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Posouzení působení mikrovln na zkušební tělesa při průchodu kontinuálním zařízením
Šitta, Ondřej
This work deals with drying of the beechwood using microwaves. In the first part there is teoretically discussed the wood in general and its behavior related with drying. The beechwood is here described in detail and also its properties. Another point of the teoretical part is focused on microwaves and its use for drying wood. Second part deals with drying of the beechwood samples using continous microwave line. Twenty beechwood samples were split on radial and tangent samples and they were put on ma-chine belt of the drying machine. Before and after each entry through the drying machi-ne each sample was weighed. This process was repeated till almost zero moisture of the tested sample. Then small parts were cut from each sample, three from each edge and three from the middle part of the tested sample. Three parts (edge, middle, edge) were used for prong test, three for finding the value of crustiness using the CEN test and three of them cut on even smaller parts for finding the moisture gradient. The result was evaluation of wood drying and its quality after drying
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Natural regeneration of Silver fir (Abies alba Mill.) in the National nature reserve Salajka
Holík, Jan
This study addressed the development of natural regeneration of tree species over the period 2009-2016 in a temperate fir-beech old-growth forest left to a spontaneous development since 1930s. The research site was located in the strictly protected National Nature Reserve Salajka, lying in the Western Carpathians mountain range. Ungulate game browsing, establishment and mortality of natural regeneration as the main drivers of species coexistence were studied, using two alternative sampling methods, permanent network of 98 inventory plots regularly positioned across the whole forest reserve and transect with 54 transect plots. Beech was found to secure gradually absolute dominance over other tree species in natural regeneration. The growth of fir, maple and spruce was hindered by browsing since the individuals rarely exceeded the height of 0.5 m. Further, the resource concentration effect was found in fir as browsing was more intense under high conspecific densities. Establishment and mortality of fir and beech differed, suggesting the species-specific life-history strategies. The results demonstrated the importance of regular and inextensive establishment of fir and huge but relatively less frequent establishment of beech. Mortality overweighed establishment in both species, though fir ratio tended to be almost balanced. The height of natural regeneration was revealed to be the only good predictor of mortality. Browsing, establishment and mortality of natural regeneration comprise an important part of forest regeneration processes and their role should be acknowledged by both forest and nature conservation management.
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Vliv doby a teploty paření na pružnostní a pevnostní charakteristiky dřeva buku
Jakeš, Ondřej
This diploma thesis primarily focuses on thermal modification of wood with superheated steam and its effect on elasticity and strength. The sample tested was 200 pcs of bending samples and 200 pcs compressive samples of European beech. These samples were divided into ten groups. One group was referential and the remaining nine groups were modified using different temperatures and during different time intervals. The main goal was to determine density, modulus of elasticity and rupture and to discover their dependence on the chosen mode of modification. The next part contains the analysis of the effect of thermal modification with superheated steam on the acoustic properties and the colour of wood. In the last part, the mass loss and the change in equilibrium moisture content was analysed in relation to the modification mode.
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Analýza tvorby dřeva buku lesního na výzkumné ploše Rájec-Holíkov
Porvalík, Radim
This bachelor thesis presents xylem formation of common beech (Fagus sylvatica L.) on sample plot in Rájec-Holíkov in one year period,specifically exeptionally dry year 2015. Total of 6 trees were used as sample trees of which micro bores were obtained around the grith with the Trephor apparathus in chronological order from 23rd March to 12th November, once in a week. In laboratory, the samples were processed into permanent slides and analysed with a light microscope. The processes of xylem growth and xylem maturing from the initial phase to the complete differentiation were observed. First symthomps of initial phase and cambium activity occurred when mean day temperature reached 7,5 °C corresponding to end of April and start of the May. The secondary cell wall and gradual lignification occurred from 4th June 2015 (155 DOY) to 20th August 2015 (232 DOY). Fully lignified cells were occurring gradually until October. Total growth of tree ring lasted 90 days. The mean size of newly formed tree ring size 1235 µm according to Gompertz function.
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Analysis of the mechanical behavior of wood by means of digital image correlation
Brabec, Martin
The full-field optical techniques such as e.g. a digital image correlation are capable to fully reflect the natural wood heterogeneity. Therefore, this thesis aspires to contribute to the experimental mechanics of wood and wood-based composites by the implementation of the full-field optical technique based on the digital image correlation to the standard mechanical tests. A supplementation of the conventional displacement sensors should help to obtain more precise mechanical characteristics and to do more sophisticated analyses of the deformation behaviour of wood and wood-based composites. The experimental part of the thesis is divided into the five independent case studies listed as the original papers. The measurements were carried out on the most wide-spread wood species in central Europe such as European beech (Fagus sylvatica, L.) and Norway spruce (Picea abies, L. Karst). Beside the solid wood, the new wood-based sandwich structure, which consists of a core made from birch plywood and the particleboard facings, was investigated too. The loading of the samples was carried out using of the standard mechanical tests such as tension, compression, three-point bending and torsion test. In the first study, the full-field deformation data were used to indentify reasons for the non-standard deformation behaviour of spruce and beech wood during compression parallel to grain. Reason for this was recognized in the abrubt compression of damage zones located near the compression plates, which induced the expansion of the middle zone located between them. The second study aimed to find out neutral axis position in native and thermally modified beech wood during the conventional three-point bending test. The relative neutral axis position was obtained from mutual position of the neutral axis and centroidal axis, which was determined based on the appropriate image processing methods. It was found that the neutral axis and centroidal sample axis are almost coincident. Objective of the third study was to determine both longitudinal shear moduli of beech wood with help of the full-field shear strains, obtained from a single torsion test, together with use of the appropriate analytical solutions for the calculation of the stress distribution within the radial and tangential direction on the longitudinal-radial and longitudinal-tangential sample surfaces. Both longitudinal shear moduli increasingly mutually differed as the load increases. Within the fourth study, verification of the elastic material model used in finite-element analyses was carried out with help of full-field deformations induced around notches within dog-bone shaped sample during the uniaxial tension. Great correlation was found between numerically predicted and experimentally measured strain data sets for both longitudinal-radial and longitudinal-tangential shear planes. The fifth study dealed with the characterization of elastic deformation behaviour of newly developed wood-based composite with a sandwich structure. Based on the full-field strain analysis the local strain concentrations were identified. They took place within the core during flatwise compression, and within the facings, when the edgewise compression test was done. A variety of presented results confirmed widespread applicability of optical methods in the mechanics of materials. Therefore, the utilization of full-field optical method based on digital image correlation in experimental mechanics of wood and wood-based composites can be highly recommended.
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Vývoj a struktura přirozeného zmlazení v NPR Razula
Mikulenčák, Josef
The National Nature Reserve Razula is a heritage of a fir-beech forest primeval character with an admixture of European spruce and sycamore maple, typical for the area of the Western Carpathians. This bachelor thesis deals with the analysis of the structure and dynamics of natural regeneration. The analysis was conducted on circular investment area, regularly situated in a square net over the entire area of the reservation. Work focuses the presence of natural regeneration of silver fir because of long term decline of its representation in the forests. Although fir is the most naturally regenerative tree species in the reservation, the individual growth rarely reaches the height of 0.5 m. The main factor is the damage by wild animals. The damage reaches nearly 60 % of individual trees higher than 0.15 m. Today there is a strong representation of beech, which thanks to its amount of natural regeneration at these habitats and ability to compensate for grazing.
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Dynamika přirozené obnovy dřevin v západních Karpatech se zaměřením na jedli bělokorou
Holík, Ján
This bachelor thesis addresses the developmental dynamics of natural regeneration in uneven-aged fir-beech forest in the Western Carpathians. The primary attention was paid to silver fir (Abies alba Mill.). One of the crucial reasons for writing this thesis was an attempt to contribute to the knowledge about long-term proportion decrease of silver fir with simultaneous increasing dominance of European beech (Fagus sylvatica L.) during the 20th century. Structure and species composition changes of natural regeneration were investigated within the measurement period 2009--2013. Research data was acquired with two inventory methods - the circular inventory plots and the line transect. Silver fir does not almost exceed a height of 0,5 m despite sufficient quantities of natural regeneration of initial stages. The damage caused by game is regarded as the most limiting factor. Natural regeneration is dominated by beech above a height of 0,15 m. The low rate of browsing does not prevent it from further development. The growth and the regeneration dynamics of trees is species-dependent, nevertheless, there is a decreasing tendency of natural regeneration quantities of all tree species up to 0,15 m in height since 2010.
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