Study On Gear Contact Fatigue-wear Failure Competition Mechanism

Gear contact fatigue issues significantly restrict the transmission efficiency,fatigue life and reliability of mechanical systems such as wind turbines,helicopters,ships,etc.However,the micropitting mechanism and the variations of failure modes during wearing within the running-in period have not been fully revealed yet.Gear contact fatigue can be affected by numerous factors which are closely related to each other,leading to the competition of occurrences among several contact failure modes.This phenomenon may result in misjudgment of potential failure modes,or inappropriate gear design and manufacturing processes,together with difficulties in contact fatigue analysis.Herein,the contact fatigue failure mechanisms and the mentioned competition phenomenon of a megawatt level wind turbine gear pair are studied based on given conditions,considering multi-source surface integrity parameters.With a view to investigating the contact fatigue-wear failure competition phenomenon,a numerical gear contact fatigue model incorporating wear effect is established based on the elastohydrodynamic lubrication(EHL)and multiaxial fatigue theories.Several surface integrity factors are taken into account in the fatigue analysis to provide reference for gear design and failure precaution.Main work is described as follows:1)Gear contact pressure and subsurface stress-strain responses.Based on the rated working condition,together with the geometric and kinematic properties of the intermediate parallel stage gear pair chosen from the 2 WM wind turbine gearbox,the EHL contact model is proposed with measured surface roughness.According to the Hertzian contact mechanics,the subsurface stress-strain fields are fast estimated.In order to describe the multiaxial stress state during gear contact,the equivalent stresses are calculated based on several multiaxial fatigue criteria(e.g.,Dang Van criterion)considering carburized properties.2)The effect of gear surface roughness on contact fatigue.Based upon the EHL theory,the modified Dang Van diagram is applied to represent the contact fatigue failure risk during a complete loading cycle with the consideration of the hardness and residual stress gradients,addressing the effect of surface roughness.Results reveal that the effect of surface roughness on subsurface is limited.Increasing surface roughness root-mean-square(RMS)will lead to the rise of failure risk at near surface,where micropitting is more likely to occur.3)Competition mechanism analysis during wear process.Based on the proposed numerical model,the Archard's equation is employed to evaluate the gear surface roughness evolution.The Palmgren-Miner rule is used to linearly estimate the damage accumulation during cyclic meshing.Results suggest that the existence of wear mainly give rise to the competition phenomenon between pitting and micropitting.If the surface roughness RMS decreases to a low level,the micropitting risk during the whole gear meshing process may be completely eliminated.