Date of Award

Fall 2021

Document Type

Open Access Thesis

Department

Civil and Environmental Engineering

First Advisor

Dimitris Rizos

Abstract

Continuously welded rail with flash-butt welded joints has become standard practice for railway construction around the world. Through the process of welding, a residual stress field develops in the joint which typically remains in the rail through its service life. Consequently, the total stress is altered locally in the presence of operation induced stresses. One such stress develops due to thermal expansion of the rail during the daily and seasonal solar radiation heating cycle. This paper seeks to ascertain the combined effects of welding residual stress with thermal expansion through computer simulations. This is aimed at two objectives: determining whether the combined stress fields are significant enough to be considered in rail design, and whether the deformation field is altered in a way that disrupts RNT estimations.

The first model simulates the welding process to determine the welding residual stress. The resulting stress field agrees with literature data, with notably high vertical tensile stress in the web and high compressive stress along the edges of the rail head and foot. The second model quantifies the thermal expansion occurring when rail temperature deviates from RNT. This provides a baseline of thermal stress and thermal deformation. The presented stress field compares well with experimental data, showing negligible stress in the transverse and vertical directions while developing relatively uniform longitudinal compression. The deformation field also agrees well with the literature. The final model assesses the combination of welding residual stress and thermal expansion by incorporating the first model’s resultant stress field as the initial state of the second model. With a rail temperature deviation, the total weldment stress distribution undergoes a non-uniform change despite interacting with a relatively uniform thermal stress. This simulated peak of the daily thermal stress cycle impacts the rail head, web, and foot differently. The foot experiences a fully compressive stress cycle, increasing the risk for buckling; the web undergoes a fully tensile stress cycle vertically and longitudinally that raises concerns for fatigue failures; and the head sees almost no stress cycle but retains high compression. Additionally, the profile of the top surface wave pattern is distorted when a weld is present. The high vertical tensile stress in the weldment web is identified as a key factor in this distortion.

The results show significant stress concentrations and/or stress cycles that occur in common weldment failure locations. This suggests that the combined welding residual and thermal stress fields should have greater consideration in rail design and rail fatigue life calculations. The perturbed patterns of stress and deformation in the weldment indicates that the area adjacent to the weld should be ignored when determining the rail neutral temperature through deformation-based and stress-based methods.

Rights

© 2021, Brennan Gedney

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