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High speed non-destructive rail testing with advanced ultrasound and eddy-current testing techniques
(2009)
Today the rails face increased exposure to heavy loads, higher speeds and a very dense overall traffic. A continued development of testing methods for the rail inspection trains became necessary to match the modern needs for a fast detection and detailed classification of defects. To guarantee the safe operation of rail traffic non-destructive inspection techniques with combined ultrasound and eddy current testing methods are used to detect damages on rails. One of the main actual challenges of automated rail testing is the high inspection speed which is very close to the physical limits. To overcome these limits digital signal processing algorithms have to be used which maintain resolution and detection quality independent of operation speed. This paper presents a recently developed state of the art rail inspection system which uses advanced ultrasonic and eddy current testing techniques. Testing results are shown in a newly developed so called Glassy-Rail-Diagram which is capable to present data with a fixed resolution independent of inspection speed.
High speed non-destructive rail testing with advanced ultrasound and eddy-current testing techniques
(2009)
High speed ultrasonic axle inspection using a phased array with an electronically rotated beam
(2016)
The ultrasonic testing of the railway axes with a hollow drilling can be realized from the inside of the drill hole without demounting the axes and without dismantling the wheels and the brake discs. Flaws in the outer surface of the hollow shafts, whose orientation lies in the radial-radial plane have to be detected. Common testing systems use scanning in the circumferential direction by mechanical rotation of the probe system in the drilling. The presented phased array probe system carries out the rotation scan by electronically steering of the sound field only. Thereby manipulation of the probe inside the drilling becomes more simple and the inspection time can be shortened significantly. The beam will additionally be focused in the plane vertical to the specimen axis to optimize sound field parameters to different axle geometries.
For in-service inspections on wheelset axles with a hollow drilling, mechanized ultrasound inspection systems with single element probes are typically used. The ultrasonic testing in the zones close to the external surface of the railway axles can be realized from the inside of the bore hole, without demounting the wheelset and without dismantling the wheels and the brake discs. The testing system must be able to find flaws in the external surface of the hollow shafts, whose surface lies in the radial-radial plane, these are called transversal flaw. Presently testing systems are used, where scanning is realized in the circumferential direction by mechanical rotation of the probe system in the actual drilling. The phased array probe system, which is presented here, can carry out the rotation scan electronically. The scan can be carried out by simply moving the system forward and backwards through the drilling without mechanical rotation. Manipulation becomes simpler and the inspection time can be shortened considerably. The ultrasonic beam can be inclined exactly and be focused in the plane vertical to the specimen axis.
The probe is designed with help of indispensable simulations using especially designed software developed by BAM. The feasibility and the alignment between the simulated and experimental results were shown in earlier projects reported by Boehm et al. (2006) and Völz et al. (2012). The main task here is to optimize a probe for bore holes with a diameter of 65 mm with an increase in sensitivity and a high spatial resolution. This development will be carried out by use of extensive simulations and result in certain changes of the relevant probe parameters.
Due to the market needs on steel for high demanding applications non-destructive methods for the determination of steel cleanliness using ultrasound have to be adapted to increase sensitivity respectively.
The basic idea is that the new standard proposal should follow the basic line outs from SEP 1927 and ASTM E588. Additional to these relatives the standard should be open to different types of specimen and inspection frequencies to cover a wide range from bars, rings and plates as well as different inspection sensitivities. For an enhance in resolution the standard draft focuses on immersion focal beam probes which should be selected according to the geometry of the specimen. The selection should be proved with the aid of simulation tools. The frequency shall be at least 10 MHz. For specimen thicknesses of less than 6 mm a frequency of at least 25 MHz shall be used.
Calibration procedures had to be improved significantly compared to the old standards to allow proper sizing of indications. Therefore calibration procedures shall take signal processing into account. For detailed evaluation of the amplitude dependency and for calibration a reference block with a sufficient number of reflectors has to be used. The recorded echo height shall be directly transferred into an equivalent disc shaped reflector EDSR by a distance amplitude curve.
The novelty in this standard draft will be that based on 3D measurements and 3D evaluation the amplitude criterion of an indication becomes just one among some other criteria. This standard takes the signal amplitude, signal amplitude distribution and signal travel time for classification into account.
The standard draft will be open to the definition of the volume to be investigated to be set by the user. This will make evaluation more comparable to other methods because the inspected area has to be user defined.
We recommend CEN/TC 138 to decide on a work item for this proposal to become an EU and an ISO standard using Vienna agreement.
The research leading to these results has received funding from the European Union's Research Fund for Coal and Steel (RFCS) research programme under grant agreement n° RFSR-CT-2013-00014.
Matrix phased array probes become more and more prominent to be used in industrial applications. The main drawbacks, using probes incorporating a very large number of transducer elements, are the needs for an appropriate cabling and an ultrasonic device offering many parallel channels.
Matrix arrays designed for extended functionality feature at least 64 or more elements. Typical arrangements are square matrices, e.g. 10 by 10 or 11 by 11 or rectangular matrices, e.g. 8 by 16 or 10 by 12 to fit a 128-channel phased array system. In some phased array systems, the number of simultaneous active elements is limited to a certain number, e.g. 32 or 64. Those setups do not allow to run the probe with all elements active which may cause a significant change in the directivity pattern of the resulting sound beam.
When only a subset of elements is possible to use during a single acquisition, different strategies may be applied to collect enough data for rebuilding the missing information from the echo signal. Omission of certain elements may be one approach, overlay of subsequent shots with different active areas may be another one.
This paper presents the influence of decreased number of active elements on the sound field and their distribution on the array. An example for 16 active elements out of 121 is given in Figure 1. The sound field divergence and its shape basically remain the same, while the sensitivity is reduced and the amplitudes of the speckle-like side lobes increase significantly.
Solutions using subsets with different element activity patterns on matrix arrays and their advantages and disadvantages concerning the sound field are evaluated using semi-analytic simulation tools. Sound field criteria regarding the consequences for NDT test results and the system setup are discussed.
Increased speed, heavier loads, altered material and modern drive system concepts result in an increasing number of flaws in railways. Caused by the rapid change in damage mechanism by modern rolling stock the appearance of the flaws also alters. Hence, interpretation of non-destructive rail testing results may become difficult. Caused by the changed interplay between detection method and flaw the recorded signals will result in an unknown type for the rail flaws type classification.
Methods for automatic rail inspection according to defect detection and classification have been developed continuously. Signal processing is a key technology to master the challenge of classification and maintain resolution and detection quality independently of operation speed.
The basic ideas of signal processing based on the Glassy-Rail-Diagram for classification purposes will be presented. Examples for the detection of damages caused by rolling contact fatigue are given. Synergetic effects of combined evaluation of diverse inspection methods are shown.
Components made of fibre-reinforced plastic are a prominently used material in modern safety-relevant structures. Periodic in-service non-destructive inspection of these structures is necesary. The EMRP-funded project VITCEA aims on the evaluation of the performance of various non-destructive testing methods on the inspection of fibre-reinforced plastics.
The physical layout of fibre layers leads to complex structures of fibre-reinforced plastic parts. Furthermore different material properties of the fibre and the resin cause anisotropic behaviour of the material.This poses a challenge for ultrasonic NDT by causing a complex acoustical response.
The acoustical behaviour of fibre-reinforced plate materials has been simulated. Specimens with artificial flaws for the evaluation of the detection thresholds have been designed and manufactured.
Mechanized ultrasonic testing methods using phased-array sensors, air-coupled transducers, immersion tank testing and contact technique have been evaluated on the specimen.
In this talk results of different ultrasonic testing methods will be compared and discussed.
Der einwandfreie Zustand der Radsätze von Schienenfahrzeugen ist von größter Bedeutung für den sicheren Betrieb. Die Radsatzwellen werden durch eine große Zahl von Lastwechseln individuell unterschiedlich beansprucht. Dabei spielen viele Einflüsse wie äußere statische und dynamische Lasten, innere Lasten aufgrund von Unwuchten und inneren Spannungen und Umweltbedingungen entscheidende Rollen. Eine regelmäßige Prüfung ist daher obligatorisch. BTD entwickelt im Rahmen eines MNPQ-Projektes in Kooperation mit der BAM eine Phased Array Technik zur automatisierten Prüfung von Radsatzwellen im eingebauten Zustand. Die schwierigen Ankoppelbedingungen aufgrund der begrenzten Zugänglichkeit, der komplexen Geometrie sowie Farbschichten und Schmutz auf der Radsatzwelle stellen hierbei große Herausforderungen dar. Zu deren Bewältigung werden neben optimierten Prüfköpfen, einer in die Wasservorlaufstrecke integrierten akustischen Linse und einer speziellen Ankoppeltechnik auch Signalverarbeitungsalgorithmen eingesetzt. Die Darstellung der Signalverarbeitung ist der Schwerpunkt dieses Beitrages. Mit Hilfe von Messdatensätzen präparierter Testwellen werden verschiedene Algorithmen erprobt und hinsichtlich der Stabilität, dem Verhalten bezüglich der Ankoppelschwankungen und veränderter Wellengeometrien und der Fähigkeit zur automatischen Unterscheidung von Fehler- und Formanzeigen bewertet. Letztlich wird die beste Lösung im entwickelten Prüfsystem eingesetzt.
Increased speed, heavier loads, altered material and modern drive systems result in an increasing number of rail flaws. The appearance of these flaws also changes continually due to the rapid change in damage mechanisms of modern rolling stock. Hence, interpretation has become difficult when evaluating non-destructive rail testing results. Due to the changed interplay between detection methods and flaws, the recorded signals may result in unclassified types of rail flaws. Methods for automatic rail inspection (according to defect detection and classification) undergo continual development. Signal processing is a key technology to master the challenge of classification and maintain resolution and detection quality, independent of operation speed. The basic ideas of signal processing, based on the Glassy-Rail-Diagram for classification purposes, are presented herein. Examples for the detection of damages caused by rolling contact fatigue also are given, and synergetic effects of combined evaluation of diverse inspection methods are shown.