Prediction Of Wheel-rail Wear And Optimization Of Rail Profile For Heavy Haul Railway

Heavy haul railway is the common development trend of railway transportation over the world because as it has large capacity,high efficiency and low cost.Among the diseases of wheel-rail system,the wheel/rail wear is the most widespread problem and is difficult to solve.The changes of wheel/rail profile due to wear significantly influence the wheel-rail contact status and dynamic characteristics of vehicle-track system,and further affect the running stability,safety of the train and the service lives of the parts of vehicle-track system.The wheel/rail wear problem is especially serious for heavy haul railway and vast maintenance work is needed.If over-worn wheel/rail is not replaced in time,major accidents such as derailment may happen.For the wheel/rail wear problem of heavy haul railway,a numerical prediction model of wheel/rail wear evolution is established based on the investigation of existing researches.The model can analyze and predict the distribution characteristics and development process of wheel/rail wear under actual operation situations.The influence of track flexibility in the wear calculation is explored firstly.In addition,systematical researches are conducted on the influences of key parameters and measures on the wheel/rail wear distribution and development.A new mathematical model for rail profile optimization is presented,and the R75 rail profile of heavy haul railway is optimized using this model.A modified profile of R75 rail is given.The main work and achievements are as follows.(1)A numerical simulation and prediction model of wheel/rail wear evolution is established.Considering the research status and existing problems on wheel/rail wear,the numerical simulation of wheel/rail wear evolution for heavy haul railway is studied deeply.A wheel/rail wear prediction model is established,which integrates the vehicle-track coupling dynamics calculation,wheel-rail rolling contact analysis,material wear model,simulation strategy of complex operation situation,adaptive step method for profile update,etc.Using the Archard material wear model,the wear depth distribution in wheel-rail contact patch is calculated based on the vehicle-track coupling dynamics simulation and wheel-rail local contact analysis.Simulations are conducted respectively for all possible cases and dimensionless weight factors are introduced in order to model the complex operation situations of railway.An adaptive step algorithm is adopted to update the wheel/rail profile,which can reduce the deviation accumulation and improve the stability and reliability of numerical model.Numerical experiments are conducted to analyze the influences of the grid density of wheel-rail contact patch on the distribution of adhesion and sliding zones,creeping force,wear depth,and the wheel/rail wear rate.The reasonable value of the grid density of contact patch in wear model is discussed.(2)The influence of track flexibility in the wheel/rail wear calculation is explored firstly.The influence of track flexibility is not considered in existing researches on numerical simulation of wheel/rail wear.In this paper,the influence of flexible track on the wheel/rail wear is explored.A simplified wheel/rail wear calculation model is established based on Pearce-Sherratt energy theory so as to raise the calculation speed.The simplified model is verified by comparing with the accurate wear model.The flexible track model is established based on the finite element floating reference frame approach(FE/FFR).The modal reduction technique is used to reduce the modal coordinate number of rail vibration and remove the high-frequency modes so as to decrease the computation cost.The vehicle system and flexible track system are coupled through specific wheel-rail contact algorithm and rail profile updating strategy.The influencing characteristics of flexible track on the wheel/rail wear evolution respectively for tracks with and without irregularities are studied through numerical experiments based on the established model.(3)The wheel/rail wear evolution laws are systematically studied for heavy haul railway under actual operation situations.The wear distribution characteristics and development laws of rails in tangent and curve sections as well as the wear distributions and developments of different wheels when the vehicle negotiates curves are studied through systematical simulation analyses.The results also verify the reasonability of the established wear prediction model.In addition,the wear development processes of every wheel are predicted for the actual vehicle running on Da-qin railway.(4)The influencing laws of key material and structure parameters and measures on the wear distribution and development are studied systematically,which provides theoretical references for the design,operation,and maintenance.Systematic numerical experiments are designed.The influencing laws of the main material and structure parameters(wheel/rail material hardness,rail cant,vehicle speed,axle load,etc.)and wear reduction methods(rail lubrication,etc.)on the wheel/rail wear level and distribution are studied systematically.And a series of suggestions and principles are given.The work can provide theoretical references for the design,operation and maintenance.(5)A new rail profile optimization model is put forward.An optimized profile of R75 rail for heavy haul railway is given,which can improve the wheel-rail dynamic interaction and reduce the wheel/rail wear development.The optimization design of rail profile of heavy haul railway is studied and a new mathematical model of rail profile optimization is put forward.The rail profile is parameterized as a generalized function for a series of coordinate variations of discrete points.Then an objective function is designed in order to achieve the best conformance between wheel and rail profile around contact point for all possible wheel-rail contact situations.During the construction of the objective function,a wheel-rail contact geometry algorithm is implemented to detect the contact point positions quickly.In order to meet some necessary conditions,a series of linear and nonlinear constrains are introduced.Then the optimization of rail profile is transformed into a typical mathematical nonlinear optimization problem with single objective,multiple variables,and multiple constrains.The sequential quadratic programming algorithm(SQP)combined with Lagrange function,quasi-Newton method are adopted so as to solve this optimization model efficiently and precisely.Based on the established optimization model,the R75 rail profile of heavy haul railway is optimized so as to better match the LM wheel profile.R75 optimized profile is put forward.Then the original and optimized profiles are compared systematically in profile geometry feature,wheel-rail contact geometry relationship,vehicle-track dynamic performance,and wheel/rail wear development.According to the results,the optimized profile can effectively improve the wheel-rail contact geometry relationship and dynamic interactions and reduce the wheel/rail wear development.It can be considered as a good choice for the rail design of heavy haul railway.