A measurement method for estimating fatigue crack initiation in metallic materials using frequency attenuation.

Abstract

This invention provides a measurement method for estimating fatigue crack initiation in metallic materials using frequency attenuation. Using a high-frequency fatigue testing machine under constant load amplitude control mode, the test frequency at which the system consisting of the high-frequency fatigue testing machine and the specimen resonates is determined. During the fatigue crack initiation process, the test frequency attenuates. By establishing a pre-defined relationship between the fatigue crack initiation scale and the test frequency attenuation, the initiation scale and initiation life of the fatigue crack are determined by detecting the attenuation of the test frequency during the test. This experimental measurement method obtains the crack initiation life at a specific initiation scale, solving the problem that while high-frequency fatigue testing machines are widely used in laboratories, there are no reports of fatigue crack initiation measurement methods based on constant load amplitude control mode for such machines. Fatigue crack initiation life accounts for a significant portion of the total fatigue life and is crucial for the safety and reliability assessment and full-life verification of engineering structures.

Description

Technical Field

[0001] This invention relates to the field of fatigue performance testing technology, and more specifically, to a measurement method for estimating the initiation of fatigue cracks in metallic materials using frequency attenuation. Background Technology

[0002] The fatigue life of metallic materials typically includes crack initiation life, crack propagation life, and fracture life. Fracture life is generally very short and often negligible. Experts and scholars have conducted extensive research on fatigue crack propagation life, and various test standards have been developed for reference, such as GB / T 6398-2017 "Metallic Materials Fatigue Testing - Fatigue Crack Propagation Method" and ASTM E647-2015 "Standard Test Method for Measuring Fatigue Crack Propagation Rate." These standards not only provide the fatigue crack propagation rate equation for metallic materials but also the corresponding fatigue life when the fatigue crack reaches a certain length. Studies have shown that, regardless of high-cycle or low-cycle fatigue, the fatigue crack initiation life of metallic materials, including stainless steel, nickel-based alloys, aluminum alloys, and copper alloys, accounts for 40% to 90% or even higher of the total fatigue life, highlighting the significance of studying fatigue crack initiation life.

[0003] Regarding fatigue crack initiation life, although some experts and scholars have proposed various theoretical prediction models, the inherent differences in materials lead to low accuracy of general theoretical prediction models, making them difficult to apply in engineering. Some scholars have also invented experimental measurement methods to indirectly obtain fatigue crack initiation, including methods under constant strain amplitude and constant displacement amplitude control conditions. These methods involve pre-studying and calibrating the relationship between stress and load attenuation and crack initiation scale, allowing the crack initiation scale to be obtained during the test by monitoring stress and load attenuation. The corresponding fatigue life is then the crack initiation life. However, this method has high testing costs and low engineering application value. To save testing costs and accelerate fatigue testing, high-frequency fatigue testing machines are currently widely used in laboratories. These machines typically operate under constant load amplitude control, and no reports have been found on experimental measurement methods for fatigue crack initiation based on this constant load amplitude control mode. Summary of the Invention

[0004] In view of this, the present invention aims to propose a method for measuring the initiation of fatigue cracks in metallic materials. This addresses the problems in existing technologies where the inherent differences in materials lead to low accuracy of general theoretical prediction models, making them difficult to apply in engineering; high sample testing costs result in low engineering application value; and existing technologies do not describe methods for calculating fatigue crack initiation under constant load amplitude using high-frequency fatigue testing machines.

[0005] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0006] A measurement method for estimating fatigue crack initiation in metallic materials using frequency attenuation is proposed. Using a high-frequency fatigue testing machine, under constant load amplitude control mode, the test frequency at which the high-frequency fatigue testing machine and the sample system resonate is determined. During the fatigue crack initiation process, the test frequency attenuates. By establishing a pre-defined relationship between the fatigue crack initiation scale and the test frequency attenuation, the fatigue crack initiation scale and initiation life are determined by detecting the attenuation of the test frequency during the test.

[0007] This measurement method can obtain the initiation life of a crack at a certain initiation scale, solving the problem that although high-frequency fatigue testing machines are widely used in laboratories, there are no reports on fatigue crack initiation test measurement methods based on constant load amplitude control mode. Fatigue crack initiation life accounts for a high proportion of the entire fatigue life and is of great significance in the safety and reliability assessment and full life verification of engineering structures.

[0008] Furthermore, the specific steps include the following:

[0009] Step 1: Determine the constant load amplitude of the specimen. Based on the yield strength and tensile strength values ​​of the test material, set a constant load amplitude as the test control parameter.

[0010] Step 2: Determine the load ratio based on the actual needs of the project;

[0011] Step 3: Determine the relationship between fatigue crack initiation scale and test frequency attenuation;

[0012] Step 4: Set data acquisition parameters; the data acquisition parameters include the number of periodic acquisition cycles and the test frequency;

[0013] Step 5: Formal test; Install the specimen onto the high-frequency fatigue testing machine, select the constant load amplitude in Step 1 and the load ratio in Step 2, start the testing machine, and begin the test until the specimen breaks, then end the test.

[0014] Step Six: Determine the crack initiation scale and initiation life; Based on the collected cycle number and test frequency data, fit the relationship between the cycle number and the test frequency attenuation, and then combine with Step Three to determine the crack initiation scale under a certain test frequency attenuation, as well as the fatigue life corresponding to the crack initiation scale, i.e., fatigue crack initiation life.

[0015] Furthermore, step three includes the following experimental equation: the test frequency at which the system consisting of the high-frequency fatigue testing machine and the test specimen resonates is calculated using the following formula (1):

[0016] (1)

[0017] In the formula, f—Test frequency, Hz; k —Stiffness of the system consisting of the high-frequency fatigue testing machine and the specimen, N / m; m —Mass acting on the sample, kg;

[0018] Based on the principles of fracture mechanics theory and compliance technology for measuring crack size, the normalized crack size is calculated using the following formula (2):

[0019] (2)

[0020] In the formula, a / W is the normalized crack size. a Where W is the crack size and W is the sample width. C 0、 C 1. C 2. C 3. C 4. C 5 is the compliance coefficient. U x The dimensionless compliance is related to the elastic modulus of the test material, the size of the specimen, and the applied load. The relationship is expressed as follows: (3)

[0021] (3)

[0022] In the formula, B, V For sample size, E The elastic modulus of the test material, P For external load, k 1 represents the system compliance of the high-frequency fatigue testing machine and the specimen. k 1 ＊k= 1;

[0023] According to formulas (2) and (3), the crack initiation scale can be obtained. a1 Among them, the scale of crack initiation a1 and system stiffness k The relationship is expressed as follows (4):

[0024] (4)

[0025] In the formula, F 1 represents the first function symbol;

[0026] According to formulas (4) and (1), the crack initiation scale can be obtained. a1 Among them, the scale of crack initiation a1 and test frequency f The relationship is calculated as follows (5):

[0027] (5)

[0028] In the formula, F 2 represents the symbol for the second function.

[0029] Furthermore, the relationship between the fatigue crack initiation scale of the specimen and the attenuation of the test frequency is as follows (6):

[0030] a1 = F 3(△ f (6)

[0031] In the formula, a1 The scale for crack initiation. F 3 represents the third function symbol, △ f This represents the attenuation of the test frequency.

[0032] Furthermore, in step three, the specific steps for calibrating the fatigue crack initiation scale and the test frequency attenuation are as follows:

[0033] S1: Select a metallic material with uniform composition, microstructure and properties, and process it into a set of samples;

[0034] S2: After the samples are processed, they are numbered as 0#, 1#, 2#, 3#, 4#, 5#, ... n#. Sample 0# is left untreated, while samples 1#, 2#, 3#, 4#, and 5#... n# are further artificially pre-introduced with cracks of different sizes. a 1. a 2. a 3. a 4 and a 5... a n The scale relationship is as follows a 1 < a 2< a 3< a 4< a 5...< a n ;

[0035] S3: After cracks of different scales are completed, determine the test parameters for the test load amplitude and load ratio. Install the specimens one by one on the high-frequency fatigue testing machine to begin the test. At the start of the test, record the stable test frequencies for each specimen. f 0、 f 1. f 2. f 3. f 4. f 5... f n Based on the previous analysis, the frequencies of these experiments are ranked as follows: f 0> f 1> f 2>f 3> f 4> f 5>...> f n In this way, we can obtain the data set ( a 1, f 0- f 1), ( a 2, f 0- f 2), ( a 3, f 0- f 3), ( a 4, f 0- f 4) and ( a 5, f 0- f 5) ... ( a n , f 0- f n );

[0036] S4: Fitted data set ( a 1, f 0- f 1), ( a 2, f 0- f 2), ( a 3, f 0- f 3), ( a 4, f 0- f 4) and ( a 5, f 0- f 5) ... ( a n , f 0- f n The relationship between the crack initiation scale of the test material and the attenuation of the test frequency was obtained.

[0037] Furthermore, data is collected once every 500 to 2000 cycles.

[0038] Furthermore, the load ratio is -1, 0, 0.1, 0.3, or 0.5.

[0039] Furthermore, the sample is either plate-shaped or rod-shaped.

[0040] Furthermore, the sample is rod-shaped, specifically a dumbbell-shaped round rod.

[0041] Furthermore, the relationship between the crack initiation scale and the test frequency attenuation is a cubic polynomial.

[0042] Compared to existing technologies, the measurement method for estimating fatigue crack initiation in metallic materials using frequency attenuation, as described in this invention, has the following advantages:

[0043] 1) The present invention proposes a measurement method for estimating the initiation of fatigue cracks in metallic materials by using frequency attenuation. Under the constant load amplitude mode control of a high-frequency fatigue testing machine, the method predicts the scale of fatigue crack initiation by measuring the attenuation of the test frequency and determines the crack initiation life, providing a basis for the safety and reliability assessment and full life verification of metallic materials in engineering applications.

[0044] 2) The measurement method described in this invention is an experimental measurement method for indirectly measuring the fatigue crack initiation scale and initiation life. It is simple to operate, easy to promote and apply, and has significant effects. Attached Figure Description

[0045] Figure 1 The crack initiation scale of this invention a1 and test frequency attenuation Δ f The relationship curve of data distribution;

[0046] Figure 2 The frequency attenuation Δ of the 0# sample test in the cycle number of the present invention is 0-440000. f and number of loops N Data distribution between;

[0047] Figure 3 The frequency attenuation Δ of the 0# sample in the test of the present invention with a cycle count of 39,000-440,000 is given. f and number of loops N The data distribution between them. Detailed Implementation

[0048] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The test frequency in the present invention refers to the frequency at which the high-frequency fatigue testing machine and the sample system resonate; the concepts of sample and test material in the present invention are not fundamentally different, the sample is merely one manifestation of the test material; the crack scale and crack initiation scale mentioned in the present invention actually both refer to crack scale.

[0049] Experimental measurement approach to predict fatigue crack initiation in metallic materials using frequency attenuation.

[0050] For high-frequency fatigue testing machines, the control mode is generally constant load amplitude. Its working principle is that after the specimen is mounted on the testing machine, a certain constant load amplitude is applied. The testing machine software automatically determines the test frequency at which the system composed of the testing machine and the specimen resonates, and starts the test at this frequency. Once the constant load amplitude is determined, it means that the mass of the weights acting on the specimen is fixed, so the test frequency depends only on the stiffness of the system; generally, the greater the system stiffness, the higher the test frequency. As fatigue cracks begin to initiate and gradually propagate in the working part of the specimen, the stiffness of the system will inevitably decrease, causing the test frequency to decay. If the relationship between the test frequency decay and the crack initiation scale can be established beforehand through some means, then during the test, the fatigue crack initiation scale can be determined by monitoring the test frequency decay. The corresponding number of cycles is the fatigue crack initiation life.

[0051] Theoretical basis for the correlation between test frequency attenuation and fatigue crack initiation scale in metallic materials

[0052] As described above, the working principle of a high-frequency fatigue testing machine is that the system consisting of the testing machine and the specimen resonates, and the test is conducted at this resonant frequency. Therefore, the resonant frequency is also called the test frequency. This resonance is similar to the resonance model of a spring oscillator, and its resonant frequency can be expressed as:

[0053] (1)

[0054] In the formula, f —Resonance frequency, i.e., the test frequency, in Hz; k —Stiffness of the system consisting of the high-frequency fatigue testing machine and the specimen, N / m; m —Mass acting on the specimen, kg. Based on the principles of fracture mechanics theory and compliance techniques for measuring crack size, the normalized crack size is expressed as:

[0055] (2)

[0056] In the formula, a / W To normalize the crack size, a Crack size, mm. W The width of the sample is in mm. C 0 , C 1 , C 2 , C 3 , C 4 , C 5 The flexibility coefficient, U xThe dimensionless compliance is related to the elastic modulus of the test material, the specimen size, and the applied load, and is expressed as follows:

[0057] (3)

[0058] In the formula, B, V The sample size is in mm. E The elastic modulus of the material, in MPa. P For external load, k 1 represents the system compliance of the high-frequency fatigue testing machine and the specimen. k 1 ＊k= 1;

[0059] According to equations (2) and (3), the crack initiation scale is obtained. a1, mm Among them, the scale of crack initiation a1 and system stiffness k There exists a certain mathematical relationship, which can be expressed as equation (4):

[0060] (4)

[0061] In the formula, F 1 represents the first function symbol;

[0062] According to formulas (4) and (1), the crack initiation scale can be obtained. a1, mm Among them, the scale of crack initiation a1 and test frequency f The relationship is calculated as follows (5):

[0063] (5)

[0064] In the formula, F 2 represents the symbol for the second function.

[0065] As can be seen from equation (5), the crack initiation scale... a1 and test frequency f There is a certain mathematical relationship, and the longer the crack size, the lower the test frequency. This provides a theoretical basis for determining the crack initiation size by the attenuation of the test frequency.

[0066] Furthermore, the relationship between the crack initiation scale of the specimen and the attenuation of the test frequency is as follows (6):

[0067] a1 = F 3(△ f (6)

[0068] In the formula, a1 The crack initiation scale, in mm. F3 represents the third function symbol, which can be obtained through least squares regression. △ f The test frequency attenuation is expressed in Hz.

[0069] III. Calibration Method for Fatigue Crack Initiation Scale and Test Frequency Attenuation

[0070] The above analysis shows that the initiation scale of fatigue cracks can be predicted by the attenuation of the test frequency, and the corresponding fatigue life is the crack initiation life. A relatively homogeneous metallic material with uniform composition, microstructure, and properties is selected, and a set (e.g., 6 pieces) of commonly used plate or rod-shaped specimens are processed. After processing, the specimens are numbered as 0#, 1#, 2#, 3#, 4#, and 5#. Specimen 0# is left untreated, while specimens 1#, 2#, 3#, 4#, and 5# are further artificially pre-introduced with cracks of different scales. a 1. a 2. a 3. a 4 and a 5. The scale relationship is as follows: a 1 < a 2< a 3< a 4< a 5. After completion, determine the test load amplitude and other relevant test parameters. Install each of the six specimens one by one on the high-frequency fatigue testing machine to begin the test. At the start of the test, record the test frequencies at which resonance occurs after each specimen has stabilized. f 0、 f 1. f 2. f 3. f 4 and f 5. Based on the previous analysis, the frequencies of these experiments are ranked as follows: f 0> f 1> f 2> f 3> f 4> f 5. In this way, we can obtain the data set ( a 1, f 0- f 1), ( a 2, f 0- f 2), ( a 3, f 0- f 3), ( a 4, f 0- f 4) and ( a 5, f 0- f5) By fitting their relationship, the relationship between the crack initiation scale of the specimen and the attenuation of the test frequency can be obtained, i.e. a = F 3(△ f ), F 3 represents the third function symbol, △ f The value represents the attenuation of the test frequency. It should be noted that this relationship does not contradict equation (5), because the same data set can be expressed by multiple functions.

[0071] IV. Test Procedure

[0072] (1) Determine the test load amplitude. Based on the yield strength and tensile strength values ​​of the test material, set a constant load amplitude as the test control parameter;

[0073] (2) Determine the load ratio and test parameters. Based on the client's requirements or the actual project conditions, determine the load ratio, such as -1, 0, 0.1, 0.3, 0.5, etc.; wherein, the test parameters include the elastic modulus of the test material, specimen size, external load, normalized crack size, test frequency at which the high-frequency fatigue testing machine and specimen system resonate, stiffness of the high-frequency fatigue testing machine and specimen system, crack initiation size, compliance coefficient, mass of weights acting on the specimen, and specimen width.

[0074] (3) Calibrate the relationship between fatigue crack initiation scale and test frequency attenuation. As mentioned above, calibrate the relationship between the two;

[0075] (4) Set data acquisition parameters. Throughout the experiment, periodically collect data such as the number of cycles and the experimental frequency;

[0076] (5) Formal test. Install the specimen onto the high-frequency fatigue testing machine, select the constant load amplitude and load ratio determined above, start the testing machine, and begin the test until the specimen fractures, then end the test;

[0077] ⑹ Determine the crack initiation scale and initiation life. The final fatigue life at fracture is the total fatigue life of the specimen. Based on the collected cycle number and test frequency data, fit the relationship between the cycle number and the test frequency attenuation, and combine with step (3) to determine the crack initiation scale at a certain frequency attenuation, as well as the fatigue life corresponding to that crack initiation scale, i.e., the fatigue crack initiation life.

[0078] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention.

[0079] This invention presents an experimental measurement method for estimating fatigue crack initiation in metallic materials using frequency attenuation, which can measure the fatigue crack initiation life of selected metallic materials. The test material is ZG35CrMo cast steel, commonly used in the machinery industry, with a yield strength of 850 MPa and a tensile strength of 1100 MPa. Six dumbbell-shaped parallel bar specimens are fabricated, with a nominal diameter of 7 mm at the smallest position. The specimens are numbered 0#, 1#, 2#, 3#, 4#, and 5#. Specimens 1#, 2#, 3#, 4#, and 5# have sharp notches (cracks) of different sizes machined sequentially at the smallest diameter position: 0.1 mm, 0.5 mm, 1.2 mm, 2.1 mm, and 3.5 mm (other sizes are also possible). Specimens 0# are not notched. A maximum stress of 350 MPa (41.2% yield strength) is selected as the maximum stress, corresponding to a maximum load of 13.47 kN, a load ratio of 0, and a constant load amplitude of 6.735 kN. Samples #1, #2, #3, #4, and #5 were sequentially mounted on a 100kN high-frequency fatigue testing machine. After resonance occurred and stabilized, the test frequency of each sample was recorded, and the samples were then removed. Sample #0 was then mounted on the testing machine, and data acquisition parameters were set. Only the test frequency and number of cycles were collected; data was collected every 1000 cycles. The test was conducted using the above parameters, recording the test frequency at the initial resonance until the sample experienced fatigue fracture, at which point the test ended. Relevant data for the six samples are shown in Table 1.

[0080] Table 1. Relevant data for 6 samples

[0081]

[0082] For ease of observation, the pre-crack size and test frequency attenuation of the samples in Table 1 are plotted. Figure 1 .from Figure 1 It is evident that the larger the crack initiation scale, the greater the attenuation of the test frequency, and the distribution of both can be described by a cubic increasing polynomial.

[0083] For sample #0, the number of cycles collected N (Due to the large amount of data, only data from every 10,000 trials is used) and the test frequency attenuation Δ f Data distribution see Figure 2 .

[0084] from Figure 2 As can be seen, the test frequency hardly decays over a large range with increasing cycle number, indicating that the fatigue crack initiation life of the test material is relatively long. When the number of cycles N is approximately 410,000, the test frequency begins to decrease, that is, the frequency begins to decay, and the rate of frequency decay begins to increase. For easier observation, the number of cycles in the later stages is... N and test frequency attenuation Δf The data is extracted and placed in a coordinate system, see... Figure 3 .

[0085] from Figure 3 It is clearly visible that when the number of cycles N is approximately 410,000, the test frequency begins to decrease, and fatigue cracks begin to initiate. As the number of cycles increases, the attenuation of the test frequency becomes larger and larger. Due to the increasing size of the crack propagation, the specimen eventually cannot withstand the external load and fractures due to the reduction in cross-sectional area. The total fatigue life is 439,100 cycles, and the fatigue crack initiation life accounts for 93.4% of the total life, which is basically consistent with the information provided in relevant literature.

[0086] Therefore, the experimental measurement method for estimating the fatigue crack initiation of metallic materials by using frequency attenuation proposed in this invention is applicable to the measurement of fatigue crack initiation life indirectly by monitoring the attenuation of the test frequency under the constant load amplitude mode control of a high-frequency fatigue testing machine, thereby determining the crack initiation size and initiation life, and can be used for the safety and reliability assessment and full life verification of engineering structures.

[0087] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A measurement method for estimating fatigue crack initiation in metallic materials using frequency attenuation, characterized in that, Using a high-frequency fatigue testing machine, under constant load amplitude control mode, the test frequency when the high-frequency fatigue testing machine and the sample system resonate is determined. The test frequency decays during the fatigue crack initiation process. By establishing the relationship between the fatigue crack initiation scale and the test frequency decay in advance, the fatigue crack initiation scale and initiation life are determined by detecting the decay of the test frequency during the test. Specifically, the steps include the following: Step 1: Determine the constant load amplitude of the specimen. Based on the yield strength and tensile strength values ​​of the test material, set a constant load amplitude as the test control parameter. Step 2: Determine the load ratio based on the actual needs of the project; Step 3: Determine the relationship between fatigue crack initiation scale and test frequency attenuation; Step 4: Set data acquisition parameters; the data acquisition parameters include the number of periodic acquisition cycles and the test frequency; Step 5: Formal test; Install the specimen onto the high-frequency fatigue testing machine, select the constant load amplitude in Step 1 and the load ratio in Step 2, start the testing machine, and begin the test until the specimen breaks, then end the test. Step 6: Determine the crack initiation scale and initiation life; Based on the collected cycle number and test frequency data, fit the relationship between the cycle number and frequency decay, and then combine with Step 3 to determine the crack initiation scale under a certain test frequency decay, and the fatigue life corresponding to the crack initiation scale, i.e. fatigue crack initiation life. The relationship between the fatigue crack initiation scale of the specimen and the attenuation of the test frequency is as follows (6): a1 = F 3(△ f )（6） In the formula, a1 The scale for crack initiation. F 3 represents the third function symbol, △ f This represents the attenuation of the test frequency. The relationship between the crack initiation scale and the test frequency attenuation is a cubic polynomial.

2. The measurement method according to claim 1, characterized in that, Step three includes the following experimental equation: the test frequency at which the system consisting of the high-frequency fatigue testing machine and the test specimen resonates is calculated using the following formula (1): （1） In the formula, f —Test frequency, Hz; k —Stiffness of the system consisting of the high-frequency fatigue testing machine and the specimen, N / m; m —Mass acting on the sample, kg; Based on the principles of fracture mechanics theory and compliance technology for measuring crack size, the normalized crack size is calculated using the following formula (2): （2） In the formula, a / W To normalize the crack size, a Crack size, W The width of the sample. C 0 , C 1 , C 2 , C 3 , C 4 , C 5 The flexibility coefficient, U x The dimensionless compliance is related to the elastic modulus of the test material, the size of the specimen, and the applied load. The relationship is expressed as follows: (3) （3） In the formula, B , V For sample size, E The elastic modulus of the test material, P For external load, k 1 represents the system compliance of the high-frequency fatigue testing machine and the specimen. k 1 ＊k= 1; According to formulas (2) and (3), the crack initiation scale can be obtained. a1 Among them, the scale of crack initiation a1 and system stiffness k The relationship is expressed as follows (4): （4） In the formula, F 1 represents the first function symbol; According to formulas (4) and (1), the crack initiation scale can be obtained. a1 Among them, the scale of crack initiation a1 and test frequency f The relationship is calculated as follows (5): （5） In the formula, F 2 represents the symbol for the second function.

3. The measurement method according to claim 1, characterized in that, In step three, the specific steps for calibrating the fatigue crack initiation scale and the test frequency attenuation are as follows: S1: Select a metallic material with uniform composition, microstructure and properties, and process it into a set of samples; S2: After the samples are processed, they are numbered as 0#, 1#, 2#, 3#, 4#, 5#, ... n#. Among them, sample 0# is not treated, while samples 1#, 2#, 3#, 4#, and 5#... n# are further artificially pre-introduced with cracks of different sizes. a 1. a 2. a 3. a 4 and a 5... a n The scale relationship is as follows a 1 < a 2< a 3< a 4< a 5...< a n ; S3: After cracks of different scales are completed, determine the test parameters for the test load amplitude and load ratio. Install the specimens one by one on the high-frequency fatigue testing machine to begin the test. At the start of the test, record the stable test frequencies for each specimen. f 0、 f 1. f 2. f 3. f 4. f 5... f n Based on the previous analysis, these frequencies are ordered as follows: f 0> f 1> f 2> f 3> f 4> f 5>...> f n In this way, we can obtain the data set ( a 1, f 0- f 1), ( a 2, f 0- f 2), ( a 3, f 0- f 3), ( a 4, f 0- f 4) and ( a 5, f 0- f 5) ... ( a n , f 0- f n ); S4: Fitted data set ( a 1, f 0- f 1), ( a 2, f 0- f 2), ( a 3, f 0- f 3), ( a 4, f 0- f 4) and ( a 5, f 0- f 5) ... ( a n , f 0- f n The relationship between the crack initiation scale of the test material and the attenuation of the test frequency was obtained.

4. The measurement method according to claim 1, characterized in that, A data sample is collected every 500 to 2000 cycles.

5. The measurement method according to claim 1, characterized in that, The load ratios are -1, 0, 0.1, 0.3, and 0.

5.

6. The measurement method according to claim 1, characterized in that, The sample is either plate-shaped or rod-shaped.

7. The measurement method according to claim 6, characterized in that, The sample is rod-shaped, specifically a dumbbell-shaped round rod.

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