The information on wood properties of sugi cultivars (Cryptomeria japonica) is very important for efficient use of sugi wood. Obi-sugi is a major group of sugi cultivars planted in Southern Kyusyu. However, the wood properties of Obi-sugi still have remained unclear. Therefore, the wood properties of 33-year-old Obi-sugi (15 cultivars) grown at one stand were determined. Mechanical properties were investigated by dynamic testing method for logs and compression test parallel to the grain for small clear specimens. In addition, basic density, latewood tracheid length and microfibril angle of middle layer in secondary wall (S2) in both earlywood and latewood tracheid were examined There were differences in the mechanical and anatomical properties of Obi-sugi among cultivars. The maximum and minimum values of static modulus of elasticity (Es) of the mature wood among the cultivars were 13.0 Gpa and 6.6 Gpa respectively. The patterns of radial variation in Es of the wood from pith to bark were also characterized by the cultivars. It was suggested that these revealed characteristics of the cultivars are quite essential information to decide the suitable end use of Obi-sugi. Both the basic density and the S2 microfibril angle affected the mechanical properties of Obi-sugi. Higher basic density and/or lower S2 microfibril angle were the cause of the higher mechanical performance of mature wood of the cultivars. S2 microfibril angle was also the most effective factor in both mature and juvenile wood.
Tensile strength tests were carried out on various glued laminated wood (GL) and laminated veneer lumber (LVL) with butt-joints (BJ), and size effects of the length of specimens were examined experimentally. In addition, laminating effects which improve strength properties were also examined on the GL. Species used for the specimens were sugi (Cryptomeria japonica D. Don), akamatsu(Pinus densiflora Sieb. et Z.), and Douglas fir (Pseudotsuga menziesii Franco) for the GL, and akamatsu and radiata pine (Pinus Radiata D. Don) for the LVL. In the case of GL, tensile strength (TS) decreased to 23.5% (sugi), 30.9% (akamatsu), and 18.2% (Douglas fir) of their raw materials. Size effect was evidently observed on the GL, and the reduction of TS by size effect was higher than that of the laminae. Coefficient of laminating effect Κ (ratio of 5% lower extrusion limit after lamination to that of before lamination) on the TS of 2 ply laminated GL ranged from 1.84 to 2.47. In the case of LVL, the thickness of veneer affected on TS remarkably, and 15 ply type specimens composed of 3mm thick veneer showed higher TS than 7 ply type specimens composed of 6mm thick veneer. Size effect of LVL depended on the thickness of veneer. While 15 ply type specimen showed no size effect, TS of the 7 ply type specimen decreased with increasing the specimen length.
Strain distributions on a cross section of softwood under transverse compression were analyzed in detail using digital image correlation method. We discussed the relationship between compression strain distributions in an annual ring and anatomical structure (earlywood and latewood). In radial compression, local large shear strains were observed in the edge of earlywood near annual ring boundary where mechanical properties change abruptly along radial direction. In a plastic region of stress-strain curve we found a row of large compression strain that is thought to be cell-wall collapse in earlywood. A start point of the row of large compression strain was the edge of earlywood in which the large shear strain were observed, because the radial wall of sheared cell are easily buckled. In the case of 45 degree compression, large compression strain along loading direction was observed in earlywood. Large expansion strain across the loading direction was also observed in the same area because of Poisson's ratio effect. As the strains were transformed to radial-tangential coordinate system, large shear strain and little normal strain were observed in early wood. The shear strain under 45 degree compression was larger than that under radial compression. The former is the shear strain that is usually called rolling shear.
In recent years there has been an increasing interest in using natural fibers as reinforcements for biodegradable plastics from the environment-friendly viewpoint. In this study the mechanical properties of bamboo fibers extracted by a steam-explosion method has been investigated by means of the tensile test. From the experimental results it was found that the tensile strength of bamboo fibers depended on the steam-explosion conditions and that the strength of the bamboo fibers extracted at relatively low temperatures and for a short period was high but the scattering of the strength also became large, thus optimum steam-explosion conditions were at 190°C for 1.8-3.6ks. Finally we found that the tensile strength of bamboo fiber extracted by the steam-explosion method was larger than that of bamboo fiber cut out from a raw bamboo indicating the steam-explosion is suitable extraction method for bamboo fibers. In addition, the tensile strength of bamboo fibers also depended on their height sampled. The bamboo fibers sampled from relatively high position had low tensile strength and these weak fibers were not suitable as reinforcements for high-strength composites.
Recently, bamboo has been reevaluated from the environment-friendly viewpoint. Bamboo is a typical yearly-renewable bio-resource and inherently has an advantage in the high growing speed. With the increase in the use of the bamboo, it is anticipated that the quantity of bamboo powder discharged in the various cutting processes will also increase. It is, therefore, important for bamboo powder to develop an adequate recycling technology. For this purpose, we developed biodegradable composite boards with bamboo powder and a starch-based plastic. It is found that the biodegradable composite boards fabricated with bamboo powder of 0.5mm in diameter had an acceptable high bending strength and high bending modulus. It is also shown that an alkali treatment to the bamboo powder affects the mechanical properties of the biodegradable composite boards with an increased bending strength of about 20 percents.
Changes in the dielectric relaxation of sugi (Cryptomeria japonica) specimens by heat treatment were investigated. Dielectric properties in the longitudinal direction for the oven-dried specimens were measured in the range from 20Hz to 1MHz and from -150°C to 20°C. The relaxation due to the orientation of methylol groups was observed for the specimens treated at the temperature up to 300°C. The relaxation magnitude obtained from the Cole-Cole plots did not change by the heat treatment up to 200°C, but it decreased remarkably above 200°C and became 0 at 300°C, showing the disappearance of methylol groups. Any relaxation was not detected within the range measured for the specimens treated at the temperature between 300°C and 450°C. However, one relaxation was recognized for the specimens treated at the temperature between 500°C and 600°C. Regarding the specimen treated at 500°C as a system in which a small amount of ellipsoids of graphite disperses in the medium of an insulator, the applicability of the Maxwell-Wagner's theory to the tanδ versus logarithmic frequency curve at 20°C was examined. A good agreement between the experimental and calculated results was obtained in the case that long and narrow ellipsoids oriente to the direction of the electrical field. These results suggested that the relaxation was due to the interfacial polarization.
To investigate the gas permeability in the radial direction in green logs of Cryptomeria japonica, the log specimen was prepared with both ends sealed and the log's bark removed. A glass tube was set in each end of the heartwood, white zone wood and sapwood sections. The specimen was then set in a vacuum chamber. Each of the glass tubes was connected to a separate mercury manometer set outside the chamber. The changes in pressures were then measured during the different stages under vacuum. The amount of exposure of the end section of the white zone wood was then varied, and the subsequent pressure changes were measured, alternating between the vacuum state and the atmospheric pressure state. Another experiment was carried out on some different specimens, in which the log's bark was retained, and the gas permeability between the white zone wood, sapwood and ambient atmosphere in the radial direction was investigated. The results obtained were as follows. 1) The first detected decrease in pressure was in the white zone wood in both experiments, which demonstrated that there were radial passages through which gas flowed from the ambient atmosphere through to the intermediate wood, regardless of the presence or absence of bark. 2) Pressure variation in the sapwood was consistently affected by the gas flow from the white zone wood rather than from the log surface.
We expected that the addition of fine wood particles in bonding materials of grinding wheels improve the polishing mechanism of surface finishing. In the experiment of finding suitable size and hardness of wood particles to be added to grinding wheels, first of all, we studied the effect of heating time and temperature to the distribution of wood (Western hemlock and Douglas fir) particles prepared to the size of 100 meshes. Experimental results showed that the heating time to the wood particles did not effect to the distribution of particles, and that finer particles were produced by the heating of higher temperature.
Polymeric materials under large deformation exhibit localized instability propagation, such as neck propagation under tension and shear band propagation under shearing. In this study, formation and growth of micro-shear bands in a glassy polymeric material, polycarbonate (PC) deformed under simple shear, were observed using an Atomic Force Microscope (AFM). In the early stage of shear deformation, the first micro-shear bands along the shearing direction was formed, and they merged together with increase in its density, and then, resulted in the formation of the macro-shear band. In this process, crossing orthogonally to the first micro-shear band, the secondary micro-shear bands were formed. After the applied force reached its maximum, the macro-shear band propagation started in the perpendicular direction to the shearing direction. As the macro-shear band propagated, the rotation of the secondary micro-shear band was observed. In addition, hierarchical structure of the secondary micro-shear band was revealed in region right after the macro-shear band propagation.
In this paper, the theoretical solutions with multi-layered circular inclusions inclined to the far-field principal stresses are presented. The medium, which is permeated by fluid, is assumed to behave as a poroelastic material with compressible constituents, while the multi-layered circular inclusions are considered as classical elastic materials. The poroelastic solutions are derived in the Laplace transform space, and are transformed to the time domain using an approximate numerical inversion technique. Several numerical examples are shown graphically.
Time and temperature dependence of recovery behavior of residual strains in largely compressed glassy poly (methyl methacrylate) (PMMA) has been studied. At several temperatures lower than the glass transition temperature Tg, uniaxially compressed specimens were isothermally kept in the stress-free state for a variation of time tf, and then subjected to thermally stimulated strain recovery measurement. Thermally stimulated recovery of residual strains in specimens right after the compression began at heating temperatures lower than Tg. With increasing time tf, residual strains recoverable at heating temperatures below Tg decreased simply from those recoverable at the lowest heating temperature. The decrease of residual strains recovering at a heating temperature less than Tg was examined as a function of time tf and was found to be expressed by a single exponential retardation function. Thus, the sub-Tg strain recovery was revealed to be a simple viscoelastic process with distribution of retardation times. Temperature dependence of the retardation time allowed us to calculate activation energy of sub-Tg strain recovery as a function of heating temperature. The activation energy of sub-Tg strain recovery was found to be approximately the same function of temperature as that of the linear viscoelastic relaxation of the polymer. This result led us to a conclusion that, as a first approximation, the molecular mechanism governing the sub-Tg recovery of strains given by large deformation is almost the same as that of linear viscoelastic relaxation.
Basic equations are derived for a cylindrically anisotropic elastic medium of two-dimensional in-plane problems and out-of-plane shear problems, and general solutions for a circular ring with prescribed stress boundary conditions are obtained by the form of Fourier series. Further, a closed-form solution is also derived for the concentrated force. Numerical results for stress distribution are also shown.
Fracture behavior under monotonic and cyclic loading in a glass fiber reinforced phenolic resin composite was experimentally characterized. First, monotonic tensile tests were conducted to measure stress-strain curves and acoustic emission (AE) behavior. Next, fatigue tests were performed to measure S-N curves for the virgin and after-cured specimens. Finally, fracture surfaces after both tests were observed by means of scanning electron microscopy (SEM). It is found that final failure abruptly takes place for both tests without showing visible damage on the surface of the specimens while permanent strain and cumulative AE events increase just before fracture. The after-cure process increases fatigue strength as well as monotonic tensile strength. Pull-out of fibers was observed on the fracture surfaces, however, it is difficult to determine the origin of fracture in both tests. The SEM fractography reveals that small resin particles are generated on the fiber surfaces in the case of a high cycle fatigue test.
Autoclave curing processes of CFRP (carbon fiber reinforced plastics) laminates composed of carbon fiber/heat-resistant tough epoxy resin prepreg used as aircraft structure material were monitored by dielectric sensors. Then, monitored dielectric properties were compared with the degree of cure predicted by Springer's model and resin viscosity, Reciprocal dielectric loss factor (1/(ε"ε0ω) or ion viscosity), which is considered to correspond to degree of cure, becomes constant at 30-40% degree of cure. And the ion viscosity before gelation does not correspond to resin viscosity. Besides, the exothermic reaction rate peak point shown as temperature overshoot does not correspond with the peak point of differential coefficient of ion viscosity. In the case of this particular resin we selected, motion of free charges or dipoles in the resin is presumed to become insensitive after the degree of cure reaches 30-40%.
To improve the pv limit of polymers, filled polyacetal (POM) and POM/polyethylene (PE) blends were studied. The fillers used were amino silane coupling agent treated and untreated bronze powder. And low density polyethylene (LDPE), high density polyethylene (HDPE) and high molecular weight high density polyethylene (HMWHDPE) were used as blended polymers in POM. Sliding tests were performed in a thrust washer type testing apparatus under unlubricated conditions. Frictional surfaces of a slider and specimens were investigated by XPS, EPMA and FT-IR. The additions of bronze powder and PE (LDPE, HDPE) in POM remarkably improved pv limit. The inclusion of bronze powder in POM/PE (LDPE, HDPE, HMWHDPE) blends and treating its bronze powder with amino silane coupling agent raised pv limit. And the pv limit of POM+25mass%HDPE+20mass%Br (treated) was approximately six times higher than that of POM. It was suggested that the POM film and the POM/PE mixed film produced in the frictional interface contributed to the elevation of pv limit.
The residual stress and microstrain of crack-free Cr layers deposited by pulse current electrolysis was evaluated by X-Ray diffraction methods. Changing the on-time and off-time periods, various residual stresses were measured. The residual stress was influenced by the off-time period in the same on-time period. In order to obtain Cr layers that have compressive residual stress, a suitable off-time period corresponding to the on-time period should exist. When the off-time period was too short or too long compared to the suitable off-time period, tensile residual stress was generated in the Cr layer. With increasing bath temperature and current density, the residual stress became more compressive. Microstrain decreased at high bath temperatures and low current densities. The amount of change in the residual stress due to heat treatment correlated with the microstrain, and became smaller and more stable with heat treatment as the microstrain decreased. The Vickers hardness of the Cr layer was governed by microstrain; the hardness increases with increasing microstrain.