Relevant properties of resonance spruce wood

Namesto tradicionalnega vizualnega in čutnega ocenjevanja kakovosti resonančne smrekovine smo v nalogi laboratorijsko analizirali njeno zgradbo ter fizikalne, mehanske in akustične lastnosti. Vzorčili smo les navadne smreke (Picea abies) s Pokljuke (1200 m n.v., oddelek 64), z majhnim letnim priraščanjem in jo primerjali s kontrolno smrekovino z nižje ležečega rastišča (Zavratec nad Idrijo, 650 m n.v.). Iz naravno posušenega lesa smo izdelali preizkušance (dimenzij 20 × 20 × 300 mm) za določanje dinamičnih in statičnih mehanskih lastnosti. Dodatno smo izdelali še poliedre (dimenzij 75 × 75 × 75 mm) in na njih izmerili hitrosti preleta ultrazvočnega valovanja v vseh anatomskih smereh in ravninah. Strukturne lastnosti smo določili s stereo-mikroskopom, izmerili smo širine branik, deleže kasnega lesa ter določili gostoto lesa. Ugotovili smo, da je smrekov les z dobrimi resonančnimi lastnostmi redek ter ima nizko gostoto (䁤 400 kg/m3), ozke (do 2 mm) in enakomerno široke branike, z majhnim deležem kasnega lesa (do 23 %). Resonančna smrekovina je bolj toga (specifična togost - E/ρ > 25 GPa) in ima značilno manjše dušenje mehanskih vibracij (tanρ 䁤 0,009). Pretvorba mehanske energije v zvočno je pri resonančni smrekovini boljša kot pri običajni smrekovini, to kažejo tudi akustični kazalniki (akustični koeficient R > 14,5 m4/s kgučinkovitost akustične pretvorbe ACE > 1500 m4/s kg).Instead of the traditional visual and sensory evaluation of the quality of resonance wood of Norway spruce (Picea abies), we analyzed its macroscopic structure and physical, mechanical and acoustic properties. We sampled spruce wood from Pokljuka (1200 m a.s.l., section 64) with narrow annual rings and compared it with a control spruce from a site at a lower altitude (Zavratec nad Idrijo, 650 m a.s.l.). Test specimens (dimensions 20 × 20 × 300 mm) were made from air-dried wood to determine dynamic and static mechanical properties. Polyhedra (75 × 75 × 75 mm) were also fabricated, on which the velocity of ultrasonic waves was measured in all anatomical directions (R, T, L) and planes. Structural properties were determined by stereo microscopewe measured the width of annual rings, the proportion of latewood, and determined the mean wood density. We found that spruce wood with good resonance properties is rare. It has low density (䁤 400 kg/m3), thin (up to 2 mm) and homogeneous annual rings with a low proportion of latewood (up to 23%). Resonance spruce wood is stiffer along the grain and usually has lower vibration damping (tanρ 䁤 0,009). The conversion of mechanical energy into sound is better with resonance spruce wood than with conventional spruce wood (acoustic coeficient R > 14,5 m4/s kgacoustic conversion efficiency ACE > 1500 m4/s kg)