Stefano Mariani

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.

Field Test Performance of Noncontact Ultrasonic Rail Inspection System

AbstractThis paper presents the latest results from a noncontact ultrasonic rail inspection system developed at the University of California, San Diego (UCSD) under the auspices of the Federal Rail...

Non-contact Ultrasonic Guided Wave Inspection of Rails: Next Generation Approach

In the last ten years, over 1,000 train derailments that occurred in the US railroad system were caused by undetected rail internal defects that suddenly and dramatically emerged as track breakages. The total cost of those accidents is quantifiable in a few hundred millions of dollars, without considering the associated tragic losses of life and bodily injuries. While there already exist a few methods for the detection of rail internal flaws, several well-known limitations prevent each of them from detecting all of the critical flaws. As a proposal to address this issue, the object of this dissertation has been the development of a novel rail inspection system based on ultrasonic guided waves propagating through rails. Both the generation and the detection of these waves are achieved in a non-contact manner through the use of piezoelectric air-coupled transducers. One of the advantages of employing such non-contact method is the potential to perform tests as the train or inspector car travels at high speed along the railroad. Nevertheless, the main drawback of using air-coupled transducers on steel rail is represented by the significant energy losses occurring at the interface between air and steel due to the large acoustic impedance mismatch between these media. As a result, the signal to noise ratio available when analyzing the data is severely penalized. In an attempt to overcome this limitation, very effective electrical impedance networks have been designed. In parallel, a statistical analysis method based on multivariate outlier detection has been implemented to enhance the defect- sensitivity of the system. Numerical analyses of the ultrasonic wave propagation and interaction with different types of rail internal defects have been carried out using both a finite difference method, based on the Local Interaction Simulation Approach (LISA), and a commercial finite element method software. The results of these analyses were instrumental in understanding salient aspects of the guided wave propagation phenomenon in rails and throughout the ever ending decision-making process for the definition of the many system operating parameters involved. prototype based on these technologies has been built and tested both in-house at the UCSD Rail Defect Test Facility located at Camp Elliott, and in the field at the Transportation Technology Center located in Colorado, in October 2014. Receiver Operating Characteristics curves were used to characterize the performance of the defect detection based on the trade-off between defect detection rate and false alarm rate. In particular, the results of the field test were found to be quite satisfactory and perfectly in line with the predictions of the numerical analyses. Future work should be aimed at improving the prototype performance, particularly in terms of test speed, based on the lessons learnt from the October 2014 field tests and in the laboratory

Non-contact ultrasonic guided wave inspections of rails

The University of California at San Diego (UCSD), under a Federal Railroad Administration (FRA) Office of Research and Development (R&D) grant, is developing a system for high-speed and non-contact rail integrity evaluation. A prototype using an ultrasonic air-coupled guided wave signal generation and air-coupled signal detection, in pair with a real-time statistical analysis algorithm, is under development. Experimental tests results, carried out at the UCSD Rail Defect Farm, indicate that the prototype is able to detect internal rail defects with high reliability. Extensions of the system are planned to add rail surface characterization to the internal rail defect detection.

Predictions of defect detection performance of air-coupled ultrasonic rail inspection system:

A rail inspection system based on ultrasonic guided waves and non-contact (air-coupled) ultrasound transduction is under development at the University of California at San Diego. The system targets defects in the rail head that are major causes of train accidents. Because of the high acoustic impedance mismatch between air and steel, the non-contact system poses severe challenges and questions on the defect detection performance. This article presents an extensive numerical study, conducted with a local interaction simulation approach, to model the ultrasound propagation and interaction with defects in the proposed system. This model was used to predict the expected detection performance of the system in the presence of various defects of different sizes and positions, and at varying levels of signal-to-noise ratios. When possible, operating variables for the model were chosen consistently with the field test of an experimental prototype that was conducted in 2014. The defect detection performance was evaluated through the computation of receiver operating characteristic curves in terms of probability of detection versus probability of false alarms. The study indicates that despite the challenges of non-contact probing of the rail, quite satisfactory inspection performance can be expected for a variety of defect types, sizes, and positions. Beyond the specific cases examined in this article, this numerical framework can also be used in the future to examine a larger variety of field test conditions.

Defect detection performance of the UCSD non-contact air-coupled ultrasonic guided wave inspection of rails prototype

The University of California at San Diego (UCSD), under a Federal Railroad Administration (FRA) Office of Research and Development (R&D) grant, is developing a system for high-speed and non-contact rail defect detection. A prototype using an ultrasonic air-coupled guided wave signal generation and air-coupled signal detection, paired with a real-time statistical analysis algorithm, has been realized. This system requires a specialized filtering approach based on electrical impedance matching due to the inherently poor signal-to-noise ratio of air-coupled ultrasonic measurements in rail steel. Various aspects of the prototype have been designed with the aid of numerical analyses. In particular, simulations of ultrasonic guided wave propagation in rails have been performed using a Local Interaction Simulation Approach (LISA) algorithm. The system’s operating parameters were selected based on Receiver Operating Characteristic (ROC) curves, which provide a quantitative manner to evaluate different detection performances based on the trade-off between detection rate and false positive rate. The prototype based on this technology was tested in October 2014 at the Transportation Technology Center (TTC) in Pueblo, Colorado, and again in November 2015 after incorporating changes based on lessons learned. Results from the 2015 field test are discussed in this paper.

Extraction of thermal Green's function using diffuse fields: a passive approach applied to thermography

In the field of non-destructive evaluation, defect detection and visualization can be performed exploiting different techniques relying either on an active or a passive approach. In the following paper the passive technique is investigated due to its numerous advantages and its application to thermography is explored. In previous works, it has been shown that it is possible to reconstruct the Green’s function between any pair of points of a sensing grid by using noise originated from diffuse fields in acoustic environments. The extraction of the Green’s function can be achieved by cross-correlating these random recorded waves. Averaging, filtering and length of the measured signals play an important role in this process. This concept is here applied in an NDE perspective utilizing thermal fluctuations present on structural materials. Temperature variations interacting with thermal properties of the specimen allow for the characterization of the material and its health condition. The exploitation of the thermographic image resolution as a dense grid of sensors constitutes the basic idea underlying passive thermography. Particular attention will be placed on the creation of a proper diffuse thermal field, studying the number, placement and excitation signal of heat sources. Results from numerical simulations will be presented to assess the capabilities and performances of the passive thermal technique devoted to defect detection and imaging of structural components.

Non-contact ultrasonic guided wave inspection of rails: field test results and updates

The University of California at San Diego (UCSD), under a Federal Railroad Administration (FRA) Office of Research and Development (R&D) grant, is developing a system for high-speed and non-contact rail defect detection. A prototype using an ultrasonic air-coupled guided wave signal generation and air-coupled signal detection, paired with a real-time statistical analysis algorithm, has been realized. This system requires a specialized filtering approach based on electrical impedance matching due to the inherently poor signal-to-noise ratio of air-coupled ultrasonic measurements in rail steel. Various aspects of the prototype have been designed with the aid of numerical analyses. In particular, simulations of ultrasonic guided wave propagation in rails have been performed using a Local Interaction Simulation Approach (LISA) algorithm. The system’s operating parameters were selected based on Receiver Operating Characteristic (ROC) curves, which provide a quantitative manner to evaluate different detection performances based on the trade-off between detection rate and false positive rate. Results from the first field test of the non-contact air-coupled defect detection prototype conducted at the Transportation Technology Center (TTC) in Pueblo, Colorado, in October 2014 are presented and discussed in this paper. The results indicate that the prototype is able to detect internal cracks with high reliability.

High Speed Non-Contact Ultrasonic Guided Wave Inspections of Rails

This paper describes a new system for high-speed and non-contact rail defect detection being developed at the University of California at San Diego (UCSD). A prototype using an ultrasonic air-coupled guided wave signal generation and air-coupled signal detection has been tested at the UCSD Rail Defect Farm. This solution presents an improvement over the previously considered laser/air-coupled hybrid system because it replaces the costly and hard-to-maintain laser with a much cheaper, faster, and easier-to-maintain air-coupled transmitter. In addition to a real-time statistical analysis algorithm, the prototype uses a specialized filtering approach to mitigate 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. Various aspects of the prototype have been designed with the aid of numerical analyses. In particular, simulations of ultrasonic guided wave propagation in rails have been performed using a Local Interaction Simulation Approach (LISA) algorithm. Many of the system operating parameters were selected based on Receiver Operating Characteristic (ROC) curves, which provide a quantitative manner to evaluate different detection performances based on the trade-off between detection rate and false positive rate. Extensions of the system capability are planned to add rail surface characterization to the internal rail defect detection to optimize rail grinding operations.Copyright

Nonlinear guided waves for neutral temperature measurement in continuous welded rails: results from laboratory and field tests

Continuous Welded Rail (CWR) is used in modern rail construction including high-speed rail transportation. The absence of expansion joints in these structures brings about the risk of breakage in cold weather and of buckling in warm weather due to the resulting thermal stresses. The University of California at San Diego (UCSD), under a Federal Railroad Administration (FRA) Office of Research and Development (RandD) grant, is developing a system for in-situ measurement of the rail Neutral Temperature in CWR. Currently, there is no well-established technique able to efficiently monitor the rail thermal stress, or the rail Neutral Temperature (rail temperature with zero thermal stress), to properly schedule slow-order mandates and prevent derailments. UCSD has developed a prototype (Rail-NT) for wayside rail Neutral Temperature measurement that is based on non-linear ultrasonic guided waves. Numerical models were first developed to identify proper guided wave modes and frequencies for maximum sensitivity to the thermal stresses in the rail web, with little influence of the rail head and rail foot. Experiments conducted at the UCSD Largescale Rail NT Test-bed indicated a rail Neutral Temperature 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 (TTC) in Pueblo, CO in collaboration with the Burlington Northern Santa Fe (BNSF) Railway. The results of these field tests were very encouraging, indicating an accuracy for Neutral Temperature measurement of 5°F at worst, on both wood ties and concrete ties.