Filtern
Dokumenttyp
Sprache
- Englisch (5)
Schlagworte
- Sound field (5) (entfernen)
Organisationseinheit der BAM
Eingeladener Vortrag
- nein (1)
There are many different methods to characterize air-coupled ultrasonic transducers for non-destructive testing. Data sheets of various manufacturers contain information about some parameters important for the performance of transducers, but this information is not standardized, so that a comparison between probes of different manufacturers is difficult. Therefore, the German Society for Non-Destructive Testing (DGZfP) is working on a guideline to characterization of air-coupled probes.
One of the topics in this guideline is the application of thermoacoustic transducers for the characterization of receivers and another topic is the application of microphones for the characterization of transmitters. In this presentation we compare various characterization methods with the particular focus on the characterization of thermoacoustic transducers using an optical microphone. Both thermoacoustic transmitters and optical microphones have a very large bandwidth compared to conventional air-coupled transducers, but their spectrum is not entirely linear, which needs to be taken into account if they are applied as reference transducers.
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.
When dealing in ultrasonic testing with inhomogeneous material structure
data interpretation can be rather difficult. This is especially the case when using
anisotropic dissimilar welds made from austenitic steel or nickel based alloys, which are
currently used for modern power plant concepts. For better understanding of the
complex interaction between the sound field and the component under test, the
visualization of sound propagation in solids is a substantial task to increase the
probability of detection of relevant defects. However, there exist only a small number of
appropriate techniques published today, such as scanning laser interferometer,
piezoelectric and optical approaches in case of transparent solids. In this work we
present an electrodynamic technique providing a simple use and a high signal to noise
ratio. By detecting the grazing beam with an electrodynamic probe with a size smaller
than 10 mm, we measured the particle displacement as a function of time with a spatial
resolution in the order of 1 mm. Adapting the electrodynamic probe and its coil
alignment allows for measuring the displacement components in all three dimensions.
This comprises the detection of the horizontal and vertical particle displacement with
respect to the surface and thus also the transformation from longitudinal waves into
transversal waves and vice versa is possible. A SNR of higher than 36 dB could be
achieved within ferromagnetic and high conductive chrome steel when using a
transversal wave generated by an angled beam transducer. We report on measurements
of the sound field in complex weld joints. One example shows a 10 mm thick narrowgap
weld joining a nickel alloy with a chrome steel yielding a substantial anisotropy of
the weld structure. The test system enables us to visualize the wave propagation within
the weld and indicates the reflection scenario and the energy losses due to both the
anisotropic structure and material defects.
The visualization of sound propagation in solids is vital for transducer adaptation and
better understanding of complex test samples and their wave propagation modeling. In this work we
present an electrodynamic technique detecting the grazing sound beam with a 10 mm-sized electrodynamic
probe. The particle displacement along the samples surface was then measured as a function
of time and position. Adapting the electrodynamic probe and its coil alignment allows for measuring
the displacement components in all three dimensions. Thus horizontal and vertical particle
displacement with respect to the surface can be detected. A SNR of up to 40 dB could be achieved
within ferromagnetic and high conductive chrome steel when using a shear wave generated by an
angle beam probe. When dealing with nonconductive materials such as PMMA we obtained a reduced
SNR of 12 dB. We report on measurements of the sound field in complex weld joints. One example
shows a narrow gap weld joining a nickel alloy with a chrome steel. The weld of the 80 mm-thick test
block shows a distinct anisotropic texture. The system enables us to visualize the wave propagation
within the weld and indicates the reflection and scattering scenario and the energy losses due to both
the anisotropic structure and material defects.