Physical and mechanical properties of kiri wood (Paulownia tomentosa) were estimated from the viewpoint of rationality as the Japanese traditional uses, such as furniture, fittings, and Japanese harp. From the responses of dimension and moisture content to the humidity change, the superiority of kiri wood among many kinds of hard-woods was verified in dimensional stability and humidity-controlling function. These properties of kiri wood accord with the aptitude to the furniture and woodcrafts. Furthermore, it was supported that the vibrational properties of kiri satisfy the necessary conditions (low loss tangent and high acoustic converting efficiency) for the soundboard of stringed instruments.
The high-temperature setting method (HTS method) was developed in order to prevent surface checking and to reduce drying time for boxed-heart timber without back splitting. It's principle is based on the sudden formation of tension set at the surface of timber under high temperature and low relative humidity condition at the initial stage of kiln-drying. Using the HTS method, while reduction of surface checks was particularly obvious, honeycombs increased when moisture content of timber decreased. To examine the optimum condition of the HTS treatment and to clarify the mechanism of occurrence of honeycomb checks during subsequent kiln-drying, a more thorough knowledge of the internal stresses in timber kiln-dried is required. The purpose of this paper is to gain the knowledge of the internal stresses in timber just after the HTS treatment as well as after subsequent kiln-drying with various schedules after the HTS treatment. Testing materials were Japanese cedar (Cryptomeria japonica D. Don) green boxed-heart timber (132 × 132 × 3000mm) without back-splittings. The procedure used for strain analysis was the modified slicing technique. Main results were shown below. 1. After the HTS treatment, the surface of timber already reversed to compressive stresses in half the number of testing materials. 2. For the timber kiln-dried after the HTS treatment, while compressive strains at the surface significantly developed as drying proceeded, strain distributions tended to show characteristic concave curves which reveal that the shell of timber is stressed in compression and the core in tension. 3. Under flat moisture gradients, strain gradients for the timber kiln-dried with medium-temperature schedule after the HTS treatment were steeper than that for the timber kiln-dried with high-temperature schedule after the HTS treatment. 4. Strain distributions for timber kiln-dried with the conventional medium-temperature schedule without the HTS treatment were almost flat compared to that for timber kiln-dried after the HTS treatment.
Sugi logs were dried with the microwave (MW) heating. The temperature and moisture content distributions in the logs were measured during MW heating. And the surface stresses were measured at the same time as released strains on the surfaces. As a result, the temperature in the center layer was higher than that in the outside layer during drying because of rapid temperature decrease for irradiation stop in intermittent heating system of MW. The moisture content in the center layer was relatively low at the end of drying. The surface stress of dried log was compression for the tangential direction related to surface checks. During seasoning after MW drying, the moisture was removed mainly in the surface layer, and the surface stress changed to tensile stress. As a result, the surface checks occurred for all logs after seasoning in about two or three months. Some dried logs had been sawn into the boxed-heart square timbers. Many surface checks appeared on these timbers because of the existence of internal checks of sugi logs, which occurred by the MW drying. These check widths did not change largely for the efficiently dried timbers as the core part of sugi logs after MW drying.
The effect of basic wood properties on strength and stiffness of timber as a full-size member is very different from that of small clear specimen. Recently a number of mechanical tests with timbers have been done. However the aims of those investigations are to get the mechanical data of timbers. Therefore which basic wood property is most effective parameter for the mechanical properties of timbers remains unclear. Especially the effects of anatomical properties of Cryptomeria japonica (sugi) timbers have not been studied. In this study, the effect of basic wood properties on strength and stiffness in bending of the timbers (1 : 400cm, b : 12cm, h : 21, 24 or 27cm) from sugi trees grown at three different sites in miyazaki district was investigated. Air-dry specific gravity, maximum knot ratio, juvenile wood ratio and ring width in juvenile and mature wood had slight effect or no effect on the mechanical properties of timbers. On the other hand, latewood tracheid length and S2 microfibril angle strongly affected the mechanical properties of timbers.
Shearing tests were carried out on mechanical timber joints composed of a main timber and two thick particleboards (side members). Six kinds of commercial screws or nails were used for mechanical fasteners. Maximum load, allowable load, stiffness and dissipated energy of the joints were calculated from load-deformation curve. Short term allowable shear strength calculated with an equation in “Standard for structural design of timber structure” was about one-third of measured maximum load. Estimated yield load with “European Yield Theory” was lower than measured yield load. Effects of shapes of fasteners on the mechanical characteristics were examined with linear or multiple regression analysis. The regression formula using the shape of the fasteners and the density of the main member as independent variables estimated each characteristic value properly. The shape of the fasteners affecting each characteristic value agreed well with classification results by principal component analysis. Stiffness of the joints was not affected with the shape of the fasteners or the density of the main member. Bending strength of the particleboard did not affect on the mechanical properties of the joints.
In Japan, the damages by the subterranean termites (Coptotermes formosanus Shiraki and Reticulitermes speratus (Kolbe)) are more common. Recently the more attention is paid to the less- or non-chemical methods for termite control. As a non-chemical treatment physical barriers using particles such as gravels were investigated in terms of environmental safety, cost effectiveness, and duration of performance, and the physical barriers using some particles have been practically used in a few countries except Japan. In this study, penetration of termites of C. formosanus into four physical barriers of different particulate materials such as crushed cement-stabilized sludge (Polynite®), palletized-stone powder, and crushed glass, and glass beads as control, were investigated. Layers with particles of Polynite® (1.70 to 2.00mm in diameter), palletized-stone powder (2.00 to 3.35mm), crushed glass (1.00 to 2.80mm), and glass beads (1.00 to 2.80mm) prevented termites from penetrating. The layers of smaller particles were tunneled by termites and the layers of larger particles were passed through. It was found from image analysis of particles that more spherical particles were more efficacious against termite penetration because of their higher compactness. It was also found from roughness measurements of particle surfaces using a stylus instrument that particles of smoother surface were efficacious against both tunneling and penetration of termites. It was recommended to use the particulate materials of smooth surface and spherical shape as a physical barrier.
The formation of nanoparticle-based nanocomposites of zirconium oxide/Poly (ethylene terephthalate) (ZrO-PET) during the polymerization process of PET was studied. Oxy zirconium compound was used as a precursor for the nanoparticles. This precursor was introduced to a ethylene therephthalate oligomer. ZrO nanoparticle-filled PET materials were obtained, when a heat treatment under low pressure condition was carried out. ZrO nanoparticles were in agglomerate condition in PET matrix. When the ratio of Cl/Zr in the starting precursor increases, particle size increases. From the structural analysis data, it was confirmed that the O/Zr ratio of the particles was almost unity, and its structure is differ from that of zirconia (zirconium oxide). It was also confirmed that the prepared particle had a structure with organic component. The thermal analysis indicated that ZrO-PET nanocomposites had two characteristic exothermic peaks observed on cooling. From the biaxial oriented film of ZrO-PET nanocomposites, an improvement of its tensile elongation break was confirmed.
We examine the deformation and localized necking mechanism of round bar specimen of nanocrystalline materials by molecular dynamics simulation, and consider the relationship between the intergranular deformation and the intragranular deformation of nanocrystalline materials. We use two atomic interaction potentials which show different values of stacking fault energy. In the case of high stacking fault energy, the model is deformed by mainly the intergranular deformation; grain boundary sliding, and a little intragranular deformation; crystal slips by the movement of perfect dislocation, but in contrast, in the case of low stacking fault energy, the deformation is caused by the intragranular deformation by the movement of partial dislocation that leaves stacking fault plane in grains. Because stacking fault planes in grains prevent the activation of other slip systems, a kind of work hardening-like effect is observed.
The microscopic plastic deformation and the surface roughening behavior of free surface of polycrystalline aluminum sheet during uniaxial tension were experimentally investigated. The free surface roughness profiles are measured during plastic deformation with a confocal laser-scanning microscope. The surface roughness curve was analyzed employing the autocorrelation function and simplified model of surface roughness curve. It is shown that the average inclination of the surface profile curve increases lineally with increasing applied strain, and the grain rotation out of the surface plane is dominant contributor to the surface roughness. The roughness in grains are less than 30% and the roughness of slip bands are less than 7%, respectively, of the total surface profile roughness. The wavelength of the surface roughness curve is about 5∼9times the averaged grain size, which increases with the applied tensile strain. Discussions are made on the autocorrelation length, the wavelength of surface profile and the grain boundary position on the surface profile.
Viscoplastic constitutive equations for polymers that properly describe strong strain recovery appearing in reverse deformation are proposed. Constitutive equations were formulated by combining the kinematic hardening creep theory of Malinin and Khadjinsky with the nonlinear kinematic hardening rule of Armstrong and Frederick. In order to describe the strain recovery, the nonlinear kinematic hardening rule was modified. First, a loading surface was defined in a viscoplastic strain space. A loading-unloading criterion was then introduced using the loading surface. Moreover, a parameter was defined by the relationship between the loading surface and the current state of the viscoplastic strain, and the evolution equation of back stress was modified using this parameter, which is applicable in reverse deformation. In the present paper, two models are proposed: Model 1, which is the evolution equation into which an additional term was introduced in order to suppress strain hardening of the back stress, and Model 2, in which a coefficient of the evolution equation was modified in order to suppress the evolution of the back stress. Experimental results for polyethylene were obtained using the modified constitutive equations, and cyclic inelastic deformation in the uniaxial state was predicted. Finally, the validity of the above-described modification was verified, and the features of the constitutive equations and the deformation were discussed.
High cycle fatigue properties of high strength steel were investigated. In the Fuel Cell(FC) system, various metals are used in hydrogen environment under cyclic loading. In this study, hydrogen was artificially charged into specimen of a Cr-Mo high strength steel, and the fatigue properties were compared with those of the specimens without hydrogen charge. Fatigue strength and fatigue life decreased with increasing hydrogen content. The fracture origin of hydrogen charged specimens showed smaller ODAs than as-heat-treated specimens. It implies that the fatigue threshold of the microstructure which contains high hydrogen content is much lower than that of the as-heat-treated microstructure, and the upper bound of the critical hydrogen content level resulting ODA lies between 1.5ppm and 2.3ppm. Hydrogen desorption properties near the fracture origin were measured with Secondary Ion Mass Spectrometer(SIMS) and Thermal Desorption Spectrometer(TDS). Measurements with TDS and SIMS revealed that hydrogen trapped in microstructure is diffusive one and the hydrogen trapped by inclusion is non-diffusive one.
A simplified analysis of crack growth in a steady state of piezoelectric ceramics was performed by using the double cantilever beam (DCB) model. A constitutive equation of piezoelectric ceramics and a damage evolution equation that have been formulated by the authors were applied to the DCB model. The crack growth in the DCB model was dealt within the framework of the continuum damage mechanics ; i.e. damage development in piezoelectric ceramics was described by the evolution equation of a damage variable and the so-called local approach was applied to the analysis. The analysis was intended for crack growth in a steady state for the sake of the simplification and moreover it was simplified by using some assumptions. By using the DCB model, a constant crack growth rate and distribution of stress, strain and damage variable in front of the crack tip under mechanical and electric loads were elucidated and the effects of applied electric field on them were discussed. Furthermore, concentration of electric field around a crack tip was taken into account in the DCB model and the effect of the concentration of electric filed on the crack growth was clarified.
In this paper, the elastic analysis is performed for isotropic materials containing layered elliptical inclusion under In-plane loads at infinity. This analysis shows importance that inclusion and matrix are influenced by interface. In this analysis, general solutions of this problem are obtained by using complex function and confomal function. Some numerical results are shown by graphical representation. And we calculate stress intensity-factor of Mode I and Mode II of slit-crack in the layered elliptic inclusion under In-plane loads.
The internal stress resided in anode-supported solid oxide fuel cells (SOFCs) was measured by high-energy X-rays from synchrotron radiation at beam line BL02B1 of SPring-8. Firstly, the X-ray elastic constants of cubic scandia stabilized zirconia (c-ScSZ) electrolyte and NiO anode were determined using laboratory X-rays. Using these values, the internal stress in unit cells was determined by the constant penetration depth method with high-energy X-rays of 71.91keV. The internal stress in electrolyte of oxidized cells measured at the room temperature was a compression of about 400 MPa and this was produced by the mismatch of the coefficient of thermal expansion between anode and electrolyte. The internal stress in NiO anode was tension of about 100MPa. The internal stress in electrolyte of reduced cells was about a compression of 100MPa. In-situ measurements of the internal stress in an oxidized cell were conducted during thermal cycling. The compressive stress in electrolyte decreased with increasing temperature and became nearly zero at 1000K, while the tensile stress in anode decreased with increasing temperature and diminished at 1000K. The coefficients of thermal expansion both of anode and electrolyte were almost same value above 1000K, which agreed with the measured change of the internal stress. The internal stresses in both electrolyte and anode returned to the initial values after thermal cycling.
The mechanical properties of WC-Co cemented carbides were investigated in order to find the way to lengthen the lives of the bits including WC-Co cemented carbides, installed in tunnel boring machines. The compression and bending tests were first carried out using the test pieces made of the WC-Co cemented carbides including Co of 10%, of which grain size was 3, 6, 20 or 30 [μm], and the ones of which grain size was 20 [μm], including Co of 5, 10, 15 or 20%. The finite-element analysis was performed to find the tensile strength using the results of the compression and bending tests. We were able to draw an interesting results as follows : WC-Co cemented carbides of which grain size is 20 or 30 [μm] has the property of ductility, while the ones of which grain size is 3 or 6 [μm] has the property of brittleness.
The liner thermal expansion coefficient of the polystyrene that was blended with porous silica has been studied. The specific porous silica was prepared using silica sol and potassium bromide (KBr) by the pseudo-phase separation method. Next, to remove KBr from the mixture of silica and KBr, this mixture was soaked into heated water. The porous silica was convenient in preparing the composite because the mechanical strength can be controlled by the processing temperature. The composite of the porous silica and polystyrene was obtained by blending in an extruder. The silica was smashed at the blending procedure by the shearing stress. The blend of the polystyrene with spherical silica was prepared to compare the effect of the silica particle in polystyrene. The coefficient of the liner thermal expansion (CTE) was measured in two regions of temperature: one was the below the glass transition temperature and the other was in the higher temperature region. The CTE of neat-polystyrene was much larger than the blends with the two kinds of silica particles and the CTE of the blend with the spherical silica was larger than that with the porous silica in both temperature regions. In particular, the difference of the CTE was remarkable in the higher temperature region and the thermal expansions were much lower than the calculation values by the equations which have been applied to the organic/inorganic composites. As the CTE is one of the fundamental characteristics of materials, it is regarded not to deviate from the theoretical value. The chain of the polystyrene could be considered to intrude into the pores in the porous silica because the diameter of the pore was too small to reject the intrusion of the chain in both temperature regions.