A method and system for predicting ultra-high cycle fatigue life based on load frequency effect

Abstract

The present invention discloses a method and system for predicting ultra-high cycle fatigue life based on load frequency effect, which belongs to the technical field of material fatigue life prediction. Taking into account the influence of load frequency effect on the crack initiation life and crack propagation life of materials, correction functions related to load frequency are introduced into the life models of crack initiation and propagation, respectively, and the corrected crack initiation and propagation life models are integrated to obtain an ultra-high cycle fatigue total life model, which can accurately predict the ultra-high cycle fatigue life of materials with load frequency effect. For engineering materials whose ultra-high cycle fatigue life is not related to load frequency, the method of the present invention can fall back to the original method that does not consider the influence of frequency. The present invention has a certain universality and can predict the ultra-high cycle fatigue life of materials with similar characteristics at different frequencies, make full use of experimental data of different frequencies in existing literature to understand the ultra-high cycle fatigue characteristics of materials, and provide theoretical support for the practical engineering application and promotion of advanced materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of material fatigue life prediction, and more specifically, relates to a method and system for predicting ultra-high cycle fatigue life based on load frequency effect. Background Art

[0002] In recent years, in order to meet the demand for ultra-long service life of engineering materials, with the advancement of ultra-high cycle fatigue test technology, ultra-high cycle fatigue test methods are also constantly being updated. Ultra-high cycle fatigue life can be obtained through traditional experimental instruments, such as servo hydraulic testing machines, electromagnetic vibration tables, etc., or through the currently popular ultrasonic fatigue testing machines. The use of ultrasonic fatigue testing technology can greatly shorten the test time. For example, using a 20kHz ultrasonic fatigue testing machine, loading to 10 9 Theoretically, a cycle takes less than a day, so it is of great significance to study a method and system for predicting ultra-high cycle fatigue life.

[0003] Existing methods for predicting ultra-high cycle fatigue life are relatively few, and all have certain limitations. For example, patent CN113642192A proposes a method, device, and storage medium for predicting ultra-high cycle fatigue life. This method uses an energy-based approach to predict the ultra-high cycle fatigue life of materials. For general metal materials, this method can achieve good prediction results. However, since some materials may have different ultra-high cycle fatigue lives at different frequencies, resulting in load-frequency effects, this method cannot accurately predict fatigue life because it does not consider the impact of frequency on ultra-high cycle fatigue life. Summary of the Invention

[0004] In response to the above-mentioned defects or improvement needs of the existing technology, the present invention provides a method and system for predicting ultra-high cycle fatigue life based on load frequency effect, which is used to solve the technical problem that the existing technology cannot accurately predict the ultra-high cycle fatigue life of materials with load frequency effect.

[0005] To achieve the above objectives, in a first aspect, the present invention provides a method for predicting ultra-high cycle fatigue life based on load frequency effect, comprising the following steps:

[0006] S1. Obtain the ultra-high cycle fatigue SN curve of the material to be tested;

[0007] S2. Fitting the parameters related to the load frequency in the ultra-high cycle fatigue total life model based on the ultra-high cycle fatigue SN curve to obtain a life prediction model for the material to be tested, so as to predict the ultra-high cycle fatigue life of the material to be tested under different stress amplitudes and load frequencies;

[0008] The method for constructing the above-mentioned ultra-high cycle fatigue total life model includes:

[0009] The first correction function related to the load frequency is introduced into the stress amplitude term of the Tanaka-Mura dislocation model to obtain the crack initiation life model.

[0010] A second correction function related to the load frequency is introduced into the Paris model. After obtaining the relationship between the crack growth rate and the load frequency, the relationship is integrated from the initial length to the limit length of the crack to obtain the crack growth life model.

[0011] The crack initiation life model and the crack propagation life model are summed to obtain the ultra-high cycle fatigue total life model.

[0012] Further preferably, the above crack initiation life model is:

[0013]

[0014] Among them, N i is the crack initiation life; G is the shear modulus of the material; W s is the specific fracture energy of the crack; g1(f) is the first correction function related to the load frequency f; Δσ is the stress amplitude; k is the dislocation friction stress; ν is the Poisson's ratio; and d is the grain size.

[0015] Further preferably, a first correction function related to the load frequency is introduced into the stress amplitude term of the simplified Tanaka-Mura dislocation model, and the crack initiation life model is obtained as follows:

[0016]

[0017] Among them, N i is the crack initiation life; G is the shear modulus of the material to be tested; W s is the specific fracture energy of the crack; g1(f) is the first correction function related to the load frequency f; Δσ is the stress amplitude; is the fatigue limit of the material under stress ratio R; a0 is the initial length of the crack.

[0018] Further preferably, the first correction function related to the load frequency f is:

[0019] g1(f)=qf+1

[0020] Where q is the first parameter related to the load frequency.

[0021] Further preferably, the relationship between the crack growth rate and the load frequency is:

[0022]

[0023] Among them, da / dN pis the crack growth rate; a is the crack length; N p is the crack growth life; C and m are the coefficients of the material to be tested; g2(f) is the second correction function related to the load frequency f; ΔK is the stress intensity factor amplitude.

[0024] Further preferably, the second correction function related to the load frequency f is:

[0025] g2(f)=bf+1

[0026] Where b is the second parameter related to the load frequency.

[0027] Further preferably, the above crack growth life model is:

[0028]

[0029] Where a0 is the initial length of the crack; C and n are the coefficients of the material to be tested; a sc is the short crack length; a f is the limit length of the crack; Δσ is the stress amplitude; β1 and β2 are both geometric constants of the material to be tested.

[0030] Further preferably, the above crack growth life model is:

[0031]

[0032] Where a0 is the initial length of the crack; C and n are coefficients of the material to be tested; Δσ is the stress amplitude; β1 is the geometric constant of the material to be tested.

[0033] Further preferably, the second correction function related to the load frequency f is:

[0034] g2(f)=bf+1

[0035] Where b is the second parameter related to the load frequency.

[0036] Further preferably, the above-mentioned step S1 includes: obtaining the number of test cycles under different load frequency conditions obtained based on the ultra-high cycle fatigue test, and performing function fitting on it to obtain the ultra-high cycle fatigue SN curve of the material to be tested; wherein, the horizontal axis of the ultra-high cycle fatigue life SN curve is the fatigue life, and the vertical axis is the stress amplitude.

[0037] Further preferably, when the first correction function and the second correction function are 1, the method of the present invention can fall back to the situation where the ultra-high cycle fatigue life is independent of the load frequency, and the ultra-high cycle fatigue life prediction method is used to predict the ultra-high cycle fatigue life of materials that do not have a load frequency effect.

[0038] In a second aspect, the present invention provides a very high cycle fatigue life prediction system based on load frequency effect, comprising: a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, it executes the very high cycle fatigue life prediction method provided by the first aspect of the present invention.

[0039] In a third aspect, the present invention further provides a computer-readable storage medium, which includes a stored computer program, wherein when the computer program is run by a processor, the device where the storage medium is located is controlled to execute the ultra-high cycle fatigue life prediction method provided in the first aspect of the present invention.

[0040] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

[0041] 1. The present invention provides a method for predicting ultra-high cycle fatigue life based on load frequency effect. Taking into account the influence of load frequency effect on the crack initiation life and crack propagation life of materials, correction functions related to load frequency are introduced into the crack initiation life model and crack propagation life model respectively. The corrected crack initiation life model and crack propagation life model are combined to obtain an ultra-high cycle fatigue total life model, which can accurately predict the ultra-high cycle fatigue life of materials with load frequency effect.

[0042] 2. The ultra-high cycle fatigue life prediction method provided by the present invention has a certain universality. It can predict the ultra-high cycle fatigue life of materials with similar characteristics at different frequencies. It can reasonably utilize the experimental data of the same material at different frequencies, obtain reliable ultra-high cycle fatigue life through as few ultra-high cycle experiments as possible, link the test results with engineering practice, make full use of the experimental data of different frequencies in existing literature to understand the ultra-high cycle fatigue characteristics of materials, and provide theoretical support for the practical engineering application and promotion of advanced materials.

[0043] 3. The ultra-high cycle fatigue life prediction method provided by the present invention is aimed at engineering materials whose ultra-high cycle fatigue life is independent of the load frequency. The method of the present invention can fall back to the original method that does not consider the influence of frequency to predict the ultra-high cycle fatigue life of general engineering materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 A flow chart of the ultra-high cycle fatigue life prediction method based on load frequency effect provided by the present invention;

[0045] Figure 2 Schematic diagram of the fatigue life prediction results of high-temperature nickel-based alloy GH4169 at different load frequencies using the ultra-high cycle fatigue life prediction method provided by Ma and Zhang and the ultra-high cycle fatigue life prediction method provided by the present invention;

[0046] Figure 3 Schematic diagram of the fatigue life prediction results of high-temperature nickel-based alloy GH4169 at different load frequencies using the ultra-high cycle fatigue life prediction method provided by Kawagoishi and the ultra-high cycle fatigue life prediction method provided by the present invention;

[0047] Figure 4 Schematic diagram of the results of predicting the fatigue life of titanium alloy TC17 at different load frequencies using the ultra-high cycle fatigue life prediction method provided by Li and Wang and the ultra-high cycle fatigue life prediction method provided by the present invention. DETAILED DESCRIPTION

[0048] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0049] In order to achieve the above objectives, in the first aspect, the present invention provides a method for predicting ultra-high cycle fatigue life based on load frequency effect, such as Figure 1 As shown, the following steps are included:

[0050] S1. Obtain the ultra-high cycle fatigue SN curve of the material to be tested;

[0051] S2. Substituting the material parameters of the material to be tested into the ultra-high cycle fatigue total life model, and fitting the parameters related to the load frequency in the ultra-high cycle fatigue total life model based on the ultra-high cycle fatigue SN curve, thereby obtaining a life prediction model for the material to be tested, so as to predict the ultra-high cycle fatigue life of the material to be tested under different stress amplitudes and load frequencies;

[0052] The method for constructing the above-mentioned ultra-high cycle fatigue total life model includes:

[0053] The first correction function related to the load frequency is introduced into the stress amplitude term of the Tanaka-Mura dislocation model to obtain the crack initiation life model N i ;

[0054] The second correction function related to the load frequency is introduced into the Paris model. After obtaining the relationship between the crack growth rate and the load frequency, the relationship is integrated from the initial length to the limit length of the crack to obtain the crack growth life model N p ;

[0055] The crack growth life model and the crack initiation life model are summed to obtain the ultra-high cycle fatigue total life model N f =N p +N i .

[0056] It should be noted that in order to introduce the influence of load frequency on the ultra-high cycle fatigue life of the material, the present invention analyzes the fatigue crack initiation and crack propagation respectively, and finds that the fatigue life corresponding to the two stages is affected by the frequency.

[0057] On the one hand, starting from the Tanaka-Mura dislocation model, the present invention considers that under different loading frequency conditions, the effective external stress of the material is related to the magnitude of the loading frequency. Therefore, the Tanaka-Mura dislocation model can be modified. By introducing a first correction function related to the loading frequency into the stress amplitude term of the Tanaka-Mura dislocation model, a crack initiation life model is obtained:

[0058]

[0059] Among them, N i is the crack initiation life; G is the shear modulus of the material; W s is the specific fracture energy of the crack; g1(f) is the first correction function related to the load frequency f; Δσ is the stress amplitude; k is the dislocation friction stress; ν is the Poisson's ratio; and d is the grain size.

[0060] In order to further reduce the amount of calculation, preferably, the simplified form of the Tanaka-Mura dislocation model of Professor Wang Qingyuan et al. can be adopted (see QY Wang, C. Bathias, N. Kawagoishi, and Q. Chen, "Effect of inclusion on subsurface crack initiation and gigacycle fatigue strength," (in English), International Journal of Fatigue, vol. 24, no. 12, pp. 1269-1274, Dec 2002, Art. no. Piis 0142-1123 (02) 00037-3). The first correction function g1(f) related to the load frequency is introduced into the stress amplitude term of the simplified Tanaka-Mura dislocation model, and the crack initiation life model is obtained as follows:

[0061]

[0062] in, is the fatigue limit of the material under stress ratio R; a0 is the initial length of the crack.

[0063] On the other hand, from the perspective of the Paris formula, the present invention considers that the crack growth rate of the material is related to the load frequency. By introducing a second correction function related to the load frequency into the Paris model, the Paris model is modified to obtain the relationship between the crack growth rate and the load frequency:

[0064]

[0065] Among them, da / dN p is the crack growth rate; a is the crack length; N p is the crack growth life; C and m are the coefficients of the material to be tested; g2(f) is the second correction function related to the load frequency f; ΔK is the stress intensity factor amplitude.

[0066] The crack growth life model is obtained by integrating the relationship between crack growth rate and load frequency from the initial length to the limit length of the crack:

[0067]

[0068] Where a0 is the initial length of the crack; C and n are the coefficients of the material to be tested; a sc is the short crack length; a f is the limit length of the crack; Δσ is the stress amplitude; β1 and β2 are both geometric constants of the material to be tested.

[0069] Furthermore, considering the ultra-high cycle fatigue life of the material, in the ultra-high cycle fatigue range, the time taken for a short crack to grow into a long crack is much shorter than the time taken for an initial crack to grow into a short crack, and the length of the initial crack is much shorter than the length of the short crack. Therefore, the value of the Paris parameter n is greater than 2. Therefore, preferably, the above crack growth life model can be simplified as follows:

[0070]

[0071] Furthermore, based on the simplified crack growth life model N p and crack initiation life model N i , the ultra-high cycle fatigue total life model is obtained as:

[0072]

[0073] It should be noted that the first correction function g1(f) and the second correction function g2(f) related to the load frequency can be expressed in various forms, such as linear functions, such as g1(f) = qf + 1, g2(f) = bf + 1, or nonlinear functions, such as g1(f) = q1f 2 +b1f+c1,g2(f)=q2f 2 +b2f+c2; g1(f)=e qf , g2(f)=e bf g1(f) = ln(qf + 1), g2(f) = ln(bf + 1); As long as the parameters related to load frequency in the VHCF total life model are fitted based on the VHCF SN curve, a fitting result is sufficient. Here, q, q1, b1, and c1 are all first parameters related to load frequency, and b, q2, b2, and c2 are all second parameters related to load frequency. More precisely, the relationship between fatigue life and load frequency can be determined by analyzing the characteristics of existing fatigue test data at different frequencies.

[0074] In order to simplify the calculation, in an optional embodiment, considering that the relationship between fatigue life and load frequency is a linear relationship, the first correction function g1(f) and the second correction function g2(f) related to the load frequency f are respectively:

[0075] g1(f)=qf+1

[0076] g2(f)=bf+1

[0077] Among them, q and b are the first and second parameters related to the load frequency, respectively. Both are frequency linear correction parameters. Substituting them into the above-mentioned ultra-high cycle fatigue total life model, we get:

[0078]

[0079] In order to verify the reliability of the correction function, the fatigue life of the high-temperature nickel-based alloy GH4169 was predicted at different load frequencies using the existing ultra-high cycle fatigue life prediction method and the ultra-high cycle fatigue life prediction method provided by the present invention, according to the ultra-high cycle fatigue test data in the existing literature. Figure 2 and Figure 3The results shown are as follows, wherein Model-52.5Hz and Model-20kHz respectively represent the ultra-high cycle fatigue life prediction results of the high-temperature nickel-based alloy GH4169 when different stresses are applied at a load frequency of 52.5Hz and 20kHz using the ultra-high cycle fatigue life prediction method provided by the present invention; Ma et al. (2010)-52.5Hz represents the ultra-high cycle fatigue life prediction results of the high-temperature nickel-based alloy GH4169 when different stresses are applied at a load frequency of 52.5Hz using the ultra-high cycle fatigue life prediction method provided by Ma et al. (see XFMa, Z.Duan, HJShi, R.Murai, and E.Yanagisawa, "Fatigue and fracture behavior of nickel-based superalloy Inconel 718 up to the very high cycle regime," Journal of Zhejiang University-Science A, vol.11, no.10, pp.727-737, Oct 2010); Zhang et al. al. (2013) -20kHz indicates the very high cycle fatigue life prediction results of the high temperature nickel-based alloy GH4169 under different stresses at a loading frequency of 20kHz using the very high cycle fatigue life prediction method provided by Zhang et al. (see YY Zhang, Z. Duan, and HJ Shi, "Comparison of the very high cycle fatigue behaviors of INCONEL 718 with different loading frequencies," Science China-Physics Mechanics & Astronomy, vol. 56, no. 3, pp. 617-623, Mar 2013); Kawagoishi et al. (2008) -52.5Hz and Kawagoishi et al. (2008) -20kHz respectively indicate the very high cycle fatigue life prediction results of the high temperature nickel-based alloy GH4169 under different stresses at a loading frequency of 20kHz using the very high cycle fatigue life prediction method provided by Kawagoishi et al. (see N. Kawagoishi, E. Maemura, Q. Chen, M. Goto, and K. JNKGRMorino, A. Hen / Transactions of the Japan Society of Mechanical Engineers, Part A, "Effect of grain size on ultrasonic fatigue properties of Ni-base super alloy Inconel718," vol. 74, no. 7, pp. 1000-1005, 2008) predicts the ultra-high cycle fatigue life of high-temperature nickel-based alloy GH4169 under different stresses at loading frequencies of 52.5 Hz and 20 kHz. Figure 2 In the present invention, the tests conducted by Zhang and Ma on the high-temperature nickel-based alloy GH4169 were 20 kHz ultrasonic fatigue tests and 52.5 Hz ultrasonic fatigue tests at room temperature, respectively. For comparison, the tests conducted by this application on the high-temperature nickel-based alloy GH4169 were also 20 kHz ultrasonic fatigue tests and 52.5 Hz ultrasonic fatigue tests at room temperature. Figure 3 In the present invention, Kawagoishi et al. conducted rotary bending tests at 20 kHz and 52.5 Hz on the high-temperature nickel-based alloy GH4169. For comparison, the present invention also conducted ultrasonic fatigue tests at 20 kHz and rotary bending tests at 52.5 Hz on the high-temperature nickel-based alloy GH4169 at room temperature. Specifically, the fitting parameter values of the ultra-high cycle fatigue life prediction method provided by the present invention are shown in Table 1, and the basic mechanical properties parameters of the GH4169 high-temperature nickel-based alloy required by the present invention are shown in Table 2. In addition, the fatigue limits of the ultrasonic fatigue test and rotary bending test at 20 kHz are 575 MPa and 535 MPa, respectively, and the fatigue limits of the ultrasonic fatigue test and rotary bending test at 52.5 Hz are 515 MPa and 480 MPa, respectively. The slip band width is 0.2 μm, and the Paris formula fatigue test parameters are n=4, C=6×10 -13 , the initial crack length is 8×10 -6 μm, and finally the ultra-high cycle fatigue life of GH4169 at different frequencies of high temperature nickel-based alloys was obtained.

[0080] Table 1 Corrected parameter fitting results of high temperature nickel-based alloy GH4169 frequency

[0081] Correction parameters q b Parameter value <![CDATA[-5.21×10 -6 ]]> <![CDATA[-4.1×10 -5 ]]>

[0082] Table 2 Mechanical properties of high temperature nickel-based alloy GH4169 at room temperature

[0083]

[0084] from Figure 2 and Figure 3 The prediction results show that the revised model can predict ultra-high cycle fatigue life at different frequencies based on frequency variations. The prediction results are generally consistent with the trends of the experimentally obtained SN curves, with errors within an acceptable range. The few abnormal data are due to the dispersion of fatigue tests. In addition, although the fatigue limits exhibited by the materials at the two sets of test frequencies are different, the frequency effects exhibited by cyclic loading at different frequencies are similar, and can be corrected using the same set of fitting parameters. The results generally conform to the SN curve characteristics exhibited by the original data.

[0085] Therefore, for materials with SN curve characteristics similar to those of GH4169 alloy, a reliable ultra-high cycle fatigue life method considering the loading frequency can be obtained by the method described in the present invention.

[0086] In order to further verify the reliability of the present invention, the present invention will predict the life of other materials based on ultra-high cycle fatigue test data at different frequencies. Consider the ultra-high cycle fatigue test data of TC17 titanium alloy at different frequencies, where the TC17 fatigue test data is provided by the high-cycle axial fatigue test at 50 Hz by Li et al. (see Li Jiukai, Liu Yongjie, Wang Qingyuan et al. High-temperature ultra-high cycle fatigue experiment of TC17 titanium alloy [J]. Journal of Aerospace Power, 2014, 29 (7): 1567-1573.) and the ultra-high cycle axial fatigue test at 20 kHz by Wang Jinlong et al. (see Wang Jinlong, Gao Sibo, Yang Yuxing et al. Fatigue failure study of titanium alloy TC17 for aeroengines [J]. Journal of Harbin Engineering University, 2021, 42 (8): 1203-1208.). Substitute the corrected parameter results (see Table 3) into the ultra-high cycle fatigue total life model to obtain the corresponding ultra-high cycle fatigue life prediction value. Among them, the basic mechanical properties of TC17 titanium alloy are shown in Table 4. Its fatigue limit at 20 kHz is 615 MPa, and its fatigue limit at 50 Hz is 561 MPa, respectively. The slip band width is 0.01 μm. The fatigue test parameters corresponding to the Paris formula are n = 4, C = 8.5 × 10 -13 , the initial crack length is 1.2×10 -5 μm.

[0087] Table 3 TC17 frequency correction parameter fitting results

[0088] Correction parameters q b Parameter value <![CDATA[-4.31×10 -6 ]]> <![CDATA[5.75×10 -5 ]]>

[0089] Table 4 Basic mechanical properties of titanium alloy TC17 at room temperature

[0090]

[0091] The fatigue life prediction results of TC17 material under different load frequencies are as follows: Figure 4As shown, Model-52.5Hz and Model-20kHz respectively represent the ultra-high cycle fatigue life prediction results of TC17 material under different stresses at load frequencies of 52.5Hz and 20kHz using the ultra-high cycle fatigue life prediction method provided by the present invention; Li et al. (2014)-50Hz represents the ultra-high cycle fatigue life prediction results of TC17 material under different stresses at load frequencies of 50Hz using the ultra-high cycle fatigue life prediction method provided by Li et al. (also see Li Jiukai, Liu Yongjie, Wang Qingyuan et al. Experimental study on ultra-high cycle fatigue of TC17 titanium alloy at high temperature [J]. Journal of Aerospace Power, 2014, 29(7): 1567-1573.); Wang et al. (2014)-50Hz represents the ultra-high cycle fatigue life prediction results of TC17 material under different stresses at load frequencies of 50Hz using the ultra-high cycle fatigue life prediction method provided by Li et al. (also see Li Jiukai, Liu Yongjie, Wang Qingyuan et al. Experimental study on ultra-high cycle fatigue of TC17 titanium alloy at high temperature [J]. Journal of Aerospace Power, 2014, 29(7): 1567-1573.); al. (2021) -20kHz means the ultra-high cycle fatigue life prediction results when different stresses are applied to TC17 material at a load frequency of 20kHz using the ultra-high cycle fatigue life prediction method provided by Wang et al. (also see Wang Jinlong, Gao Sibo, Yang Yuxing, et al. Research on fatigue failure of titanium alloy TC17 for aerospace engines [J]. Journal of Harbin Engineering University, 2021, 42 (8): 1203-1208.). Figure 4 It can be seen that the prediction results of the ultra-high cycle fatigue life of TC17 material at different frequencies basically conform to the SN curve characteristics of the original data. Therefore, the present invention can predict the ultra-high cycle fatigue life at different frequencies with similar SN curve characteristics.

[0092] In a second aspect, the present invention provides a very high cycle fatigue life prediction system based on load frequency effect, comprising: a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, it executes the very high cycle fatigue life prediction method provided by the first aspect of the present invention.

[0093] The related technical solutions are the same as the ultra-high cycle fatigue life prediction method provided in the first aspect of the present invention, and will not be described in detail here.

[0094] In a third aspect, the present invention further provides a computer-readable storage medium, which includes a stored computer program, wherein when the computer program is run by a processor, the device where the storage medium is located is controlled to execute the ultra-high cycle fatigue life prediction method provided in the first aspect of the present invention.

[0095] The related technical solutions are the same as the ultra-high cycle fatigue life prediction method provided in the first aspect of the present invention, and will not be described in detail here.

[0096] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for predicting ultra-high cycle fatigue life based on load frequency effect, characterized in that: The following steps are involved: S1. Obtain the ultra-high cycle fatigue SN curve of the material to be tested; S2. Fitting the parameters related to the load frequency in the ultra-high cycle fatigue total life model based on the ultra-high cycle fatigue SN curve to obtain a life prediction model for the material to be tested, so as to predict the ultra-high cycle fatigue life of the material to be tested under different stress amplitudes and load frequencies; The method for constructing the ultra-high cycle fatigue total life model includes: The first correction function related to the load frequency is introduced into the stress amplitude term of the Tanaka-Mura dislocation model to obtain the crack initiation life model. A second correction function related to the load frequency is introduced into the Paris model. After obtaining the relationship between the crack growth rate and the load frequency, the relationship is integrated from the initial length to the limit length of the crack to obtain the crack growth life model. Summing the crack initiation life model and the crack propagation life model to obtain the ultra-high cycle fatigue total life model; The crack initiation life model N i for: or, The crack growth life model N p for: or, Where G is the shear modulus of the material to be tested; W s is the specific fracture energy of the crack; g1(f) is the first correction function related to the load frequency f; Δσ is the stress amplitude; k is the dislocation friction stress; v is the Poisson's ratio; d is the grain size; is the fatigue limit of the material under stress ratio R; a0 is the initial length of the crack; a sc is the short crack length; a f is the limit length of the crack; C and n are coefficients of the material to be tested; g2(f) is the second correction function related to the load frequency f; β1 and β2 are geometric constants of the material to be tested.

2. The ultra-high cycle fatigue life prediction method according to claim 1, characterized in that: The first correction function is: g1(f)=qf+1 Where q is the first parameter related to the load frequency.

3. The ultra-high cycle fatigue life prediction method according to claim 1, characterized in that: The relationship between the crack growth rate and the load frequency is: Among them, da / dN p is the crack growth rate; a is the crack length; N p is the crack growth life; C and m are the coefficients of the material to be tested; g2(f) is the second correction function related to the load frequency f; ΔK is the stress intensity factor amplitude.

4. The method for predicting ultra-high cycle fatigue life according to claim 1 or 3, characterized in that: The second correction function is: g2(f)=bf+1 Where b is the second parameter related to the load frequency.

5. The ultra-high cycle fatigue life prediction method according to claim 1, characterized in that: The step S1 comprises: obtaining the number of test cycles under different load frequency conditions obtained from the ultra-high cycle fatigue test, and performing function fitting on the number of test cycles to obtain an ultra-high cycle fatigue SN curve of the material to be tested; wherein the abscissa of the ultra-high cycle fatigue SN curve is fatigue life, and the ordinate is stress amplitude; When the first correction function and the second correction function are 1, the ultra-high cycle fatigue life prediction method is used to predict the ultra-high cycle fatigue life of a material that does not have a load frequency effect.

6. A very high cycle fatigue life prediction system based on load frequency effect, characterized in that: include: A memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the ultra-high cycle fatigue life prediction method according to any one of claims 1 to 5 is executed.

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