Research Of Curvature And Residual Stress Before Straightening On 100-meter Rail

With the development of the high-speed railway, the super demand on the technical quality of the steel rail has been proposed, and the straightness and the residual stress are two most important indexes. The impacts of the straightness and the residual stress are very many, and one of which is the curvature before straightening. Simultaneously, the curvature before straightening also affects the size of force on straightening, and it also affects the life span of straightening machine deeply. Therefore, the curvature before straightening and the residual stress after bending deformation on the steel rail has been studied on the paper and the methods to lower the curvature have been proposed.This article based on the heat transfer analysis's basic principle, the hot elasto-plasticity analysis's basic principle, the contact analysis's basic principle as well as the finite element theory, used large-scale misalignment finite element analysis software ABAQUS to establish U75V-rail's 3-D transient nonlinear finite element analysis model. Firstly, using this analysis's model, the numerical simulation computation about the straight rail in the natural cooling process has been carried and the changing laws on the temperature field, bending deformation and residual stress after bending deformation about the straight rail during the natural cooling process have been analyzed. Secondly, the numerical simulation computation about the rail under the pre-bending condition in the natural cooling process has been carried, and the relationship on the bending deformation and residual stress after bending deformation between the straight and pre-bending rails has been analyzed, and the pre-bending programs at the different initial conditions on the rail have been proposed. Finally, through the field test, the pre-bending programs have been verified.Through the numerical simulations and the experiments on-site, several results have been received. During the process of cooling on rail, the initial temperature field, initial stress, initial plastic strain, and the sink temperatures have little affection on the changing law on the temperature field. The bending deformations during cooling process on the straight steel rail are circulation repeated process, and their bending deformations eventually are bent to the rail head and their values are between 1.84m and 2.07m. The longitudinal stresses at the bottom of the section apart from the sawing 3 meters place are also circulation repeated process during the cooling process, but the residual stress after bending are between 70MPa and 90MPa. There is not any plastic deformation, but only elastic deformation during the cooling process on the conditions of non-considering the initial stress and the initial plastic strain, and the cause to the residual deformations are uniform initial temperature field and their different changing rates. Both the bending deformations and residual stresses after bending deformations are affected by the initial stress and the initial plastic strain, but the influent on the residual deformation is greater, therefore, the bending lines are not straightly determined, and they must be revised before applied in practical. Experiments showed that the bending lines revised had better effects, and the residual stresses after bending deformations have been controlled in 70MPa~90MPa, the bending deformations have been controlled about 40mm.The research results in the paper can provide the theory basis and the advisory opinion for the cooling craft and the pre-bending craft of the rail.