Low molecular-weight (Mn=369) phenolic impregnating resin and high molecular-weight (Mn=1143) bonding phenolic resin were mixed and sprayed on Japanese cedar (Cryptomeria japonica) semi-strand (22.8mm×2.6mm×0.6mm) particles, and then 10mm thick single-layer particleboards (PBs) (SG=0.7) were produced. The effects of moisture content (MC) on bending properties and creep behavior of the PBs were investigated. The maximum value of modulus of rupture (MOR) was achieved at 7 to 9 percent MC, and at 19 to 28 percent MC the PBs retained 60 to 70 percent of the MOR value in the oven dry condition. The modulus of elasticity of PBs decreased with increasing MC. The creep compliance of PBs increased with increasing MC and decreased with increasing total resin content. The creep compliance after 48 hours under bending load at 7 to 9 percent MC was about 1.8 times the value in the dry condition.
Wood-based boards were manufactured under heat and pressure using softwood powder of #100 in size as furnish bonded by a novolac type of phenol-formaldehyde powder resin. The bending properties, internal bond strength and dimensional stability were determined to evaluate the effects of the specific gravity (SG), resin content (RC) of the board and platen temperature at pressing. The results obtained were summarized as follows: (1) After a rapid temperature rise during pressing, the core temperature of the mat showed the plateau stage around 140°C for all the press conditions in this experiment ranged from 160°C to 220°C. (2) The bending properties, modulus of rupture and modulus of elasticity increased linearly with increasing resin content up to about 20% and leveled off above 30% RC. A linear relationship was found between bending properties and SG of the board. (3) It was found that the boards made from the wood powder can have higher internal bond strength compared with that of particleboards. (4) The boards with 15% resin content or more showed a fairly good dimensional stability against the water soaking treatment.
The mechanical properties in bending and in compression of full size cylindrically laminated veneer lumbers (C-LVL) made by spiral winding method were tested. The C-LVLs have about 300mm outer diameter, 25mm wall thickness, and 3600mm length. The results obtained are as follows: 1) The modulus of elasticity (MOE) of C-LVL depends on the species of veneer raw materials, that is, MOE of C-LVL was the same as the MOE of solid lumber of the same species. 2) The number of plies affects the modulus of rupture (MOR) and the mode of failure of C-LVL. It has no effect on MOE. 3) The interlocked grain structure of C-LVL with ±10 degree in alternate layers effectively prevented decrease in MOE of C-LVL compared to that of solid lumber. 4) There was little effect on MOE or MOR by the addition of radial filler in C-LVL with 10 plies or more. 5) The properties in compression is about equal to those in bending. In the compression test, buckling failure was observed. These results show that C-LVL is suitable for structural uses, especially as building and construction posts.
The objective of this research was to investigate the characteristics of KIC for wood species with reference to the infomation of wood crack induced by nailing. The wood crack characteristics by nailing were investigated using barium soaking method. According to the relationship between specific gravity and maximum crack length (Lm), three wood species groups were employed; Group C1: easy to crack such as Douglas-fir, Hemlock, and Lawson sypress, Group C3: hard to crack such as Radiata pine, Agathis, Japanese beech, Group C2: intermediate between C1 and C3. The same wood group concept was applicable to describe the characteristic of KIC. The relationship between specific gravity and KIC could not be described by one regression curve, but within each wood group, specific gravity had a good correlation with KIC. Also, the relationship between KIC and Lm had a good correlation within each wood group.
Logs of Sugi (Cryptomeria japonica D. Don) were treated by a smoke-heating system with increased far-infrared radiation. Logs were smoke-heated for about 35 hours at a temperature inside the logs of more than 80°C. No damage was found in the logs by the treatment. After the treatment, the changes of some wood qualities (bending strength, shrinkage, swelling, degree of crystallinity, amounts of chemical components) were examined. The modulus of elasticity (MOE) in bending of sapwood increased about 13% by the treatment, whereas in heartwood almost no difference in bending strength between the smoke-heated and control logs was found. The degree of crystallinity increased about 8% in sapwood, almost corresponding to the increase ratio of MOE. The smoke-heated logs increased both their shrinkage and swelling in heartwood, but decreased both of them in sapwood. The results obtained here suggested almost no difference in wood qualities between the smoke-heated and control logs. This fact indicates that smoke-heating of logs did not causes any thermal deterioration in wood.
Moisture gradient during drying of Sugi lumber with core brings about large tensile strain in the tangential direction. Since this strain could be reduced with smaller moisture gradient in the radial direction, Sugi disk pieces with core were pierced along the fiber direction (diameter: 100mm, thickness: 20mm, diameter of hollow: 40mm) and dried under the condition of 80°C and 40%RH. The relationship between the moisture gradient and the strain was studied. The results obtained were as follows: (1) The disk pierced along the fiber direction could be dried rapidly and without split because of large moisture gradient between the center and the outside or surface of hollow. But in the case of sealed hollow disk specimen, the drying time became long and large split occurred. (2) Shrinkage in the hollow diameter was greater than that in the overall diameter of the disk and still greater than the tangential shrinkage measured according to the Japanese Industrial Standards. (3) The tangential strain at the hollow surface remained compressive in the final stage because hoop stress acted on the disk. (4) The tensile strain on the outside was reduced by hoop stress.
It is well known that the first moisture increase of wood under constant bending load causes an increase in deflection, but the second and later adsorption of moisture tends to produce some recovery of deformation. This suggests that creep during adsorption depends upon the loading history of wood during past desorption/adsorption. So, to clarify the effect of past loading history on recovery and creep of wood during adsorption, two types (D-set and A-set) of small bending-set wood specimens (0.3cm by 1.0cm by 12cm: Tx Lx R) were prepared from air-dried Hinoki (Chamaecyparis obtusa Endl.) and Buna (Fagus crenata Bl.). D-set specimens were subjected to desorption (MC 16%→8%) under constant loads. A-set specimens were subjected to adsorption (MC 8%→16%) under constant loads and then to the following desorption (MC 16%→8%) after unloading at about 16% MC. Then, the recovery of deflection and the creep during adsorption (from about 8% MC to about 25% ) were measured on these two types of bending set wood. The recovery of D-set specimens during adsorption was significant at MCs below about 16% (the upper limit of MC interval where bending load was applied), but was not so significant at MCs above this value. On the other hand, the recovery of A-set specimens was not so significant at MCs below about 16%, but was significant at MCs above this value. After making compensation for the effect of recovery of set, the resultant creep curves during adsorption for the two types of set specimens were similar to those for the control specimens with no loading-history. From these results, it is concluded that the experimental creep curve of wood subjected to bending set is the resultant of the superposition of recovery of set and mechano-sorptive creep deflection of wood with no loading-history.
The effect of the specific surface area of added ρ-alumina on hardening of α-alumina slurry was investigated by the measurement of the penetration resistance of α-alumina slurry. ρ-alumina was made by the heating of Al(OH)3 from 200 to 700°C in vacuum. The penetration resistance increased with increasing holding time. The holding time required to reach the same penetration resistance decreased with increasing specific surface area of ρ-alumina, when it contained neither Al(OH)3 nor η-alumina. In the case where Al(OH)3 remained in ρ-alumina (heat treated below 300°C), the hardening of the slurry proceeded more rapidly than that of the slurry without Al(OH)3, exhibiting about the same specific surface area. When η-alumina was formed (heat treated above 600°C), then the hardening of the slurry proceeded more slowly than that of the slurry without η-alumina.
This paper describes a work which is a part of systematic study for understanding the mechanism of particleboard dimensional stabilization by steam pretreatment. Particular interest was centered on an in-plane swelling stress of wood particles which causes the breakage of adhesive bond between particles. The effects of steam temperature on the following factors were investigated by the use of uncompressed wood blocks: swelling stress by water absorption, hygroscopic swelling, and Young's modulus in the tangential direction. The swelling stress was found to decrease with increasing steam temperature and became one fifth of the control when steamed at 220°C for 10 minutes. The hygroscopic swelling, the maximum swelling, and the Young's modulus also showed a trend of decreasing with increasing steam temperature. Therefore, the elastic model which describes swelling stresses by elastic strain and Young's moduli was applied. The calculated change of swelling stress by steaming was found to agree well with the observed one, which suggests that the decrease of swelling stress can be derived from the synergistic effect of decrease in both swelling and elasticity.
Waves propagating in fiber-reinforced composite materials exhibit dispersion and attenuation due to wave scattering by fibers. In the present study, the overall characteristics of ultrasonic transverse waves propagating in a composite material with fiber-matrix interface debonding are examined via scattering analysis. The study is concerned with shear waves polarized parallel with unidirectionally reinforced fibers which are randomly distributed in an elastic matrix. The scattered wave generated by a single fiber embedded in an infinite matrix with various degrees of debonding is computed by two-dimensional boundary element analysis for several incidence angles of the plane waves in a wide frequency range. The results are used to determine the effective complex wave number for the composite, accounting also for statistical nature of the interface debonding. The attenuation coefficient and the phase velocity of the composite can be readily obtained from the complex wave number as a function of the frequency and a damage parameter characterizing the extent of interface debonding. Numerical illustrations are provided for a composite made of titanium alloy reinforced with silicon-carbide fibers. The dependence of the phase velocity and the attenuation coefficient on the frequency, the extent of debonding and the propagation direction is discussed in detail. The apparent decrease in effective composite density due to debonding is also explored through comparison between the static-limit velocity and the corresponding effective shear modulus.
Fracture mechanisms in randomly oriented discontinuous carbon fiber reinforced borosilicate glass matrix composites are experimentally characterized. Two types of composite specimens with identical constituents but different microstructure were produced. The first type shows the three-stage behavior in the tensile stress-strain curve. In the second type which has the initial cracks, the stress-strain response is almost linear, but the initial Young's modulus is lower than that of the first type. Monotonic and static cyclic tensile and four point bend tests are conducted on those two specimens to measure the microcrack density, Young's modulus and Poisson's ratio as a function of applied strain. The experimentally determined crack density is used to estimate the interfacial shear stress. In the bend tests, evolution of microcracking on the tensile surface and through the thickness has been studied. Acoustic emission (AE) during the tests is monitored to understand the fracture mechanisms. It is proved that the difference in fracture mode between the two specimens is due to the difference in microstructure and the presence of initial defects. The AE behavior shows good correlation with the evolution of microcracking and can explain the fracture processes. Young's modulus can be a damage parameter to estimate the microcrack density. Microcracking during the flexural tests begins on the tensile surface and the cracks progress gradually towards the neutral axis.
In order to evaluate the shear-delamination strength of thermally sprayed coatings, an “edge-indentation method” was newly proposed in the present study, and the method was applied to WC-Co coating deposited on a tool steel (JIS: SKD5) specimen by high-velocity flame spraying and Al2O3-TiO2 coating on a mild steel (JIS: SS400) specimen by plasma spraying. The delamination energy of coating, Ed, is defined by the following equation based on the indentation load P vs. displacement δ curve: Ed=∫δ00P·dδ-∫δ0-B10P'·dδ/S×2θ/2π Where δ0 is the displacement at delamination, B1 is the coating thickness, S is the delamination area, 2θ is the delamination angle and P' is the indentation load only for substrate. The delamination energy Ed of WC-Co coating obtained by experiment reveals almost the same value irrespective of coating thickness B1 and relative indentation distance from edge x/B1. The Ed of Al2O3-TiO2 coating increases slightly with an increase in B1, and the Ed is smaller than that of WC-Co coating. The edge-indentation method is effective to evaluate the shear-delamination strength especially when the substrate is very hard.
To establish the measuring technique of neutron diffraction for the internal residual stress distribution in a structural component, a neutron diffraction apparatus was designed and manufactured in Modified Japan Research Reactor 3 (JRR3M). At the first step of measurement, a basic characteristics of the diffractometer was evaluated. The incident neutron beam flux was 104n/cm2/sec and the Full Width at Half Maximum (FWHM) was about 0.3 degree. This indicates that the manufactured neutron diffractometer is capable for the residual stress measurement. As the first application of the neutron diffraction measurement, the residual stress distribution in plastically bent carbon steel plate was measured. A typical compressive-tensile-compressive-tensile residual stress pattern in the tangential directiton in the bent plane was confirmed. The maximum stress near the surface was about 180MPa. This means that the technique far residual stress measurement by neutron diffraction can be established in Japan.