This study was performed to investigate the relationship between the cellulose crystal lattice strain (crystalline region) and the macroscopic surface strain in specimens of Chamaecyparis obtusa wood under repeated uniaxial tension stress in the fiber direction. Changes in the strain of the crystal lattice were measured from the peak of (004) reflection using the transit X-ray method. The macroscopic surface strain of each specimen was measured with a strain gauge. In both loading and unloading, the surface strain changed linearly with changes in stress. However, crystal lattice strain was not linear but exhibited changes along a curve with changing stress. Under stressed conditions, the crystal lattice strain was always less than the surface strain, regardless of the frequency of repetition in the loading and unloading cycle. The ratio of the crystal lattice strain to the surface strain showed a negative correlation for stress in both loading and unloading. That is, the ratio decreased with increasing stress, and finally tended to converge to a specific value. The ratio (I/I0) between the diffracted intensity (I0) in the (004) plane in the unloaded condition and the diffracted intensity (I) in the (004) plane in the loaded condition tended to converge on a specific value with increasing frequency of repetition. When the substantial Young's modulus of the wood in the longitudinal direction decreased, the ratio of the strain of the crystal lattice to the surface strain also decreased. Moreover, the ratio decreased with increasing microfibril angle of the specimen.
It is well known that Sugi (Cryptomeria japonica D. Don) boxed-heart square timber, which is usually used as columns for wooden residential houses in Japan, is one of the hardest species to be kiln-dried. Then we tried to apply the high-temperature setting method, which is one of the high-temperature kiln-drying that green timber is thermalsoftened and rapidly kiln-dried under high temperature and low relative humidity condition before the subsequent various usual drying. It was expected by the method that drying tension sets at the shell of timber should reduce occurrences of surface checks. Sugi green square timbers (132mm×132mm) without back-splitting were kiln-dried on various schedules to examine drying time, surface checks, and honeycombs (inner checks). The results were shown below. For each schedule, variations of initial moisture content (MC) were very large, and then final MC also varied widely. When the focus was limited on the timber whose initial MC was from 60% to 120%, average of final MC was 18.5% after 4.25-day drying time in high temperature kiln drying at dry bulb temperature (DBT) of 110°C after the high-temperature setting process. In medium temperature kiln drying at DBT of 90°C after the pre-process, drying time was 8 days and mean final MC was 19.8%. In conventional kiln drying at 70-80°C, drying time was 14 days and mean MC was 25.6%. By the high-temperature setting method, reduction of surface checks was particularly obvious, and timbers with lower final MC tended to cause fewer surface checks. When MC dropped, the widths of surface checks decreased or closed. On the other hand, honeycombs increased when MC decreased. The subsequent medium temperature kilndrying after the pre-process obviously reduced occurrences of honeycombs, though differences between DBT and wet bulb temperature was 30°C, that meant very low humidity condition. The honeycombs were also few in the conventional kiln-drying.
The distributions of drying set in Sugi (Cryptomeria japonica D. Don) and Hinoki (Chamaecyparis obtusa Endl.) boxed-heart timbers without back-splitting dried by the high-temperature setting method (HTS method) are reported. The lengths of slices cut from dried timber were measurerd before and after recovery treatments (moistening or immersion in boiling water). By moisture and heat treatment, the dimension of each slice is restored to it's original one. Therefore, the differences in lengths of slices between before and after treatment denote recovered set. The residual stresses in boxed-heart timber dried by the HTS method were also measuerd by a modified slicing technique with putting in a stainless pin (∅=0.5mm). Main results are shown below. (1) Remarkable tension set (about 2.1%) developed in shells (slices No. 1 and 10). (2) Hygro-recovery of drying set was observed only in the surface slices No. 1 and 10 and their values were about 0.6-0.8% (28-38% of total set). (3) Hygrothermal recovery of drying set was observed in most of slices. The set recovery in slice No. 1 and 10 were big (aboult 1.3-1.5%), Which is equivaleht to 62-72% of total set. (4) Boxed-heart square timbers without back-splitting dried by the HTS method were severely casehardened, that is, the shell of timber is stressed in compression and the core in tension.
The smoke-heat treating of Sugi (Cryptomeria japonica D. Don) is receiving attention these days because it improves the quality of Sugi and it is as effective as the traditional method of drying. The cutting force, tool wear, and cutting noise level of the smoke-heat treated Sugi was investigated to determine the effects of its improved quality on machining properties. The results obtained in this paper were as follows: 1) The cutting force in the cutting direction was smaller for the smoke-heat treated Sugi than for the non smoke-heat treated Sugi. It decreased with increasing cutting speeds for both the smoke-heat treated and the non smoke-heat treated Sugi. 2) The cutting force in the feed direction was almost equal under feed speeds investigated for the smoke-heat treated and the non smoke-heat treated Sugi. 3) The resultant cutting force calculated by the sum of the cutting forces in the cutting and feed directions was smaller for the smoke-heat treated Sugi than for the non smoke-heat treated Sugi. This tendency was more evident for higher moisture content. 4) The amount of tool wear was smaller for the smoke-heat treated Sugi than for the non smoke-heat treated Sugi. 5) Difference in cutting noise level was not observed for the smoke-heat treated and the non smoke-heat treated Sugi. However, the cutting noise level was reduced with increase in moisture content for the smoke-heat treated and the non smoke-heat treated Sugi due to the reduction in the sound pressure level of higher frequency ranges.
Wood-mineral composed (WMC) veneers were manufactured with Japanese cedar (Sugi: Cryptomeria japonica) and Japanese oak (konara: Quercus serrata) using the colloidal silica-boric acid system for the purpose of enhancing the fire retardancy of veneers. The evaluation of fire retardancy was experimented by two burning tests with oxygen index (OI) and microburner methods. In addition, the residual char produced after the OI-burning test was observed by electron probe X-ray microanalysis (EPMA). Weight percent gains (WPGs) for sugi (sapwood and heartwood) and konara veneers were about 50% and 14%, respectively. Ratios of fixation of unleached inorganic substances in WMC veneers were about 80% for sugi and 62% for konara. OI Values of untreated veneers were 22% regardless of wood species and the presence of leaching procedure, whereas WMC veneers of sugi and konara showed OI values of about 57% and 33%, respectively. The burning time and the percent weight of residual char were increased by combination of wood and silicate. As a result of EPMA observation, carbonized cell walls of untreated veneers became thinner, showing an abnormal shrinkage of tracheids and vessels. In the case of WMC veneers of sugi and konara, silica bodies filled up the lumina of tracheids and vessels or sometimes coated the lumen surfaces, and the abnormal shrinkage of cells and the thinning of cell walls hardly occurred. Also, the distribution of silica in the carbonized walls of tracheids, vessel, and wood fibers was found interestingly, giving a fire retardant effect to WMC veneers together with boron compound. The correlation between WPG and OI was recognized and consequently the evaluation of fire retardancy with WPG would be possible. In the burning test of WMC veneers with a microburner, the increase in temperature on the upper side of specimen was slow. The ignition of WMC sugi veneer was not recognized in 30 minutes and the carbonized area on the under side of specimen was small. When WMC sugi veneer was directly exposed to fire and OI values estimating from the linear regression equation were more than 60%, the fire retardancy could be evaluated to be better.
The presence and distribution particularly of boron compounds among inorganic substances are related greatly to the enhancement of performances such as decay, termite, and fire resistances in wood-mineral composites (WMCs). Regarding ashes obtained by removing an organic matter with heat-burning, the quantitative ratios of inorganic components like silicic acid, boron compounds, and others in composites made using various silicate solution system were investigated by means of the weighing method, X-ray fluorescence analysis, and ICP (inductivity coupled plasma) spectrometry. Also, the silicon concentration in leached solution from WMC specimens was determined by atomic absorption spectrometry. Further, we conducted the decay test to examine the relation between the presence of inorganic compounds and the performance enhancement. The WMCs were prepared by diffusion-penetrating the water glass-boron compound system (double treatment) and the colloidal silica solution system in the sapwood specimens of Sugi (Cryptomeria japonica) in addition to the new impregnating process of water glass-boron acid mixing solution (single treatment). From the above analyses, the general tendency on the contents of silicic acid, sodium oxide, and boron became clear. There existed a considerable amount of sodium oxide in WMC specimens made with the water glass-boron compound system and the water glass-boric acid mixing solution. It decreased in quantity owing to exudation out of specimen by leaching procedure and hence the relative ratio of silicic acid increased greatly. Almost all of inorganic substances consisted of silicic acid in the colloidal silica solution system and it hardly leached out because of the tight fixation in the specimen. The content of boron could be determined by ICP spectrometry and it decreased considerably in quantity by leaching procedure. However, even a small amount of boron left proved to be very effective to the enhancement of decay resistance from the result of decay test.
When wood based panels are nailed and/or bonded to lumber frame, effects of mechanical restraint on the panel hygroscopic linear expansion (LE) sometimes differ at in-plane biaxial directions. Even the adverse effect that LE in one direction becomes larger than its free LE is recognized when the other direction is strongly restrained. To give a better understanding for this phenomenon, this study was designed to investigate “Poisson's effect” of LE by comparing a free LE and biaxial LEs of a uniaxially restrained specimen of medium density fiberboard (MDF). Results showed that LE perpendicular to a restrained direction was much greater than free LE and “Poisson's effect” of LE was confirmed. Also, its apparent Poisson's ratio was found to be time dependent and associated with swelling stress. Conducting a static in-plane compressive test revealed that the apparent Poisson's ratio in LE was greater than that as an elastic constant. Furthermore, Poisson's ratios by a standard test were compared among panels with different element size, namely, plywood, oriented strand board, particleboard and MDF. Poisson's ratio of these panels ranged 0.14 to 0.28 and had a tendency to be greater as element size became smaller and elements were more randomly oriented.
Woven fabric composites have superior mechanical properties such as ductility and tear strength, compared with unidirectional fiber reinforced composites. As the application of their laminates to main parts of various structures increases, the damage behaviors of woven fabric composites become a subject of considerable interest for recent years. Although the mechanical behaviors of laminates are affected strongly by stacking configuration, their mechanism has not been completely revealed due to the geometric complexity of fabric architecture. In this paper, the effect of mismatch of stacking phase on damage development has been investigated numerically by a three-dimensional finite element analytical code based on damage mechanics. Our finite element analysis has an advanced point in anisotropic post-failure constitutive equation considering mesoscale failure modes. The mechanical behaviors of plain woven fabric composites under on-axial tensile load have been analyzed for 2-layered laminates with different stacking phase. As a result, it has been recognized that out-of-phase laminate shows stronger performance compared with iso-phase laminate. Additionally, it has been revealed that 2-layered laminate with 1/4 phase mismatch in perpendicular direction to tensile load shows slower damage occurrence and development of transverse cracks in wefts, and that ones with 1/4 phase mismatch in parallel direction show more rapid damage progress than iso-phase laminate.
A computational procedure for the local stress field of multiple fibers in a unidirectional composite is formulated based on the eigenfunction expansion of the displacement field and a collocation technique. This paper deals with the longitudinal shear deformation of a unidirectional composite consisting of clustered multiple fibers embedded in the matrix. Based on the proposed procedure, the influence of the fiber arrangement and the fiber volume fraction on the local stress field is analyzed. In particular, the correlation between the maximum interface shear stress for each fiber and the distance to the neighboring fiber is examined in detail for both regular and irregular fiber arrangements. For regular arrangements, high interface shear stresses are found for fibers located at the periphery of the cluster, especially for the square arrangement of fibers aligned with the shearing direction. For random fiber distributions, the interface stresses are found to be high in the interior of the cluster when the neighboring fibers are closely aligned parallel to the shearing direction. The correlation between the neighboring-fiber distance and the magnitude of the maximum interface shear stress for random fiber distributions is discussed in comparison with the results for regular fiber arrangements.
Biocompatible materials, such as bioactive ceramics and bioactive glasses can be effective in the repair of bone defects during orthopaedics surgery. These materials have been found by observation to exhibit varying degrees of osteoconductive behavior. The hydroxyapatite ceramics and bioactive glass ceramics was known as a highly bioactive ceramics, and replacements of lost bone. However, it is to be inferior to a fracture characteristic in a weak point of apatite ceramics. In the present study, surface structural changes of apatite ceramics with the bioactive function and mechanical property in simulated body fluid were investigated. Sub-micrometer hydroxyapatite ceramics powder was used as starting materials for making hydroxyapatite ceramics. Pressure less sintering was preformed at 1300°C in O2 atmosphere using the pre-sintered bodies. Fracture resistance (KQ) was evaluated by ASTM E399-90 method. And also, fracture resistance tests were performed using compact tension specimens. It has been confirmed by SEM observation, thin-film X-ray diffraction matter and FT-IR reflection spectroscopy that the apatite layer can be reproduced on the surface of the hydroxyapatite ceramic even in a cellular simulated body fluid with in concentrations nearly equal to those of human blood plasma. As a result, corrosion degradation of hydroxyapatite ceramics were preferentially recognized on hydroxyapatite particle after short time immersion into simulated body fluid. The general tendency of drastic decrease in fracture resistance was recognized in these materials. The fracture resistance of the specimen was found to decrease with increasing corrosion degradation, especially after 3 weeks immersion in simulated body fluid. This remarkable degradation in fracture resistance is considered to be caused by crack propagation through corroded pit. However, the specimens after 4 weeks immersion into simulated body fluid showed improved fracture resistance compared with those of corroded hydroxyapatite ceramics. There improvements in fracture resistance may be brought about through the mechanics was shown to induce the apatite layer formation on it's surface in some areas between 4 and 8 weeks by simulated body fluid.
The effect of mechanical degradation in a long-term-operated component on the creep- and fatigue-crack growth rates was studied. Creep-crack-growth tests and fatigue-crack growth tests were performed on creep-pre-strained and cyclic-strained CrMoV rotor-steel specimens. It was found that under constant load, creep-crack growth rates, da/dt, of the creep-pre-damaged specimens were higher than those of virgin specimens. It was also found that under the same stress intensity factor K, da/dt in the case of about 10%-crept and creep-void-induced specimens was increased 5 times, while in the case of 0.8%- and 2.8%-crept specimens, it only increased a little. However, all the data fall in a narrow scatter band in the relationship between creep J integral C* and da/dt. Another result showed that fatigue-crack growth rates, da/dN, of creep- and fatigue-pre-damaged specimens were higher than those of virgin specimens. Under the same stress intensity factor range ΔK, da/dN in an about 10%-crept specimen was increased 20 times. And da/dN in fatigue-pre-damaged specimens were accelerated 10 times. However, the results of the strain-controlled crack growth test fall in a narrow scatter band in the relationship between J integral range ΔJ and da/dN. These results suggest that the creep remaining lives and fatigue remaining lives of the mechanically damaged CrMoV rotor steel can be estimated by using C* & ΔJ of the damaged material and the da/dt and da/dN values of the virgin material.
Influence of accumulative passing tonnage on fatigue crack growth in rail steels was investigated. The fatigue crack growth was measured using compact tension specimens cut from three kinds of rails with accumulative passing tonnage of 100MGT, 200MGT, 600MGT respectively. The fatigue crack growth rate was estimated by the effective stress intensity range ΔKeff obtained by an unloading elastic compliance method. In addition, the measurements of crack opening displacement and the analysis of fatigue fracture surfaces were carried out to clarify the mechanism of crack closure behavior by a scanning electron microscope. It was concluded that the roughness of fatigue crack surface dependent on the grain size of each rail steel influences the crack growth behavior, and that the influence of accumulative passing tonnage on fatigue crack growth behavior can be estimated by the threshold effective stress intensity range ΔKeff, th.
Several raw coal ashes which were not finely divided, were used as admixtures for high volume coal ash shotcrete. Rheological properties of the concretes before projecting were evaluated by the modified slump cone test. Microstructure of the projected concretes was examined by the quantitative image analysis for backscattered electron images. Differences in the strength development between the shotcretes and conventional cast concretes were discussed in relation with influences of pneumatic projection on the initial packing of binder particles and the subsequent changes in coarse capillary pore structure. The modified slump test was useful for evaluating flow and projection properties of concrete. Plastic viscosity of coal ash concrete depended on types of coal ash even when the same slump value was attained. When a coal ash with a high carbon content was used, the plastic viscosity increased. The increase in viscosity resulted in the increase in pumping pressure for projection. The coarse capillary pore structure in the projected concrete without accelerator was not greatly different from that in the cast concretes. However, when a large amount of coal ash was incorporated, the threshold diameter of coarse capillary pores at early ages was reduced. The development of compressive strength in shotcrete was not notable compared to the conventional compacted concrete. It was suggested from the evolution of capillary pore structures that the accelerator for shotcrete prevented further densification in microstructure at long ages.
Internal frictions and dynamic moduli were measured by a forced torsional vibration method at 0.5-5Hz in the temperature range of -120-300°C on the metaphosphate glasses such as 50CaO·50P2O5 (CaP), 50Na2O·50P2O5 (NaP) and 25CaO·25Na2O·50P2O5 (CaNaP). Three peaks of internal friction were shown in the results measured as a function of temperature on both the glasses of CaP and NaP. The three peaks appeared at --50°C, -80°C and -210°C on the CaP, and at --50°C, -55°C and -170°C on the NaP. For the CaNaP, two peaks were obtained at --50°C and -75°C although the third peak was missed because of the rise of the base line. As those peak temperatures (T) depended on the vibration frequency (f), apparent activation energies (ΔE) to the relaxation were calculated from the equation, Inω=(ΔE/RT), where ω=2πf, R; gas constant. ΔE obtained from the first peaks (low temperature range) were -120kJ/mol with the CaP, -70kJ/mol with the NaP and -75kJ/mol with the CaNaP. From the second peaks at the intermediate temperature range, ΔE were -180kJ/mol with the CaP, -200kJ/mol with the NaP and -170kJ/mol with the CaNaP. ΔE obtained from the third peaks in the high temperature range were the high values with -640kJ/mol on the CaP and -530kJ/mol on the NaP. The dynamic moduli (G') gradually decreased a little with increasing temperature in the present range on all specimens.
Large deformation and convergence have been commonly observed in tunneling through shale layers in the Shimanto Belt, in South Wakayama (Nanki) Region. They have caused serious damage to supporting members. The authors investigated the deterioration mechanism of the Tertiary Shimanto Shale (classified into several groups), appearing in tunneling, through the slaking test, polarizing microscopic observation and X-ray diffraction analyses in order to clarify the relationship between the deformation and geological characteristics. As a result, it was concluded that the deformation of shales was caused with the opening of the tectonically generated micro-fissure (aperture) by the reduction of confining pressure to rock which is associated with tunnel excavation. In addition, it was also found from the convergence measurement that the early installation of the invert lining was compulsory to control large deformation in tunneling.
This research was carried out to examine biodegradation behavior of “green” composites reinforced by Manila hemp fibers. The composites are consisted of Manila hemp fibers as a reinforcement and starch-based emulsion-type biodegradable polymer as a matrix. Manila hemp fibers, biodegradable resin and unidirectional fiber-reinforced “green” composites were composted from 1day to 30days using a composting machine. After composting tests, the tensile tests and microscopic observation were performed. The experimental results showed that tensile strength and weight of “green” composites decreased with increasing composting time. In the case of composting time of 1 day, the tensile strength of hemp fibers and “green” composites did not decrease. However the tensile strength of these rapidly decreases after 2 days composting, and the tensile strength of “green” composites decreased 80% after 20 days composting. It can be seen that “green” composites degrade faster than biodegradable resin.
Thermally grown oxide layer formation between ceramic top coating layer and metal bond coating layer in “Thermal Barrier Coating (TBC)” is known to cause reduction of interface cohesion. This cohesion reduction is practically associated with a serious damage such as coating spallation due to thermal cycling, prolonged isothermal exposure and thermo-mechanical fatigue. Interface crack mechanics have been used widely to evaluate such interface strength. In the mechanics, an ideal interface condition was considered, because of the difficulty of mathematic treatment for stress field solution. However, actual interface strength is predominated by the effect of interface oxidation growth by Al diffusion process and interface instinctive problem such as a wavy interface geometry. In this study, the interface cohesive model, which is based on a spring connection between the interface nodes in the top coating and the substrate, is developed for evaluating TBC interface delamination strength with taking into account coating instinctive characterization, such as thermally grown oxide formation. Application of finite element analysis included with the developed model to the TBC delamination test by four-point bending is shown. Also, delamination energy, which is defined by energy stored in the interface spring until interface fracture surface formation, is proposed newly as TBC delamination strength.