training, future studies will look at power spectral densities
generated numerically in addition to the exploration of a
physics informed network to help assist the training process.
ACKNOWLEDGMENTS
This work and the first author were supported by AAR/TTCI under the
program: Grand Challenge Research Topic: In-motion Track Stability
Assessment, agreement no. 20-0701-007537. Funding to perform the field
tests and to support the second author were provided by the US Federal
Railroad Administration under contract FR19RPD3100000022. The authors
acknowledge the logistic support of the host MxV Rail and Mr. Christopher
Johnson during the planning and execution of the field test. The authors
are also grateful to the host for sharing the ground truth RNT. Currently,
the second author is supported by the 2023 ASNT Fellowship Award.
Finally, the authors would like to acknowledge the contribution of Mr.
Charles (Scooter) Hager, at the University of Pittsburgh, for the technical
support provided during the preparation and execution of the experi-
ments.
DATA AVAILABILITY
Some or all data, models, or code that support the findings of this study
are available from the corresponding author upon reasonable request.
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ABSTR ACT
This paper discusses the development of an in situ
noncontact electromagnetic acoustic transducer
(EMAT) nondestructive evaluation technology to
determine rail neutral temperature and estimate
rail stress in continuous welded rail (CWR). Stresses
develop in CWR due to a lack of expansion joints to
accommodate thermal expansion and contraction of
the rail when ambient temperatures vary over time.
The novelty of the work presented is the usage of
ultrasonic birefringence properties using EMATs to
estimate thermally induced stresses in rails. EMATs
produce polarized shear waves propagating through
the rail web in the pulse-echo mode. Experimental
tests were performed on machined 136RE and
141RE rail material with applied compressive and
tensile stresses to explore the stress-birefringence
behavior. Two additional sets of experimental tests
were conducted on full-size rail sections with in situ
surface conditions to study variations in the in situ
birefringence and the acoustic stress constant in
different rail materials including 115RE rail, 119RE
rail, two different 136RE rails, and 141RE rail. The
results show a highly linear relationship between
the stresses applied and the measured acoustic
birefringence.
KEYWORDS: continuously welded rails, acoustic birefringence,
EMAT, rail buckling, thermal stresses
Introduction
Continuous welded rail (CWR) has been an invaluable
enhancement to the rail transportation system around the
world since the evolution of thermite welding in the late 19th
century and the employment of this welding technique in the
railway industry in 1924 by the German State Railway and in
1930 by the Central of Georgia Railway in the United States
(Lonsdale 1999). CWR offers excellent advantages over the tra-
ditional mechanically connected rails using joint bars. CWR
allows it to operate at higher speeds, provide a smoother ride,
and need less maintenance due to the absence of joint gaps.
However, CWRs are susceptible to buckling or fracture due
to thermal stresses that develop in the rail due to the lack of
expansion devices to accommodate thermal expansion and
contraction. The rail is susceptible to buckling at elevated tem-
peratures, and tensile thermal stresses can lead to cracking
and propagation of existing defects during cold weather. Rail
buckling and defects can eventually lead to derailment of the
train from the track, which can result in increased costs and
safety issues (Huang et al. 2023 Liu et al. 2012).
Rail neutral temperature (RNT) is the temperature at which
the rail is neither in tension nor compression and is often
linked with the temperature at which the track was installed
and fastened. Designated rail-laying temperatures are often
established by railroads and are based on geographic and
average yearly ambient temperature to provide a specific
desired rail neutral temperature (DRNT) to prevent track
buckling in hot weather and pull-aparts and broken rails in
cold weather. However, RNT is not a fixed value and varies
along the length of the track and throughout the track’s lifetime
for several reasons. Repair of the damaged rail sections or
destressing operations to adjust to a desired RNT following
repair or maintenance can also affect the RNT. Heavy mechan-
ical forces from braking and tractive forces at specific segments
of the track (Kish et al. 2013) and the variability of constraint
from rail anchoring and track fasteners can also impact the
RNT (Miri et al. 2021).
Longitudinal rail stresses must be monitored and evaluated
periodically to prevent such scenarios and provide safe train
operations. Investigating the state of having a zero longitudinal
force is interchangeable with finding the RNT and can be gen-
erally related to the thermal forces in the rail as a function of
temperature using Equation 1: ​ ​ ​
(​​1)​​ ​ P =EAα(​​ ​ ​ TR​​ ​ − ​ TN​​​)​​​​​
BIREFRINGENCE TECHNIQUE FOR EVALUATING
THERMAL STRESSES IN RAILROAD RAILS
AQEEL T. FADHIL*, GLENN WASHER†, AND ANISH POUDEL‡
*University of Missouri, Department of Civil and Environmental Engineering,
416 S. 6th St., Columbia, MO 65201 aqeel.fadhil@uobaghdad.edu.iq
† University of Missouri, Department of Civil and Environmental Engineering,
416 S. 6th St., Columbia, MO 65201 washerg@missouri.edu
‡ MxV Rail, Research and Development, 350 Keeler Parkway, Pueblo, CO 81001
1-719-696-1848 anish_poudel@aar.com
Materials Evaluation 82 (1): 79–87
https://doi.org/10.32548/2024.me-04382
©2024 American Society for Nondestructive Testing
NDTTECHPAPER
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