CN110909905A - Fatigue life prediction method for improving Coffin-Manson relation from energy perspective - Google Patents
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Abstract
The invention discloses a fatigue life prediction method for improving a Coffin-Manson relation from the energy perspective, which is characterized in that a cyclic hardening index and a cyclic strength coefficient are introduced on the basis of an energy life prediction model to obtain a Coffin-Manson equation improved from the energy perspective, and the fatigue life can be predicted more accurately.
Description
Technical Field
The invention relates to a fatigue life prediction method for improving a Coffin-Manson relation from the energy perspective, namely, a Coffin-Manson equation containing a cyclic hardening index and a cyclic strength coefficient is obtained on the basis of an energy life prediction equation.
Background
The energy structure mainly based on coal burning is one of the main causes of haze weather in China, and coal burning power generation is the most main power generation mode in China at present, and the trend exists for a long time. Therefore, besides changing the energy structure, the development of a high-efficiency clean Ultra Supercritical (USC) unit is one of the important ways of energy conservation and emission reduction. For an ultra-supercritical unit, the working temperature is over 700 ℃, and the main steam pressure is over 35MPa, so that the service life of a working component can be greatly shortened under the severe working environment. For the superheater and reheater, cyclic thermal stresses are experienced during startup and shutdown, as well as during operation when temperature gas flows vary. This means that such components often suffer from high temperature low cycle fatigue failure. Therefore, for a new generation of heat resistant steel to be applied to an ultra supercritical unit, prediction of its high temperature low cycle fatigue life becomes very important.
For decades, several methods for predicting high temperature low cycle fatigue life have been developed at home and abroad. Wherein mainly include: the method comprises the steps of establishing a fatigue life prediction model on the basis of a microscopic structure, establishing the fatigue life prediction model on the basis of a probability density function for generating defects, establishing the fatigue life prediction model by considering independent accumulated damage and establishing the fatigue life prediction model from the energy perspective. The energy life prediction model is a damage-based model, so that the fatigue life can be predicted more accurately. At present, the high-temperature low-cycle fatigue life prediction of novel heat-resistant steel is not systematically researched. Therefore, based on the angle of energy, the influence of the cyclic deformation behavior on the cyclic life is reflected more comprehensively by the obtained Coffin-Manson equation containing the cyclic hardening index and the cyclic strength coefficient, and therefore the precision of fatigue life prediction can be greatly improved.
Disclosure of Invention
The invention aims to provide a method for improving fatigue life prediction of a coffee-Manson relation from the perspective of energy aiming at the technical defects in the prior art.
The technical scheme adopted for realizing the purpose of the invention is as follows:
a method of improving fatigue life prediction of the Coffin-Manson relationship from an energy perspective, comprising the steps of:
wherein, is Delta WpIs hysteresis energy, and the unit is MJ/m3(ii) a n' is the cycle hardening index, dimensionless; k' is the coefficient of the circulating strength MPa,. DELTA.. epsilon p2 is the plastic strain amplitude in dimensionless units;
in formula (1) < delta > WpAnd Δ εpThe data are obtained from experimental data of fatigue process, n 'and K' are obtained by formula (2)
In formula (2): delta sigma/2 is a stress amplitude value, the unit is MPa, and the delta sigma/2 is obtained through experimental data of a fatigue process;
in formula (3): sigmamaxIs the maximum stress, the unit is MPa, and is obtained through experimental data of a fatigue process;
and 3, calculating material parameters m and C by software fitting:
n' obtained by calculation in the step 1 and delta W obtained through experimental data of the fatigue processp、NfAnd σmaxSubstituted into equation (4):
parameters m and C can be obtained by software fitting;
and 4, substituting the a obtained by the calculation in the step 1, the b obtained by the calculation in the step 2 and the m and C obtained by the calculation in the step 3 into the formula (3) to obtain a fatigue life prediction formula (5) for improving the Coffin-Manson relation from the energy perspective
The fatigue life N can be obtained by the formula (5)f，NfThe unit of (c) is weekly.
In the above technical solution, the software used for software fitting in step 2 and step 3 is Origin software.
In the above technical scheme, the fatigue process experimental data in step 1, step 2 and step 3 are a room temperature low cycle fatigue experiment, a room temperature high cycle fatigue experiment, a high temperature low cycle fatigue experiment and a creep-fatigue experiment.
Compared with the prior art, the invention has the beneficial effects that:
compared with the conventional prediction method, the fatigue life prediction method based on the energy life prediction model introduces the cyclic hardening index n 'and the cyclic strength coefficient K' to obtain the improved Coffin-Manson equation, and can predict the fatigue life more accurately.
Drawings
FIG. 1 is a relationship of stress amplitude and plastic strain amplitude for different total strain amplitudes;
FIG. 2 shows the fitting results of the energy life prediction model;
FIG. 3 is a graph of hysteresis energy versus plastic strain amplitude for different total strain amplitudes;
FIG. 4 is a graph of maximum stress versus plastic strain magnitude for different total strain magnitudes.
Detailed Description
The invention is described in further detail below with reference to the figures and specific examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Example 1
S1: novel heat-resistant steel Saniro 25 is selected as a research object. A series of low cycle fatigue tests with total strain amplitudes of 0.3%, 0.35%, 0.4% and 0.5% were performed at 700 ℃. For specific experimental procedures, reference may be made to the documents Jing H, Luo Z, XuL, et al, Low cycle failure analysis and microstructure analysis of a novel9 Cr-3W-3 Co temporal mapping at 650 ℃ [ J ]. Materials Science & Engineering A,2018,731.
S2: through the above experiments, the delta sigma and the delta epsilon can be obtainedp，ΔWpAnd σmaxThe numerical value of (c).
By stress amplitude delta sigma/2 and plastic strain amplitude delta epsilonpThe cyclic hardening index n' can be obtained from the relationship of/2: reference (G.J.Fan, H.Choo, P.K.Liaw, E.J.Lavernia.Plastic formation and fractional-fine Al-Mg alloys with a bimodal grain size distribution ActaMater 2006; 54:1759-
Wherein n' is calculated as follows: experimental data are fitted by Origin software, firstly, the experimental data are input in Origin, 4 experimental data are drawn in a coordinate system, then, an exponential function is selected for fitting, and the fitting result is shown in fig. 1, so that n ═ 0.17 and K ═ 1150MPa can be obtained.
The value of n' is then substituted into the following formula (2), reference (S.Zhu, H.Huang, L.He, Y.Liu, Z.Wang.Ageneralated energy-based-bed robust-sieve data parameter for life prediction of turbine disk alloys. Eng Frach 2012; 90:89-100.)
It is possible to obtain:
wherein: Δ WpIs hysteresis energy, and the unit is MJ/m3；σmaxIs the maximum stress in MPa; n is a radical offIs fatigue life in units of weeks; n' is the cycle hardening index, dimensionless, and m and C are material parameters, dimensionless.
By substitution of X
And replacement of 1/N with Yf. Equation (3) is modified as:
the experimental data were then fitted using Origin software, the fitting results being shown in fig. 2, with the following expression:
Y＝1.92×10-9X1.76, (5)
therefore, the coefficients of the terms are equal according to equations 4 and 5, and the values of m and C can be obtained, where m is 0.48 and C is 1.11 × 10-5。
Then n' is 0.17, m is 0.48 and C is 1.11 × 10-5The energy life prediction model can be expressed as:
the fatigue life N at a total strain amplitude of 0.4% was calculated by equation 6fp1336 and the actual fatigue life N obtained by experimentftThe deviation of the calculated values was within 9.95% compared to 1215. The calculation process is as follows:
the model can be proved to be capable of well predicting the high-temperature low-cycle fatigue life.
Hysteresis energy Δ W in equation 6 abovepThe theoretical formula (8) of (a) can be expressed as: (references: Sivaprasad S, Paul S K, Das A. cyclic plastic leather of primary leather transport materials: infiluence of loading schemes on hystersis loop. Mater Sci Eng, A2010; 527:6858-
In conjunction with experimental data for hysteresis energy (as shown in FIG. 3), we can revise equation 8 above, with the following results:
in addition, the maximum stress σmaxAnd magnitude of plastic strain Δ εpThe/2 relationship can be fitted as shown in FIG. 4, with the results shown below:
therefore, substituting equations 9 and 10 into equation 6, a modified Coffin-Manson relationship from an energy perspective can be expressed as:
the improved Coffin-Manson relationship from an energy perspective was verified:
by setting the parameter n 'to 0.17, K' to 1150MPa, Δ ∈ at a total strain amplitude of 0.3%p0.0542%, the fatigue life N can be obtained by substituting the formula (11)f9960, true fatigue life N from the experimentftThe deviation of the calculated value was 10.76% compared to 11161.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (3)
1. A method for improving fatigue life prediction of the Coffin-Manson relationship from an energy perspective, comprising the steps of:
step 1, obtaining a correction coefficient a by the following formula (1):
wherein, is Delta WpIs hysteresis energy, and the unit is MJ/m3(ii) a n' is the cycle hardening index, dimensionless; k' is the coefficient of the circulating strength MPa,. DELTA.. epsilonp2 is the plastic strain amplitude in dimensionless units;
in formula (1) < delta > WpAnd Δ εpThe data are obtained from experimental data of fatigue process, n 'and K' are obtained by formula (2)
In formula (2): delta sigma/2 is a stress amplitude value, the unit is MPa, and the delta sigma/2 is obtained through experimental data of a fatigue process;
step 2, calculating a parameter b through software fitting:
in formula (3): sigmamaxIs the maximum stress, the unit is MPa, and is obtained through experimental data of a fatigue process;
and 3, calculating material parameters m and C by software fitting:
n' obtained by calculation in the step 1 and delta W obtained through experimental data of the fatigue processp、NfAnd σmaxSubstituted into equation (4):
parameters m and C can be obtained by software fitting;
and 4, substituting the a obtained by the calculation in the step 1, the b obtained by the calculation in the step 2 and the m and C obtained by the calculation in the step 3 into the formula (3) to obtain a fatigue life prediction formula (5) for improving the Coffin-Manson relation from the energy perspective
The fatigue life N can be obtained by the formula (5)f，NfThe unit of (c) is weekly.
2. The method for improving fatigue life prediction of Coffin-Manson relationship from an energy perspective as claimed in claim 1, wherein said software in step 2 and step 3 is fitted with Origin software.
3. The method for improving fatigue life prediction of the Coffin-Manson relationship from an energy perspective as claimed in claim 1, wherein the experimental data of the fatigue process in step 1, step 2 and step 3 are room temperature low cycle fatigue test, room temperature high cycle fatigue test, high temperature low cycle fatigue test and creep-fatigue test.
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| CN113239477A (en) * | 2021-04-01 | 2021-08-10 | 四川大学 | Application of cyclic hardening model based on welding line dislocation entanglement in fatigue life prediction of welding joint |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108170905A (en) * | 2017-12-08 | 2018-06-15 | 南昌航空大学 | A kind of life-span prediction method under nickel base superalloy blade thermal mechanical fatigue load |
| CN108256192A (en) * | 2018-01-10 | 2018-07-06 | 中国科学院金属研究所 | A kind of Life Prediction of Thermomechanical Fatigue method of metal material based on low-cycle fatigue |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN108170905A (en) * | 2017-12-08 | 2018-06-15 | 南昌航空大学 | A kind of life-span prediction method under nickel base superalloy blade thermal mechanical fatigue load |
| CN108256192A (en) * | 2018-01-10 | 2018-07-06 | 中国科学院金属研究所 | A kind of Life Prediction of Thermomechanical Fatigue method of metal material based on low-cycle fatigue |
Non-Patent Citations (1)
| Title |
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| SHUN-PENG ZHU ETL.: "A generalized energy-based fatigue–creep damage parameter for life prediction of turbine disk alloys", 《ENGINEERING FRACTURE MECHANICS》 * |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN113239477A (en) * | 2021-04-01 | 2021-08-10 | 四川大学 | Application of cyclic hardening model based on welding line dislocation entanglement in fatigue life prediction of welding joint |
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