Monitoring the reflection from an artificial defect in rail track using guided wave ultrasound

Abstract

Abstract. Guided wave ultrasound has the potential to detect relatively large defects in continuously welded rail track at long range. As monitoring can be performed in near real time it would be acceptable to only detect fairly large cracks provided this is achieved prior to complete rail breakage. Heavy haul rail lines are inspected periodically by conventional ultrasound and sections with even relatively small cracks are removed; therefore, no sizable defects are available to demonstrate monitoring in the presence of realistic environmental operating conditions. Instead, we glued a small mass to the rail to simulate reflection from a crack and monitored the guided wave signals as the glue joint deteriorated over time. Data was collected over a two week period on an operational heavy haul line. A piezoelectric transducer mounted under the head of the rail was used in pulse-echo mode to transmit and receive a mode of propagation with energy confined mainly in the head of the rail. The small mass was attached under the head of the rail, at a distance of 375m from the transducer, using a cyanoacrylate glue, which was not expected to remain intact for long. Pre-processing of the collected signals involved rejection of signals containing train noise, averaging, filtering and dispersion compensation. Reflections from aluminothermic welds were used to stretch and scale the signals to reduce the influence of temperature variations. Singular value decomposition and independent component analysis were then applied to the signals with the aim of separating the reflection caused by the artificial defect from the background signal. The performance of these techniques was compared for different time spans. The reflection from the artificial defect showed unanticipated fluctuations.

Rail Diagnostics Based on Ultrasonic Guided Waves: An Overview

“…If not detected in time, defects can lead to rail failures, which, in some cases, happen without any previous indication. The prediction of crack growth rates and of the size of defects at failure are both influenced by various parameters [4,9]. In the following two paragraphs, we focus on the different types of defects and on the techniques that can be employed for their detection.…”

“…2. Land-based systems [9,[50][51][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67]-The employed equipment is placed on the ground near to the railway infrastructure, and its actuators and sensors are attached to the rails under test. The detection of defects in the rails is achieved through a pulse-echo approach.…”

“…For example, the use of electromagnetic acoustic transducers (EMATs) has been taken into consideration [55]. In the meantime, the reflection characteristics of defects and their dependence on time and environmental conditions are under evaluation [9,56,57,65].…”

“…An important advantage offered by land-based solutions is represented by the fact that monitoring can be accomplished in near real-time, so that defect growth can be analyzed over time and an alarm set only when a crack assumes a potentially critical size [9,65].…”

Ultrasonic guided wave monitoring of an operational rail track

“…15 In that work, a single measurement was performed as in the case of an inspection rather than in the situation of monitoring where a large amount of data is gathered over a period of time. A monitoring experiment was described in the study by Loveday et al, 16 where data were gathered over a period of time. Initial analysis of only the pulse-echo signal obtained from a single transducer was presented in that article.…”