An Investigation On The Evolution Of Polygonal Wear Of Locomotive Wheels And Its Countermeasures

Polygonal wear that widely exits around the circumference of railway wheels can result in the poignant wheel/rail impacts and noise,ambient vibrations and radiation noise as well as the abnormal vibration problems,which therefore is a popular focus and attract extensive attention all around the world.The manufacturer has to aggrandize the axle load and traction power of the locomotives aiming to meet the increasing requirement upon the runing speed and hauling tonnage,which doubtlessly deteriorate wheel/rail interactions and exacerbate the evolution of wheel polygonal wear.Until now,the formation mechanism of polygon wear of railway wheels which attracts the most research attention is still unclear,and the according countermeasures are also lacking.Hence,it is of great significance to investigate the forming mechanism of wheel polygonization and implement the mitigation measures with propuse to slow down the resulting issues.This dissertation focuses on the evolution mechanism of locomotive polygonization and its effective countermeasures,which involves the following research work.（1）A heavy-haul train-ballast track spatially interactional model is extended based on the vehicle-track coupled dynamics theory proposed by Wanming Zhai,which mainly covers the heavy-haul train sub-model,track sub-ballast sub-model and wheel/rail interaction sub-model.The flexible effect of locomotive wheelsets is implemented in view of its effect on the evolution of wheel polygonal wear,and the influence of which on wheel/rail dynamic contact is also carefully considered.Moreover,the anti-slip control is also considered in the dynamics model since it plays an important role in bolding back the slipping phenomena of the powered wheelsets under poor friction conditions.（2）Wheel/rail rolling contact model has a significant influence on sloving wheel/rail frictional contact and wear propagated on wheel profiles.Commonly,the wheel/rail contact patch and its internal stress distributions exhibit the pronounced non-Hertzian features,especially with the worn profiles.Thus performing an exact and fast wheel/rail non-Hertzian contact model in train-track interaction simulations is of importance to depict the non-elliptic contact patch and its internal stress distributions.In term of this,the non-Hertzian normal model and according tangential model,namely the MKP-Yaw model and MKP-Fa Strip-Yaw model,are employed to respectively calculate the normal and tangential wheel/rail contact.Moreover,the USFD model based on non-Hertzian contact model,namely the MKP-Fa Strip-USFD model,is used to predict wheel polygonal wear,in which the changeable wheel/rail friction conditions（covering the dry,wet and greasy conditions）are treated.（3）The relationship between wheel polygonal wear and wheel/rail impacting contact and abnormal vibration problems occurring on traveling locomotives is meticulously studied based on the experimental and numerical investigations.The on-site measurements on wheel polygonal wear and locomotive vibrations suggest that the high-order polygonization has a direct effect on the medium-high frequency vibration behaviours of locomoitves,especially for the unsprung components.The 77～135 Hz vibration performances that recorded by the triaxial accelerometers are directly related to 16～19 and 24 harmonic orders wheel polygonal wear.（4）The effect of wheel polygonal wear on wheel/rail frictional contact with consideration of the complex wheel/rail adhesion conditions and traction/braking effort is analyzed by the established rigid-flexible dynamics model.The severe wheel polygonal wear can not only intensify the vertical wheel/rail impacts but can also aggravate the longitudinal interactions between the wheel and rail,especially when the adhesion condition is poor.That is to say,the serious wheel polygonal wear will increase wheel/rail wear and even affect the traction or braking efficiency of heave-haul locomotives.Moreover,the effect of characteristics of wheel polygonal wear on the dynamic interactions of wheel/rail system is also analyzed.The numerical results prove that wheel/rail interactions become more intense with a higher polygonal wear amulitude.On the other hand,wheel/rail interactions show a nonlinear trend with the increase of polygonal wear order.（5）The influence of flexible effect of wheelset and heavy-haul line on the initiation and development of polygonal wear of locomotive wheels is determined by the modal testings as well as train-track rigid-flexible coupled dynamics simulations.Extensive measurements of wheel polygonal wear were conducted on more than 40 heavy-haul electric locomotives.The tested wheels are divided into the normal operation and vibration alarm ones according to the monitoring information delivered from vibration monitoring system（VMS）installed on the locomotive unsprung parts.Prominent peaks around 17^th-19^th and 24^th harmonic orders can be found in vibration-alarm wheels,which correspond to the central wavelength of 160-250mm.The modal testing against the locomotive wheelset suggests that the natural frequencies of 81.2 Hz（manifested as first bending mode of wheelset axle）and 129.4 Hz（manifested as lateral bending mode of wheel disc）are close to the excitation frequencies of 17^th-19^th and24^th harmonic order wheel polygonal wear with the traveling speed of 68～76 km/h.It further suggests that the flexible deformations of the wheelset are the root cause of high-order wheel polygonal wear.Furthermore,the evolution of wheel polygonal wear can be more accurately obtained with consideration of the flexible effect of both locomotive wheelsets and track in train-track coupled dynamics and polygonal wear prediction simulations.（6）The effect of heavy-haul locomotive routing strategy,wheel re-profiling method and anti-slip control on slowing down the development of wheel polygonal wear is examined by on-site and numerical investigations.It is stated that the locomotives that travel on different lines can avoid the formation of high-order wheel polygonal wear and the resulting abnormal vibrations.The re-profiling method affacts the elimination effect of wheel polygonal wear to a great extent.The serious high-order wheel polygonizations can be eliminated thoroughly by the wheel lathe with a superior fixed form,and little development generated in the OOR wear of which after long times of operation.The development of wheel polygonal wear with excitation of a wheel flat,especially the high-order components(17^th～23^rd order polygonal wear),can be suppressed by adopting a relatively lower anti-slip control threshold with the purpose of reducing the dissipated energy in the low-adhesion region.