Shear moduli of wood were obtained with the shear block test, using the strain distribution measured with Digital Image Correlation (DIC). For comparison, the shear moduli were also measured by the torsion of rectangular bars, which afterward were processed to fabricate shear block specimens. A good agreement was found between the shear moduli obtained from the shear block and the torsion tests. The relation between the shear modulus and the nominal shear strength obtained from the shear block test showed good correlation (correlation coefficient of 0.59). Thus it is concluded that by applying the DIC the shear modulus can be determined from shear block test and the shear modulus can be used as an estimator of the nominal shear strength.
Using the longitudinal and flexural vibration method, the Young's modulus and shear modulus of the interlocked laminated veneer lumber (LVL) with symmetric angle-ply laminates were measured by tapping ; in addition, the connection strength was tested with a drift pin. The measured mechanical properties of the interlocked LVL were consistent with those predicted by the so-called classical lamination theory ; further, it was found that the properties change to a great extent with the interlock angle (orientation angle of veneer) but do not vary with small changes in the interlock angle. The connection strength of the interlocked LVL was determined by a dowel bearing strength test (embedment strength test). The dowel bearing strength tended to decrease to a small extent with an increase in the interlock angle. While the Young's modulus decreased to a great extent for changes in the interlock angle exceeding 10 degrees, the initial stiffness obtained from the embedment stress-displacement curve decreased to a small extent with the interlock angle. The analysis of the curve after the yield point revealed that the stress increased (strain hardening) when the interlock angle was greater than 10 degrees. The connection properties tested with a drift pin depend on not only the Young's modulus of the main member but also its shear modulus ; further, the angle-ply laminates prevent the member from cracking due to its expansion after yielding.
The law concerning the construction recycling was enforced in Japan in 2002. Therefore, the discretion dismantlement of the building and housing was obligated. As a result, the discretion dismantlement with a wood, wood-based material and metallic joint tools is becoming a problem now. If the joint materials and the whole building materials can be composed of the wood-based material, it is very effective for the dismantlement of building. In addition, wood-based materials have a big advantage to earthquake-proof because of light materials. Bamboo having high-strength fiber is a quick grower, and has received attention as a lingo-cellulosic material. In this research, the drift pin and the plate were made by using the long fiber of the bamboo. The fiber was obtained by alkali treatment. The drift pin was made for the direction of one axis. The plate has three layers, the surface layers were composed of short fibers and the core layer was composed of long fibers. The performance of these joint materials was evaluated by bending and two types of shear tests. The bending strength and young's modulus of the Φ12mm drift pin were 350-400MPa and 50GPa, respectively. The bearing strength of the plate which is parallel to the grain was about 10kN. Moreover, the two types of connection were proposed and tensile strength of both types exceeded 15kN.
In order to attain the fruitful effects of wood properties by aging, we conducted the thermal treatment at a moderately high temperature (85°C), which does not cause drastic thermal degradation, under a cyclic humidity changes between 30 and 80% R.H. for 3 months. For wood and cellulose samples, the weight losses were significantly accelerated by the existence of moisture, however the weight loss of cellulose was 1 order lower than wood sample. Loss tangent of wood specimens decreased for a few percent by the heating for 3 months without humidity change, whereas it increased under cyclic humidity changes. By the heating accompanied with humidity change, the degradation may excessively occur even only 1 month and as low as 85°C. The decrease of holocellulose content and relative increase of Klason lignin content were observed, which were remarkable under the heating with humidity change. Because plural factors may participate to the changes of equilibrium moisture content and crystallinity, the changing behaviors were complicated. In conclusion, it was proved that the existence of moisture merely accelerated the thermal degradation and positive effect was not virtually founded.
To clarify the dynamic viscoelastic properties of wood in nonequilibrium states, dynamic viscoelasticity of water-swollen wood with different drying or heating histories were measured at several frequencies. In the measurements after soaking in water at 10% of moisture content or after quenching from boiling state, the storage elastic modulus (E') increased and the loss elastic modulus (E'') and the loss tangent (tanδ) decreased with time at 30°C at all frequencies, except E' of the sample measured at 50Hz after soaking. The changing rates of these properties increase with decrease in frequency. In the measurement under stepwise heating and cooling cycles (5°C→35°C→5°C→65°C→5°C→95°C→5°C), lager E', and less E'' and tanδ were found during cooling processes than heating processes in the every cycles. This trend was remarkable at lower frequencies and for the samples with higher lignin contents. Each curve of E', E'' and tanδ in the every heating processes traced each curve of them in the every latest cooling processes. These results suggest that the dynamic viscoelasticity of water-swollen wood largely depend on the conformation of lignin, i.e., the thermodynamic states of lignin.
To clarify effects of lignin on the thermal-softening properties of water-swollen wood, dynamic viscoelasticities of water-swollen wood were measured in the temperature range from 5°C to 100°C. The results obtained were as follows. 1) Delignified wood and moso bamboo did not show thermal softening around 60∼80°C which was found for untreated wood and moso bamboo. From this result, it was found that the thermal softening of lingo-cellulosic materials around 60∼80°C were attributable to lignin. Decrease in storage elastic moduli (E') of wood and moso bamboo from 20 to 100°C remarkably decreased with decreasing in their lignin contents. From this result, it can be concluded that the degree of thermal softening around 60∼80°C largely depends on lignin contents. 2) The thermal-softening temperatures were different among many kind of wood species (softwood, Japanese hardwood, Tropical hardwood) and between an untreated katsura (Cercidiphyllum japonicum) sample and a sample slightly delignified. Consequently, it is deduced that the thermal-softening behaviors of water-swollen wood were largely affected by cross-linking of lignin. 3) The thermal softening behaviors of katsura were quite different among specimens experienced cooling with different rates. This suggests that the thermal-softening behaviors of water-swollen wood largely depend on the conformation of lignin.
As the first stage to clarify effects of heating on dynamic viscoelastic properties of dry wood, dynamic viscoelasticities and weight loss of dry wood were continuously measured in dry air at constant temperatures ranging from 120°C to 200°C for 100 minutes. The results obtained were as follows. 1) Relative storage elastic modulus per residual weight increased with time at all measuring temperatures. This means the elastic modulus of residual part increased by heating. 2) Relative loss modulus per residual weight at higher temperatures remarkably decreased with time in the initial stages of heating below 180°C. 3) Relative loss modulus per residual weight in the late stages of heating decreased similarly among different temperatures below 160°C, decreased slightly at 170°C and 180°C, and then decreased markedly at 190°C and 200°C. Both decrease in fluidity by developing more compact microstructures and increase in fluidity by thermal degradation affected the dynamic viscoelasticity of dry wood. The results 1) and 2) are attributable to development of more compact microstructures of dry wood caused by activation of the molecular motion. The result 3) is possibly explained that below 160°C influence of becoming more compact microstructure on dynamic viscoelasticity overcame that of thermal degradation below 160°C, both influences were almost same at 170°C and 180°C, and the former influence largely overcame the latter influence at 190°C and 200°C, at which dry lignin and hemicellulose have been considered to reach their thermal softening temperatures. 4) The changes in dynamic viscoelasticity differed in measurement frequencies. This is deduced that the sizes of responsive units affected by developing the more compact microstructures and thermal degradation were different each other.
Cone-shaped graphitic whiskers were formed by secondary heat treatment of powdered wood charcoal loaded with SiC following heat treatment at 2500°C. As the formation mainly occurred outside the cell wall, microscopic observation was possible without great difficulty. As the result, the following unique characters were recognized : (1) By optical polarization microscopy on reflection mode, periodical structure in the direction perpendicular to the whisker axis was observed on the whisker surface. Considering these findings together with those of electron microscopy, wound carbon nanotube-like surface structure was suggested. (2) Whisker suspended in water was oriented with the whisker axis perpendicular to the magnetic field. These features were well explained by the highly ordered structure of the whisker showing stack of hexagonal carbon layers arranged as cone.
Molecular dynamics (MD) simulations of screw dislocation behavior in KCl crystal under uniaxial compression along the  axis direction were performed to discuss elastoplastic transition under shock compression. The original screw dislocation was dissociated into one screw dislocation and two edge dislocations then generated edge dislocations moved along 45degrees to the compression direction under uniaxial compression. Simulation results showed the minimum stress for dissociation of screw dislocation and generated edge dislocation motion was from 3.1 to 3.3GPa. Its stress is larger than the stress in case of uniaxial compression for edge dislocation. The large stress may be caused by the difficulty in moving ions due to a helical configuration around screw dislocation core and dissociation of screw dislocations.
In this research, the impact between the racket and the ball was studied experimentally. The behavior of the ball during the impact was analyzed using high speed images. The purpose of this research is to clarify the effect of both impact area and strings tension on the rotational speed and the velocity of ball after impact. The deformation of the ball, the impact time, and the movements of the ball during the impact were studied experimentally. According to the experimental results, the following conclusions can be obtained. It was found that the rotational speed and the velocity after the impact increased with increasing deformation of the strings and decreasing deformation of the ball. Moreover, the rotational speed and the velocity after the impact increased with increasing impact time. And, the rotational speed of the ball after the impact increased with increasing displacement of the ball in the parallel direction to the surface of the strings.
The fracture behavior of a brittle polymer, polymethyl methacrylate(PMMA) resin, under static and impact tensile loadings was studied using single-edge-cracked specimens. The impact load and displacement were measured with a Piezo sensor and a high-speed extensometer, respectively. The load and displacement diagram, i.e., the external work Uex applied to the specimen was used to determine the elastic energy Ee and non-elastic energy En due to viscoelastic and plastic deformation, and the fracture energy Ef for creating new fracture surface As. The energy-release rate was then estimated using Gf = Ef/As. The values of Ee, En, Ef and Gf were correlated with the fracture loads, and the two results determined for the static and impact loadings were compared to study the effect of loading conditions.
Stress-strain loops of several engineering plastics in compression at strain rates of nearly 600/s are determined using the standard split Hopkinson pressure bar. Four plastics or typical thermoplastics PA-6, PA-66, PC and POM are tested at room temperature. Cylindrical specimens with slenderness ratio (= height/diameter) of 0.5 are used in the Hopkinson bar tests, and those with slenderness ratio of 1.5 as specified in the ASTM Standards are used in the static tests. The low and intermediate strain-rate stress-strain loops in compression are measured in an Instron testing machine. The effects of strain rate on Young's (or secant) modulus, 2.5% flow stress and dissipation energy (energy loss due to damping) are examined. It is demonstrated that the area within the stress-strain loop (or dissipation energy) increases with increasing strain rate as well as strain, that is, all plastics tested exhibit intrinsic dynamic viscoelasticity and a high elastic aftereffect following complete unloading.
High strain-rate compressive stress-strain characteristics of AA2024-T3 and its welds as produced by the friction stir welding (FSW) process are investigated using the conventional split Hopkinson pressure bar. Friction stir welded AA2024-T3 joints are made under a fixed set of welding conditions. Cylindrical specimens machined along the thickness direction of both the base material and the friction stir weld nugget region are used in the static and impact compression tests. It is shown that the compressive flow stress of the weld nugget is reduced by 7 to 11% compared with that of the base material, and that both the base material and the weld nugget exhibit almost no strain rate effect up to nearly ε= 103/s.
The authors have applied micro computed tomography (μCT) with synchrotron radiation of SPring-8 to imaging of fatigue cracks in cast aluminum alloy AC4CH. Theoretical evaluation showed that the edge of a sample apart from an X-ray detector was enhanced in the radiographic image due to the refraction of X-rays. The edge enhancement was confirmed with 28keV monochromatic X-ray under the arrangement where the detector was set behind the sample by 800mm. The enhancement also appeared on the tomographic image reconstructed by FBP (filtered back projection) algorithm. The fatigue cracks were clearly observed in both reconstructed images of laser-peened and unpeened samples. The crack image of the unpeened sample was evidently larger than that of the laser-peened sample, which implies that laser peening retarded the fatigue crack propagation.
Because of the lessening number of maintenance experts, a method to rationalize pipe inspection interval is desired. For this purpose, the evaluation method for the pipe integrity in the form of failure probability has been developed based on the Bayesian inference method in the previous paper. In this paper, the previous method is called the linear-Bayes method. The linear-Bayes method assumes wall thinning due to Flow Accelerated Corrosion (FAC) as the principal damage mechanism, and it can define the safety margin of a pipe's residual life depending on the number of inspections. However, the linear-Bayes method ignores the corrosion rate fluctuation against time, which may be caused by the change of environment such as water chemistry and flow velocity. Therefore, the linear-Bayes method may underestimate the failure probability of the pipe segments if the online monitoring of the environments is not used. In this paper, the linear-Bayes method is extended for the wall-thinning model with the corrosion rate fluctuation. The extension is carried out through following two approaches : correction-term and error-term approaches. In this paper, the formulation and the procedure for each approach are shown at first. And then, the accuracy and the merit of the extended method are examined through the evaluation using the artificial and the actual inspection records. Through the examination, it is confirmed that the extended method makes the evaluation of the pipe integrity available in view of safety margin for the corrosion rate fluctuation, keeping the merits of the linear-Bayes method.
The authors have been applying the Electric Resistivity Method (ERM) to heritage sites since 1995. ERM is one of the non-destructive prospecting techniques which is conveniently employed in the geotechnical field. Information obtained through ERM suggests rock properties, characteristics of discontinuities such as faults, joints and in-bedding materials, water content, and so on. The objective site of this paper is the Longyou Grottoes, situated in the central west of Zhejiang Province, China. 24 large caves, which are presumed to have been constructed around 2300-2400 years ago, were found by chance in 1992, and 5 of them were drained in full scale. The distribution of local lineaments was analyzed in terms of a satellite image, then electric resistivity around the caves, mineral components of the rock formation and cave walls, water qualities of the river, ground surface, and seepage into the caves were investigated. In conclusion, low resistivity zone shows the deterioration of rock formation, and the control of surface water should be materialized as soon as possible.