Full size tensile tests were made on thirteen types of laminated veneer lumbers (LVL) for structural use. Factors affecting the strength distribution of these materials were discussed. The dispersions of specific gravity, modulus of elasticity (MOE), and tensile strength (TS) were considerably lower than those of sawn lumber. The effects of veneer quality on the stiffness and strength properties were significant. The classifications certificated in the previous Japanese Agricultural Standard (JAS) for structural LVL did not always reflect the strength properties. The correlation between TS and MOE was low for LVL as a whole, but was high for those within a grade specified by the JAS. Three parameter Weibull distribution functions generally provided better fit to the MOE, TS, compression strength, and horizontal-shear strength data than normal and log-normal distribution functions. The lower five percent exclusion limit calculated non-parametrically did not differ much from the values calculated parametrically.
This paper deals with the validity of the resonance frequency of longitudinal vibration as a parameter for prediction of the Young's modulus of structural timbers and the relationships among quality parameters such as density, Young's modulus and specific Young's modulus. Seven hundred and seventy-nine pieces of 2″ by 4″ dimension lumber, eighty pieces of sugi post and forty pieces of hinoki post for the traditional Japanese wood construction were tested. Ten sugi logs and nine hinoki logs were also examined. The resonance frequency by tapping the cross section of the specimens was determined by using a Fast Fourier Transformation spectrum analyzer. The specific Young's modulus, E/ρ (E: Young's modulus, ρ: density) was independent of the density of specimens. However, it was recognized that the specific Young's modulus was high correlation with Young's modulus of structural timbers. These facts were ascertained not only in the dimension lumber at dry condition but also in the sawn square timbers at green condition. The linear regression analysis proved the validity of the resonance frequency of longitudinal vibration as a parameter for prediction of the Young's modulus of structural timbers. This result enables the simple mechanical grading of structural timbers based on the Young's modulus measurement, which does not require mass measurement of heavy timbers such as large beams and logs.
For the quantitative evaluation of two-dimensional cell arrangement on the transverse section of wood, the angle and frequency distribution functions were extracted by some mathematical treatments of the power spectral pattern (PSP) which were obtained by the two dimensional FFT of simplified images of transverse sections. The transverse sections of seven softwoods and ten hardwoods were used for the analysis, and the arrangement of about one thousand tracheids and fibers within the sections was converted to the arrangement of small uniform-sized dots, where each dot corresponded to the center of cells. PSPs of these dot maps were normalized, transformed on the polar coordinate and then deconvoluted for the purification of the information of only cell arrangement and for the comparison among the specimens. From the angle distribution function, it was possiblee to estimate the array regularity of cells on the radial files, as well as to clarify the oblique-arrangement of cells in all softwoods and in some hardwoods. Furthermore, the two-dimensional cell size and its variation was able to be evaluated based on the frequency distribution function.
In order to evaluate the effect of minute damages such as slip planes on wood quality, the relationship between some mechanical properties (σt, Et, Wu) and development of slip planes in konara wood (Quercusserrata Thunb.) specimens, which were precompressioned under different percentages of the failing load, was investigated. Furthermore, for the determination of fracture site within the precompression wood under tensile re-loading conditions, the slip plane angle (θp) in the damaged fibers and the inclination angle (θs) of the fracture surface of the cell walls of the precompression wood were measured by a polarizing microscope and the SEM stereo analysing method, respectively. In the case of the fracture of the precompression wood, it is concluded that cracks almost took place at the slip-plane sites, because the θp and the θs showed fairly good agreement at about 64 degrees. The existence of the slip planes within the wood seriously affected the deterioration of wood quality, especially the decrease of toughness of wood.
Firstly, we investigated the effect of reverse load on creep of wood during drying. Secondly, we examined the restoration during adsorption of bending set wood, which had been dried under three different loading conditions: (1) normal bending-load was applied in the range of 30-17% moisture contents (MCs), (2) reverse bending-load was applied in the range of 17-7% MC, (3) normal bending-load and then reverse bending-load were applied. The results are summarized as follows. (1) When the reverse bending-load was applied during drying, creep became greater than that in the condition when the normal bending load was applied again. This suggests that the reverse load stimulated the recovery of the normal set developed just before in the limited narrow range of MC. (2) When the restoration curves of bending set wood during adsorption under loading conditions (1), (2) and (3) are referred to as M, P and K, respectively, the curve K was closely similar to the resultant curve by the superposition of the curves M and P. Therfore, the set developed at the higher levels of MC and that at the lower level of MC are almost independent each other, although not completely independent from the result of (1).
To make the use of timber more efficient, it is considered that the log should be selected based on the structural characteristics before carried into the saw mill, and the log-sawing design should be determined suitable to the wood products in the mill. The natural frequency of longitudinal wave due to sound when hitting cross section of log and lumber was measured to determine the modulus of elasticity (Et). Et was recognized to be highly linear to the modulus of elasticty due to static bending test (Es). The potential application of the relationship between the Et of log and that of sawn lumber and laminae gained from the log was discussed from practical aspect. As a high correlation between Et of log and structural properties of sawn lumber is recognized, measuring Et of log could be one of the mechanical gradings which would be effective and easy to conduct on site before carrying to the saw mill. Since Et of log practically was presented as the average value of Et of laminae, the design of sawing for laminae should be considered based on the estimated distribution of modulus of elasticity of laminae within log. It could be effective as a rough classification for mechanical grading of lumber and quality control of selecting log for the laminae of glue laminated lumber in the mill.
Graphite and phenol-formaldehyde resin spheres (GPS) were used in the manufacture of fire resistive and electromagnetic shield composites. The effects of specific gravity, thickness and phenol-for-maldehyde resin content of GPS on the fire resistivity and electromagnetic shield of composites were discussed. The carbonizing temperature of the composites relative to the fire resistive and electromagnetic shielding properties was also discussed. The fire resistivity was tested by a burn-through method, by cutting with an oxygen-acetylene torch and by an oxygen index method in accordance with the Japanese Industrial Standards (JIS) K 7201. The electromagnetic shielding property was tested by a DUAL chamber method in accordance with ASTM ES7-83. The fire resistive and electromagnetic shielding properties of the composites were improved by increasing the specific gravity and thickness of the GPS composites as well as increasing the carbonizing temperature, and reducing the phenol-formaldehyde resin content.
In this report, the piezoelectricity and the crystallinity of Hinoki treated with sodium hydroxide for a long period were investigated. The results obtained are summarized as follows. (1) A remarkable increase in piezoelectric moduli was observed by the treatment of sodium hydroxide, though there was a decrease in the degree of crystallinity of wood. However, the piezoelectric moduli of wood treated for one year decreased to a half compared with those treated for three months. (2) By the alkali treatment, the degree of crystallinity and crystallite size of the treated wood decreased, and the 2θ002 shifted toward low angle. These results suggest that some change in crystalline structure took place in wood. (3) The temperature variation of the plane distance of cellulose crystallites in the alkali-treated wood was measured. The lattice widening took place in the (002) plane with increasing temperature. With increasing period of alkali treatment, the temperature variation of the ratio Δd/d of the treated wood decreased compared with that of the untreated wood. It may be considered that new hydrogen bonds appeared on the (101) plane and they restrained the widening of the (002) plane distance due to thermal expansion. In the case of Ramie cellulose, the temperature variations showed a tendency approximately similar to those of wood. (4) It is assumed that the increase of the piezoelectric moduli of wood and cellulose occurs by piezoelectric polarization due to the hydrogen bond which is formed by the change in crystalline structure of cellulose.
This paper deals with the simulation of thermal behavior at a boundary between skin and woody materials when the woody materials laid over a cement mortar block are in contact with a man's palm. Plywoods, MDF (medium density fiberboards), and cork boards with different thickness were used as the overlays. Changes in temperature at the skin-overlay-underlayment interfaces were measured with thermo-couples at 10 to 30sec intervals. Furthermore, a thermal transfer model based on a numerical method with finite differences was proposed to analyze the changes in temperature and rate of heat transfer at the interfaces. Thermal constants for the model were obtained by fitting them with the experimental values. Then the changes in temperature and rate of heat transfer were simulated by this model for various overlay materials having different thickness. Not only the model is able to obtain the thermal behavior at the interfaces in good agreement with the experimental results on the samples of various woody materials, but also it is valuable to estimate the sensory warmth felt by man's palm in contact with the surface of the overlays, since both the temperature at the skin surface and the heat transfer across the boundary are highly related with the sensory warmth.
In order to study the physical basis of scatter in fatigue life, fatigue tests were carried out on the smooth specimens of a normalized 0.21% C steel. Fifteen specimens were fatigued at each stress level and the behavior of all cracks which led to the fracture of the specimens was examined. Fatigue data were analyzed statistically by assuming the Weibull distribution. The results show that the scatter in the number of cycles required to attain a crack length 0.2mm is particularly large. There is only slight scatter for the propagation life from 0.2mm up to fracture. The distribution relating to all phases of lifetime can be expressed by the three-parameter Weibull distribution. The values of the coefficient of variance, CV, for the initiation life of a crack length of 0.2mm and fatigue life increase with decreasing stress level. However, CV for crack growing from 0.2mm to failure shows only a slight dependency on the stress level. The scatter in fatigue life is due mainly to the behavior of microcracks. The influence of microstructure on microcrack propagation is especially large at lower stress levels, i.e. near the fatigue limit.
Rotating bending fatigue tests have been carried out using materials with three different microstructures of a Ti-6Al-4V alloy, prepared with different heat treatments, i.e. annealed at 705°C (AN705) and 850°C (AN850), and solution treated and aged (STA). Emphasis was placed on the effect of microstructure on fatigue behaviour, in particular, fatigue crack initiation and small crack growth. The highest fatigue strength was obtained in STA, followed by AN850 and AN705. Fatigue cracks initiated within α phase in the annealed materials and the crack initiation resistance for AN750 with fine microstructure was superior to that for AN850 with coarse microstructure. For STA, cracks generated within (α+β) phase. Small cracks in all the materials exhibited much higher growth rates just after crack initiation, followed by a retardation and experienced a minimum value, and then showed monotonic increase in growth rate. In the extremely small crack regime below approximately 80μm, the most excellent growth resistance was achieved in AN850, followed by STA and AN705. Based on the observations on fatigue crack initiation and small crack growth, it was concluded that the highest fatigue strength of STA was due to the excellent crack initiation resistance of its microstructure, while the higher fatigue strength of AN850 than AN705 was attributed to higher small crack growth resistance of the former material.
Reversed plane bending fatigue tests were carried out on two kinds of forged Al-25Si P/M (Powder Metallurgy) aluminum alloys having different sizes and distributions of Si particles. The initiation and growth behaviors of small surface fatigue cracks were continuously monitored by the replica technique and investigated in detail. It was found that the crack initiation strength of the material with fine Si particles was higher than that with coarse Si particles. Although little difference in strength was observed between the forged and transverse directions in the former material, some difference was found depending on the specimen orientations in the latter material. When the stress intensity range was calculated by considering the difference of the projected area of Si particles to the plane perpendicular to the loading axis, the difference in fatigue strength among the specimens oriented differently could be explained. The macroscopic crack growth rate, da/dn, could be expressed by the Paris equation in terms of the maximum stress intensity factor, Kmax, irrespective of stress level and specimen orientation. The fatigue crack growth rate was found faster in the coarse grained material than that in the fine grained material, and as the crack propagated along the Si particles, more deflective behavior of crack growth was observed in the material with fine Si particles, which was thought to result in the increase in crack growth resistance.
Fatigue crack growth and crack closure in 3% NaCl solution have been investigated in spheroidal graphite cast irons with four types of microstructure, i.e. ferrite, pearlite, bull's eye and aus-ferrite. In high ΔK regime, crack growth rates were enhanced by stress corrosion cracking (SCC) due to hydrogen embrittlement. Crack closure level was reduced by SCC, which promoted the acceleration in 3% NaCl solution. In low ΔK regime, crack growth rates were decreased by the corrosion debris induced crack closure, but the crack growth characteristics allowing for crack closure were the same with those in air. Thus, the environmental effect on the essential crack growth resistance was negligible in 3% NaCl solution. These behaviors were seen for all the materials investigated, and thus the dependence of microstructure on environmental effects was obscure. Fracture toughness has also been measured in air and in 3% NaCl solution for these materials. The fracture toughness values in both environments were the same for the ferrite, pearlite and bull's eye microstructures, but the value in 3% NaCl solution was definitely lower than that in air for the aus-ferrite microstructure.
The flexural fatigue behavior of unidirectional CFRP laminates using two kinds of pitch based carbon fibers was investigated by three point bendind fatigue test at several levels of temperature and two levels of loading rate. By comparing the flexural fatigue behavior of the two types of CFRP laminates, the characteristics of pitch based CFRPs was clarified as follows: (1) The flexural fatigue behavior of these CFRPs changed considerably with loading rate, and temperature, as well as the number of loading cycles to failure. The dependence on loading rate, temperature or number of cycles to fatilure is clearly divided into two regions by the fracture mechanism of the CFRPs. The two fracture mechanisms are the tensile fracture on the tension side of specimen and the compressive fracture on the compression side of specimen. (2) The flexural fatigue strengths of these CFRPs considerably decrease with loading rate and temperature as well as number of loading cycles to failure in the region of compressive fracture. The fatigue strength does not change with loading rate, temperature or number of loading cycles to failure in the region of tensile fracture unlike the compressive fracture region. (3) The reciprocation law between time and temperature holds for the flexural fatigue strength as well as the flexural static strength. (4) In the region of tensile fracture, the fatigue strengths of the two types of CFRP differ, that is, the fatigue strength of CFRP, which includes the high tensile strength fiber, has a higher tensile fatigue strength. On the other hand, in the region of compressive fracture, the fatigue strengths of the two types of CFRP show the same value at the same temperature and loading rate.
The effects of ionic concentrations of Ca2+ and OH- ions and crystallinity of Ca(OH)2 on its carbonation reaction were investigated. The process of carbonation was followed by the measurement of electrical conductivity in slurry. Calcite was produced via an intermediate amorphous product, whose composition was determined to be Ca1+xCO3(OH)2x·yH2O(x>0.05, y=0.6-0.8) by means of DTA, TGA and CHN analysis. The particles of calcite obtained varied from a dispersed cubic shape to a needle-like or spindle-like condensed shape. This change was ascribed to the decrease in ionic concentration during the crystallization process from the intermediate amorphous phase to calcite.
Experiments using SUS304, Si3N4, WC-9%Co as well as boron-ion-implanted SUS304, Si3N4 and WC-9%Co were performed with a self-manufactured reciprocating type tribology testing apparatus. The tribology tests were carried out under unlubricated conditions in air at room temperature. Compared with the unimplanted SUS304, the hardness of the boron-ion-implanted SUS304 increased. No iron borides were, however, identified in the boron-ion-implanted SUS304. In addition, neither the formation of new chemical compounds nor significant hardening was observed in Si3N4 and WC-9%Co. The coefficients of friction of the boron-ion-implanted Si3N4 and WC-9%Co indicated higher values than those of unimplanted Si3N4 and WC-9%Co, respectively. From the experimental results, some tribological improvements were obtained by the boron ion implantation treatment into SUS304. On the other hand, the boron ion implantation into Si3N4 and WC-9%Co does not seem to be a satisfactory treatment for improving their tribological properties. In particular, the wear scar of the boron-ion-implanted Si3N4 was significantly enlarged. This could be related to the microscopic surface damages produced by sputtering during the ion implanting process.
By using newly developed soft gripping devices, a quite simple and economical test method was realized in tensile tests of engineering ceramics. The gripping device consists of high strength polymer tube and a Duralumin vessel. So long as the testing samples of circular ceramic bar are straight enough, whether machined or not, they can be directly delivered to tensile tests without any special machining of the gripping portions. This simple gripping method will bring in low-cost tensile tests which have never been achieved. Although the bending effect on the fracture load is often serious in the tensile tests of engineering ceramics, the soft gripping devices were also successful in removing the bending strain. The regulation of JIS for the bending component of the strain, which should be below 10% at a half of specimen's fracture load, was cleared without any labourious work.