UDK: 630*81:674.031.632.2(497.6 Kladanj)            582.632.2:674.038.17(497.6 Kladanj) There are many factors that affect appearance and spreading of the red heart in beech stands. Therefore, this research presents an analysis of site quality class and taxation elements (diameter at the breast height, height of the tree and age of the tree) influence on the participation and distribution of the red heart in the forest compartments 107. M.U. „Gosteljaˮ - (II- quality class) and 47. M.U. „Srednja Drinjačaˮ - (III- quality class). The appearance of the red heart on the beech trees considering on the site quality class was researched, as well as the red heart appearance frequency in dependence on the tree diameter at the breast height and age of the tree, size and distribution of the red heart in the longitudinal and transverse direction. The results of research showed that the number of trees with the red heart and the length of the technical roundwood with the red heart increase with increase of diameter at the breast height (age of the tree). As well, it was established that the appearance frequency of the trees with red heart considering the diameter at the breast height (the age of the tree) was larger on the stands belonging low quality site classes. The site quality class affects the distribution of the red heart at the thicker beech trees in the longitudinal direction, while at the thinner and trees of medium diameter, the influence of site quality class on the distribution of the red heart is not expressed in great extent. Larger diameters of the red heart in average have beech trees on the low quality site classes.

Abstract This paper presents numerical analysis of the effects of tenon length on flexibility of mortise and tenon joints. Numerical calculations are carried out with a linear elastic model for orthotropic material. The mathematical model is solved by a finite element method. The results of the calculation indicate that a mortise and tenon joint becomes stiffer as tenon length increases. A satisfactory agreement was found between the experimental data taken from literature and the obtained results, thus confirming the conclusions made. Rotation stiffness was determined and also used in the structural analysis of a simple furniture frame. The results revealed that stiffness of joints in a frame had a considerable impact on the structure deflection.

The FV method was originally developed for fluid flow, heat and mass transfer calculations (Patankar, 1980), and later generalized for stress analysis in isotropic linear and non-linear bodies (Demirdžic & Muzaferija, 1994; Demirdžic et al., 1997; Demirdžic & Martinovic, 1993). For the purpose of the stress analysis in the wood, the method is modified to take into account the anisotropic nature of the wood and influence of the moisture content and the temperature on the deformation and stresses (Horman, 1999). Also, performance of the wood is found to be very sensitive to the moisture content and the temperature. Thus, it is of a great importance to be able to predict behavior of such materials under different hygrothermo-mechanical loads. In order to demonstrate the methods capabilities, a transient analysis of fields of temperature, moisture, and stresses and displacement in the wood subjected to hygro-thermal or mechanical loads is performed.

This paper presents numerical analysis of stress and strain conditions of a three-dimensional furniture skeleton construction and its joints. The fi nite volume method is used in the calculation. Orthotropy of the wood material is accounted for by approximating it with an isotropic material whose elastic modulus and Poisson’s ratio are calculated by employing the least-square method. The displacement of the edge point for the loaded joint was also determined experimentally. The agreement of results of the calculation and experimental data can be considered satisfactory. The numerical results presented in this paper also provided an opportunity for identifi cation of the region with the largest load and strain in the complex chair skeleton construction, which is one of the most complex pieces of furniture.

• This paper investigated the withdrawal capacity of the double-threaded nuts mounted in 3D-printed materials. The basic technical properties and the withdrawal force of the double-threaded nuts for the specimens made of PLA, WPLA, and layered WPLA+PLA configuration (with and without STP adhesive) were investigated. The results are compared with the literature data of withdrawal force for beech wood, MDF, and par-ticleboard with and without the adhesive. The research has determined the effects of the properties of 3D printed materials (density, compressive and tensile strength), the infill and printing patterns, and adhesive on withdrawal capacity of double-threaded nuts. Double-threaded nuts mounted with adhesive had higher withdrawal forces (about 25 % for PLA and WPLA specimens, and 15 % for layered WPLA+PLA specimens) than those mounted without adhesive. The highest values of withdrawal forces, regardless of the adhesive, were obtained for layered WPLA+PLA configuration, followed by WPLA, and the lowest for PLA. No significant difference was found be-tween the withdrawal forces for WPLA and layered WPLA+PLA specimens for both cases – with and without an adhesive. The withdrawal forces of double-threaded nuts for the PLA specimens were higher than the withdrawal forces for the beech (16.7 % mounted without adhesive and 11.6 % mounted with an adhesive), and other combinations showed a difference higher than 35 % in favor of 3D printed materials. The present analysis, which determines and compares used traditional dismountable connectors in 3D-printed furniture elements, is applicable for research and practice.