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Volume: 1995/3

Title: Mechanical properties of juvenile wood of fir-wood (Abies alba Mill.) from Gorski Kotar
Author: Tomislav Sinković

In this paper we discuss mechanicul properties of juvenile wood and mature wood of fir wood. Following mechanical properties have been investigated: static bending strength, modulus of elasticity in static bending, impact bending, compression strength parallel to the grain, compression strength perpendicular to the grain in radial direction, compression strength perpendicular to the grain in tangential direction and hardness per Janka in longitudinal direction. Bending strength, compression strength parallel to the grain and compression strength perpendicular to the grain in tangential direction show signgificant difference between juvenile and mature wood, the former being weaker than the latter.

Title: Assessment of Wood Photodegradation by Microtensile Testing
Author: Hilary Derbyshire, Eric Roy Miller, Jürgen Sell, Hrvoje Turkulin

The susceptibility to weathering of wood surfuces and their consequential high maintenance demands discourage the exterior use of wood and highlight the need for methods of enhancing the resistance of wood to photodegradation. Weathering processes in the surface layers of wood have been studied by measurement of the tensile strength changes occurring in 75 μm thick softwood strips during exposure to natural weathering or several regimes of artificial weathering. Microtensile testing at zero and 10 mm span enabled the relative changes in cellulose microfibril strength and the lignin-dependent properties of the matrix to be distinguished. The technique was found to offer a rapid, accurate and reproducible means of evaluating the chemical und structural changes involved in the weathering of wood and coated wood surfaces during weathering. Tensile strength curves indicated three phases in the degradation process. The initial phase was characterised by a slow rate of strength loss, and at high humidity levels even an increase in strength. During the second and third phases believed to be associated with the successive degradation of lignin and cellulose, strangth losses were more rapid. Differences in the weathering behaviour of three softwood species were distinguished, and temperature, moisture and radiation source shown to exert strong influences on degradation rate. Artificial weathering was found to provide a valid alternative to natural weathering in systematic investigation of degradation mechanisms. SEM studies revealed that structured changes in the wood are associated with the eurly stages of photodegradation. Fractography showed that the progression of degradation involves the development of brittleness und reduction of stress transfer capabilities through lignin degradation, followed by reductions in microfibril strength resulting from cellulose degradation.

Title: Quality assurance of wood quality products
Author: Mladen Figurić, Vladimir Koštal

Quality costs have always presented a major item in overall expenses of a firm. This paper describes, in view of cost management, the research on quality assurance, conducted in several Croatian firms that manufacture wood items. The first part of the paper is an analysis of defect proportion in several firms dealing with solid wood processing. The data were obtained by using cross control cards and were analyzed by means of priority diagrams. After that a model of cost distribution of processing and material waste is presented through work phases. The phase in which there appeared the highest amount of waste material was analyzed step by step. Likewise, there is a quality cost report for several plant sections within a firm, classified by costs appearing in a particular business system. The costs of complaints and internal shortages in two different sections within one firm were analyzed, as they formed the highest cost item in the overall expenses for the particulur section. Finally, the complaints as to their causes in another firm over one year were analyzed. The priority diagram (Pareto) was used in all analyses.

Title: Wood-technological sciences-structure and trends
Author: Mladen Figurić, Darko Motik

Along with the general increase and intensification of scientific and technological processes, we are witnessing favourable structural changes in the field of wood technology as well. This paper is therefore an attempt to explain the development trends based on the dynamics of a particulur period of time. The research carried out in the wood-technological sciences has shown that in future years considerable structural changes will take place. The results have shown that a redefinition of wood - technological sciences will have to take place so that it will have to be put into the context of technological development und practical use of wood. The structure of scientific work and its trends have been analyzed. The research has been carried out according to the number of diploma theses and the main courses taken and according to the number of master’s and doctor’s theses. Likewise, the structure of published scientific papers has been analyzed as well as the research trends within the individual subordinate fields. In addition, the papers have been classified in the usual way: the science of wood; sawmill wood processing; manufactured boards and chemical wood processing; structures and final wood processing; production organization and other operations defined as the applications of basic wood technological techiques. As a result, a need for redefinition of wood-technological sciences has emerged together with the need for a new systematization of the subordinate fields of work. The results of the application of the wood-technological sciences in practice, which took place together with the presented research, have been published in a separate publication.

Title: Biotechnical wood protection in timber storage yards of woodworking plants
Author: Gorazd Babuder

The article discusses the use of traps and synthetic aggregation pheromones as control measures against bark beetles (Coleoptem, Scolytidae) in timber storage yards. The emphasis is placed on biotechnical wood protection, whose significance has increased in recent years for reasons of ecological acceptability and cost-effectiveness. A survey of other bark beetle suppressive methods is given. By monitoring the scope of trapped bark beetles the density of beetle population and the level of hazard to yarded timber can be controlled. In this way, the damage on wood in spring and summer months caused by attacks of scolytids can be avoided to a large extent.

Title: Wood protection and European regulations - part II
Author: Božidar Petrić, Radovan Despot, Jelena Trajković

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