Study On Gear Contact Fatigue-Wear Coupling Mechanism With Surface Micro Topography

With the urgent demand of heavy loading capacity and high power density,the problem of gear contact fatigue becomes increasingly prominent,which significantly restricts the transmission efficiency,fatigue life and reliability of gear-driven transmission systems such as wind turbines,helicopters,vehicles and ships.At the same time,under the combined effect of the tooth surface micro topography and the slide-roll movement,the tooth surface will be worn to some extent.The evolution of tooth surface micro topography results in prominent local stress concentration near the surface,severely affecting the service life of the gear.However,the mechanisms such as contact fatigue failure considering surface micro topography and the evolution of micro topography caused by wear have not been fully understood and revealed.Furthermore,the coexistence of fatigue damage and micro topography evolution increases the complexity of gear contact fatigue analysis.In many heavy-duty gear transmissions,aviation gear gears often fail due to tooth fatigue or wear.To solve this problem,an elastic-plastic finite element model of an aviation gear pair is developed based on its geometry and operating parameters in this paper.The fatigue-wear coupling failure analysis of gear pair is carried out.It is of great theoretical and practical significance to study the failure mechanism and failure competition mechanism of gear contact fatigue.In this work,the coupling failure mechanism of gear contact fatigue and wear is emphasized.The evolution process of surface micro topography is simulated based on the measured tooth surface micro topography and the classical Archard wear model during the gear repeated meshing process.The fatigue damage accumulations of critical material points on and underneath the contact surface is captured with the Brown-Miller-Morrow multiaxial fatigue criterion.And the elastic-plastic constitutive behaviors of damaged material points are updated incorporating the defined damage variable.A fatigue-wear coupling model of an aviation gear pair is developed based on the elastic-plastic finite element method.The failure competition mechanism of wear-fatigue coupling is studied aiming to provide some theoretical guidance for gear anti-fatigue design and failure prevention.Main contents are described as follows:1)Influence of micro topography on gear deformation and stress.Based on the working condition of an aviation gear pair and the experiment of measuring surface micro topography with optical profilometer,the finite element contact model of a gear pair considering the measured surface micro topography is established.Linear kinematic hardening elastic-plastic constitutive behavior is used.The contact state during the fifth gear rolling contact is adopted.The stress-strain results of a smooth surface and a rough surface are analyzed.The relationship between the contact area ratio and the normalized load,the results of contact pressure distribution and the results of maximum von Mises stress and maximum Tresca stress under different root mean square values of roughness are analyzed.The results show that with the increase of the root mean square value of roughness,the local contact pressure,surface displacement,maximum von Mises stress and maximum Tresca stress increase.Under the same load,the contact area ratio decreases with the increase of surface roughness RMS.2)Influence of micro topography on gear contact fatigue.Considering the measured surface micro topography,an elastic-plastic finite element model of an aviation gear pair is developed.The elastic-plastic behavior of the material is simulated by the kinematic hardening elastic-plastic constitutive behavior.The plane angle of the maximum shear strain is calculated based on the critical plane method,and the results of maximum shear strain amplitude,normal strain amplitude and mean normal stress are analyzed.And the influence of the surface micro topography on the shear strain amplitude,normal strain amplitude and mean normal stress on the critical plane is analyzed.The Brown-Miller-Morrow multiaxial fatigue criterion is used to analyze contact fatigue life of smooth surfaces,the influence of different surface roughness states on rolling contact stress history and contact fatigue failure risk in the meshing process.The results show that the fatigue life of the material points near the surface fluctuate greatly due to the existence of the surface micro topography,while the distribution of the subsurface fatigue damage is not affected.There is competition in the position where the minimum fatigue life occurs,that is,there is competition failure mechanism between surface failure and subsurface failure,and the competition result depends on the roughness level.3)Coupling analysis of gear wear and fatigue considering the evolution of micro topography.Based on the above finite element model of gear considering the measured surface micro topography,the Archard wear model is established by using the mesh motion constraint subroutine UMESHMOTION to simulate the evolution of the tooth surface micro topography in the gear cyclic contact.The degradation behavior of material properties is analyzed based on the elastic-plastic constitutive behavior coupled with damage.The Brown-Miller-Morrow multiaxial fatigue criterion coupled with damage is derived and the Miner damage linear accumulation criterion is adopted to calculate and accumulate the fatigue damage at the material points under the current loading block.The influence of root mean square value of roughness on contact failure mechanism of wear-fatigue coupling gear is investigated.The study shows that when the tooth surface wear is considered,the minimum surface displacement on tooth profile appears near pitch point due to nearly pure rolling condition.The farther away from the pitch point along tooth profile,the larger is the wear depth.The damage of material points at near surface asperities accumulates rapidly in early stage and as wear proceeds,their damage accumulation slows down.Under the given condition,the subsurface-initiated failure occurs when surface roughness RMS is below a critical level of 0.2 μm,while surfaceinitiated failure appears as RMS exceeds it.