Method for predicting fatigue life and critical current degradation of superconducting material

Abstract

The invention relates to the technical field of superconducting material fatigue damage detection, and discloses a method for predicting the fatigue life and critical current degradation of a superconducting material, and the method comprises the following steps: S1, calibrating material parameters in a fatigue life model, and calculating the fatigue life of the superconducting material through the fatigue life model; s2, calculating a fatigue damage factor of the superconducting material under the fatigue load, and measuring a critical current of the superconducting material under the fatigue load; and S3, by taking the calculated fatigue damage factor as an independent variable and the measured critical current as a dependent variable, establishing a Weibull model of fatigue damage factor and critical current degradation, fitting and determining parameters of the Weibull model, and calculating a critical current degradation value of the superconducting material through the Weibull model. By establishing a non-contact fatigue life and critical current degradation prediction model, the fatigue life and critical current degradation of the superconducting material can be predicted only based on the theoretical load applied to the superconducting material, and the method has important guiding significance for optimization design of the superconducting material.

Description

Technical Field

[0001] The present invention belongs to the technical field of fatigue damage detection of superconducting materials, and particularly relates to a method for predicting the fatigue life and critical current degradation of superconducting materials. Background Art

[0002] Superconducting materials have broad application prospects in high-energy physics, nuclear magnetic resonance, energy storage devices, etc. Compared with conventional conductors, superconducting materials have the characteristics of carrying a higher critical current density, generating a higher magnetic field, and excellent mechanical strength. However, when a superconducting material is subjected to high-intensity external mechanical pressure or deformation, it will cause a decrease in its critical temperature Tc or critical magnetic field Hc. In severe cases, it will also cause an irreversible degradation of the critical current of the superconducting material, and even completely lose its superconducting properties. It can be seen that in addition to being affected by its own physical properties, the critical characteristics of superconducting materials will also change significantly under the action of external forces. Especially under the action of alternating dynamic loads, phenomena such as delamination, cracking, or peeling of superconducting materials are the fundamental reasons for the degradation of their critical current.

[0003] However, in the prior art, the phenomenon of critical current degradation caused by this defect-type failure cannot be accurately predicted, nor can the damage degree and fatigue life of superconducting materials be accurately estimated, which brings great challenges to the optimal design of superconducting materials. Summary of the Invention

[0004] In order to solve the deficiencies of the above-mentioned prior art, the present invention provides a method for predicting the fatigue life and critical current degradation of superconducting materials. By establishing a non-contact prediction model for fatigue life and critical current degradation, based only on the theoretical load applied to the superconducting material, the fatigue life and critical current degradation of the superconducting material can be predicted, which has important guiding significance for the optimal design of superconducting materials.

[0005] The technical effects to be achieved by the present invention are realized through the following technical aspects:

[0006] The present invention provides a method for predicting the fatigue life and critical current degradation of superconducting materials, including the following steps:

[0007] S1. Calibrate the material parameters in the fatigue life model, and calculate the fatigue life of the superconducting material using the fatigue life model;

[0008] S2. Calculate the fatigue damage factor of the superconducting material under the fatigue load, and measure the critical current of the superconducting material under the fatigue load;

[0009] S3. Using the calculated fatigue damage factor as the independent variable and the measured critical current as the dependent variable, establish a Weibull model for the fatigue damage factor and the degradation of the critical current, fit and determine the parameters in the Weibull model, and calculate the degradation value of the critical current of the superconducting material through the Weibull model.

[0010] As a further description of the technical solution of the present invention, the fatigue life model is:

[0011]

[0012] where N f is the fatigue life;

[0013] α is the stress exponent;

[0014] β, M0 and m are material parameters;

[0015] σ a is the applied stress amplitude;

[0016] σ m is the applied mean stress.

[0017] As a further description of the technical solution of the present invention, the method for calibrating the material parameters in the calibrated fatigue life model includes the following steps:

[0018] Measure the fatigue life of the superconducting material under different stress amplitudes under fully symmetric loading, establish the logarithmic relationship between the stress amplitude and the fatigue life under fully symmetric loading, linearly fit the relationship between the stress amplitude and the fatigue life according to the measured data, and calculate the material parameters β and the material parameter M0;

[0019] Measure the fatigue life of the superconducting material under different stress amplitudes under asymmetric loading, establish the exponential relationship between the stress amplitude and the fatigue life under asymmetric loading, fit the relationship between the stress amplitude and the fatigue life using a power function according to the measured data, and calculate the material parameter m.

[0020] As a further description of the technical solution of the present invention, the calculation formula for the stress exponent α is:

[0021]

[0022] where h is the empirical coefficient;

[0023] σ max is the maximum stress applied with the fatigue load;

[0024] σ1(σ m ) is the fatigue limit under the applied fatigue load;

[0025] σ u is the tensile strength of the superconducting material;

[0026] Let be x, <x>It means that when x ≤ 0, <x>= 0; when x > 0, <x) = x.

[0027] As a further description of the technical solution of the present invention, the fatigue limit σ1(σ m ) under the applied fatigue load is calculated by the formula:

[0028] σ1(σ m ) = σ m + σ0(1 - mσ m );

[0029] Wherein, σ0 is the fatigue limit under a fully symmetric load.

[0030] As a further description of the technical solution of the present invention, the calculation formula of the fatigue damage factor is:

[0031]

[0032] Wherein, D is the fatigue damage factor;

[0033] N is the number of cycles.

[0034] As a further description of the technical solution of the present invention, the fatigue damage factor D = 0 to 1 is used to represent the damage degree of the superconducting material.

[0035] As a further description of the technical solution of the present invention, the Weibull model is:

[0036]

[0037] Wherein, I c is the critical current after fatigue degradation;

[0038] I c0 is the critical current in the initial state;

[0039] is the critical current degradation ratio;

[0040] e is the exponential;

[0041] λ is the scale parameter of the Weibull model;

[0042] k is the shape parameter of the Weibull model.

[0043] As a further description of the technical solution of the present invention, S2 specifically calculates the fatigue damage factor of the superconducting material under different fatigue loads and numbers of cycles, and measures the critical current of the superconducting material under the different fatigue loads and numbers of cycles.

[0044] As a further description of the technical solution of the present invention, the superconducting material is a REBCO high-temperature superconducting tape.

[0045] In summary, the present invention has at least the following advantages:

[0046] The method for predicting the fatigue life and critical current degradation of superconducting materials provided by the present invention, based on the established fatigue life model of superconducting materials, combines the Weibull statistical model and experimental data to establish a non-contact model for predicting the critical current degradation of superconducting materials based on the fatigue damage factor. Based only on the theoretical load applied to the superconducting material, it is possible to predict the service life and critical current degradation of the superconducting material under different fatigue loads and numbers of cycles, which has important guiding significance for the optimal design of superconducting materials, provides important design criteria for ensuring the healthy operation of superconducting materials, and at the same time, can also provide a high-value and low-cost prediction method for studying the fatigue and failure mechanisms of superconducting materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 (a-b) are schematic diagrams of the S-N (stress amplitude - number of cycles) curve and the linear fitting straight line of the REBCO high-temperature superconducting tape under fully symmetric load in Embodiment 1 of the present invention, and schematic diagrams of the S-N (stress amplitude - number of cycles) curve and the power function fitting curve of the REBCO high-temperature superconducting tape under asymmetric load;

[0048] Figure 2 (a-d) are schematic diagrams of the calculation results of the fatigue damage factor of the REBCO high-temperature superconducting tape under different stresses (σ min = 0.2σ u , σ max = 0.9σ u ; 0.85σ u ; 0.8σ u ; 0.75σ u ) and number of cycles in Embodiment 1 of the present invention;

[0049] Figure 3 are schematic diagrams of the calculation results of the fatigue damage factor of the REBCO high-temperature superconducting tape under different stresses (σ min = 0.2σ u , σ max = 0.9σ u ; 0.85σ u ; 0.8σ u ; 0.75σ u ) and cycle ratio in Embodiment 1 of the present invention;

[0050] Figure 4 (a-b) are schematic diagrams of the REBCO high-temperature superconducting tape under different stresses (σ min = 0.2σ u , σ max = 0.9σ u ; 0.85σ u ; 0.8σ u ; 0.75σ u ) and the calculation results of the critical current degradation ratio under the number of cycles;

[0051] Figure 5 It is a schematic diagram of the Weibull model of the fatigue damage factor and critical current degradation of the REBCO high-temperature superconducting tape in Example 1 of the present invention;

[0052] Figure 6 (a-d) In Example 2 of the present invention, the REBCO high-temperature superconducting tape is under different stresses (σ min = 0.3σ u , σ max = 0.9σ u ; 0.85σ u ; 0.8σ u ; 0.75σ u ) and the schematic diagram of the calculation results of the fatigue damage factor under the number of cycles;

[0053] Figure 7 In Example 2 of the present invention, the REBCO high-temperature superconducting tape is under different stresses (σ min = 0.3σ u , σ max = 0.9σ u ; 0.85σ u ; 0.8σ u ; 0.75σ u ) and the schematic diagram of the calculation results of the fatigue damage factor under the cycle ratio;

[0054] Figure 8 (a-b) In Example 2 of the present invention, the REBCO high-temperature superconducting tape is under different stresses (σ min = 0.3σ u , σ max = 0.9σ u ; 0.85σ u ; 0.8σ u ; 0.75σ u ) and the schematic diagram of the calculation results of the critical current degradation ratio under the number of cycles;

[0055] Figure 9 It is a schematic diagram of the Weibull model of the fatigue damage factor and critical current degradation of the REBCO high-temperature superconducting tape in Example 2 of the present invention;

[0056] Figure 10 (a-b) In Example 3 of the present invention, the REBCO high-temperature superconducting tape is under different stresses (σ min = 0.4σ u , σ max = 0.9σ u ; 0.85σ u ) and the schematic diagram of the calculation results of the fatigue damage factor under the number of cycles;

[0057] Figure 11 This is the schematic diagram of the calculation results of the fatigue damage factor of the REBCO high-temperature superconducting tape in Example 3 of the present invention under different stresses (σ min = 0.4σ u , σ max = 0.9σ u ; 0.85σ u ) and the cycle ratio;

[0058] Figure 12 (a - b) This is the schematic diagram of the calculation results of the critical current degradation ratio of the REBCO high-temperature superconducting tape in Example 3 of the present invention under different stresses (σ min = 0.4σ u , σ max = 0.9σ u ; 0.85σ u ) and the number of cycles;

[0059] Figure 13 This is the Weibull model schematic diagram of the fatigue damage factor and critical current degradation of the REBCO high-temperature superconducting tape in Example 3 of the present invention. Detailed implementation manners

[0060] To facilitate the understanding of the present invention, the present invention will be described more comprehensively below in conjunction with specific embodiments and drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive.

[0061] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0062] The present invention provides a method for predicting the fatigue life and critical current degradation of superconducting materials, including the following steps:

[0063] S1. Calibrate the material parameters in the fatigue life model and calculate the fatigue life of the superconducting material using the fatigue life model;

[0064] S2. Calculate the fatigue damage factor of the superconducting material under the fatigue load and measure the critical current of the superconducting material under the fatigue load;

[0065] S3. Taking the calculated fatigue damage factor as the independent variable and the measured critical current as the dependent variable, establish a Weibull model for the fatigue damage factor and the degradation of the critical current, fit and determine the parameters in the Weibull model, and calculate the degradation value of the critical current of the superconducting material through the Weibull model.

[0066] It should be noted that in the method for predicting the fatigue life and critical current degradation of superconducting materials of the present invention, the fatigue load mentioned is an alternating load.

[0067] The method for predicting the fatigue life and critical current degradation of superconducting materials of the present invention is based on the established fatigue life model of superconducting materials, combines the Weibull statistical model, and combines experimental data to establish a non-contact model for predicting the critical current degradation of superconducting materials based on the fatigue damage factor. Based only on the theoretical load applied to the superconducting material, it is possible to predict the service life and critical current degradation of the superconducting material under different fatigue loads and numbers. It not only retains the interpretability of the physical model but also enhances the ability to describe the dispersion of experimental data. By using the fatigue damage factor as an intermediate variable, the cross-scale correlation between fatigue life prediction and critical current degradation prediction is achieved, avoiding the difficulty of directly establishing complex multi-field coupling equations. In addition, the method for predicting the fatigue life and critical current degradation of superconducting materials of the present invention has important guiding significance for the optimal design of superconducting materials, provides important design criteria for ensuring the healthy operation of superconducting materials, and at the same time, can also provide a high-value and low-cost prediction method for studying the fatigue and failure mechanisms of superconducting materials.

[0068] In some embodiments, the fatigue life model is:

[0069]

[0070] where N f is the fatigue life;

[0071] α is the stress exponent, which is determined by the applied stress amplitude and the recorded fatigue limit;

[0072] β, M0 and m are material parameters;

[0073] σ a is the applied stress amplitude;

[0074] σ m is the applied mean stress.

[0075] In some embodiments, the method for calibrating the material parameters in the fatigue life model includes the following steps:

[0076] Measure the fatigue life of the superconducting material under different stress amplitudes under a fully symmetric load, establish the logarithmic relationship between the stress amplitude and the fatigue life under a fully symmetric load, linearly fit the relationship between the stress amplitude and the fatigue life according to the measured data, and calculate the material parameter β and the material parameter M0. Among them, the material parameter β is determined by the slope of the linear fitting line, and the material parameter M0 is determined by the intercept of the linear fitting line;

[0077] Measure the fatigue life of the superconducting material under different stress amplitudes under an asymmetric load, establish the exponential relationship between the stress amplitude and the fatigue life under an asymmetric load, fit the relationship between the stress amplitude and the fatigue life using a power function according to the measured data, and calculate the material parameter m. The material parameter m is determined by the power function fitting curve equation, that is, substituting the power function fitting curve equation into the fatigue life model can calculate the material parameter m.

[0078] Furthermore, the calculation formula for the stress exponent α is:

[0079]

[0080] where h is an empirical coefficient, usually set to 0.0801;

[0081] σ max is the maximum stress applied by the fatigue load;

[0082] σ1(σ m ) is the fatigue limit under the applied fatigue load;

[0083] σ u is the tensile strength of the superconducting material;

[0084] It should be noted that let be x, <x>It means that when x ≤ 0, <x>= 0; when x > 0, <x>= x, that is, equivalent to, <x>≥0.

[0085] Furthermore, the calculation formula for the fatigue limit σ1(σ m ) under the application of fatigue load is:

[0086] σ1(σ m ) = σ m + σ0(1 - mσ m );

[0087] Wherein, σ0 is the fatigue limit under a completely symmetric load.

[0088] In some embodiments, the calculation formula for the fatigue damage factor is:

[0089]

[0090] Wherein, D is the fatigue damage factor;

[0091] N is the number of cycles.

[0092] It should be noted that the fatigue damage factor D = 0 to 1, which is used to represent the damage degree of the superconducting material.

[0093] Specifically, the Weibull model is:

[0094]

[0095] Wherein, I c is the critical current after fatigue degradation;

[0096] I c0 is the critical current in the initial state;

[0097] is the critical current degradation ratio;

[0098] e is the exponential;

[0099] λ is the scale parameter of the Weibull model, which reflects the critical damage strain threshold of the superconducting material, that is, the critical strain value corresponding to the irreversible damage of the superconducting material;

[0100] k is the shape parameter of the Weibull model, which reflects the uniformity of the internal defect distribution of the superconducting material;

[0101] The λ parameter and the k parameter are determined by the values obtained from test fitting and can be used as general model parameters for evaluating the critical current degradation of superconducting materials. Specifically, the λ parameter and the k parameter can be obtained by fitting the fatigue damage factor and the critical current measurement data. According to the calculation method of the fatigue damage factor, the fatigue damage data of the superconducting material are calculated, and then the corresponding critical current value of the superconducting material is measured. Taking the fatigue damage factor as the abscissa and the critical current degradation ratio as the ordinate, and using the Weibull model for fitting, the specific values of the λ parameter and the k parameter can be obtained.

[0102] In some embodiments, S2 is specifically to calculate the fatigue damage factors of the superconducting material under different fatigue loads and numbers of cycles, and measure the critical current of the superconducting material under different fatigue loads and numbers of cycles. At the same time, mark the critical current in the initial state, and record the critical current degradation ratios under different fatigue loads and numbers of cycles respectively.

[0103] It should be noted that the method for predicting the fatigue life and critical current degradation of superconducting materials according to the present invention is particularly applicable to high-temperature superconducting materials. As one of the embodiments, the superconducting material is a REBCO high-temperature superconducting tape.

[0104] Example 1

[0105] This example provides a method for predicting the fatigue life and critical current degradation of superconducting materials, including the following steps:

[0106] S1. Measure the fatigue life of the REBCO high-temperature superconducting tape under different stress amplitudes under fully symmetric loading, establish the logarithmic relationship between the stress amplitude and the fatigue life under fully symmetric loading, linearly fit the relationship between the stress amplitude and the fatigue life according to the measurement data, and calculate the material parameter β, the material parameter M0, and the stress exponent α. The material parameter β is determined by the slope of the linearly fitted straight line, the material parameter M0 is determined by the intercept of the linearly fitted straight line, and the stress exponent α is determined by the applied stress amplitude (yield strength) and the recorded fatigue limit;

[0107] Considering that the REBCO high-temperature superconducting tape belongs to a thin-film material and cannot directly perform a fully symmetric fatigue test, it is necessary to perform an equivalent conversion on the stress amplitude applied to the REBCO high-temperature superconducting tape. The conversion equation is:

[0108]

[0109] where σ is the actual stress applied to the REBCO high-temperature superconducting tape;

[0110] The schematic diagram of the S-N (stress amplitude - number of cycles) curve and the linearly fitted straight line of the REBCO high-temperature superconducting tape under fully symmetric loading is as Figure 1 (a) shown;

[0111] Measure the fatigue life of REBCO high-temperature superconducting tapes under different stress amplitudes under asymmetric loads, establish an exponential relationship between the stress amplitude and the fatigue life under asymmetric loads, fit the relationship between the stress amplitude and the fatigue life using a power function according to the measured data, and calculate the material parameter m. The material parameter m is determined by the power function fitting curve equation. The schematic diagram of the S-N (stress amplitude - number of cycles) curve and the power function fitting curve of the REBCO high-temperature superconducting tape under asymmetric loads is as Figure 1 (b) shown, and the specific values of the relevant parameters calibrated are shown in Table 1;

[0112] Table 1

[0113]

[0114] Calculate the fatigue life of the REBCO high-temperature superconducting tape using the fatigue life model. The fatigue life model is:

[0115]

[0116] Among them, the calculation formula for the stress exponent α is:

[0117]

[0118] The fatigue limit σ1 (σ m ) under the applied fatigue load is calculated as:

[0119] σ1 (σ m ) = σ m + σ0(1 - mσ m );

[0120] By substituting the theoretical load (i.e., each stress parameter) applied to the REBCO high-temperature superconducting tape into the fatigue life model, the fatigue life of the REBCO high-temperature superconducting tape can be predicted.

[0121] S2. Calculate the fatigue damage factor of the REBCO high-temperature superconducting tape under different stresses and numbers of cycles. The calculation formula for the fatigue damage factor is:

[0122]

[0123] The calculation results of the fatigue damage factor of the REBCO high-temperature superconducting tape under different stresses (σ min = 0.2σ u , σ max = 0.9σ u ; 0.85σ u ; 0.8σ u ; 0.75σ u ) and numbers of cycles are as Figure 2 As shown, the fatigue damage factor calculation results of REBCO high-temperature superconducting tapes under different stresses (σ min = 0.2σ u , σ max = 0.9σ u ; 0.85σ u ; 0.8σ u ; 0.75σ u ) and cycle ratios are as shown in Figure 3 ;

[0124] Measure the critical current of REBCO high-temperature superconducting tapes under different stresses (σ min = 0.2σ u , σ max = 0.9σ u ; 0.85σ u ; 0.8σ u ; 0.75σ u ) and number of cycles. At the same time, mark the critical current in the initial state, record the critical current degradation ratios under different fatigue loads and numbers of cycles respectively. The calculation results of the critical current degradation ratios of REBCO high-temperature superconducting tapes under different stresses (σ min = 0.2σ u , σ max = 0.9σ u ; 0.85σ u ; 0.8σ u ; 0.75σ u ) and number of cycles are as shown in Figure 4 ;

[0125] S3. Taking the calculated fatigue damage factor as the independent variable and the measured critical current as the dependent variable, establish a Weibull model for the fatigue damage factor and critical current degradation, and fit to determine the parameters in the Weibull model. The Weibull model equation is:

[0126]

[0127] By fitting and determining the λ parameter and k parameter in the Weibull model, it is obtained that the λ parameter and k parameter are -0.5 and 2.13 respectively. The Weibull model for the fatigue damage factor and critical current degradation of REBCO high-temperature superconducting tapes is as shown in Figure 5 ;

[0128] By substituting the fatigue damage factor into the Weibull model, the nominal critical current degradation ratio can be deduced, thereby predicting the critical current degradation of REBCO high-temperature superconducting tapes.

[0129] Example 2

[0130] This embodiment provides a method for predicting the fatigue life and critical current degradation of superconducting materials, including the following steps:

[0131] S1. The same as in Embodiment 1, refer to Embodiment 1;

[0132] S2. Calculate the fatigue damage factor of REBCO high-temperature superconducting tapes under different stresses and numbers of cycles. The calculation formula for the fatigue damage factor is:

[0133]

[0134] The calculation results of the fatigue damage factor of REBCO high-temperature superconducting tapes under different stresses (σ min = 0.3σ u , σ max = 0.9σ u ; 0.85σ u ; 0.8σ u ; 0.75σ u ) and numbers of cycles are as shown in Figure 6 The calculation results of the fatigue damage factor of REBCO high-temperature superconducting tapes under different stresses (σ min = 0.3σ u , σ max = 0.9σ u ; 0.85σ u ; 0.8σ u ; 0.75σ u ) and cycle ratios are as shown in Figure 7 ;

[0135] Measure the critical current of REBCO high-temperature superconducting tapes under different stresses (σ min = 0.3σ u , σ max = 0.9σ u ; 0.85σ u ; 0.8σ u ; 0.75σ u ) and numbers of cycles. At the same time, mark the critical current in the initial state, and record the critical current degradation ratios under different fatigue loads and numbers of cycles respectively. The calculation results of the critical current degradation ratios of REBCO high-temperature superconducting tapes under different stresses (σ min = 0.3σ u , σ max = 0.9σ u ; 0.85σ u ; 0.8σ u ; 0.75σ u ) and numbers of cycles are as shown in Figure 8 ;

[0136] S3. Taking the calculated fatigue damage factor as the independent variable and the measured critical current as the dependent variable, establish a Weibull model for the fatigue damage factor and the degradation of the critical current, and fit to determine the parameters in the Weibull model. The Weibull model equation is:

[0137]

[0138] By fitting and determining the λ parameter and the k parameter in the Weibull model, it is obtained that the λ parameter and the k parameter are -0.5 and 2.13 respectively. The Weibull model for the fatigue damage factor and the degradation of the critical current of the REBCO high-temperature superconducting tape is as Figure 9 shown;

[0139] By substituting the fatigue damage factor into the Weibull model, the nominal critical current degradation ratio can be inferred, thereby predicting the degradation of the critical current of the REBCO high-temperature superconducting tape.

[0140] Example 3

[0141] This example provides a method for predicting the fatigue life and critical current degradation of superconducting materials, including the following steps:

[0142] S1. The same as in Example 1, refer to Example 1;

[0143] S2. Calculate the fatigue damage factors of the REBCO high-temperature superconducting tape under different stresses and numbers of cycles. The calculation formula for the fatigue damage factor is:

[0144]

[0145] The calculation results of the fatigue damage factors of the REBCO high-temperature superconducting tape under different stresses (σ min = 0.4σ u , σ max = 0.9σ u ; 0.85σ u ) and numbers of cycles are as Figure 10 shown. The calculation results of the fatigue damage factors of the REBCO high-temperature superconducting tape under different stresses (σ min = 0.4σ u , σ max = 0.9σ u ; 0.85σ u ) and cycle ratios are as Figure 11 shown;

[0146] Measure the REBCO high-temperature superconducting tape under different stresses (σ min = 0.4σ u , σ max = 0.9σ u ; 0.85σ u ) and the critical current under different fatigue loads and cycle numbers. At the same time, mark the critical current in the initial state, and record the critical current degradation ratio under different fatigue loads and numbers respectively. For REBCO high-temperature superconducting tapes under different stresses (σ min = 0.4σ u , σ max = 0.9σ u ; 0.85σ u ) and the calculation results of the critical current degradation ratio under different cycle numbers are as Figure 12 shown.

[0147] S3. Taking the calculated fatigue damage factor as the independent variable and the measured critical current as the dependent variable, establish a Weibull model for the fatigue damage factor and critical current degradation, and fit to determine the parameters in the Weibull model. The Weibull model equation is:

[0148]

[0149] By fitting and determining the λ parameter and k parameter in the Weibull model, it is obtained that the λ parameter and k parameter are -0.5 and 2.13 respectively. The Weibull model for the fatigue damage factor and critical current degradation of REBCO high-temperature superconducting tapes is as Figure 13 shown;

[0150] By substituting the fatigue damage factor into the Weibull model, the nominal critical current degradation ratio can be inferred, thereby predicting the critical current degradation of REBCO high-temperature superconducting tapes.

[0151] The above content is only an example and description of the structure of the present invention. Its description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the present invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can be made, and these obvious replacement forms all belong to the protection scope of the present invention.< / x> < / x> < / x> < / x> < / x> < / x>

Claims

1. A method for predicting the fatigue life and critical current degradation of superconducting materials, characterized in that, It includes the following steps: S1. Calibrate the material parameters in the fatigue life model and calculate the fatigue life of the superconducting material using the fatigue life model; S2. Calculate the fatigue damage factor of the superconducting material under the fatigue load and measure the critical current of the superconducting material under the fatigue load; S3. Taking the calculated fatigue damage factor as the independent variable and the measured critical current as the dependent variable, establish a Weibull model for the degradation of the fatigue damage factor and the critical current, fit and determine the parameters in the Weibull model, and calculate the critical current degradation value of the superconducting material through the Weibull model.

2. The method for predicting the fatigue life and critical current degradation of a superconducting material according to claim 1, characterized in that, The fatigue life model is: where N f is the fatigue life; α is the stress exponent; β, M0 and m are material parameters; σ a is the applied stress amplitude; σ m is the applied mean stress.

3. The method for predicting the fatigue life and critical current degradation of a superconducting material according to claim 2, wherein The method for calibrating the material parameters in the fatigue life model includes the following steps: Measure the fatigue life of the superconducting material under different stress amplitudes under a fully symmetric load, establish the logarithmic relationship between the stress amplitude and the fatigue life under the fully symmetric load, linearly fit the relationship between the stress amplitude and the fatigue life according to the measured data, and calculate the material parameter β and the material parameter M0; Measure the fatigue life of the superconducting material under different stress amplitudes under an asymmetric load, establish the exponential relationship between the stress amplitude and the fatigue life under the asymmetric load, fit the relationship between the stress amplitude and the fatigue life using a power function according to the measured data, and calculate the material parameter m.

4. The method for predicting the fatigue life and critical current degradation of a superconducting material according to claim 2, wherein The calculation formula for the stress exponent ɑ is: where h is an empirical coefficient; σ max is the maximum stress for applying the fatigue load; σ1(σ m ) is the fatigue limit under the applied fatigue load; σ u is the tensile strength of the superconducting material; Let be x, <x>It means that when x ≤ 0, <x>= 0; when x > 0, <x> ＝x。< / x> < / x> < / x> 5. The method for predicting the fatigue life and critical current degradation of a superconducting material according to claim 4, wherein The fatigue limit σ1(σ m ) under the applied fatigue load is calculated by the formula: σ1(σ m ) = σ m + σ0(1 - mσ m ); where σ0 is the fatigue limit under a fully symmetric load.

6. The method for predicting the fatigue life and critical current degradation of a superconducting material according to claim 2, characterized in that, The calculation formula for the fatigue damage factor is: where D is the fatigue damage factor; N is the number of cycles.

7. The method for predicting the fatigue life and critical current degradation of a superconducting material according to claim 6, wherein The fatigue damage factor D = 0 to 1, which is used to represent the damage degree of the superconducting material.

8. The method for predicting the fatigue life and critical current degradation of a superconducting material according to claim 7, characterized in that, The Weibull model is: Among them, I c is the critical current after fatigue degradation; I c0 is the critical current in the initial state; is the critical current degradation ratio; e is the exponent; λ is the scale parameter of the Weibull model; k is the shape parameter of the Weibull model.

9. The method for predicting the fatigue life and critical current degradation of a superconducting material according to claim 1, characterized in that, Specifically, S2 is to calculate the fatigue damage factor of the superconducting material under different fatigue loads and numbers of cycles, and measure the critical current of the superconducting material under the different fatigue loads and numbers of cycles.

10. The method for predicting the fatigue life and critical current degradation of a superconducting material according to claim 1, characterized in that, The superconducting material is REBCO high-temperature superconducting tape.

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