Method Of Determining The Load Sample Size Of The Wheel Loader Axle Shaft Based On The Multi-criteria Technology

The loaders work in complex operating conditions, hence the tested load timehistory should be accomplished in various regions in order to well estimate thevehicle's overall performance. As the experimental period of the whole-life load timehistory test is very long and a lot of manpower and material will be spended, enoughtypically sample load spectrum is the only reasonable issue to focus on. It is thecritical basis to accomplish the establishment of typical operating conditions of loadspectrum analysis, improvement of the currently service equipment and thecomponents reliability. The load spectrum is the foundation for estimating the fatiguelife and reliability analysis.This paper is carried out based on the National Natural Science Foundationfunded project, named: Research on the key technologies for compiling the loadspectrum of engineering vehicles transmission. In this paper, how to omit the smallamplitude load cycles and the method to determine the optimal sample size based onthe multi-criteria technology are investigated first, after which the whole-life loadspectrums of the semi-axle on the operating conditions of Primary Soil, Block Stoneand Small Stonework are complied. Finally, the fatigue life of the semi-axle under thethree operating conditions are estimated.The specific contents of this article are as follows:(1) Obtain the valid load signal for the estimation of the sample size. Thecharacters of the load time history of the semi-axle are analyzed from the aspects ofload cycles and load extreme values. According to fatigue damage and POT theory, acriterion for omitting the small amplitude load cycles is provided, which can be usedto exactly obtain the valid load time history for estimating the sample size.(2) Establish the method for estimating the optimal sample size based on multi-criteria technology. By comparing the classic methods to estimate the loadsample size of engineering vehicles, the advantages and disadvantages of eachmethod can be concluded. Based on the multi-criteria technology and the existedmethods, the load cycles, the mean of load extreme value and the standard deviationof load extreme value are selected as the criteria for estimating the optimal samplesize. The optimal sample sizes of the Primary Soil, Block Stone and Small Stoneworkare provided also.(3) Compile the whole-life load spectrum of the operating conditions. The loadsignals as the load amplitude, load mean and the cycle frequence can be obtainedusing the rain-flow counting method. By fitting the distribution functions of the meanand amplitude under multiple operating conditions, the joint probability densityfunction of the mean and amplitude can be determined, by which the whole-life loadspectrum under various operating conditions are also compiled. Further, thewhole-life load spectrum according to different sample sizes are also provided forchecking the validity of the estimated optimal sample size.(4) Predict the fatigue life of the semi-axle. The model of the drive axle isestablished first, and after refining the structure, the finite-element analysis of thesemi-axle is carried out. Then, according to the Miner theory, the fatigue life of thesemi-axle under various operating conditions are estimated using the Nsoft.The method for determining the optimal sample size based on multi-criteriatechnology takes multiple load characteristics into account, so the estimated samplesize will be reasonable and credible. And the method has more practical value in thefield of determining the sample size and compiling the load spectrum accurately.