The purpose of this paper is to investigate the moisture recovery of drying set and the force induced when the set wood was prevented from the recovery during moistening in torsion and bending. The specimens used were Buna (Fagus crenata Blume.) and their dimensions were 2(T)×10(L) ×105mm (Radial direction). The results obtained were as follows. (1) The set wood specimen, unloaded after drying under torsional load or bending load, showed a trend to return to its initial configuration during moistening in saturated air. The moisture recovery of set occurred in proportion to the moisture content except for the low moisture content region. (2) When the set wood was prevented from the recovery, a certain force was induced in the set wood specimen. When the force or the stress was defined as the recovery force Fr or the recovery stress, Fr increased rapidly in the initial stage of moistening until the recovery reached 20∼30%, and subsequently increased in proportion to the recovery of set during moistening in saturated air in torsion and bending. (3) During moistening in water, Fr increased to a maximum value and then decreased slightly in torsion. (4) The ratio Frm/P0 (Frm: maximum value of Fr, P0: load applied during drying) was 0.93 in water and 0.71 in saturated air in torsion. (5) There was a linear relationship between Frm and the degree of restraint, that is, the constant deformation imposed on the set specimen during moistening.
The total heat of wetting in water has been determined calorimetrically on extractive-free wood (red pine and beech) as well as on the major components derived from it. The major components used for the present tests were; holocellulose, α-cellulose, hemicelluloses, lignin-carbohydrate complex, and lignin. Especially, acetyl glucomannan and acetyl glucuronoxylan were used in order to get informations on the native state of hemicellulose in wood. The results obtained are as follows: (1) The total heat of wetting of extractive-free red pine and beech wood in water are 20.49 cal/g and 19.67cal/g, respectively. (2) The total heat of wetting of α-cellulose is almost the same as those of the wood. (3) Of the materials tested, hemicelluloses had the highest total heat of wetting; acetyl glucomannan: 26.80cal/g, arabinoglucuronoxylan: 30.18cal/g and acetyl glucuronoxylan: 24.42cal/g. (4) The total heat of wetting of lignin is markedly affected by the method used for the preparation of samples. The values for lignin such as milled wood lignin and alcohol lignin, are lower than those of the other major components. The value for Klason lignin is somewhat larger than those for lignin mentioned above. (5) From these results it is possible to estimate the relative contributions of its three major components to the total heat of wetting of wood. The proportion of contributions of the three components to the total heat of wetting of extractive-free red pine wood is 0.43 for cellulose, 0.38 for hemicelluloses and 0.19 for lignin. Also the values for beech wood are 0.36, 0.48 and 0.16, respectively.
In this study, we investigated some mechanical properties during growth of Japanese red pine (Pinus densiflora Sieb. et Zucc.) seedlings in air-dry. The results obtained are summarized as follows. (1) The values of tensile strength for pine seedlings having different growing duration varied depending upon the growing duration, and the variation could be divided into two steps on the basis of the degree of growth of pine seedlings; in the early step, pine seedlings contained only primary xylem, and, in the late step, pine seedlings contained secondary xylem. (2) The fracture surface by tension test differed depending upon the degree of growth for seedlings; at the early stage of growth, the fracture surface showed a simple fracture type at the cell wall in primary xylem, separation of intercellular layer, deformation in cell shape and etc., and, at the late stage of growth, the fracture surface showed a complex fracture type at each layer of cell wall in secondary xylem but did not show any clear deformation of cell shape and separation of intercellular layer. (3) Tensile relaxation tests were carried out on three pine seedlings having different growing duration. The difference in relaxation spectra among three seedlings could be shown by the position of maximum in the short-time range, and the position of the maximum seemed to be related to the growing of xylem tissue within seedlings.
This paper presents a modified hole-drilling technique for measuring residual stresses in tree trunk. The primary advantage of the modification is that it can be applied to a standing tree. Two holes drilled above and below the strain measuring point release completely the strain in the longitudinal direction of a trunk. On the other hand, two holes drilled on both sides of the measuring point bring in a relaxation of the strain in the tangential direction of a trunk but, at the same time, create a new strain due to the diagonal stresses at above and below the holes. The occurance of such new stresses can be avoided by drilling a number of holes at above and below the measuring point. The strain in this study was determined by a wire-strain-gage sticked with α-cyanoacrylate instant-curing adhesive.
The stress distributions within the cell wall subjected to a tensile force in the tangential direction were discussed on the basis of a Finite Element Solution for the late-wood cell model. The values of Young's modules and Poisson's ratio of the cell obtained from this analysis were also compared with the experimental ones reported by Boutelje on the samples consisting of isolated latewood from Swedish pine-wood. The model structure was constructed by considering the geometrical parameters representing the anatomical features of Hinoki-wood and the distribution of chemical constituents in the cell wall layer. Using the elastic constants and the volume fractions of framework and matrix components given by Mark and adopting two methods of analysis for estimating the elastic parameters of a laminated system, the material constants of each cell wall layer were calculated. Furthermore, the other values for the material constants, which are obtained as the intersection of Young's modulus-specific gravity curves in radial and tangential directions, were used to compare the mechanical behaviour of the model mentioned above with that of the model without considering the fine structures in the cell wall. The results were as follows; (1) The maximum stress occurred in the lumen side of cell wall, and the stresses in S1, which are considered to be the initiation point of failure by Mark, and the stresses in S2 were considerably low. These results were different from those on the isotropic material with a circular hole. (2) It was proposed that a large amount of intrawall failure, which is the separation of two adjacent tracheids, might result from the failure in M+P or S3. The failure in M+P occurs when the strength of matrix is near or less than 600kg/cm2 and the failure in S3 occurs when the tensile strength of fibril is near or less than 1.1×104kg/cm2. The former is more possible. (3) Young's modulus of late-wood cell was calculated with the consideration of the distribution of framework and matrix (Table IV) and a good agreement between the calculated value and the experimental one was obtained.
In low frequency vibratory cutting of wood, the effect of elastic recovery of chip deformation during cutting on cutting force was clarified by means of a high-speed motion analysis technique. In addition, the changes in shearing angle and shearing strain were investigated. At a cutting speed lower than the critical cutting speed, the actual cutting duration was longer than the theoretical one, because of the elastic recovery of chip deformation during cutting. The mean effective cutting force excluding the force due to the elastic recovery of chip deformation well coincided with the calculated value of mean cutting force (based on the concept of critical cutting speed). In general, however, the cutting force measured in vibratory cutting is not the mean effective cutting force, but the mean actual cutting force including the force due to the elastic recovery of chip deformation. Hence, the mean actual cutting force in the vibratory cutting is greater than the calculated value of mean cutting force. The cutting ratio and shearing angle in the vibratory cutting were greater than those in the conventional one (cutting without vibration). On the contrary, the shearing strain in the former was slightly smaller than in the latter. This means that the plastic deformation of chip in the vibratory cutting is smaller than that in the conventional one.
Continued from the previous papers, the mechanical characteristics of plywood shallow shells with roller supported edges are investigated. Especially, “the influence of the restraint of sliding along the edges or expansion of the edges”, which is closely related to“the effect of the edge beams”, is analysed. Since it is very difficult to solve the fundamental equations (1) and (2) precisely for the geometrically nonlinear analysis of the orthotropic shallow shells, the authors attempted to get the numerical solution of them, as shown in the previous paper, by applying the finite difference method with the aid of the large scale digital computers (FACOM 230-60 and -75, Kyoto Univ.), and succeeded in solving them with good accuracy. To compare the behavior of the orthotropic plywood shells with that of isotropic shells, the isotropic elastic moduli which are equivalent to those of the orthotropic shells were derived (Eqs. (3)∼(19)). The influence of the restraint of sliding on the deformation rigidity of the shells is greater in the case of Ortho. 45°(the cross laminated shells With face grain inclined 45°to x-edge) than in the case of Ortho. 0°or 90°(Table I, Fig. 1). When the sliding along the edges is restrained, the rigidity of Ortho. 45°is nearly equal or a little higher than that of the isotropic shells, and much higher than that of Ortho. 0°or 90°. The rigidity of the parallel laminated cylindrical shells is lower than that of the cross laminated shells, and the parallel laminated shells are destroyed by the tensile membrane stress under a considerably low load (Table I, Figs. 1 and 2). In the case of the rectangular shells, the more the ratio of the side lengths, the less the influence of the edge restraint of the Ortho. 45°shells becomes (Table III). And the optimum face grain angle in which the rigidity is the highest changes gradually from 45°to 0°with an increase of the ratio of the side lengths (Table III). The maximum deflection under a central concentrated load is about 3 times larger than that under the uniformly distributed same load, and in the case of Ortho. 45°and the isotropic cylindrical shells, the ratio is much larger. However, the defection of Ortho. 45°shells under a central concentrated load is about a half of that of Ortho. 0°or 90°(Tables IV and V).
This paper concerns with evaluation of cleavage fracture toughness of a wood-epoxy resin bond system using a double cantilever type specimen (Fig. 1). Wood has, generally, a non-uniform distribution of elastic constants even in one block. With consideration for this, a recommendable formula to determine cleavage fracture toughness gIC on a double cantilever type specimen was derived as follows: gIC=Pcδc/2th·3(α+1.4)2+5.4/(α+1.4)3+5.4α(for softwoods), orPcδc/2th·3(α+1.4)2+4/(α+1.4)3+4α(for hardwoods), where, Pc is the fracture load, δc is the opening of loading Points at the beginning of fracture, t is the thickness of specimen, h is the height of an adherend, α=a/h and a is the length of unbonded part (or crack) of a specimen. As these formulae include the observed deflection of the cantilevers (opening δc), the variation of elastic constants existing among adherends is automatically compensated and gIC obtained by these formulae has less variation than that by ordinary methods (Table I). The factors affecting on cleavage fracture toughness gIC obtained by these formulae for a wood-epoxy resin bond system were discussed experimentally. The results are as follows: (1) The thicker the glue-line is, the higher the cleavage fracture toughness is (Fig. 6). (2) The glue-line having a suitable flexibility gives higher cleavage fracture toughness (Fig. 5). (3) The cleavage fracture toughness of a specimen having a thicker and flexible glue-line has higher dependence on test speed (Fig. 7).
In order to improve the properties of wood, the vapor phase reaction of 2, 4-tolylenediisocyanate (TDI) with heartwood of Hinoki (Chamaecyparis obtuse Sieb. et Zucc.) in nitrogen atmosphere was investigated. As the results, the formation of urethane in wood was identified in its infrared spectrum. The nitrogen content in the treated sample reached almost a constant value after 2 hours of reaction, and the maximum nitrogen content in non-swelled wood and pre-swelled wood with pyridine was about 1.2% and 3.5%, respectively. It was recognized that the reaction of TDI took place in the amorphous region near the surface of wood and 85∼95% of the urethane formed in wood was apparently combined with wood components. The hygroscopic and swelling properties of treated wood decreased with increasing nitrogen content, and in the equilibrium state at 20°C and 93% relative humidity the moisture-excluding efficiency and anti-swelling efficiency of wood containing 5.4% nitrogen were 45% and 50%, respectively. Also, the compressive strength and the modulus of elasticity in bending increased with increasing nitrogen content, and the loss of toughness was not recognized.
The temperature dependence of viscoelastic properties of wood (Makanba)-polymethyl methacrylate (PMMA) composites prepared by various methods was investigated to elucidate the interaction between wood and polymer. The following results were obtained by using a vibrating reed method over the temperature range of 30∼200°C. (1) The dispersion due to the micro-Brownian movement of PMMA formed in the cell wall of wood appears at a higher temperature than that of PMMA deposited on the permanent internal surface of wood. (2) The wood-polymer composites prepared by polymerizing methyl methacrylate (MMA) in the cell wall of wood show a new dispersion above 150°C due to wood itself. (3) A new dispersion appears around 120°C in the composites with MMA polymerized in decrystallized as well as originally amorphous regions of wood, but it does not appear in the composites prepared by the polymerization of MMA only in amorphous regions. (4) When compared with the result of Handa et al., the above results 1 and 3 show that the form or the state of existence (coagulation) of polymer as well as the location of polymer within wood significantly affects the viscoelastic feature of wood-polymer composites.
Mechanical properties of paper are closely related to the geometric factors of fiber assemblages such as the number of fibers, fiber length distribution, fiber weight distribution, etc., which describe the network structure of paper as well as the single fiber properties. In the present paper, the dependence of in-plane elastic moduli of handsheets made from softwood and hardwood bleached kraft pulps on the basis weight which is associated with the number of fibers per unit area, Nf, has been studied. Two independent in-plane elastic moduli, Young's modulus Exy and Poisson's ratio νxy were determined by use of a biaxial tensile tester of Bistron type that was modified for testing paper. The results obtained are summarized as follows; (1) The dependence of Young's modulus, Exy on the basis weight is caused by the associative effect of thickness T and Exy (defined by Exy T), both of which depend on the basis weight. (2) Since the Young's modulus of paper varies with thickness which can not be defined explicitly, the Young's modulus seems to be unsuitable as a mechanical constant. (3) The newly defined Exy is a linear function of the basis weight or Nf within the limit of this experiment but nonlinearity may appear for weights less than 20g/m2. The gradient in the linear region of Exy-Nf relation for the softwood pulp is much larger than that for the hardwood pulp and this quantity may be used as a new characteristic value of paper. (4) The Poisson's ratio for the hardwood pulp is slightly larger than that for the softwood pulp but both of them do not markedly change with the basis weight or Nf.
The physical and chemical changes of polyethylene films exposed to oxygen corona and ozone were studied at various voltages and periods of treatment. Besides ethanolic sodium hydroxide solution, sulfur tetrafluoride was used to determine carboxyl groups in the presence of carbonyl groups in oxidized films. The results obtained are as follows. Corona treatment produced ethanol-soluble fraction on the surface, while ozone exposure caused no remarkable surface change. The quantity of ethanol-soluble fraction remarkably increased with voltage and time of corona treatment, and reached to 9.3% in weight, equivalent to 1.7μm in thickness for the 15kv-120min corona treated film. SF4 method was a rapid method for determining ketone and acid contents, and caused no reaction product loss in corona treated films in the analysis process. At approximately equal carbonyl contents, the acid contents in corona treated films were always higher than those in ozone exposed films. For example, 69% of carbonyl groups was ketone and 31% was acid in the 10kv-90min corona treated film, while the proportion was 74% ketone and 26% acid in the 13kv-120min ozone exposed film.