TY - THES A1 - Hasenstab, Andreas Georg Maximilian T1 - Integritätsprüfung von Holz mit dem zerstörungsfreien Ultraschallechoverfahren N2 - Schadstellen im Inneren von Holzbauteilen (z. B. Innenfäule) oder baulich unzugängliche Oberflächenfäule stellen ein besonderes Problem dar, da diese von außen schlecht erkannt werden können und bei einer ausgeprägten Schädigung zu einem plötzlichen Versagen des Bauteils führen können. Ziel der vorliegenden Arbeit war es, eine Messapparatur zu entwickeln und damit zu untersuchen, ob und unter welchen Bedingungen Ultraschallechoverfahren an Holzbauteilen möglich sind. Weiter sollte untersucht werden, welche Schäden und Minderdicken mit Ultraschallecho von nur einer zugänglichen Seite aus geortet werden können. N2 - Wooden construction components bear serious problems, if they hold inner damage (e.g. interior rot) or damage of its surfaces at inaccessible locations. These failures are difficult to recognize from the outside, and might cause sudden malfunction of the structure. The aim of this work was to develop suitable measurement devices and to carry out investigations under which conditions ultrasonic echo technique can be successfully applied to wooden construction components. A further objective was to examine what kind of damage can be located with ultrasonic echo technique applied from only one accessible surface and if areas of reduced thickness can be determined. The investigations have shown that ultrasonic echo technique can be used at wooden constructions with longitudinal and transverse waves. For the first time, it was also possible to determine the different speeds of sound in wood for all polarizations and directions with low-frequency ultrasound. The coupling of the planar longitudinal wave probes (center frequency 100 kHz) required coupling media such as ultrasonic gel and Vaseline. This technique was better suited for smaller specimen with a thickness of less than 10 cm. No coupling media is necessary for the coupling of the transverse wave point contact probes (center frequency 55 kHz). With these probes also structures with larger dimensions could be examined. The use of transverse waves is better suited for several applications and many measurements have been carried out using the TD20 probes. The tests took place from one accessible side using pulse echo technique. Areas of reduced thickness can often be detected by receiving a direct echo, all other damage, e.g. rot, is indicated by shadowing the echo of the back wall. The sound velocity is calculated from the sound path and the transit time of the signal at an accessible part of the component. The echo impulse received from areas with reduced thickness or cavities can thus be related to a specific depth in the material. As the reason for the shadowing of the back wall echo is often not known, radiography with x-rays was used as a further non-destructive testing method and as second NDT method in special cases (reference method). A combination of digital radiography and mobile flash tube was also used and optimized for tests on wooden construction components and trees. The direct comparison between ultrasound technique and x-ray showed a trend towards similar detecting of defects. The ultrasound technique was more sensible for early damage detection. The combination of ultrasonic echo technique and radiography led to a very substantial reduction of possible misinterpretations of damage. Another example for the combination of methods was a fast investigation of large areas with ultrasonic echo technique, followed by an exact investigation at selected points with the minor destructive drilling resistance method. The research showed that ultrasonic echo applied from an accessible component side (only) permits the direct localisation of areas of reduced thickness, cavities, wooden pegs and large branches. Other damages such as rot or insect attack can be located indirectly by shadowing of the back wall echo. Thus a new testing method is available now for the non-destructive testing of wooden components. T3 - BAM Dissertationsreihe - 16 KW - Integritätsprüfung KW - Ultraschallechoverfahren KW - Holz PY - 2006 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-1427 SN - 978-3-86509-527-5 SN - 1613-4249 VL - 16 SP - 1 EP - 190 PB - Wirtschaftsverlag NW CY - Bremerhaven AN - OPUS4-142 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -