| The quantitative prediction and comprehensive appraisement of maneuverability of self-propelled gun have provided theoretic foundation for maintenance guarantee of weapon equipments. Based on the transmission gears, this paper has studied systematically the method of fatigue lifetime prediction under stochastic loads, through probability statistics, finite element and fatigue analysis. The influences of uncertainty of load statistical distribution, finite element model and mechanical performance parameters of material on fatigue life prediction are analyzed.Firstly, based on simulated random loads, the parameters estimation and validation of probability distributions of mean and amplitude value are carried on using rain flow counting and correlation coefficient method. By the weight coefficient method and probability density method, the two-dimensional joint probability density function is synthesized and mean and amplitude values are extended. As a result, 1×8 and 8×8 load spectrums are established. Simultaneity the original load sequence is revisesed considering load distribution along contact line, the effect of load distribution on the characteristic parameters of load spectrum is discussed.Secondly, the numerical simulation of bending stress and contact stress of gear are carried on by finite element method. The effects of boundary condition and grid quality on analysis result are discussed. Based on stress of hazard points, the stress spectrum used for fatigue analysis are established.Thirdly, based on P-S-N curve of material, stress concentration factor, size factor and surface quality factors, P-Sa-Sm-N surface is fitted according equilife curve. Fatigue life prediction has been carried out respectively based on MM-Miner rule and EM-Miner rule. Moreover, the interval of fatigue life between 50% and 99.9% reliability is presented.The results show that amplitude value obeys weibull distribution and mean value obeys normal distribution. The adaptability of transmission gears is better and side-decelerator gears' is worse. In relation to one dimensional load spectrum, fatigue life under two-dimensional load spectrum is smaller and fatigue life considering load distribution along contact line is smaller. |
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