Search

This paper presents the formulation of strain-based finite elements for modelling composite beams with finger joints considering slip between the layers. The finite elements are derived according to Reissner beam theory based on the modified principle of virtual work where the displacements and rotations are eliminated from the problem and the axial deformation, shear deformation and curvature of the layers remain only functions to be approximated within the finite element. Lagrange polynomials are used as shape functions to approximate the deformations and various interpolation methods are applied to numerical examples, with the Lobatto integration scheme giving slightly better results than Equidistant. The experimentally measured mechanical properties needed as input data for the numerical model are given for the four glued laminated beech beams. The numerical model is thoroughly verified and validated. The results show that the presented finite element formulation is an efficient tool for practical and accurate calculations.

Finger joints with standard geometries and adhesives used for joining coniferous wood are not sufficient in terms of strength when gluing beech wood. A numerical model of finger joined beech lamellas was prepared and simulations of tension tests were made. Parametric studies with multiple variables referring to geometrical properties of finger joints and two different types of applied adhesives were performed. The results showed a high influence of the finger joint geometrical parameters. Experimental tests on the tension strength of the finger joints were performed. To validate the numerical model, 20 mm long finger joints were produced and tested. Two types of adhesives were used, MUF and PRF. The finger joints were pressed under two different pressures. Prior to tension testing, the dynamic modulus of elasticity was measured with a strength grading machine and strength grade assignments were made. The influence of joining of the boards on the dynamic modulus of elasticity was analysed. The results of the tension tests of the finger joints showed a clear influence of the finger joint geometry, where highest strengths were obtained with longer and thinner fingers, while the influence of the adhesive seems to decrease with the length of finger joints

V letih sodelovanja z navtičnimi podjetji, ki izdelujejo in vgrajujejo pohištvo, smo opazili, da spoji na podbojih, ki jih vgrajujemo, ne prenesejo obremenitev vgradnje - pokajo. V predhodnih raziskavah pri mizarstvu Bobič d.o.o iz Novega mesta smo ugotovili, da problemi nastajajo že pri obdelavi lesa, kjer so spoji narejeni na zobati spoj. Proučevali smo vpliv lepila na mehanske lastnosti spoja oziroma na upogibno trdnost lepljenca z zobatim spojem. Uporabili smo masiven les smreke (Picea abies), macesna (Larix europea), rdečega merantija (Shorea leplosula), evropske češnje (Prunus avium)in hrasta - gradna (Quercus petrae). Les smo obdelali na dimenzijo 20x20x250 mm, ki je predpisana za 4 točkovni upogib po standardu EN 408. Za lepljenje smo uporabili več vrst lepil, ki so na slovenskem trgu: PVA-C RAKOLL E-WB 0301 D3 in RAKOLLr-GXL-4 Plus, PVA-C dvokomponentno Rakollit TM 80+ trdilec WS 1, PVA-C Titebond D3, AURO kazeinsko-hladno lepilo in PU lepilo Icema r 145/12. Ugotovili smo, da sta lepili RAKOLL E-WB 0301 D3 in RAKOLLr-GXL-4 Plus najbolj kakovostni in primerni za tako zahtevna lepljenja lesa. Through years of corporating and working with nautic factories, producing and building in furniture, we have noticed that doorjamb`s junctions crack, because they can not stand the burdening, caused by building in. In a preceding research at joiner`s Mizarstvo Bobič d.o.o. Novo mesto workshop we found out that the problems are taking shape through the treatment of the wood, where the junctions are toothed. To present how glue affects mechanical characteristics of the junction, respectively hardness, and how and where the mistakes are through treatement, preparing and on final sticking of the wood. The spruce (Piceas abies), larch (Larix europea), red meranti (Shorea leplosula), European cherry tree (Prunus avium) and oak tree (Quercus petrae) were used. The wood was cut under dimensions 20x20x250 mm, which are prescribed for 4-point bending test in occordance to EN 408. The following glues: PVA-C RAKOLL E-WB 0301 D3 and RAKOLLr-GXL-4 Plus, PVA-C two-composing Rakollit TM 80 + harder WS 1, PVA-C Titebond D3, AURO casein-cold glue and PU glue Icema r 145/12 , all avaliable on Slovenian market, were used. The glues RAKOLL E-WB 0301 D3 and RAKOLLr-GXL-4 Plus a of the best quality and appropriate for such a pretentious gluing.