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The springback effect in molded wood laminations within the elastic range has, to date, not yet been mathematically described. Once cured, residual internal stresses within the laminations cause the final form to deviate from that of the die. Test pieces of beech laminations of 1 mm, 2 mm and 4 mm thicknesses and stack sizes of between 2 and 16 laminations were used. The elasticity value of each stack was obtained using non-glued laminations in a three-point bending test within the elastic region. The laminations were glued with polyurethane resin and mounted in a radius form die. The stress induced by the die onto the stack is within the elastic region of the material without any prior chemical or physical plasticisation of the wood. After curing was complete and the laminations removed from the die, the actual radius was calculated using a circular equation within the CAD program, using three measurement points taken from the stack. The radius of the die within the limits of this study has a negligible effect when predicting the springback of the stack. The exponential correlation between springback and the number of laminations, was used to calculate the springback effect on molded laminated stacks.
Similar to a normal wave, a shock wave travels as energy through matter but it causes an abrupt raise of pressure, temperature and density. In this study the influence of shock waves on wood structure were investigated in the light of possible future industrial utilization e.g. timber impregnating treatment.
Similar to a normal wave, a shock wave travels as energy through matter but it causes an abrupt rise of pressure, temperature and density. In this study, the influence of shock waves on wood structure were investigated in the light of possible future industrial utilization e.g. timber impregnating treatment. The constructed autoclave is capable of creating shock waves either by an electrical pulse breakdown of a spark gap arrangement or by electromagnetic actuators. The penetration depths of the fir wood test samples were measured using light microscopy, SEM and micro-computed tomography. Our results showed that by varying the intensity of the incident shock wave, the distance between the shock wave generating device and the test sample, and/or the orientation of test sample in relation to the shockwave, the wood tissue structure had been heavily disintegrated or hardly affected at all. An improvement on impregnation could not be found.
Einfluss der Schlichte von Celluloseregeneratsfasern auf die Zugscherfestigkeit bei Holzverklebungen
(2020)
Es wurden Längszugscherversuch an mit Celluloseregenaratfaser (CRF) verstärktem Epoxidharz durchgeführt. Dabei wurden die Festigkeiten von CRF mit und ohne Schlichtemittel verglichen. Die dauerhafte Ausbildung eines stabilen Verbundes zwischen CRF und Epoxidharz ist weiterhin problematisch. Der Einsatz eines Schlichtemittels wirkt sich nicht auf die Verklebbarkeit der Fasern in der Matrix aus. Sowohl die Werte des Zugscherversuchs als auch die makroskopischen Bruchbilder und die mikroskopischen Analysen von Rissen in der Matrix zeigen keine nennenswerten Unterschiede zwischen beiden untersuchten Varianten.