Analysis Of Contact Performance And Near-Surface Stress For Transmission System

Gear is an important part of mechanical transmission system,which has a wide range of applications in many fields such as aerospace,vehicle and etc.When the gear is in meshing transmission,the gear surface comes into contact and elastically deforms.Usually,a high-level stress concentration occurs at the contact asperities for the actual rough surface,causing uneven stress distribution and serious wear.In order to reduce the direct contact between the surfaces,lubricating oil is added between the contacting surfaces.Lubrication can reduce the direct contact between surfaces,which is particularly important for reducing friction and wear and prolongating service life.However,the property mismatch properties of the coating and the substrate causes stress concentration at the interface,which leads to the initiation and propagation of cracks,especially under the condition of fretting contact.In this paper,numerical methods are applied to study the stress distribution of the contact between the regular rough surface.The influences of gear transmission ratio on the thickness and pressure of the lubricating oil film are analyzed.The starved lubrication behavior mechanism of the gear with coating structure when the surface is rough is analyzed.Finite element method was used to study the variation of contact stress with coating on the contact surface.The main research contents of the thesis are outlined as follows:(1)This paper establishes a two-dimensional model of line contact.Elastic deformation characteristics of the surface after loading and morphology characteristics of rough surface are taken into account.Considering the influence of the actual rough surface considering the running-in effect,this paper adopts the moving average filtering method to simulate the surface morphology after the running-in process.Numerical methods are used to study the stress distribution of rough surface contact.The results show that the established numerical model can quickly and accurately calculate the stress in the contact area.When the circular surface is in contact with the micro asperities on the plane,stress concentration will be formed in the contact area of the micro asperities.The stress will increase due to the influence of the tangential force,and the near-field stress will shift along the friction direction.(2)Based on the theory of line contact elastohydrodynamic lubrication and the meshing process of gear transmission,a starved lubrication model for gears was established.Firstly,the influence of gear transmission ratio on thickness and pressure of lubricating oil film during gear transmission is studied;secondly,the influence of sine shape and actual roughness on the oil film thickness and oil film pressure during gear meshing is analyzed;finally,the effect of the coating modulus and inlet oil film thickness on the oil film stiffness is studied.The results show that model can be applied to rough surface conditions.When the working conditions and the number of pinion gears remain unchanged,the pressure of the central oil film decreases and the thickness of the central oil film increases with the increase of transmission ratio;the oil film thickness and oil film are greatly affected by the change of load and entrainment velocity during the meshing period of gear in starved state.The stiffness of the oil film increases with the Young’s modulus of the coating,and the thickness of the inlet oil film hardly influence the stiffness of the oil film.(3)A finite element model of micro-slip contact was established to study the contact stress at coated contact surface and the stress concentration at the interface.The influence of different loading processes on the friction force of micro-slip contact surface is analyzed.The stress on the contact surface increases as the Young’s modulus of the coating increases,and stress concentration is formed at the interface.The stress on the contact surface decreases with the thickness of the single coating increases.When the tangential force is considered,the stress on the contact surface increases with the increase of the friction coefficient and tangential force,and the near-field stress in the coating will shift along the friction direction.The contact conditions are determined by the tangential force and independent on the loading history.