Study On Rail Development Rules Of Corrugation Based On Non-Uniform Material Properties

Rail corrugation is a periodic wear similar to undulation along longitudinal direction on top of rail,and a typical non-uniform wear phenomenon.In the scientific research and engineering practice,the rail corrugation formation and growth are closely related to the non-uniform of rail materials properties.The change of rail material properties from surface to bulk has an impact on corrugation growth by influencing the wheel-rail contact and rail wear.The weaken of materials mechanical properties of rail surface caused by rail decarburized layer aggravate corrugation growth.At the same time,in the process of corrugation growth,the corrugation peak and trough have different variation rule of mechanical properties.The difference between corrugation peak and trough will also affect corrugation growth;even decide on different corrugation growth trend in many cases.Therefore,it is of great cognitive and practical importance to investigate rail corrugation with non-uniform material for deeply understanding of corrugation phenomenon and appropriate measures to prevent.However,existing the constitutive relation of non-uniform material,wheel-rail rolling contact theoretical models and rail corrugation growth models can’t support the rail corrugation research considering the effects of non-uniform material.Firstly,existing research on rail corrugation lacks understanding regarding constitutive relation of non-uniform material.Secondly,the evolution rules of non-uniform properties of rail materials in the process of rail wear and evolution mechanisms of materials microstructure remains unknown.Thirdly,existing the wheel-rail rolling contact theoretical models rest on uniform materials assumption.The high demand of finite element method on computation resource prevents it from coupling with vehicle dynamics to calculate corrugation growth,resulting in the lack of wheel-rail rolling contact theoretical models with non-uniform material.Finally,existing corrugation researches can’t take into consideration non-uniform material properties,and it also can’t accurately reflect the corrugation growth under non-uniform material properties.To address the above problems,this dissertation focuses on the rail corrugation with nonuniform material and the research work involves:(1)The constitutive relation of non-uniform material are established.The elastic modulus,hardness and yield stress critical parameters of non-uniform rail material,such as decarburized layer and rail corrugation,are obtained using study methods of nano-indentation,finite element and dimensional analysis.Results show that the elastic modulus and hardness increase from rail bulk to the surface of the corrugation,and the values of corrugation trough is greater than peak.The elastic modulus and hardness near the surface are 40% and 73% high than those in the rail bulk.The residual stress decreases the limit of yielding,result in that the yield stress is lower near the “harder” trough than the “softer” peak.The variation rules of constitutive relation of non-uniform material are understood along depth direction and wheel-rail rolling direction.(2)In the process of rail wear,the evolution mechanisms of non-uniform properties of rail materials are investigated from the mechanical properties,damage mechanisms and microstructure points of view.The rail corrugation test stand was made and the laboratory reappearance of corrugation was achieved.The non-uniform properties of rail materials were investigated in detail during different wear period using techniques of microstructure and micro mechanical properties.The experiments show that form the initiation to the steady stages of corrugation,the damage mechanisms of peak and trough surface material transform from adhesive mechanism to fatigue mechanism,and the speed of transformation of trough is faster;the depth of plastic deformation of rail material due to wheel-rail rolling contact hardening gradually increases and approaches stable,and the plastic deformation is greater nearly trough than those nearly peaks;the elastic modulus and hardness of surface marital gradually increases and approaches stable,and the values of mechanical properties are greater nearly trough than those nearly peaks.(3)The two-dimensional wheel-rail rolling contact theory model that can consider the effects of non-uniform material is established.In this thesis proposes to release the uniform material assumption in classical wheel-rail rolling contact theory,derive wheel-rail rolling contact theoretical model that takes non-uniform material into consideration,and obtain a semianalytical solution of its displacement and stress field,combined with exponential layered model.The influences of non-uniform properties of rail materials on wheel-rail rolling contact behavior are incarnated by in this model,and the efficiency of this model accelerate nearly 4 times of the finite element methods,which solved a major problem that existing the wheel-rail rolling contact theoretical models only calculate uniform material and finite element method can’t couple with vehicle dynamics to calculate corrugation growth due to high demand on computation resource(4)The rail corrugation growth theoretical calculation model that can consider the effects of non-uniform material is established to study the influence of non-uniform properties on corrugation growth,which includes vehicle-track coupled dynamic model,wheel-rail rolling contact theoretical model and rail wear model that takes non-uniform material into consideration.It explained that the difference of mechanical properties between corrugation peak and trough is the basic reason of rail corrugation growth.The influence rule of elastic modulus and hardness on corrugation growth are clarified.The phenomenon that corrugation develops rapidly and approaches stable with non-uniform rail material is simulated,and the results show the different corrugation growth trend depend on the hardening ratio of trough and peak.When the ratio exceeds 2.2,depth of corrugation will approach stable.The more the hardening ratio,the faster the stability and the smaller the depth of corrugation.The problem that existing corrugation growth theoretical calculation model accurately reflect the corrugation growth failed to take into consideration the non-uniform material is solved.In this thesis,the constitutive relation of non-uniform material is established,the evolution mechanisms of non-uniform properties of rail materials are understood,wheel-rail rolling contact theory model and corrugation growth theoretical calculation model that can consider the effects of non-uniform material are established.The influence of non-uniform properties of rail material on corrugation growth is investigated in detail and clarified.