression analysis and calculation, obtain the fitting equation corresponding to the stress ratio and calculate its goodness of fit value R 2 Next, let the highest degree of the equation in (1-3) be m = 3, and the Celsius temperature T and fatigue strength σ corresponding to each fracture specimen fractured under the same stress ratio are f , fracture cycle number N f Input formula (1-3) to perform regression analysis and calculation, obtain the fitting equation corresponding to the stress ratio and calculate its goodness of fit value R 2 ; The maximum goodness of fit value R 2 The fitting equation corresponding to each stress ratio under the condition is taken as the optimal fitting equation, so as to determine each stress ratio R f The corresponding fatigue-temperature regression parameter P F ;

[0054] S25, each fatigue-temperature regression parameter P F and the corresponding stress ratio R f Perform exponential function fitting to obtain the values ​​of fitting parameters A, B, and C, and determine the fatigue-temperature regression parameter P F and stress ratio R f The fitting formula is:

[0055]

[0056] Where A, B, and C are fitting parameters.

[0057] S3. Establish fatigue strength σ f The relationship with the fatigue-temperature-stress ratio parameter FTRP is:

[0058]

[0059] Where: α, n are both positive integers; c j are polynomial fitting parameters;

[0060] S4, determining the working environment type of the target material, wherein the working environment type is a single Celsius temperature condition or a multi-Celsius temperature condition; calculating the fatigue-temperature-stress ratio parameter FTRP corresponding to each fracture specimen under the corresponding working environment type, and calculating the fatigue-temperature-stress ratio parameter FTRP and stress ratio R corresponding to each fracture specimen under the working environment type. f and fatigue strength σ f Input different α and n into formula (2) for regression analysis and calculation, and find the maximum goodness of fit value R 2 , select the corresponding α, n and c j ;

[0061] Specifically, according to the fracture cycle characteristics, α is generally 1 or 2, and n is generally 1, 2 or 3. Let α and n in formula (2) be 1, and the fatigue-temperature-stress ratio parameter FTRP and stress ratio R corresponding to each fracture specimen are f , fatigue strength σ f Input formula (2) to perform regression analysis, obtain the corresponding fitting equation and calculate its goodness of fit value R 2 ; Let α = 1, n = 2 in equation (2), and the fatigue-temperature-stress ratio parameter FTRP and stress ratio R corresponding to each fracture specimen f , fatigue strength σ f Input formula (2) to perform regression analysis, obtain the corresponding fitting equation and calculate its goodness of fit value R 2 ; Let α = 1, n = 3 in equation (2), and the fatigue-temperature-stress ratio parameter FTRP and stress ratio R corresponding to each fracture specimen f , fatigue strength σ f Input formula (2) to perform regression analysis, obtain the corresponding fitting equation and calculate its goodness of fit value R 2 ; Let α = 2, n = 1 in equation (2), and the fatigue-temperature-stress ratio parameter FTRP and stress ratio R corresponding to each fracture specimen f , fatigue strength σ fInput formula (2) to perform regression analysis, obtain the corresponding fitting equation and calculate its goodness of fit value R 2 ; Let α = 2, n = 2 in formula (2), and the fatigue-temperature-stress ratio parameter FTRP and stress ratio R corresponding to each fracture specimen f , fatigue strength σ f Input formula (2) to perform regression analysis, obtain the corresponding fitting equation and calculate its goodness of fit value R 2 ; Let α = 2, n = 3 in formula (2), and the fatigue-temperature-stress ratio parameter FTRP and stress ratio R corresponding to each fracture specimen f , fatigue strength σ f Input formula (2) to perform regression analysis, obtain the corresponding fitting equation and calculate its goodness of fit value R 2 ; By selecting the largest goodness of fit value R 2 , to determine the optimal fitting equation, and thus obtain the specific values ​​of each parameter in formula (2) (i.e., α, n and polynomial fitting parameter c j specific value).

[0062] S5. Obtained α, n and polynomial fitting parameters c j Substituting into formula (2) and combining with formula (1), we can obtain the high temperature high cycle fatigue strength fitting formula under the corresponding working environment type:

[0063]

[0064] S6. Evaluate the fatigue strength corresponding to the service temperature, service stress ratio, and service cycle number according to formula (3).

[0065] The following are two specific embodiments of the present invention:

[0066] Embodiment 1:

[0067] The target material is FB2 alloy, and the target material is processed into a group (i.e., multiple) hourglass-shaped specimens with a specimen center diameter D=6 mm, which include two heads and a connecting shaft for connecting the two heads, and the hourglass-shaped specimen is a centrally symmetrical structure, and its cross-section at any position is circular; the specimen center diameter of the hourglass-shaped specimen refers to the diameter of the cross-section of the connecting shaft.

[0068] The first embodiment provides a method for evaluating the high temperature and high cycle fatigue strength of a material under multi-stress ratio cyclic stress, including:

[0069] S1. Test several hourglass-shaped specimens at 630℃ with different maximum stresses σ max , stress ratio R f The high cycle fatigue tests were performed at -1, -0.5, 0, 0.4, and 0.8, and the fatigue strength σ of each fractured specimen was recorded. f, fracture cycle number N f , and the test temperature in degrees Celsius T f and stress ratio R f ; Among them, the fatigue strength σ of each fracture specimen f is the maximum stress σ corresponding to the fracture specimen test loading max ;

[0070] S2. Set the fatigue-temperature-stress ratio parameter FTRP:

[0071]

[0072] Where: T K is the thermodynamic temperature, T K =T f +273.15;P F is the fatigue regression parameter. For the target material working at a single temperature, P F =0; For target materials working at multiple Celsius temperatures, their P at different stress ratios F It is determined by fitting the fracture test data of each fracture specimen at the corresponding stress ratio obtained in step S1.

[0073] Since the target material of this embodiment is tested at a single Celsius temperature and multiple stress ratios, P F =0;

[0074] S3, calculate the fatigue-temperature-stress ratio parameter FTRP corresponding to each fracture specimen, and the fatigue-temperature-stress ratio parameter FTRP and stress ratio R corresponding to each fracture specimen f , fatigue strength σ f Enter different α and n (i.e. α = 1 or 2, n = 1 or 2 or 3) into formula (2) for regression calculation to determine the goodness of fit value R 2 The highest regression equation;

[0075]

[0076] Goodness of fit value R 2 The fitting curve corresponding to the largest regression equation is as follows Figure 1 As shown, its goodness of fit value R 2 =0.998, the corresponding regression equation is

[0077] lg(σ f (1-R f ) 2 )=3.083-0.558lgFTRP-0.142lg 2 FTRP formula (3)

[0078] Substituting formula (1) into formula (3), the high temperature high cycle fatigue strength fitting formula under single Celsius temperature and multiple stress ratio conditions can be obtained.

[0079] The Celsius temperature T corresponding to each fracture specimen f , stress ratio R f , fatigue strength σ f Input the high temperature high cycle fatigue strength fitting formula to calculate the fatigue strength evaluation value of each fracture specimen; compare each fatigue strength evaluation value with the corresponding fatigue strength test value (such as Figure 2 As shown. The ordinate is the fatigue strength evaluation value, and the abscissa is the fatigue strength test value). It is found that the fatigue strength evaluation value is basically consistent with the corresponding fatigue strength test value (within the 1.2 times dispersion band), which verifies the accuracy of the method of the present invention.

[0080] Embodiment 2

[0081] The target material is FW2 alloy, and the target material is processed into a group (i.e., multiple) hourglass-shaped specimens with a specimen center diameter D=6 mm, which include two heads and a connecting shaft for connecting the two heads, and the hourglass-shaped specimen is a centrally symmetrical structure, and its cross-section at any position is circular; the specimen center diameter of the hourglass-shaped specimen refers to the diameter of the cross-section of the connecting shaft.

[0082] The second embodiment provides a method for evaluating the high temperature and high cycle fatigue strength of a material under multi-stress ratio cyclic stress, including:

[0083] S1. Test multiple hourglass-shaped specimens at different maximum stresses σ at 20℃, 530℃, 620℃, and 630℃. max , stress ratio R f The high cycle fatigue tests were performed at -1, -0.3, 0.5, and 0.9, and the fatigue strength σ of each fractured specimen was recorded. f , fracture cycle number N f , and the test temperature in degrees Celsius T f and stress ratio R f ; Among them, the fatigue strength σ of each fracture specimen f is the maximum stress σ corresponding to the fracture specimen test loading max ;

[0084] S2. Set the fatigue-temperature parameter FTP,

[0085]

[0086] Where: T K is the thermodynamic temperature, T K =T f +273.15;P F is the fatigue regression parameter; for the target material working at a single temperature, PF =0; For target materials working at multiple Celsius temperatures, their P at different stress ratios F Determined by fitting the fracture test data of each fracture specimen at the corresponding stress ratio obtained in step S1;

[0087] Since the target material of this embodiment is tested at multiple temperatures and multiple stress ratios, P F It needs to be determined by fitting. The specific determination method is as follows:

[0088] S21, set the fatigue-temperature parameter FTP,

[0089] FTP = T K (P F +lgN f ) / 1000 Formula (1-1)

[0090] S22. Establish the relationship between fatigue-temperature parameter FTP and fatigue strength σ under the same stress ratio and multi-degree Celsius temperature conditions. f Relationship:

[0091]

[0092] Where: m is a positive integer, a i is the first fitting parameter;

[0093] S23, combine equation (1-1) and equation (1-2) to obtain lgN f and lgσ f The relationship is:

[0094]

[0095] S24, the Celsius temperature T corresponding to each fracture specimen that fractures under the same stress ratio f , fatigue strength σ f , fracture cycle number N f Input different m (i.e. m = 1 or 2 or 3) in formula (1-3) for regression analysis and calculation, and find the maximum goodness of fit value R 2 , select the corresponding P F , determine the stress ratio R f The corresponding fatigue-temperature regression parameter P F ;

[0096] After calculation, the stress ratio R f When it is -1, -0.3, 0.5, 0.9, the corresponding fatigue-temperature regression parameter P Fi They are -4.38, -4.04, -2.95 and -0.293 respectively.

[0097] S25, each fatigue-temperature regression parameter P F and the corresponding stress ratio R f Perform exponential function fitting to obtain the values ​​of fitting parameters A, B, and C, and determine the fatigue-temperature regression parameter P F and stress ratio R f The fitting formula is:

[0098]

[0099] S3. Establish fatigue strength σ f The relationship with the fatigue-temperature-stress ratio parameter FTRP is:

[0100]

[0101] Where: α, n are both positive integers; c j are polynomial fitting parameters;

[0102] S4, combined with equation (1) and equation (1-4), calculate the fatigue-temperature-stress ratio parameter FTRP corresponding to each fracture specimen, and the fatigue-temperature-stress ratio parameter FTRP and stress ratio R corresponding to each fracture specimen are calculated. f , fatigue strength σ f Input different α and n (i.e. α = 1 or 2, n = 1 or 2 or 3) into formula (2) for regression analysis and calculation, and find the maximum goodness of fit value R 2 , select the corresponding α, n and c j ;

[0103] Goodness of fit value R 2 The fitting curve corresponding to the highest regression equation is as follows Figure 3 As shown, its goodness of fit value R 2 =0.967, the corresponding regression equation is

[0104] lg(σ f (1-R f ))=2.695-0.231lgFTRP-0.045lg 2 FTRP formula (3)

[0105] Substituting equation (1) into equation (1-4) again into equation (3), we can obtain the high temperature high cycle fatigue strength fitting formula under multiple Celsius temperatures and multiple stress ratios.

[0106] The Celsius temperature T corresponding to each fracture specimen f , stress ratio R f , fracture cycle number N fBy inputting the high temperature high cycle fatigue strength fitting formula, the fatigue strength evaluation value of each fracture specimen can be calculated; each fatigue strength evaluation value is compared with the corresponding fatigue strength test value (such as Figure 4 As shown. The ordinate is the fatigue strength evaluation value, and the abscissa is the fatigue strength test value). It is found that the fatigue strength evaluation value is basically consistent with the corresponding fatigue strength test value (within a 1.8-fold dispersion band), which verifies the accuracy of the method of the present invention.

[0107] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A method for evaluating the high temperature and high cycle fatigue strength of materials under multi-stress ratio cyclic stress, characterized in that: The method comprises the following steps: S1. Conduct high cycle fatigue tests on multiple samples made of target materials under cyclic stress control at different temperatures, different stress ratios and different maximum stresses, and record the fracture test data of each fractured sample; the fracture test data includes fatigue strength σ f , fracture cycle number N f , and the test temperature in degrees Celsius T f and stress ratio R f ; S2. Set the fatigue-temperature-stress ratio parameter FTRP: Where: T K is the thermodynamic temperature, T K =T f +273.15;P F is the fatigue regression parameter. For the target material working at a single temperature, P F =0; For target materials working at multiple Celsius temperatures, their P at different stress ratios F Determined by fitting the fracture test data of each fracture specimen at the corresponding stress ratio obtained in step S1; S3. Establish fatigue strength σ f The relationship with the fatigue-temperature-stress ratio parameter FTRP is: Where: α, n are both positive integers; c j are polynomial fitting parameters; S4, determining the working environment type of the target material, wherein the working environment type is a single Celsius temperature condition or a multi-Celsius temperature condition; calculating the fatigue-temperature-stress ratio parameter FTRP corresponding to each fracture specimen under the corresponding working environment type, and calculating the fatigue-temperature-stress ratio parameter FTRP and stress ratio R corresponding to each fracture specimen under the working environment type. f and fatigue strength σ f Input different α and n into formula (2) for regression analysis and calculation, and find the maximum goodness of fit value R 2 , select the corresponding α, n and c j ; S5. Obtained α, n and c j Substituting into formula (2) and combining with formula (1), we can obtain the high temperature high cycle fatigue strength fitting formula under the corresponding working environment type: S6. Evaluate the fatigue strength corresponding to the service temperature, service stress ratio, and service cycle number according to formula (3).

2. The high temperature and high cycle fatigue strength evaluation method of materials under multi-stress ratio cyclic stress according to claim 1, characterized in that: In step S2, the P of the target material working at multiple temperatures at different stress ratios is F The method to determine is: S21, set the fatigue-temperature parameter FTP, FTP = T K (P F +lgN f ) / 1000 Formula (1-1) S22. Establish the relationship between fatigue-temperature parameter FTP and fatigue strength σ under the same stress ratio and multi-degree Celsius temperature conditions. f Relationship: Where: m is a positive integer, a i is the first fitting parameter; S23, combine equation (1-1) and equation (1-2) to obtain lgN f and lgσ f The relationship is: S24, the Celsius temperature T corresponding to each fracture specimen that fractures under the same stress ratio f , fatigue strength σ f , fracture cycle number N f Input different m into formula (1-3) for regression analysis and calculation, and find the maximum goodness of fit value R 2 , select the corresponding P F , determine the stress ratio R f The corresponding fatigue-temperature regression parameter P F ; S25, each fatigue-temperature regression parameter P F and the corresponding stress ratio R f Perform exponential function fitting to obtain the values ​​of fitting parameters A, B, and C, and determine the fatigue-temperature regression parameter P F and stress ratio R f The fitting formula is: Where A, B, and C are fitting parameters.

3. The high temperature and high cycle fatigue strength evaluation method of materials under multi-stress ratio cyclic stress according to claim 1, characterized in that: α is 1 or 2, and n is 1 or 2.

4. The high temperature and high cycle fatigue strength evaluation method of materials under multi-stress ratio cyclic stress according to claim 2, characterized in that: m is 1 or 2.

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