Aldinton Allie, Ph.D. (2010)

Dissertation Topic:
Strength and Durability of Welded Rail Steel Repairs
Major Professor:  Dr. Heshmat Aglan, Professor of Mechanical Engineering & Associate Dean, College of Engineering
M.S.:  Mechanical Engineering, Tuskegee University
B.S.: Mechanical Engineering, Northern Caribbean University, Jamaica
Employment:  Nucor Steel Company, Memphis,TN

Dissertation Abstract:

Current rail welding techniques, such as thermite and flash-butt welding, are very expensive and time consuming.  Thermite welding is used in many railroad applications but has very low weld efficiency; flash-butt welding has high efficiency but is not suitable for in-track applications.  Development and evaluation of alternative repairs has great economical importance as well as great technical challenges.  Slot welding, using multi-pass gas metal arc welds (GMAW), is a promising method that could address these issues.  Prior to repairs, the defects in the railhead are accurately mapped and removed via machining.  The welding process uses multi-pass GMAW to fill the slots with the filler materials.  Any excess weld material is then ground to conform to the contour of the rail.  This research focuses on developing slot weld repair techniques pertinent to specific materials with the aim of increasing the weld efficiency and durability of rail repairs.  The parameters that are of interest includes:  the filler material, preheat and interpass temperatures, heat input and post-weld heat treatment procedures.  Three materials have been identified for this study, namely, pearlitic, bainitic and Hadfield manganese steels.  Finite element analyses were performed to determine the heat distribution during the slot welding process and the size of the fusion and heat affected zones (HAZ).  The hardness distribution of the welded steels was established.  Tensile, fracture toughness, fatigue crack propagation, fracture surface morphology and microstructural analysis were performed on specimens from the parent materials and welded joints to characterize and qualify the slot welding process.