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Research On Fatigue Life For Structures Under Random Vibration Loading

Posted on:2018-07-01Degree:MasterType:Thesis
Country:ChinaCandidate:F YeFull Text:PDF
GTID:2322330542984942Subject:Structural engineering
Abstract/Summary:PDF Full Text Request
As one of the main failure modes with strong sudden and severe destruction,fatigue is the focus of attention in the design of engineering.The length of structure's fatigue life is closely related to the form of fatigue load,and in the actual loadings always have a great deal of uncertainty.However,currently researches devote more on the conventional fatigue loads,ignoring the randomness of fatigue loading.Thus,the systematical study on the fatigue life estimation under random vibration has great theoretical significance and engineering practical value.Random fatigue has a multidisciplinary theoretical background.It is a combination of statistical theory,structural dynamics,communication noise,and concepts and methods of stochastic mathematics with mechanical vibration.Firstly,the definition and characteristics of random process was expounded,and the methods of random fatigue life estimation was introduced in detail based on the time domain method and the frequency domain method.In the fatigue life estimation of wideband stationary Gaussian random process,the frequency domain method has been widely used with its fast and efficient characteristics.Secondly,simulations on power spectral densities with different types were performed,the general process of frequency-domain and time-domain conversion was proposed with MATLAB,and the rain flow counting method was programed to calculate the rain flow fatigue life of the structure.The comparisons of accuracy and applicability were made between the currently common frequency domain methods through the different types of simulated spectral and different materials.Then by constructing a series of typical wideband spectral-band-limited white noise,the fitting models of rain-flow amplitude and mean probability density function were obtained,the functional relationship was established between the probability density functions and spectral parameters.For wideband stationary Gaussian random process,the fatigue life prediction model considering the mean stress was put forward,and a new method for random fatigue life estimation based on frequency domain was derived.Furthermore,the new method was applied for random fatigue life estimation of the various simulated spectra and materials.Results showed that the proposed method has better universality,and could significantly reduce the error.At last,based on random vibration theory and stochastic fatigue strength theory,the finite element software ANSYS was used for the dynamic characteristics analysis of blade structures under random vibration loadings,and the stress response power spectral density curve was obtained.With the three-parameter S-N curve formula and Miner linear cumulative damage theory,a variety of frequency domain methods and the proposed new method were applied to estimate fatigue life,in comparison with the traditional rain flow counting method.And it was proved that the proposed new random fatigue life estimation frequency domain method could give a satisfactory life prediction result,so it could be served as a recommended method for random fatigue life estimation in the field of civil engineering.
Keywords/Search Tags:Random fatigue, Life estimation, Frequency method, Power spectral density, Rain flow counting, The probability density distribution
PDF Full Text Request
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