Changes in Vibrational Properties of Wetwood of Japanese Fir (Abies Sachalinensis Mast) with Time During Drying

Temporal changes in vibrational properties of wetwood of Japanese fir (Abies sachalinensis Mast.) during a drying process were investigated. Specimens were cut from wetwood defined as heartwood with extremely high moisture content and normal wood whose moisture content was not so high, and matched in the R-direction. Green and water-saturated wood specimens were prepared. The specimens and the vibration testing system were put in an electric drying oven, where a free-free vibration test was conducted at intervals of 5 to 20 minutes. When the green specimens were used, the resonance frequency and loss tangent of both wetwood and normal wood reached the minimum and maximum, respectively, early in the drying. The minimum and maximum of the wetwood were smaller and larger than those of the normal wood. These differences between the wetwood and normal wood were mainly caused by the differences in initial moisture content because such differences, which existed in the green wood, disappeared once a water-saturated condition was reached

Implicit finite element analysis of ductile fracture of a steel frame under cyclic deformation

A ductile fracture model is implemented to an elastoplastic constitutive model of steel material for large-scale finite element analysis of steel frames. The stress modified critical strain model is extended to simulate the structural response after initiation of ductile fracture. The yield stress, Young's modulus, as well as the stress are reduced using the fracture variable. Positive definiteness of the material tangent stiffness matrix is always maintained, and the unbalanced loads are carried over to the succeeding step to analyze the responses in the range of degrading strength using an implicit finite element analysis. It is shown using a notched rod model and a double notched plate that the proposed model can simulate steep stiffness degradation due to strain localization after ductile fracture. Applicability to a large-scale finite element analysis is investigated using a component frame of moment frame subjected to cyclic forced deformation

Comparisons of Shear Stress/Shear Strain Relations of Wood Obtained By Iosipescu And Torsion Tests

In this paper, we compared the shear stress/shear strain relations of wood obtained by Iosipescu and torsion tests.Quartersawn boards of Sitka spruce (Picea sitchensis Carr.) and shioji (Japanese ash, Fraxinus spaethiana Lingelsh.) provided the specimens. Iosipescu tests were conducted with specimens loaded in the radial direction, and the shear stress/shear strain relations were obtained. Shear stress/shear strain relations were obtained independently of the Iosipescu tests by torsion tests of rectangular bars. The following results were obtained:(1) The shear moduli, shear yield stresses, and shear strengths obtained from both methods showed good agreement with each other, except for the shear strength of ash.(2) As for spruce, the difference between the shear stress/shear strain relations obtained by Iosipescu and torsion tests was significant in the 5% significance level, whereas that for the ash was not significant.(3) Although the Iosipescu test can derive the shear stress/shear strain relation directly, it has the drawback that failure occurs earlier than with the torsion test. In contrast, the torsion test has the drawback that the procedure for obtaining the stress/strain relation is quite complicated. In determining the shear stress/shear strain relation of wood properly, shear stress/shear strain data should be measured more frequently by these methods

Structural analysis of SiO2 gel films by high energy electron diffraction

The structure of SiO2 gel-films prepared from acid and basic TEOS solutions is analyzed by high energy transmission electron diffraction method. The Si-O bond length of gel-films is 1.58 to 1.60 Å, which is shorter than that of vitreous silica (1.61 Å) but similar to that of 80 Å thick evaporated a-SiO2 film. An atomic pair peak with 0.81 Å distance exists on the reduced radial distribution functions of the gel-films, which is believed to be O-H, but being smaller than that of H2O (0.969 Å)

Electron diffraction analysis of the structure of SiO2 gel-film

The structure of self-supported SiO2 gel-films prepared from acid and basic TEOS solutions is analysed by high energy transmission electron diffraction method. The reduced radial distribution function (RDF) curves show that all the films are already well dense despite the low drying temperature (≤50°C) and short drying time (≤30 s). The Si-O bond length of the gel-films prepared from highly acid and basic solutions is about 1.58 Å; it is smaller than that of bulk vitreous silica (1.61 Å) but similar to that of 80 Å thick evaporated a-SiO2 film

Electron diffraction analysis of the structure of SiO2 gel-film

The structure of self-supported SiO2 gel-films prepared from acid and basic TEOS solutions is analysed by high energy transmission electron diffraction method. The reduced radial distribution function (RDF) curves show that all the films are already well dense despite the low drying temperature (≤50°C) and short drying time (≤30 s). The Si-O bond length of the gel-films prepared from highly acid and basic solutions is about 1.58 Å; it is smaller than that of bulk vitreous silica (1.61 Å) but similar to that of 80 Å thick evaporated a-SiO2 film

Structural difference of surface and sub-surface native oxides of evaporated amorphous silicon

Evaporated amorphous silicon (a-Si) films, oxidized in air or O2 at room temperature, present two native oxides with different structures. The surface oxide is constructed from SiO4-tetrahedron structural units with a 110° O-Si-O angle, which is the common structural unit of stable silicon oxides. The internal oxide has a different structure having a 120° O-Si-O angle. The results of molecular orbital (MO) calculations for (SiO3)m− and (SiO4)n− anionic clusters support the presence of the two stable structures of silicon oxides and also reveal the importance of the ionic character of the oxidized sites

Structural difference of surface and sub-surface native oxides of evaporated amorphous silicon

Evaporated amorphous silicon (a-Si) films, oxidized in air or O2 at room temperature, present two native oxides with different structures. The surface oxide is constructed from SiO4-tetrahedron structural units with a 110° O-Si-O angle, which is the common structural unit of stable silicon oxides. The internal oxide has a different structure having a 120° O-Si-O angle. The results of molecular orbital (MO) calculations for (SiO3)m− and (SiO4)n− anionic clusters support the presence of the two stable structures of silicon oxides and also reveal the importance of the ionic character of the oxidized sites

Intra-ring radial cracks in Sakhalin spruce (Picea glehnii) from artificial forest

The occurrence of radial cracks in Sakhalin spruce (Picea glehnii), differences in the degree of cracking among five habitats, and the relationship between cracks and wood density were investigated in a total of 79 logs collected from five sites in Hokkaido, Japan. The cracks were divided into two types: intra-ring radial cracks that were restricted to cracks within an annual ring and larger radial cracks that extended beyond a single annual ring. The number and the longitudinal length of cracks in log varied depending on habitat, and it was considered that the cold temperature conditions in winter might affect the incidence and length of cracks. The results of soft X-ray densitometry showed that the annual ring density with cracks was lower than the annual ring density without cracks. It is considered that this low wood density affected the occurrence of cracks