Failure Mechanism And Experimental Investigation Of Fatigue Pitting For Spur Gear

Gears are widely used in various mechanical equipment due to the advantages of large carrying capacity, high transmission precision, fixed transmission ratio and compact structure. Recently, with the demand of heave load and high torque gear, the steady performance and durability of gears become critical. The lubrication state and fatigue failure of tooth surface are all research emphasis. Most gear failures belong to surface damage, which fatigue pitting is one of the most common surface failures, can produce tooth profile errors and vibration noise, and even lead to major equipment failure.Based on the elastohydrodynamic lubrication (EHL) theory, the roughness of surface topography, the subsurface stress state of 40Cr spur gear in a single meshing period under the condition of pure rolling contact and sliding contact was studied. The equivalent cylindrical rollers were used to simulate and analyze the fatigue pitting process under the same EHL conditions, the occurrence, development and morphology characteristics of micro-pitting under different tooth surface stress level were contrast analyzed. The formation mechanism of micro-pitting and macro-pitting was obtained by combining theoretical analysis and experimental investigation. The results show that micro-pitting and macro-pitting are a gradual fatigue phenomenon under the action of the shear stress, the shear stress of subsurface is a major factor leading to tooth surface fatigue pitting. Meanwhile a new multiaxial fatigue life prediction model was built, the major research contains three parts:(1) Gear meshing process model built. Determine the distribution trend of radius, speed, slide-roll ratio and engaging force of gear meshing point, and simplify the meshing point model as a foundation for the subsequent EHL analysis.(2) EHL properties research of rough tooth surface. A general three dimension surface roughness model was established based on fractal theory. Taking full account of roughness, lubrication and deformation, a unified EHL model including Reynolds equation, film thickness equation, lubricating oil viscosity-pressure equation, dense-pressure equation, load balancing condition equation was built and solved. The tooth surface stress state in a single meshing period and the EHL characteristic differences under smooth surface and rough surface condition were researched.(3) The investigation of fatigue pitting failure mechanism and the life prediction model built. Calculating tooth surface and subsurface stress based on the tooth contact characteristics and elastic mechanics, the trends of subsurface stress were assessed in single meshing period. Pitting development process was explored under specific operating conditions through cylindrical roller friction and wear test, next the failure pitting failure mechanism was explained in terms of stress state through comparing the theoretical analysis and experimental results. Finally, a new multiaxial fatigue life prediction model was built based on material property, stress history and the uniaxial fatigue data.