Previously, we reported that the sound radiated in an ordinary woodworking shop sometimes creates a non-uniform field of sound pressure. For example, the sound radiated from a woodworking machine such as a single surface planer has low frequency noise components, and produce an interference pattern in the test region. The interference between the direct sound wave from the source and the reflected sound wave from the boundary wall causes errors in evaluating the sound power of a machine considered. To eliminate this, a new measuring space having a volume of 27m3 and a surface area of 54m2 was constructed with two types of cloth curtains. This space is thought to be small for the measurement of radiated sound pressure, but can be constructed easily and cheaply. Although several wall conditions of boundary curtains were tried using an isotropic sound source fed with random noise, it was not possible to get an effective result about the distribution of sound pressure levels in this new space. For the router machine noise, however, the distribution of sound pressure level inside of this space was rather uniform than in the original space. Besides, no interference pattern was noticed in this new space tested.
In the wood cutting process, it is important to obtain the actual stress distribution on the rake face during cutting and to investigate the changes in stress distribution and frictional coefficient with workpiece condition. In order to obtain quantitative information on them, the basic orthogonal cutting tests were performed using the same conventional and composite tools as used in the previous reports3)4). The results obtained are summarized as follows: (1) The distributions of the frictional stress (τ) and normal stress (σ) on the rake face can be expressed by Eq. (7). (2) On the basis of the experimental results (Eqs. (1), (3) and (5), Figs. 4 and 5), the ratio of the cutting force on the tool face near the edge to the total force can be calculated from Eq. (8), and the values are shown in Table II. (3) The frictional coefficients (μ2) on the rake face can be expressed by Eq. (9). On the rake face, μ2 can be considered to be constant, and the values of μ2 are shown in comparison with the other frictional coefficients, in Table III.
Nonmetals, especially wooden materials are considered suitable for processing by CO2 laser. In the present study, cutting experiments were carried out on kraft paper and filter paper made of cellulose fiber which is one of the main elements of wood. The experimental factors were the laser power, defocusing distance, flow rate of assistant gas and feed speed. The efficiency of CO2 laser cutting was evaluated on the basis of external appearance of sections and measurements of kerf width. The results are summarized as follows; (1) It was observed that the pyrolysis-like residue adhered on the both cut edges as solid droplets. The color and quantity of the solid droplets varied largely with the condition of laser irradiation. (2) The kerf width varied largely with the above factors as illustrated in Figs. 6-10. (3) The minimum power needed to cut filter or kraft paper was about 2.5W when the feed speed was 2m/min. (4) The laser energy required to destroy a unit volume of filter paper was about 0.23J/mm3. The calculation showed that the net energy expended for the paper cutting was only 0.2-8.7% of the total irradiated energy of CO2 laser.
The present paper deals with the relation between maximum compressive load and witdth of wood-stud walls, and with the estimation of the maximum loads. Test walls were made of S-P-F lumber (204 D) and structural plywood of 7.5mm thick (Fig. 1). Before compression tests the walls were bent by small loads and the load-deflection curves were obtained. After the bending test the walls were compressed under centroidal loading until compressive failures occurred in the walls (Fig. 2). The results obtained are as follows: (1) Flexural rigidities of the walls were nearly constant for all the walls with various widths. Thus, plywood contributes little to the flexural rigidity of the walls (Fig. 3). (2) Three different types of failure occurred in the walls: the breaking of plywood (Fig. 4), the delamination of plywood (Fig. 5), and the breaking at a knot in studs (Fig. 6). (3) There were two levels in maximum compressive loads: the higher level corresponding nearly to the delamination of plywood and the lower one to the breaking of plywood (Table II). (4) Mechanical models of the walls in compression were presented (Fig. 7), and the equation for the estimating the maximum compressive loads was derived from the models (Eq. (16)). (5) It was proved that the estimation by the above equation gave a fairly good agreement with the experimental (Fig. 8).
Wood screws were withdrawn from side and end grains of solid red lauan to investigate the effects of crests of screws and pilot holes on driving torque and withdrawal resistance. After the withdrawal tests the test specimens were tangentially sliced into thin veneer of 0.23mm thickness to measure the area of distorted wood fiber (Fig. 2). Crests of brass screws were ground off to prepare five different level heights of crest (Table II and Fig. 1), and driving torque and withdrawal resistance were measured. It was found that even a slight crest of a screw brought in a small increase in driving torque and a large increase in withdrawal resistance. (Figs. 3 and 4). Pilot holes of various diameters were predrilled (Table III). With decreasing gradually the diameter ratio of a pilot hole in side grain from fifty percent, the driving torque increased but the withdrawal resistance decreased. Therefore, the diameter of a pilot hole should be five-tenths the outer diameter of a screw. Similarly, the most effective one was a pilot hole of which diameter was seven-tenths that of a screw when driven into end grain (Figs. 6 and 7). It should be noted that the withdrawal resistance decreased remarkably if the diameter was larger than that of the inner diameter of a screw. In the case of withdrawing a screw from side grain without a pilot hole, the outline of the area where fiber was distorted resembled an ellipse of which major axis was along L-axis of wood and minor one along R-axis (Fig. 8).
Mechanical properties of timber joints with metal plate connectors have been tested so far mainly by static loading. Works on fatigue properties of the joints subjected to cyclic loading, which are needed for determining safe design loads and for predicting the safe service life of the joints, are scarce and the effect of moisture cycling on the fatigue properties of the joints has not been clarified at all. Rotating bending fatigue tests were therefore carried out on the timber joints of air-dried, water-saturated or moisture-cycled specimens. The effects of moisture content and moisture cycling on the fatigue properties of the joints were discussed with considering the failure modes of the joints and the strain distribution in the metal plate connector. The results obtained are as follows; (1) The relationship between the applied bending moment and the cycles to failure was expressed as a single continuous curve. The fatigue limit of air-dried and water-saturated specimens are 9% and 11% of the static strength, respectively. (2) The failure modes of joints in fatigue tests could be divided into three categories. All teeth were pulled out of the wood block at relatively high moment levels, but they were sheared off at the root of teeth at relatively low moment levels. At intermediate moment levels, some were pulled out and the rest were sheared off. (3) The fatigue strength of the joints was much influenced by the pre-treatments of moisture cycling, while the static strength was rather insensitive to the treatments.
A simple statistical analysis of elastic modulus field of paper sheet has been made on the basis of the staler stress-strain equation proposed by C.T.J. Dodson7)8). Paper sheet was assumed to be an inhomogeneous body whose elastic state at a point x is characterized by the equation σ(x)=Kl(x)ε(x), where σ is the isotropic (two dimensional) stress, ε the areal dilatation and Kl the local elastic modulus for areal dilatation. Under the condition of statistical homogeneity9) of the elastic modulus field, the effective modulus (overall modulus10)11)) K, defined as the ratio of mean stress to mean strain, was shown to be equal to the reciprocal of the mean elastic compliance as the zero-th order approximation. By assuming that the local modulus Kl(x) is proportional to the mass density at a point x, the effective modulus K can be expressed as K=MH2/H+1=Mf(H), where M is the proportional constant and H the mean number of overlapping fibers12) which corresponds to the basis weight. The function f(H) is a nonlinear function of H, but in the range of sufficiently high H(>2) it shows almost linear dependence on H, and the gradient of f(H) is approximately unity. The areal dilatation modulus K and other in-plane moduli were determined as a function of the basis weight by use of a biaxial tensile tester for the sheet made from the bleached kraft pulp (spruce) beaten in various degrees. The results showed that with increasing the revolution number of PFI mill the gradient of the linear regression equation of K against the basis weight increases, while the corresponding intercept on the basis weight axis, which is caused by the sheet inhomogeneity, does not vary markedly. The specific elastic modulus defined as the gradient of the regression line, which can be regarded as the mean local modulus per unit basis weight, was proposed as a new characteristic quantity of paper elasticity, and the effect of beating on in-plane specific moduli was also discussed.
This paper is concerned with the prediction of transverse Poisson's ratio for softwoods on the basis of their laminated porous structures. The arrangement of cell cavities which appear in the cross section of wood was simplified by two kinds of porous models with regularly arranged circular holes, corresponding to the early-and latewood portions, respectively. Effective Young's moduli, E*, and Poisson's ratios ν*, of these models made of an isotropic material, for which Young's modulus is E0 and Poisson's ratio, ν0, were calculated by using the finite element analysis. The results are expressed in the following equations. E*=aE0 ν*=b+aν0 where a is the normalized Young's modulus specified by volume fraction of pores and arrangements, and b represents a part of Poisson's ratio depending only on porous structures. For the purpose of estimating Poisson's ratio of woods, equations were derived from these simplified models. The results were compared with the experimental one reported in literature. They agreed each other qualitatively well.
In this study, the water potential (WP), stem strain and growth strain on surface in young Japanese black pine (Pinus Thunbergii Parl.) were measured at intervals during a single day in various seasons in order to investigate the evolution process of growth stress in young Japanese black pine. The results obtained are summarized as follows. (1) From the relationship between the changes of xylem contained in the stem and the WP during a single day in various seasons, the WP of all trees was found to increase steadily for about 4 hours after sunrise from the minimum value at dawn, and become constant at that level until about 2 hours before sunset, and then decrease steadily to the minimum of the following day. The stem strain reached a minimum value at the time when the WP remained high in its value, and then increased steadily toward the maximum value of the following day, corresponding to the decrease of WP. It was suggested that the stem strain in xylem was about 15% of the stem with bark. (2) The change in growth strain on the surface during a single day could be shown by a curve with a maximum for all seasons. The growth strain on the surface in all trees reached a maximum after 2 to 4 hours after sunrise, and then decreased gradually to reach a minimum near sunset. Those results on the growth strain on the surface seems to suggest that the change in growth strain on the surface during a single day is connected with the change in WP. (3) Though the trees examined at various seasons contained different conditions of cell wall, the change of the growth strain on surface during the whole day was almost the same for all trees. The seasonal change of growth strain on surface was observed in the distribution of the growth strain on surface at a certain height of tree. It appeared clearly on top of trees, but not so at breast height.
In order to improve the mechanical and physical properties of fiberboard, the graft copolymerization of methyl methacrylate (MMA) onto wood fiber (Lauan Asplund pulp) was investigated, and the effects of the grafting on the dimensional stability and strength properties of the fiberboard prepared from Asplund pulp-MMA graft copolymer were examined. The results are as follows: (1) It was found that H2O2-Fe(II) redox initiation system was very effective for the graft copolymerization and MMA was grafted onto the inner part of wood fiber, mainly on carbohydrate in the early stage of the reaction, and on lignin in later. The molecular weight (Mn) of poly (methyl methacrylate) branches of graft copolymer was in the range of 6.5×105∼9.5×105 and somewhat higher than that of homo polymer. (2) The dimensional change of the fiberboard made from Asplund pulp-MMA graft copolymer in humidity or watersoak tests decreased with increasing degree of grafting, and the thickness swelling of the grafted board (PMMA content: 15.5%) was less than 8% at 40°C and 90% relative humidity, or less than 15% in watersoak for 24 hours. The decrease of dimensional change was considered as resulted from the dimensional stability of each wood fiber much more than the increase of bonding strength between the grafted wood fiber. (3) The modulus of rupture and the modulus of elasticity of the fiberboard made from Asplund pulp-MMA graft copolymer in bending increased with increasing degree of grafting, but the effect by MMA grafting was not so much as that by urea- or phenol-formaldehyde resin.
In order to prepare a composite material having dimensional stability and hygroscopicity similar to wood itself, the liquid phase reaction of ethylene glycol (EG) and 4, 4'-diphenylmethane diisocyanate (MDI) with heartwood of Hinoki (Chamaecyparis obtusa SIEB. et ZUCC.) was investigated. The hygroscopicity and dimensional stability were evaluated by the amounts of hydroxyl group and combined urethane which were introduced into wood. In the reaction of EG and MDI in wood, the nitrogen content and the reactant combined with wood components increased with an increase in mole fraction of MDI in MDI-EG system, but the degree of crystallinity decreased. This shows that the reaction took place somewhat in the crystalline region. The formation of urethane in the treated wood was also identified. The anti-swelling efficiency (ASE) and moisture-excluding efficiency (MEE) showed the maximum values at about 0.5 of MDI mole fraction in any concentration of solutions. ASE and MEE were 69.3% and 59.4% at 15% concentration, respectively. ASE was directly proportional to the MEE and bulking. When the free EG was removed from the treated wood, ASE and MEE decreased remarkably, and MEE tended to decrease with an increase in ASE. It suggests that free EG considerably affects ASE, MEE and bulking.
In order to prepare a wood-polymer composites having dimensional stability and hygroscopicity similar to wood itself, the radical copolymerization of a hydrophilic monomer, 2-hydroxyethyl methacrylate (HEMA), with a hydrophobic monomer, methyl methacrylate(MMA), in heartwood of Hinoki (Chamaecyparis obtusa SIEB. et ZUCC.) was investigated. The hygroscopicity and dimensional stability were evaluated by the mole fraction of HEMA in MMA-HEMA system, the moisture content in the wood part and the polymer content in the wood-polymer composite. The results obtained are as follows: (1) The hygroscopicity of the wood-polymer composite is improved with increasing mole fraction of HEMA in MMA-HEMA system. At 1.0 of HEMA mole fraction, the moisture-excluding efficiency in the equilibrium state at 20°C and 93% or 75% relative humidity is about 10%. (2) The anti-swelling efficiency decreases linearly with an increase in mole fraction of HEMA, and above 0.3 of HEMA mole fraction, the dimensional stability cannot be attained. The anti-swelling efficiency is directly proportional to the moisture-excluding efficiency. The dominating factor for dimensional stabilization due to the impregnation of MMA-HEMA copolymer in wood is the bulking effect and reduction of hygroscopic sites in wood components. (3) The moisture-excluding efficiency is nearly proportional to polymer content. The anti-swelling efficiency changes with polymer content and exhibits a remarkable increase at about 100% of polymer content.
Polysaccharide components dissolved into chlorite Liquor under various treating conditions in the process of delignification with acidic sodiumn chlorite at 70°C were investigated for Akamatsu wood meal. The determination of lignin contents in the residual meal treated with sodium chlorite showed that the acid soluble portion of the remaining lignin was maximum at near 50% delignification. The polysaccharide components were isolated as precipitates from the solution by adding ethanol, and their carbohydrate compositions and contents were analyzed and determined by means of gas liquid chromatography after changing them into alditol acetates. The results revealed that the amounts of galactose and arabinose residues were rich in the polysaccharide fractions isolated from the solution at the early stage of delignification and furthermore the residues of mannose, glucose and xylose increased with progress of the delignification, while those of galactose and arabinose decreased.