Research On The Fatigue Life Prediction Method Of Transmission Gears Of Aero-engine Accessory

As the heart of the aircraft,the aero-engine determines to a certain extent the development of China’s aerospace industry.The accessory transmission of an aero-engine is a key rotating component,which is subjected to mechanical loads such as centrifugal force,cyclic load and impact load under complex working conditions.Its structure,processing,assembly and working conditions are harsh and complex,and its reliability and life prediction is an urgent problem to be solved in current research.The lack of domestic experience in the independent development of gear materials and gear design has led to frequent failures such as tooth surface wear,tooth galling and tooth root fracture,with serious consequences.At present,for the research of fatigue life prediction methods of mechanical structures,the corresponding theoretical system has been formed in China,but there are still many problems that need to be solved.In this paper,considering the average stress,the interaction between the loads and the influence of uncertainty factors on the fatigue life,the fatigue life prediction methods are studied from the following three aspects:（1）A fitting formula for the Walker index was established and a strain-based fatigue life prediction model considering the effect of mean stress was proposed.In the Walker mean stress correction model,the sensitivity parameter was introduced to take into account the different degrees of influence of mean stress on different materials,making it a better correction for most materials,but the high cost of obtaining its Walker index limits the application in engineering.In this paper,by investigating the experimental data of different materials in the literature,a fitting formula for determining the Walker index was established by analyzing the relationship between the Walker index and the strength limit of the material,and an improved strain-life model considering the effect of average stress was proposed based on the M-C model.（2）A non-linear fatigue cumulative damage model considering the effect of loadinteraction was developed.By analyzing the mechanism of the effect of load-interaction on fatigue damage,it is found that under high-low loading,the load-interaction will shorten the fatigue life;while under low-high loading,the fatigue life will be extended.In this paper,an improved non-linear cumulative damage model is proposed on the basis of Duyi Yeh’s toughness dissipation model,taking into account the inter-load interaction effect.（3）Establishing a probabilistic fatigue life prediction method that considers the effects of uncertainty factors.Gears are often subject to a large number of uncertainties in operation,and the deterministic fatigue life prediction methods often do not yield satisfactory results.This paper adopts polynomial chaos theory to deal with the uncertainty problem,treats the uncertainty factors as random variables obeying a certain distribution,and combines the non-linear cumulative damage model proposed in Chapter3 to propose a probabilistic fatigue life prediction method that considers the influence of uncertainty factors.