Utjecaj posmične brzine i vrste drva na hrapavost obrađene površine

In this study, the surface roughness values of planed beech-wood (Fagus L.), oak-wood (Quercus L.) and fir-wood (Abies alba Mill.) specimens were examined. The samples of beech-wood were cut from steamed beech-wood and from thermally modified beech-wood (212oC). The specimens were machined by planing in radial directions with two knives at 6, 12, 18 and 24 m/min feed speed. The cutting depth of 2.0 mm was constant and knife rake angle was 15o. The machining experiments were carried out using a single cutter-block of a Weinig Powermat 400. The cutter-block with a diameter of Ø 125 mm rotated at 6000 revolutions per minute (RPM). Surface roughness was measured from the radial face of each sample according to DIN 4768 (1990) by using Mitutoyo SJ-201 stylus scanner. Comparison between the results of surface roughness of four species showed that surface roughness increases with the increase of feed rate. The surface quality of samples of planed beech-wood, oak-wood and fir-wood were significantly different. The samples of planed surface of oak-wood had the best quality and the samples of fir wood had the highest values of surface roughness. There were no significant differences in the surface quality of thermally modified and steamed beach-wood samples despite the significant difference in mechanical and physical properties of thermally modified and steamed wood.Rad predstavlja istraživanja kvalitete blanjane površine bukovih, hrastovih i jelovih uzoraka. Bukovi su uzorci izrađeni od parene bukovine i termički modificirane bukovine (212 oC). Istraživanja su provedena na uzorcima blistača, koji su blanjani u radijalnom smjeru. Alat za blanjanje imao je dvije oštrice, a blanjano je pri posmičnim brzinama 6, 12, 18 i 24 m/min. Dubina blanjanja bila je konstantna i iznosila je 2,0 mm, a prsni je kut oštrica alata bio γ = 15o. Eksperiment je proveden na četverostranoj blanjalici Weinig Powermat 400. Promjer putanje rezne oštrice bio je 125 mm, a broj okretaja radne osovine 6 000 min-1. Hrapavost površine mjerena je po duljini obrade, u skladu sa normom DIN 4768 (1990) upotrebom elektromehaničkog profilometra Mitutoyo SJ-201. Usporedbom dobivenih rezultata za sve četiri vrste uzoraka može se zaključiti da se s povećanjem posmične brzine povećava hrapavost površine. Kvaliteta blanjane površine za različite je vrste drva različita u jednakim uvjetima obrade. Najmanju hrapavost imali su uzorci hrasta, a najveću uzorci jele. U istraživanjima nije zabilježena značajna razlika između kvalitete površine uzoraka od parene bukovine i termički modificirane bukovine usprkos mnogo lošijim mehaničkim svojstvima termički modificiranog drva u odnosu prema parenom drvu

Utjecaj tehnologije lijepljenja na fizikalna i mehanička svojstva lamelirane drvne građe

This paper presents the analysis of the influence of conventional hot (CH) and high frequency (HF) gluing on relevant physical and mechanical properties of Laminated Veneer Lumber (LVL) made from beech peeled veneer with the thickness of 2.1 mm. Student’s T-test was applied to determine the signifi cance of differences between mean values of results obtained for the two different treatments. A significant difference has been determined for the thickness loss, density, moisture and bending strength, while no statistically significant difference has been established for the modulus of elasticity and shear strength of gluing between the means of the tested samples.U radu je istraživan utjecaj klasičnoga vrućeg (KV) i visokofrekventnog (VF) lijepljenja na neka relevantna fizikalna i mehanička svojstva uzoraka lamelirane drvne građe (LVL) dobivene od listova ljuštenoga bukova furnira debljine 2,1 mm. Prikazani su i analizirani dobiveni rezultati. Primijenjen je T-test za određivanje značajnosti razlike artimetičkih sredina dvaju skupova uzoraka. Za smanjenje debljine, gustoću, sadržaj vode i čvrstoću na savijanje utvrđena je signifikantna razlika, a za modul elastičnosti i čvrstoću lijepljenja nije utvrđena signifikantna razlika artimetičkih sredina ispitivanih uzoraka izrađenih primjenom različitih tehnologija lijepljenja

Analiza naprezanja i deformacije furnirskog otpreska sjedala

In this paper, the stress and strain analysis of common laminated wood seat shell is performed. Experimental stiffness evaluation is conducted by measuring displacement of the point on the backrest, and experimental stress analysis is carried out by tensometric measuring at the critical transition area from the seat to the backrest. Finite element analysis is carried out layer by layer with a “2D linear elastic model” for orthotropic materials. Good matching is found between numerical and experimental results of displacement. It is also shown that the results of the principal stress in the measurement points of the seat shell compare favourably with experimental data. The applied in-plane stress analysis of each individual veneer is not applicable for interlaminar stress calculations that are a significant factor in curved forms of laminated wood. Curved forms of laminated wood products require more complex numerical analysis, but the method can be used to achieve approximate data in early phase of product design.U radu je provedena analiza naprezanja i deformacija uobičajenog otpreska sjedala. Eksperimentalna procjena krutosti napravljena je mjerenjem pomaka točke na naslonu sjedala, a eksperimentalna analiza naprezanja obavljena je tenzometrijskim mjerenjem na kritičnom prijelazu između sjedala i naslona. Analiza metodom konačnih elemenata provedena je sloj po sloj 2D linearnim elastičnim modelom za ortotropne materijale. Dobivena je dobra podudarnost računskih i eksperimentalnih rezultata pomaka. Također je potvrđeno da su rezultati glavnog naprezanja u mjernim točkama furnirskog otpreska sjedala usporedivi s eksperimentalnim podatcima. Odabrana analiza naprezanja u ravnini svakoga pojedinačnog furnira nije primjenjiva za izračun interlaminarnih naprezanja, koja su važan čimbenik zakrivljenog oblika uslojenog drva. Naime, takvi oblici uslojenog drva zahtijevaju složeniju računsku analizu, no metoda se može primijeniti za postizanje približnih podataka u ranoj fazi projektiranja proizvoda

Odnosi šumarstva i drvne industrije u Federaciji BiH

Šumarstvo i drvna industrija važne su gospodarske grane u Federaciji Bosne i Hercegovine (FBiH), a svoj razvoj zasnivaju na korištenju domaćih prirodnih resursa. Drvna industrija ima višegodišnju tradiciju i najstarija je industrijska grana u BiH. Ekološki je prihvatljiva, ima velik izvozni potencijal i bilježi visok suficit. Iako predstavljaju povezani lanac u stvaranju dodatne vrijednosti, dosadašnja je praksa pokazala da odnosi između šumarskih poduzeća i poduzeća koja se bave preradom drva nisu u dovoljnoj mjeri i na najbolji način uređeni, kako u vrijeme dok su bili zajedno organizirani, tako ni sada kada su odvojeni. U stručnoj i znanstvenoj javnosti prevladava opća ocjena da iskorištenost drva i šumskoga potencijala, funkcionalnost i raspoloživost kapaciteta za preradu drva ne zadovoljava. Također je očito da nema koordiniranoga strateškoga sektorskoga i međusektorskoga pristupa za snažniji razvoj ove grane gospodarstva. Cilj je ovoga rada sagledavanje i analiziranje odnosa šumarstva i prerade drva u FBiH, identificiranje najznačajnijih problema, te davanje prijedloga mjera za unapređenje tih odnosa odnosno za unapređenje stanja ovih gospodarskih djelatnosti u cjelini. Dobiveni rezultati nakon provedene podrobne analize pokazuju vrlo slabu institucionalnu povezanost ovih djelatnosti i nemogućnost donošenja i/ili usuglašavanja zajedničkih strateških ciljeva. Utvrđeno je i značajno odstupanje između instaliranih kapaciteta prerade drva u odnosu na trenutačne proizvodne mogućnosti šumarskih poduzeća te su definirane mjere za ublažavanje navedenoga stanja. Provedenom SWOT analizom drvnoindustrijskih poduzeća identificirane su i vrednovane sve unutarnje snage i slabosti, vanjske prilike i prijetnje, te je u konačnici definirana najprikladnija strategija – strategija saveza. Sve provedene analize upućuju na opći zaključak da se strateški ciljevi drvne industrije ne mogu, realno uzevši, ostvariti bez suradnje i koordiniranoga djelovanja sa šumarstvom, i obratno

Numerical and experimental investigations of polymer viscoelastic materials obtained by 3D printing

The aim of this research is to determine the relaxation and creep modulus of 3D printed materials, and the numerical research is based on the finite volume method. The basic material for determining these characteristics is ABS (acrylonitrile butadiene styrene) plastic as one of the most widely used polymeric materials in 3D printing. The experimental method for determining the relaxation functions involved the use of a creep test, in which a constant increase of the stress of the material was performed over time to a certain predetermined value. In addition to this test, DMA (dynamic mechanical analysis) analysis was used. Determination of unknown parameters of relaxation functions in analytical form was performed on the basis of the expression for the storage modulus in the frequency domain. The influence of temperature on the values of the relaxation modulus is considered through the determination of the shift factor. Shift factor is determined on the basis of a series of tests of the relaxation function at different constant temperatures. The shift factor is presented in the form of the WLF (Williams-Landel-Ferry) equation. After obtaining such experimentally determined viscoelastic characteristics with analytical expressions for relaxation modulus and shift factors, numerical analysis can be performed. For this numerical analysis, a mathematical model with an incremental approach was used, as developed in earlier works although with a certain modification. In the experimental analysis, the analytical expression for relaxation modulus in the form of the Prony series is used, and since it is the sum of exponential functions, this enables the derivation of a recursive algorithm for stress calculation. Numerical analysis was performed on several test cases and the results were compared with the results of the experiment and available analytical solutions. A good agreement was obtained between the results of the numerical simulation and the results of the experiment and analytical solutions

Bending moment of mortise-and-tenon joints in a crossed chair base. : [Moment savijanja spojeva s čepom i rupom na križnoj potkonstrukciji sjedala stolice]

This paper investigated the bending moment of chair base joints. The ultimate bending moments (maximum moment), calculated on the base of the measured maximum applied loads (maximum force), were compared for the front leg and rear leg joints of a chair base. The joints had different angles between the stretcher and the leg (joint angle) as well different tenon lengths (30 mm and 32 mm). The results of the tests indicated that for different test specimen configurations but the same tenon-and-mortise geometry, the maximum force of joints with a smaller value of joint angle (front leg joints) was higher than the force values of joints with a larger angle (rear leg joints) for all tenon lengths. However, the results showed less difference among the calculated bending moments of the analysed sets of joints. A significant difference was not revealed between the bending moments of joints with a smaller value of joint angle and the bending moments of joints with a larger angle for all tenon lengths. A significant difference between the bending moments for the tenon length of 30 mm and tenon length of 32 mm was determined for rear leg joints but not for front leg joints. The presented approach of joint strength analysis through the testing of specimens with different shapes and dimensions are applicable to research and practice. U radu je proučavan moment savijanja spojeva na križnoj potkonstrukciji sjedala stolice. Krajnji momenti savijanja (najveći moment), izračunani na temelju izmjerenih najvećih opterećenja (najveća sila), uspoređeni su za spojeve prednjih i stražnjih nogu križne potkonstrukcije sjedala stolice. Spojevi su imali različite kutove između poveznika i noge (kut spoja), kao i različitu duljinu čepova (30 i 32 mm). Rezultati ispitivanja pokazali su da je za različitu konfiguraciju ispitnih uzoraka, ali za istu geometriju čepa i rupe, najveća sila bila veća za spojeve s manjim kutom (spojevi prednjih nogu) nego za spojeve s većim kutom (spojevi stražnjih nogu), i to za čepove obiju duljina. Rezultati su također pokazali manju razliku između izračunanih momenata savijanja analiziranih grupa spojeva. Nije utvrđena značajna razlika momenata savijanja spojeva s manjim i većim kutom za čepove obiju duljina. Značajna razlika između momenata savijanja za čepove dužine 30 i 32 mm utvrđena je za spojeve stražnjih nogu, ali ne i za spojeve prednjih nogu stolice. Prikazani pristup analize čvrstoće spojeva ispitivanjem uzoraka različitih oblika i dimenzija primjenjiv je u istraživanju i u praksi.Validerad;2023;Nivå 2;2023-04-17 (hanlid)</p

Strength and stiffness of 3D-printed connectors compared with the wooden mortise and tenon joints for chairs

In this study, 3D-printed connectors to replace the typical L-shaped joints in the construction of a chair were developed, tested and numerically analysed. Different connectors were designed and manufactured with a fused deposition modelling (FDM) 3D printer using acrylonitrile butadiene styrene (ABS) with the aim to find a simple shaped connector which could be used to build chairs and withstand standard chair loading requirements. The strength and stiffness of the joints were tested and compared with traditional beech mortise-and-tenon joints. Numerical stress and strain analyses were performed with the finite element method for an orthotropic linear-elastic model. The experimental results showed that joints with 3D-printed connectors achieved lower strength than the traditional wooden mortise-and-tenon joints with similar dimensions. The results indicate that the effect of reinforcement of the connector were not recognised due to the small thickness and inadequate geometric position and arrangement of the reinforcement ABS material. The chair assembled with 3D-printed connectors could withstand the loads for seating, but failed the backrest test according to standard EN 1728:2002. The connectors need to be optimised and reinforced to withstand standard loads