Search results for: Eliska Oberhofnerova

Authors: Eliska Oberhofnerova, Milos Panek, Stepan Hysek, Martin Lexa

Abstract:

Nowadays the use of wood, both indoors and outdoors, is constantly increasing. However wood is a natural organic material and in the exterior is subjected to a degradation process caused by abiotic factors (solar radiation, rain, moisture, wind, dust etc.). This process affects only surface layers of wood but neglecting some of the basic rules of wood protection leads to increased possibility of biological agents attack and thereby influences a function of the wood element. The process of wood degradation can be decreased by proper surface treatment, especially in the case of less naturally durable wood species, as spruce. Modern coating systems are subjected to many requirements such as colour stability, hydrophobicity, low volatile organic compound (VOC) content, long service life or easy maintenance. The aim of this study is to evaluate the colour stability of spruce wood (Picea abies), as the basic parameter indicating the coating durability, treated with two layers of transparent natural oil wood stain and exposed to outdoor conditions. The test specimens were exposed for 2 years to natural weathering and 2000 hours to artificial weathering in UV-chamber. The colour parameters were measured before and during exposure to weathering by the spectrophotometer according to CIELab colour space. The comparison between untreated and treated wood and both testing procedures was carried out. The results showed a significant effect of coating on the colour stability of wood, as expected. Nevertheless, increasing colour changes of wood observed during the exposure to weathering differed according to applied testing procedure - natural and artificial.

Keywords: colour stability, natural and artificial weathering, spruce wood, transparent coating

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Authors: O. Dvorak, M. Panek, E. Oberhofnerova, I. Sterbova

Abstract:

Extractives contained in larch wood (Larix decidua, Mill.) reduce the service-life of exterior coating systems, especially transparent and semi-transparent. The aim of this work was to find out whether the initial several-week leaching of extractives from untreated wood in the exterior will positively affect the selected characteristics and the overall life of the semi-transparent oil-based coating. Samples exposed to exterior leaching for 10 or 20 weeks, and the reference samples without leaching were then treated with a coating system. Testing was performed by the method of artificial accelerated weathering in the UV chamber combined with thermal cycling during 6 weeks. The changes of colour, gloss, surface wetting, microscopic analyses of surfaces, and visual damage of paint were evaluated. Only 20-week initial leaching had a positive effect. Both to increase the color stability during aging, but also to slightly increase the overall life of the tested semi-transparent coating system on larch wood.

Keywords: larch wood, coating, durability. extractives

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Authors: I. Sterbova, E. Oberhofnerova, M. Panek, M. Pavelek

Abstract:

With growing popularity, wood of European larch (Larix decidua, Mill.) is being more often applied into the exterior, usually as facade elements, also without surface treatment. The aim of this work was to compare two laboratory tests of artificial accelerated weathering of wood with two ways of natural weathering in the exterior. To assess changes in selected surface characteristics of larch wood, accelerated weathering methods in the Xenotest and UV chamber were used, both in combination with temperature cycling, for 6 weeks. They were compared with natural weathering results at exposition under 45° and 90° in the exterior for 12 months. The changes of colour, gloss, contact angle of water and also changes in visual characteristics were evaluated. The results of wood surfaces changes after 6 weeks of accelerated weathering in Xenotest are closer to 12 months of natural weathering in the exterior at an angle of 90° compared to the UV chamber testing. The results, especially the colour changes, of the samples exposed at an angle of 45° in the exterior were significantly different. Testing in Xenotest more closely simulates the weathering of façade elements in the exterior compared to the UV chamber testing.

Keywords: larch wood, wooden facade, wood accelerated weathering, weathering methods

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Authors: Jan Karl, Ondrej Suchy, Eliska Fiserova, Milan Ruzicka

Abstract:

The evolving electromobility and all the electronics also bring an increase of danger with used Li-batteries. Li-batteries have been used in many industries, and currently many types of the batteries are available. Batteries have different compositions that affect their behavior. In the field of Li-battery safety, there are some areas of little discussion, such as extinguishing of fires caused by Li-batteries as well as toxicity of gaseous compounds released from Li batteries, transport or storage. Technical Institute of Fire Protection, which is a part of Fire Brigades of the Czech Republic, is dealing with the safety of Li batteries. That is the reason why we are dealing with toxicity of gaseous compounds released under conditions of fire, mechanical damage, overcharging and other emergencies that may occur. This is necessary for protection of intervening of fire brigade units, people in the vicinity and other envirnomental consequences. In this work, different types of batteries (Li-ion, Li-Po, LTO, LFP) with different kind of damage were tested, and the toxicity and total amount of released gases were studied. These values were evaluated according to their environmental hazard. FTIR spectroscopy was used for the evaluation of toxicity. We used a FTIR gas cell for continuous measurement. The total amount of released gases was determined by collecting the total gas phase through the absorbers and then determining the toxicants absorbed into the solutions. Based on the obtained results, it is possible to determine the protective equipment necessary for the event of an emergency with a Li-battery, to define the environmental load and the immediate danger in an emergency.

Keywords: Li-battery, toxicity, gaseous toxic compounds, FTIR spectroscopy

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Authors: Eliska Smidova, Petr Kabele

Abstract:

This paper describes non-linear finite element simulation of laminated veneer lumber (LVL) under tensile and shear loads that induce cracking along fibers. For this purpose, we use 2D homogeneous orthotropic constitutive model of tensile and shear fracture in timber that has been recently developed and implemented into ATENA® finite element software by the authors. The model captures (i) material orthotropy for small deformations in both linear and non-linear range, (ii) elastic behavior until anisotropic failure criterion is fulfilled, (iii) inelastic behavior after failure criterion is satisfied, (iv) different post-failure response for cracks along and across the grain, (v) unloading/reloading behavior. The post-cracking response is treated by fixed smeared crack model where Reinhardt-Hordijk function is used. The model requires in total 14 input parameters that can be obtained from standard tests, off-axis test results and iterative numerical simulation of compact tension (CT) or compact tension-shear (CTS) test. New engineered timber composites, such as laminated veneer lumber (LVL), offer improved structural parameters compared to sawn timber. LVL is manufactured by laminating 3 mm thick wood veneers aligned in one direction using water-resistant adhesives (e.g. polyurethane). Thus, 3 main grain directions, namely longitudinal (L), tangential (T), and radial (R), are observed within the layered LVL product. The core of this work consists in 3 numerical simulations of experiments where Radiata Pine LVL and Yellow Poplar LVL were involved. The first analysis deals with calibration and validation of the proposed model through off-axis tensile test (at a load-grain angle of 0°, 10°, 45°, and 90°) and CTS test (at a load-grain angle of 30°, 60°, and 90°), both of which were conducted for Radiata Pine LVL. The second finite element simulation reproduces load-CMOD curve of compact tension (CT) test of Yellow Poplar with the aim of obtaining cohesive law parameters to be used as an input in the third finite element analysis. That is four point bending test of small-size arch of 780 mm span that is made of Yellow Poplar LVL. The arch is designed with a through crack between two middle layers in the crown. Curved laminated beams are exposed to high radial tensile stress compared to timber strength in radial tension in the crown area. Let us note that in this case the latter parameter stands for tensile strength in perpendicular direction with respect to the grain. Standard tests deliver most of the relevant input data whereas traction-separation law for crack along the grain can be obtained partly by inverse analysis of compact tension (CT) test or compact tension-shear test (CTS). The initial crack was modeled as a narrow gap separating two layers in the middle the arch crown. Calculated load-deflection curve is in good agreement with the experimental ones. Furthermore, crack pattern given by numerical simulation coincides with the most important observed crack paths.

Keywords: compact tension (CT) test, compact tension shear (CTS) test, fixed smeared crack model, four point bending test, laminated arch, laminated veneer lumber LVL, off-axis test, orthotropic elasticity, orthotropic fracture criterion, Radiata Pine LVL, traction-separation law, yellow poplar LVL, 2D constitutive model

Procedia PDF Downloads 253