Award Date

8-1-2022

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

First Committee Member

Zhiyong Wang

Second Committee Member

Hualiang Teng

Third Committee Member

Mohamed Trabia

Fourth Committee Member

Brendan O'Toole

Fifth Committee Member

Samir Moujaes

Sixth Committee Member

Jee Woong Park

Number of Pages

200

Abstract

The frequent replacement of worn rails on tracks brings an immense economic burden on the railroad industry, and also causes significant interruptions to railroad operation. Restoration of worn rails via additive manufacturing, i.e., 3D printing, can considerably reduce the associated maintenance costs.The scope of this dissertation is to utilize metal additive manufacturing (AM) technology to repair worn rails that are used in the U.S. railway transportation system (e.g. 75-lb/yd light transit rails, or 136-lb/yd heavy freight rails). More specifically, this study aims to understand the interactive mechanisms between the deposited materials and the high-carbon rail steel to identify and alleviate the effect of the associated drawbacks, i.e., residual thermal stresses, micro pores, micro cracks, and martensite nucleation, on the resulting mechanical and metallurgical properties of the repaired rail. Submerged arc welding (SAW) and laser powder deposition (LPD) have been selected as two potential AM approaches for rail repair. Various deposition steels such as rutile E71T-1C and Lincore 40-S wire for the SAW process, and 304L stainless steel, 410L stainless steel, Stellite 6, and Stellite 21 in the powder form for the LPD process have been chosen to be deposited on the surface of the railhead. The study starts with the investigation of repairing the 75-lb/yd light transit rail through SAW and LPD processes. It then continues with exploration of LPD- and SAW-repairing of the 136-lb/yd (136RE) heavy freight/passenger rail. A finite element (FE) model is developed in which the thorough process of the AM rail repair is simulated through an element-birth-and-kill method and all of the involved interactions including thermal interactions, mechanical evolutions, and kinetics of phase transformation are defined and given to the model. The FE model development is simultaneously followed by similar experimental lab investigations to verify the model outcomes and hence, validate the developed FE model. This dissertation will try to modify the mechanical and metallurgical properties of the repaired rail through different approaches, i.e., preheating, post heat treatment, AM method alteration, tool path alteration, and deposition material alteration. Regarding the mechanical properties, distribution of hardness and residual stresses are measured via Rockwell hardness test and X-ray diffraction (XRD) stress measurement, respectively. Evaluation of the distribution of micro-pores, micro-cracks, and metallurgical phases is carried out through scanning electron microscope (SEM), optical microscope (OM), and XRD analysis. The tensile/compressive yield and shear strength of the repaired rail are assessed via 3-point bending and tensile tests, respectively. Initial efforts are performed through experimental lab measurements, and further efforts for various deposition materials and AM process parameters are conducted through the validated FE model.

Keywords

Additive Manufacturing; Bending Test; Hardness Test; Residual Stress; SEM; XRD

Disciplines

Mechanical Engineering

File Format

pdf

File Size

9800 KB

Degree Grantor

University of Nevada, Las Vegas

Language

English

Rights

IN COPYRIGHT. For more information about this rights statement, please visit http://rightsstatements.org/vocab/InC/1.0/

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