doktorska disertacija
Matjaž Dremelj (Avtor), Aleš Straže (Mentor), Maks Merela (Komentor)

Povzetek

Raziskali smo vpliv naravnega staranja na izbrane fizikalne in mehanske lastnosti konstrukcijskega lesa navadne smreke (Picea abies) in bele jelke (Abies alba). Konstrukcijski les smo pridobili z 10 objektov in ga dendrokronološko datirali. Starost lesa je bila 95 do 391 let po poseku. Kemijske lastnosti lesa smo analizirali s FT-IR spektroskopijo, strukturne in histokemijske lastnosti pa s svetlobno in elektronsko vrstično mikroskopijo (SEM), podprto z energijsko rentgensko spektroskopijo (EDX). Barvo smo določali vizualno, ter instrumentalno, po CIELab standardu. Med fizikalnimi lastnostmi smo določali gostoto lesa, gostoto celičnih sten, difuzivnost za vodno paro, sorpcijske lastnosti ter krčenje in dimenzijsko stabilnost lesa. Mehanske lastnosti smo določali statično, s standardnimi tehnikami, ter dinamično z ultrazvokom in z metodo frekvenčnega odziva. Reološke lastnosti lesa smo določali s statičnimi leznimi in mehanosorptivnimi testi. Pri starem lesu smo glede na recentni (nedavno posekani) les potrdili manjšo gostoto celičnih sten, temnejšo barvo, s potrjeno celotno barvno spremembo (⠆E*), kjer je svetlost barve (L*) s starostjo lesa značilno padala. V ranem lesu smo pri obeh lesnih vrstah ugotovili večanje kromatičnosti barve (+a*, +b*), v kasnem lesu pa nižanje rumenega barvnega odtenka (-b*). S staranjem lesa se je značilno zniževal relativni delež hemiceluloz (RDH), povečevala pa se je stopnja kristaliničnosti celuloze (IK), ter v kasnem lesu smrekovine tudi O/C-razmerje. V celičnih stenah starega lesa smo lokalno zaznali razslojevanje in radialne mikro porušitve. Ugotovili smo, da ima star les obeh vrst nižjo ravnovesno vlažnost in higroskopnost (Δs = -0,04 %/%), ter nižjo vlažnost nasičenja celičnih sten (TNCS), pri čemer dimenzijska stabilnost in difuzivnost ostajata enaki. Vzdolž lesnih vlaken smo pri starem lesu potrdili višje hitrosti zvoka in ultrazvoka, nižje dušenje, višjo specifično dinamično in statično togost, ter višjo natezno in specifično tlačno trdnost ter trdoto lesa. Upogibna trdnost in udarna žilavost se pri starem lesu nista spremenili. V prečni ravnini, le v tangencialni smeri, je bila pri starem lesu manjša specifična normalna in strižna togost, ter nižja specifična trdota, ter natezna in specifična strižna trdnost. Pri starem lesu smo v primerjavi z recentnim lesom potrdili manjše relativno lezenje ter mehanosorptivne deformacije.

Ključne besede

les;naravno staranje lesa;kemijske lastnosti;zgradba lesa;fizikalne lastnosti;mehanske lastnosti;lezenje;

Podatki

Jezik: Slovenski jezik
Leto izida:
Tipologija: 2.08 - Doktorska disertacija
Organizacija: UL BF - Biotehniška fakulteta
Založnik: [M. Dremelj]
UDK: 630*833:630*812(043.3)
COBISS: 197363971 Povezava se bo odprla v novem oknu
Št. ogledov: 118
Št. prenosov: 31
Ocena: 0 (0 glasov)
Metapodatki: JSON JSON-RDF JSON-LD TURTLE N-TRIPLES XML RDFA MICRODATA DC-XML DC-RDF RDF

Ostali podatki

Sekundarni jezik: Angleški jezik
Sekundarni naslov: Effect of natural ageing on selected physical and mechanical properties of structural timber
Sekundarni povzetek: The influence of natural ageing on selected physical and mechanical properties of Norway spruce (Picea abies) and silver fir (Abies alba) structural timber was investigated. The wood was obtained from 10 buildings and dendrochronologically dated. The with ages were 95 to 391 years after felling. The chemical properties of the wood were analysed by FT-IR spectroscopy and the structural and histochemical properties by light and scanning electron microscopy (SEM), supported by energy dispersive X-ray spectroscopy (EDX). Colour was determined visually and instrumentally according to the CIELab standard. Physical properties included wood density, cell wall density, water vapour diffusivity, sorption properties, shrinkage and dimensional stability of the wood. The mechanical properties were determined statically using standard techniques and dynamically using ultrasound and vibration resonance method. The rheological properties of the wood were determined by static creep and mechanosorption tests. For aged wood, we confirmed a lower cell wall density compared to recently felled wood, a darker colour with a confirmed overall colour change (⠆E*), whereby the colour lightness (L*) decreased significantly with the age of the wood. An increase in colour chromaticity (+a*, +b*) was observed in the earlywood and a decrease in the yellow hue (-b*) in the latewood. The relative proportion of hemicelluloses (RDH) decreased with wood ageing, while the degree of cellulose crystallinity (IK) increased and the O/C-ratio in the late wood of the spruce also increased. Local delaminations and radial microcracks were found in the cell walls of the aged wood. We found that aged wood of both species exhibited lower equilibrium moisture content (EMC) and hygroscopicity (Δs = -0.04 %/%) and lower cell wall saturation moisture content (FSP), while dimensional stability and diffusivity remained the same. Parallel to the grain, higher sound and ultrasonic velocities, lower damping, higher specific dynamic and static stiffness as well as higher tensile and specific compressive strength and hardness of the wood were confirmed in the aged wood. Bending strength and impact toughness are unchanged in aged wood. In the transverse plane, the aged wood exhibited a lower specific normal and shear stiffness and a lower specific hardness, tensile and specific shear strength only in the tangential direction. Relative creep and mechanosorptive deformations were lower in aged wood than in recent wood.
Sekundarne ključne besede: wood;natural ageing;chemical properties;wood structure;physical properties;mechanical properties;creep;
Vrsta dela (COBISS): Doktorsko delo/naloga
Študijski program: 0
Komentar na gradivo: Univ. v Ljubljani, Biotehniška fak.
Strani: 1 spletni vir (1 datoteka PDF (XXI, 183 f., [6] f. pril.)
ID: 24245286