CN110348167B - Determination of metal detail fatigue rated strength cut-off value DFRcutoffIs a probabilistic model method - Google Patents

Determination of metal detail fatigue rated strength cut-off value DFRcutoffIs a probabilistic model method Download PDF

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CN110348167B
CN110348167B CN201910659526.3A CN201910659526A CN110348167B CN 110348167 B CN110348167 B CN 110348167B CN 201910659526 A CN201910659526 A CN 201910659526A CN 110348167 B CN110348167 B CN 110348167B
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熊峻江
成正强
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Beihang University
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Abstract

Determination of metal detail fatigue rated strength cut-off value DFRcutoffThe method comprises three steps: step one, measuring fatigue performance data by a grouping method; step two, establishing a metal fatigue S-N curve probability model; step three, obtaining a metal detail fatigue rated strength cut-off value DFRcutoffAnd solving the formula. The method does not need to carry out the tedious work of evaluating the inclination parameter and the dispersion parameter, is simple and practical, has high precision, and can provide technical support for the structural strength design and the service life evaluation of the airplane.

Description

Determination of metal detail fatigue rated strength cut-off value DFRcutoffIs a probabilistic model method
Technical Field
The invention provides a method for measuring the metal detail fatigue rated strength cut-off value DFRcutoffBelonging to the technical field of fatigue reliability of metal material structures.
Background
The detail fatigue rated strength method is one of important design methods for fatigue strength design and service life evaluation of large airplanes in China. In practical applications, the design allowable values of the slope parameter and the dispersion parameter significantly affect the detailed fatigue rated strength value and the fatigue life of the aircraft structure, and the two design parameter values must be evaluated to ensure the safety and the reliability of the aircraft structure. However, the slope parameter and the dispersion parameter are influenced by various factors such as metallurgical quality and stability, process level and sample processing quality, and even though the same grade of domestic and foreign materials have different design allowable values, a large number of tests are required for measuring the slope parameter and the dispersion parameter of each material, and the test cost is high. Therefore, the invention provides a method for measuring the metal detail fatigue rated strength cut-off value DFRcutoffThe probability model method does not need to carry out the tedious work of evaluating the inclination parameter and the dispersity parameter, is simple and practical, has high precision, can provide technical support for the structural strength design and the service life evaluation of the airplane, and has very important engineering application value and academic significance.
Disclosure of Invention
1. The purpose is as follows: the invention aims to provide a method for measuring the fatigue rated strength cut-off value DFR of metal detailscutoffThe probability model method does not need to carry out the tedious work of evaluating the inclination parameter and the dispersity parameter, is simple and practical, has high precision, can provide technical support for the structural strength design and the service life evaluation of the airplane, and has very important engineering application value and academic significance.
2. The technical scheme is as follows: the invention provides a method for measuring the metal detail fatigue rated strength cut-off value DFRcutoffThe method comprises the following specific steps:
step one, grouping method for measuring fatigue performance data
Fatigue test with stress ratio of 0.06 is carried out on the metal material by using a grouping method, the fatigue performance data is measured, and the maximum fatigue stress S is recordediFatigue loading cycle number NiWherein i is a sample number;
step two, establishing a metal fatigue S-N curve probability model
Fitting to obtain an S-N curve probability model by using the measured metal fatigue performance test data:
Figure GDA0002883718930000021
in the formula, NpγThe fatigue loading cycle times under any reliability p and any confidence gamma, S is the maximum stress, S is0To fit the fatigue limit, m and C are material constants, upIs a standard normal offset, k is a standard deviation correction factor, and S is a normal distribution N (lg C-mlg (S-S)0),σz) Sample standard deviation of (1), tγIs the gamma quantile of t (n-1) distribution, n is the size of the subsample;
randomizing and logarithm taking the formula (1), and obtaining undetermined constants m and C by adopting a maximum likelihood method:
Figure GDA0002883718930000022
Figure GDA0002883718930000023
in the formula
Figure GDA0002883718930000024
Step three, obtaining a metal detail fatigue rated strength cut-off value DFRcutoffSolving formula
Metal material detail fatigue rated strength cut-off value DFRcutoffThe maximum stress corresponding to the number of fatigue loading cycles of 10 ten thousand times is determined in consideration of 95% reliability and 95% confidence under the condition that the stress ratio R is 0.06, and therefore, p is 95%, γ is 95%, and N are expressed in the formula (1)pγ＝105The corresponding maximum stress S is the detail fatigue rated strength cut-off value DFR of the metal materialcutoffTo obtain a solution formula of
Figure GDA0002883718930000025
In the formula
Figure GDA0002883718930000031
Drawings
FIG. 1 is a block flow diagram of the method of the present invention.
Detailed Description
Fig. 1 is a flow chart of the method of the present invention, which is implemented in three steps, specifically:
step one, grouping method for measuring fatigue performance data
Fatigue test with stress ratio of 0.06 is carried out on the metal material by using a grouping method, the fatigue performance data is measured, and the maximum fatigue stress S is recordediFatigue loading cycle number NiWherein i is a sample number;
step two, establishing a metal fatigue S-N curve probability model
Fitting to obtain an S-N curve probability model by using the measured metal fatigue performance test data:
Figure GDA0002883718930000032
in the formula, NpγThe fatigue loading cycle times under any reliability p and any confidence gamma, S is the maximum stress, S is0To fit the fatigue limit, m and C are material constants, upIs a standard normal offset, k is a standard deviation correction factor, and S is a normal distribution N (lg C-mlg (S-S)0),σz) Sample standard deviation of (1), tγIs the gamma quantile of t (n-1) distribution, n is the size of the subsample;
randomizing and logarithm taking the formula (1), and obtaining undetermined constants m and C by adopting a maximum likelihood method:
Figure GDA0002883718930000033
Figure GDA0002883718930000034
in the formula
Figure GDA0002883718930000041
Step three, obtaining a metal detail fatigue rated strength cut-off value DFRcutoffSolving formula
Metal material detail fatigue rated strength cut-off value DFRcutoffThe maximum stress corresponding to the number of fatigue loading cycles of 10 ten thousand times is determined in consideration of 95% reliability and 95% confidence under the condition that the stress ratio R is 0.06, and therefore, p is 95%, γ is 95%, and N are expressed in the formula (1)pγ＝105The corresponding maximum stress S is the detail fatigue rated strength cut-off value DFR of the metal materialcutoffTo obtain a solution formula of
Figure GDA0002883718930000042
In the formula
Figure GDA0002883718930000043

Claims (1)

1. Determination of metal detail fatigue rated strength cut-off value DFRcutoffThe method comprises the following specific steps:
step one, grouping method for measuring fatigue performance data
Fatigue test with stress ratio of 0.06 is carried out on the metal material by using a grouping method, the fatigue performance data is measured, and the maximum fatigue stress S is recordediFatigue loading cycle number NiWherein i is a sample number;
step two, establishing a metal fatigue S-N curve probability model
Fitting to obtain an S-N curve probability model by using the measured metal fatigue performance test data:
Figure FDA0002883718920000011
in the formula, NpγThe fatigue loading cycle times under any reliability p and any confidence gamma, S is the maximum stress, S is0To fit the fatigue limit, m and C are material constants, upIs a standard normal offset, k is a standard deviation correction factor, and S is a normal distribution N (lg C-mlg (S-S)0),σz) Sample standard deviation of (1), tγIs the gamma quantile of t (n-1) distribution, n is the size of the subsample;
randomizing and logarithm taking the formula (1), and obtaining undetermined constants m and C by adopting a maximum likelihood method:
Figure FDA0002883718920000012
Figure FDA0002883718920000013
in the formula
Figure FDA0002883718920000014
Step three, obtaining a metal detail fatigue rated strength cut-off value DFRcutoffSolving formula
Metal material detail fatigue rated strength cut-off value DFRcutoffThe maximum stress corresponding to the number of fatigue loading cycles of 10 ten thousand times is determined in consideration of 95% reliability and 95% confidence under the condition that the stress ratio R is 0.06, and therefore, p is 95%, γ is 95%, and N are expressed in the formula (1)pγ＝105The corresponding maximum stress S is the detail fatigue rated strength cut-off value DFR of the metal materialcutoffTo obtain a solution formula of
Figure FDA0002883718920000021
In the formula
Figure FDA0002883718920000022
。
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CN112487561B (en) * 2020-12-10 2023-05-02 北京航空航天大学 Method, system, equipment and medium for determining DFR of additive titanium alloy
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