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Random Vibration Accelerated Test And Reliability Evaluation Of Small Samples Components

Posted on:2005-04-03Degree:DoctorType:Dissertation
Country:ChinaCandidate:C LiFull Text:PDF
GTID:1102360125453150Subject:Mechanical design and theory
Abstract/Summary:PDF Full Text Request
Under the background of requirement of scientific research item, theory and application of small samples components reliability test and reliability evaluation are studied.Reliability TestBased on random vibration accelerated fomula and supposed life distribution following exponent, log-normal and weibull, the model ,which is related to samples, accelerated stress, normal stress, work time, overload test time, confidence and reliability, is constructed. Samples are decreased by enhancing stress and increasing test time. In order to unchange products failure mechanism, the problem of maximum stress is discussed under accelerated life test. An optimum test designs method is prensted under many step-stress. And, the plan for step-stress accelerated life tests is provided by simulation annealing algorithm.Reliability Evaluation1 Parameters estimation. Parameters estimation methods of different life distributions are disscussed under constant stress tests and step-stress tests. Maximum likehilood-least square methods and a Bayes method for parameters estimation are studied.2 Small samples reliability evaluation. A reliability evaluation method for small samples products is presented based on classical methods, overload and stress-strength model. When fatigue life following lognormal distribution, fatigue life scatter factor(LSF) methods are constructed to evaluate component reliability with very small samples. Life standard error can be acquired basing on maximum entropy principle and fuzzy synehesis analysis. The mode of the life distribution takes into account the total fit, the consistency with fatigue physics and the safety of the tail regions. The quantitative comprehensive evaluation mode is constructedunder limited data based on information theory when life ststistical distribution satisfy the total fit, the consistency with fatigue physics and the safety of the tail regions. The definition of environmental factor are discussed. At the same time, environmental factor estimation fomula is provided combing with the result of parameter estimation under accelerated test. The common process of using environmental factor to synthesize the experimental data is illuminated.3 Based on the information of the power spectral density(PSD),the calculation method for predicting fatigue life of components under narrow band random vibration is proposed using random vibration theory,strength theory and Miner cumulative damage mode.And the calculation method can be coped with wide band random vibration according to the modified result of PSD.The life prediction method has the advantag of convenience to use and do not perform cycle counting.4 Local strain reliability.A probability density function of the strain applied is derived from random vibration theory.The curve approximated by the mean value and standard deviation cyclic strain-life curves of Coffin-Manson law.Cyclic life mean value and standard deviation functions can be acquired according to the inverting relationship between strain and life.The dynamic strain applied-strength model is presented on the basis of the probability density function of the strain applied and strength.Fatigue notch factor and theoretical stress concentration factor is used to modify the mean and standard error of fatigue strength respectively.The modified fatigue life prediction method is suitable for high cycle life components.5 System reliability comprehensive methods. Reliability comprehensive methods based on components information are presented when there is no complex system reliability information. The methods do not necessary to assume the components time-to-failure distribution. Thus, error of reliability and variance decreases. Complex systems reliability mean and variance can be acquired based on components reliability information, at the same time, the only restriction is that it must be possible to decompose the system into series or parallel elements. The test data of components are converted into the test data of the complex system based on th...
Keywords/Search Tags:Small samples, Random accelerated test, Parameters estimatoion, Fatigue life, Reliability evaluation
PDF Full Text Request
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