Investigation Into The Formation Mechanism Of The Polygonal Wear Of HXD Electric Locomotive Wheels

Wheel polygonal wear is a difficult problem in railway industry.In recent years wheel polygonal wear has been found on high-and normal-speed trains and metro trains,making it become a research hotspot.The mechanism of wheel polygonal wear is complicated and different for different type of rolling stock.Sometimes the characteristics of wheel polygonal wear are different for the same type of rolling stock operating on different lines.Moreover,different researchers may have different opinions on the formation mechanism of wheel polygonal wear even for the same type of rolling stock.The wheel polygonal wear can significantly increase the vibration and noise levels of the rolling stock,and decrease the running safety and quality.Moreover,the vibrations induced by the wheel polygonal wear reduce the service life of components of rolling stock and track.Therefore,it is of great cognitive and practical importance to investigate the mechanism of the wheel polygonal wear.This dissertation focuses on the polygonal wear of HXD electric locomotive wheels and the research work involves:(1)The studies on wheel polygonal wear and wheel wear simulation in the past and present are reviewed.The significance and research orientation of wheel polygonal wear are indicated.(2)The characteristics of the out-of-round(OOR)wheels of electric locomotives in China are systematically investigated.The initial mechanism of polygonal wear of HXD electric locomotive wheels and its key influence factors are clarified through vibration tests conducted in the railway field and modal analysis of key bogie components.Improvement measures to mitigate the development of polygonal wear are proposed.The influence of wheel re-profiling with underfloor wheel lathe on the formation and development of wheel OOR is studied and measures to improve the re-profiling quality are presented.A new wheelset is designed to mitigate or eliminate the initial formation and development of wheel polygonal wear.The effects of the new wheelset are evaluated through the analysis of the characteristics of the dynamic response of the wheelset.Results indicate that the resorance of the wheelset should be responsible for the formation and development of wheel polygonal wear.Unreasonable wheel re-profiling plays an important role in the formation and development of wheel polygonal wear.The wheel polygonal wear can be eliminated or mitigated by improving the thickness of wheel web to change the dynamic characteristics of the wheelset and improving the wheel re-profiling quality.(3)The influence of wheel rail contact modelling on calculation accuracy of normal and tangential contact solutions is investigated in detail.Its influence on calculation accuracy and efficiency of wheel wear prediction is also studied to provide theoretical support for the selection of contact algorithm in wheel wear prediction model.Results show that using Hertz's method to solve the contact problem in wheel wear simulation may be a good choice from a compromise between the calculation efficiency and accuracy,but a validation is definitely needed to compare the simulation results with the field measured ones in the future.(4)A locomotive wheel wear prediction model is established,which includes a 3D locomotive-track coupled dynamics model,a rolling contact model considering the creep characteristics in the condition of large creepage,a proportional-integral(PI)based creep control model,a wheel material wear model based on wear index and wheel wear smoothing and updating strategy.A corresponding numerical algorithm is developed.The dynamics model is verified by commercial dynamics software SIMPACK and experiment results.The simulation results are in good agreement with both commercial software calculation results and test results.The wheel wear model established in this study is more completed and complicated compared with other models presented in published papers.The wheel wear prediction can be employed in online solutions rather than in post-processing.Moreover,this model can be employed to simulate the locomotive wheel wear under the condition of traction/braking,large creep or complicated wheel rail interface.The effects of track flexibility,wheel profile updating strategies,traction/braking control and wheel rail interface condition are investigated in detail.The results show that the flexibily of the track,traction/braking and creep control have nonnegligible influence on wear of locomotive wheels,which should be taken into account in wheel wear simulation.It is a better way to control creep by using a control mode with variable creep threshold value,which can not only guarantee the exertion of traction effort but also reduce wheel wear effectively.(5)Based on the wheel wear prediction model,a wheel polygonal wear simulation model is developed.The sub-model of locomotive is modelled with more details.The flexibility and rotation effect of the wheelset and the flexibility of the bogie frame are taken into account.A corresponding numerical algorithm is developed.The high frequency dynamic interaction between the locomotive and the track can be considered in the dynamics model,which makes it possible to study the initial formation of high order polygonal wear.The wheel polygonal wear model is a more advanced model compared with other models presented in published papers.It can consider the effects of the flexibility of the track and bogie and the traction/braking control on the initiation and development of wheel polygonal wear.A parallel calculation method is proposed to improve the efficiency of wheel polygonal wear simulation.The rigid-flexible coupling dynamics model of locomotive and track and the wheel polygonal wear model are validated by field measurement results.The simulation results are consistent with experiment results.The wheel polygonal wear prediction model is employed to study the influence of wheel flats,line slope and wheelset structure on the initiation and development of wheel OOR.The initiation mechanism of wheel polygon induced by wheel flats is revealed.The results indicate that it will cause the depth of wheel flat to deepen gradually and wheel polygonal wear if the scratch on the wheel is not dealt with in time.It is easy to induce high-order polygonal wear if the wavelength of wheel flat is less than 0.25 m.The track slope(or traction/braking forces)has a great influence on the development of wheel polygonal wear.The wheel polygonal wear will develop rapidly if the track slope is larger than 7.5‰.Changing wheelset structure can significantly affect the formation and development of wheel polygonal wear.