Ojačanje spojeva između LVL elemenata polimerima ojačanim staklenim vlaknima i analiza metodom konačnih elemenata

The goal of this study was to investigate the effect of glass fiber reinforced polymer (GFRP) on joints made of laminated veneer lumber (LVL), through experimental data and evaluation by ANSYS finite element (FE) software. In order to fabricate LVL, veneer from poplar (Populus deltoides Bartr. ex Marsh) with 2.5 mm thickness and PVA adhesive were used. T-shape joints out of LVL were made and two wooden dowels were incorporated as well. Then GFRP was applied to reinforce the joints. GFRP in three grammages (100, 200 and 300 g/ m2) was adhered to joints with epoxy resin. Joints reinforcement was performed by a two-layer reinforcing agent. For comparing the effectiveness, half of the specimens were reinforced on sides and the other half on edges. Specimens were tested in static bending. The results have shown that GFRP had a significant effect on the strength of joints. Reinforced joints on both sides were stronger than those reinforced on edge. Joints reinforced with 300 g/m2 GFRP were improved by 35 % and 43 %, respectively, compared to 100 and 200 g/m2 grammage. Failure modes of specimens are dependent on GFRP grammage. The results of FE have shown that the highest concentration of stress and elastic strain was generated in the tension and compression zones of joints.Cilj rada bio je na temelju eksperimentalnih podataka i analize konačnih elemenata (FE) te uz pomoć softvera ANSYS istražiti utjecaj polimera ojačanog staklenim vlaknima (GFRP) na spojeve od lamelirane drvne građe (LVL). Za izradu LVL-a upotrijebljen je furnir drva topole (Populus deltoides Bartr. ex Marsh) debljine 2,5 mm i PVA ljepilo. Izrađeni su T-spojevi od LVL-a i ugrađena su dva drvena moždanika. Zatim je za ojačanje spojeva primijenjen GFRP u tri gramature (100, 200 i 300 g/m2) tako da je epoksidnom smolom zalijepljen na spojeve. Ojačanje spojeva izvedeno je dvoslojnim armaturnim sredstvom. Radi usporedbe učinkovitosti, polovica uzoraka ojačana je sa strane, a druga polovica na rubovima. Uzorci su ispitani na statičko savijanje. Rezultati su pokazali da GFRP ima značajan utjecaj na čvrstoću spojeva. Spojevi ojačani s obje strane bili su jači od onih ojačanih na rubu. Spojevi ojačani GFRP-om od 300 g/m2 poboljšani su za 35 % odnosno za 43 % u usporedbi s GFRP-om gramature100 i 200 g/m2. Načini loma uzoraka ovisili su o gramaturi GFRP-a. Rezultati analize konačnih elemenata pokazali su da se najveća koncentracija naprezanja i elastične deformacije pojavljuje u vlačnoj i tlačnoj zoni spojeva

Lijepljene lamelirane ploče kao radne ploče u kuhinji

The present study was conducted to investigate the possibility of using PVA-glued laminated panels in place of conventional kitchen countertops namely 32 mm thick MDF and 38 mm thick particleboard. Three types of glued laminated panels were manufactured by laminating two 16 mm thick MDFs, two 16 mm thick particleboards, and three 12 mm thick particleboards at a pressure of 3 MPa , a temperature of 25 0C and variable pressing times of 20, 30, and 40 minutes. Bending and shear strengths, water absorption, and thickness swelling of the laminates were measured and compared with a 32 mm thick MDF and 38 mm thick particleboard. The results indicated that the glued laminated panels remained more dimensionally stable compared to the conventional kitchen countertops. Particleboard laminates had improved bending and shear strengths compared to 38 mm thick particleboard. The results of this study demonstrated that PVA-glued laminated panels could be used as kitchen countertops.Istraživanje prikazano u radu provedeno je s ciljem ispitivanja mogućnosti uporabe lamelirane ploče lijepljene PVA ljepilom umjesto konvencionalnih kuhinjskih radnih ploča,MDF ploča debljine 32mm i iverica debljine 38 mm. Tri tipa lijepljenih lameliranih ploča proizvedena su od dvije MDF ploče debljine 16 mm, dvije ploče iverice debljine 16 mm i tri ploče iverice debljine 12 mm pri tlaku prešanja 3 MPa i temperaturi 25 oC, uz promjenjivo vrijeme prešanja od 20, 30 i 40 minuta. Mjerene su čvrstoća savijanja i čvrstoća smicanja, apsorbcija vode te debljinsko bubrenje lamelirane ploče i uspoređeno sa svojstvima MDF ploče debljine 32 mm i iverice debljine 38 mm. Rezultati su pokazali da su lijepljene lamelirane ploče dimenzionalno stabilnije od konvencionalnih kuhinjskih ploča. Lamelirana ploča od iverice imala je bolju čvrstoću savijanja i smicanja od ploče iverice od 38 mm. Rezultati istraživanja pokazuju mogućnost uporabe lameliranih ploča lijepljenih PVA ljepilom za kuhinjske radne ploče

Cell wall thickening in developing tension wood of artificially bent poplar trees

International audienceTrees can control their shape and resist gravity thanks to their ability to produce wood under tensile stress. This stress is known to be produced during the maturation of wood fibres but the mechanism of its generation remains unclear. This study focuses on the formation of the secondary wall in tension wood produced in artificially tilted poplar saplings. Thickness of secondary wall layer (SL) and gelatinous layer (GL) were measured from cambium to mature wood in several trees sampled at different times after tilting. Measurements on wood fibres produced before tilting show the progressive increase of secondary wall thickness during the growing season. After the tilting date, SL thickness decreased markedly from normal wood to tension wood while the total thickness increased compared to normal wood, with the development of a thick GL. However, even after GL formation, SL thickness continues to increase during the growing season. GL thickening was observed to be faster than SL thickening. The development of the unlignified GL is proposed to be a low cost, efficient strategy for a fast generation of tensile stress in broadleaved trees

Effect of extractions on dynamic mechanical properties of white mulberry (Morus alba)

International audienceVibrational properties of wood are affected by several parameters, of which extractives can be one of the most important ones. Wood for European musical instruments has been often studied, but traditional Middle Eastern ones had been left unnoticed. In this study white mulberry (Morus alba L.), the main material for long-necked lutes in Iran, was extracted by five solvents of various polarities (water included). Free-free bar forced vibrations were used to measure longitudinal (L) loss tangent (tanδ), storage (elastic) modulus (E′) and specific modulus (E′/γ) in the acoustic range. Their anisotropy between the 3 axes of orthotropy was determined by DMA (dynamic mechanical analysis). Native wood had a quite low EL′/γ but its tanδ was smaller than expected, and the anisotropy of tanδ and E′/γ was very low. Removal of extractives caused tanδ to increase and moduli to decrease. Acetone, the most effective solvent on damping despite a moderate extraction yield, increased tanδL by at least 20% but did not modify E′/γ as much. When used successively, its effects masked those of solvents used afterwards. Anisotropy of E′/γ was nearly unchanged after extraction in methanol or hot water, while tanδ was much more increased in R than in T direction. Results suggest that in white mulberry, damping is governed more by nature and localization of extractives rather than by their crud abundance

The effect of traditional hygro-thermal pretreatments on the acoustical characteristics of white mulberry wood (Morus alba)

The wood used in making musical instruments usually undergoes pre-treatments or conditioning. Some processes have resulted from laboratory research, while many treatments are applied by craftsmen usingtraditional methods that have not yet been scientifically assessed. This paper is based on laboratory methods which simulate hydrothermal pre-treatments traditionally applied by Iranian lute makers tomulberry (Morus alba), an important wood for lutes from the Middle East to Japan. By applying a cyclic process, drying (60°C) and ambient re-conditioning, which mimics wood seasoning and short-termaging, the damping coefficient (tanδ) was decreased down to 10% without negatively affecting specific modulus of elasticity (E’/ρ). Long-term (up to 4 months) soaking in cold water removed extractives, and decreased density as well as E’/ρ, but did not affect tanδ. Short-term hot water treatment removed as many extractives, but caused a smaller decrease in E’/ρ than cold water, and significantly increasedtanδ. This paper helps to clarify some traditional processes used by instrument makers, and can provide a basis for necessary cross-cultural scientific studies in the future

Intra-annual Secondary Growth Rate-Climate Relations of Fagus orientalis Lipsky in the Center of Hyrcanian Forests

Weekly rate of Beech tree ring increment were related to the changes of climatic factors in weekly intervals. In order to do so, small samples were extracted from 5 Oriental beech trees located in Nowshahr educational forest in the central part of the Hyrcanian forests of Iran during 2008 growing season. Microscopic sections were prepared and average increases in tree ring width were measured, standardized and modeled using Gompertz equation. The results showed that the minimum air temperature and water evaporation had the strongest and positive effect on the secondary growth rate while the role of precipitation was minor and negative. Air temperature and evaporation variations during growing season were assumed to remain in their optimum level; increasing xylem formation by accelerating carbohydrate production and carbon uptake of trees, respectively. Since the studied site had warm and humid climate receiving sufficient amount of rainfall before and during growing season, water availability was not a limiting factor of radial growth and its minor negative relation was interpreted according to its small hampering effect on the air temperature and sunlight absorption of trees. It was concluded that meteorological factors affecting secondary growth rate of trees should be interpreted as a package rather than analyzed disconnectedly

Study of linseed oil on white poplar wood (Populus alba L.) as a traditional treatment for historical wooden relics against weathering

Large part of wooden relics is located in open air spaces under weathering exposure. Conservation of the relics has a great importance due to their cultural values. Application of linseed oil in conservation backs to centuries ago. Today, it is used as a traditional treatment of wooden relics extensively. Regarding to importance of historical wooden relics, there is a need for detail study of traditional treatments. Therefore, conservative properties of linseed oil treatment on white poplar wood (Populus alba L.) was studied under weathering exposure. Firstly, linseed oil absorption of the wood samples was measured and its leaching was evaluated according to BS EN 84:1997. Treated wood samples were artificially weathered regarding to ASTM 2565-99. After 300 and 800 hours weathering, samples were analyzed by Colorimeter, FTIR spectroscopy and Scanning electron microscopy. Results showed that linseed oil treatment has a good resistance against leaching but causes to serious aesthetical changes which were continued during weathering process. FTIR data were indicated structural degradation of treated samples after weathering. The degradation was clarified as rupture and cracks of cell walls and vessel pits in SEM images of wood surface. Results signified inappropriate effects of linseed oil for conservation of wood in open air spaces

Wood Anatomical Structure of Morus alba L. and Morus nigra L., Native to Iran

Iran is a wast country with many different tree species. Among those there are two species of Morus genus including alba and nigra. Since long time ago, white mulberry�s wood (Morus alba) has been used for making musical instruments especially bowl shaped instruments in Iran.. In contrast, black mulberry�s wood (Morus nigra) has never been used for these types of applications. In order to investigate the possible replacement choices, this study has been carried out to investigate the anatomical differences and similarities between these two species. Wood samples of the two species have been collected from same site and microsections for light microscopic studies and maceration samples have been prepared. The anatomical characteristics were studied according to the IAWA List of Hardwoods. The most important similarities between them are: vessel solitary in short radial multiples or irregular clusters, fiber nonseptate, rays uniseriate and multiseriate type, paratracheal parenchyma, varying from vasicentric to aliform confluent, apotracheal as marginal bands, Rhombic crystals present in rays and sometimes in parenchyma. The main differences are: semi-ring porous distribution of vessels in M. alba, fewer number of vessels and presence of aliform parenchyma in M. nigra. Taking these results into consideration, the most important features of both species are similar and it could be recommended to use the nigra species as well as the alba for making musical instruments