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This paper presents a numerical procedure for the analysis of complex laminate structures. The procedure is based on the application of reduced stiffness of complex laminate. Introduction of reduced stiffness of composite facilitates both linear and nonlinear numerical integration, i.e. the tangential stiffness matrix is translated in the classical plate theory problem. The formulated numerical procedure was implemented in the program system KOMIPS. Special subroutine REDKRUT that calculates reduced stiffness of the laminate was written, and its application in numerical verification of experiments conducted on chairs was presented in (Nestorovic, 2010). At the end of this work, for 3D stress and strain analysis of veneer composites, recommendations were given for experimental determination of all nine independent material constants E-x, E-y, E-z, v(xy), v(xz), G(xy), G(xz), G(yz), five of which were determined in the previous paper of the author (Nestorovic, 2010).

Fenomen linearnog izvijanja je očito vrlo bitan za stabilnosti tlačenih nosača. Kritična sila izvijanja predstavlja važnu karakteristiku za projektiranje čeličnih konstrukcija. Osim toga, postojanje ukrućenja na konstrukcijskim elementima ploče ima vitalnu ulogu u cilju povećanja kritične sile izvijanja. Međutim, ova ukrućenja izazvaju preraspodjelu načina izvijanja u smislu lokalnog i globalnog izvijanja. U ovom radu uvedena su poprečna i uzdužna ukrućenja stvarne gredne konstrukcije sa zadatkom da maksimalno povećaju kritične sile izvijanja. Funkcija cilja je pronaći optimalnu geometrijsku karakteristiku ukrućenja. Na osnovu metode konačnih elemenata, numerički model je napravljen uporabom Abakus programa za utvrđivanje kritične sile izvijanja. Rezultati su pokazali da poprečna ukrućenja i njhov položaj imaju znatan utjecaj na lokalno izvijanje, dok uzdužna ukrućenja imaju mali utjecaj na lokalno i globalno izvijanje., The linear buckling phenomenon is obviously very important for stability of compressed supports. The determination of buckling resistance is an important characteristic of the design of steel structure. Besides, the presence of stiffeners in structural plate elements has a vital role in order to increase critical buckling load capacity. However, these stiffeners cause a redistribution in buckling behaviour in terms of local and global buckling. In this paper the transverse and longitudinal stiffeners were employed on a real beam-column structure to maximize the critical buckling loads. The objective is to find the optimum geometry of stiffeners. Based on the finite element method, a numerical model is made using the Abaqus program in order to observe the critical buckling capacity. The results showed that the local critical buckling has been significantly affected by stiffener's position in the case of transverse stiffeners, but little effect is observed on the critical local and global buckling in the case of longitudinal stiffeners.

Experimental determination of the elastic constants of orthotropic composite materials and their bearing capacity (strength) for furniture intended for sitting, and numerical verification of the experiment results by analysing with the final elements, was performed on the basis of the theory of elasticity of orthotropic and anisotropic composite materials. The requisite and sufficient material constants were determined in the experiments: moduli of elasticity and Poisson’s coefficients (longitudinal and tangential) and skate modulus for plain stress. These constants, calculated by 3D measurements of deformation, are sufficient for determining the constitutive matrix of the lamina, and for reducing stiffness of the composite irrespective of the thickness of the layers, fibre orientation and choice of material. Experiments were conducted for the stiffness, shear and flexing of uniformly and complexly layered beech veneer sheets, while for new materials experiments for stiffness and shear in a uniform orientation were sufficient. Analysis of stiffness and deformations were conducted layer by layer, as well as by reduced volume stiffness for multi-layered orthotropic shells of chair systems by a method of final elements by application of a composite final element, where combined reduced membrane matrices and flexing matrices are used. Numerical verification of the experiments, including systems of furniture intended for sitting – chairs – was conducted using the KOMIPS software system, which contains in its library a composite final element of the sheet. Experiments with chairs were performed with the aim of determining the stiffness of such systems, and they were confirmed by analytical results and measurement of the real movements on selected models. The results of research provide the design, re-design, construction and determination of the dimensions of not just chairs, but also of any other girder or surface system based on laminates.

This paper describes the numerical and experimental methodology for analysis of plastic packaging buckling characteristics that are representative of its strength in the real life. The experiments were executed with 'GOM' equipment and 'ARAMIS' software application for modern optical 3D measurement of deformations. Numerical analysis was conducted by the application of finite elements using 'KOMIPS' software. The fundamental question to be answered is related to the mechanism of failure of foldable packaging - does the buckling precede plasticity or vice versa? This article will show how experimental results can be predicted by means of finite element analysis; this is found a very strong learning tool that would enable designers to improve the structural strength of the new products in future. Experimental and numerical analysis results to date have shown high degree of correlation. This paper describes the access that allows real structure behavior diagnostic, reliable prospect for structure in exploitation reacting, elements receiving for different decision making (operating regime, rehabilitation, reconstructions, revitalizations, optimization, confirmation to variable solution selection and so on), poor performance sample defining or structure loosening, structure life time estimation and similar. The described developed diagnosis access is shown in solved examples.

Products quality presents one of the main causes of every contemporary organized production, which includes it, in group of basic exit characteristics. According to national standard, quality mark is based on testing of its quality characteristics. A characteristic of quality has been divided into four groups of demands: functionality (functional dimensions and stability tests), rigidity, surface rigidity, quality of materials and work piece accuracy. Dining chair has been investigated by use of different wood joints, and some remarks on construction has been given. Two groups of investigated chairs has been mounted by use of metal fittings, and one group has been connected with wood dowels by use of PVA wood glue.

This paper presents a numerical procedure for the analysis of complex laminate structures. The procedure is based on the application of reduced stiffness of complex laminate. Introduction of reduced stiffness of composite facilitates both linear and nonlinear numerical integration, i.e. the tangential stiffness matrix is translated in the classical plate theory problem. The formulated numerical procedure was implemented in the program system KOMIPS. Special subroutine REDKRUT that calculates reduced stiffness of the laminate was written, and its application in numerical verification of experiments conducted on chairs was presented in (Nestorovic, 2010). At the end of this work, for 3D stress and strain analysis of veneer composites, recommendations were given for experimental determination of all nine independent material constants Ex, Ey, Ez, vxy, vxz, Gxy, Gxz, Gyz, fi ve of which were determined in the previous paper of the author (Nestorović, 2010)., Rad prikazuje numeričku proceduru za analizu struktura izrađenih od kompleksnih laminata. Postupak se temelji na primjeni reducirane krutosti komplesnog laminata. Uvođenjem reducirane krutosti kompozita numerička se integracija, kako linearne, tako i nelinearne, odnosno tangencijalne matrice krutosti, prevodi u problem klasične teorije ploča. Formulirana numerička procedura implementirana je u sklopu programskog paketa KOMIPS. Napisana je posebna subrutina REDKRUT, kojom se proračunavaju reducirane krutosti laminata, a njegova primjena u provjeri numeričkih eksperimenata provedenih na stolcima prikazana je u radu (Nestorovic, 2010.). Za 3-D analizu naprezanja i deformacija furnirskih kompozita na kraju ovog rada dane su preporuke za eksperimentalno određivanje svih devet neovisnih materijalnih konstanti: Ex, Ey, Ez, vxy, vxz, Gxy, Gxz, Gyz, od kojih je pet određeno u prethodnom autoričinu radu (Nestorović, 2010.).