The soil of former farmland greatly differs from forest soil, and significantly influences tree growth and development compared with other site factors. The effect may also be reflected indirectly in radial variability of wood. This study compared radial variation of wood density, compressive strength along the grain and static bending strength of wood of Scots pine trees growing on former farmland and forest soils. The analyses were conducted in eight mature pine stands. On the basis of the stand description, four stands were classified as growing on forest soil (L) and four as growing on former farmland soil (P). A total of 24 model trees were selected, twelve on each soil type. Analyses of wood properties were conducted along four axes from the cross sectional radius of the trees at breast height. Our analyses showed that radial variation in wood properties of Scots pine (from selected locations in Poland) growing on former farmland is similar to the variation among the control trees growing on forest soils. In both groups of trees, the lowest density and the lowest strength were in the pith (juvenile) zone. Wood with the highest density and greatest strength was located in the central part of the radius. Wood of Scots pine trees growing on former farmland soils in comparison to that of trees growing on forest soil was characterised by a statistically lower basic density, lower compressive strength along the grain and static bending strength.
This paper deals with results of preliminary analysis to determine the bending strength of approximately 150 year old oak timber obtained from structural elements used in construction. The test procedures were those specified in the PN-EN 408 standard. The experiments involved subjecting specimens to four-point static loading using three different loading rates: 5, 7 and 10 mm/min. The specimens were sampled from full-size timber beams. The experimental data revealed that after such a long period of use the structural oak timber elements had retained high strength. The failure mode and the behaviour of the beams during tests were dependent on the location of wood defects as well as the rate of deflection gain in time.
:2009 Dentistry - Polymer - based restorative materials.
24. Karbhari V.M., Strassler H., Effect of fiber architecture on flexural characteristics and fracture of fiber-reinforced dental composites. Dental Materials, 23(8) (2007).
25. Camanho P.P., Davila C.G.: Mixed-mode decohesion finite elements for the simulation of delamination on composite materials, NASA/TM-2002-0211737, 2002.
26. Walczak A., Pieniak D., Niewczas A., Niewczas A.M. Kordos P., Study of ceramic-polymer composites reliability based on the bendingstrength test. Journal of KONBiN, 35
The aim of this study was to determine relationships between selected properties of juvenile wood and characteristics of the stem and crown of Scots pine. Analyses were conducted in northern Poland on eight mature pine monocultures. Nine trees were selected in each experimental site and their stems were divided into five sections. The centers of the sections were established at a height of 1.3 m from the tree base and at points corresponding to 20, 40, 60 and 80% tree height. Samples were taken from these locations, and these samples were prepared for analyses of basic density, compressive strength along the grain and static bending, as well as the modulus of elasticity during bending. The mean height of the investigated group of trees was 26.0 m with an average diameter breast high of 33.6 cm. The mean crown depth was 7.8 m and crown diameter was 3.6 m, and the mean basic density (Qu) of juvenile pine wood was 416 kg/m3. The average compressive strength along the grain (CS) was determined to be 22.3 MPa, while static bending strength (BS) was 45.8 MPa. The recorded modulus of elasticity (MOE) was 4726 MPa.
Both in general terms and when dividing stems into sections, the wood properties correlated with tree characteristics to various degrees. All indexes were negative indicating that trees of greater dimensions produce juvenile wood of inferior quality. Properties of juvenile wood formed during various periods of tree life were mostly related to diameter breast high and crown depth. They were also correlated with tree height, but only to a limited extent. In contrast, properties of wood from the middle stem sections were significantly correlated with crown diameter.
Agata Walczak, Daniel Pieniak, Andrzej Niewczas, Agata M. Niewczas and Paweł Kordos
In this paper the reliability assessment of structural reliability of the selected light-cured dental composites based on the biaxial flexural strength test results has been presented. A two-parameter Weibull distribution was applied as a reliability model in order to estimate probability of strength maintenance in the analysed population. Weibull distribution parameters were interpreted as a characteristic material strength (scale parameter) and structural reliability parameter in terms of ability to maintain strength by each of specimen from the general population (shape parameter). 20 composite specimens underwent strength tests, including 2 “flow” type composites and 2 standard composites (with typical filler content). “Flow” type composites were characterized with lower characteristic strength and higher structural reliability comparing to other studied composites.
Waldemar Moliński, Przemysław Mania and Gabriel Tomczuk
PN-77/D-04100 Wood. Determination of moisture content (standard in Polish).
PN-77/D-04101 Wood. Determination of density (standard in Polish).
PN-77/D-04103 Wood. Determination of the static bendingstrength (standard in Polish).
Wagenführ R. 2007. Holzatlas. Fachbuchverlag Leipzig im Carl Hanser Verlag, München.
Arkadiusz Denisiewicz, Tomasz Socha, Krzysztof Kula and Marcin Pasula
The article presents results of laboratory tests of selected mechanical and physical properties of fine-grained fiber concrete. Tests were conducted on samples with a different degree of reinforcement made on the basis of steel and polypropylene fibers. For the designed concrete mixtures and prepared samples, slump class, shrinkage, compressive and bending strength and water tightness were determined.
Arkadiusz Denisiewicz, Krzysztof Kula, Tomasz Socha and Grzegorz Kwiatkowski
The article presents the results of laboratory tests of selected mechanical and physical properties of fine-grained concrete. The tests were carried out on samples with varying degrees of microsilica addition. The consistency class, shrinkage, compressive and bending strength, water resistance and frost resistance were determined for the designed concrete mixtures and made samples.
Al-Mg-Mn-Sc-Zr alloy plates of 5mm thick were welded successfully using Friction stir welding (FSW). Three-factor five-level central composite design was adopted for experimentation. Response surface methodology (RSM) was employed to construct a mathematical regression model. Optimization of FSW process parameters obtained by using response surface plots for maximize hardness, tensile strength, %elongation, impact strength and bending strength, the results were validated with confirmation tests at identified optimum conditions.
Sang-Sub Lim, Jae-Chul Mun, Tae-Won Kim and Chung-Gil Kang
In casting steels for offshore construction, manufacturing integral casted structures to prevent fatigue cracks in the stress raisers is superior to using welded structures. Here, mold design and casting analysis were conducted for integral casting steel. The laminar flow of molten metal was analyzed and distributions of hot spots and porosities were studied. A prototype was subsequently produced, and air vents were designed to improve the surface defects caused by the release of gas. A radiographic test revealed no internal defects inside the casted steel. Evaluating the chemical and mechanical properties of specimens sampled from the product revealed that target values were quantitatively satisfied. To assess weldability in consideration of repair welding, the product was machined with grooves and welded, after which the mechanical properties of hardness as well as tensile, impact, and bending strengths were evaluated. No substantive differences were found in the mechanical properties before and after welding.