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- Impact-Echo (3)
- Impact-echo (3)
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- Automated NDE (1)
- Automated testing (1)
- Brückenuntersuchungen (1)
- Concrete (1)
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Laser vibrometric contactless sound field measurements at a concrete test block are presented. Both excitation by an ultrasonic probe and by an impactor were used. The wave modes can be identified by their geometric wave forms and propagation velocities. Additionally, numerical simulation of the experimental situation is used to support this interpretation. Possible applications of the presented technique are discussed. ©2005 American Institute of Physics
Impact-Echo (IE) measurements on concrete structures with compact
dimensions are influenced by geometry effects, i.e. reflections especially of the
surface waves at the boundaries of the test object, which in fact can lead to
misinterpretation of the results. In contrast to the normal reflection arrangement, in
which the excitation and the measuring sensor are placed on the same side of the
specimen, measurements were carried out in a transmission arrangement, where the
impactor and the measuring sensor are placed opposite to each other. This serves to
reduce the influence of surface waves, and to investigate further their responsibility
for the existence of geometry effects. Results obtained from laboratory specimens
with smooth surfaces were still seriously affected by geometry effects. Numerical
simulations led to the conclusion that surface waves travel around the edges of the
specimen, thus creating geometry effects even on the opposite side. Measurements
on a specimen, which was cut out from a bridge structure and had irregular
connecting planes between the excitation and the measurement side, proved to be
remarkably less affected.
In order to analyze and visualize the surface wave propagation an arrangement is
used, in which the excitation is fixed at a certain point on one plane of the specimen.
A transducer scans all planes of the specimen in phase with the excitation. Time
slices show the instantaneous wave field on all planes of the specimen. These are
compared with numerical simulations. In particular, it can be proved that surface
waves indeed travel around the edges of a specimen with smooth connecting planes,
thus creating geometry effects even in the transmission arrangement.