A Statistical Analysis on the Fatigue Life Characteristics of Structural Materials

2007 ◽  
Vol 353-358 ◽  
pp. 1137-1140
Author(s):  
Sang Tae Kim ◽  
Seong Soo Jang
Keyword(s):  
Fatigue Life ◽  
Statistical Analysis ◽  
Fatigue Loading ◽  
Structural Materials ◽  
Strength Degradation ◽  
New Method ◽  
Parameter Determination ◽  
Life Distribution ◽  
Degradation Model ◽  
Minimization Technique

A new method of parameter determination in the fatigue residual strength degradation model is proposed. The new method and minimization technique are compared experimentally to account for the effect of tension-compression fatigue loading on structural materials. It is shown that the correlation between experimental results and the theoretical prediction of the fatigue life, fatigue life distribution obtained by the proposed method is very reasonable.

A Thermal Fatigue Model for Probabilistic Lifetime Strength of Propulsion System Components

1993 ◽  
Author(s):  
L. Boyce ◽  
C. C. Bast
Keyword(s):  
High Temperature ◽  
Statistical Analysis ◽  
Thermal Fatigue ◽  
Inconel 718 ◽  
Strength Degradation ◽  
Material Strength ◽  
Central Feature ◽  
Degradation Model ◽  
Mechanical Fatigue ◽  
Current Value

This paper describes the development of methodology for a probabilistic material strength degradation model, that provides for quantification of uncertainty in the lifetime material strength of structural components of aerospace propulsion systems subjected to a number of diverse random effects. The model has most recently been extended to include thermal fatigue. The discussion of thermal fatigue, in the context of probabilistic material strength degradation, is the central feature of this paper. The methodology, for all effects, is embodied in two computer programs, PROMISS and PROMISC. These programs form a “material resistance” model that may be used in the aerospace structural reliability program, NESSUS or in other applications. A probabilistic material strength degradation model for thermal fatigue and other relevant effects, in the form of a postulated randomized multifactor interaction equation, is used to quantify lifetime material strength. Each multiplicative term in the model has the property that if the current value of an effect equals the ultimate value, then the lifetime strength will be zero. Also, if the current value of an effect equals the reference value, the term equals one and lifetime strength is not affected by that particular effect. Presently, the model includes up to four effects that typically reduce lifetime strength: high temperature, mechanical fatigue, creep and thermal fatigue. Statistical analysis of experimental data for Inconel 718 obtained from the open literature and laboratory reports is also included in the paper. The statistical analysis provided regression parameters for use as the model’s empirical material constants, thus calibrating the model specifically for Inconel 718. Model calibration was carried out for four variables, namely, high temperature, mechanical fatigue, creep and thermal fatigue. Finally, using the PROMISS computer program, a sensitivity study was performed with the calibrated random model to illustrate the effects of mechanical fatigue, creep and thermal fatigue, at about 1000 °F, upon random lifetime strength.

scholarly journals Engineering assessment of minimum fatigue life for given probability of its non-exceedance

2021 ◽  
Vol 1 (395) ◽  
pp. 55-64
Author(s):  
K. Proskuryakov ◽  
◽  
O. Shagniev ◽  
A. Shkadova ◽  
◽  
...  
Keyword(s):  
Fatigue Life ◽  
Cross Section ◽  
Analytical Formula ◽  
Structural Materials ◽  
Statistical Simulation ◽  
Life Distribution ◽  
Relative Cross Section ◽  
Number Of Cycles ◽  
Temporary Resistance ◽  
Cycles To Failure

Object and purpose of research. This paper discusses structural materials under cyclic load. The purpose is to determine the minimum fatigue life corresponding to a certain non-exceedance probability of this value. Materials and methods. The study was performed on three structural materials: steel 15ХМ, steel 08Kh18N10Т and titanium alloy PТ-7М. Initial estimate of fatigue life distribution parameters relied on the data about guaranteed maximum and minimum values of temporary resistance and relative cross-section tapering. The assessment was performed as per a common curve “conditionally elastic stress amplitude versus number of cycles to failure” taking into account the mechanical prop-erties of given material. The values of minimum fatigue life were obtained as per two different methods: statistical simulation of the random values following the Weibull distribution law and the analytical expression for probability density of the lows for given distribution function of random value and fixed scope of sampling. Main results. The lows yielded by statistical simulation are more conservative than those yielded by the analytical formula. The margin in terms of the number of cycles to failure stipulated as 10 in several regulatory documents seems to be somewhat unsubstantiated. This margin is too great in the low-cycle domain and too small in the high-cycle one. Conclusion. This paper postulates the existence of guaranteed maximum and minimum values for mechanical properties of structural materials, namely temporary resistance and relative cross-section tapering. These values were applied to well-known analytical curves of fatigue, which finally yielded possible variation ranges for fatigue life at various amplitudes of conditionally elastic reduced stresses, assuming the existence of a certain shift in the sensitivity limit of fatigue life distribution. These data were further used to establish standard deviations and mathematical expectations for the number of cycles to failure.

A New Model for Fatigue Life Distribution of Concrete

2007 ◽  
Vol 348-349 ◽  
pp. 201-204 ◽  
Author(s):  
Dong Fu Zhao ◽  
Qui Ying Chang ◽  
Jian Hui Yang ◽  
Yu Pu Song
Keyword(s):  
Fatigue Life ◽  
Test Data ◽  
Fuzzy Optimization ◽  
Fatigue Loading ◽  
Static Strength ◽  
Multiaxial Fatigue ◽  
Life Distribution ◽  
New Model ◽  
Kolmogorov Smirnov ◽  
Smirnov Test

Based on the S-N relationship and statistical property of concrete static strength, a function of fatigue life of concrete,1 (a − blog N) , is found to follow the normal distribution. Thus a new probabilistic model of fatigue life distribution of concrete is presented in this paper. The model connects statistical properties of static strength and fatigue life of concrete together in theory, so it is of clear physical meaning. An experiment was conducted. The experiment was a part of the project of The State Natural Science Foundation—Failure Criterion of Plain Concrete Under Multiaxial Fatigue Loading. 2 χ -test and Kolmogorov-Smirnov test are employed to test the proposed model. Fuzzy optimization is used to compare the model with lognormal distribution. 2 χ -test, Kolmogorov-Smirnov test and fuzzy optimization are also conducted for test data from references. The results show that the new model is more flexible to fit test data.

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