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Eingeladener Vortrag
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Die Detektion von Rissen in Eisenbahnschienen erfolgt mit Hilfe von
Ultraschall- und Wirbelstromprüftechniken. Zur Verbesserung der Aussage der
Tiefenbestimmung von zur Fahrfläche hin geöffneten tiefen Rissen wurde von der
BAM ein entsprechender Lösungsansatz erarbeitet und im Labormaßstab erprobt.
Eine spezielle Sender-Empfänger-Anordnung ermöglicht in Verbindung mit einer
auf der TOFD-Technik basierenden Datenerfassung mit anschließender
Laufzeitanalyse des Signals die Bestimmung von Risstiefen bis 30 mm.
When dealing in ultrasonic testing with inhomogeneous and anisotropic material structure such as
diverse types of components made from austenitic or nickel based cast, which are currently used
for modern power plant concepts, data interpretation is quite difficult. For better understanding of
the complex interaction between the sound field and the component under test, the mathematical
modeling of sound propagation in solids is a substantial task to increase the probability of
detection of relevant defects.
First we present a mathematical approach for modeling the three dimensional transient
particle displacement as a function of time in each point in a half space excited by an impulsive
point load at the surface. The transient ultrasonic field of a rectangular array element is calculated
with this approach by a point source synthesis. Based on this solution we model the wave
propagation of a phased array transducer by time delayed superposition of the wave field of the
transducer elements.
Next we use an electrodynamic technique to visualize the grazing sound field at the surface
of a test block radiated by a phased array probe. By detecting the grazing beam at the samples
surface with a small electrodynamic probe, we measured the particle displacement as a function of
time. It allows for measuring the displacement in all three spatial directions. This comprises the
detection of the horizontal and vertical particle displacement with respect to the surface and thus
also the detection of longitudinal and shear waves is possible.
The calculated and measured wave fields will be compared for different delay laws in
isotropic and transversely isotropic media. The results support the theoretical activities to model
the wave propagation and to find optimal testing parameters for different components and
configurations.