CN116525036A - Method for predicting fatigue crack growth threshold and fatigue life based on martensite content - Google Patents
Method for predicting fatigue crack growth threshold and fatigue life based on martensite content Download PDFInfo
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- 229910000734 martensite Inorganic materials 0.000 title claims abstract description 102
- 238000000034 method Methods 0.000 title claims abstract description 33
- 238000012360 testing method Methods 0.000 claims abstract description 57
- 229910000885 Dual-phase steel Inorganic materials 0.000 claims abstract description 51
- 125000004122 cyclic group Chemical group 0.000 claims abstract description 28
- 238000004364 calculation method Methods 0.000 claims abstract description 27
- 229910000831 Steel Inorganic materials 0.000 claims description 25
- 239000010959 steel Substances 0.000 claims description 25
- 230000008018 melting Effects 0.000 claims description 5
- 238000002844 melting Methods 0.000 claims description 5
- 229910001220 stainless steel Inorganic materials 0.000 claims 1
- 239000010935 stainless steel Substances 0.000 claims 1
- 239000000463 material Substances 0.000 abstract description 8
- 206010016256 fatigue Diseases 0.000 description 70
- 229910001039 duplex stainless steel Inorganic materials 0.000 description 6
- 230000008569 process Effects 0.000 description 5
- 230000000977 initiatory effect Effects 0.000 description 3
- 229910001566 austenite Inorganic materials 0.000 description 2
- 238000013461 design Methods 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000009661 fatigue test Methods 0.000 description 2
- 230000003993 interaction Effects 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 230000007246 mechanism Effects 0.000 description 2
- 239000007769 metal material Substances 0.000 description 2
- 229910018648 Mn—N Inorganic materials 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000001351 cycling effect Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
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- 230000006911 nucleation Effects 0.000 description 1
- 238000010899 nucleation Methods 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
- 230000009897 systematic effect Effects 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0058—Kind of property studied
- G01N2203/0069—Fatigue, creep, strain-stress relations or elastic constants
- G01N2203/0073—Fatigue
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- G06F2119/02—Reliability analysis or reliability optimisation; Failure analysis, e.g. worst case scenario performance, failure mode and effects analysis [FMEA]
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- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F2119/00—Details relating to the type or aim of the analysis or the optimisation
- G06F2119/14—Force analysis or force optimisation, e.g. static or dynamic forces
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Abstract
The invention provides a method for predicting fatigue crack growth threshold and fatigue life based on martensite content, which comprises the following steps: s1, constructing a martensite content calculation model; s2, constructing a fatigue crack propagation threshold prediction model; s3, constructing a fatigue life prediction model; s4, setting different strain amplitudes and cyclic cycles, and taking a test dual-phase steel sample to respectively carry out repeated cyclic loading under strain control by the different strain amplitudes; s5, calculating the martensite content of the dual-phase steel; s6, calculating a fatigue crack propagation threshold value of the dual-phase steel; s7, predicting the fatigue life of the dual-phase steel based on the fatigue life prediction model. The fatigue crack propagation threshold value prediction formula is established based on the martensite content, the operation is simple, the martensite content generated by the material under the cyclic loading condition can be calculated by utilizing the strain amplitude, the cyclic cycle and the inherent parameters of the dual-phase steel to be detected, and the fatigue crack propagation threshold value and the fatigue life of the dual-phase steel can be predicted.
Description
Technical Field
The invention relates to the technical field of metal material fatigue life prediction, in particular to a method for predicting fatigue crack growth threshold and fatigue life based on martensite content.
Background
According to the previous data statistics, 50% -90% of the damage suffered by the mechanical parts is fatigue damage, particularly, in recent 30 years, as the mechanical parts are developed to high temperature, high speed and large scale, the required stress of the mechanical parts is higher and higher, the use condition is worse and worse, and the fatigue damage accident is worse. Such as shafts, crankshafts, connecting rods, gears, springs, bolts, pressure vessels, ocean platforms, turbine blades, welded structures and the like, many mechanical parts and structural members are damaged in a fatigue damage mode. Thus, structural components and systems subjected to cyclic loads need to be based on the highest and most reliable fatigue life assessment. The fatigue strength has very important significance in the advanced industrial departments of aerospace, aviation, shipbuilding, atomic energy and the like, and is also an important factor influencing the use reliability and the service life of common mechanical products. Therefore, the development of fatigue strength work is not very slow for the mechanical industry. Failure of a metal material is often accompanied by the generation of fatigue cracks, and fatigue life depends on the interaction of crack initiation and propagation, and the initiation and propagation of the cracks are inseparable from the microstructure around the cracks, so that the analysis of the microstructure around the fatigue cracks and the related prediction of the fatigue life are particularly important.
Considering the huge application prospect of TRIP duplex stainless steel and the characteristic of repeated bearing of structural members in the service process, the low-cycle fatigue behavior of the duplex stainless steel is very important, and is influenced by the cyclic hardening and softening behavior of materials and the microstructure evolution during cyclic loading, and the transformed martensite and the non-transformed austenite meet the Kurdjumov-Sachs (K-S) orientation relation, so that the cooperative deformability between two phases can be improved. However, with continuous cycling, more martensite is formed, these new phasesThe formed martensite grains are more prone to form micro-voids/cracks due to their brittleness, thereby reducing the initial life of the crack, becoming a rapid path for crack propagation, thereby deteriorating the propagation life of the crack. This suggests that fatigue life may be closely related to the interaction of mechanically induced martensite with crack initiation and propagation from retained austenite. However, at present, the mechanism of crack propagation by cyclic loading strain induced martensite for duplex stainless steel is rarely studied, and the influence of martensite generated by the save-type TRIP duplex steel on fatigue crack propagation and low cycle fatigue life in the cyclic loading process is not clear. Therefore, systematic study of the effect of martensite on the low cycle fatigue life of duplex stainless steel and establishment of an accurate fatigue life assessment prediction model is particularly important for promoting the industrial application of such high-performance metastable duplex stainless steel. And fatigue crack growth threshold is an important predictor of the safety of crack-containing components during their life expectancy. The fatigue crack propagation threshold reflects the fatigue resistance of the material, has important reference significance for the design of long-life and infinite-life components in engineering, and is an important basis for the design of damage tolerance. The propagation of fatigue cracks is generally experienced: slip (planar or corrugated), crack nucleation, microcrack propagation, macrocrack propagation and fracture. Although the stages are difficult to distinguish strictly, the generation and expansion mechanisms of the stages are different after all. In the theoretical hypothesis describing fatigue crack growth, the Paris formula applies most widely. It has been found in practice that when the stress intensity factor at the crack tip is less than a certain value, the fatigue crack no longer propagates or propagates very slowly. This value is referred to as the fatigue crack growth threshold. There are two general definitions in engineering: 1. material warp 10 7 ～10 8 After the secondary fatigue, when the crack is no longer expanded or the expansion amount is no more than 0.05mm, the corresponding stress intensity factor value is the fatigue expansion threshold value. 2. Define fatigue extension Rate as 10 -7 ～10 -6 The stress intensity factor value corresponding to mm/c or the threshold rate according to the actual service life requirement of the component is 10 -9 ～10 -8 Corresponding values in mm/c.
The experimental acquisition of the fatigue crack growth threshold is the most basic means, but the experimental process is complicated, the operation time is long, the required parameters are many, and engineering production and application popularization are not easy to carry out, so that a fatigue crack growth threshold prediction method which is simple and easy to operate and has accurate prediction results is needed to be researched for accurately evaluating and predicting the fatigue crack growth threshold and the fatigue life of the experimental steel.
Disclosure of Invention
Based on the defects of the prior art, the invention aims to provide a method for predicting the fatigue crack growth threshold and the fatigue life based on the martensite content, and the method for predicting the fatigue crack growth threshold is simple, high in accuracy and easy to obtain related parameters.
In order to achieve the above object, specifically, the present invention provides a method for predicting fatigue crack growth threshold and fatigue life based on martensite content, which is characterized in that: which comprises the following steps:
s1, establishing a martensite content database of the dual-phase steel under different strain amplitudes and cyclic cycles, and constructing a martensite content calculation model based on the martensite content database;
s2, constructing a fatigue crack growth threshold prediction model, wherein the fatigue crack growth threshold prediction model specifically comprises the following steps:
wherein Δkth is a fatigue expansion threshold; e is Young's modulus, tm is the melting point of the test steel, δb is tensile strength, δs is yield strength, R is stress ratio, f M The martensite content, n' is the cyclic hardening coefficient, and B is the fatigue crack propagation threshold coefficient;
s3, constructing a fatigue life prediction model, wherein the fatigue life prediction model is specifically as follows:
wherein x, y and z are all intermediate parameters, whereinf M Is of martensite content, epsilon a The strain amplitude and the delta Kth are fatigue crack growth thresholds;
s4, setting different strain amplitudes and cyclic cycles, taking a test dual-phase steel sample, respectively carrying out repeated cyclic loading under the strain control of the different strain amplitudes, and recording the strain amplitudes and the cyclic cycles;
s5, substituting the strain amplitude and the cycle frequency obtained in the step S4 into the martensite content calculation model constructed in the step S1, and calculating the martensite content of the dual-phase steel by using the martensite content calculation model;
s6, substituting the martensite content obtained in the step S5 into the fatigue crack growth threshold prediction model in the step S2, and calculating the fatigue crack growth threshold of the dual-phase steel;
s7, substituting the fatigue crack expansion threshold value, the martensite content and the strain amplitude of the dual-phase steel into the fatigue life prediction model in the step S3, and predicting the fatigue life of the dual-phase steel.
Preferably, the fatigue life prediction model in step S3 is specifically as follows:
preferably, the fatigue crack growth threshold coefficient B in step S3 is calculated as follows:
B＝F test on test *V Adding *Q Strong strength *L Delay line *b*T Shaft
Wherein F is Test on test For the test frequency, V Adding For sample loading rate, Q Strong strength The yield ratio is the ratio of the yield strength to the tensile strength, L Delay line Is the elongation of the dual-phase steel, b is the Bose vector, T Shaft Is an axial strain control parameter.
Preferably, the martensite content calculation model in step S2 is as follows:
f M ＝-kε a [1-exp(-q4Nε a )] m
wherein f M Is of martensite content epsilon a For the total strain amplitude, N is the cycleAnd (5) carrying out cycle times.
Preferably, in the above formula
Wherein a, b, c, d, e, f, g, h, i, j, k and m are fitting parameters.
Preferably, wherein:
preferably, the dual phase steel is an economical TRIP dual phase steel.
Compared with the prior art, the invention has the following beneficial effects:
(1) According to the method, a martensite content calculation model is established, the martensite content of the test steel can be calculated according to the strain amplitude and the cycle time, the operation is simple, a large number of parameters are not required to be acquired through test measurement, and the martensite content generated in the cyclic loading process of the dual-phase steel can be rapidly calculated, so that the time cost and the operation cost required by the test are greatly saved, and the method is easy to use in various working scenes.
(2) According to the invention, a fatigue crack expansion threshold prediction formula is established based on the calculated martensite content, so that the fatigue crack expansion threshold of the test steel can be rapidly predicted, and the fatigue crack expansion threshold can be rapidly and accurately obtained based on the martensite content without damaging the test piece, thereby guiding the use process of the subsequent test piece.
(3) According to the invention, the fatigue life prediction model is established based on the strain amplitude, the fatigue crack expansion threshold value and the martensite content, the fatigue life of the dual-phase steel is obtained by substituting the strain amplitude, the fatigue crack expansion threshold value and the martensite content into the fatigue life prediction model and outputting a calculation result, namely the fatigue life of the dual-phase steel, fitting parameters related in the fatigue life prediction model are accurate parameters which are easy to calculate and obtained based on a large amount of data, and the service life of the dual-phase steel can be accurately estimated in practical application.
Drawings
FIG. 1 is a flow chart of a method for predicting fatigue crack growth threshold and fatigue life based on martensite content in an embodiment of the method of the present invention;
FIG. 2 is a graph showing the comparison of the martensite content prediction and experimental measurement variables at different strain amplitudes in the example of the method of the present invention;
FIG. 3 is a graph comparing fatigue crack growth threshold predictions with empirical model calculations in accordance with the present invention;
FIG. 4 is a graph comparing actual fatigue life and predicted fatigue life of the reduced TRIP dual phase steel according to an embodiment of the present invention.
Detailed Description
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The invention provides a method for predicting fatigue crack growth threshold and fatigue life based on martensite content, as shown in fig. 1, which specifically comprises the following steps:
s1, establishing a martensite content database of the dual-phase steel under different strain amplitudes and cyclic cycles, and establishing a martensite content calculation model based on the martensite content database; the martensite content database is obtained and established according to test data of a large number of dual-phase steels under different strain amplitudes and cyclic cycles, and the accuracy of a calculation result of the martensite content calculation model is ensured.
S2, constructing a fatigue crack growth threshold prediction model, wherein the fatigue crack growth threshold prediction model specifically comprises the following steps:
wherein Δkth is a fatigue crack growth threshold; e is Young's modulus, tm is the melting point of the test steel, δb is tensile strength, δs is yield strength, R is stress ratio, f M The martensite content, n' is the cyclic hardening coefficient, and B is the fatigue crack growth threshold coefficient.
S3, constructing a fatigue life prediction model, wherein the fatigue life prediction model is specifically as follows:
wherein x, y and z are all intermediate parameters, wherein f M Is of martensite content, epsilon a The strain amplitude, Δkth, is the fatigue crack growth threshold.
S4, setting different strain amplitudes and cyclic cycles, taking a test dual-phase steel sample, respectively carrying out cyclic loading for multiple times under the strain control of the different strain amplitudes, and recording the strain amplitudes and the cyclic cycles.
S5, substituting the strain amplitude and the cycle frequency obtained in the step S4 into the martensite content calculation model constructed in the step S1, and calculating the martensite content of the dual-phase steel by using the martensite content calculation model. The related parameters of the dual-phase steel can be obtained under the condition of not damaging the test piece.
S6, substituting the martensite content obtained in the step S5 into a fatigue crack expansion threshold prediction model, and calculating a fatigue crack expansion threshold of the dual-phase steel;
s7, substituting the fatigue crack expansion threshold value, the martensite content and the stress amplitude value of the dual-phase steel into a fatigue life prediction model to predict the fatigue life of the dual-phase steel.
Preferably, the fatigue crack growth threshold coefficient B in step S3 is calculated as follows:
B＝F test on test *V Adding *Q Strong strength *L Delay line *b*T Shaft
Wherein F is Test on test For the test frequency, the test frequency of the test steel is 0.03-0.1 Hz, the upper limit is 0.1Hz in the embodiment, V Adding For the sample loading rate, the test steel loading rate takes a value of 0.2X10 -2 /s，Q Strong strength The yield ratio is the ratio of yield strength to tensile strength, and the yield ratio of the test steel is 0.58.L (L) Delay line To test the elongation of the steel, the elongation of the test steel was 0.5871.b is the Boss vector, and the value of the test steel is 0.25.T (T) Shaft Axial strain control parameter T of the test steel Shaft Take 0.60 x 10 -6 . After calculation of the data from this test steel, b=1.0×10 -1 This value is dimensionless.
S4, according to the fatigue expansion threshold prediction model and the martensite content calculation model, a fatigue life prediction model of the dual-phase steel is obtained, and the fatigue life of the test steel can be predicted by using the fatigue life prediction model of the dual-phase steel. The fatigue life prediction model is as follows:
wherein x, y and z are all intermediate parameters; wherein f M Is of martensite content, epsilon a The strain amplitude, Δkth, is the fatigue crack growth threshold.
Calculating to obtain a fitted intermediate parameter value and substituting the intermediate parameter value into the following formula:
in actual work, the fatigue life of the steel can be predicted through the formula, the fatigue life prediction model can accurately predict the fatigue life of the dual-phase steel based on the strain amplitude, the fatigue crack expansion threshold value and the martensite content, reference is provided for the engineering application of the dual-phase steel, and the fatigue life of the dual-phase steel can be accurately predicted without damaging a sample.
The overall flow diagram of the method is shown in fig. 1, and the test material used in the method is Mn-N alloyed economic duplex stainless steel, hereinafter referred to as saving TRIP duplex steel.
The whole method comprises the following specific steps:
s1, circularly loading a plurality of pieces of saving TRIP dual-phase steel under strain control of different strain amplitudes, recording related data, establishing a martensite content database of the dual-phase steel under different strain amplitudes and circulation cycles based on a large amount of data, and establishing a martensite content calculation model based on the martensite content database.
Specifically, the martensite content calculation model of the test steel is specifically as follows:
f M ＝-kε a [1-exp(-q4Nε a )] m
wherein the method comprises the steps of
S2, constructing a fatigue crack growth threshold prediction model, wherein the fatigue crack growth threshold prediction model specifically comprises the following steps:
wherein Δkth is a fatigue crack growth threshold; e is Young's modulus, tm is the melting point of the test steel, δb is tensile strength, δs is yield strength, R is stress ratio, f M The martensite content, n' is the cyclic hardening coefficient, and B is the fatigue crack growth threshold coefficient.
The calculation formula of B is as follows: b=f Test on test *V Adding *Q Strong strength *L Delay line *b*T Shaft
Wherein F is Test on test For the test frequency, the value was 0.1Hz, V Adding For sample loading rate, the value is 0.2x10 -2 /s，Q Strong strength The yield ratio is the ratio of yield strength to tensile strength, and is 0.58L Delay line The elongation of the test steel is 0.5871, b is a Berth vector, and the elongation is 0.25; t (T) Shaft For the axial strain control parameter, the value is 0.60 x 10 -6 . According to the above value substituted into the calculation formula, the fatigue crack growth threshold coefficient B=1.0x10 of the test steel is calculated -11 This value is dimensionless.
S3, constructing a fatigue life prediction model, wherein the fatigue life prediction model is specifically as follows:
wherein x, y and z are fitting parameters, wherein f M Is of martensite content, epsilon a The strain amplitude, Δkth, is the fatigue crack growth threshold.
Substituting relevant fitting parameters to obtain:
s4, selecting a piece of test steel again as a prediction object, setting different strain amplitudes and cycle times, taking a test dual-phase steel sample, respectively carrying out repeated cyclic loading under the strain control of the different strain amplitudes, and recording the strain amplitudes and the cycle times.
S5, substituting the strain amplitude and the cycle frequency obtained in the step S4 into the martensite content calculation model constructed in the step S1, and calculating the martensite content of the dual-phase steel by using the martensite content calculation model.
S6, substituting the martensite content obtained in the step S5 into a fatigue crack growth threshold prediction model, and calculating the fatigue crack growth threshold of the dual-phase steel.
S7, substituting the fatigue crack expansion threshold value, the martensite content and the stress amplitude value of the dual-phase steel into a fatigue life prediction model to predict the fatigue life of the dual-phase steel.
Based on the above formula, the martensite contents under a plurality of different strain amplitudes are calculated, the specific martensite contents are shown in fig. 2, and the comparison of the test values and the predicted values of the martensite contents under the different cycles of 0.7, 0.9 and 1.1 strain amplitudes are shown in fig. 2, so that the predicted values, which are the martensite contents under the different cycles calculated by the martensite content calculation formula in the present patent, are very similar to the test values obtained by the test under the 0.7, 0.9 and 1.1 strain amplitudes.
The fit values of the material constants at 4 strain amplitudes are shown in Table 1 below:
TABLE 1
| Strain amplitude | k | q | m |
| 0.5 | -372.613 | 0.51857 | 1.13238 |
| 0.7 | -473.926 | 1.01661 | 2.51472 |
| 0.9 | -432.791 | 0.67634 | 1.55887 |
| 1.1 | -446.587 | 0.55144 | 1.26126 |
Polynomial fitting is carried out by taking the fatigue crack growth threshold value, the martensite content and the strain amplitude as an abscissa X and the fatigue life Y as an ordinate, so as to obtain a fitting curve as shown in fig. 3, and the relation among the fatigue crack growth threshold value, the martensite content, the strain amplitude and the life is expressed as follows:
Y＝258949.66601-139474.40055*X+24849.9213*X 2 -1460.70955*X 3
namely:
the fatigue life can be calculated through the model, and the method is applied to engineering practice. The fatigue life prediction model is simple, convenient to operate and apply and capable of guaranteeing the accuracy of a prediction result.
According to the method, an approximate crack expansion threshold is obtained by calculating the crack expansion threshold through an empirical formula, namely the approximate expansion threshold in the graph 3 is used as a reference, meanwhile, the martensite content under different cycles is substituted into a fatigue crack expansion threshold prediction model, so that a predicted fatigue crack expansion threshold is obtained, namely the predicted expansion threshold in the graph 3, the prediction accuracy of the fatigue crack expansion threshold prediction model is measured by comparing the predicted expansion threshold with the approximate expansion threshold, the predicted expansion threshold is very close to the approximate expansion threshold in the graph, and the fatigue crack expansion threshold obtained through the fatigue crack expansion threshold prediction model can be proved to have very high accuracy. The relevant data of the fatigue crack growth threshold calculated by the fatigue crack growth threshold prediction model of the test steel are shown in table 2.
Table 2 comparison of two threshold values at different strain amplitudes
And substituting the fatigue crack expansion threshold value, the martensite content and the strain amplitude value of the dual-phase steel into a fatigue life prediction model to obtain a fatigue life prediction result, thereby predicting the fatigue life of the dual-phase steel.
Fig. 4 is a schematic diagram of a result of comparing a fatigue life prediction result with an actual life, and it can be seen from the figure that the predicted fatigue life value in the graph is almost completely consistent with the actual life, that is, the trend of the actual fatigue life value in the graph, which indicates that the fatigue life prediction model can well predict the fatigue crack growth threshold of the TRIP dual-phase steel and predict the fatigue life based on the fatigue crack growth threshold, thereby providing a reference for engineering application of the dual-phase steel.
By comparison, the accuracy and the practicability of the fatigue crack growth threshold prediction model and the fatigue life prediction model for predicting the crack growth threshold and the fatigue life are verified. The verification result shows that the quantitative influence of the martensite content on the fatigue crack growth threshold is successfully characterized, the fatigue crack growth threshold prediction model can accurately predict the fatigue crack growth threshold in a larger strain amplitude range, and the fatigue life prediction model can well predict the life. And the two models can be predicted by only a small amount of material parameters, so that engineering application is facilitated. The model does not relate to meaningless fitting parameters, and can be calculated without a large number of experiments, so that the calculation difficulty and the parameter acquisition difficulty are reduced, and the model is convenient to popularize in multiple fields.
In addition, fatigue testing is a difficult challenge for the durability and reliability of the equipment, and the time and cost required is enormous. The model provided by the method can predict the fatigue crack propagation threshold under the reference martensite content and the martensite content under different strain amplitudes only by obtaining the reference martensite content, and the reference martensite content is usually selected as the martensite content data at room temperature, wherein the test data are easy to obtain. Compared with the traditional fatigue test, the fatigue crack expansion threshold and the fatigue life of different martensite contents can be rapidly and easily predicted, and particularly, the Young modulus E related to martensite and the material melting point Tm can be obtained in a non-destructive manner to characterize the martensite content.
The above examples are only illustrative of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention, and various modifications and improvements made by those skilled in the art to the technical solution of the present invention should fall within the scope of protection defined by the claims of the present invention without departing from the spirit of the present invention.
Claims (7)
1. A method for predicting fatigue crack growth threshold and fatigue life based on martensite content is characterized in that: which comprises the following steps:
s1, establishing a martensite content database of the dual-phase steel under different strain amplitudes and cyclic cycles, and constructing a martensite content calculation model based on the martensite content database;
s2, constructing a fatigue crack growth threshold prediction model, wherein the fatigue crack growth threshold prediction model specifically comprises the following steps:
wherein Δkth is a fatigue crack growth threshold; e is Young's modulus, tm is the melting point of the test steel, δb is tensile strength, δs is yield strength, R is stress ratio, f M Is the martensite content, n' is the cyclic hardening coefficientB is a fatigue crack propagation threshold coefficient;
s3, constructing a fatigue life prediction model, wherein the fatigue life prediction model is as follows:
wherein N is f For fatigue life, x, y and z are all intermediate parameters, f M Is of martensite content epsilon a For strain amplitude, Δkth is fatigue crack growth threshold;
s4, setting different strain amplitudes and cyclic cycles, taking a test dual-phase steel sample, respectively carrying out repeated cyclic loading under strain control by the different strain amplitudes, and recording the strain amplitudes and the cyclic cycles;
s5, substituting the strain amplitude and the cycle frequency obtained in the step S4 into the martensite content calculation model constructed in the step S1, and calculating the martensite content of the dual-phase steel by using the martensite content calculation model;
s6, substituting the martensite content obtained in the step S5 into the fatigue crack growth threshold prediction model in the step S2, and calculating the fatigue crack growth threshold of the dual-phase steel;
s7, substituting the fatigue crack expansion threshold value, the martensite content and the strain amplitude of the dual-phase steel into the fatigue life prediction model in the step S3, and predicting the fatigue life of the dual-phase steel.
2. The method for predicting fatigue crack growth threshold and fatigue life based on martensite content according to claim 1, wherein: the fatigue life prediction model in step S3 is specifically as follows:
3. the method for predicting fatigue crack growth threshold and fatigue life based on martensite content according to claim 1, wherein: the calculation formula of the fatigue crack growth threshold coefficient B in step S3 is as follows:
B＝F test on test *V Adding *Q Strong strength *L Delay line *b*T Shaft
Wherein F is Test on test For the test frequency, V Adding For sample loading rate, Q Strong strength The yield ratio is the ratio of the yield strength to the tensile strength, L Delay line Is the elongation of the dual-phase steel, b is the Bose vector, T Shaft Is an axial strain control parameter.
4. The method for predicting fatigue crack growth threshold and fatigue life based on martensite content according to claim 1, wherein: the martensite content calculation model in step S1 is as follows:
f M ＝-kε a [1-exp(-q4Nε a )] m
wherein f M Is of martensite content epsilon a For the total strain amplitude, N is the cycle number.
5. The method for predicting fatigue crack growth threshold and fatigue life based on martensite content according to claim 4, wherein: in the above formula:
wherein a, b, c, d, e, f, g, h, i, j, k and m are fitting parameters.
6. The method for predicting fatigue crack growth threshold and fatigue life based on martensite content according to claim 5, wherein: in the above formula:
7. the method for predicting fatigue crack growth threshold and fatigue life based on martensite content according to claim 1, wherein: the dual-phase steel is saving TRIP dual-phase stainless steel.
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