Gary Carr

Noncontact ultrasonic guided wave inspection of rails

This article describes a new system for high-speed and noncontact rail integrity evaluation being developed at the University of California at San Diego. A prototype using an ultrasonic air-coupled guided wave signal generation and air-coupled signal detection has been tested at the University of California at San Diego Rail Defect Farm. In addition to a real-time statistical analysis algorithm, the prototype uses a specialized filtering approach due to the inherently poor signal-to-noise ratio of the air-coupled ultrasonic measurements in rail steel. The laboratory results indicate that the prototype is able to detect internal rail defects with a high reliability. Extensions of the system are planned to add rail surface characterization to the internal rail defect detection. In addition to the description of the prototype and test results, numerical analyses of ultrasonic guided wave propagation in rails have been performed using a Local Interaction Simulation Approach algorithm and some of these results are shown. The numerical analysis has helped designing various aspects of the prototype for maximizing its sensitivity to defects.

TRACK DEGRADATION ASSESSMENT USING GAGE RESTRAINT MEASUREMENTS

Gage restraint is an important indicator of track condition and safety. In 1999, approximately 13 percent of derailments were caused by reductions in gage restraint and the resulting widening of the track gage. Existing techniques for the measurement of gage restraint allow identification of track sections with weak lateral support. However, little has been done to investigate the change in, or weakening of, gage restraint over time as a function of track, traffic, and environmental parameters. A track degradation assessment study is under way to develop models that can be used to predict changes in gage restraint by using data obtained from the automated Gage Restraint Measurement System. The degradation models will be useful for forecasting the future condition of the track, determining the appropriate frequency and timing of track inspections, and evaluating the effectiveness of maintenance strategies. A literature review of track degradation models and previous work on gage restraint analysis is presented. The rationale for adoption of an empirical approach to gage restraint degradation modeling is explained. The processing applied to the automatically collected data and the preliminary database program developed to store the information and estimate track degradation equations are also described. The track degradation analysis and database development study currently focuses on gage restraints and track geometry parameters as measures of condition. In the future, this can be extended to include other degradation parameters for a comprehensive track performance analysis.

Stress Dependence of Ultrasonic Guided Waves in Rails

Most modern railways use continuous welded rails (CWRs). A major problem in these structures is the almost total absence of expansion joints, which can create severe issues such as buckling in hot weather and breakage or pulling apart in cold weather. To minimize these risks, CWRs are built by connecting track segments that are prestressed before welding. A related critical parameter is the rail neutral temperature (NT), which is defined as the temperature at which the net longitudinal force in the rail is zero. When the ambient temperature is higher or lower than the NT, the rail is under compression and tension, respectively. Knowledge of the NT provides a potential method for indirect measurement of the stress and load in the rail. Unfortunately, the measurement of the in situ stress (or NT) has been a long-standing challenge for railway owners and operators. This paper presents numerical results on the dynamic behavior of CWRs subjected to a static axial stress. The results show how ultrasonic guided waves are sensitive to variations in stress and could potentially be used to estimate the stress level or the NT in rails. The present work represents the initial concept phase of a research and development study funded by the FRA. The ultimate objective of this study is to develop and test a prototype system that uses noncontact dynamic sensing to measure in situ rail stress in motion at speeds up to 30 mph to determine rail NTs and the related incipient buckling risks in CWRs.

Estimation of rail bending stress from real-time vertical track deflection measurement

High traffic volume, heavy axle loads, and high train speed can produce large rail bending stresses which contribute to increased track deterioration. Rail stress problems are further exacerbated by poor support conditions such as abrupt changes in vertical track modulus and poor track geometry. This paper summarizes the development of a measurement technique, based on a system being developed over the past few years at the University of Nebraska and sponsored by the Federal Railroad Administration, to determine the actual bending stress in the rail in real-time from a car moving at revenue speeds. The UNL system measures the rail height relative to the line created by the wheel/rail contact points. The system functions continuously over long distances and in revenue service. The system establishes three points of the rail shape beneath the loaded wheels and over a distance of ten feet. These points include the location of high bending stress below the loaded wheels. This direct measurement of the rail shape can then be mapped into rail stress through the curvature of the rail and beam theory. As verification of the UNL measurement system, results from tests conducted on the Union Pacific Railroad’s Yoder Subdivision are discussed. In these tests, bondable resistance strain gages were mounted to the lower flange of the rail at several locations. The track was then loaded by spotting the measurement car over the strain gages and by moving the car over the gages at various speeds. The loaded and unloaded rail profiles were measured using surveying equipment and the relationship between the UNL deflection measurement and the measured rail stress was explored. These early results suggest the UNL system is capable of measuring real-time bending stress in the rail.Copyright

Noncontact Ultrasonic Guided-Wave System for Rail Inspection: Update on Project at University of California, San Diego

The University of California, San Diego (UCSD), with an FRA Office of Research and Development grant, is developing a system for high-speed and noncontact rail defect detection. A prototype was designed and field tested with the support of Volpe National Transportation Systems Center and ENSCO, Inc. The goal of this project was to develop a rail defect detection system that provided (a) better defect detection reliability (including internal transverse head defects under shelling and vertical split heads) and (b) higher inspection speed than achievable by current rail inspection systems. This effort was also in direct response to safety recommendations issued by the National Transportation Safety Board after the disastrous train derailments at Superior, Wisconsin, in 1992 and Oneida, New York, in 2007, among others. The UCSD prototype used noncontact ultrasonic probing of the rail head (laser and air-coupled sensors), ultrasonic guided waves, and a proprietary real-time statistical analysis algorithm that maximized the sensitivity to defects while it minimized false positives. The design allowed potential inspection speeds up to 40 mph, although to date all field tests were conducted up to 15 mph. This paper (a) summarizes the latest technology development test conducted at the rail defect farm of Herzog, Inc., in Saint Joseph, Missouri, in June 2010 and (b) describes the completion of the new rail defect farm facility at the UCSD Camp Elliott Field Station with partial in-kind donations from the Burlington Northern Santa Fe Railway.

Stress dependence of guided waves in rails

This paper presents numerical results on the dynamic behavior of continuously welded rails (CWR) subjected to a static axial stress. The results quantify the sensitivity of guided waves to stress variations and could be potentially used to estimate the stress level in CWR or alternatively the rail Neutral Temperature (stress free rail temperature). This work represents the initial concept phase of a research and development study funded by the Federal Railroad Administration. The ultimate objective of this study is to develop and test a prototype system that uses non-contact dynamic sensing to measure in-situ rail stress in motion, to determine rail Neutral Temperatures (NT) and the related Incipient Buckling Risks in CWR.

Noncontact Ultrasonic Guided Wave Detection of Rail Defects

Recent train accidents, increasing tonnage, and aging rail transportation infrastructure have reaffirmed the need to improve current rail inspection technologies, consisting primarily of ultrasonic wheel testing. A recent development in rail inspection is the use of ultrasonic guided waves in the 20 kHz to 1 MHz range and noncontact probing techniques. This paper first reports on theoretical studies of ultrasonic guided wave propagation in rails based on a semianalytical finite element approach. The paper then describes the latest version of the University of California, San Diego, and FRA rail defect detection prototype, which is based on noncontact guided wave testing and real-time statistical pattern recognition for defect detection and classification. The system specifically targets transverse head cracks such as transverse fissures and detail fractures. It is also expected to be sensitive to longitudinal head cracks such as vertical split heads and mixed-mode cracks such as compound fractures. The system was field tested in March 2008 at speeds of up to 10 mph with excellent results under changing environmental conditions. Plans are in place for further improvements, including higher test speeds of up to 40 mph and installation of the system in an FRA research car for technology demonstration.

System for In Situ Measurement of Neutral Temperature in Continuous-Welded Rail: Results from Laboratory and Field Tests

Research has been focused on developing a system for in situ measurement of stress in continuous-welded rail to use as a basis for the determination of neutral temperature (NT). Continuous-welded rail is known to break in cold weather and buckle in hot weather because of thermally induced stresses. The need for a reliable technique for determination of NT (rail temperature with zero thermal stress) has been an ongoing challenge for railroads since the advent of continuous-welded rail more than 40 years ago. Railroads need to know the level of stress in the rail to schedule slow-order mandates properly and prevent derailments. A prototype (Rail-NT) was developed for wayside rail NT measurement based on nonlinear ultrasonic guided waves. Numerical models were first developed to identify optimum guided wave modes and frequencies for maximum sensitivity to the thermal stresses in the rail web, with minimal influence of the rail head and rail foot. Experiments indicated a rail NT measurement accuracy of a few degrees. The first field tests of the Rail-NT prototype were performed in June 2012 at the Transportation Technology Center in Pueblo, Colorado, in collaboration with the Burlington Northern Santa Fe Railway. The results of these field tests were encouraging; the tests indicated an accuracy for NT measurement of 5°F at worst on both wood and concrete ties. One of the issues that remains to be investigated is the effect of passing trains on the rail NT measurements.

NONLINEAR GUIDED WAVES IN CONTINUOUSLY WELDED RAILS FOR BUCKLING PREDICTION

Most modern railways use Continuous Welded Rail (CWR). A major problem is the almost total absence of expansion joints that can create severe issues such as buckling in hot weather and breakage in cold weather. A related critical parameter is the rail Neutral Temperature (NT), or the temperature at which the net longitudinal force in the rail is zero. In June 2008 the University of California, San Diego (UCSD), under the sponsorship of a Federal Railroad Administration (FRA) Office of Research and Development (R&D) grant, began work to develop a technique for in‐situ measurement of NT and detection of incipient buckling in CWR. The method under investigation is based on ultrasonic guided waves, and the ultimate goal is to build and test a prototype that can be used in motion. A large‐scale full rail track (70 feet in length) has been constructed at UCSD’s Powell Structural Laboratories, the largest laboratories in the country for structural testing, to validate the NT measurement and buckling detection te...

Monitoring thermal stresses and incipient buckling of continuous-welded rails: results from the UCSD/BNSF/FRA large-scale laboratory test track

Most modern railways use Continuous Welded Rail (CWR). A major problem is the almost total absence of expansion joints that can create buckling in hot weather and breakage in cold weather due to the rail thermal stresses. In June 2008 the University of California, San Diego (UCSD), under the sponsorship of a Federal Railroad Administration (FRA) Office of Research and Development (R&D) grant, began work to develop a technique for in-situ measurement of stress and detection of incipient buckling in CWR. The method under investigation is based on ultrasonic guided waves, and the ultimate goal is to develop a prototype that can be used in motion. A large-scale full rail track (70 feet in length) has been constructed at UCSDs Powell Structural Laboratories, the largest laboratories in the country for structural testing, to validate the CWR stress measurement and buckling detection technique under rail heating conditions well controlled in the laboratory. This paper will report on the results obtained from this unique large-scale test track to date. These results will pave the road for the future development of the rail stress measurement & buckling detection prototype.