Mechanics of roller straightening

One of the last steps in the manufacture of railway rails is cold roller straightening. In this process, the rail is passed through nine rollers and plastically deformed to uniform straightness. The plastic deformation gives rise to large longitudinal residual stresses in the rail web near the mid length of the rail. The relief of these stresses near the end of the rail leads to large vertical tensile stresses in the web. These tensile stresses can lead to the initiation of cracks at a rail end in service. Relief of the residual bending stresses in the web during crack growth can cause catastrophic failures and are of particular concern to the design of proposed high speed rail track in the Northeast corridor of the U.S.A. A simple model is developed using elastic-plastic beam finite elements for the prediction of the effect of roller straightening parameters on web residual stress. The model agrees well with experimentally measured residual stresses. Proposals for modifying the roller straightening process to decrease the level of deleterious residual stresses are discussed.