Influence Of Hollow-worn Wheels On Metro Vehicle Dynamic Performance And Rail Rolling Contact Fatigue

Hollow wear is a common form of metro wheel wear.Serious metro wheel hollow wear will affect vehicle running performance and easily lead to wheel–rail rolling contact fatigue(RCF),which not only affects the operation safety of the vehicle,but also increases the maintenance cost of the vehicle and track.Therefore,it is very important to study the influence of metro wheel hollow wear on vehicle–track interaction(e.g.wheel–rail contact relationship,vehicle dynamic performance,wheel–rail RCF)to ensure the safety of the vehicle operation and to formulate reasonable maintenance strategy.Aiming at the problem of serious wheel hollow wear of a metro line in China,this thesis investigated the influence of metro wheel hollow wear using both field test and numerical simulation.The main work and conclusions are as follows.(1)The wheel–rail profiles were measured and the wheel–rail surface state was observed on the metro line.It is found that hollow wear is the main wear form of wheels with almost no flange wear.When the tread wear exceeds 1 mm,the wheel tread begins to be hollow.There is an approximate linear relationship between the hollow wear and the tread wear.After three years of operation,the rail wear is small,showing vertical wear and small side wear.The fatigue damage at gauge corner of high rail is serious on the curves with radii of 400 m,600 m and 800 m.The vibration test of the vehicle is carried out and it is shown that the lateral ride quality of the vehicle with hollow-worn wheel is better than that of the vehicle with new wheel in most sections.(2)A metro vehicle dynamic model was developed and verified by measured vehicle vibration data.Based on the interpolated wheel profile,the influence of hollow wear on wheel–rail contact geometry and vehicle dynamic performance was investigated.The results show that with the development of hollow wear,the wheel–rail contact points change from the initial uniform distribution to three regions: the middle part of the tread,the root of the flange and the inner part of the false flange.The development of wheel hollow wear increases the rolling radius difference and equivalent conicity and reduces the nonlinear critical speed,however,improves the curving performance.For the metro vehicle studied in this thesis,hollow wear has little effect on vertical ride quality,but can improve the lateral ride quality of the vehicle.(3)Based on the surface fatigue index and damage function,the influence of wheel hollow wear on rail RCF damage was investigated.Under the action of the leading wheelset of the bogie,wear damage occurs on the top of low rail,while RCF damage occurs at the gauge corner of high rail.For the trailing wheelset,RCF occurs on the field side and gauge corner of low rail,but wear occurs on the top of high rail.However,the wear and fatigue damage for the trailing wheelset are much smaller than those of the leading wheelset.The development of wheel hollow wear will increase the wear width of rail top and make the range of fatigue damage at the gauge corner be more concentrated.Based on the interpolated wheel profile and the metro line studied in this thesis,the fatigue damage of the high rail is serious in the curves with radii of 450～500 m.The RCF is more serious with rail side lubrication than without rail side lubrication for curve with radius of 400 m.For the curves with radii of 400 m,600 m and 800 m,the rail fatigue damage for 1/20 rail cant is smaller than that for 1/40.The smaller the curve radius is,the more obvious the rail fatigue damage decreases.For the curves with radii of 600 m and 800 m,the hollow-worn wheel matches better with the worn rail and the fatigue damage of the rail is smaller.(4)A three-dimensional finite element model of wheel–rail elastoplastic contact was established.Based on the interpolated wheel profile,the influence of wheel hollow wear on the shape of wheel–rail contact patch,contact stress and equivalent stress of rail under different wheelset displacement and yaw angle was investigated.The results show that the yaw angle has little effect on the contact patch,and only makes the contact patch shift in the longitudinal position.When the vehicle passes the curve,because hollow wear increases the rolling radius difference,the development of wheel hollow wear reduces the lateral displacement of the wheelset,but still increases the wheel–rail contact stress and the equivalent stress of the rail,makes the position of the maximum equivalent stress of the rail move from the subsurface to the surface,which lead to the plastic deformation of rail surface material and rail RCF.For the motro vehicle studied in this thesis,according to the variation of equivalent stress and plastic strain of rail when different hollow-worn wheels matching with the rail under the lateral displacement of 3 mm of wheelset,the re-profiling threshold of wheel hollow wear is suggested to be 0.75 mm in order to mitigate rail RCF.