Short description
(German)
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Holzverklebungen gewinnen zunehmend an Bedeutung. Die Klebfugen werden im praktischen Gebrauch neben statischen Belastungen durch die Konstruktion auch durch erhöhte Feuchtigkeit und Klimaschwankungen stark beeinflusst. Äussere Belas-tung und klimabedingte Eigenspannungen können verbunden mit dem mechanosorpti-ven Effekt zur Rissbildung und auch Delaminierung der Fugen führen. So ist bekannt, dass es im trockenen Wechselklima zum lokalen Delaminieren von furnierten Oberflä-chen kommen kann. Auch im Holzbau sind Schäden durch starke Zugspannungen in der Trocknungsphase bekannt. Im praktischen Gebrauch kommt es zu einer Überlage-rung von statischen und durch Klimawechsel bedingten Spannungen. Im Rahmen der Arbeit sollen Methoden der künstlichen Alterung von Vollholzverklebungen getestet werden und der Mechanismus des Versagens im Bereich der Klebfuge untersucht werden. Mittels Methoden der zerstörungsfreien Werkstoffprüfung (Durchschallung, Eigenfrequenzmessung) soll die Früherkennung einer Schädigung im Bereich der Klebfugen analysiert werden. Die Bearbeitung erfolgt in Kooperation der HSB Biel mit der ETH Zürich, Institut für Baustoffe, Holzphysik.
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Partners and International Organizations
(English)
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AT, BE, BG, CH, DE, DK, ES, FI, FR, GR, HR, HU, IE, IT, LT, LV, NL, NO, PL, PT, RS, SE, SI, SK, UK
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Abstract
(English)
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Adhesive bonds can improve the material behaviour of wood for special requirements and thus allow the utilisation of this natural material in many application areas. In practice such adhesive joints will be influenced by static loads and additionally by climate changes as well. These external loads and climatic eigenstresses in conjunction with the mechano-sorptive effect can result in crack propagation and delamination of the adhesive bond. It is well known that veneered surfaces show local delamination effects in dry-level climate variation. Moreover, heavy damages in timber structures caused by tensile stresses in consequence of drying processes can be observed. Thus the analyses had to be splitted into two general kinds of investigation. On the one hand methods for artificial and natural ageing processes of wood bondings were tested and on the other hand a numerical model for the prediction of failure mechanisms of the adhesive joints was developed. Using non-destructive test equipment, possible prediction characteristics of damaged adhesive bonds were analysed. Therefore, basic research about the influences of glue lines on the velocity of ultrasonic waves and their natural frequency response were carried out and verified at concrete examples of use. In this context measurements with shock and vibration equipment as well as different ultrasonic test devices were conducted to test their performance according to the detection of delamination effects in glued spruce and beech wood components. Thereby small and clean specimens were used to investigate the fundamental just as realistic glulam samples to verify the possible application of this method to wooden structures. Additionally, delamination experiments with spruce and beech wood glued with three different licensed adhesives exposed to natural and artificial weathering as well as specific climate changes were prepared, tested and analysed. Furthermore, the effect of the nonlinear material behaviour (creep, plasticity) with respect to the development of gluing failures in timber structures is investigated and partly integrated in the simulation. The project is conducted in cooperation with the HSB AHB Biel and the ETH Zurich, Institute for Building Materials, Wood Physics. Hence, at HSB bond lines of glued-laminated timber produced with melamine urea formaldehyde (MUF), phenol resorcine formaldehyde (PRF) and polyurethane (PUR) were investigated. The glued-laminated timber was tested according to the EN 302-2 delamination test. After this test the adhesive layers were laid open to investigate the adhesive with attenuated total reflection FT IR spectroscopy. The IR spectra are compared with those of adhesive layers in glued-laminated timber samples without a delamination test. Furthermore the application of MALDI TOF mass spectrometry was tested to characterise the hardened glues.
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