222. MEASUREMENT OF THERMAL STRESSES IN RAILS BY ELECTRO MECHANICAL IMPEDANCE (EMI) MEASUREMENT

Department: Structural Engineering
Faculty Advisor(s): Francesco Lanza di Scalea

Primary Student
Name: Xuan Zhu
Email: xuz009@ucsd.edu
Phone: 858-534-5279
Grad Year: 2014

Student Collaborators
Robert Phillips, rrphilli@ucsd.edu

Abstract
This poster presents the feasibility of using an impedance-based Structural Health Monitoring technique to monitor thermal stresses in Continuous Welded Rail (CWR). In order to reduce maintenance cost and equipment wear the majority of modern railways use CWR, which reduces the number of joints that are a source for excessive wear. However, the absence of joints for expansion can create the potential of buckling in hot weather and breakage in cold weather due to the rail thermal stresses. The University of California, San Diego (UCSD), under the sponsorship of a Federal Railroad Administration (FRA) Office of Research and Development (R&D) grant, has began work to develop a technique for in-situ measurement of stress and detection of incipient buckling in CWR. Several studies have shown the feasibility of EMI measurements in the detection of structural defects. The objective of this research is to utilize the capability of the impedance method in identifying and characterizing the thermal stress in CWR. The principle of EMI utilizes high frequency structural vibrations measured through a piezoelectric transducer to detect differences in the structural mechanical impedance due to the presence of change in the structural integrity such as in-situ stress. In practical CWR health monitoring, the rail track structure that is monitored is undergoing variations due to the effect of thermal stress and environmental factors. The temperature effects on the piezoelectric material and structure are investigated so that a corresponding temperature compensation algorithm can then be applied to the application in order to isolate the thermal stress measurement. Three experimental investigations were performed first under axial loads only, then temperature changes only, and finally axial loading thru temperature variation. Upon validation of this experimental investigation, the practicality of this method will be tested in a real field environment.

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