Contact Fatigue Crack Initiation And Life Prediction Of Rough Tooth Surface

Gear drives are widely used in important equipment,such as aerospace,high-speed rail,wind power,ships,and precision machine tools.Under the action of alternating loads,the tooth surface inevitably produces contact fatigue,and pitting,spalling,cracks and broken teeth occur.Such failures seriously affect the transmission accuracy of the transmission system,and even cause serious safety accidents.In order to prevent catastrophic accidents caused by gear failures in time,it is necessary to study the mechanism of failure and the rules of failure characteristics.However,the study of gear transmission systems has multiple tooth surface contacts,variable operating conditions,and many factors that affect the initiation of tooth surface contact fatigue cracks.The complexity of the rough tooth surface features has brought great significance to the research of gear contact fatigue mechanism.It is difficult to identify the fault characteristics in time when the mechanism of the initiation and change of gear contact fatigue cracks has not been fully clarified.Therefore,it is urgent to study the influence of rough tooth surface asperity contact on gear contact fatigue,reveal its influence on crack initiation mechanism and fatigue life,and study the time-varying stiffness of cracks at different stages and the initial under different loads.The crack life provides a solid theoretical basis and practical support for the continued development of gear fault feature identification.In this paper,a gearbox two-stage speed-increasing spur gear is the research object.Based on the fatigue contact theory,the real tooth surface asperity parameters are used to study the contact fatigue crack initiation mechanism of the spur gear.The asperity finite element contact model and time-varying contact model are established.The meshing stiffness model is used to study the influence of the rough tooth surface asperity on the crack initiation,and to predict the initial crack initiation and propagation life.The main research contents are as follows:(1)Based on the Hertz contact theory,establish a contact model of single and rough tooth surface considering the radius of curvature of the apex of the asperity,height and density of the asperity,and use the measured parameters of the real rough tooth surface to study the deformation of the asperity.Three stages and the distribution of gear subsurface stress-strain field,analyze the influence of matrix deformation on gear stress and strain,clarify the internal correlation of the curvature radius and height density of the micro-convex body on the contact load and contact area,and reveal the initiation of initial cracks on the gear tooth surface mechanism.(2)Detect any area on the tooth surface of the sample through the atomic force microscope AFM,and obtain the coordinate point data of the gear contact surface topography.According to the measured gear surface topography data,MATLAB is used to simplify the data and reconstruct the surface topography features.The morphological characteristics of different surfaces were simplified,and the finite element model of the single micro protrusion and the single micro protrusion considering the deformation of the matrix was established to study the influence of the deformation of the matrix on the elastoplastic contact of the micro protrusion.In order to compare and analyze the influence of rough peak distribution density and direction-related characteristics on the Von Mises stress of the subsurface,four different rough peak distribution forms were selected,and four finite element contact models with different roughness topography were established.Through the change of the maximum Von Mises stress on the subsurface,the influence of different roughness peak distributions on the initial fatigue crack initiation is pointed out.(3)Based on the energy method,the time-varying meshing stiffness of the initial crack at the tooth root and the initial crack of the index circle were calculated,and the influence of different initial crack positions on the time-varying meshing stiffness of the gear was studied.The time-varying meshing stiffness of the different initial crack lengths in 3 was analyzed and compared.The effect of variable meshing stiffness is calculated by the finite element method to verify the results obtained by the energy method.(4)Using the Coffin-Manson calculation model and Smith-Watson-Topper calculation model,the stress and strain values obtained from the finite element model were substituted into the formula to compare and analyze the influence of different rough peak distribution forms and morphological characteristics on the initial crack initiation life of gear meshing.The initial crack stress intensity factor is obtained by the finite element method,and the propagation life of different initial cracks is analyzed and calculated.