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A new approach for the investigation of geometry effects in impact-echo measurements

Experimental results and numerical simulations
Eine neue Näherung für die Untersuchung von Geometrieeinflüssen bei Impakt-Echo-Messungen. Experimentelle Ergebnisse und numerische Simulationen
: Algernon, D.; Wiggenhauser, H.; Schubert, F.

Deutsche Gesellschaft für Zerstörungsfreie Prüfung e.V. -DGZfP-, Berlin; European Federation for Non-Destructive Testing -EFNDT-:
9th European Conference on NDT. ECNDT Berlin 2006. CD-ROM : September 25 - 29, 2006
Berlin: DGZfP, 2006 (DGZfP Proceedings BB 103-CD)
ISBN: 3-931381-86-2
10 S.
European Conference on NDT (ECNDT) <9, 2006, Berlin>
Fraunhofer IZFP, Institutsteil Dresden ( IKTS-MD) ()
zerstörungsfreie Prüfung; Schlagprüfung; Impulsechoverfahren; Geometrische Form; Einflußgröße; Näherungsverfahren; Theorie-Experiment-Vergleich

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.
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