The behavior of pit membrane was examined from the dehydration process under the centrifugal field. According to this method, an arbitrary pressure difference (water potential by the centrifuge) is obtained by the rotational speed and the distance inward the dehydration surface. The pressure differential required to close the pit aperture by the pit membrane was evaluated as the range from 0.119MPa to 0.178MPa for sapwood of Sugi. The portion treated by the pressure differential of 0.252MPa was easier to dehydrate and it was estimated that the pit membranes in sapwood were broken by the pressure differential of 0.332MPa. The SEM observation showed the breaks of the pit membrane. The pressure differential up to 1.32MPa did not make the pit membrane in heartwood break. The centrifugal method was possible to determine the pressure differential that produces the pit aspiration and the break of pit membrane in sapwood of softwood.
For the development of the partial coloring technique using Japanese beech (Fagus crenata), it is necessary to clarify the methods for prevention of tylose development. Three logs felled in midsummer were immediately immersed in a hot bath at temperatures of 20°C, 40°C, 50°C, 60°C. Another three logs felled in midwinter were each cut into 4 sections then treated in the following conditions; outdoors under snow, a stockroom well-ventilated within -30.9°C-11.3°C, a thermostatic room at 4°C, a stock room well-ventilated within 1°C-18°C for 90 days, and a half of each section was immediately immersed in a hot bath at a temperature of 50°C. Then, they were each penetrated with a dye solution by the capillary rise method for four hours. Results obtained were as follows; 1. The wood felled in summer and treated in hot baths of 50°C and 60°C absorbed a dye solution very well. And as the dye solution penetrated into the wood deeply through the vessels of earlywood, color contrast between the earlywood and the latewood was emphasized clearly. 2. Wood felled in winter needs to be sawed and dried within a low temperature period. Or the wood needs to be heated above 50°C before drying.
Fracture toughness tests were performed on the surface layer of boxed-heart square timber of sugi, after and during drying. Experiments were carried out using of notched tensile specimens with single edge. The critical stress intensity factor (KIc) in the TR system was investigated to clarify effects of drying temperature on resistance against drying surface check of the boxed-heart square timber of sugi. Timbers dried with temperatures of 20°C and 80°C had higher resistance against drying check than dried with temperature of 40°C and 60°C. AE cumulative events increased slowly at the occurrence state for the tension tests of the specimens dried with temperature of 20°C and 80°C, whose KIc values were relatively high. On the other hand, AE cumulative events increased relatively fast for the specimens dried with temperature of 40°C and 60°C. Cell-wall break type of micro-fracture occupied the most of fracture in the early wood, when the large amplitude of AE were detected in the early state. Therefore, it was found that the characteristics of AE were closely concerned with KIc values and micro-fracture. The KIc values of the fracture toughness decrease with drying until moisture content of 20%, because of drying stresses. After then, the KIc values increase rapidly with drying under moisture content of 20%. In the drying processes the KIc values have a tendency to be higher with lower drying temperature within this experiment conditions.
Boxed heart square timbers of sugi (Cryptomeria japonica D. Don) were treated by smoke-heating system with increased far-infrared radiation for about 50 hours at a temperature inside the square timbers of 70°C-80°C. After smoke-heat treatment (SHT), wood qualities (moisture content, surface check, dynamic Young's modulus) were examined. Average moisture contents of boxed heart square timbers were largely decreased by SHT, but moisture contents near the pith still remained high. No surface checks occurred in 29 specimens (24.8%) of 117 square timbers smoke-heated. In addition, decrease of dynamic Young's modulus by SHT was not recognized. The results obtained indicate that SHT has effect on pre-drying of square timbers, without any damages, followed by kiln drying.
Fatigue properties under cyclic non-linear in bending were examined at room temperature for laminated wood with resorcinol resin adhesive (RF) and aqueous-polymer-isocyanate resin adhesive (API). The change of both the relative stress (σ/σ0) and temperature rising (ΔT) which was measured at the point of the maximum temperature rising depended upon mechanical properties of adhesives in a neutral layer of specimens. This is because, for laminated wood with API, an adhesive layer causes heating by cyclic deflection so that the stress in a neutral layer decreases, while, for RF, such heating does not cause. It was found that the peak of ΔT related to fatigue life. Both (σ/σ0)p and (σ/σ0)b are linear to the peak temperature ΔTp, and more the logarithmic cyclic number to failure, logNb, is linear to the logarithmic cyclic number to the peak of ΔT, logNp.
To examine the low cycle fatigue properties of laminated beech (Fagus crenata Bl.), compression-compression tests are carried out at high loading levels in the direction parallel to wood grain. A test specimen has shallow notches in order to avoid the die-test piece interface fractures. The notch effect on the static stress distribution is analyzed by a three dimensional FEM. Upper limit load is given by assigning the increment of strain from basic stress state and load amplitude remains unchanged through the tests. Experimental results show that the critical number of cycles to fracture becomes smaller with increasing magnitudes of the strain increment, although the scatter of its values is observed to some extent. Furthermore, it is found that typical fracturing pattern is the type of a inclined straight-line originating from the root of a groove.
Following the previous paper treating with the production and properties of wood-mineral composites using the colloidal silica solution system, we investigated termite resistance, photo stability, hardness, and abrasion resistance of composites. The composites were prepared by the same process previously reported using a colloidal silica solution and sapwood or heartwood of Sugi (Cryptomeria japonica D. Don). The composites made by using the colloidal silica-boric acid system showed an excellent termite resistance with the neglible weight losses of specimens and 100% mortalities of workers and soldiers, and the metal compounds (Cu, Ag, and Ti)-added system had a certain extent of resistance against termite attack. As a result of photo stability test with ultraviolet (UV) light, the changes in color difference in the radial section of the composites irradiated with UV light were smaller than those of the untreated wood, particularly the smallest change for the titanium dioxide-added system, showing the enhancement of photo stability. The composites remained the photo proof even after leaching. The brightness in the cross section changed greatly in the boric acid-and titanium dioxide-added system compared with the untreated wood. The Brinell hardness in the cross section showed an increase up to 70% compared with the untreated wood, and it increased with an increase in weight percent gain (WPG). This hardness held an increase up to 22% compared with the untreated wood even after leaching and the hardness in the radial section increased up to 30%, revealing little reduction of hardness in any case. The Taber type abrasion index in the tangential section tended to increase with an increase in WPG. This result showed the reduction of abrasion resistance.
The object of this study was to investigate the dimensional stability (DS) for particleboards (PBs) made by changing factors of board preparation, this is, density of boards, resin content, adhesives, particle size and wood species. The measurement of moisture absorption, in-plane linear expansion (LE) and thickness swelling (TS) were done to evaluate DS of PBs. The results are summarized as follows: It was clear that the values of LE and TS were decreased with decreasing density of boards and increasing resin content. DS of adhesives used was superior in order of phenolic resin (PF)>Isocyanate resin (IC)>Urea resin (UF). The oriented boards prepared from birch and Hinoki showed excellent resistance against moisture absorption, and anti-swelling efficiency on their LE values (L-ASE) in 50% and 35%, respectively.
In this paper we examine the analytical structure for the simulation of localized necking in sheet metal. The stress rate components which are not associated with the equilibrium condition on the necking plane can be assumed to be continuous, based on the verification given by Hill. This assumption makes it possible to apply the conventional constitutive equations for the study of the analytical structure. In many analyses reported in the literature the necking plane is assumed to be normal to the sheet plane a priori. In such a case the discontinuous velocity gradient vector has two components which are related with the three equations binding three components between the stress and strain rates in the necking plane. Hence, all the velocity gradient components must vanish in order to satisfy these conditions. This means that they must be continuous and then their multiplicity cannot occur. Furthermore, it is shown that the volume constancy requires the normality of the velocity gradient vector with the normal vector to necking plane.
The adhered joint composed of polymer and metal is a useful and practical method to take advantage of the both material properties. However, there are some basic problems for the material mismatch due to the different Young's modulus. Inthis study, the stress singularity at the intersection between the free surface and the interface betweenpoly-methyl-methacrylate (PMMA) and structural carbon steel (JIS SS400) was analyzed to clarify the joint strength using a finite element method. As a result, the stress singularity was found above 130 degree of PMMA apex angle and between 35 and 41 degree of PMMA apex angle. In this experiment, it was confirmed that the no free-edge stress singularity was useful conditions to insure the reliability of bending strength for the adhered joint composed of SS400 and PMMA.
Carbon fiber is one of the high performance fibers employed in advanced composites. However, the use of carbon fibers as a structural component is often limited owing to their poor compressive properties. In the present work, compressive damage of carbon fiber monofilaments was investigated for various type of fibers. The tensile recoil technique and the SEM observation for looped fiber were conducted to evaluate compressive damage. The compressive strengths evaluated at the tensile recoil test and the loop test were smaller in the higher tensile modulus fibers. However, whether the compressive damage (kink) was occur or not in the loop test was well dependent on the elastic modulus ratio between in tensile and in torsion. The torsional modulus for each fiber was also measured with the torsional vibration method. For the evaluation of the crystalline structures, the grazing incident X-ray diffraction method was performed. Even in similar tensile modulus fibers, the polyacrylonitrile based fiber, which showed the higher compressive strength, had the more disordered graphite crystalline phase in the fiber surface region than the mesophase-pitch based fiber. The disordered crystal in the surface layer might locally lead the more isotropic mechanical properties than ordered crystal and this isotropic properties in the surface layer could increase the compressive strength of the carbon fiber. It was suggested the possibility of the optimum crystalline structure for the compressive strength, maintaining the tensile properties.
The influences of ZrO2 particle addition upon improvement in mechanical properties of Al2O3 ceramics and their degradation due to a deionized water environment under high temperature and high pressure were investigated in terms of the microstructural changes and residual strength characteristics. Sintered Al2O3 bodies containing, 3.3, 10.2, 21.7vol.% of 3mol% Y2O3-doped tetragonal ZrO2 were made using a pressureless sintering process at 1550, 1600, 1650°C, respectively. These ceramic composites were corroded in deionized water under its equilibrium vapor pressure of 1.59MPa at 200°C. The effects of microstructure upon mechanical properties of Al2O3/ZrO2 composites were studied for the specimens treated with, and not treated with water under high temperature and pressure, by residual bending strength measurement, FE-SEM with EDX spectrometry observation and XRD and FE-TEM structural analysis. The mechanical properties were found to be superior when specimens were 21.7vol.% of ZrO2 contents and sintered at 1550°C. It was shown that the strength degradation due to the corrosion by deionized water molecule was suppressed in the case of the specimens with higher contents of ZrO2 particles sintered at lower temperatures. The correlation between bending strength scatter and microstructural defects was discussed.
Alumina FRP is anticipated to be a good thermal insulating support system under cryogenic conditions, because of its outstanding thermal conductivity, and high specific stiffness and strength. In this paper, the internal fatigue damage progress in Alumina FRP tubes subjected to cyclic compressive loading at room temperature and 77K were studied. In order to evaluate the fatigue properties at a macroscopic level, the complex modulus and the damping from the hysteresis of the stress-strain curves, were examined. It was found that the complex modulus at room temperature decreased gradually due to internal fatigue damage during stage II. On the other hand, there was no distinct change in the complex modulus at 77K, with damage occurring just before breaking. The relationship between the fatigue properties at a macroscopic level and the internal fatigue damage was subsequently analyzed. It was found that the density of the matrix cracks influenced the energy loss by the static friction. It is proposed that the energy loss by the static friction is a useful parameter for predicting the fatigue life.
SMC (Sheet Molding Compound) is one of composite materials used in compression moldings. SMC products have smooth surface without any particular technique. This is superior point of SMC products. SMC molding process is rather simple, namely easy to fabricate complex shape products. SMC products has been used in structural parts of transportation vehicles, water tank, bathtub and other variety of products. In the SMC products, material flow during manufacturing process affects fiber distribution of reinforcement. Fiber distribution which lead to scatter of mechanical properties of SMC products. In this study, three point bending tests of SMC products were performed. Short and long glass fibers random mats were used for the reinforcement. The charge patterns and ratio of charge were varied in order to investigate their influence on bending properties. Material flow behavior during molding was different by the charge pattern. It became clear that bending properties were greatly influenced by the fiber orientation occurred during material flow. Furthermore, the bending stress at knee point by the occurrence of initial crack was calculated. It seems that ratio of the knee point stress to maximum stress is one of the useful parameter to evaluate the bending properties of SMC.
For applicability in the field of semiconductor, it is important that the thermal expansion coefficient of heat sink materials approximates to those of semiconductor chip and peripheral materials. In addition, high thermal conductivity also is required. The authors have studied a composite of molybdenum (Mo) and copper (Cu) prepared by two kinds of method, the mixing method (M/CM) and the cladding method (L/CM). The mechanical and thermal properties of these Cu-Mo composites can be controlled by varying the composition ratio. In this paper, mechanical properties of the Cu-Mo composites were investigated. The thermal expansion coefficient α of M/CM increased with increase in copper content. The mean measured values of α in the temperature of about 30°C nearly corresponded with those calculated from Turner's equation and Kerner's equation. The observed anisotropy in α values was maximum for 50 mass% Cu content. The measured values of tensile strength, Young's modulus, Poisson's ratio and Vickers hardness showed a behavior similar the linear law of a mixture rule, but their values were a little smaller than the values calculated by the rule. The elongation and Erichsen value were discontinuous with the rule. The α of L/CM was increased with an increase in Cu content. With the rise in temperature, Mo of the middle layer strongly controlled the thermal expansion. The mean measured values of α in the temperature of about 30°C were smaller than the values calculated by the mixture rule of material dynamics. Comparing L/CM with M/CM, the α values of L/CM were smaller than those of M/CM over the entire range of Cu content.
The wear characteristics of the ductile cast irons were investigated under a dry friction condition at room temperature. The Pin-on-Disk wear test rig was used, where a pin specimen of the ductile cast iron was pressed against a disk of carbon steel for machine structure use. Four kinds of ductile cast iron were prepared; ferritic (FDI), ferritic/pearlitic (FPDI), pearlitic (PDI) and austempered (ADI) ductile cast iron. Two kinds of wear behavior appeared in FDI and FPDI. One type was markedly worn for a short sliding distance, and the other type was mildly worn for a long sliding distance. For the long sliding distance, the wear resistance of the ductile cast iron was increased with the increase of hardness except FDI. The wear resistance of FDI stands comaprison with that of ADI. The remarkably wear registance of FDI is caused by the graphite.