Failure Mechanism And Life Prediction For Gear And Structure Materials Under High Cycle Fatigue And Very High Cycle Fatigue

The gear,because it has the characteristics of high transmission efficiency,stable transmission ratio,long service life and high reliability,etc,is widely used in the field of aerospace,aviation and vehicle,etc.In view of the fact that the actual bearing load of the gear is more than 10~7 cycles,it is very important to carry out the research on the high cycle fatigue(HCF)and very high cycle fatigue(VHCF)characteristics,life evaluation and other aspects of gear and structure materials,which has extremely important significance on the implementation of general gear in design method.This paper starts with the characteristics of gear materials,considering the comprehensive effect of carburized layer and stress ratio,the HCF and VHCF behaviors of gear materials under constant/variable amplitude loading are investigated and the failure mechanism and life prediction methods are determined.Then,based on the contact stress distribution of gear under the actual load conditions,considering the effect of the failure mechanism and crack initiation and propagation behaviors,the gear contact and bending fatigue life prediction evaluation methods are constructed.The main conclusions are summarized as follows:(1)With the increasing of stress ratio,under the influence of carburized layer and the allowably applied maximum tensile stress,the failure probability of carburized Cr-Ni steel for the interior failure decreases and that for the surface failure increases;The decreasing of compressive stress and stress amplitude may restrain the fine granular area(FGA)formation with the increasing of stress ratio;The threshold value controlling surface crack growth,the threshold values controlling stable growth and the threshold value controlling unstable growth tend to decrease with the increasing of stress ratio;(2)Based on the failure mechanism and the probability statistics law,competitive failure mode of three kinds of fatigue failure modes are presented;For the interior failure with FGA,based on the dislocation energy method and the small+long crack propagation behaviors,the whole life prediction model involved crack initiation and propagation behaviors is established;For the interior failure without FGA and the surface failure,considering the influence of stress ratio,the fatigue crack propagation life method is constructed;In comparison with the experimental results,the prediction accuracy is fairly good within the factor-of-three boundaries;(3)When the maximum stress amplitude is determined,the variable amplitude fatigue life is greater than the corresponding fatigue life under constant amplitude loading and are regardless of stress series;Based on the method of dislocation energy,considering the comprehensive effects of stress series,failure mechanism,load sequence,the crack length and the mean stress,the variable amplitude fatigue life prediction and evaluation method of carburized Cr-Ni steel is established;In comparison with the experimental results,the prediction accuracy is fairly good within the factor-of-four boundaries;(4)Based on the numerical calculation model of three-dimensional dynamic gear,conbining with the local stress-life curve,the multiaxial stress criteria,the critical plane method and the dislocation energy method,four kinds of gear contact fatigue life model are established;By comparison,the initiation life model of the dislocation energy method which considering the effect of residual stress and crack size has the higher prediction accuracy;Based on the linear elastic fracture mechanics and crack growth rate,considering the comprehensive effect of the materials hardness,the stress gradient,the crack length,the residual stress and the crack propagation angle,conbining with the shear stress failure criterion,the contact fatigue crack growth life prediction model is established;Under higher stress level,the contact fatigue life is mainly consumed in the crack growth stage;In comparison with the experimental results,the prediction accuracy of the whole life model involved crack initiation and propagation behaviors,is fairly good within the factor-of-three boundaries;(5)Based on the the dislocation energy method,considering the comprehensive effect of the residual stress,the stress gradient and crack size,the gear bending fatigue life model is established;With the decrease of the stress level,the proportion of the fatigue crack initiation life in the whole life is becoming more and more larger;Based on the the maximum shear stress failure criterion and the damage evolution,conbining with the extended finite element method,the crack propagation path and the variation rule of stress intensity factor are determined and the bending fatigue crack growth life prediction model is established;In comparison with the experimental results,the prediction accuracy of the whole life model involved crack initiation and propagation behaviors,is fairly good within the factor-of-three boundaries.