Research On The Applicability Of The Cycle Counting Methods In The Statistics Of Aero-engine Load Spectrum

Aero engine load spectrum is the basis of fatigue life prediction and fatigue life test of the whole machine and its components.It is necessary to carry on the statistical analysis of the load in the fatigue life prediction and the compilation of fatigue test load spectrum,and the cycle counting method is the main method of load statistical analysis.Different cycle counting method is used to count the same load spectrum,and the different cumulative frequency distributions are obtained,which leads to different prediction life.Therefore,it is of great significance to improve the accuracy of fatigue life prediction by studying on the applicability of cycle counting methods.This paper expounds the cycle counting method for aero-engine load spectrum.The matlab's program of the peak counting method,simple range-mean counting method,rain-flow counting method and level-crossing counting method was compiled and verified.The load spectrum of aeroengine was filtered based on different threshold,the statistical analysis and comparison of the filtering results were carried out by using different cycle counting methods.In this paper,the fatigue life analysis method of the engine load spectrum is introduced.By using EGD3 standard,S-N fitted curve of 0Cr17Ni4Cu4 Nb material by experiment and linear cumulative damage theory,the predicted fatigue life under different cycle counting method is calculated.Finally,the fatigue test under the spectral loading is carried out.According to the above statistical results and the results of life prediction and test,the applicability of the cycle counting methods in the statistics of aero-engine load spectrum is obtained.The results show that the predicted fatigue life by the rain flow counting method is closer to the experimental results,the prediction results of the peak counting method are the most conservative,and the prediction results of the level-crossing counting method are also conservative,the prediction result of the simple range-mean counting method is unsafe;As the increase of the filtering threshold,regular coefficient of engine load spectrum also increases,the predicted fatigue life of the rain flow counting method is almost no change,the prediction result of the level-crossing counting method is not change very large,the prediction results of the peak counting method is obviously increased and the predicted fatigue life of the simple range-mean counting method is obviously reduced.Finally,the statistical results of each cycle counting method tend to be consistent.