Study On Gear Contact Fatigue Based On A Material Microstructure Sensitive Model

The research subject of the dissertation stems from the National Key R&D Program of China “Dynamic service characteristics and basic test of high performance gear”(Grant No.: 2018YFB2001300)and National Natural Science Foundation of China “Research on the damage evolution mechanism of gears contact fatigue based on micro-mechanics and continuous damage theory”(Grant No.: 51805049).With the development of mechanical equipment towards high power density and high reliability,the fatigue failure of gear has become the bottleneck of equipment reliability and human-machine safety.Among the factors influencing gear fatigue failure,the important role of material factor has been proved by a large number of references and engineering practice.In addition to the factor which is already known,such as hardness gradient,those material factors affecting the contact fatigue performance of gears also include microstructure,inclusions and phase states.These material factors influence each other and are coupled with working conditions and geometry factor,which increase the complexity of gear fatigue failure mechanism.Meanwhile,gear contact fatigue failure occurs at the near surface or sub-surface area,where suffer a typical multi-axial time varied stress state during the gear meshing process,this makes it is more difficult to reveal the contact fatigue failure mechanism of gear.In addition,adopting experiment method to explore the influence of material factors on gear contact fatigue failure is a time consuming task,the economic consumption is also unacceptable.Therefore,establishing microstructure sensitive model of gear contact fatigue analysis has great theoretical value and engineering significance.This work focused on the contact fatigue issue of typical large-module heavy-duty wind turbine gear.The numerical model of fatigue analysis incorporating multi-factor has been established to reveal the contact fatigue mechanism of gear.This work is expected to provide theoretical support to the anti-fatigue manufacturing and design.Main work is described as follows:(1)Modeling the gear material microstructure.Based on the experiment characterization,the microstructure sensitive model was established by considering the grain size gradient and the mechanical property gradient.The multi-phase model was established by considering austenite phase,martensite phase and subsurface inclusion.The stress-strain responses of microstructure sensitive model are analyzed and compared with the results from the traditional isotropic model.(2)Establishing the contact fatigue damage equation of gear upon the micro-level.The back stress evolution on slip systems is included to consider the influence of cycle loading on stress-strain responses.Based on the Fatemi-Socie criterion,the contact fatigue damage equation of gear upon the micro-level is established by considering the time varied multi-axial stress state during the gear meshing process.The fatigue indicate parameters and fatigue damage were calculated under the cycle loading process to evaluate the gear contact fatigue failure based on the stress-strain response on slip systems.(3)Investigating the effect of carburizing on gear contact fatigue.The mechanism of the improvement of gears contact fatigue resistance by hardness gradient was analyzed.The results show that the depth position and value of maximum fatigue damage of non-carburized gear are more sensitive to the grain orientation because of the coarse grain,which will trigger the contact fatigue failure.Carburization reduce the fatigue failure risk by improving the local strength and fine grain of gear material.(4)Analyzing the effect of phase states and inclusion on gear contact fatigue.The influence of inclusions and different phase states of surrounding matrix on contact fatigue failure of gears was analyzed by considering the fatigue damage and ratcheting damage.The results show that in the first few loading cycles,the austenite phase has higher ratcheting damage but the damage of martensite is dominated by the fatigue damage.Inclusion induced ratcheting damage occurs at the neighboring matrix within a highly localized area.The higher ratcheting damage is mainly found following the direction of approximately 45° with respect to the rolling direction.This result match well with the “butterfly wings” in the reference,indicating that ratcheting damage plays an important role in the formation of “butterfly wings” characteristic.