Time Dependent Random Fatigue Analysis Based On Point Estimate Method And Its Applications

Fatigue failure is a common physical phenomenon in aeronautical engineering,mechanical engineering, ship engineering, communication and transportationengineering, civil engineering and so on. There are many accidents raised from fatigue.For example, airplane and nuclear pressure vessel and bridge, they have the risk ofserious fatigue failure. The paper research random fatigue employed the point estimatemethod and by using theoretical analysis and test data, and illustrate the analysisprocess by the applications of the random fatigue analysis based on the point estimatemethod in the power transmission tower system. Mainly include the following contents:(1) Based on the shortage of current counting methods, the time dependentcounting method (TDCM) of suiting the time dependent damage analysis is establishedby researching the previous typical counting methods. First, the counting principle ofthe previous typical counting methods and implement method are introduced; theshortage especially in the time dependent damage analysis be found by qualitativeanalysis and making use of the results of correlative documents. Second, utilized theideal of increment dynamic analysis, the time dependent counting method which canuse the previous results is developed, and the high efficiency of the propositionalmethod for the time dependent fatigue damage analysis is verified by theoreticalanalysis. Finally, by two examples, the counting results of the Bannantine method andthe Amzallag method are comprised and the validity of time dependent counting methodis proved. It’s worth noting that the Bannantine method, the Amzallag method, the timedependent counting method have the same results, but have different sequence of thepairs of amplitude-mean.(2) The deterministic time dependent fatigue analysis method is presented, and themethod is used in the wind-induced fatigue process of a power transmission towersystem. In the First, the common rain flow counting methods are replaced by the timedependent counting method, and the general method of time dependent fatigue analysisis established; and then, based on the general method, to aim at different condition, theapplicability of method is verified to the classical time dependent fatigue analysismethod; at the last, the time dependent fatigue analysis is carried out to a actual powertransmission tower system.(3) The point estimate method of statistical moment is expanded to the field of mixture distribution variables; the general applied point estimate method are developed,and it is combined to the time dependent counting method to present the random fatiguedamage analysis method. In the first place, the several method of statistical moment isintroduced. And then, the difficult of the previous point estimate method for treatingmixture distribution variables system is found by analyzing these methods. Next, byemploying the simple and rational processing method, based on the Zhao&Onomethod, the point estimate method involving mixture variables is presented, and itsrationality is examined by cases. And then, the framework of random fatigue damageanalysis is established by combining point estimate method with the idea ofdeterministic fatigue damage analysis.(4) The random fatigue analysis method based on the point estimate method isapplied to the power transmission tower system. Firstly, the probability density functionof average wind speed is calculated by employing the meteorological data ofsomewhere in Chongqing. Secondly, considering the randomicity of average wind speedand S-N curve model, the computer points and weight coefficient is calculated by thepoint estimate method. Then, random wind load is simulated by the compuer points ofaverage wind speed, and is loaded in the power transmission tower system. Finally, thefirst four moment of key member of tower body is calculated.