Upogibna trdnost in togost slojnatega furnirnega lesa (LVL) iz termično modificirane in nemodificirane bukovine / Bending strength and stiffness of laminated veneer lumber (LVL) made from thermally modified and unmodified beech veneer:

Cilj raziskave je bil definirati in razviti lesni kompozit z majhnim presekom, ki bo lepljen pri sobni temperaturi in bo lahko uporabljen kot ojacitveni material v lesenih okenskih profilih velikih dimenzij. Na osnovi pregleda objav je bil kot najprimernejsi kompozit izbran slojnat furnirni les (LVL). Izbran material za njegovo izdelavo je bil rezan 0,5 mm debel bukov (Fagus sylvatica L.) furnir, ki je bil zlepljen s poliuretanskim lepilom (Purbond HB 440) v 20 mm debel LVL. Ker je bil proucevan tudi ucinek termicne modifikacije, je bilo pol preizkusancev narejenih iz termicno modificiranega furnirja, pol pa iz nemodificiranega. Upogibna trdnost in togost preizkusancev sta bili doloceni s tritockovnim upogibnim testom. Termicno modificirani preizkusanci so dosegli 19 % nižjo upogibno trdnost kot nemodificirani, medtem ko se upogibni modul elasticnosti (togost) ni znacilno spremenil. Povprecne upogibne trdnosti do 150 MPa so bile zadovoljive, upogibni moduli elasticnosti okoli 13 GPa pa so bili bistveno pod želenimi vrednostmi, kar je bilo pripisano izboru pretankega furnirja in lepljenju pri sobni temperaturi, ki ne omogoca zgoscevanja lepljenca. The aim of the research was to define and develop a wooden composite with a thin cross-section and which could be used as reinforcement material in oversized wooden window profiles. An additional limitation was to bond the composite at room temperature. Based on a review of the literature, laminated veneer lumber (LVL) was chosen as the best option. The researched LVL samples were made of 0.5 mm thick, cut, beech (Fagus sylvatica L.) veneer, bonded with polyurethane adhesive (Purbond HB 440). Half of the samples were made of thermally modified veneers, and other half of unmodified. Bending strength and stiffness were determined with a three-point bending test. Thermally modified samples had on average 19 % lower bending strength compared to the unmodified samples, but the modulus of elasticity (stiffness) did not change significantly. The bending strength of up to 150 MPa was satisfactory, but the modulus of elasticity of 13 GPa was far below expectations. This is attributed to the selection of too thin veneer and too low bonding temperature, which does not enable densification of the composite.