Istraživanje faktora trenja između furnira kao funkcije smjera protezanja vlakanaca i sadržaja vode

During the manufacture of veneer based moulded parts, veneers move against one another. Friction is caused due to this movement. Different conditions, such as gluing or fibre direction, could influence the friction coefficients and thus the moulding process. For a better understanding of the manufacturing process of veneer based moulded parts, it is important to know which parameters influence friction and friction coefficients. In this paper, results of friction investigations are presented. Thereby the moisture content of the used veneers was varied as well as the fibre direction. Considering the manufacture conditions, the investigations were also conducted with glue-coated veneers. The results prove an influence of fibre direction but this influence depends on moisture content.Tijekom proizvodnje furnirskih otpresaka furniri se gibaju jedan nasuprot drugome. Zbog toga gibanja nastaje trenje. Različiti uvjeti kao što su lijepljenje i smjer protezanja vlakanaca mogu utjecati na faktor trenja, a time i na proces izrade otpresaka. Za bolje razumijevanje procesa proizvodnje furnirskih otpresaka važno je znati koji čimbenici utječu na trenje i faktor trenja. U ovom su radu prezentirani rezultati istraživanja trenja između furnira. Varirani su sadržaj vode upotrijebljenih furnira, kao i smjer protezanja vlakanaca. Uzimajući u obzir i proizvodne uvjete, istraživanje se provodilo i s furnirima premazanim ljepilom. Rezultati su potvrdili utjecaj smjera protezanja vlakanaca, ali taj utjecaj ovisi o sadržaju vode u furniru

Composites en matières premières renouvelables et leurs procédés

National audienceThe development of new bio-based composites and efficient manufacturing methods that are suitable for series processing is the purpose of the current sub-project C4 of the Excellence Cluster MERGE, sponsored by DFG (Deutsche Forschungsgemeinschaft). Two different types of materials are combined: bio-based thermoplastic biopolymers such as bio-polyethylene (BioPE) or bio-polyamides (BioPA) and renewable reinforcing materials such as thin wood veneer or unidirectional flax fibers. To achieve a high-efficiency in terms of mass-production, reproducibility and flexibility, it is required to overlap several steps in the realization of semi-finished and final products. The improvement of the adhesion at the interface of the components, the implementation of continuous processes in order to increase energetically the yielding and the final design, through several methods, for the future potential applications are so many perspectives to achieve. MOTS-CLÉS : polymère bio-basé thermoplastique; renforcement naturel (Lin ou placage en bois) ; Amélioration de l'adhésion à l'interface matrice/renforcement ; Procédés plastic/textile continu ; Application dans l'automobile et équipement sportifsLe développement de matériaux bio-basés et de méthodes efficaces de mise en forme, adaptable à la production en série, est le but de l'actuel sous-projet C4 du programme d'excellence MERGE financé par la DFG (Deutsche Forschungsgemeinschaft). Ainsi, deux types de matériaux sont combinés : Des polymères bio-ressourcés thermoplastiques tels que bio-polyéthylène (BioPE) ou bio-polyamide (BioPA) et des matériaux de renforcements renouvelables tels que le placage en bois ou des fibres de lin unidirectionnelles continues. Pour atteindre un haut rendement en termes de production en masse, de reproductibilité et de flexibilité, il est requis de suivre plusieurs étapes dans la réalisation de produits semi-finis et finis. L'amélioration de l'adhésion à l'interface des composantes, la mise en place de procédés continus afin d'augmenter leur rendement, et la mise en forme finale, par diverses méthodes, pour des futures potentiels applications sont autant d'objectifs à atteindre

Experimental analysis of the forming behavior of ash wood veneer with nonwoven backings

In the present study, the forming behavior of veneer with nonwoven backings was analyzed. The paper contributes to the lack of data on numerical predictions of the formability of veneers for the manufacturing of automotive trim parts. Tensile and shear tests were carried out at normal climate conditions and after water immersion to obtain material parameters for a transverse isotropic material description. The Tsai Wu failure criterion was applied to the estimation of strength under different stress combinations. Analysis of the directional deep drawing capacity of the veneer laminate was done by the Nakajima test. Stress states from biaxial to uniaxial were induced into the material depending on the geometry of the sample. Strains were evaluated locally until material failure using the digital image correlation method. Major strain was defined in the direction perpendicular to the grain. Increasing major strain was found from biaxial to uniaxial stress states. Highest strain limits were found for wet veneers tested with heated forming tools. Cracks occurred in the early wood zone for all geometries and propagated in the direction parallel to the grain. Generally, the Nakajima test is suitable for the evaluation of the formability of veneer laminate sheets. The presented data and, in general, the suggested experimental program can be used for the development and validation of veneer laminate material models for forming simulations

Testing of set recovery of unmodified and furfurylated densified wood by means of water storage and alternating climate tests

Densification is a well-known method for improving the mechanical properties of wood. In the present study, unmodified and furfurylated wood samples were densified and submitted to cyclic water storage tests and cyclic alternating climate tests. Swelling coefficients and spring-back data were determined for the evaluation of the quality of densification. The study shows that results depend on the test method applied. Simple water storage tests do not reflect the behavior of densified wood in the high humidity range. The spring-back data of unmodified samples are more influenced by the testing method than those of the furfurylated ones

Legislative Documents

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Transfer of the Interlaminar Shear Test to Veneer Layer-based Composites for Qualitative Evaluation of Layer Adhesion

This study aimed to investigate the suitability of the interlaminar shear (ILS) testing method for veneer-based composites. The ILS testing method is an established method for composite materials as a qualitative evaluation of the adhesion within the composite. The applicability of this method to veneer based composites enables a simple qualitative statement on the adhesion of the individual layers. The ILS method complements existing wood-based material tests that focus on bonding, using significantly smaller material dimensions

Istraživanje kompresijskih svojstava furnira u smjeru debljine

Compression tests were conducted with veneers in the thickness direction. Thereby differences between the stress-strain curves of veneers and other known stress-strain curves were observed. Based on microscopic studies during the compression, it was possible to describe the deformation behaviour of the veneer, and deviations from known, typical stress-strain curves were substantiated and explained. It was found that a considerable part of the strain occurs by straightening the veneer at a relatively low stress level due to the waved form of veneer sheets and specimens. A distinctive stress plateau has not been established.Na furnirima su provedeni kompresijski testovi u smjeru njihove debljine. Uspoređene su dobivene krivulje naprezanja-deformacije furnira s drugim poznatim krivuljama naprezanja-deformacija. Na osnovi mikroskopske studije tijekom kompresije furnira moguće je opisati deformacije furnira i objasniti odstupanje od dosad poznatih, tipičnih krivulja naprezanja-deformacija. Istraživanja su pokazala da se zbog valovitosti listova furnira i uzoraka velik dio deformacija pojavljuje pri ispravljanju furnira već uz relativno nisku razinu naprezanja