CN116341216A - Measuring method for calculating fatigue crack initiation of metal material by using frequency attenuation - Google Patents

Measuring method for calculating fatigue crack initiation of metal material by using frequency attenuation Download PDF

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CN116341216A
CN116341216A CN202310206909.1A CN202310206909A CN116341216A CN 116341216 A CN116341216 A CN 116341216A CN 202310206909 A CN202310206909 A CN 202310206909A CN 116341216 A CN116341216 A CN 116341216A
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张亚军
徐宁
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Luoyang Shipbuilding Materials Research Institute 725th Research Institute Of China Shipbuilding Corp
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Abstract

The invention provides a measuring method for estimating the fatigue crack initiation of a metal material by using frequency attenuation, which uses a high-frequency fatigue testing machine, under a constant load amplitude control mode, determines the test frequency when a system consisting of the high-frequency fatigue testing machine and a sample resonates, and in the fatigue crack initiation process of the sample, the test frequency is attenuated, and in the test process, the fatigue crack initiation scale and the fatigue crack initiation service life are determined by detecting the attenuation of the test frequency by establishing the relation between the fatigue crack initiation scale of the sample and the attenuation of the test frequency in advance. The method for testing and measuring the crack initiation life under a certain initiation scale solves the problems that the high-frequency fatigue testing machine is applied more in a laboratory at present, but the report of the testing machine based on the method for testing and measuring the fatigue crack initiation under a constant load amplitude control mode is not seen, the fatigue crack initiation life occupies higher proportion in the whole fatigue life, and the method has important significance in the engineering structure safety reliability assessment and the whole life check.

Description

Measuring method for calculating fatigue crack initiation of metal material by using frequency attenuation
Technical Field
The invention relates to the technical field of fatigue performance test, in particular to a measuring method for calculating fatigue crack initiation of a metal material by using frequency attenuation.
Background
The fatigue life of metallic materials generally includes crack initiation life, propagation life, and fracture life, which is generally short and often negligible. The fatigue crack growth life has been studied by expert students, and various test standards which can be executed by reference are formed, such as GB/T6398-2017 fatigue crack growth method for fatigue test of metal materials, ASTM E647-2015 standard test method for fatigue crack growth rate measurement, and the like, and in the standards, besides the fatigue crack growth rate equation of the metal materials can be obtained, the corresponding fatigue life when the fatigue crack is grown to a certain length can also be obtained at the same time. Researches show that the fatigue crack initiation life of metal materials such as stainless steel, nickel-based alloy, aluminum alloy, copper alloy and the like occupies 40% -90% of the total life, even higher, which is enough to be significant in researching the fatigue crack initiation life.
For fatigue crack initiation life, although some expert scholars propose various theoretical prediction models, the accuracy of the general theoretical prediction model is lower due to the difference of materials, and the general theoretical prediction model is difficult to be applied to engineering. The test measurement method for indirectly obtaining the fatigue crack initiation is invented by a learner, and comprises the steps of researching and calibrating the relation between the attenuation of stress and load and the crack initiation scale in advance under the control conditions of constant strain amplitude and constant displacement amplitude, so that the crack initiation scale is obtained by monitoring the attenuation of stress and load in the test process, and the corresponding fatigue life is the crack initiation life, however, the test cost of the test sample is higher, and the application value in engineering is lower. In order to save test cost and accelerate fatigue test progress, a plurality of high-frequency fatigue test machines are applied to a laboratory at present, the control mode of the test machines is usually constant load amplitude, and no report of a fatigue crack initiation test measurement method based on the constant load amplitude control mode is found at present.
Disclosure of Invention
In view of the above, the present invention aims to provide a method for measuring fatigue crack initiation of a metal material. The method solves the problems that in the prior art, the accuracy of a general theoretical prediction model is low due to the difference of materials, and the method is difficult to obtain application in engineering; the test sample has high test cost and low engineering application value, and the problem of the fatigue crack initiation method can be estimated under the constant load amplitude of the high-frequency fatigue tester is not recorded in the prior art.
In order to achieve the above purpose, the technical scheme of the invention is realized as follows:
a measuring method for calculating the fatigue crack initiation of a metal material by using frequency attenuation uses a high-frequency fatigue testing machine, under a constant load amplitude control mode, the test frequency when the high-frequency fatigue testing machine and a sample composition system resonate is determined, the test frequency is attenuated in the fatigue crack initiation process of a sample, the relation between the fatigue crack initiation scale of the sample and the attenuation of the test frequency is established in advance, and in the test process, the initiation scale and the initiation service life of the fatigue crack are determined by detecting the attenuation of the test frequency.
The measurement method can obtain the crack initiation life under a certain initiation scale, and solves the problems that the high-frequency fatigue testing machine is applied more in a laboratory at present, but the report of the testing machine based on the fatigue crack initiation test measurement method under a constant load amplitude control mode is not seen, the fatigue crack initiation life occupies higher proportion in the whole fatigue life, and the fatigue crack initiation life has important significance in engineering structure safety reliability assessment and whole life check.
Further, the method specifically comprises the following steps:
step one: determining a constant load amplitude of a sample, and setting a constant load amplitude as a test control parameter according to the yield strength and the tensile strength value of a test material;
step two: determining a load ratio according to the actual engineering requirements;
step three: calibrating the relation between the fatigue crack initiation scale and the test frequency attenuation;
step four: setting data acquisition parameters; the data acquisition parameters comprise periodic acquisition cycle times and test frequency;
step five: formal test; installing the sample on a high-frequency fatigue testing machine, selecting a constant load amplitude in the first step and a load ratio in the second step, starting the testing machine, starting the test until the sample breaks, and ending the test;
step six: determining crack initiation scale and initiation life; fitting the relation between the cycle times and the test frequency attenuation according to the acquired cycle times and test frequency data, and combining the third step to determine the crack initiation scale under a certain test frequency attenuation and the fatigue life corresponding to the crack initiation scale, namely the fatigue crack initiation life.
Further, in the third step, the test equation is included, and the test frequency when the system consisting of the high-frequency fatigue tester and the sample resonates is calculated according to the following formula (1):
Figure BDA0004111257930000031
wherein f is the test frequency, hz; k-system rigidity consisting of the high-frequency fatigue testing machine and the sample, N/m; m-mass acting on the sample, kg;
according to the principle of measuring crack dimensions by fracture mechanics theory and flexibility technology, the normalized crack dimensions are calculated according to the following formula (2):
Figure BDA0004111257930000032
wherein a/W is normalized crack scale, a is crack scale, W is sample width, C 0 、C 1 、C 2 、C 3 、C 4 、C 5 As a coefficient of compliance, U x Is of non-dimensional flexibility, and the elasticity of the test materialModulus, sample size, applied load, the expression relationship is calculated as follows (3):
Figure BDA0004111257930000033
wherein B, V is the sample size, E is the elastic modulus of the test material, and P is the applied load;
as can be seen from the formula (2) and the formula (3), a crack initiation scale a1 is obtained, wherein the expression relationship between the crack initiation scale a1 and the rigidity k of the system is calculated as follows (4):
Figure BDA0004111257930000034
wherein F is 1 Is a first function symbol;
as can be seen from the formula (4) and the formula (1), a crack initiation scale a1 is obtained, wherein the relation between the crack initiation scale a1 and the test frequency f is calculated as the following formula (5):
Figure BDA0004111257930000035
wherein F is 2 Is a second function symbol.
Further, the relationship between the fatigue crack initiation scale of the test sample and the test frequency attenuation is represented by the following formula (6):
a1＝F 3 (△f)(6)
wherein a1 is crack initiation scale, F 3 And as a third function symbol, Δf is the test frequency attenuation.
Further, in the third step, the method for calibrating the fatigue crack initiation scale and the test frequency attenuation comprises the following specific steps:
s1: selecting a metal material with uniform components, tissue structures and properties, and processing the metal material into a group of samples;
s2: after the sample was processed, it was numbered 0#, 1#, 2#, 3#, 4#, 5#, n #, respectively. Which is a kind ofIn the test pieces 0# sample, no treatment was performed, and the test pieces 1#, 2#, 3#, 4# and 5 #..n # samples were further manually prefabricated for cracks a of different dimensions, respectively 1 、a 2 、a 3 、a 4 And a 5 ...a n The dimension relation is a 1 ＜a 2 ＜a 3 ＜a 4 ＜a 5 ...＜a n ；
S3: after the cracks with different dimensions are completed, determining test parameters of test load amplitude and load ratio, installing the test samples on a high-frequency fatigue testing machine one by one to start the test, and recording test frequencies after stabilization respectively at the beginning of the test, wherein the test frequencies are f respectively 0 、f 1 、f 2 、f 3 、f 4 、f 5 ...f n According to the previous analysis, the magnitudes of these test frequencies are ordered as f 0 ＞f 1 ＞f 2 ＞f 3 ＞f 4 ＞f 5 ＞...＞f n Thus, a 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: fitting 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 ) And obtaining the relation between the crack initiation scale of the test material and the attenuation of the test frequency.
Further, the cycle times reach 500-2000 times, and the collection is performed once.
Further, the load ratio is-1, 0, 0.1, 0.3, 0.5.
Further, the sample is one of a plate-like or a rod-like.
Further, the sample is a bar, and the bar is a dumbbell-shaped round bar.
Further, the relation between the crack initiation scale and the test frequency attenuation is a unitary three-degree increasing polynomial.
Compared with the prior art, the measuring method for estimating the fatigue crack initiation of the metal material by using the frequency attenuation is disclosed. Has the following advantages:
1) The measuring method for calculating the fatigue crack initiation of the metal material by using the frequency attenuation is used for realizing the prediction of the fatigue crack initiation scale by measuring the attenuation of the test frequency under the control of a constant load amplitude mode of the high-frequency fatigue testing machine, determining the crack initiation life and providing a basis for the safe reliability assessment and the full life check of the metal material in engineering application.
2) The measuring method provided by the invention is a test measuring method for indirectly measuring the fatigue crack initiation scale and the initiation life, is simple to operate, is convenient to popularize and apply, and has a remarkable effect.
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FIG. 1 is a graph showing the relationship between crack initiation scale a1 and test frequency attenuation Δf data distribution according to the present invention;
FIG. 2 is a data distribution between the test frequency attenuation Δf and the number of cycles N of the sample # 0 among the number of cycles 0 to 440000 according to the present invention;
FIG. 3 shows the data distribution between the test frequency attenuation Δf and the number of cycles N of the sample No. 0 among 39000 to 44000th cycles according to the present invention.
Detailed Description
In order that the above objects, features and advantages of the invention will be readily understood, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. The test frequency in the invention refers to the frequency when the high-frequency fatigue testing machine and the sample composition system generate resonance; the sample is not essentially different from the concept of the test material, and is only one expression form of the test material; the crack scale and the crack initiation scale described in the invention are actually referred to as crack scale.
1. The test measurement thinking of estimating the fatigue crack initiation of the metal material by using the frequency attenuation is that for a high-frequency fatigue testing machine, the control mode is generally constant load amplitude. The working principle of the test device is that after the test sample is clamped on the test device, a certain constant load amplitude is applied, and test device software automatically requires test frequency when the test device and the system consisting of the test sample resonate, and the test is started at the test frequency. After the constant load amplitude is determined, it means that the mass of the weight acting on the sample is determined, so that the test frequency depends only on the stiffness of the system, and in general, the greater the stiffness of the system, the higher the test frequency. When the working part of the sample starts to initiate fatigue cracks and gradually expands, the rigidity of the system is inevitably lowered, so that the test frequency is attenuated. If the relation between the attenuation of the test frequency and the crack initiation scale can be established through a certain way in advance, the fatigue crack initiation scale can be determined by monitoring the attenuation of the test frequency in the test process, and the corresponding cycle number is the fatigue crack initiation life.
2. Theoretical basis for correlation between test frequency attenuation and metal material fatigue crack initiation scale
As stated above, the high-frequency fatigue testing machine operates on the principle that the system of testing machine and specimen resonates and tests at this resonant frequency, and therefore the resonant frequency is also called the test frequency. This resonance is similar to the resonance model of a spring vibrator, and its resonance frequency can be expressed as:
Figure BDA0004111257930000061
wherein, f-resonance frequency, namely test frequency, hz; k-system rigidity consisting of the high-frequency fatigue testing machine and the sample, N/m; m-mass acting on the sample kg. According to the principle of measuring crack dimensions by fracture mechanics theory and flexibility technology, the normalized crack dimensions are expressed as follows:
Figure BDA0004111257930000062
wherein a/W is normalized crack scale and a isCrack dimensions, mm, W is sample width, mm, C 0 、C 1 、C 2 、C 3 、C 4 、C 5 As a coefficient of compliance, U x The non-dimensional flexibility is related to the elastic modulus, the sample size, the applied load and the like of the test material and expressed as follows:
Figure BDA0004111257930000063
wherein B, V is the sample size, mm, E is the elastic modulus of the material, MPa, and P is the applied load.
From the formulas (2) and (3), crack initiation dimensions a1, mm are obtained, wherein the crack initiation dimensions a1 and the rigidity k of the system have a certain mathematical relationship, and the relationship can be expressed as the formula (4):
Figure BDA0004111257930000064
wherein F is 1 Is a first function symbol;
as can be seen from the formula (4) and the formula (1), crack initiation dimensions a1, mm are obtained, wherein the relation between the crack initiation dimensions a1 and the test frequency f is calculated as the following formula (5):
Figure BDA0004111257930000065
wherein F is 2 Is a second function symbol.
From the formula (5), a certain mathematical relationship exists between the crack initiation scale a1 and the test frequency f, and the longer the crack scale is, the lower the test frequency is, so that a theoretical basis is provided for determining the crack initiation scale through the test frequency attenuation.
Further, the relation between the crack initiation scale of the sample and the test frequency attenuation is as follows formula (6):
a1＝F 3 (△f)(6)
wherein a1 is crack initiation scale, mm, F 3 The third function symbol, the representative function, can be obtained by regression through the least square method, and Δf is the test frequency attenuation, hz.
3. Calibration method for fatigue crack initiation scale and test frequency attenuation
From the above analysis, it is known that the fatigue crack initiation scale can be predicted by the attenuation of the test frequency, and the corresponding fatigue life is the crack initiation life. A metal material with uniform composition, structure and performance is selected, and a group (such as 6 pieces) of common plate-shaped or rod-shaped samples are processed. After the sample was processed, it was numbered 0#, 1#, 2#, 3#, 4# and 5# respectively. Wherein, the No. 0 sample is not processed, and the No. 1, no. 2, no. 3, no. 4 and No. 5 samples are further prefabricated with cracks a with different scales manually respectively 1 、a 2 、a 3 、a 4 And a 5 The dimension relation is a 1 ＜a 2 ＜a 3 ＜a 4 ＜a 5 . After the test is completed, determining other relevant test parameters such as test load amplitude and the like, arranging 6 samples on a high-frequency fatigue testing machine one by one to start the test, and recording test frequencies when resonance occurs after the test is stable at the beginning of the test, wherein the test frequencies are f respectively 0 、f 1 、f 2 、f 3 、f 4 And f 5 According to the previous analysis, the magnitudes of these test frequencies are ordered as f 0 ＞f 1 ＞f 2 ＞f 3 ＞f 4 ＞f 5 . In this way, a 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 ) Fitting the relationship, the relationship between the crack initiation scale of the sample and the test frequency attenuation, namely a=F, can be obtained 3 (△f)，F 3 And as a third function symbol, Δf is the test frequency attenuation. It should be noted that this relationship is not contradictory to equation (5), since the same data set may have a plurality of functional expressions.
4. Test procedure
The method comprises the steps of determining a test load amplitude. Setting a constant load amplitude as a test control parameter according to the yield strength and the tensile strength value of the test material;
the load ratio and the test parameters are determined. According to the requirements of the first party or engineering practice, determining the load ratio, such as-1, 0, 0.1, 0.3, 0.5 and the like; the test parameters comprise the elastic modulus of a test material, the size of a test sample, an applied load, a normalized crack size, the test frequency when the high-frequency fatigue testing machine and a test sample composition system resonate, the system rigidity of the high-frequency fatigue testing machine and the test sample composition, the crack initiation size, the flexibility coefficient, the weight mass acting on the test sample and the test sample width.
And thirdly, calibrating the relation between the fatigue crack initiation scale and the test frequency attenuation. As described above, the relationship between the two is calibrated;
and setting data acquisition parameters. In the whole test process, periodically collecting data such as cycle times, test frequency and the like;
and (5) carrying out formal experiments. Mounting a test piece on a high-frequency fatigue testing machine, selecting the constant load amplitude and the load ratio determined above, starting the testing machine, starting the test until the test piece breaks, and ending the test;
and determining crack initiation scale and initiation service life. The fatigue life at the final break is the total fatigue life of the test specimen. According to the acquired cycle times and test frequency data, fitting the relation between the cycle times and the test frequency attenuation, and combining the step (3), the crack initiation scale under a certain frequency attenuation and the fatigue life corresponding to the crack initiation scale, namely the fatigue crack initiation life, can be determined.
The technical solutions in the embodiments of the present invention will be clearly and completely described below in connection with the embodiments of the present invention.
According to the test measurement method for estimating the fatigue crack initiation of the metal material by using the frequency attenuation, the fatigue crack initiation life measurement of the selected metal material can be completed. The test material is cast steel ZG35CrMo commonly used in the mechanical industry, and the yield strength and the tensile strength are 850MPa and 1100MPa respectively. 6 dumbbell-shaped round bar parallel test pieces are processed, and the nominal diameter of the smallest position of each test piece is 7mm. Sample numbers are 0#, 1#, 2#, 3#, 4# and 5# respectively. Wherein, the 1# sample, the 2# sample, the 3# sample, the 4# sample and the 5# sample are sequentially processed with sharp notches (cracks) with different dimensions at the minimum diameter positions, namely 0.1mm, 0.5mm, 1.2mm, 2.1mm and 3.5mm (of course, other dimensions can be adopted), and the 0# sample is not processed with the notches. The 41.2% yield strength of 350MPa is selected as the maximum stress, the corresponding maximum load is 13.47kN, the load ratio is 0, and the constant load amplitude is 6.735kN. Samples # 1, # 2, # 3, # 4 and # 5 were sequentially mounted on a 100kN high frequency fatigue tester, and after resonance and stabilization, the test frequency of each sample was recorded and the sample was removed. And then the No. 0 sample is mounted on a testing machine, data acquisition parameters are set, only the test frequency and the cycle number are acquired, and the acquisition is performed once every 1000 times the cycle number is. And (3) carrying out the test by adopting the test parameters, and recording the test frequency when resonance occurs initially until the test sample is subjected to fatigue fracture, and ending the test. The data relating to the 6 samples are shown in Table 1.
Table 1 6 data relating to the samples
Figure BDA0004111257930000081
Figure BDA0004111257930000091
For ease of observation, the pre-crack dimensions and test frequency decay of the samples in Table 1 are plotted, see FIG. 1. As can be seen from fig. 1, the larger the crack initiation scale, the higher the test frequency attenuation, and the distribution of both can be described by a unitary cubic increasing polynomial.
For sample # 0, the data distribution of the number of cycles N (data obtained at 10000 intervals only) and the test frequency attenuation Δf obtained are shown in fig. 2.
As can be seen from fig. 2, the test frequency was hardly attenuated over a wide range with an increase in the number of cycles, indicating that the fatigue crack initiation life of the test material was long, and when the number of cycles N was about 410000, the test frequency began to decrease, i.e., the frequency began to attenuate, and the frequency attenuation began to increase. For the convenience of observation, the cycle number N in the later cycle and the test frequency attenuation Deltaf data are extracted and placed in a coordinate system, as shown in FIG. 3.
As is clear from fig. 3, when the number of cycles N is about 410000, the test frequency starts to decrease, fatigue cracks start to develop, as the number of cycles increases, the attenuation amount of the test frequency becomes larger and larger, the cracks become larger and larger due to the expansion size, and the final test specimen cannot bear the action of an applied load to fracture due to the decrease in the sectional area, the fatigue total life is 439100 times, the fatigue crack initiation life occupies 93.4% of the total life, and the substantial agreement is presented in the related data.
Therefore, the test measurement method for calculating the fatigue crack initiation of the metal material by using the frequency attenuation is suitable for indirectly realizing the measurement of the fatigue crack initiation life by monitoring the attenuation of the test frequency under the control of the constant load amplitude mode of the high-frequency fatigue testing machine, and can be used for the safety reliability assessment and the full life check of the engineering structure.
Although the present invention is disclosed above, the present invention is not limited thereto. Various changes and modifications may be made by one skilled in the art without departing from the spirit and scope of the invention, and the scope of the invention should be assessed accordingly to that of the appended claims.

Claims (10)

1. A measuring method for calculating the fatigue crack initiation of a metal material by using frequency attenuation is characterized in that a high-frequency fatigue testing machine is used, under a constant load amplitude control mode, the test frequency when the high-frequency fatigue testing machine and a sample composition system resonate is determined, the test frequency of a sample is attenuated in the fatigue crack initiation process, the relation between the fatigue crack initiation scale of the sample and the attenuation of the test frequency is established in advance, and in the test process, the initiation scale and the initiation life of the fatigue crack are determined by detecting the attenuation of the test frequency.
2. The method according to claim 1, characterized in that it comprises the following steps:
step one: determining a constant load amplitude of a sample, and setting a constant load amplitude as a test control parameter according to the yield strength and the tensile strength value of a test material;
step two: determining a load ratio according to the actual engineering requirements;
step three: calibrating the relation between the fatigue crack initiation scale and the test frequency attenuation;
step four: setting data acquisition parameters; the data acquisition parameters comprise periodic acquisition cycle times and test frequency;
step five: formal test; installing the sample on a high-frequency fatigue testing machine, selecting a constant load amplitude in the first step and a load ratio in the second step, starting the testing machine, starting the test until the sample breaks, and ending the test;
step six: determining crack initiation scale and initiation life; fitting the relation between the cycle times and the frequency attenuation according to the acquired cycle times and test frequency data, and combining the third step to determine the crack initiation scale under a certain test frequency attenuation and the fatigue life corresponding to the crack initiation scale, namely the fatigue crack initiation life.
3. The method according to claim 2, wherein in the third step, the test frequency at which the system of the high-frequency fatigue tester and the specimen resonates is calculated according to the following equation (1):
Figure FDA0004111257920000011
wherein f is the test frequency, hz; k-system rigidity consisting of the high-frequency fatigue testing machine and the sample, N/m; m-mass acting on the sample, kg;
according to the principle of measuring crack dimensions by fracture mechanics theory and flexibility technology, the normalized crack dimensions are calculated according to the following formula (2):
Figure FDA0004111257920000021
wherein a/W is normalized crack scale, a is crack scale, W is sample width, C 0 、C 1 、C 2 、C 3 、C 4 、C 5 As a coefficient of compliance, U x The expression relationship is calculated as the following formula (3) according to the relation of the non-dimensional flexibility, the elastic modulus of the test material, the size of the sample and the applied load:
Figure FDA0004111257920000022
wherein B, V is the sample size, E is the elastic modulus of the test material, and P is the applied load;
as can be seen from the formula (2) and the formula (3), a crack initiation scale a1 is obtained, wherein the expression relationship between the crack initiation scale a1 and the rigidity k of the system is calculated as follows (4):
Figure FDA0004111257920000023
wherein F is 1 Is a first function symbol;
as can be seen from the formula (4) and the formula (1), a crack initiation scale a1 is obtained, wherein the relation between the crack initiation scale a1 and the test frequency f is calculated as the following formula (5):
Figure FDA0004111257920000024
wherein F is 2 Is a second function symbol.
4. The measurement method according to claim 1, wherein the relationship between the specimen fatigue crack initiation scale and the test frequency attenuation is represented by the following formula (6):
a1＝F 3 (△f)(6)
wherein a1 is crack initiation scale, F 3 And as a third function symbol, Δf is the test frequency attenuation.
5. The method according to claim 2, wherein in the third step, the method for calibrating the fatigue crack initiation scale and the test frequency attenuation comprises the following specific steps:
s1: selecting a metal material with uniform components, tissue structures and properties, and processing the metal material into a group of samples;
s2: after the sample was processed, it was numbered 0#, 1#, 2#, 3#, 4#, 5#, n #, respectively; wherein, no. 0 sample is not processed, no. 1, no. 2, no. 3, no. 4 and No. 5. N. samples are further prefabricated with cracks a of different dimensions manually, respectively 1 、a 2 、a 3 、a 4 And a 5 ...a n The dimension relation is a 1 ＜a 2 ＜a 3 ＜a 4 ＜a 5 ...＜a n ；
S3: after the cracks with different dimensions are completed, determining test parameters of test load amplitude and load ratio, installing the test samples on a high-frequency fatigue testing machine one by one to start the test, and recording test frequencies after stabilization respectively at the beginning of the test, wherein the test frequencies are f respectively 0 、f 1 、f 2 、f 3 、f 4 、f 5 ...f n According to the previous analysis, the frequencies are ordered in magnitude f 0 ＞f 1 ＞f 2 ＞f 3 ＞f 4 ＞f 5 ＞...＞f n Thus, a 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: fitting 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 ) And obtaining the relation between the crack initiation scale of the test material and the attenuation of the test frequency.
6. The method according to claim 2, wherein the number of cycles is up to 500-2000, and is collected once.
7. The method of measurement according to claim 2, wherein the load ratio is-1, 0, 0.1, 0.3, 0.5.
8. The method according to claim 1, wherein the sample is one of a plate-like or a rod-like.
9. The method according to claim 8, wherein the sample is a bar, and the bar is a dumbbell-shaped round bar.
10. The method of claim 1, wherein the relationship between the crack initiation scale and the test frequency attenuation is a unitary three-degree increasing polynomial.
CN202310206909.1A 2023-03-06 2023-03-06 Measuring method for calculating fatigue crack initiation of metal material by using frequency attenuation Pending CN116341216A (en)

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CN117935997A (en) * 2024-03-25 2024-04-26 洛阳船舶材料研究所(中国船舶集团有限公司第七二五研究所) Dynamic measurement method for metal material fatigue crack tip plastic region
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CN117935997A (en) * 2024-03-25 2024-04-26 洛阳船舶材料研究所(中国船舶集团有限公司第七二五研究所) Dynamic measurement method for metal material fatigue crack tip plastic region
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CN117954022B (en) * 2024-03-25 2024-06-07 洛阳船舶材料研究所(中国船舶集团有限公司第七二五研究所) Estimation method of fatigue crack growth rate of metal material under elastoplastic condition
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