Semi-strand particles (ca. 0.5×2.3×26.4mm) of sugi (Cryptomeria japonica D. Don) were aligned by a laboratory-size mechanical orienter having many reciprocating plates of regular intervals. Wood particles were collected on a paper sheet on the caul placed at the free-fall distance of 0 to 10cm from the reciprocating plates. The pictures of particles on the sheets were fed to an image analyzer equipped with the fast Fourier transform (FFT) function, and transformed to the power spectral patterns after the adjustment of contrast and the removal of window infection. With this procedure, it became possible to evaluate angular distribution of particles quantitatively by the polar coordinate analysis of these patterns.
In addition, the surface pictures of particle boards were printed and recorded on papers by a Xerox, and then the degree of particle alignment was estimated by the similar method.

View full abstract

To investigate the effects of the number of laminations on the mechanical properties of wood laminates, block-shear and bending tests were made on laminated veneer lumbers composed of 5, 10, 15 and 20 plies of sawn Douglas-fir veneers.
A probability theory that “Standard deviation for the mechanical properties of wood laminates with N laminations is proportional to the reciprocal of the square root of N” was applied to the distributions of specific gravity, modulus of elasticity, block-shear and bending strengths. It was found that the theory was applicable to the properties of the wood laminates less than 15 plies, but not applicable to those for 20 plies.

View full abstract

In the processes of drying, preservation and chemical treatment of wood, the permeability is of importance. Generally the heartwood of softwood has poor permeability because of aspirated bordered pit-pair. An attempt is now being made to develop the local steam explosion method to improve it. In this study, the improvement of dryability and its distribution by the local steam explosion was examined. A repeat of explosion and heating methods were investigated as the factors which affect the drying distribution. The results obtained were as follows;
(1) The local steam explosion was better than the steaming for the improvement of drying rate.
(2) The improvement of dryability by the explosion was affected by the repeat of explosion. In case of a heating method by steam and radio frequency, the improvement of dryability progressed from the cross section to the central part of timber because temperature in timber was approximately uniform.
(3) In case of a heating method by steam only, there was a large distribution in temperature and the appearance of the effect of explosion corresponded to it.

View full abstract

Woodceramics is a carbon material sintered from wood or woodymaterial to be used as an industrial material. All the woodceramics has the following characteristics: porous structure, light weight, hard property, heat resistance, anticorrosion and low cost in production. Today, the woodceramics is being studied for practical applications in various fields.
In the present study, the electric conduction of woodceramics was investigated to use it as a porous conductor in low temperature. The temperature dependence of electric resistance of the woodceramics was measured in low temperature and the carrier transport process was discussed. The temperature variation of resistivity was the same as that of semiconductor; it decreases with increasing temperature. This semiconductive behavior may be attributed to the intra-layer interaction of π-electron in graphite microcrystals.

View full abstract

The volume resistivity and electromagnetic shielding properties of “Woodceramics” made of porous carbon material were investigated for the purpose of developing a new shielding material.
The measured values of volume resistivity depended on the burning temperature, and changed from 10¹⁰Ω·cm to 10^-2Ω·cm with increasing burning temperature.
On the shielding tests with the electromagnetic waves from frequencies of 1000kHz to 1GHz, a good electric shielding effect was observed for those burned above 650°C. When the burning temperature was higher than 700°C, some magnetic shielding effect also appeared. Above 900°C, the shielding effet of more than 40dB on was observed for both of the electric and magnetic shielding in wide frequencies.

View full abstract

The glueability and fire resistance of wood-mineral composites were investigated, which were made by introducing inorganic substances into wood (buna) veneer using the water glass (sodium silicate)-boron compound system (double treatment). The composites were also made with boron compounds alone (single treatment), and two-ply plywoods were prepared by bonding with a phenol-resorcinol resin adhesive. Dry gluejoint strength was determined by tensile-shear test, and fire resistance was evaluated by burning test using a microburner.
The glue-joint strength was reduced by both single and double treatments in comparison with the untreated wood, and the values for the double treatment were 44% to 65% of the value for the untreated wood. Besides the bulking of the composites and the deterioration resulting from soaking in an alkaline solution, the lessening of a mechanical anchoring effect was considered to be one of the main reasons for the reduction of glue-joint strength by combination of wood and mineral. There was a negative correlation between glue-joint strength and weight percent gain; the strength reduced linearly with an increase in weight percent gain.
The wood-mineral composites showed a good wettability, but it did not contribute to enhance the bonding strength because there was a tendency for the bonding strength to reduce with an increase in contact angles (cosθ). However, the high values of wood failure indicate that the wood-mineral composites have a sufficiently good glueability for practical use in spite of the reduction of bonding strength.
Plywoods prepared from wood-mineral composites had heat-resisting and flame-resisting effects of the single and double treatments. Particularly, the double treatments with boron trioxide, ammonium borate, and boric acid were confirmed to show an excellent fire-resistance effect.

View full abstract

Lumbers of sapwood of western hemlock (Tsuga heterophylla Sarg.) were impregnated with CCA wood preservatives. The treated lumbers and their ash obtained after burning them were extracted by cold water. The concentrations of copper, chromium, and arsenic in the extracts were determined by using an atomic absorption analyzer. The extracts were given to mice for three months to observe their effect on the living body.
Copper, chromium and arsenic were detected in the extracts from the preserved wood, and chromium and arsenic were detected in the extracts from the ash. The results showed that the concentrations of arsenic and chromium flown out from CCA treated wood or its ash exceeded the criteria specified in the law. However, no significant difference was observed in the weight increase and the serum biochemical properties between the mice that took the water extracts of the treated wood or its ash, and the mice that took the water extracts of the untreated wood or its ash.

View full abstract

Low pressure plasma spraying is well suited for high-temperature corrosion-resistant coatings of gas turbine components. In this coating process, coating adhesion is an important problem, and so surface roughness and cleaning achieved by the transferred arc treatment with negative substrate polarity have to be investigated in order to improve the adhesion. In this paper, an experimental investigation was conducted to clarify the effect of the transferred arc treatment on the bonding strength of sprayed coatings. As a result, it was verified by SEM observations that surface cleaning and surface roughening could be made by the transferred arc treatment in case of IN738LC, SUS304, tungsten and copper. It was also confirmed that grit-blasting before the transferred arc treatment was effective for the uniformity of surface cleaning and roughening, which means to improve the adhesion of sprayed coating. And it was confirmed that the surface roughness achieved by the transferred arc treatment could be evaluated by thermal conduction parameter c·ρ·(T_m-T₀), c; specific heat, ρ; density, T_m; melting point, T₀; initial temperature.

View full abstract

The quenching process of a Japanese sword is simulated by a CAE system “HEARTS” developed by one of the authors. The system is available to consider the coupling effect among metallurgical change due to phase transformation, temperature and inelastic stress/strain.
In the quenching process of the Japanese sword, a special kind of clay is pasted on the surface to control the heat transfer coefficient between metal and water. The dependence of the coefficient on the thickness of clay and also the surface temperature is experimentally evaluated first by using a cylindrical rod of silver. The results show a relatively higher value with thin-pasted clay than that without clay at a high temperature range. The data are then applied to simulate the variation of temperature coupled with the structural change from austenite to martensite and pearlite as well as the variation of stress. It gives an attractive result that the sword is bent two times to the direction opposite to the normal shape due to the complicated time difference between martensitic and pearlitic transformation and thermal contraction. The simulated results of residual stress distributions are compared with the measured data by X-ray diffraction technique.

View full abstract

In order to clarify the mechanism of slurry erosion of polymeric materials, the ductile type eroded volume and erosion rate were analyzed theoretically by considering a motion of an impact particle on polymethylmethacrylate and epoxy resin specimens. In the analysis, it was assumed that the ductile type erosion damage was due to plastic deformation caused by impact of particles, and that the volume of plastic deformation was quite small compared with that of elastic deformation. Therefore, the ductile type erosion damage was analyzed as the extended problem of elastic deformation. The erosion rate for the ductile type erosion damage was computed from the energy consumed during impact of one particle and the volume of elastic deformation of a material which was calculated by Hertz's theory. The calculated results well coincided with the experimental ones.

View full abstract

In order to evaluate the interfacial strength between coating film and substrate, a new equation was proposed by expanding the Kendall's equation to the case where the substrate material was in plastic deformation, and the tensile tests were carried out on steel specimens with thermally-sprayed ceramic film and heat-resistant paint film.
When a specimen with partially delaminated film is under tensile load, the interfacial energy between film and substrate, 2γ₁₂ is expressed by the following equation;
2γ₁₂=[P-bB₂σ_ys{1-(E_p/E_e)}]²/2b²·B₁E₁/B₂E_p(B₁E₁+B₂E_p)
where P is the load at the beginning of delamination, b is the width of specimen, B₁ and B₂ are the thickness of film and substrate, E₁ is the elastic constant of film, E_e, E_p and σ_ys are the elastic constant, plastic constant, and yield strength of substrate, respectively. The above equation is applicable also for the specimen with smooth film without precrack or partially delaminated portion as long as the cracking of film occurs before the delamination. The interfacial energy of ceramic film obtained by experiment reveals a maximum at a certain film thickness and decreases with an increase in film thickness. The interfacial energy of heat-resistant paint reveals almost the same behavior as the ceramic film, but the film thickness at maximum interfacial energy is much smaller than that of ceramic film.

View full abstract

When a load is applied to a structure reinforced by composite materials, the mechanical behavior is different from the one without composites. As the technology in which the surface of structure is reinforced by fiber reinforced plastics (FRP) is used widely to prohibit the reduction of strength caused by cracking, it is necessary to establish the method of fracture simulation applicable to the reinforced structure. Therefore, a computer program of fracture simulation for the cement mortar reinforced by CFRP or AFRP has been developed in this paper. In order to evaluate the computational results, three point bending tests on mortar beams were carried out. The cement mortar beams whose surface is reinforced by FRP sheet are superior in strength to those of cement mortar only. The computational results have a good agreement with the experimental ones. As a result, it is clear that the developed computer program of fracture simulation is very useful for design of structures with composites.

View full abstract

Fiber reinforced composite materials are widely used in many structures. It is well known that composite materials inelastically deform. Although there are some researches on fatigue failure, damage and crack progagation of composite materials, the cyclic inelastic behavior of composite materials subjected to cyclic loading whose direction is different from that of the fiber has not been investigated in detail. In this paper, in order to investigate the cyclic inelastic behavior and the fatigue failure of composite materials, cyclic tension-compression loading under several conditions are carried out using laminated graphite/epoxy tubular specimens. The definition of fatigue failure is also discussed based on the test results. It is found that the CFRP subjected to cyclic loading shows the characteristic cyclic inelastic deformation. Moreover, using the concept of the plastic strain energy density and the concerned defintition of fatigue failure, the relation between the number of fatigue failure and the plastic strain energy density can be expressed by a formula.

View full abstract

In reusing, a bolt is repeatedly tightened and loosened. In this study, the reusing properties of a shank-elongation bolt and a thread-elongation bolt tightened in plastic region were investigated from a viewpoint of fatigue strength. The fatigue tests were carried out on both types of bolts which were subjected to 10-cycle tightening in plastic region. As a result, the 10-cycle tightening had little influence on the fatigue limit of the bolts. However, on the thread-elongation bolt, the microcracks (about 7μm length) appeared at the thread root after repeated tightening in plastic region. Then, the fatigue limit of a cracked bolt was predicted by using the fracture mechanics method. The threshold stress intensity factor range (ΔK_th) of the bolt material was determined from the fatigue crack propagation tests with pre-strained smooth specimens under a high stress ratio. The stress intensity factor range (ΔK) of the thread root was calculated by using the equation for a single edged crack without considering a stress concentration. In this equation, the crack length made of the actual and latent crack length was used as the effective crack length. The fatigue limit predicted from the above mentioned ΔK_th and ΔK agreed approximately with the fatigue limit of a cracked bolt. This prediction clarified that the microcracks of about 7μm length had little influence on the fatigue limit of bolts but that the fatigue limit decreased with increasing the crack length beyond 7μm.

View full abstract

Laser irradiation treatment is a surface hardening technique developed recently. It has been applied to the improvement of fatigue strength and the prevention of fracture of a cracked specimen etc. But few studies on the laser cladding method have been reported so far, though it is not only efficient to improve the fatigue strength but also can form a heat-, corrosion- and wear-resisting alloy layer on materials. In this paper, fatigue tests using two kinds of laser cladding specimens were carried out in order to investigate the cladding effect.
It was found that the fatigue life of the laser cladding specimens increased by 2-5 times as compared with the non-treatment specimen, but it was accompanied with a larger scatter in fatigue life and crack growth rate. The fractography on the fracture surfaces showed the existence of some defects (voids) in the cladding layer. These defects control the fatigue strength and cause the scatter. It was observed that the specimens without large defects were strengthened more notably.

View full abstract

Based on the measurement of crack opening-closing behavior, the effect of temperature on small fatigue crack growth behavior was investigated in three kinds of Ni-base superalloys at the temperature range of 873K to 1123K, in comparison with the physically long crack properties; a polycrystalline alloy (CM247LC-CC), a directionally-solidified alloy (CM247LC-DS) and a single crystal alloy (CMSX-2) at temperatures of 873K, 1023K and 1123K. It was found that the propagation resistance and the fatigue threshold of long crack increased with temperature in all of the materials on an appearance. However, the long crack growth rates at three different temperatures were approximately represented by an unique curve, by taking account of temperature dependences not only of crack closure level but also of elastic modulus. On the other hand, the small fatigue crack growth resistance decreased with temperature even when the crack closure phenomenon was taken into account. In addition, the small fatigue crack exhibited considerably higher growth rate than the long crack at a given effective stress initensity factor range, and grew even at the lower effective stress intensity factor range than the long crack threshold. Based on the results thus obtained and the chemical analysis near crack propagation plane, the factors which lead to the lack of similitude in propagation law between small and long cracks were also discussed.

View full abstract

This paper presents the analytical solutions and their numerical examples for the displacement caused by various loading on the inner surface of circular or elliptic hole in isotropic or anisotropic rock masses, to evaluate the loading tests in the pilot tunnel or borehole. The effects of loading width, Poisson's ratio, the ratio of maximum and minimum orthotropic elastic moduli of rock mass and the inclination angle of loading direction from their principal axes on the displacement was investigated, and then the evaluation procedure of elastic moduli by plate loading test was examined.

View full abstract

Variations of repulsive load and temperature in a ceramic slab subjected to rapid heating on one side under mechanical three-point restriction, were measured to estimate the thermal fracture stress and thermal shock resistance. The thermal stress at fractured point was estimated by comparing the calculated repulsive load with the experimental one. The temperature dependences of thermal conductivity and thermal diffusivity were introduced in the numerical calculations to realize the practical heat conductive condition. Alumina ceramic having high and changeable thermal conductivity with temperature and mica ceramic having low and constant thermal conductivity were used as the specimens. The thermal fracture stress and thermal shock resistance of slab were easily obtained by measuring the repulsive load at restricted point. The temperature dependences of thermal properties had significant effects on the generated repulsive load and thermal stress. The thermal properties of alumina changed with temperature to induce a significant increase in repulsive load and thermal stress. The thermal fracture stress estimated in the experiments showed lower values than the mechanical three-point bending strength.

View full abstract

In recent years, ultrarapid-hardening polymer-modified cement concretes have been used for the repair works of concrete structures. The purpose of this study is to establish the mix design method for the ultrarapid-hardening polymer-modified cement concretes, and to examine its applicability in the field. The ultrarapid-hardening polymer-modified cement concretes for the laboratory test were prepared with various polymer-cement ratios, unit cement contents, water-cement ratios, sand-aggregate ratios and retardercement ratios, and tested for slump, air content, handling time (which was defined as the elapsed time when the slump decreased to about 2cm) and compressive strength.
The conclusions obtained from the test results are summarized as follows:
(1) The slump of the ultrarapid-hardening polymer-modified cement concretes with various mix proportions may generally be expressed by the following equation:
Sl=Ae^{-B(V_ag+V_c)/V_w}
where Sl is the slump of the ultrarapid-hardening polymer-modified cement concretes, V_ag, V_c and V_w are the volumes of aggregate, cement and water per unit volume of the ultrarapid-hardening polymer-modified cement concretes respectively, and A and B are empirical constants.
(2) The compressive strength and handling time of ultrarapid-hardening polymer-modified cement concretes with various mix proportions may generally be expressed as a function of “void-cement ratio (α)”, “retarder-cement ratio (β)” and “polymer-cement ratio (γ)” by the following equations:
F=J/(K^α·L^β·M^γ)
Ht=S·T^α·U^β·V^γ
where F and Ht are the handling time and compressive strength of the ultrarapid-hardening polymer-modified cement concretes respectively, α is the void-cement ratio [α=(V_w+V_a)/V_c], β is the retarder-cement ratio (β=V_r/V_c), γ is the polymer-cement ratio (γ=V_p/V_c), V_a, V_r and V_p are the volumes of air, retarder and polymer per unit volume of the ultrarapid-hardening polymer-modified cement concretes respectively, and J, K, L, M, S, T, U and V are empirical constants.
(3) The mix design system for the ultrarapid-hardening polymer-modified cement concretes is proposed by use of the respective equations for slump, handling time and compressive strength predictions.
(4) The applicability of the mix design system for the ultrarapid-hardening polymer-modified cement concretes is confirmed in the field.

View full abstract