Session: Track 1-1B: Rail

Paper Number: 131626

131626 - Investigating Optimization of the Rail Roller Straightening Process: 3d Finite Element Analysis of Residual Stresses and Process Modifications 

Roller straightening is a process that is used to ensure the straightness of the rail during the manufacturing phase. This process utilizes a series of rollers to apply consecutive and repeated bending to the rail. However, it was found for modern rails that the roller straightening process was one of the main sources of longitudinal residual stresses. Notably, as a result of this process, high longitudinal tensile stresses were observed in the rail head, which are particularly damaging for detail fracture growth.

The most significant objective of this work was an understanding of the potential modifications of the roller straightening process that could lead to substantial rail life extension and therefore material savings, and reduction of the carbon footprint. To achieve this, the study focused on thoroughly investigating the roller straightening process and associated residual stresses. A dynamic roller straightening model was developed and refined to understand how the residual stress is generated during this complex process. The model was then used to investigate if modifications to the process have the potential to introduce a more favorable residual stress state, particularly within the head of the rail.

This study explored a range of scenarios, including several which would require significant alterations to the current process, in addition to smaller changes which would be feasible with the current adjustability of a typical machine. In this effort, the longitudinal plastic strain developed at each stage of the roller straightening process has been explored. This investigation considers how each bend contributes to the final residual stress profile within the head. The analysis was conducted by running a 9 m length of rail through the roller straightening process and examining the longitudinal plastic strain profile through the height of the rail at each bend.

Further simulations were conducted to investigate the possibility of introducing a beneficial compressive residual stress into the head, or to determine if measures could be introduced to reduce the magnitude of the tensile stress. Consideration was made for the practical feasibility of implementing changes within the process and with that in mind the initial proposed alterations were kept within the adjustment tolerances of the machine. In contrast, another scenario considered a modification to the process where the rail was inverted and passed through a similar straightening setup. This idea stems from the understanding that the primary cause of tensile residual stress in the rail head results from a specific bend inducing compressive plastic strain, which is not fully recovered by subsequent bends. The simulation aimed to determine if inverting the rail, thereby reversing the sign of bending moments, could generate tensile plastic strains in the head, resulting in a more favorable, compressive residual profile.

Overall, this research developed a deeper understanding of how the roller straightening process contributes to the development of longitudinal residual stresses in the rail. It also identified limitations in the material model data which should be developed to improve the accuracy of future simulations.   

Presenting Author: James Taylor Thornton Tomasetti

Presenting Author Biography: James Taylor is a chartered engineer (Institute of Mechanical Engineers) with over 13+ years’ experience as a consultant for Thornton Tomasetti. He works as part of Applied Science team providing support to clients across a range of industries including rail, oil & gas, nuclear & defence. James has been involved in several FRA sponsored, safety focused research projects related to both track and rolling stock.

Authors:

Sena Kizildemir Thornton Tomasetti
James Taylor Thornton Tomasetti
Peter Taylor Thornton Tomasetti
Philip Taylor Thornton Tomasetti
John Hutchinson Independent Consultant
Frederick Fletcher Independent Consultant
David Jeong Independent Consultant
Herman Nied Lehigh University
Haomin Fu Lehigh University