It is very important for designing the safety of a timber structure to evaluate a strength durability of wood. Especially, the influence such as water is received easily for timbers used in outdoor, and there are a lot of use at harsh terms. In this study, the relation between a pilodyn driving depth and a bending strength was investigated, to develop the technique for presuming the strength deterioration by a simple method for members of a wooden dam for soil conservation that had been build in Kyoto Prefecture since 1999. A wooden dam for soil conservation has divided into two parts in wings set up by ground and counduit in state of often flood. Therefore, the feature of the strength deterioration in these two parts was experimentally confirmed. As a result, we found followings, 1) the increase speed of wings of a pilodyn driving depth is faster than that of a counduit. 2) there is a correlation between a pilodyn driving depth, the bending strength, and the young's modulus. 3) the strength deterioration can be presumed by using these findings in the maintenance work.
Wood has the unique gloss property originated in its anatomical structures. The objective of this study is to characterize such gloss property quantitatively by using image analyses. Smooth radial surfaces (edge grain) with various grain angles of Japanese cypress (Chamaecyparis obtusa) were finished with a microtome. A series of the surface images of the specimen was taken by a digital still camera while changing the incident angle by 5° in the range from 0° to 70°. Lightness values of the surfaces were calculated by the image analysis, and was compared to glossiness measured by a glossmeter. Two profiles of the relation between the incident angle and the lightness and the relation between the incident angle and the glossiness were similar very much. The image analysis also could elucidate the gloss property of the wood surface with the grain angle as like as goniophotometry by the glossmeter. Furthermore, the surface images were captured by a flat-bed scanner and an epi-illumination type microscope. A ratio of the latewood in the surface and a ratio of cell wall section in the small earlywood or latewood area were computed using the scanned image and the microscopic image, respectively. Combining both ratios, a total ratio of the cell wall section in the surface was estimated. The specular glossiness of the surface tended to depend on the amount of the smooth section of cell walls.
Decorative pattern showing up on wood surface, because of special and abnormal alignment in cell or tissue, is generally called a figured grain. Because the figured grain is characteristically seen by human eye position and by the angle of incident light, it is prized. For this reason, optical characteristics in the figured grain are considered very important. Accordingly in this study the spectral reflectivity in the broad ray area and the axial element area was measured on surface figured with tiger stripes of Japanese oak (Quercus crispula) , and how the spectral reflectivity concerns relatively to surface roughness was studied. The main results are shown as follows : 1) When the broad ray area was illuminated perpendicularly to the grain, the reflectance curve showed a clear peak in a condition of the mirror reflection. Meanwhile the reflectance curve was gentle in the axial element. When the both broad ray and axial element areas were illuminated parallel to the grain, the reflectance curve showed almost the same pattern. 2) When the surface was illuminated perpendicularly to the grain, the difference of lightness between the axial element and the broad ray area was recognized easily compared with the incidence parallel to the grain. When the surface was illuminated parallel to the grain, the difference of lightness between the axial element and the broad ray area was small and indistinguishable. 3) The difference of L*, a*, b* between both the axial element and the broad ray area was bigger in the incidence perpendicular to the grain than the incidence parallel to the grain. 4) The surface roughness parameter of the axial element showed more than that of broad ray area. It is regarded that the surface roughness has an effect on optical characteristics corresponding to each incident direction. As a result, the surface of the broad ray area in Japanese oak appears in silver or black color, depending on the incident and receiving angle of light, contrasted with axial element areas.
The sensory tests by an elderly person and a young person were carried out by method of paired comparisons using coated oak wood (quarter-sawn grain) without seeing the specimens. The sensory tests were accompanied by measurements of the properties of the palm of the hand, the roughness of the specimen surface and the temperature change at the interface. The elderly person made more definite judgments regarding the sensory warmth and sliding than the young person, and the definition of judgment is the contrary in the sensory unevenness. There was no difference in judgment of the sensory dampness between the elderly person and the young person. The properties of the palm of the hand were significantly different between the elderly person and the young person. These properties were closely related to the judgment of tactile sensation. The temperature change at the interface had a close relation to the sensory warmth, and the roughness of the specimen surface related closely to the sensory warmth, sliding and unevenness. The comfortable surface differed between the elderly person and the young person. The elderly person made more definite judgments regarding comfortability than the young person. The multiple linear regression analysis showed that the comfortability could be predicted by the sensory sliding and dampness in elderly person, and by the sensory dampness in young person.
To investigate the effect of drying time on the thermal behavior as well as the dynamic viscoelastic behavior of wood, thermal analyses such as modulated temperature differential scanning calorimetry (MT-DSC), thermal gravimetry (TG) and dynamic mechanical analysis (DMA) were performed under a similar temperature schedule in which three times cyclical heating and cooling processes between 105 and 180°C was conducted after drying at 105°C for from 15 to 960 min. Results obtained showed as follows. 1) From the TG measurements, mass losses were hardly recognized during drying and heating-cooling processes, whereas heat flows in the first heating process of the DSC measurements showed different behaviors. The heat flow got exothermic around 140°C compared with those of the second and third heating processes. The beginning of the exothermic behavior showed at a higher temperature when the drying time set longer. The release of some amounts of energy seen as an exothermic behavior during the first heating could be believed that finestructure of wood changed to a lower energy level, and it was thought that a longer drying time resulted in a lower energy level in the finestructure of wood which was likely observed in an enthalpy relaxation of a glassy polymer during annealing. 2) Dynamic heat capacities obtained from MT-DSC measurements showed different behaviors in the first heating process, and it was slightly larger than those of the second and third heating processes. For a longer dry time, the dynamic heat capacity was decreased at temperatures lower than about 150°C. This decreased heat capacity suggested a packing of finestructure occurred during the first heating. 3) tanδ from DMA measurements showed a similar temperature dependency to the dynamic heat capacity, and this supported the finestructure change of wood deduced from the DSC results.
In a production of compound-type wood plastic composite (WPC), hydrophobic treatments of wood elements were expected to improve interfacial adhesion between hydrophilic woods and hydrophobic plastics. However, some of results obtained by such process did not show improvements on mechanical properties of resultant products. This difference in an effectiveness of hydrophobic treatments of wood seemed to be caused by the mixing and compounding conditions for treated woods and plastics used in previous studies. There were a few studies focused on the mixing condition in WPC productions for treated wood elements. From these points of view, WPC was prepared from hydrophobized wood flour by acetylation (A-WF) and commercialized polypropylene (PP) to investigate the mixing properties as well as the mechanical properties. A blend of wood flour with PP in same weight was compounded in a closed mixing blender under the condition that mixing time was varied from 5 to 30 min at a constant temperature of 180°C with a constant blender revolution of 30rpm. The mixing properties were evaluated by measuring the torque change during the mixing and the dispersion state of the untreated/treated wood flour in the PP compounded in each mixing time. As evaluation of the mechanical properties, the static bending modulus and the impact strength were measured. Results were summarized as follows; 1) It was found from microscopic observations that A-WF has poor dispersiveness than that of the untreated wood flour. 2) By increasing mixing time, the flexural modulus of the WPC tended to be slightly decreased, although the impact strength was obviously improved. 3) By the SEM examination, the A-WF improved interfacial wetting between the wood flour and the PP and increased mutual contact surface by deformation due to softening in the mixing temperature. From the results, it appeared that dispersiveness was changed by hydrophobization of wood and the mechanical properties were consequently affected by this change.
The effects of environmental temperature on the tensile strength and fracture behavior of notched plates made from virgin material and recycled material were investigated. The virgin material was a short-glass-fiber-reinforced polypropylene (GFPP). GFPP plates, each containing 30% E-glass fiber by weight, were made by injection molding. The pellets were kneaded again, and an injection-molded plate was made. This plate is referred to as recycled GFPP (R-GFPP) plate. The mean fiber lengths of GFPP and R-GFPP were 3.5 and 0.4mm, respectively. The notch-root radius was 0.5, 1, and 2mm. The tensile test was carried out in thermostatic chamber at temperatures of 22, 40, 60, 80, 100, 120, and 140°C for a constant crosshead speed. The process of initiation and growth of damage near the notch root during tensile test was measured by means of the luminance measuring technique using a CCD camera. The experimental results show that the configuration of the damaged zone and that of the fracture surface were dependent on the environmental temperature. At temperatures lower than a certain value, the initial formation of the damaged zone was observed only near the notch root. The specimen failed in a brittle manner at the maximum load. In this temperature range, the fracture criterion could apparently be applied on the basis of the severity near the notch root. The effect of the notch geometry on the tensile strength decreased with an increase in the environmental temperature. Furthermore, over a certain temperature range, the maximum nominal stress of the notched specimen was approximately equal to that of the smooth specimen. Damage was also observed outside the stress concentration zone in the notch root. The specimen failed in a ductile manner. R-GFPP showed a more remarkable deterioration in strength with an increase in the environmental temperature.
Low-density porous materials are useful in the design of shock absorption structure due to the properties of shock absorption, lightweight and formability. The mechanical behaviors of the materials have high-nonlinearity because they have complex inner structure in comparison with dense materials, and the structure causes difficulties in the analysis of their problems for the design. In this paper, the nonlinear behavior of the materials before the macroscopic crush condition is inspected to define the elastic properties of them by some tests of compression and shearing. Here, the nonlinearities in the initial of compression is eliminated by the adhered contact condition of specimen because the condition can reduce the localization of the mesoscopic cellular crush of the materials. Then, the elastic properties derived from the tests are compared with each other for validation, and it is revealed that the derived properties are coincided and the compression test with adhered contact condition can measure the Young's modulus with less influence of the localization of the mesoscopic cellular crush.
Fiber reinforced mortar is expected to be used for the construction of the external walls of buildings, and in particular, pedestal required to operate magnetic levitated trains because of its nonmagnetism. Although many impact experiments for concrete and armored concrete have been reported thus far, few impact experiments for fiber reinforced mortar have been reported. In this study, we determined the effect of polyethylene (PE) fiber contained in mortar on the fracture behavior. A spherical SUJ2-steel projectile (diameter : 4 mm, mass : 0.26g) was accelerated using a one-stage light gas accelerator and a two-stage light gas accelerator such that it would impact the test specimens at an impact velocity ranging from 200 - 1100 m/s. All the specimens used for the impact tests had dimensions of 75 mm × 75 mm and a thickness of 11.5 mm. Three kinds of specimens were used and contained PE fiber from 0% to 1.5%. The use of PE fibers in mortar effectively affect the generation of radial cracks, cone slope angle and ballistic limit. On the other hand, it did not affect the absorbed energy. Formulation of ballistic limit indicated that PE fiber reinforced mortar was able to be adapted formulation of ballistic limit which was used for armored concrete.
Nowadays, in the middle east region where sulfate is abundantly found in soil, the sulfate attack on concrete structures is one of the serious problem. For this purpose, a material design of cementitous material is expected to obtain high sulfate resistance, leading to the research on the high durability of the cementitous material using γ-2CaO·SiO2 (hereafter “γ-C2S”). The authors have proposed the material design as follows : the cementitous material mixed with γ-C2S and conducted with autoclave and accelerated carbonation curing to obtain high durability performance due to the generation of tobermorite in the hardened body by autoclave curing, and densification at the surface of hardened body by accelerated carbonation curing. However, its sulfate resistance has not been investigated yet. Therefore, the purpose of this research is to evaluate the effect of using γ-C2S, autoclave curing and accelerated carbonation curing to permeability of sulfate ions related to the sulfate resistance, and clarify the mechanism of sulfate resistance from the view point of the reaction product and sulfate ion penetration. As a result, in the case of 80% γ-C2S substitution ratio with autoclave and carbonation curing, the sulfate ion penetration was the smallest due to the generation of vaterite. In addition, dissolution of tobermorite in the hardened body could be inhibited. Also, low-Ca/Si C-S-H at the surface of hardened body could possibly contribute to the resistance of sulfate ion penetration.
In order to investigate the effect of humidity on fatigue strength of an extruded and age-hardened Al alloy 7075-T6, rotating bending fatigue tests were carried out using plain specimens in environments of controlled relative humidity of 25% and 85%. Both of initiation and propagation of a crack were accelerated by high humidity, causing the decrease in fatigue strength. In high humidity, a crack tended to propagate in a shear mode macroscopically and it was ductile accompanied with glide plane decohesion and void formation microscopically, though the propagation was a tensile mode with striations in low humidity. The shear mode propagation inclined about 35° to the extruded direction due to the marked texture of the alloy.
It is necessary to separate two important factors of dissimilar materials and interface strength, in order to discuss fatigue crack propagation behavior along the interface of composite materials. As model specimens with different interface strength, a diffusion bonding between the same materials (SK7s) is expected to have different interface strength with different bonding temperature. In addition, a fatigue testing was conducted under a certain displacement constrained by base plate so that the fatigue crack propagation behavior could be observed stably even for the interface without sufficient strength. As a result, the fatigue crack showed almost continuous propagation along the interface bonded at higher temperature, but slow and then abrupt propagation behavior intermittently on the interface bonded at lower temperature even under smaller stress amplitude condition. This abrupt propagation was related closely to crack tip opening displacement increased gradually during fatigue, which was understood by a cohesive crack model relating to a decrease of cohesive force near the crack tip in terms of liner fracture mechanics. The increase of crack tip opening displacement due to stress cycling was discussed using a potential-energy model in connection with fatigue damage.