Mahmood Fateh

Power harvesting for railroad track health monitoring using piezoelectric and inductive devices

One of the most limiting factors for distributed sensor networks used for railroad track health monitoring applications is the lack of a long-term, low-maintenance power supply. Most existing systems still require a change of battery, and remoteness of location and low frequency of maintenance can limit their practical deployment. In this paper we describe an investigation of two principal methods for harvesting mechanical power from passing railcars in order to supply electrical power to remote networks of sensors. We first considered an inductive voice coil device directly driven by vertical rail displacement. We then considered a piezoelectric device that is attached to the bottom of the rail and is driven by the longitudinal strain produced by rail bending due to passing railcars. Theoretical models of the behavior of these devices were integrated with an analytical model of rail track deflection to perform numerical simulations of both of these power scavenging techniques. Lab and field tests were also performed to validate the simulation results. Resulting values of average power production show promise for scavenging near the targeted level of 1 mW, and the field data matched well with the simulations.

Fatigue Damage Tolerance of Bainitic and Pearlitic Rail Steels

The microstructure-properties relationships, fatigue crack growth, and fracture surface morphology of J6 bainitic and premium pearlitic rail steels are studied. Specimens are cut from the middle of each railhead along the longitudinal direction of the rail using electrical discharge machining. Fatigue crack propagation tests are conducted under load control conditions using a servo hydraulic material testing system. A simple form of the fatigue power law is used to rank the fatigue crack growth kinetics of the two materials. The results show that bainitic steel has superior fatigue damage tolerance as represented by the fatigue lifetime, fatigue crack propagation kinetics, and fatigue fracture surface morphological features. Fracture surface analysis of fatigue failed specimens revealed the various mechanisms by which bainitic steel acquired its superior resistance to fatigue crack growth. Bainitic rail steel displayed more ductile fracture features such as tearing, and extensive ridge formation during the stable crack propagation process than pearlitic steel. These features are responsible for the crack deceleration and indicate a considerably high energy consuming process associated with the crack propagation of bainitic steel. Pulled-up pearlitic lamella, limited microcracks, and microvoid coalescence are found on the fracture surface of pearlitic rail steel during the stable crack process. The unstable crack propagation region of bainitic steel exhibits both large and small dimples indicative of high resistance to material separation. On the other hand, cleavage and intergranular separation are associated with the unstable crack region in pearlitic steel.

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.

High-Speed Defect Detection in Rails by Noncontact Guided Ultrasonic Testing

Recent train accidents have reaffirmed the need to develop rail defect detection systems that are more effective than those used today. This paper proposes new inspection systems for detecting transverse-type cracks in the rail head, notoriously the most dangerous flaws in rails. In principle these systems can be applied to both continuous welded rail and jointed tracks because bidirectional inspection can be implemented. However, the systems may fail to detect defects located close to a joint. The proposed technology uses ultrasonic guided waves that are detected by remote sensors positioned as far away as 76 mm (3 in.) from the top of the rail head. An impulse hammer is used to generate waves below 50 kHz that can successfully detect cracks larger than 15% of the head cross-sectional area. For smaller crack-those as shallow as 1 mm-a pulsed laser is used for generating waves above 100 kHz. The inspection ranges are at least 10 m (32 ft) for cracks larger than 15% of the head area and at least 500 mm (20...

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.

Power harvesting for railroad track safety enhancement using vertical track displacement

A significant portion of railroad infrastructure exists in areas that are relatively remote. Railroad crossings in these areas are typically only marked with reflective signage and do not have warning light systems or crossbars due to the cost of electrical infrastructure. Distributed sensor networks used for railroad track health monitoring applications would be useful in these areas, but the same limitation regarding electrical infrastructure exists. This motivates the search for a long-term, low-maintenance power supply solution for remote railroad deployment. This paper describes the development of a mechanical device for harvesting mechanical power from passing railcar traffic that can be used to supply electrical power to warning light systems at crossings and to remote networks of sensors via rechargeable batteries. The device is mounted to and spans two rail ties such that it directly harnesses the vertical displacement of the rail and attached ties and translates the linear motion into rotational motion. The rotational motion is amplified and mechanically rectified to rotate a PMDC generator that charges a system of batteries. A prototype was built and tested in a laboratory setting for verifying functionality of the design. Results indicate power production capabilities on the order of 10 W per device in its current form. This is sufficient for illuminating high-efficiency LED lights at a railroad crossing or for powering track-health sensor networks.

On-track testing of a power harvesting device for railroad track health monitoring

A considerable proportion of railroad infrastructure exists in regions which are comparatively remote. With regard to the cost of extending electrical infrastructure into these areas, road crossings in these areas do not have warning light systems or crossing gates and are commonly marked with reflective signage. For railroad track health monitoring purposes, distributed sensor networks can be applicable in remote areas, but the same limitation regarding electrical infrastructure is the hindrance. This motivated the development of an energy harvesting solution for remote railroad deployment. This paper describes on-track experimental testing of a mechanical device for harvesting mechanical power from passing railcar traffic, in view of supplying electrical power to warning light systems at crossings and to remote networks of sensors. The device is mounted to and spans two rail ties and transforms the vertical rail displacement into electrical energy through mechanical amplification and rectification into a PMDC generator. A prototype was tested under loaded and unloaded railcar traffic at low speeds. Stress analysis and speed scaling analysis are presented, results of the on-track tests are compared and contrasted to previous laboratory testing, discrepancies between the two are explained, and conclusions are drawn regarding suitability of the device for illuminating high-efficiency LED lights at railroad crossings and powering track-health sensor networks.

Simulation and control system of a power harvesting device for railroad track health monitoring

With the vastness of existing railroad infrastructure, there exist numerous road crossings which are lacking warning light systems and/or crossing gates due to their remoteness from existing electrical infrastructure. Along with lacking warning light systems, these areas also tend to lack distributed sensor networks used for railroad track health monitoring applications. With the power consumption required by these systems being minimal, extending electrical infrastructure into these areas would not be an economical use of resources. This motivated the development of an energy harvesting solution for remote railroad deployment. This paper describes a computer simulation created to validate experimental on-track results for different mechanical prototypes designed for harvesting mechanical power from passing railcar traffic. Using the Winkler model for beam deflection as its basis, the simulation determines the maximum power potential for each type of prototype for various railcar loads and speeds. Along with calculating the maximum power potential of a single device, the simulation also calculates the optimal number and position of the devices needed to power a standard railroad crossing light signal. A control system was also designed to regulate power to a battery, monitor and record power production, and make adjustments to the duty cycle of the crossing lights accordingly. On-track test results are compared and contrasted with results from the simulation, discrepancies between the two are examined and explained, and conclusions are drawn regarding suitability of the device for powering high-efficiency LED lights at railroad crossings and powering track-health sensor networks.

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