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- Ultrasonic echo (6)
- Reconstruction calculation (4)
- SAFT (4)
- Ultraschallecho (4)
- Spannbeton (3)
- Spannkanäle (3)
- Ultrasonic imaging (3)
- Verpressfehler (3)
- Betonbauteile (2)
- Concrete (2)
Characterization of reflector types by phase-sensitive ultrasonic data processing and imaging
(2008)
Ultrasonic and radar imaging techniques are limited in resolution by the wavelength in the material, yet information beyond those limits is hidden in complex frequency dependent reflection coefficients. The analysis of the phase of complex reflection coefficients together with the properties of imaging algorithms can help to characterize and to classify indications of defects in concrete buildings. This paper describes a method to extract phase information from measurements and SAFT reconstructed images. The influencing factors like material properties, transducer characteristics, and imaging algorithms based on Born or Physical Optics approximations are elaborated. Simulated and experimental results are briefly discussed.
This paper presents the progress of successful location of grouting faults in tendon ducts with ultrasonic imaging. The examples were obtained in the research group FOR 384 funded by DFG (German Research Foundation). The co-operation of experimental research and modeling allowed imaging and identification of grouted and ungrouted areas of tendon ducts (including strands) in a large test specimen (40 m²). In addition to the criteria for indicating grouting faults in post-tensioned ducts known until now the phase evaluation of reflected ultrasonic pulses is described. Experiments and modeling of wave propagation are presented for reflections at metal plates in concrete (thickness range 0.5 mm to 40 mm) and for tendon ducts including strands.
The main part of the progress was achieved by automated measurements using dry contact transducers, 3D-SAFT reconstruction including phase evaluation and modeling considering wave propagation for typical elastic parameters and exact experimental site conditions. The results for shear waves as well as for pressure waves are compared in the frequency range from 50 kHz to 120 kHz.
Ultrasonic Reflection Properties at Interfaces Between Concrete Steel and Air: Imaging and Modelling
(2006)
Ultrasonic imaging of tendon ducts enables the precise localisation of grouting faults in many cases. Additionally to well known criteria for detecting grouting faults in tendon ducts recently new possibilities were developed. Two main effects influence the complex behaviour of wave propagation and reflection: a) different arrangement and number of strands or internal rebars; b) superposition of reflecting signals and different wave modes propagating into the interface region around the tendon duct. In order to understand the experimental results, EFIT modelling is performed (EFIT: Elastodynamic Finite Integration Technique).
Inhalt ist die zerstörungsfreie Detailuntersuchung von Holzbauteilen mit einem dreidimensional abbildenden Ultraschall-Echoverfahren. Das neu entwickelte 3D-Verfahren berücksichtigt den anisotropen Aufbau des Holzes. Die Bildschnitte und Projektionen werden aus flächigen Ultraschallaufnahmen berechnet. Die Messungen erfolgen an Probekörpern sowie an Bauteilen aus der Praxis. In dem Forschungsvorhaben wird die für Holz neue 3D-Rekonstruktionsrechnung verwendet und mit dem Ziel weiterentwickelt, unter Berücksichtigung der anisotropen Struktur des Holzes eine dreidimensional aufgelöste Abbildung von Reflektoren im Inneren der Holzbauteile zu ermöglichen. Damit werden die bisher für Holzbauteile zur Verfügung stehenden Verfahren entscheidend ergänzt, weil nun eine hochgenaue dreidimensionale Abbildung erreichbar ist (Auflösung: 20 mm und besser).
Investigations for the improvement of SAFT imaging quality of a large aperture ultrasonic system
(2015)
In parallel to the hardware development of an ultrasonic system for the investigation of thick concrete structures, a software package for interactive reconstruction of data for that special arrangement of ultrasonic transducers was developed. The system which is presented in a further contribution to this conference as "large aperture ultrasonic system" (LAUS) requires special features to the evaluation software because measuring positions can be in a non equidistant grid and there is the possibility to improve the measurement by adding measuring points interactively.
Starting from theoretical considerations to the image generation by measuring arrangements of synthetic aperture problems, solution approaches for imaging with SAFT (Synthetic Aperture Focusing Technique) algorithms in space and frequency domain of data from insufficient grid density are presented.
A wide range of issues that may arise in the application is precalculated by simulations and experimental studies, so that unavoidable artifacts can be identified and classified. A special focus is put on the application of thick concrete structures considering missing measuring points in a grid, grating lobes and surface waves.