Graduate Studies


Date of this Version

Summer 7-2011


A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Engineering Mechanics, Under the Supervision of Professor Joseph A. Turner. Lincoln, NE: July 2011

Copyright 2011 Christopher M. Kube


Thermally-induced longitudinal stress in continuously welded rail (CWR) is a recognized problem within the railroad industry in terms of both safety and maintenance. Daily and seasonal temperature cycles can lead to high longitudinal rail stress that can result in rail failure. Ultrasonic nondestructive techniques have been previously attempted to monitor this stress. These techniques have had many limitations such that alternative methods are of great interest. The research illustrated in this thesis is a novel attempt at a solution to address these needs. The technique is based on ultrasonic backscatter which results from the multitude of reflections that occur at grain boundaries due to the variation of the single-crystal elastic constants. The resultant backscatter has previously been theoretically modeled and is influenced by the material’s stress state through the covariance of elastic moduli. This thesis aims to present experimental confirmation of the stress influence on ultrasonic backscatter. Backscatter results are presented for mechanically and thermally-induced uniaxial stresses in various samples. The results indicate that backscatter is a sensitive indicator of a material’s stress state. The sensitivity leads to the belief that this technique may form the starting point for reliable stress measurement devices used on CWR and other structural components.

Advisor: Joseph A. Turner