The high-temperature setting method may be put to practical use in Japanese sawmills for drying square timbers including pith. In order to prevent splits and cracks, green timber is softened by heating and then rapidly dried at high temperature in low humidity air, so as to generate compression stress on the surface. In this study, we perform wedge splitting tests to obtain the fracture energy, and discuss how thermal treatment affects the timber's fracture toughness. Spruce specimens were curved to perform the wedge splitting test. The curved air-dried specimens impregnated with sufficient distilled water to imitate green wood. Two sets of timber specimens were used : the first set, to test the degradation caused by the initial heating process, and the second set, to examine the further degradation effects attributable to the so-called drying set process. The wet specimens were heated for 12 hours, at one of four temperatures (105°C, 85°C, 75°C and 65°C) in saturated humidity air. For the drying set process, those specimens initially heated at 85°C were dried for 12 hours in four temperature conditions (120°C, 90°C, 75°C and 55°C) in low humidity air (33% of relative humidity). As a result, the fracture toughness of almost all specimens was less than that of the control specimen. In particular, that of heated wet specimen was lower with increasing process temperature. This also seems to be based on the thermal decomposition of wet hemicelluloses, since wet hemicelluloses are thought to decompose at 80-90°C. The specimen dried at 55°C displayed the least toughness of all. As this glass transition temperature of wet lignin is approximately 60°C, this specimen was probably insufficiently softened to prevent splits and cracks from occurring on the surface.
To clarify the mechanism of the heat-treatment for wood between 100°C and 200°C, the behaviors of endothermic and exothermic of wood and wood components (cellulose, hemicellulose, lignin) between 100°C and 200°C under the dried air condition were measured using the temperature-modulated DSC. The measurement were carried out in the heating processes under stepwise heating and cooling cycles (100°C→140°C→100°C→160°C→100°C→180°C→100°C→200°C, ±5°C/min). The total heat flow (THF) and the nonreversing heat flow (NRHF) curves of wood, cellulose and hemicellulose in the 1st heating process (100°C→140°C) were found in the exothermic side compared with the curves in other heating processes. The reversing heat flow (RHF) curves of wood in the 4th heating process (100°C→200°C) were found in the exothermic side compared with the curves in other heating processes. However the RHF curves of cellulose and hemicellulose were observed on the almost same line. The THF and NRHF curves of lignin were shifted to the exothermic side with the stepwise heating and cooling cycles. On the other hand, the RHF curves of lignin were shifted to the endothermic side with the cycles. These results suggest that the effects of the heat-treatment for wood between 100°C and 200°C are based on the thermodynamic stabilization of the conformation of cellulose, hemicellulose and especially lignin due to the heating history.
To investigate the relationship between microstructures of wood and the physical and mechanical properties, creep behaviors during and after drying and microstructures after drying of wood swollen by water, methanol and ethanol were studied in this report. Results obtained were as follows. 1) Creeps for every swollen wood during drying were greater than immediately after drying, and much greater than after conditioned at the before and after contents. Wood samples with greater degree of creep during and immediately after drying were; methanol-swollen wood, ethanol-swollen wood and water-swollen wood when similar amount of content were changed. 2) Similar degree of creep occurred during drying despite drying rate. Degree of creep immediately after drying depended on drying rate and elapsed time after drying. 3) Larger amount of micropores existed in wood after desorption of methanol and ethanol than in wood after desorption of water when vacuum-dried at 110°C. 4) One and a half times as much as greater creep occurred during drying for liquid mixtures (water : methanol = 0.2 : 0.8, water : ethanol = 0.8 : 0.2) swollen wood than for water-swollen wood. Accordingly, it was considered that different swollen states of wood produced different wood microstructures during and after drying.
To investigate the friction characteristics between wood and metal tool under high pressure conditions, we analyzed the nominal friction coefficient between them in various normal pressures (1.1∼11MPa). The effects of anisotropy of wood were examined by changing friction surfaces and sliding directions of wood samples. The wood samples were slid about 10mm. The results showed as follows. 1) The nominal friction coefficient behaviors varied according to normal loads and friction surfaces or sliding directions of the wood samples. 2) In longitudinal compression conditions, the nominal friction coefficient could be considered that there were no effects of the normal loads. In tangential or radial compression conditions, the nominal friction coefficient decreased as the normal load increased. The nominal friction coefficients of longitudinal direction were larger than that of radial direction in the edge grain friction surface. 3) By observation of friction surfaces after sliding, it appears that the nominal friction coefficients were more influenced by deformation force in the wood sample.
The sensory tests by an elderly person and a young person were carried out by method of paired comparisons using coated kiri and teak wood (flat-sawn grain) without seeing the specimens. The properties of the palm of the hand and the heat flow from a metal disk heated at temperature of the palm to the specimen were measured. The density of wood influenced the sensory warmth and hardness of coated wood. The coating changed the tactile sensation of wood. The elderly person made more definite judgment regarding the sensory sliding than the young person, but the definition of judgment is the contrary in the sensory hardness. The comparison of the tactile sensation between elderly person and young person having the similar properties of palm showed that in the elderly person the decline of perceptivity on the sensory hardness was recognized, but wasn't on the sensory sliding. The heat flow from the heated metal disk to the specimen had a very close relation to the sensory warmth. The comfortable surface was different between the elderly and young person. The elderly person made more definite judgments regarding comfortability. The multiple linear regression analysis showed that the comfortability in the elderly person could be predicted by the sensory warmth.
Glued laminated timber (glulam) composed of mechanical-graded lamina shows higher strength reliability than lumber. However the glulam still has wider strength distribution than steel or concrete for structural applications because of the large difference between the mean and the lower limit value. This study aimed at reduction of the coefficient of variation of the glulam in bending strength by partial reinforcement technique using wooden sheets. The wooden sheets made from bamboo or white oak were covered to several defects on the surface of glulam such as large knots and finger joints. The strength performance and the reinforcement effect for the bending test of the glulam with reinforcement materials were evaluated. As a result, it was clarified that a bamboo sheet (two layers) or a white oak sliced veneer sheet could reinforce the defects, and the average of bending strength was improved due to the improvement in the lower value in the strength distribution.
In this study, the pulled out strength of mortise and tenon joint, which is a Japanese traditional timber connection, were investigated, in order to find out an influence that strength by a width of a tenon and a position of a mortice. Specimens had 3 types of a tenon, which had a 30mm, 45mm or 60mm width, and 3 types of position, which was 30mm, 52.5mm, or 75mm depth. As a result of experiments, a komisen-dowel was broken in a mortise of 52.5mm depth type, many tenons were broken by shearing in mortises of 75mm depth, and a type of 30mm depth were frequently split off at a mortise. And then, the stiffness and strength were evaluated by mechanical models. The stiffness was similar to a secant stiffness of 0.7 Pmax, and the strength calculated as a yield load was mostly evaluated on a safety side.
We designed water soluble copolymer for corrosion inhibition effects in aqueous enviroment. This copolymer was pursued for the goal of environmental adaptability. Water soluble copolymers were prepared from methoxypolyethylene glycol methacrylate (MPEG-MA) and acrylic acid units. We polymerized 5 to 65wt% of methoxypolyethylene glycol methacrylate and 95 to 35wt% of acrylic acid monomers by azobisisobutyronitrile (AIBN) and sodium peroxodisulfate in organic and water media, respectively. The solution containing these copolymers was evaluated inhibition of corrosion effect for steel materials. These results suggested that combination of MPEG-MA and acrylic acid in polymerizing in water media was most effective to inhibit corrosion for steel materials. It is important to contain 4 to 6 mol unit of ethylene oxide side chain in MPEG-MA.
The objective of this study is to prepare a powder sintered body, inside which there are macroscopic hollow connected to the outer surface through open pores, and to obtain aromatic sintered metal by impregnating this structure with an aromatic agent. The macroscopic hollow was fabricated using an infiltration method. Specifically, a pre-formed copper powder compact was buried in iron powder and compacted, and the obtained compact was sintered under vacuum at 1150°C for 30min. The weight of copper powder was adjusted so that 20% of the open pore volume in the iron powder compact remained. When the temperature of the sintering process reached the melting point of copper, the copper infiltrated into these pores. Consequently, regions that had been occupied by the copper powder compact became macroscopic hollow, and part of the pores remained open. When an aromatic agent was allowed to impregnate the hollow through the open pores, the hollow became reservoirs for the aromatic agent and weight of the agent increased 1.2 times compared with the non-infiltrated compact. Moreover, mechanical strength of iron powder compact by copper infiltration increased more than 3 times compared with the non-infiltrated compact.
Tensile tests were conducted at 650°C on five different types of austenitic stainless steels varying in grain size. Each test was terminated at strain from 5 to 15 % followed by sample preparation for EBSD. Crystal direction at each point was measured by EBSD and misorientation was determined by Intra-granular Distortion, GOS (Grain Orientation Spread) and KAM (Kernel Average Misorientation). Plastic strain was found to be correlated with the results obtained by these methods, despite the differences in grain size and material type. At a certain plastic strain, Intra-granular Distortion indicated essentially the same result as that by GOS, since average crystal direction in a grain corresponds approximately to this direction at the center of a grain. Plastic strain was also seen to be correlated with results obtained by KAM, though the latter was noted to increase with reduction in grain size. KAM corresponded to the degree of misorientation within grains owing to dislocation density which has been seen to increase with reduction in grain size.
The effect of ratcheting deformation and pre-strain on fatigue and creep-fatigue life in Mod.9Cr-1Mo steel was investigated. Uni-axial fatigue and creep-fatigue tests with pre-strain and progressive strain were performed to evaluate the effect of pre-strain and ratcheting strain on the failure cycle. In a series of tests, a specific amount of progressive strain was accumulated in each cycle. The accumulated strain as ratcheting deformation and cycles to reach the accumulated strain were varied in the tests. In the fatigue tests with pre-strain, failure lives were not declined. In the fatigue tests with progressive strain, slight reductions of failure lives were observed, however, they were within a factor of 1.5 of the failure life in normal fatigue test. The apparent relationship between failure cycles and testing parameters were not observed. Analyses of the test results indicated that the effect of ratcheting strain on the fatigue failure life is negligible as long as the parameters are within the strain limit of FR code (strains at surface less than 2%). In the creep-fatigue tests with progressive strain, the same conclusion of the fatigue tests was obtained. In both kinds of tests, maximum mean stresses during the tests were insignificant and/or generated in early cycle in the tests, and this character is considered as a reason of that the effect of ratcheting deformation on the fatigue and creep-fatigue lives are insignificant.
Rotating bending fatigue tests were carried out using a radical nitrided nickel base superalloy, Alloy 718, at 500°C, to investigate the effect of radical nitriding on the initiation of a fatigue crack at elevated temperature. The nitriding was conducted after normal double-aging at two different conditions, i.e. at 500°C for 12h and at 570°C for 20h, in mixed gases of hydrogen and ammonia. By the nitriding, compound layers were formed on the specimen surface with the thickness of about 4μm at 500°C and 10μm at 570°C, respectively. Fatigue strength at 500°C was larger than that at room temperature in both nitrided alloys in wide life region. Fracture origins of the nitrided alloys changed from the base alloy beneath the compound layer to the interior of the alloy with decreasing in stress level, causing that S-N curves showed a step wise shape similar to the result of the aged alloy. The crack initiation was suppressed by the compound layer. Fatigue strength was increased by nitriding in the horizontal region in S-N curves where fatigue strength was controlled by the crack initiation and the propagation of a small crack, though the effect of nitriding on fatigue strength was very small in the region where fatigue life was occupied by the growth of a crack, i.e. in the region except for the horizontal one in S-N curves. Although a surface crack in the nitrided alloy propagated in a brittle manner, the crack propagated steadily similar to the one in the aged alloy propagated in a ductile manner.