diplomsko delo
Filip Žagar (Author), Željko Gorišek (Reviewer), Aleš Straže (Mentor), Luka Krajnc (Co-mentor)

Abstract

Pri konstrukcijskem žaganem lesu smo proučevali vpliv velikosti prereza in dolžine preizkušancev na določanje dinamičnih mehanskih lastnosti lesa. Izbrali smo smrekove preizkušance (Picea abies Karst.) brez vidnih anomalij, prečnega prereza 42 mm × 42 mm ter 42 mm × 84 mm, dolžine 4000 mm. Material smo uravnovesili v laboratoriju pri 20 °C in 50 % relativni zračni vlažnosti, gostoto lesa pa smo določali gravimetrično. Dinamične mehanske lastnosti smo določali z analizo frekvenčnega odziva pri vzdolžnem nihanju prosto vpetih preizkušancev ter s časom preleta ultrazvoka. Meritve smo izvajali sukcesivno, v 8 korakih, s krajšanjem preizkušancev v 500 mm intervalu, do končne dimenzije 500 mm. Gostota lesa je variirala med 400 kg/m3 in 656 kg/m3, z majhno variabilnostjo vzdolž posamičnega preizkušanca (KV = 13,5 %; KV - koef. variacije). Gostota lesa absolutno ni vplivala na hitrost preleta zvoka (vf), s povprečjem pri 4564 m/s (KV = 5,8 %), in na hitrost ultrazvoka (vUZ), kjer je znašala 5079 m/s (KV = 9,5 %). Hitrost zvoka in modul elastičnosti (Ef), določena pri frekvenčnem odzivu, sta bila neodvisna od dolžine preizkušancev. V več primerih pa smo opazili naraščanje hitrosti ultrazvoka ter posledično ultrazvočnega modula elastičnosti (EUZ) s povečevanjem dolžine preizkušancev. Razmerji vUZ/vf ter EUZ/Ef sta bili večji od ena, ter sta naraščali s povečevanjem prereza ter dolžine preizkušancev.

Keywords

les;dinamične mehanske lastnosti lesa;hitrost zvoka;hitrost ultrazvoka;nedestruktivno določanje;

Data

Language: Slovenian
Year of publishing:
Typology: 2.11 - Undergraduate Thesis
Organization: UL BF - Biotechnical Faculty
Publisher: [F. Žagar]
UDC: 630*812.149
COBISS: 74337539 Link will open in a new window
Views: 235
Downloads: 15
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Other data

Secondary language: English
Secondary title: Influence of specimen geometry on determination of dynamic mechanical properties of wood
Secondary abstract: In the case of structural timber, the influence of the cross - sectional size and the length of the specimens on the determination of the dynamic mechanical properties of wood were studied. We selected spruce (Picea abies Karst.) specimens without visible anomalies, having cross section of 42 mm × 42 mm and 42 mm × 84 mm, and length of 4000 mm. The material was conditioned in the laboratory at 20 ° C and 50 % air humidity, and the density of the wood was determined gravimetrically. The dynamic mechanical properties of wood were determined by analyzing the longitudinal vibration of free supported specimens and by the time of flight of the ultrasound. Measurements were performed successively, in 8 steps, by shortening the specimens in a 500 mm interval, to a final dimension of 500 mm. The density of wood varied between 400 kg/m3 and 656 kg/m3, with little variability along an individual specimen (CV = 13.5 %; CV – Coef. of variation). The density of wood had no effect on the sound velocity (vf), with an average at 4564 m/s (CV = 5.8 %), and on ultrasound velocity (vUZ), where it was 5079 m/s (CV = 9.5 %). The sound velocity and the modulus of elasticity (Ef) determined in the longitudinal vibration were independent of the length of the specimens. In several cases, we observed an increase in the ultrasound velocity and consequently the ultrasonic modulus of elasticity (EUZ) with increasing length of the specimens. The ratio vUZ/vf and EUZ/Ef were greater than one, and increased with increasing cross-section and length of the specimens.
Secondary keywords: wood;dynamic mechanical properties;sound velocity;ultrasound velocity;non-destructive testing;
Type (COBISS): Bachelor thesis/paper
Study programme: 0
Embargo end date (OpenAIRE): 1970-01-01
Thesis comment: Univ. v Ljubljani, Biotehniška fak., Oddelek za lesarstvo
Pages: X, 29 f.
ID: 13285850